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Diverse Applications of Nanomedicine

Pelaz, Beatriz; Alexiou, Christoph; Alvarez -Puebla, Ramon A.; Alves, Frauke; Andrews, Anne M.; Ashraf, Sumaira; Balogh, Lajos P.; Ballerini, Laura; Bestetti, Alessandra; Brendel, Cornelia; Bosi, Susanna; Carril, Monica; Chan, Warren C. W.; Chen, Chunying

The design and use of materials in the nanoscale size range for addressing medical and health-related issues continues to receive increasing interest. Research in nanomedicine spans a multitude of areas, including drug delivery, vaccine development, antibacterial, diagnosis and imaging tools, wearable devices, implants, high-throughput screening platforms, etc. using biological, nonbiological, biomimetic, or hybrid materials. Many of these developments are starting to be translated into viable clinical products. Here, we provide an overview of recent developments in nanomedicine and highlight the current challenges and upcoming opportunities for the field and translation to the clinic.

ACS Nano, 11 (2017) 2312-2381 | DOI: 10.1021/acsnano.6b06040

1-dimensional TiO2 nano-forests as photoanodes for efficient and stable perovskite solar cells fabrication

Salado, M; Oliva-Ramirez, M; Kazim, S; Gonzalez-Elipe, AR; Ahmad, S

During the last years, perovskite solar cells have gained increasing interest among the photovoltaic community, in particularly after reaching performances at par with mature thin film based PV. This rapid evolution has been fostered by the compositional engineering of perovskite and new device architectures. In the present work, we report the fabrication of perovskite solar cells based on highly ordered 1-dimensional vertically oriented TiO2 nano-forests. These vertically oriented porous TiO2 photoanodes were deposited by physical vapor deposition in an oblique angle configuration, a method which is scalable to fabricate large area devices. Mixed (MA0.15FA0.85)Pb(I0.85Br0.15)3 or triple cation Cs0.05(MA0.15FA0.85)0.95Pb(I0.85Br0.15)3 based perovskites were then infiltrated into these 1-dimensional nanostructures and power conversion efficiencies of 16.8% along with improved stability was obtained. The devices fabricated using 1D-TiO2 were found to be more stable compare to the classical 3-dimensional TiO2 photoanodes prepared by wet chemistry. These 1-D photoanodes will be of interest for scaling up the technology and in other opto-electrical devices as they can be easily fabricated utilizing industrially adapted methodologies.

Nano Energy, 35 (2017) 215-222 | DOI: 10.1016/j.nanoen.2017.03.034

Critical Role of Oxygen in Silver-Catalyzed Glaser-Hay Coupling on Ag(100) under Vacuum and in Solution on Ag Particles

Orozco, N; Kyriakou, G; Beaumont, SK; Sanz, JF; Holgado, JP; Taylor, MJ; Espinos, JP; Marquez, AM; Watson, DJ; Gonzalez-Elipe, AR; Lambert, RM

The essential role of oxygen in enabling heterogeneously catalyzed Glaser–Hay coupling of phenylacetylene on Ag(100) was elucidated by STM, laboratory and synchrotron photoemission, and DFT calculations. In the absence of coadsorbed oxygen, phenylacetylene formed well-ordered dense overlayers which, with increasing temperature, desorbed without reaction. In striking contrast, even at 120 K, the presence of oxygen led to immediate and complete disruption of the organic layer due to abstraction of acetylenic hydrogen with formation of a disordered mixed layer containing immobile adsorbed phenylacetylide. At higher temperatures phenylacetylide underwent Glaser–Hay coupling to form highly ordered domains of diphenyldiacetylene that eventually desorbed without decomposition, leaving the bare metal surface. DFT calculations showed that, while acetylenic H abstraction was otherwise an endothermic process, oxygen adatoms triggered a reaction-initiating exothermic pathway leading to OH(a) + phenylacetylide, consistent with the experimental observations. Moreover, it was found that, with a solution of phenylacetylene in nonane and in the presence of O2, Ag particles catalyzed Glaser–Hay coupling with high selectivity. Rigorous exclusion of oxygen from the reactor strongly suppressed the catalytic reaction. Interestingly, too much oxygen lowers the selectivity toward diphenyldiacetylene. Thus, vacuum studies and theoretical calculations revealed the key role of oxygen in the reaction mechanism, subsequently borne out by catalytic studies with Ag particles that confirmed the presence of oxygen as a necessary and sufficient condition for the coupling reaction to occur. The direct relevance of model studies to a mechanistic understanding of coupling reactions under conditions of practical catalysis was reaffirmed.

ACS Catalysis, 7 (2017) 3113-3120 | DOI: 10.1021/acscatal.7b00431

Gold promoted Cu/ZnO/Al2O3 catalysts prepared from hydrotalcite precursors: Advanced materials for the WGS reaction

Santos, JL; Reina, TR; Ivanova, S; Centeno, MA; Odriozola, JA

Outstanding catalysts for the water was shift reaction are reported in this work. The combination of gold nanoparticles with Cu/ZnO/Al2O3 prepared from hydrotalcite-like precursors leads to very promising systems for pure hydrogen production. Full CO conversion is reached at temperatures as low as 180 degrees C. The key point seems to be the cooperation of Au and Cu and the optimal metal-oxide contact derived from the synthesis method. The high activity of gold for low temperature CO oxidation and the suitability of copper for the WGS results in a perfect synergy. Moreover the materials developed in this work present good stability and tolerance towards start/stop cycles an indispensable requisite for a realistic application in an integrated hydrogen fuel processor.

Applied Catalysis B-Envionmental, 201 (2017) 310-317 | DOI: 10.1016/j.apcatb.2016.08.017

Pt-impregnated catalysts on powdery SiC and other commercial supports for the combustion of hydrogen under oxidant conditions

Arzac, G. M.; Montes, O.; Fernandez, A.

We report the study of the catalytic hydrogen combustion over Pt-impregnated powdery silicon carbide (SiC) using H2PtCl6 as precursor. The reaction was conducted in excess of oxygen. beta-SiC was selected for the study because of its thermal conductivity, mechanical properties, chemical inertness and surface area. The obtained Pt particles over SiC were medium size (average particle diameter of 5 nm for 0.5 wt% Pt). The activity of the Pt-impregnated catalyst over SiC was compared to those obtained in oxidized form over TiO2 and Al2O3 commercial supports (Pt particles very small in size, average particle diameter of 1 nm for 0.5 wt% Pt in both cases). The case of a SiO2 support was also discussed. Those Pt/SiC particles were the most active because of their higher contribution of surface Pt, indicating that partially oxidized surfaces have better activity than those totally oxidized in these conditions. SiC was modified with an acid treatment and thus bigger (average particle diameter of 7 nm for 0.5 wt% Pt) and more active Pt particles were obtained. Durability of the SiC and TiO2 supported catalysts was tested upon 5 cycles and both have shown to be durable and even more active than initially. Exposure to the oxidative reaction mixture activates the catalysts and the effect is more pronounced for the completely oxidized particles. This is due to the surface oxygen chemisorption which activates catalystsi surface.

Applied Catalysis B-Envionmental, 201 (2017) 391-399 | DOI: 10.1016/j.apcatb.2016.08.042

NO photooxidation with TiO2 photocatalysts modified with gold and platinum

Rodriguez, MJH; Melian, EP; Santiago, DG; Diaz, OG; Navio, JA; Rodriguez, JMD

In this study, a comparative analysis is made of TiO2 modified with Pt or Au in NO photoxidation under different radiation and humidity conditions. The metals were deposited on the TiO2 surface using two methods, photodeposition and chemical reduction. All catalysts were supported on borosilicate 3.3 plates using a dip-coating technique. These modified photocatalysts were characterized by X-ray diffraction analysis (XRD), UV-vis diffuse reflectance spectra (DRS), Brunauer-Emmett-Teller measurements (BET), transmission electron microscopy (TEM) and X-ray photoelectron spectrum analysis (XPS). It was found from the XPS results that Pt and oxidized Pt species coexist on the samples obtained by photodeposition and chemical reduction. In the case of Au, though other oxidation states were also detected the dominant oxidation state for both catalysts is Au. TEM results showed most Au-C particles are below 5 nm, whereas for Au-P the nanoparticles are slightly bigger. With UV irradiation, the Pt modified catalysts do not show any significant improvement in NO photocatalytic oxidation in comparison with the unmodified P25. For Au, both modified photocatalysts (Au-P and Au-C) exceed the photocatalytic efficiency of the unmodified P25, with Au-C giving slightly better results. The incorporation of metals on the TiO2 increases its activity in the visible region. 

Applied Catalysis B-Environmental, 205 (2017) 148-157 | DOI: 10.10161/j.apcatb.2016.12.006

Structuring Pt/CeO2/Al2O3 WGS catalyst: Introduction of buffer layer

Gonzalez-Castano, M; Ivanova, S; Laguna, OH; Martinez, LM; Centeno, MA; Odriozola, JA

This work is devoted to the development of novel structured catalytic system for WGS reaction. The new concept is related to the presence of a pre-catalytic "buffer" layer formed by WGS-inert oxide, i.e. not involved in CO conversion, but able to increase the number of participating sites in water dissociation step during the reaction. The performance of the proposed systems appears to depend strongly on the stream composition, being its effect beneficial in highly reducing atmospheres making it ideal for cleanup application. An increment of the partial kinetic order for water species is observed and reveals the key role of the water activation for superior catalytic behavior. 

Applied Catalysis B-Envionmental, 200 (2017) 420-427 | DOI: 10.1016/j.apcatb.2016.07.039

Study of the E. coli elimination from urban wastewater over photocatalysts based on metallized TiO2

Murcia, JJ; Avila-Martinez, EG; Rojas, H; Navio, JA; Hidalgo, MC

In this study, a series of photocatalysts based on TiO2 was tested in the elimination of Escherichia coli (E. coli) from urban wastewater. Firstly, TiO2 obtained by sol-gel method was modified by sulfation, and then gold or platinum nanoparticles were photodeposited on sulfated titania surface. Platinized samples were also prepared with different Pt content of 0.5 and 2 wt.%. The samples thus obtained were extensively characterized and it was found that sulfation considerably increases the S-BET value of TiO2 and promotes the anatase phase formation; it was also found that 0.5 wt.% Pt-TiO2 sample presents the lowest noble metal particle size and the best particle dispersion. All the photocatalysts synthesized have shown bactericidal effect and the results obtained by using bare and metalized TiO2 were considerably better than the results obtained with the commercial TiO2 P25 Evonic. Different light intensities were also evaluated in the photocatalytic tests and it was found that 120 W/m(2) leads to obtain the highest E. coli elimination from wastewater samples; however no total elimination of E. coli or other species of bacteria was achieved even after 5 h of photocatalytic treatment without catalyst. Total elimination of the E. coli was achieved after 3 h of photocatalytic reaction by using 120 Wim(2) of light intensity and 2 wt.% Pt-TiO2 as photocatalyst; no bacterial regrowth was observed even after 72 h. 

Applied Catalysis B-Envionmental, 200 (2017) 469-476 | DOI: 10.1016/j.apcatb.2016.07.045

High vacuum synthesis and ambient stability of bottom-up graphene nanoribbons

Fairbrother, A; Sanchez-Valencia, JR; Lauber, B; Shorubalko, I; Ruffieux, P; Hintermann, T; Fasel, R

Carbon-based nanomaterials such as graphene are at a crucial point in application development, and their promising potential, which has been demonstrated at the laboratory scale, must be translated to an industrial setting for commercialization. Graphene nanoribbons in particular overcome one limitation of graphene in some electronic applications because they exhibit a sizeable bandgap. However, synthesis of bottom-up graphene nanoribbons is most commonly performed under ultra-high vacuum conditions, which are costly and difficult to maintain in a manufacturing environment. Additionally, little is known about the stability of graphene nanoribbons under ambient conditions or during transfer to technologically relevant substrates and subsequent device processing. This work addresses some of these challenges, first by synthesizing bottom-up graphene nanoribbons under easily obtained high vacuum conditions and identifying water and oxygen as the residual gases responsible for interfering with proper coupling during the polymerization step. And second, by using Raman spectroscopy to probe the stability of nanoribbons during storage under ambient conditions, after transfer to arbitrary substrates, and after fabrication of field-effect transistor devices, which shows structurally intact nanoribbons even several months after synthesis. These findings demonstrate the potential of graphene nanoribbon technologies by addressing some limitations which might arise in their commercialization.

Nanoscale, 9 (2017) 2785-2792 | DOI: 10.1039/C6NR08975E

Multicolored Emission and Lasing in DCM-Adamantane Plasma Nanocomposite Optical Films

Alcaire, M; Cerdan, L; Zamarro, FL; Aparicio, FJ; Gonzalez, JC; Ferrer, FJ; Borras, A; Espinos, JP; Barranco, A

We present a low-temperature versatile protocol for the fabrication of plasma nanocomposite thin films to act as tunable emitters and optical gain media. The films are obtained by the remote plasma-assisted deposition of a 4-(dicyano-methylene)-2-methy1-6-(4-dimethylamino-styry1)-4Hpyran (DCM) laser dye alongside adamantane. The experimental parameters that determine the concentration of the dye in the films and their optical properties, including light absorption, the refractive index, and luminescence, are evaluated. Amplified spontaneous emission experiments in the DCM/adamantane nano composite waveguides show the improvement of the copolymerized nano composites' properties compared to films that were deposited with DCM as the sole precursor. Moreover, one-dimensional distributed feed-back laser emission is demonstrated and characterized in some of the nanocomposite films that are studied. These results open new paths for the optimization of the optical and lasing properties of plasma nanocomposite polymers, which can be straightforwardly integrated as active components in optoelectronic devices.

ACS Applied Materials & Interfaces, 9 (2017) 8948-8959 | DOI: 10.1021/acsami.7b01534

Monitoring the Reaction Mechanism in Model Biogas Reforming by InSitu Transient and Steady-State DRIFTS Measurements

Bobadilla, LF; Garcilaso, V; Centeno, MA; Odriozola, JA

In this work, the reforming of model biogas was investigated on a Rh/MgAl2O4 catalyst. In situ transient and steady-state diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements were used to gain insight into the reaction mechanism involved in the activation of CH4 and CO2. It was found that the reaction proceeds through of an initial pathway in which methane and CO2 are both dissociated on Rh metallic sites and additionally a bifunctional mechanism in which methane is activated on Rh sites and CO2 is activated on the basic sites of the support surface via a formate intermediate by H-assisted CO2 decomposition. Moreover, this plausible mechanism is able to explain why the observed apparent activation energy of CO2 is much lower than that of CH4. Our results suggest that CO2 dissociation facilitates CH4activation, because the oxygen-adsorbed species formed in the decomposition of CO2 are capable of reacting with the CHx species derived from methane decomposition.

Chemsuschem, 10 (2017) 1193-1201 | DOI: 10.1002/cssc.201601379

Aperiodic Metal-Dielectric Multilayers as Highly Efficient Sunlight Reflectors

Alberto Jiménez-Solano; Miguel Anaya; Mauricio E. Calvo; Mercedes Alcon-Camas; Carlos Alcañiz; Elena Guillén; Noelia Martínez; Manuel Gallas; Thomas Preussner; Ramón Escobar-Galindo; Hernán Míguez

The optimum reflection of the solar spectrum at well-defined incident directions as well as its durability in time are, both, fundamental requirements of the optics of thermosolar and photovoltaic energy conversion systems. The stringent high performance needed for these applications implies that, almost exclusively, second face mirrors based on silver are employed for this purpose. Herein, the possibility to develop solar mirrors using other metals, such as copper and aluminum, is theoretically and experimentally analyzed. It is found that reflectors based on these inexpensive metals are capable of reflecting the full solar spectrum with efficiencies comparable to that of silver-based reflectors. The designs herein proposed are based on aperiodic metal-dielectric multilayers whose optimized configuration is chosen employing a code based on a genetic algorithm that allows selecting the best one among 108 tested reflectors. The use of metals with wider spectral absorption bands is compensated by the use of multilayered designs in which metal absorption is almost suppressed, as the analysis of the electric field intensity distribution demonstrates. The feasibility of the proposed mirrors is demonstrated by their actual fabrication by large area deposition techniques amenable for mass production.

Advanced Optical Materials, 5 (2017) 1600833 | DOI: 10.1002/adom.201600833

Strong Quantum Confinement and Fast Photoemission Activation in CH3NH3PbI3 Perovskite Nanocrystals Grown within Periodically Mesostructured Films

Miguel Anaya; Andrea Rubino; Teresa Cristina Rojas; Juan Francisco Galisteo-López; Mauricio Ernesto Calvo; Hernán Míguez

In this Communication, a synthetic route is demonstrated to obtain stabilized MAPbI3 nanocrystals embedded in thin metal oxide films that display well-defined and adjustable quantum confinement effects over a wide range of 0.34 eV. Mesostructured TiO2 and SiO2 films displaying an ordered 3D pore network are prepared by evaporation-induced self-assembly of a series of organic supramolecular templates in the presence of metal oxide precursors. The pores in the inorganic films obtained after thermal annealing are then used as nanoreactors to synthesize MAPbI3crystallites with narrow size distribution and average radius comprised between 1 and 4 nm, depending on the template of choice. Both the static and dynamic photoemission properties of the ensemble display features distinctive of the regime of strong quantum confinement. Photoemission maps demonstrate that the spectral and intensity properties of the luminescence extracted from the perovskite quantum dot loaded films are homogeneous over squared centimeters areas. At variance with their bulk counterparts, constant emission intensity is reached in time scales at least four orders of magnitude shorter.

Advanced Optical Materials | DOI: 10.1002/adom.201601087

Improving the pollutant removal efficiency of packed-bed plasma reactors incorporating ferroelectric components

Gomez-Ramirez, Ana; Montoro-Damas, Antonio M.; Rodriguez, Miguel A.; Gonzalez-Elipe, Agustin R.; Cotrino, Jose

In this work we have studied the plasma removal of air contaminants such as methane, chloroform, toluene and acetone in two parallel plate packed-bed dielectric barrier discharge (DBD) reactors of different sizes. Removal and energy efficiencies have been determined as a function of the residence time of the contaminated air within the reactor, the kind of packed-bed material (ferroelectrics or classical dielectric materials), the frequency and the incorporation of a ferroelectric plate onto the active electrode together with the inter-electrode ferroelectric pellets filling the gap. Results at low frequency with the small reactor and the ferroelectric plate showed an enhancement in energy efficiency (e.g., it was multiplied by a factor of six and three for toluene and chloroform, respectively) and in removal yield (e.g., it increased from 22% to 52% for chloroform and from 15% to 21% for methane). Such enhancements have been attributed to the higher energy of plasma electrons and a lower reactor capacitance found for this plate-modified configuration. A careful analysis of reaction efficiencies and electron energy distributions for the different investigated conditions and the simulation of the electric field at the necks between ferroelectric/dielectric pellets complete the present study. Overall, the obtained results prove the critical role of the barrier architecture and operating conditions for an enhanced performance of pollution removal processes using DBD systems.

Chemical Engineering Journal, 314 (2017) 311-319 | DOI: 10.1016/j.cej.2016.11.065

Deep insight into Zr/Fe combination for successful Pt/CeO2/Al2O3 WGS catalyst doping

Gonzalez-Castano, M; Ivanova, S; Ioannides, T; Centeno, MA; Odriozola, JA

Efficient promotion of the Pt/CeO2/Al2O3 catalytic system was achieved by the addition of two different ceria promoters, Zr and Fe. From the exhaustive data analysis, the key features for enhanced catalytic performance and the roles of each doping metal are established. The combination of both doping agents manifests a synergistic effect reflected in noteworthy improvements in H2 reducibility. In addition, the catalyst's doping influences its chemisorptive properties, which is reflected in an increase of the easiness of carbonaceous species desorption, thus leading to superior catalyst resistance toward deactivation.

Catalysis Science & Technology, 7 (2017) 1556-1564 | DOI: 10.1039/c6cy02551j

Large-Scale Storage of Concentrated Solar Power from Industrial Waste

Perejon, Antonio; Valverde, Jose Manuel; Miranda-Pizarro, Juan; Sanchez-Jimenez, Pedro E.; Perez-Maqueda, Luis A.

Deep penetration of renewable energies into the grid relies on the development of large-scale energy storage technologies using cheap, abundant, and nontoxic materials. Concentrated solar power (CSP) is particularly suitable to massively store thermal energy for dispatchable electricity generation. This is currently accomplished in a few demonstration plants by using molten salts albeit in a not competitive way yet. Process simulation studies indicate that thermochemical energy storage of CSP by means of the calcium looping (CaL) technology would reduce the cost of storage and increase the flexibility of energy supply provided that widely available and cheap CaO precursors with high and stable multicycle activity are used. In this work, we investigate the behavior of calcium rich steel slag at CaL conditions that would expectedly maximize the efficiency of CSP energy storage and power production. When treated with acetic acid, this nontoxic widely abundant waste yields a CaO rich solid with stable conversion near 0.8 over successive carbonation/calcination cycles at these CaL conditions

ACS Sustainable Chemistry & Engineering, 5 (2017) 2265-2272 | DOI: 10.1021/acssuschemeng.6b02576

Electron injection and scaffold effects in perovskite solar cells

M. Anaya, W. Zhang, B. Clasen Hames, Y. Li, F. Fabregat-Santiago, M.E. Calvo, H.J. Snaith, H. Míguez, I. Mora-Seró

In spite of the impressive efficiencies reported for perovskite solar cells (PSCs), key aspects of their working principles, such as electron injection at the contacts or the suitability of the utilization of a specific scaffold layer, are not yet fully understood. Increasingly complex scaffolds attained by the sequential deposition of TiO2 and SiO2 mesoporous layers onto transparent conducting substrates are used to perform a systematic characterization of both the injection process at the electron selective contact and the scaffold effect in PSCs. By forcing multiple electron injection processes at a controlled sequence of perovskite–TiO2 interfaces before extraction, interfacial injection effects are magnified and hence characterized in detail. An anomalous injection behavior is observed, the fingerprint of which is the presence of significant inductive loops in the impedance spectra with a magnitude that correlates with the number of interfaces in the scaffold. Analysis of the resistive and capacitive behavior of the impedance spectra indicates that the scaffolds could hinder ion migration, with positive consequences such as lowering the recombination rate and implications for the current–potential curve hysteresis. Our results suggest that an appropriate balance between these advantageous effects and the unavoidable charge transport resistive losses introduced by the scaffolds will help in the optimization of PSC performance.

Journal of Materials Chemistry C, 5 (2017) 634-644 | DOI: 10.1039/C6TC04639H

Non-enzymatic hydrogen peroxide detection at NiO nanoporous thin film-electrodes prepared by physical vapor deposition at oblique angles

Salazar, Pedro; Rico, Victor; Gonzalez-Elipe, Agustin R.

In this work we report a non-enzymatic sensor for hydrogen peroxide (H2O2) detection based on nanostructured nickel thin films prepared by physical vapor deposition at oblique angles. Porous thin films deposited on ITO substrates were characterized by X-ray diffraction analysis, scanning electron microcopy (SEMs), X-ray photoelectron spectroscopy (XPS) and electrochemical techniques such as Cyclic Voltammetry (CV) and Constant Potential Amperometry (CPA). The microstructure of the thin films consisted of inclined and separated Ni nanocolumns forming a porous thin layer of about 500 nm thickness. Prior to their use, the films surface was electrochemically modified and the chemical state studied by CV and XPS analysis. These techniques also showed that Ni2+/Ni3+ species were involved in the electrochemical oxidation and detection of H2O2 in alkaline medium. Main analytical parameters such as sensitivity (807 mA M(-1)cm(-2)), limit of detection (3.22 mu M) and linear range (0.011-2.4 mM) were obtained under optimal operation conditions. Sensors depicted an outstanding selectivity and a high stability and they were successfully used to determine H2O2 concentration in commercial antiseptic solutions.

Electrochimica Acta, 235 (2017) 534-542 | DOI: 10.1016/j.electacta.2017.03.087

New method for carbon dioxide mineralization based on phosphogypsum and aluminium-rich industrial wastes resulting in valuable carbonated by-products

Romero-Hermida, I; Santos, A; Perez-Lopez, R; Garcia-Tenorio, R; Esquivias, L; Morales-Florez, V

A new carbon mineralization method was designed based on a sequestration agent synthesised exclusively from industrial wastes. Phosphogypsum waste from the fertiliser industry was dissolved into caustic aqueous waste from the aluminium anodising industry. The resulting precipitate consisted of katoite (Ca3Al2(OH) 12, a Si-free hydrogrossular solid solution end-member of the Al-containing hydrogarnet) and thenardite (Na2SO4); the latter easily removed by rinsing with water. The carbonation performance of this katoite-rich sequestration agent was evaluated using two different methods, by bubbling in aqueous media and by weathering. Both procedures yielded high carbonation efficiencies (80% and 100%, respectively), and resulted in a solid precipitate composed primarily of calcite (CaCO3) and aluminium hydroxide (Al(OH)(3)). Priority attention was given to the transfer of trace elements and radionuclides of the uranium series typically present in the phosphogypsum. Results confirmed that the traces were transferred to resulting final solid carbonate at concentrations similar to those present in the raw phosphogypsum. In conclusion, these carbonated minerals would trap substantial amounts of CO2 and produce final materials with similar civil engineering uses to those proposed for current phosphogypsum wastes. This work offers new methods for jointly managing specific industrial wastes oriented to more sustainable industrial processes and controlling CO2 emissions.

Journal of CO2 Utilization, 18 (2017) 15-22 | DOI: 10.1016/j.jcou.2017.01.002

Cholesterol biosensing with a polydopamine-modified nanostructured platinum electrode prepared by oblique angle physical vacuum deposition

Martin, M; Salazar, P; Alvarez, R; Palmero, A; Lopez-Santos, C; Gonzalez-Mora, JL; Gonzalez-Elipe, AR

This paper reports a novel cholesterol biosensor based on nanostructured platinum (Pt) thin films prepared by Magnetron Sputtering (MS) in an oblique angle (OAD) configuration. Pt thin films were deposited onto a gold screen-printed electrode and characterized using Rutherford Back Scattering (RBS), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Cyclic Voltammetry (CV), X-ray Photo-electron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and wetting analysis. Our results confirmed that the film is highly porous and formed by tilted nanocolumns, with an inclination of around 40 degrees and a total thickness of 280 nm. XRD and CV analysis confirmed the polycrystalline nature of the Pt thin film. Cholesterol oxidase (ChOx) was covalently immobilized using a bioinspired polymer, polydopamine (PDA), via Schiff base formation and Michael-type addition. After being immobilized, ChOx displayed apparent activation energy of 34.09 kJ mol(-1) and Michaelis constant (K-M) values of 34.09 kJ mol(-1) and 3.65 mM, respectively, confirming the high affinity between ChOx and cholesterol and the excellent ability of the PDA film for immobilizing biological material without degradation. Under optimized working conditions the developed biosensor presented a sensitivity of 14.3 mA M(-1)cm(-2) (R-2:0.999) with a linear range up to 0.5 mM and a limit of detection of 10.5 mu M (S/N= 3). Furthermore, the biosensor exhibited a fast response (<8 s), good anti-interference properties and high stability after relatively long-term storage (2 months). 

Sensors and Actuators B-Chemical, 240 (2017) 37-45 | DOI: 10.1016/j.snb.2016.08.092

Comprehensive and Systematic Analysis of the Immunocompatibility of Polyelectrolyte Capsules

Zyuzin, MV; Diez, P; Goldsmith, M; Carregal-Romero, S; Teodosio, C; Rejman, J; Feliu, N; Escudero, A; Almendral, MJ; Linne, U; Peer, D; Fuentes, M; Parak, WJ

The immunocompability of polyelectrolyte capsules synthesized by layer-by-layer deposition has been investigated. Capsules of different architecture and composed of either non-degradable or biodegradable polymers, with either positively or negatively charged outer surface, and with micrometer size, have been used, and the capsule uptake by different cell lines has been studied and quantified. Immunocompatibility studies were performed with peripheral blood mononuclear cells (PBMCs). Data demonstrate that incubation with capsules, at concentrations relevant for practical applications, did not result in a reduced viability of cells, as it did not show an increased apoptosis. Presence of capsules also did not result in an increased expression of TNF-α, as detected with antibody staining, as well as at mRNA level. It also did not result in increased expression of IL-6, as detected at mRNA level. These results indicate that the polyelectrolyte capsules used in this study are immunocompatible.

Bioconjugate Chemistry, 28 (2017) 556-564 | DOI: 10.1021/acs.bioconjchem.6b00657

Gold catalysts screening in base-free aerobic oxidation of glucose to gluconic acid

Benitez, JJ; Heredia-Guerrero, JA; Cruz-Carrillo, MA; Barthel, MJ; Knicker, HE; Heredia, A

Base-free aerobic oxidation of glucose in presence of Au/Al2O3, Au/CeO2, Au/CeO2(20 wt%)/Al2O3, Au/CeO2(25 wt%)/ZrO2 and Au/CeO2(50 wt%)/ZrO2 catalysts using molecular oxygen at atmospheric pressure is studied. Within the whole series high conversion and selectivity to gluconic acid are observed after 18 h of reaction at 120 degrees C. The activity and especially the selectivity changes are related to the support nature in a way that the higher the Lewis acidity of the support the lower the selectivity to gluconic acid and the higher the production of lactic acid. The highest yield to gluconic acid is obtained over Au/Al2O3 for which the influence of the reaction time, temperature and stirring rate are further evaluated and discussed.

Catalysis Today, 279 (2017) 148-154 | DOI: 10.1016/j.cattod.2016.06.046

High UV-photocatalytic activity of ZnO and Ag/ZnO synthesized by a facile method

C. Jaramillo-Páez; J.A. Navío; M.C. Hidalgo; M. Macías

ZnO nanoparticles have been successfully synthesized by a facile precipitation procedure by mixing aqueous solutions of Zn(II) acetate and dissolved Na2CO3 at pH ca. 7.0 without template addition. We have investigated the effect of annealing temperature in the final surface and structural properties. Photocatalytic studies were performed using two selected substrates, Methyl Orange and Phenol, both as single model substrates and in mixtures of them.

It has been stated that calcination treatments lead to a significant improvement in the photocatalytic properties of the studied samples, even better than TiO2(P25). As expected, the addition of Ag+ during the photocatalytic degradation of MO increases the reaction rate of the degradation of MO, giving a resultant Ag/ZnO photocatalyst which, after recovery, can be reused at least 18 times for the MO degradation tests, being even more photoactive than ZnO.

Catalysis Today, 284 (2017) 121-128 | DOI: 10.1016/j.cattod.2016.11.021

Morphology control of uniform CaMoO4 microarchitectures and development of white light emitting phosphors by Ln doping (Ln = Dy3+, Eu3+)

Laguna, Mariano; Nunez, Nuria O.; Becerro, Ana I.; Ocana, Manuel

A very simple synthesis procedure based on precipitation reactions at moderate temperature (120 degrees C) from solutions containing calcium nitrate and sodium molybdate, using mixed solvents (polyols and water) has been developed, which produces uniform tetragonal CaMoO4 microarchitectures with different morphologies (peanuts, cocoons, spindles and spheres) composed of self-assembled entities. The morphology and crystal size of such assemblies could be tuned by a simple change of the nature of the components of the solvent mixture or their volumetric ratio in such a mixture. All particles presented similar excitation and emission spectra arising from a charge transfer process within the MoO4 2-groups. The emitted light presented a bluish-green color and its intensity was higher for the spindle-type particles. This synthesis procedure was also suitable for doping peanut-like CaMoO4 architectures with Eu3+ or Dy3+ cations up to a 1% molar ratio (Ln/Ln + Ca), without altering their morphology or crystalline structure. The so prepared phosphors emitted an intense red (Eu-doped) or greenish (Dy-doped) light when excited through the MoO42- group excitation band, indicating the presence of an energy transfer process from such groups to the Ln(3+) cations. Finally, a white light emitting phosphor with chromaticity coordinates x = 0.335 and y = 0.365 and a correlated color temperature of 5407 K was developed by codoping peanut-type CaMoO4 particles with suitable amounts of Dy3+ (0.35%) and Eu3+ (0.15%) cations, which could find applications in white light emitting diodes.

Crystengcomm, 19 (2017) 1590-1600 | DOI: 10.1039/c6ce02611g

CO2 capture performance of Ca-Mg acetates at realistic Calcium Looping conditions

Miranda-Pizarro, J; Perejon, A; Valverde, JM; Perez-Maqueda, LA; Sanchez-Jimenez, PE

The Calcium Looping (CaL) process, based on the cyclic carbonation/calcination of CaO, has emerged in the last years as a potentially low cost technique for CO2 capture at reduced energy penalty. In the present work, natural limestone and dolomite have been pretreated with diluted acetic acid to obtain Ca and Ca-Mg mixed acetates, whose CO2 capture performance has been tested at CaL conditions that necessarily imply sorbent regeneration under high CO2 partial pressure. The CaL multicycle capture performance of these sorbents has been compared with that of CaO directly derived from limestone and dolomite calcination. Results show that acetic acid pretreatment of limestone does not lead to an improvement of its capture capacity, although it allows for a higher calcination efficiency to regenerate CaO at reduced temperatures (similar to 900 degrees C) as compared to natural limestone (>similar to 930 degrees C). On the other hand, if a recarbonation stage is introduced before calcination to reactivate the sorbent, a significantly higher residual capture capacity is obtained for the Ca -Mg mixed acetate derived from dolomite as compared to either natural dolomite or limestone. The main reason for this behavior is the enhancement of carbonation in the solid-state diffusion controlled phase. It is argued that the presence of inert MgO grains in the mixed acetate with reduced segregation notably promotes solid state diffusion of ions across the porous structure created after recarbonation.

Fuel, 196 (2017) 497-507 | DOI: 10.1016/j.fuel.2017.01.119

Formation of nitrile species on Ag nanostructures supported on a-Al2O3: a new corrosion route for silver exposed to the atmosphere

Pelaez, RJ; Espinos, JP; Afonso, CN

The aging of supported Ag nanostructures upon storage in ambient conditions (air and room temperature) for 20 months has been studied. The samples are produced on glass substrates by pulsed laser deposition (PLD); first a 15 nm thick buffer layer of amorphous aluminum oxide (a-Al2O3) is deposited, followed by PLD of Ag. The amount of deposited Ag ranges from that leading to a discontinuous layer up to an almost-percolated layer with a thickness of <6 nm. Some regions of the as-grown silver layers are converted, by laser induced dewetting, into round isolated nanoparticles (NPs) with diameters of up to ~25 nm. The plasmonic, structural and chemical properties of both as-grown and laser exposed regions upon aging have been followed using extinction spectroscopy, scanning electron microscopy and x-ray photoelectron spectroscopy, respectively. The results show that the discontinuous as-grown regions are optically and chemically unstable and that the metal becomes oxidized faster, the smaller the amount of Ag. The corrosion leads to the formation of nitrile species due to the reaction between NO x species from the atmosphere adsorbed at the surface of Ag, and hydrocarbons adsorbed in defects at the surface of the a-Al2O3 layer during the deposition of the Ag nanostructures by PLD that migrate to the surface of the metal with time. The nitrile formation thus results in the main oxidation mechanism and inhibits almost completely the formation of sulphate/sulphide. Finally, the optical changes upon aging offer an easy-to-use tool for following the aging process. They are dominated by an enhanced absorption in the UV side of the spectrum and a blue-shift of the surface plasmon resonance that are, respectively, related to the formation of a dielectric overlayer on the Ag nanostructure and changes in the dimensions/features of the nanostructures, both due to the oxidation process.

Nanotechnology, 28 (2017) 175709 | DOI: 10.1088/1361-6528/aa65c0

Solid lubricant behavior of MoS2 and WSe2-based nanocomposite coatings

Dominguez-Meister, S; Rojas, TC; Brizuela, M; Sanchez-Lopez, JC

Tribological coatings made of MoS2 and WSe2 phases and their corresponding combinations with tungsten carbide (WC) were prepared by non-reactive magnetron sputtering of individual targets of similar composition. A comparative tribological analysis of these multiphase coatings was done in both ambient air (30-40% relative humidity, RH) and dry nitrogen (RH<7%) environments using the same tribometer and testing conditions. A nanostructural study using advanced transmission electron microscopy of the initial coatings and examination of the counterfaces after the friction test using different analytical tools helped to elucidate what governs the tribological behavior for each type of environment. This allowed conclusions to be made about the influence of the coating microstructure and composition on the tribological response. The best performance obtained with a WSe x film (specific wear rate of 2 x 10(-8) mm(3) N(-1)m(-1) and a friction coefficient of 0.03-0.05) was compared with that of the well-established MoS2 lubricant material.

Science and Tecnology of Advances Materials, 18 (2017) 1 | DOI: 10.1080/14686996.2016.1275784

Front contact optimization of industrial scale CIGS solar cells for low solar concentration using 2D physical modeling

Delgado-Sanchez, JM; Lopez-Gonzalez, JM; Orpella, A; Sanchez-Cortezon, E; Alba, MD; Lopez-Lopez, C; Alcubilla, R

Cu(In,Ga)Se-2 (CIGS) technology is one of the best absorber materials with record efficiencies among photovoltaic thin-film technologies (22.3% at lab scale and 16% at large commercial module). Although research on this material was originally motivated by low-cost, glass-glass applications focusing to fixed photovoltaic structures, the high efficiency values make CIGS an interesting alternative for low concentration systems. In this paper a 2D model for Cu(In,Ga)Se-2 (CIGS) solar cells under low solar concentration is described and contrasted with experimental data. Using simulation, the effect of front electric contact design parameters: finger width, finger separation, and number of buses are analyzed for solar concentrations from 1 up to 10 suns. Efficiency maps allowing front contact grid optimization are shown and analyzed for each concentration factor (Cx), assessing the viability of CIGS solar cells for low concentration applications, where commercial CIGS solar cells may exhibit 35% of electrical power increases with proper front grid optimization under low concentration respect to conventional grid design. 

Renewable Energy, 101 (2017) 90-95 | DOI: 10.1016/j.renene.2016.08.046

Preferential oxidation of CO on a La-Co-Ru perovskite-type oxide catalyst

Pereniguez, R; Caballero, A; Ferri, D

A Ru-containing perovskite-type oxide La(Co,Ru)O3 of nominal composition LaCo0.8Ru0.2O3 was prepared by ultrasonic spray combustion and tested for the preferential oxidation of CO (PROX). EXAFS indicated that Ru adopted the coordination environment of Co in LaCoO3 while Co was present as LaCoO3 and Co3O4. PROX activity was replaced by CO hydrogenation activity above 250 °C. Short oxidation at 500 °C between temperature programmed reaction ramps did not restore the initial La(Co,Ru)O3 structure but generated a catalyst with improved PROX activity compared to the initial La(Co,Ru)O3. Under reductive PROX conditions the material experienced structural changes that improved its overall catalytic activity only if the catalyst was oxidized after each temperature programmed ramp.

Catalysis Communication, 92 (2017) 75-79 | DOI: 10.1016/j.catcom.2016.12.020

Ceramics of Ta-doping stabilized orthorhombic ZrO2 densified by spark plasma sintering and the effect of post-annealing in air

Sponchia, G; Moshtaghioun, BM; Benedetti, A; Riello, P; Gomez-Garcia, D; Dominguez-Rodriguez, A; Ortiz, AL

16 mol% Ta-doped ZrO2 powders were synthesized and densified by spark-plasma sintering (SPS) in vacuum, followed by post-SPS annealing in air, thus obtaining two ultrafine-grained ceramics consisting of Ta-doping stabilized orthorhombic ZrO2. The as-SPSed ceramic is black because it is actually a suboxide essentially with reduced cations and abundant oxygen vacancies, whereas the post-annealed ceramic is white because it is an oxide without vacancies and with only partially reduced cations. Both ceramics are relatively hard and brittle, but the as-SPSed ceramic was slightly more so, attributable to crystallographic and microstructural differences. Implications of interest for the ceramics community are discussed.

Scripta Materialia, 130 (2017) 128-132 | DOI: 10.1016/j.scriptamat.2016.11.021

Outstanding visible photocatalytic activity of a new mixed bismuth titanatate material

Zambrano, P; Sayagues, MJ; Navio, JA; Hidalgo, MC

In this work, a new photocatalyst based on bismuth titanates with outstanding visible photocatalytic activity was prepared by a facile hydrothermal method. The synthesised material showed visible activity as high as UV activity of commercial TiO2 P25 under the same experimental conditions for phenol degradation. A wide characterisation of the photocatalyst was performed. The material was composed of three phases; majority of Bi20TiO32 closely interconnected to Bi4Ti3O12 and amorphous TiO2. The high visible activity showed by this material could be ascribed to a combination of several features; i.e. low band gap energy value (2.1 eV), a structure allowing a good separation path for visible photogenerated electron-holes pairs and a relatively high surface area. This photocatalyst appeared as a promising material for solar and visible applications of photocatalysis.

Applied Surface Science, 394 (2017) 16-24 | DOI: 10.1016/j.apsusc.2016.10.042

Microcalorimetry: A powerful tool for quantitative analysis of aging hardening response of Cu-Ni-Sn alloys

Donoso, E; Dianez, MJ; Perejon, A; Sanchez-Jimenez, PE; Perez-Maqueda, LA; Sayagues, MJ; Criado, JM

The method for the deconvolution of overlapping DSC peaks here proposed has been used by the first time for the quantitative determination of the enthalpies associated to the phase transitions undergone during the aging of an alloy. They have been determined the enthalpies evolved along the first and the second overlapping DSC traces of Cu-10 wt%Ni-5.5 wt%Sn alloy, which are associated, respectively, to the spinodal decomposition of the alloy and the segregation of a DO22 (CuxNi1-x)(3)Sn tetragonal phase. The fraction of the DO22 phase (responsible of the aging hardening of this alloy) has been successfully determined from DSC as a function of the annealing treatment, while TEM and XRD failed for this purpose. It has been demonstrated that a threshold higher than 50% of crystallization of the DO22 phase is required for achieving a significant increase of the hardness as a function of the crystallization percentage. These results suggest that microcalorimetric measurement can be a powerful tool to establish quantitative relationships between the mechanical, electrical or functional properties of alloys and their structural changes undergone by aging.

Journal of alloys and compounds, 694 (2017) 710-714 | DOI: 10.1016/j.jallcom.2016.10.060

Preparation of ytterbium substituted BiFeO3 multiferroics by mechanical activation

Gil-Gonzalez, E; Perejon, A; Sanchez-Jimenez, PE; Hayward, MA; Perez-Maqueda, LA

Samples in the system Bi1-xYbxFeO3 (0.02 <= x <= 0.07) have for the first time been prepared by mechanical activation followed by sintering. XRD and DSC measurements show that the solubility limit of ytterbium in the R3c Bi1-xYbxFeO3 system is reached at x similar to 0.03. Higher ytterbium contents lead to a two-phase mixture of a main R3c phase of approximate composition Bi0.97Yb0.03FeO3 and ytterbium enriched secondary phases that cannot be readily indexed or quantified due to their small amount. DSC and temperature-dependent XRD showed that while the magnetic ordering temperature, T-N, was unaffected by Yb substitution, the ferroelectric ordering, T-C, declined. Temperature-dependent XRD patterns show that all samples exhibit rhombohedral R3c to orthorrhombic Pnma phase transitions. Diffuse reflectance spectroscopy suggests the potential use of the samples in photocatalytic applications due to their low band gap energy. Impedance spectroscopy and magnetic measurements show that samples are electrically homogenous and highly insulating, exhibiting antiferromagnetic behaviour at room temperature. 

Journal of the European Ceramic Society, 37 (2017) 945-954 | DOI: 10.1016/j.jeurceramsoc.2016.09.014

Regenerative Endodontic Procedures: A Perspective from Stem Cell Niche Biology

M. Marí-Beffa, J.J. Segura-Egea, A. Díaz-Cuenca

Introduction

Endodontics uses cell therapy strategies to treat pulpal and periapical diseases. During these therapies, surgeons aim to reconstruct the natural microenvironments that regulate the activity of dental stem cells.

Methods

We searched for more than 400 articles in PubMed using key words from regenerative endodontics and dental stem cell biology. In 268 articles, we reviewed what factors may influence histologic results after preclinical dental treatments that use regenerative endodontic procedures after pulpectomy.

Results

Several factors, such as the origin of stem cells, the biomimicry of scaffolds used, and the size of lesions, are considered to influence the histologic appearance of the regenerated pulp-dentin complex after treatments. Information is accumulating on transcription factors that generate the pulp-dentin complex and survival/trophic factors that would benefit niche recovery and histologic results.

Conclusions

In this article, we discuss the noninterchangeability of stem cells, the influence of dentin-entrapped molecule release on pulp regeneration and survival of stem cells, and the need of positional markers to assess treatments histologically. The ex vivo amplification of appropriate dental stem cells, the search for scaffolds storing the molecular diversity entrapped in the dentin, and the use of positional transcription factors as histologic markers are necessary to improve future preclinical experiments.

Journal of Endodontics, 43 (2017) 52-62 | DOI: 10.1016/j.joen.2016.09.011

Effect of Thermal Pretreatment and Nanosilica Addition on Limestone Performance at Calcium-Looping Conditions for Thermochemical Energy Storage of Concentrated Solar Power

Valverde, Jose Manuel; Barea-Lopez, Manuel; Perejon, Antonio; Sanchez-Jimenez, Pedro E.; Perez-Maqueda, Luis A.

The share of renewable energies is growing rapidly, partly in response to the urgent need for mitigating CO2 emissions from fossil fuel power plants. However, cheap and efficient large-scale energy storage technologies are not yet available to allow for a significant penetration of renewable energies into the grid. Recently, a potentially low-cost and efficient thermochemical energy storage (TCES) system has been proposed, based on the integration of the calcium-looping (CaL) process into concentrated solar power plants (CSPs). The CaL process relies on the multicycle carbonation/calcination of CaO, which can be derived from calcination of widely available, cheap, and nontoxic natural limestone (CaCO3). This work explores the effect on the multicycle activity of limestone-derived CaO of thermal pretreatment under diverse atmospheres and the addition of nanosilica, which would be expected to hinder CaO grain sintering. Importantly, optimum CaL conditions for CSP energy storage differ radically from those used in the application of the CaL process for CO2 capture. Thus, calcination should be ideally carried out under low CO2 partial pressure at moderate temperature (below 750 degrees C), whereas CO2 concentration and temperature should be high for carbonation in order to maximize thermoelectric efficiency. When limestone is subjected to carbonation/calcination cycles at these conditions, its performance is critically dependent on the type of pretreatment. Our results indicate that the multicycle CaO activity is correlated with the size of the particles and the CaO pore size distribution. Thus, CaO activity is impaired as particle size is increased and/or CaO pore size is decreased. These observations suggest that pore plugging poses a main limitation to the multicycle performance of limestone-derived CaO at the optimum CaL conditions for TCES in CSPs, which is supported by scanning electron microscopy analysis. Strategies to enhance the performance of natural limestone at these conditions should be therefore oriented toward minimizing pore plugging rather than CaO grain sintering, which stands as the main limitation at CaL conditions for CO2 capture.

Enery & Fuels, 31 (2017) 4226-4236 | DOI: 10.1021/acs.energyfuels.6b03364

A Promising approach to the kinetics of crystallization processes: The sample controlled thermal analysis

Perejon, A; Sanchez-Jimenez, PE; Criado, JM; Perez-Maqueda, LA

Constant Rate Thermal Analysis (CRTA) method implies controlling the temperature in such a way that the reaction rate is maintained constant all over the process. This method allows determining simultaneously both the kinetic parameters and the kinetic model from a single experiment as the shape of the CRTA -T curves strongly depends on the kinetic model. CRTA method has been developed in the market only for thermogravimetric and thermodilatometric systems and, therefore, its use has been limited until now to the kinetic study of processes involving changes in mass or size of the samples, respectively. To overcome this obstacle, a method has been developed in this work for using the DSC signal for controlling the process rate in such a way that CRTA would be applied to the kinetic analysis of either phase transformations or crystallizations. The advantages of CRTA for performing the kinetics of crystallization processes have been here successfully demonstrated for the first time after selecting the crystallization of zirconia gel as test reaction.

Journal of the American Ceramic Society, 100 (2017) 1125-1133 | DOI: 10.1111/jace.14604

Fabrication of black-gold coatings by glancing angle deposition with sputtering

Vitrey, A; Alvarez, R; Palmero, A; Gonzalez, MU; Garcia-Martin, JM

The fabrication of black-gold coatings using sputtering is reported here. Glancing angle deposition with a rotating substrate is needed to obtain vertical nanostructures. Enhanced light absorption is obtained in the samples prepared in the ballistic regime with high tilt angles. Under these conditions the diameter distribution of the nanostructures is centered at about 60 nm and the standard deviation is large enough to obtain black-metal behavior in the visible range.

Beilstein Journal of Nanotechnology, 8 (2017) 434–439 | DOI: 10.3762/bjnano.8.46

A compact and portable optofluidic device for detection of liquid properties and label-free sensing

Lahoz, F; Martin, IR; Walo, D; Gil-Rostra, J; Yubero, F; Gonzalez-Elipe, AR

Optofluidic lasers have been widely investigated over the last few years mainly because they can be easily integrated in sensor devices. However, high power pulse lasers arc required as excitation sources, which, in practice, limit the portability of the system. Trying to overcome some of these limitations, in this paper we propose the combined use of a small CW laser with a Fabry-Perot optofluidic planar microcavity showing high sensitivity and versatility for detection of liquid properties and label-free sensing. Firstly, a fluorescein solution in ethanol is used to demonstrate the high performances of the FP microcavity as a temperature sensor both in the laser (high pump power above laser threshold) and in the fluorescence (low pump power) regimes. A shift in the wavelength of the resonant cavity modes is used to detect changes in the temperature and our results show that high sensitivities could be already obtained using cheap and portable CW diode lasers. In the second part of the paper, the demonstration of this portable device for label-free sensing is illustrated under low CW pumping. The wavelength positions of the optolluidic resonant modes are used to detect glucose concentrations in water solutions using a protein labelled with a fluorescent dye as the active medium.

Journal of Physics D: Applied Physics, 50 (2017) 21 | DOI: 10.1088/1361-6463/aa6cdd

Spark plasma sintering of fine-grained alumina ceramics reinforced with alumina whiskers

Tamura, Y; Moshtaghioun, BM; Gomez-Garcia, D; Rodriguez, AD

Densification of alumina whisker-reinforced alumina ceramics by spark plasma sintering (SPS) has been investigated with the aim of obtaining a fine-grained microstructure and also studying the effect of whisker addition on the room-temperature mechanical properties. It was found that whisker addition retards slightly the sinterability of alumina by whisker hindering of particle rearrangement. Besides, the internal stress on the alumina matrix particles reduced due to the presence of a whisker network structure of strong rigid boundaries. Nevertheless near fully-dense and fine-grained alumina ceramics with alumina whisker content between 3 wt% and 10 wt% could be obtained under appropriate SPS conditions. The hardness of alumina ceramics with 3 wt% was comparable to that of pure alumina ceramics (similar to 26 GPa) whereas its fracture toughness (5.6 MPa m(1/2)) was higher (4.2 MPa m(1/2)). Crack bridging by well-dispersed whiskers and whiskers pull-out were identified as the main toughening mechanisms.

Ceramis International, 43 (2017) 658-663 | DOI: 10.1016/j.ceramint.2016.09.210

Preparation and Optimization of Fluorescent Thin Films of Rosamine-SiO2/TiO2 Composites for NO2 Sensing

Guillen, MG; Gamez, F; Suarez, B; Queiros, C; Silva, AMG; Barranco, A; Sanchez-Valencia, JR; Pedrosa, JM; Lopes-Costa, T

The incorporation of a prototypical rosamine fluorescent dye from organic solutions into transparent and microstructured columnar TiO2 and SiO2 (MO2) thin films, prepared by evaporation at glancing angles (GAPVD), was evaluated. The aggregation of the adsorbed molecules, the infiltration efficiency and the adsorption kinetics were studied by means of UV-Vis absorption and fluorescence spectroscopies. Specifically, the infiltration equilibrium as well as the kinetic of adsorption of the emitting dye has been described by a Langmuir type adsorption isotherm and a pseudosecond order kinetic model, respectively. The anchoring mechanism of the rosamine to the MO2 matrix has been revealed by specular reflectance Fourier transform infrared spectroscopy and infiltration from aqueous solutions at different pH values. Finally, the sensing performance towards NO2 gas of optimized films has been assessed by following the changes of its fluorescence intensity revealing that the so-selected device exhibited improved sensing response compared to similar hybrid films reported in the literature.

Materials, 10 (2017) art 124 | DOI: 10.3390/ma10020124

Analytical investigation of Mudejar polychrome on the carpentry in the Casa de Pilatos palace in Seville using non-destructive XRF and complementary techniques

Garrote, MA; Robador, MD; Perez-Rodriguez, JL

The pigments, execution technique and repainting used on the polychrome wood ceilings and doors in the Casa de Photos (Seville, Spain) were studied using portable X-ray fluorescence equipment. Cross-sections of small samples were also analysed by optical microscopy, SEM with EDX analysis, micro-Raman and micro-infrared spectroscopy and X-ray diffraction. These carpentry works are magnificent examples of the Mudejar art made in Spain in the early 16th century. Portable X-ray fluorescence gave good information on the different components of the polychrome. The SEM-EDX study of the surfaces of small samples gave information on their components and also characterized the compounds that had been deposited or formed by environmental contamination or by the alteration of some pigments. The SEM-EDX study of cross-sections facilitated the characterization of all layers and pigments from the support to the most external layer. The following pigments were characterized: red (cinnabar/vermillion, lead oxide, iron oxides and orpiment/realgar), black (carbon black), white (white lead and titanium barium white), yellow-orange-red-brown (orpiment/realgar and iron oxides), green (chromium oxide), blue (indigo blue and ultramarineblue), and gilding (gold leaf on bole). False gold, bronze and brass were also found. The pigments were applied with the oil painting technique over a support layer that had been primed with animal glue. This support layer was gypsum in some cases and white lead in others. This study is essential to the polychrome conservation of the studied artwork, and it will help clarify uncertainties in the history and painting of Mudejar art. 

Spectrochimica Acta Part A-Molecular and Biomolecular Spectroscopy | DOI: 10.1016/j.saa.2016.09.027

Precision and accuracy of stress measurement with a portable X-ray machine using an area detector

Lee, SY; Ling, JJ; Wang, SH; Ramirez-Rico, J

The use of portable X-ray stress analyzers, which utilize an area detector along with the newly adopted 'cos alpha' or full-ring fitting method, has recently attracted increasing interest. In laboratory conditions, these measurements are fast, convenient and precise because they employ a single-exposure technique that does not require sample rotation. In addition, the effects of grain size and orientation can be evaluated from the Debye ring recorded on the area detector prior to data analysis. The accuracy of the measured stress, however, has been questioned because in most cases just a single reflection is analyzed and the sample-to-detector distances are relatively short. This article presents a comprehensive analysis of the uncertainty associated with a state-of-the-art commercial portable X-ray device. Annealed ferrite reference powders were used to quantify the instrument precision, and the accuracy of the stress measurement was tested by in situ tensile loading on 1018 carbon steel and 6061 aluminium alloy bar samples. The results show that the precision and accuracy are sensitive to the instrument (or sample) tilt angle (0) as well as to the selected hkl reflection of the sample. The instrument, sample and data analysis methods all affect the overall uncertainty, and each contribution is described for this specific portable X-ray system. Finally, on the basis of the conclusions reached, desirable measurement/analysis protocols for accurate stress assessments are also presented.

Journal of Applied Crystallography, 50 (2017) 131-144 | DOI: 10.1107/S1600576716018914

Mixed alpha-Fe2O3/Bi2WO6 oxides for photoassisted hetero-Fenton degradation of Methyl Orange and Phenol

Jaramillo-Paez, C; Navio, JA; Hidalgo, MC; Bouziani, A; El Azzouzi, M

Mixed oxides, alpha-Fe2O3/Bi2WO6, were prepared using a mechanical mixing procedure by adding to the Bi2WO6 previously obtained by hydrothermal method the corresponding amount of a prepared alpha-Fe2O3, the latter obtained by thermal decomposition of Fe(NO3)center dot 9H(2)O. The physicochemical surface, structural, morphological characteristics and optical properties of the samples, single and mixed, were determined by BET, XRD, FE-SEM, XPS and UV-vis diffuse reflectance spectroscopy. UV-vis diffuse reflectance spectra showed that incorporating a 5%wt. of alpha-Fe2O3 to the corresponding amount of Bi2WO6 sample broadened the visible light absorption of Bi2WO6 as expected. The photocatalytic activity, of single and mixed catalysts, to degrade a selected dye such as Methyl Orange (MO) as well as the transparent substrate Phenol (Ph) was studied, in aqueous medium (pH 5.5) under UV and sun-like illumination conditions in the absence and presence of H2O2. In the present study the use of a alpha-Fe2O3/Bi2WO6/H2O2 system demonstrate much higher photocatalytic efficiency to degrade both MO and Ph than pristine Bi2WO6 or alpha-Fe2O3, single or mixed. Using the system alpha-Fe2O3/Bi2WO6/H2O2, around 85% of MO was degraded in 60 min under sun-like illumination whereas 100% was degraded in 60 min under UV-illumination. However, just around 30% of Ph was degraded in 120 min in the alpha-Fe2O3/Bi2WO6/H2O2 system under sun-like illumination whereas around a 95% was degraded in 90 min under UV-illumination. Under UV illumination, the generation of hydroxyl radicals is favorable; whereas under sun-like illumination, only the small fraction of the UV can produces the center dot OH. Under illumination, the H2O2 could react with photoinduced electrons from the photocatalysts leading to the production of hydroxyl radicals (center dot OH).

Journal of Photochemistry and Photobiology A-Chemistry, 332 (2017) 521-533 | DOI: 10.1016/j.jphotochem.2016.09.031

Structural and catalytic properties of Au/MgO-type catalysts prepared in aqueous or methanol phase: application in the CO oxidation reaction

Hernandez, Willinton Y.; Alic, Funda; Navarro-Jaen, Sara; Centeno, Miguel A.; Vermeir, Pieter; Van der Voort, Pascal; Verberckmoes, An

Au/MgO and Au/Mg(OH)(2)-type catalysts for CO oxidation reaction were prepared by using two different synthesis methods in presence of either an aqueous or methanol phase. The influence of the porous and morphological properties of the starting magnesium oxide supports was analyzed and correlated with the catalytic performances of the final gold-supported catalysts. It was found that the deposition of gold in the presence of methanol as a solvent avoids the total rehydration of the MgO support and maintains the textural and morphological properties of the starting oxides. The support synthesized by a surfactant-assisted hydrothermal route, having a combined meso-macroporous structure (i.e., MgO-P) showed a positive influence on the CO oxidation reaction as it favored the dispersion of gold and the surface-to-gas phase interaction during the catalytic process.

Journal of Materials Science, 52 (2017) 4727-4741 | DOI: 10.1007/s10853-016-0715-9

A new family of cermets: Chemically complex but microstructurally simple

de la Obra, AG; Aviles, MA; Torres, Y; Chicardi, E; Gotor, FJ

Cermets based on Ti(C,N) have interesting properties, such as high wear resistance, high chemical stability and good mechanical strength at high temperature, but to become a viable alternative to cemented carbides, the fracture toughness and damage tolerance must be significantly improved. Complete solid-solution cermets (CSCs) have been proposed to further improve the mechanical properties of these materials. However, to develop this family of cermets with a high level of quality and reliability, using pre-fabricated complex carbonitrides is necessary instead of unalloyed mixtures as the raw ceramic material. A mechanochemical process called mechanically induced self-sustaining reaction (MSR) is suitable to obtain these complex carbonitrides with high stoichiometric control. On the other hand, high entropy alloys (HEAs), which can also be obtained by mechanochemical processes, are a good candidate to replace the current binder phase in cermets because they exhibit high strength and ductility at high temperature and good resistance to both wear and corrosion. In this work, a new family of CSCs based on (Ti,Ta,Nb)CxN1-x, with HEAs belonging to the Fe-Co-Ni-Cr-Mn-V system as the binder phase is developed by mechanochemical processes. With only two constituent phases, these cermets have a simple microstructure but a high compositional complexity because both the ceramic and binder phases are complex solid solutions with at least five components.

International Journal of Refractory Metals & Hard Materials, 63 (2017) 17-25 | DOI: 10.1016/j.ijrmhm.2016.04.011

Antibacterial response of titanium oxide coatings doped by nitrogen plasma immersion ion implantation

Esparza, J; Fuentes, GF; Bueno, R; Rodriguez, R; Garcia, JA; Vitas, AI; Rico, V; Gonzalez-Elipe, AR

Plasma immersion ion implantation technology has been utilized to enhance the photocatalytic activity of the anatase phase of TiO2 thin films deposited by cathodic arc evaporation PVD. The main objective of this study is to shift the light absorbance of the titania in order to obtain antibacterial activity under visible light irradiation. TiO2 thin films, deposited on polished stainless steel AISI 304 and silicon wafers, were implanted with nitrogen ions (N+/N2+) at 20 kV energy and different temperatures between 250 and 350 °C. The antibacterial activity of nitrogen implanted titania coatings has been monitored for Escherichia coli under visible light irradiation. Additionally ultra violet/visible spectrophotometry tests have been carried out to measure the changes in the light absorbance of the doped films. Further characterization has been performed, including X-ray photoelectron spectroscopy, X-ray diffraction and glow discharge optical emission spectrometry. As a result of Nitrogen implantation, the light absorption peak shifted from ultra violet region (UV-A) to visible wavelength range, which led to an increase of the antibacterial efficacy under visible light irradiation.

Surface and Coatings Technology, 314 (2017) 67-71 | DOI: 10.1016/j.surfcoat.2016.11.002

Optical Gas Sensing of Ammonia and Amines Based on Protonated Porphyrin/TiO2 Composite Thin Films

Castillero, Pedro; Roales, Javier; Lopes-Costa, Tania; Sanchez-Valencia, Juan R.; Barranco, Angel; Gonzalez-Elipe, Agustin R.; Pedrosa, Jose M.

Open porous and transparent microcolumnar structures of TiO2 prepared by physical vapour deposition in glancing angle configuration (GLAD-PVD) have been used as host matrices for two different fluorescent cationic porphyrins, 5-(N-methyl 4-pyridyl)-10,15,20-triphenyl porphine chloride (MMPyP) and meso-tetra (N-methyl 4-pyridyl) porphine tetrachloride (TMPyP). The porphyrins have been anchored by electrostatic interactions to the microcolumns by self-assembly through the dip-coating method. These porphyrin/TiO2 composites have been used as gas sensors for ammonia and amines through previous protonation of the porphyrin with HCl followed by subsequent exposure to the basic analyte. UV-vis absorption, emission, and time-resolved spectroscopies have been used to confirm the protonation-deprotonation of the two porphyrins and to follow their spectral changes in the presence of the analytes. The monocationic porphyrin has been found to be more sensible (up to 10 times) than its tetracationic counterpart. This result has been attributed to the different anchoring arrangements of the two porphyrins to the TiO2 surface and their different states of aggregation within the film. Finally, there was an observed decrease of the emission fluorescence intensity in consecutive cycles of exposure and recovery due to the formation of ammonium chloride inside the film.

Sensors, 17 (2017) 24 | DOI: 10.3390/s17010024

Insolubilization and thermal stabilization of a long-chain polyester by noncatalyzed melt-polycondensation synthesis in air

Benitez, JJ; Heredia-Guerrero, JA; Cruz-Carrillo, MA; Barthel, MJ; Knicker, HE; Heredia, A

Self-standing films of poly(-hydroxyl hexadecanoic acid) [poly(-OHC16)] have been prepared by noncatalyzed melt-polycondensation in air at 150, 175, and 200 degrees C. Poly(-OHC16)s obtained are characterized as polyesters by infrared spectroscopy (FT-IR) and solid state magic angle spinning C-13 nuclear magnetic resonance (C-13 MAS-NMR). Structurally, poly(-OHC16)s are quite crystalline as revealed by wide angle X-ray diffraction (WAXD). The presence of oxygen in the reaction atmosphere causes a mild oxidation in the form of peroxyester species, tentatively at the interphase between poly(-OHC16) crystallites, and the structure amorphization. The interfacial peroxyester phase ends up in the encapsulation of the polyester grains and provides a barrier towards the action of solvents. Thermal stabilization and insolubility resulting from the synthesis conditions used are interesting features to prepare solvent and heat resistant poly(-OHC16) coatings. Thus, a few microns thick poly(-OHC16) layer has been fabricated on aluminum foil and its resistivity towards a chloroform:methanol (1:1, v:v) mixture has been confirmed.

Journal of Applied Polymer Science, 134 (2017) 1 art 44350 | DOI: 10.1002/app.44350

New findings on thermal degradation properties of fluoropolymers

Liu, SE; Zhou, WL; Yan, QL; Qi, XF; An, T; Perez-Maqueda, LA; Zhao, FQ

In this paper, the thermal degradation properties of Viton A and Fluorel are investigated by both isoconversional and combined kinetic analysis methods using non-isothermal thermogravimetry technique. It has been found that the heating rate has little affect on the degradation residue of Fluorel and Viton A, where around 1.3% char was formed for Fluorel and 3.5% for Viton A. Different from the literature, the decomposition of Viton A should be considered as an overlapped dehydrofluorination and carbon chain scission process, with activation energy of 214 +/- 11 and 268 +/- 13 kJ mol(-1), respectively. The effect of dehydrofluorination on degradation of Fluorel is not so significant due to low content of H, and hence, it could be considered as a single-step mechanism with average activation energy of 264 +/- 14 kJ mol(-1). The thermal stability of Fluorel is much better than that of Viton A, and the predicted half-life is around 218 min for Fluorel and 49 min for Viton A at 420 A degrees C, which are consistent with experimental values. If using a single-step model as in the literature for Viton A, its half-life at 420 A degrees C would be underestimated for > 20%.

Journal of Thermal Analysis and Calorimetry, 128 (2017) 675-685 | DOI: 10.1007/s10973-016-5963-z

Absorption capacity, kinetics and mechanical behaviour in dry and wet states of hydrophobic DEDMS/TEOS-based silica aerogels

Morales-Florez, V; Pinero, M; Braza, V; Mesa, MD; Esquivias, L; La Rosa-Fox, N

This work is a new approach to the study of the structural, mechanical and absorption properties of hybrid organic/inorganic silica-based aerogels. Diethoxydimethylsilane and tetraethoxysilane have been used as precursors. Changes in properties such as specific surface area, porous volume, pore radius, and surface texture and chemistry were researched as a function of the relative organic content. In addition, the absorption properties were tested for different organic liquids. The discrepancy in the absorption mechanisms and the kinetics of pure inorganic and hybrid samples were discussed. It was confirmed that swelling occurs in samples with high organic content, which, in turn, governs the absorption process. Finally, the mechanical behaviour was studied by uniaxial compression. A significant rise of the rupture strain up to 0.45 and a 10-fold decrease in the Young's modulus to 7.8 MPa were measured in the dry samples by increasing the organic content. The mechanical response of the samples after saturation by the absorption of two reference oily liquids, namely, common motor oil and liquid polydimethylsiloxane, was also compared with the behaviour of dry samples. The presence of liquid within the sample reduced the value of the mechanical parameters in almost all cases. Moreover, the inclusion of organic chains also made the wet aerogels highly deformable. In summary, these first results suggest that tuning the organic ratio of the hybrid aerogels allows the control of not only the structural and mechanical properties but also the absorption properties.

Journal of Sol-Gel Science and Technology | DOI: 10.1007/s10971-016-4203-0

Failure mode and effect analysis of a large scale thin-film CIGS photovoltaic module

Delgado-Sanchez, JM; Sanchez-Cortezon, E; Lopez-Lopez, C; Aninat, R; Alba, MD

The efficiency of thin-film CIGS based cells at the laboratory scale is now getting closer to conventional Silicon technologies. As a consequence, the long-term stability of CIGS is now one of the main challenges left to address in order to assess its potential as an alternative for photovoltaic plants. This paper reports an overview of the critical risks for the commercial viability of the CIGS thin-film technology. The key causes of the potential failures of this technology are determined through the Failure Mode Analysis and Effects (FMEA) methodology. To validate the results obtained from the FMEA, aging tests and outdoor monitoring were also carried out. Based on the results obtained, we argue that the encapsulation material is the main cause of degradation in CIGS modules. 

Engireering failure analysis, 76 (2017) 55-60 | DOI: 10.1016/j.engfailanal.2017.02.004

Analysis of Ni species formed on zeolites, mesoporous silica and alumina supports and their catalytic behavior in the dry reforming of methane

Drobna, Helena; Kout, Martin; Soltysek, Agnieszka; Gonzalez-Delacruz, Victor M.; Caballero, Alfonso; Capek, Libor

The presented investigation is focused on the analysis of Ni species formed on microporous (zeolites MFI and FAU) and mesoporous materials (Al-MCM- 41 and SBA-15) and alumina supports and their catalytic behavior in the dry reforming of methane. The paper lays emphasis on the relationship between the catalytic behavior of Ni-based catalysts and their textural/structural properties. Ni-based catalysts were prepared by wet impregnation (11 wt% of Ni) followed by calcination in air and reduction in hydrogen. The properties of Ni-based catalysts were also compared prior and after the catalytic tests. The critical role was played by the high value of the specific surface area and the high strength of the interaction between the Ni species and the support, which both determined the high dispersion and stability of metal Ni-0 particles. Ni-Al-MCM-41 and Ni-SBA-15 showed the values of the conversion of CO2 and CH4 above 90% (stable during 12 h). Slightly lower values of the conversion of CO2 and CH4 were observed over Ni-Al2O3 (also stable during 12 h). In contrast to these materials, Ni-MFI and Ni-FAU exhibited the worse metallic Ni-0 particles dispersion and very bad catalytic behavior.

Reaction Kinetics Mechanisms and Catalysis, 121 (2017) 255-274 | DOI: 10.1007/s11144-017-1149-3

On the effect of wall slip on the determination of the yield stress of magnetorheological fluids

Caballero-Hernandez, J; Gomez-Ramirez, A; Duran, JDG; Gonzalez-Caballero, F; Zubarev, AY; Lopez-Lopez, MT

We study the effect of wall slip on the measured values of the yield stress of magnetorheological (MR) fluids. For this aim we used a rheometer provided with parallel-plate geometries of two types, distinguished by having smooth or rough surfaces. We found that wall slip led to the underestimation of the yield stress when measuring geometries with smooth surfaces were used, and that this underestimation was more pronounced for the static than for the dynamic yield stress. Furthermore, we analysed the effect that both irreversible particle aggregation due to colloidal interactions and reversible magnetic fieldinduced particle aggregation had on the underestimation provoked by wall slip. We found that the higher the degree of aggregation the stronger the underestimation of the yield stress. At low intensity of the applied magnetic field irreversible particle aggregation was dominant and, thus, the underestimation of the yield stress was almost negligible for well-dispersed MR fluids, whereas it was rather pronounced for MR fluids suffering from irreversible aggregation. As the magnetic field was increased the underestimation of the yield stress became significant even for the best dispersed MR fluid.

Applied Rheology, 27 (2017) 15001 (8 pages) | DOI: 10.3933/ApplRheol-27-15001

Processing and characterization of surrogate nuclear materials with controlled radial porosity

Torres, Y; Garcia-Ostos, C; Arevalo, C; Gotor, FJ; Pavon, JJ; Trueba, P; Rodriguez-Ortiz, JA

Irradiated fuel pellets present radial gradient porosity. CeO2 has been proven as a surrogate material to understand irradiated mixed oxide (MOX) due to its similar structural and mechanical properties. A novel compaction device was developed to produce CeO2 cylindrical pellets with controlled radial porosity. Three blends of CeO2 with different binder contents (0.5, 3 and 7.5 vol.% of ethylene-bis-stearamide, EBS) were prepared and used to obtain three different porosities for the core, intermediate and outer rings of pellets, respectively. Different compaction pressures were employed in each region to get the intended porosities. The whole pellet was subjected to a heating rate up to 500 degrees C to remove the EBS binder. Finally, a pressureless sintering step was performed at 1700 degrees C for 4 h. A microstructural characterization was performed in the three areas, including grain size and porosity. Mechanical properties like hardness, fracture toughness and tribo-mechanical response, as scratch resistance, were also determined. Pellets fabricated from this device have shown microstructural and mechanical properties with a good correlation to those of irradiated nuclear fuel.

Journal of Nuclear Science and Technology, 54 (2017) 167-173 | DOI: 10.1080/00223131.2016.1222918

Reliability of new poly (lactic-co-glycolic acid) membranes treated with oxygen plasma plus silicon dioxide layers for pre-prosthetic guided bone regeneration processes

Castillo-Dali, G; Castillo-Oyague, R; Batista-Cruzado, A; Lopez-Santos, C; Rodriguez-Gonzalez-Elipe, A; Saffar, JL; Lynch, CD; Gutierrez-Perez, JL; Torres-Lagares, D

Background: The use of cold plasmas may improve the surface roughness of poly(lactic-co-glycolic) acid (PLGA) membranes, which may stimulate the adhesion of osteogenic mediators and cells, thus accelerating the biodegradation of the barriers. Moreover, the incorporation of metallic-oxide particles to the surface of these membranes may enhance their osteoinductive capacity. Therefore, the aim of this paper was to evaluate the reliability of a new PLGA membrane after being treated with oxygen plasma (PO2) plus silicon dioxide (SiO2) layers for guided bone regeneration (GBR) processes. 
Material and Methods: Circumferential bone defects (diameter: 11 mm; depth: 3 mm) were created on the top of eight experimentation rabbits' skulls and were randomly covered with: (1) PLGA membranes (control), or (2) PLGA/ PO2/SiO2 barriers. The animals were euthanized two months afterwards. A micromorphologic study was then performed using ROI (region of interest) colour analysis. Percentage of new bone formation, length of mineralised bone, concentration of osteoclasts, and intensity of ostheosynthetic activity were assessed and compared with those of the original bone tissue. The Kruskal-Wallis test was applied for between-group com asignificance level of a=0.05 was considered. 
Results: The PLGA/ PO2/SiO2 membranes achieved the significantly highest new bone formation, length of miner-alised bone, concentration of osteoclasts, and ostheosynthetic activity. The percentage of regenerated bone supplied by the new membranes was similar to that of the original bone tissue. Unlike what happened in the control group, PLGA/PO2/SiO2 membranes predominantly showed bone layers in advanced stages of formation. Conclusions: The addition of SiO2 layers to PLGA membranes pre-treated with PO2 improves their bone-regeneration potential. Although further research is necessary to corroborate these conclusions in humans, this could be a promising strategy to rebuild the bone architecture prior to rehabilitate edentulous areas.

Medicina Oral Patología Oral y Cirugia Oral, 22 (2017) E242-E250 | DOI: 10.4317/medoral.21512

Features of electrical properties of BE-C(Fe) biocarbons carbonized in the presence of an Fe-containing catalyst

Popov, VV; Orlova, TS; Gutierrez-Pardo, A; Ramirez-Rico, J

The effect of partial graphitization on electrical and galvanomagnetic properties of BE-C(Fe) biomorphic carbons produced by beech wood carbonization at temperatures of 850-1600A degrees C in the presence of an iron-containing catalyst is studied. The use of an Fe catalyst at D cent (carb) ae<yen> 1000A degrees C leads to the formation of nanoscale graphite-phase inclusions; its total volume and nanocrystallite sizes increase with D cent (carb). The data on the carrier concentration and mobility are obtained. It was shown that partially graphitized BE-C(Fe) carbons with D cent (carb) ae<yen> 1000A degrees C in the conductivity type and magnetoresistance features relate to highly disordered metal systems whose conductivity can be described taking into account the contribution of quantum corrections, mainly the correction caused by the electron-electron interaction. It is shown that nonmonotonic dependences of the Hall constant R on the magnetic field are characteristic of BE-C(Fe) samples with 1000 ae<currency> D cent (carb) < 1600A degrees C, which is most probably caused by the contribution of various carrier groups, i.e., electrons and holes. In BE-C(Fe) samples with D cent (carb) = 1600A degrees C, the Hall coefficient corresponds to the metal state, which is associated with conducting medium homogenization resulting from the formation of a significant graphite phase volume.

Physics of the Solid State | DOI: 10.1134/S1063783417040205

Structural and Chemical Characteristics of Sisal Fiber and Its Components: Effect of Washing and Grinding

Benitez-Guerrero, M; Perez-Maqueda, LA; Artiaga, R; Sanchez-Jimenez, PE; Pascual-Cosp, J

This work covers the study of microstructural changes of natural sisal fibers induced by different conditioning pre-treatments: mechanical grinding, cryogenic grinding, and hot waterwashing. The aim of the work is to clarify the effects of the pre-treatments on crystallinity and infrared spectra of sisal. Scanning electron microscopy results allowed to identify morphological changes on the fiber surface. Deeper changes of chemical origin were studied by attenuated total reflectance/Fourier transform infrared spectroscopy (FTIR) and focused on the main components of cellular walls: cellulose, lignin, and xylan. The work was complemented with crystallinity index (I-c) data determined by two very different methods: the widely used for lignocellulosic fibers Segal equation based on X-ray diffraction measurements, and the other based on FTIR through the 1430/900 cm(-1) band intensity ratio, which is mostly used with cellulosic samples.

Journal of Natural Fibers, 14 (2017) 26-39 | DOI: 10.1080/15440478.2015.1137529

Identification of Outer and Inner Nickel Particles in a Mesoporous Support: How the Channels Modify the Reducibility of Ni/SBA-15 Catalysts

Rodriguez-Gomez, A; Caballero, A

Two different nickel supported on SBA-15 catalytic systems have been prepared by means of impregnation (Ni/SBA-15-ImU) and deposition-precipitation (Ni/SBA-15-DP) methodologies. Upon calcination, Ni/SBA-15DP presents a well-developed nickel phyllosilicate phase, which after reduction gives rise to a dispersed and homogeneous metallic phase, mainly located inside the 5 nm in diameter mesoporous structure of the support. On the contrary, as evidenced by XRD and a double temperature programmed reduction (TPR) peak, the Ni/SBA-15-ImU catalyst presents two different NiO phases, which after reduction in hydrogen generate nickel particles in a wide range of sizes. In situ XAS and XPS have unambiguously showed that the distinct TPR profiles obtained for each system are related with particles located in and out the mesoporous structure of the SBA-15 channels. The particles inside the porous are more difficult to reduce, clearly showing a kind of confinement effect of the SBA-15 mesostructure, modifying the reducibility of the NiO phase.

Chemnanomat, 3 (2017) 94-97 | DOI: 10.1002/cnma.201600297

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

Barranco, A; Borras, A; Gonzalez-Elipe, AR; Palmero, A

The oblique angle configuration has emerged as an invaluable tool for the deposition of nanostructured thin films. This review develops an up to date description of its principles, including the atomistic mechanisms governing film growth and nanostructuration possibilities, as well as a comprehensive description of the applications benefiting from its incorporation in actual devices. In contrast with other reviews on the subject, the electron beam assisted evaporation technique is analyzed along with other methods operating at oblique angles, including, among others, magnetron sputtering and pulsed laser or ion beam-assisted deposition techniques. To account for the existing differences between deposition in vacuum or in the presence of a plasma, mechanistic simulations are critically revised, discussing well-established paradigms such as the tangent or cosine rules, and proposing new models that explain the growth of tilted porous nanostructures. In the second part, we present an extensive description of applications wherein oblique-angle-deposited thin films are of relevance. From there, we proceed by considering the requirements of a large number of functional devices in which these films are currently being utilized (e.g., solar cells, Li batteries, electrochromic glasses, biomaterials, sensors, etc.), and subsequently describe how and why these nanostructured materials meet with these needs. 

Progress in Materials Science, 78 (2016) 59-153 | DOI: 10.1016/j.pmatsci.2015.06.003

Maximized performance of dye solar cells on plastic: a combined theoretical and experimental optimization approach

Li, Yuelong; Carretero-Palacios, Sol; Yoo, Kicheon; Kim, Jong Hak; Jimenez-Solano, Alberto; Lee, Chul-Ho; Miguez, Hernan; Ko, Min Jae

We demonstrate that a combined optimization approach based on the sequential alternation of theoretical analysis and experimental realization gives rise to plastic supported dye solar cells for which both light harvesting efficiency and electron collection are maximized. Rationalized configurations with optimized light trapping and charge extraction are realized to achieve photoanodes on plastic prepared at low temperature, showing a power conversion efficiency of 8.55% and a short circuit photocurrent of 16.11 mA cm−2, unprecedented for plastic based dye solar cell devices. Furthermore, the corresponding fully flexible designs present stable mechanical properties after several bending cycles, displaying 7.79% power conversion efficiency, an average broadband internal quantum efficiency above 90%, and a short circuit photocurrent of 15.94 mA cm−2, which is the largest reported value for bendable cells of this sort to date.

Energy & Environmental Science, 9 (2016) 2061-2071 | DOI: 10.1039/C6EE00424E

Unbroken Perovskite: Interplay of Morphology, Electro-optical Properties, and Ionic Movement

Correa-Baena, JP; Anaya, M; Lozano, G; Tress, W; Domanski, K; Saliba, M; Matsui, T; Jacobsson, TJ; Calvo, ME; Abate, A; Gratzel, M; Miguez, H; Hagfeldt, A

Hybrid organic-inorganic perovskite materials have risen up as leading components for light-harvesting applications. However, to date many questions are still open concerning the operation of perovskite solar cells (PSCs). A systematic analysis of the interplay among structural features, optoelectronic performance, and ionic movement behavior for FA(0.83)MA(0.17)Pb(I0.83Br0.17)(3) PSCs is presented, which yield high power conversion efficiencies up to 20.8%.

Advanced Materials, 28 (2016) 5031-5037 | DOI: 10.1002/adma.201600624

High-Throughput Fabrication of Resonant Metamaterials with Ultrasmall Coaxial Apertures via Atomic Layer Lithography

Yoo, D; Nguyen, NC; Martin-Moreno, L; Mohr, DA; Carretero-Palacios, S; Shaver, J; Peraire, J; Ebbesen, TW; Oh, SH

We combine atomic layer lithography and glancing angle ion polishing to create wafer-scale metamaterials composed of dense arrays of ultrasmall coaxial nanocavities in gold films. This new fabrication scheme makes it possible to shrink the diameter and increase the packing density of 2 nm-gap coaxial resonators, an extreme subwavelength structure first manufactured via atomic layer lithography, both by a factor of 100 with respect to previous studies. We demonstrate that the nonpropagating zeroth-order Fabry-Perot mode, which possesses slow light-like properties at the cutoff resonance, traps infrared light inside 2 nm gaps (gap volume similar to lambda(3)/10(6)). Notably, the annular gaps cover only 3% or less of the metal surface, while open-area normalized transmission is as high as 1700% at the epsilon-near-zero (ENZ) condition. The resulting energy accumulation alongside extraordinary optical transmission can benefit applications in nonlinear optics, optical trapping, and surface-enhanced spectroscopies. Furthermore, because the resonance wavelength is independent of the cavity length and dramatically red shifts as the gap size is reduced, large-area arrays can be constructed with lambda(resonance) >> period, making this fabrication method ideal for manufacturing resonant metamaterials.

Nano Letters, 16 (2016) 2040-2046 | DOI: 10.1021/acs.nanolett.6b00024

Metallic nanostructures for efficient LED lighting

Lozano, G; Rodriguez, SRK; Verschuuren, MA; Rivas, JG

Light-emitting diodes (LEDs) are driving a shift toward energy-efficient illumination. Nonetheless, modifying the emission intensities, colors and directionalities of LEDs in specific ways remains a challenge often tackled by incorporating secondary optical components. Metallic nanostructures supporting plasmonic resonances are an interesting alternative to this approach due to their strong light-matter interaction, which facilitates control over light emission without requiring external secondary optical components. This review discusses new methods that enhance the efficiencies of LEDs using nanostructured metals. This is an emerging field that incorporates physics, materials science, device technology and industry. First, we provide a general overview of state-of-the-art LED lighting, discussing the main characteristics required of both quantum wells and color converters to efficiently generate white light. Then, we discuss the main challenges in this field as well as the potential of metallic nanostructures to circumvent them. We review several of the most relevant demonstrations of LEDs in combination with metallic nanostructures, which have resulted in light-emitting devices with improved performance. We also highlight a few recent studies in applied plasmonics that, although exploratory and eminently fundamental, may lead to new solutions in illumination.

Light: Science and Applications | DOI: 10.1038/lsa.2016.80

Optofluidic Modulation of Self-Associated Nanostructural Units Forming Planar Bragg Microcavities

Oliva-Ramirez, M; Barranco, A; Loffler, M; Yubero, F; Gonzalez-Elipe, AR

Bragg microcavities (BMs) formed by the successive stacking of nanocolumnar porous SiO2 and TiO2 layers with slanted, zigzag, chiral, and vertical configurations are prepared by physical vapor deposition at oblique angles while azimuthally varying the substrate orientation during the multilayer growth. The slanted and zigzag BMs act as wavelength-selective optical retarders when they are illuminated with linearly polarized light, while no polarization dependence is observed for the chiral and vertical cavities. This distinct optical behavior is attributed to a self-nanostructuration mechanism involving a fence-bundling association of nanocolumns as observed by focused ion beam scanning electron microscopy in the slanted and zigzag microcavities. The outstanding retarder response of the optically active BMs can be effectively modulated by dynamic infiltration of nano- and mesopores with liquids of different refraction indices acting as a switch of the polarization behavior. The unprecedented polarization and tunable optofluidic properties of these nanostructured photonic systems have been successfully simulated with a simple model that assumes a certain birefringence for the individual stacked layers and accounts for the light interference phenomena developed in the BMs. The possibilities of this type of self-arranged nanostructured and optically active BMs for liquid sensing and monitoring applications are discussed.

ACS Nano, 10 (2016) 1256-1264 | DOI: 10.1021/acsnano.5b06625

Electrocatalytic System for the Simultaneous Hydrogen Production and Storage from Methanol

Gonzalez-Cobos, J; Rico, VJ; Gonzalez-Elipe, AR; Valverde, JL; de Lucas-Consuegra, A

This paper reports a groundbreaking approach for simultaneous hydrogen production and storage that entails catalysis, electrochemistry, surface science, and materials synthesis. A novel electrocatalytic system is developed based on nickel nanocolumnar films of controlled microstructure prepared on K-βAl2O3 solid electrolyte supports by oblique angle physical vapor deposition. The outstanding characteristics of this system are a hydrogen storage capacity of up to 19 g of H2 (100 g of Ni)−1, which is unparalleled in the literature and the possibility of controlling its release electrochemically, under fixed mild conditions (280 °C and normal pressure). H2 is produced in situ by methanol steam re-forming on the Ni catalyst, and it spills over onto graphene oxide aggregates formed during the catalytic process, as confirmed by SEM, FTIR, and Raman spectroscopy. The proposed storage mechanism considers a synergetic contribution of both Ni and graphene oxide, promoted by K+ ions, in enhancing the hydrogen storage capacity of the system.

ACS Catalysis, 6 (2016) 1942-1951 | DOI: 10.1021/acscatal.5b02844

Three-Dimensional Optical Tomography and Correlated Elemental Analysis of Hybrid Perovskite Microstructures: An Insight into Defect-Related Lattice Distortion and Photoinduced Ion Migration

Galisteo-Lopez, JF; Li, YL; Miguez, H

Organic lead halide perovskites have recently been proposed for applications in light-emitting devices of different sorts. More specifically, regular crystalline microstructures constitute an efficient light source and fulfill the geometrical requirements to act as resonators, giving rise to waveguiding and optical amplification. Herein we show three-dimensional laser scanning confocal tomography studies of different types of methylammonium lead bromide microstructures which have allowed us to dissect their photoemission properties with a precision of 0.036 mu m(3). This analysis shows that their spectral emission presents strong spatial variations which can be attributed to defect-related lattice distortions. It is also largely enhanced under light exposure, which triggers the migration of halide ions away from illuminated regions, eventually leading to a strongly anisotropic degradation. Our work points to the need for performing an optical quality test of individual crystallites prior to their use in optoelectronics devices and provides a means to do so.

Journal of Physical Chemistry Letters, 7 (2016) 5227-5234 | DOI: 10.1021/acsjpclett.6b02456

WGS and CO-PrOx reactions using gold promoted copper-ceria catalysts: "Bulk CuO-CeO2 vs. CuO-CeO2/Al2O3 with low mixed oxide content"

Reina, TR; Ivanova, S; Laguna, OH; Centeno, MA; Odriozola, JA

A copper-ceria bulk catalyst has been compared to a series of catalysts designed according to the as called "supported approach", corresponding to the dispersion of low content mixed copper-ceria oxide on alumina matrix. The principal characteristics of both types of catalysts are contemplated and the differences in their electronic and redox properties discussed in details. As a plus, the gold metal promotion of the catalysts is also envisaged. The advantages of the systems in the CO clean up reactions, WGS and CO-PrOx are commented. While the WGS activity appears to be ruled especially by the Cu/Ce surface to volume ratio, the CO-PrOx reaction is governed by the CuO loading. Gold addition provides benefits only at the low temperature WGS regime. Very importantly, the supported systems are always superior to the bulk configuration in terms of specific activity, a key factor from the catalyst's design perspective. 

Applied Catalysis B-Environmental, 197 (2016) 62-72 | DOI: 10.1016/j.apcatb.2016.03.022

Stabilization of catalyst particles against sintering on oxide supports with high oxygen ion lability exemplified by Ir-catalyzed decomposition of N2O

Yentekakis, IV; Goula, G; Panagiotopoulou, P; Kampouri, S; Taylor, MJ; Kyriakou, G; Lambert, RM

Iridium nanoparticles deposited on a variety of surfaces exhibited thermal sintering characteristics that were very strongly correlated with the lability of lattice oxygen in the supporting oxide materials. Specifically, the higher the lability of oxygen ions in the support, the greater the resistance of the nanoparticles to sintering in an oxidative environment. Thus with gamma-Al2O3 as the support, rapid and extensive sintering occurred. In striking contrast, when supported on gadolinia-ceria and alumina-ceria-zirconia composite, the Ir nanoparticles underwent negligible sintering. In keeping with this trend, the behavior found with yttria-stabilized zirconia was an intermediate between the two extremes. This resistance, or lack of resistance, to sintering is considered in terms of oxygen spillover from support to nanoparticles and discussed with respect to the alternative mechanisms of Ostwald ripening versus nanoparticle diffusion. Activity towards the decomposition of N2O, a reaction that displays pronounced sensitivity to catalyst particle size (large particles more active than small particles), was used to confirm that catalytic behavior was consistent with the independently measured sintering characteristics. It was found that the nanoparticle active phase was Ir oxide, which is metallic, possibly present as a capping layer. Moreover, observed turnover frequencies indicated that catalyst-support interactions were important in the cases of the sinter-resistant systems, an effect that may itself be linked to the phenomena that gave rise to materials with a strong resistance to nanoparticle sintering. 

Applied Catalysis B-Environmental, 192 (2016) 357-364 | DOI: 10.1016/j.apcatb.2016.04.011

Cascade charge separation mechanism by ternary heterostructured BiPO4/TiO2/g-C3N4 photocatalyst

Obregon, S; Zhang, YF; Colon, G

A complex ternary BiPO4/TiO2/gC(3)N(4) heterostructure has been obtained from a simple impregnation method having good photoactivities for the degradation of phenol under solar-like irradiation. From the wide structural, surface and electronic characterization, we have stated that the formation of the ternary heterojunction notably affect photoactivity of pristine TiO2. Thus, the best result for the binary system was obtained for 70 wt%TiO2-30 wt% BiPO4 system. The incorporation of gC(3)N(4) leads to a further improvement on the photocatalytic activity when it is specifically done over TiO2. By means of photoluminescence spectroscopy and reactive oxygen species formation test, we propose that the effective charge carrier separation is taking place through a cascade-driven electronic mechanism. Therefore, by choosing the adequate band-engineering tailoring an important improved photoactivity can be achieved. 

Applied Catalysis B: Enviromental, 184 (2016) 96-103 | DOI: 10.1016/j.apcatb.2015.11.027

O-2-assisted Water Gas Shift reaction over structured Au and Pt catalysts

Gonzalez-Castano, M; Reina, TR; Ivanova, S; Tejada, LMM; Centeno, MA; Odriozola, JA

Platinum and gold structured catalysts were compared as active phases in classical and O2-assisted Water Gas Shift (WGS) reaction. Both metals were supported on iron-doped ceria mixed oxide and then, structured on metallic micromonolithic devices. As expected the WGS activity of both micromonoliths is conditioned by the nature of the noble metals being Pt the most active metal in traditional conditions. However, the addition of oxygen to the classical water gas feed turns the balance in favor of the gold based catalysts, being the presence of gold responsible for an excessive improvement of the catalytic activity.

Applied Catalysis B: Enviromental, 185 (2016) 337-343 | DOI: 10.1016/j.apcatb.2015.12.032

Investigation of a Pt containing washcoat on SiC foam for hydrogen combustion applications

Fernandez, A; Arzac, GM; Vogt, UF; Hosoglu, F; Borgschulte, A; de Haro, MCJ; Montes, O; Zuttel, A

A commercial Pt based washcoat, used for catalytic methane combustion, was studied supported on a commercial SiC foam as catalytic material (Pt/SiC) for catalytic hydrogen combustion (CHC). Structural and chemical characterization was performed using Electron Microscopy, X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS). The reaction was monitored following water concentration by Fourier Transform Infrared spectra (FTIR). The FTIR method was compared with H2 detection by Gas Cromatography (GC) and has shown to be adequate to study the kinetics of the CHC reaction in steady state under our experimental conditions (very lean 1% (v/v) H2/air mixtures). The catalyst is composed of 5–20 nm disperse Pt nanoparticles decorating a mixture of high surface area Al2O3 and small amounts of ceria supported on the SiC foam which also contains alumina as binder. The Pt/SiC catalytic material has demonstrated to be active enough to start up the reaction in a few seconds at room temperature. The material has been able to convert at least 18.5 Lhydrogen min−1 gPt−1 at room temperature in conditions of excess of catalyst. The Pt/SiC material was studied after use using XPS and no significant changes on Pt oxidation states were found. The material was characterized from a kinetic point of view. From the conversion-temperature plot a T50(temperature for 50% conversion) of 34 °C was obtained. Activation energy measured in our conditions was 35 ± 1 kJ mol−1.

Applied Catalysis B: Environmental, 180 (2016) 336-343 | DOI: 10.1016/j.apcatb.2015.06.040

The role of Au, Cu & CeO2 and their interactions for an enhanced WGS performance

Reina, TR; Ivanova, S; Centeno, MA; Odriozola, JA

The WGS reaction over multicomponent Au/Ce1-xCuxO2/Al2O3 catalysts is studied in this work. The systems are carefully designed aiming to take advantage of every active phase included in the formulation: gold, ceria and copper. Special emphasis is given to the CeO2-CuO synergy and its influence on the displayed catalytic performance with and without gold. To this aim a meaningful correlation between the physicochemical properties of the mixed materials and their activity/stability is proposed. In general terms the developed catalysts present high activity under realistic WGS reaction conditions, with fairly good long term stability. In addition, the systems successfully withstand start-up/shut-downs situations, indispensable requisite for real applications in the field of pure hydrogen production for fuel cell goals. 

Applied Catalysis B: Environmental, 187 (2016) 98-107 | DOI: 10.1016/j.apcatb.2016.01.031

Photocatalytic removal of patent blue V dye on Au-TiO2 and Pt-TiO2 catalysts

Vaiano, V; Iervolino, G; Sannino, D; Murcia, JJ; Hidalgo, MC; Ciambelli, P; Navio, JA

In this work it was studied the efficiency of a photocatalytic process for the removal of patent blue V. This dye is very difficult to remove by conventional treatments such as adsorption or coagulation therefore the photocatalytic process is a very interesting alternative for the removal this dye mainly because it does not require expensive oxidants and it can be carried out at mild temperatures and pressures. In this work it was tested the efficiency of Au-TiO2 and Pt-TiO2 photocatalysts in the Patent blue V removal. The Au-TiO2 catalysts were prepared by two different methods: chemical reduction and photochemical deposition; Pt-TiO2 catalysts were obtained only by photochemical deposition. In the synthesis of the catalysts prepared by photochemical deposition, it was evaluated the influence of some parameters, such as deposition time and the intensity of the light source over the physicochemical properties and photocatalytic activity of the materials obtained. An analysis of the effect of the catalyst dosage and initial patent blue V concentration over the dye degradation efficiency was also attempted. 
In general, it was observed that the presence of Au or Pt on TiO2 enhances the patent blue V photodegradation; it was found that noble metal particle size and distribution on TiO2 surface are important factors influencing the dye removal. The highest dye degradation was obtained over the Au-TiO2 catalyst prepared by photochemical deposition, using high light intensity and 15 min of deposition time during the synthesis. A discoloration and a total organic carbon (TOC) removal of 93 and 67% respectively, were obtained over this material after 180 min of UV irradiation. These values are higher than that the obtained on S-TiO2 (discoloration and TOC removal of about 25% and 3%, respectively).

Applied Catalysis B: Environmental, 188 (2016) 134-146 | DOI: 10.1016/j.apcatb.2016.02.001

Efficient bifacial dye-sensitized solar cells through disorder by design

Miranda-Munoz, JM; Carretero-Palacios, S; Jimenez-Solano, A; Li, YL; Lozano, G; Miguez, H

Herein we realize an optical design that optimizes the performance of bifacial solar cells without modifying any of the usually employed components. In order to do so, dielectric scatterers of controlled size and shape have been successfully integrated in the working electrodes of dye-sensitized solar cells (DSSCs), resulting in bifacial devices of outstanding performance. Power conversion efficiencies (PCEs) as high as 6.7% and 5.4% have been attained under front and rear illumination, respectively, which represent a 25% and a 33% PCE enhancement with respect to an 8 μm-thick standard solar cell electrode using platinum as the catalytic material. The remarkable bifacial character of our approach is demonstrated by the high rear/front efficiency ratio attained, around 80%, which is among the largest reported for this sort of device. The proposed optimized design is based on a Monte Carlo approach in which the multiple scattering of light within the cell is fully accounted for. We identified that the spherical shape of the scatterers is the key parameter controlling the angular distribution of the scattering, the most efficient devices being those in which the inclusions provide a narrow forward-oriented angular distribution of the scattered light.

Journal of Materials Chemistry A, 4 (2016) 1953-1961 | DOI: 10.1039/C5TA10091G

Light management: porous 1-dimensional nanocolumnar structures as effective photonic crystals for perovskite solar cells

Ramos, FJ; Oliva-Ramirez, M; Nazeeruddin, MK; Graetzel, M; Gonzalez-Elipe, AR; Ahmad, S

Hybrid organic-inorganic perovskite solar cells are a topic of increasing interest, as in a short time span they are able to lead in the third generation photovoltaics. Organohalide perovskites possess exceptional optoelectronic and physical properties, thus making their implementation possible in many diverse configurations of photovoltaic devices. In this work, we present three different configurations of porous 1-dimensional photonic crystals (1-DPCs) based on alternated nanocolumnar layers of oxides with different refractive indices (n) that were deposited by Physical Vapor Deposition at Oblique Angle Deposition (PVD-OAD). They are then implemented as the photoanode in CH3NH3PbI3 solar cells to improve the management of light into the device. These configurations improved the performance of the photovoltaic system by designing a light interference structure capable of enhancing the absorption capability of the perovskite. A device fabricated using these photonic crystal structures presented an efficiency >12% in contrast with only 10.22% for a reference device based on non-photonic crystal TiO2 layers deposited under analogous conditions.

Journal of Materials Chemistry A, 4 (2016) 4962-4970 | DOI: 10.1039/c5ta08743k

Optical analysis of CH3NH3SnxPb1−xI3 absorbers: a roadmap for perovskite-on-perovskite tandem solar cells

Anaya, M.; Correa-Baena, J.P.; Lozano, G.; Saliba, M.; Anguita, P.; Roose, B.; Abate, A.; Steiner, U.; Gratzel, M.; Calvo, M.E.; Hagfeldt, A.; Mígues, H.

Organic–inorganic perovskite structures in which lead is substituted by tin are exceptional candidates for broadband light absorption. Herein we present a thorough analysis of the optical properties of CH3NH3SnxPb1−xI3 films, providing the field with definitive insights about the possibilities of these materials for perovskite solar cells of superior efficiency. We report a user's guide based on the first set of optical constants obtained for a series of tin/lead perovskite films, which was only possible to measure due to the preparation of optical quality thin layers. According to the Shockley–Queisser theory, CH3NH3SnxPb1−xI3 compounds promise a substantial enhancement of both short circuit photocurrent and power conversion efficiency in single junction solar cells. Moreover, we propose a novel tandem architecture design in which both top and bottom cells are made of perovskite absorbers. Our calculations indicate that such perovskite-on-perovskite tandem devices could reach efficiencies over 35%. Our analysis serves to establish the first roadmap for this type of cells based on actual optical characterization data. We foresee that this study will encourage the research on novel near-infrared perovskite materials for photovoltaic applications, which may have implications in the rapidly emerging field of tandem devices.

Journal lf Materials Chemistry A, 4 (2016) 11214-11221 | DOI: 10.1039/C6TA04840D

Colloidal crystals and water: Perspectives on liquid-solid nanoscale phenomena in wet particulate media

Gallego-Gomez, F; Morales-Florez, V; Morales, M; Blanco, A; Lopez, C

Solid colloidal ensembles inherently contain water adsorbed from the ambient moisture. This water, confined in the porous network formed by the building submicron spheres, greatly affects the ensemble properties. Inversely, one can benefit from such influence on collective features to explore the water behavior in such nanoconfinements. Recently, novel approaches have been developed to investigate in-depth where and how water is placed in the nanometric pores of self-assembled colloidal crystals. Here, we summarize these advances, along with new ones, that are linked to general interfacial water phenomena like adsorption, capillary forces, and flow. Water-dependent structural properties of the colloidal crystal give clues to the interplay between nanoconfined water and solid fine particles that determines the behavior of ensembles. We elaborate on how the knowledge gained on water in colloidal crystals provides new opportunities for multidisciplinary study of interfacial and nanoconfined liquids and their essential role in the physics of utmost important systems such as particulate media.

Advances in Colloid and Interface Science, 234 (2016) 142-160 | DOI: 10.1016/j.cis.2016.05.004

Optical sensing by integration of analyte-sensitive fluorophore to particles

Carrillo-Carrion, C; Escudero, A; Parak, WJ

Analyte-sensitive fluorophores are a common tool in analytical chemistry. In case they are conjugated to the surface of colloidal nanoparticles new or improved applications are possible. An overview of the potential of such fluorophore-particle conjugates is given by means of several examples. First, using pH-sensitive fluorophores attached to particles are a helpful tool for investigating particle uptake by cells, as they can indicate whether particles are in the neutral slightly alkaline extracellular medium, or in acidic intracellular vesicles after endocytosis. Second, relating to lifetime-based methodologies, the fluorescence resonance energy transfer between fluorophores attached to quantum dots leads to longer lifetimes, improving their performance and expanding the possibilities of methods, such as lifetime imaging for in vivo applications. It also can be exploited for multiplexing approaches, in which the effective lifetime of the fluorophores can be tuned, allowing thus for the detection of several analytes based on temporal discrimination. Attention is focused to these three areas of application, because they are among the most reported in recent literature, and therefore of particular interest.

TrAC Trends in Analytical Chemistry, 84 (2016) 84-85 | DOI: 10.1016/j.trac.2016.05.001

Photocatalytic hydrogen production from degradation of glucose over fluorinated and platinized TiO2 catalysts

Iervolino, G; Vaiano, V; Murcia, JJ; Rizzo, L; Ventre, G; Pepe, G; Campiglia, P; Hidalgo, MC; Navio, JA; Sannino, D

The present work reports the renewable hydrogen production by photocatalytic degradation of glucose over commercial and home prepared TiO2 modified by the simultaneous presence of fluorine and Pt (Pt-F-TiO2). The obtained materials were widely characterized by different techniques (XRD, SBF, UV-Vis DRS, XRF, SEM and TEM) and it was found that surface area, anatase/rutile ratio and the distribution and size of the platinum particles are important factors influencing the effectiveness of these materials in the H-2 production. The photocatalytic H-2 production from the glucose solution was 97 mu mol of H-2 after 3 h of irradiation on home prepared TiO2 modified by F and Pt addition, while a lower value corresponding to 31 mu mol of H-2 was obtained on commercial TiO2 modified by F and Pt, after 3 h of irradiation. The hydrogen production rate increased by decreasing the initial pH of solution reaching the highest value of about 590 mu mol h(-1) g(-1) after 3 h of irradiation time at pH = 2. Accordingly, sugar containing wastewaters from food industry has the potential for producing hydrogen by photocatalytic process while removing organics before disposal or reuse. 

Journal of Catalysis, 339 (2016) 47-56 | DOI: 10.1016/j.jcat.2016.03.032

Manganese Dioxide Supported on Porous Biomorphic Carbons as Hybrid Materials for Energy Storage Devices

Gutierrez-Pardo, A; Lacroix, B; Martinez-Fernandez, J; Ramirez-Rico, J

A facile and low-cost method has been employed to fabricate MnO2/C hybrid materials for use as binder-free electrodes for supercapacitor applications. Biocarbon monoliths were obtained through pyrolysis of beech wood, replicating the microstructure of the cellulosic precursor, and serve as 3D porous and conductive scaffolds for the direct growth of MnO, nanosheets by a solution method. Evaluation of the experimental results indicates that a homogeneous and uniform composite material made of a carbon matrix exhibiting ordered hierarchical porosity and MnO, nanosheets with a layered nanocrystalline structure is obtained. The tuning of the MnO2 content and crystallite size via the concentration of KMnO4 used as impregnation solution allows to obtain composites that exhibit enhanced electrochemical behavior, achieving a capacitance of 592 F g(-1) in electrodes containing 3 wt % MnO2 with an excellent cyclic stability. The electrode materials were characterized before and after electrochemical testing.

ACS Applied Materials & Interfaces, 8 (2016) 30890-30898 | DOI: 10.1021/acsami.6b09361

Laser Treatment of Nanoparticulated Metal Thin Films for Ceramic Tile Decoration

Rico, VJ; Lahoz, R; Rey-Garcia, F; Yubero, F; Espinos, JP; de la Fuente, GF; Gonzalez-Elipe, AR

This paper presents a new method for the fabrication of metal-like decorative layers on glazed ceramic tiles. It consists of the laser treatment of Cu thin films prepared by electron-beam evaporation at glancing angles. A thin film of discontinuous Cu nanoparticles was electron-beam-evaporated in an oblique angle configuration onto ceramic tiles and an ample palette of colors obtained by laser treatment both in air and in vacuum. Scanning electron microscopy along with UV–vis–near-IR spectroscopy and time-of-flight secondary ion mass spectrometry analysis were used to characterize the differently colored layers. On the basis of these analyses, color development has been accounted for by a simple model considering surface melting phenomena and different microstructural and chemical transformations of the outmost surface layers of the samples.

Applied Materials & Interfaces, 8 (2016) 24880-24886 | DOI: 10.1021/acsami.6b07469

Growth Assisted by Glancing Angle Deposition: A New Technique to Fabricate Highly Porous Anisotropic Thin Films

Sanchez-Valencia, JR; Longtin, R; Rossell, MD; Groning, P

We report a new methodology based on glancing angle deposition (GLAD) of an organic molecule in combination with perpendicular growth of a second inorganic material. The resulting thin films retain a very well-defined tilted columnar microstructure characteristic of GLAD with the inorganic material embedded inside the columns. We refer to this new methodology as growth assisted by glancing angle deposition or GAGLAD, since the material of interest (here, the inorganic) grows in the form of tilted columns, though it is deposited under a nonglancing configuration. As a “proof of concept”, we have used silver and zinc oxide as the perpendicularly deposited material since they usually form ill-defined columnar microstructures at room temperature by GLAD. By means of our GAGLAD methodology, the typical tilted columnar microstructure can be developed for materials that otherwise do not form ordered structures under conventional GLAD. This simple methodology broadens significantly the range of materials where control of the microstructure can be achieved by tuning the geometrical deposition parameters. The two examples presented here, Ag/Alq3 and ZnO/Alq3, have been deposited by physical vapor deposition (PVD) and plasma enhanced chemical vapor deposition (PECVD), respectively: two different vacuum techniques that illustrate the generality of the proposed technique. The two type of hybrid samples present very interesting properties that demonstrate the potentiality of GAGLAD. On one hand, the Ag/Alq3 samples present highly optical anisotropic properties when they are analyzed with linearly polarized light. To our knowledge, these Ag/Alq3 samples present the highest angular selectivity reported in the visible range. On the other hand, ZnO/Alq3 samples are used to develop highly porous ZnO thin films by using Alq3 as sacrificial material. In this way, antireflective ZnO samples with very low refractive index and extinction coefficient have been obtained.

ACS Applied Materials & Interfaces, 8 (2016) 8686-8693 | DOI: 10.1021/acsami.6b00232

Template-Assisted Hydrothermal Growth of Aligned Zinc Oxide Nanowires for Piezoelectric Energy Harvesting Applications

Ou, C; Sanchez-Jimenez, PE; Datta, A; Boughey, FL; Whiter, RA; Sahonta, SL; Kar-Narayan, S

A flexible and robust piezoelectric nanogenerator (NG) based on a polymer-ceramic nanocomposite structure has been successfully fabricated via a cost-effective and scalable template assisted hydrothermal synthesis method. Vertically aligned arrays of dense and uniform zinc oxide (ZnO) nanowires (NWs) with high aspect ratio (diameter similar to 250 nm, length similar to 12 mu m) were grown within nanoporous polycarbonate (PC) templates. The energy conversion efficiency was found to be similar to 4.2%, which is comparable to previously reported values for ZnO NWs. The resulting NG is found to have excellent fatigue performance, being relatively immune to detrimental environmental factors and mechanical failure, as the constituent ZnO NWs remain embedded and protected inside the polymer matrix.

ACS Applied Materials & Interfaces, 8 (2016) 13678-13683 | DOI: 10.1021/acsami.6b04041

Electrochemical Energy Storage Applications of CVD Grown Niobium Oxide Thin Films

Fiz, Raquel; Appel, Linus; Gutierrez-Pardo, Antonio; Ramirez-Rico, Joaquin; Mathur, Sanjay

We report here on the controlled synthesis, characterization, and electrochemical properties of different polymorphs of niobium pentoxide grown by CVD of new single-source precursors. Nb2O5 films deposited at different temperatures showed systematic phase evolution from low-temperature tetragonal (TT-Nb2O5, T-Nb2O5) to high temperature monoclinic modifications (H–Nb2O5). Optimization of the precursor flux and substrate temperature enabled phase-selective growth of Nb2O5 nanorods and films on conductive mesoporous biomorphic carbon matrices (BioC). Nb2O5 thin films deposited on monolithic BioC scaffolds produced composite materials integrating the high surface area and conductivity of the carbonaceous matrix with the intrinsically high capacitance of nanostructured niobium oxide. Heterojunctions in Nb2O5/BioC composites were found to be beneficial in electrochemical capacitance. Electrochemical characterization of Nb2O5/BioC composites showed that small amounts of Nb2O5 (as low as 5%) in conjunction with BioCarbon resulted in a 7-fold increase in the electrode capacitance, from 15 to 104 F g–1, while imparting good cycling stability, making these materials ideally suited for electrochemical energy storage applications.

ACS Applied Materials & Interfaces, 8 (2016) 21423–21430 | DOI: 10.1021/acsami.6b03945

A panchromatic modification of the light absorption spectra of metal-organic frameworks

Otal, E. H.; Kim, M. L.; Calvo, M. E.; Karvonen, L.; Fabregas, I. O.; Sierra, C. A.; Hinestroza, J. P.

The optical absorption of UiO-66–NH2 MOF was red-shifted using a diazo-coupling reaction. The modifications performed with naphthols and aniline yielded reddish samples, and the modifications with diphenylaniline yielded dark violet ones. The photocatalytic activity of these modified MOFs was assessed for methylene blue degradation, showing a good performance relative to traditional TiO2. The degradation performance was found to correlate with the red shift of the absorption edge. These findings suggest potential applications of these materials in photocatalysis and in dye sensitized solar cells.

Chemical Communications, 52 (2016) 6665-6668 | DOI: 10.1039/c6cc02319c

Isotope labelling to study molecular fragmentation during the dielectric barrier discharge wet reforming of methane

Montoro-Damas, AM; Gomez-Ramirez, A; Gonzalez-Elipe, AR; Cotrino, J

Isotope labelling is used to study the wet plasma reforming of methane in a dielectric barrier discharge reactor using D2O and CH4 as reactants. Besides the formation of CO and hydrogen as main products, different partitions of H and D atoms are found in the hydrogen (i.e., Hz, HD, D-2), methane (i.e., CH4, CH3D and CH2D2) and water (D2O, DHO) molecules detected by mass spectrometry as outlet gases of the plasma process. The effect of operating parameters such as applied current, residence time and the addition of oxygen to the reaction mixture is correlated with the H/D distribution in these molecules, the overall reaction yield and the energetic efficiency of the process. The results prove the plasma formation of intermediate excited species that rendering water and methane instead of CO and hydrogen greatly contribute to decrease the overall energy efficiency of the reforming process.

Journal of Power Sources, 325 (2016) 501-505 | DOI: 10.1016/j.jpowsour.2016.06.028

Synthesis, characterization and performance of robust poison resistant ultrathin film yttria stabilized zirconia nickel anodes for application in solid electrolyte fuel cells

Garcia-Garcia, FJ; Yubero, F; Espinos, JP; Gonzalez-Elipe, AR; Lambert, RM

We report on the synthesis of undoped ∼5 μm YSZ-Ni porous thin films prepared by reactive pulsed DC magnetron sputtering at an oblique angle of incidence. Pre-calcination of the amorphous unmodified precursor layers followed by reduction produces a film consisting of uniformly distributed tilted columnar aggregates having extensive three-phase boundaries and favorable gas diffusion characteristics. Similarly prepared films doped with 1.2 at.% Au are also porous and contain highly dispersed gold present as Ni-Au alloy particles whose surfaces are strongly enriched with Au. With hydrogen as fuel, the performance of the undoped thin film anodes is comparable to that of 10–20 times thicker typical commercial anodes. With a 1:1 steam/carbon feed, the un-doped anode cell current rapidly falls to zero after 60 h. In striking contrast, the initial performance of the Au-doped anode is much higher and remains unaffected after 170 h. Under deliberately harsh conditions the performance of the Au-doped anodes decreases progressively, almost certainly due to carbon deposition. Even so, the cell maintains some activity after 3 days operation in dramatic contrast with the un-doped anode, which stops working after only three hours of use. The implications and possible practical application of these findings are discussed.

Journal of Power Sources, 324 (2016) 679-686 | DOI: 10.1016/j.jpowsour.2016.05.124

The Calcium-Looping technology for CO2 capture: On the important roles of energy integration and sorbent behavior

Perejon, A; Romeo, LM; Lara, Y; Lisbona, P; Martinez, A; Valverde, JM

The Calcium Looping (CaL) technology, based on the multicyclic carbonation/calcination of CaO in gas-solid fluidized bed reactors at high temperature, has emerged in the last years as a potentially low cost technology for CO2 capture. In this manuscript a critical review is made on the important roles of energy integration and sorbent behavior in the process efficiency. Firstly, the strategies proposed to reduce the energy demand by internal integration are discussed as well as process modifications aimed at optimizing the overall efficiency by means of external integration. The most important benefit of the high temperature CaL cycles is the possibility of using high temperature streams that could reduce significantly the energy penalty associated to CO2 capture. The application of the CaL technology in precombustion capture systems and energy integration, and the coupling of the CaL technology with other industrial processes are also described. In particular, the CaL technology has a significant potential to be a feasible CO2 capture system for cement plants. A precise knowledge of the multicyclic CO2 capture behavior of the sorbent at the CaL conditions to be expected in practice is of great relevance in order to predict a realistic capture efficiency and energy penalty from process simulations. The second part of this manuscript will be devoted to this issue. Particular emphasis is put on the behavior of natural limestone and dolomite, which would be the only practical choices for the technology to meet its main goal of reducing CO2 capture costs. Under CaL calcination conditions for CO2 capture (necessarily implying high CO2 concentration in the calciner), dolomite seems to be a better alternative to limestone as CaO precursor. The proposed techniques of recarbonation and thermal/mechanical pretreatments to reactivate the sorbent and accelerate calcination will be the final subjects of this review.

Applied Energy, 162 (2016) 787-807 | DOI: 10.1016/j.apenergy.2015.10.121

Influence of temperature and time on the Eu3+ reaction with synthetic Na-Mica-n (n=2 and 4)

Garcia-Jimenez, MJ; Cota, A; Osuna, FJ; Pavon, E; Alba, MD

Bentonite is accepted as the best clay material for the engineered barrier of Deep Geological Repositories (DGRs). The performance of clay as the main component of the engineered barrier in the DGR has been intensively studied and the structure of the selected clay mineral play a crucial role. In this sense, a new family of synthetic swelling silicates, Na-Mica-n, with tuned layer charge (n) values between 2.0 and 4.0 per unit cell has recently been synthesized and a general synthetic method has been reported. These swelling high-charge micas could be highly valuable for the decontamination of harmful cations. The ability of these micas to immobilize Eu3+ under subcritical conditions has been probed. The adsorption was in both non-specific sites (cation exchange mechanism) and specific sites (chemical reaction or surface defects adsorption). Moreover, its adsorption capacity, under the same conditions is higher than in saponite and far superior to the bentonites. 

Chemical Engineering Journal, 284 (2016) 1174-1183 | DOI: 10.1016/j.cej.2015.09.077

Hot-pressing of (Ti,Mt)(C,N)-Co-Mo2C (Mt = Ta,Nb) powdered cermets synthesized by a mechanically induced self-sustaining reaction

Chicardi, E; Gotor, FJ; Medri, V; Guicciardi, S; Lascano, S; Cordoba, JM

A mechanically induced self-sustaining reaction (MSR) has been successfully employed for manufacturing powdered cermets based on Ti, Ti–Ta and Ti–Nb carbonitrides using Co as the binder phase and Mo2C as the sintering additive. The powders were sintered by hot-pressing, and complete chemical, microstructural and mechanical characterizations were performed on the densified cermets. When elemental Ta, Nb and/or Mo2C were added to the initial raw mixture submitted to the MSR process, smaller ceramic grains were observed after sintering, which suggested that ceramic particle growth was hindered by the presence of Ta, Nb and/or Mo in the host titanium carbonitride structure. Nanoindentation measurements enabled the determination of the hardness of the ceramic and binder phases, and values in the range of 26–29 GPa and 14–16 GPa were found, respectively. The high hardness values of the binder were related to the formation of intermetallic phases.

Chemical Engineering Journal, 292 (2016) 51-61 | DOI: 10.1021/acsami.6b00232

Intensifying glycerol steam reforming on a monolith catalyst: A reaction kinetic model

Bobadilla, LF; Blay, V; Alvarez, A; Dominguez, MI; Romero-Sarria, F; Centeno, MA; Odriozola, JA

In this work, a structured monolithic catalyst has been tested under a wide range of conditions (partial pressure, residence time, temperature and time-on-stream), with the aim of modeling its kinetic behavior and assessing its economic and upscaling potential. We have developed a sequential model to help us interpret both main trends and salient features. Unexpected behavior was found for certain parameter values, which led us to consider kinetic parasitic effects such as mass or heat transfer limitations. By independently invoking these effects, a conciliatory view of the results observed could not be reached. A combined explanation may prove successful, although overfitting could not be ruled out at this point. More importantly, however, the observed salient features of this stable and selective monolith catalyst may hold potential for process intensification of glycerol steam reforming, thus contributing to a more sustainable industry.

Chemical Engineering Journal, 306 (2016) 933–941 | DOI: 10.1016/j.cej.2016.08.021

Effect of TiO2-Pd and TiO2-Ag on the photocatalytic oxidation of diclofenac, isoproturon and phenol

Espino-Estevez, MR; Fernandez-Rodriguez, C; Gonzalez-Diaz, OM; Arana, J; Espinos, JP; Ortega-Mendez, JA; Dona-Rodriguez, JM

The effects of silver and palladium metals on the photocatalytic degradation of diclofenac sodium salt (DCF), isoproturon (IP) and phenol (PHL) in water over lab-made TiO2 synthesized following a sol-gel method were investigated. Silver and palladium catalysts were prepared by photodeposition at 1 wt.% of loading metal. The resulting materials were characterized through BET, XRD, TEM, SEM, XPS and DRS-UV-Vis. The photodeposition test conditions of both metals determined their final oxidation state, with reduced particles of palladium and silver as well as silver oxides found on the catalysts. The results showed that the type of metal had different effects on the photodegradation mechanism depending on the nature of the pollutants. Accordingly, the highest degradation rate for IP and DCF was obtained when using the catalyst photodeposited with palladium and for PHL the catalyst photodeposited with silver. The photodegradation intermediates of PHL, DCF and IP were also identified.

Chemical Engineering Journal, 298 (2016) 82-95 | DOI: 10.1016/j.cej.2016.04.016

Forced deactivation and postmortem characterization of a metallic microchannel reactor employed for the preferential oxidation of CO (PROX)

Laguna, OH; Dominguez, MI; Centeno, MA; Odriozola, JA

This manuscript is one of the few works presenting evidences of the effect of prolonged use of a microreactor. Our reactor has been designed for the PROX reaction. Near to 550 h of operation under different feed-streams, including CO2 and H2O, in the 100-300 degrees C temperature range, and several regeneration cycles, and a final forced deactivation during similar to 360 h resulted in the permanent loss of activity of the microreactor. This could be attributed to some phenomena whose have compromised the chemical nature of the catalyst and that of the reactor including: displacement of the coating to the mouth of the channels, detachments and cracks of the catalytic layer, migration of some elements of the metallic substrate to the surface (Fe, Cr, Y), and deposition of carbonaceous species from the reaction over the catalytic layer and/or the metallic substrate. Furthermore, sulfur compounds were detected in both inlet and outlet zones of the microreactor, coming probably from a lubricant applied over the screws that sealed the assembling of the microreactor. 

This is a first approach for understanding possible effects of deactivation during long-term applications of a microreactor in the PROX reaction that could be considered as a case study useful for future designs of this kind of devices. The presented information could be extrapolated to similar reactions where thermal treatments along with highly corrosive atmospheres would be applied, in order to carry out a more appropriate design of future generations" of microreactors, with a longer useful life. For that purpose not only the adequate selection of the catalysts must be done, but also the adequate choice of the fabrication material of the reactors is needed. 

Chemical Engineering Journal, 302 (2016) 650-662 | DOI: 10.1016/j.cej.2016.05.104

Vacuum template synthesis of multifunctional nanotubes with tailored nanostructured walls

Filippin, AN; Macias-Montero, M; Saghi, Z; Idigoras, J; Burdet, P; Barranco, A; Midgley, P; Anta, JA; Borras, A

A three-step vacuum procedure for the fabrication of vertical TiO2 and ZnO nanotubes with three dimensional walls is presented. The method combines physical vapor deposition of small-molecules, plasma enhanced chemical vapor deposition of inorganic functional thin films and layers and a post-annealing process in vacuum in order to remove the organic template. As a result, an ample variety of inorganic nanotubes are made with tunable length, hole dimensions and shapes and tailored wall composition, microstructure, porosity and structure. The fabrication of multishell nanotubes combining different semiconducting oxides and metal nanoparticles is as well explored. This method provides a feasible and reproducible route for the fabrication of high density arrays of vertically alligned nanotubes on processable substrates. The emptying mechanism and microstructure of the nanotubes have been elucidated through SEM, STEM, HAADF-STEM tomography and energy dispersive X-ray spectroscopy. In this article, as a proof of concept, it is presented the straightforward integration of ZnO nanotubes as photoanode in a photovoltaic cell and as a photonic oxygen gas sensor.

Scientific Reports, 5 (2016) 20637 | DOI: 10.1038/srep20637

Biological strategy for the fabrication of highly ordered aragonite helices: the microstructure of the cavolinioidean gastropods

Checa, AG; Macias-Sanchez, E; Ramirez-Rico, J

The Cavolinioidea are planktonic gastropods which construct their shells with the so-called aragonitic helical fibrous microstructure, consisting of a highly ordered arrangement of helically coiled interlocking continuous crystalline aragonite fibres. Our study reveals that, despite the high and continuous degree of interlocking between fibres, every fibre has a differentiated organic-rich thin external band, which is never invaded by neighbouring fibres. In this way, fibres avoid extinction. These intra-fibre organic-rich bands appear on the growth surface of the shell as minuscule elevations, which have to be secreted differentially by the outer mantle cells. We propose that, as the shell thickens during mineralization, fibre secretion proceeds by a mechanism of contact recognition and displacement of the tips along circular trajectories by the cells of the outer mantle surface. Given the sizes of the tips, this mechanism has to operate at the subcellular level. Accordingly, the fabrication of the helical microstructure is under strict biological control. This mechanism of fibre-by-fibre fabrication by the mantle cells is unlike that any other shell microstructure.

Scientific Reports, 6 (2016) article number 25989 | DOI: 10.1038/srep25989

Integration of Photonic Crystals into Flexible Dye Solar Cells: A Route toward Bendable and Adaptable Optoelectronic Devices Displaying Structural Color and Enhanced Efficiency

Li, YL; Calvo, ME; Miguez, H

Herein is presented what is believed to be the first example of integration of photonic structures in a flexible optoelectronic device. The resulting devices may be designed to display any color in the visible range and, simultaneously, present enhanced power conversion efficiency as a consequence of the increased light harvesting caused by the colored back reflection. The achievement results from the incorporation of nanoparticle-based multilayers with photonic crystal properties that are modified to be compatible with the chemical and physical processing of flexible nanocrystalline titania electrodes of dye solar cells. The photovoltaic performance of these colored flexible cells remains unaltered after one hundred bending cycles, thus showing the high-mechanical stability of the ensemble. These devices reunite most characteristics required for building integration or for the construction of solar window panes, such as light weight, stability upon bending, adaptability, and color. This work may trigger promising applications of these highly adaptable and versatile photonic crystals in other flexible devices.

Advanced Optical Materials, 4 (2016) 464-471 | DOI: 10.1002/adom.201500547

A Full Vacuum Approach for the Fabrication of Hybrid White-Light-Emitting Thin Films and Wide-Range In Situ Tunable Luminescent Microcavities

Y. Oulad-Zian, J.R. Sánchez-Valencia, M. Oliva, J. Parra-Barranco, M. Alcaire, F.J. Aparicio, A. Mora-Boza, J.P. Espinós, F. Yubero, A.R. González-Elipe, A. Barranco, A. Borras

A wide-range in situ tunable 1D Bragg microcavity including a hybrid layer as white light emitter defect is shown by J. R. Sanchez-Valencia, A. Borras, and co-workers on page 1124. White emission is obtained by Förster resonance energy transfer between blue (1,3,5-triphenyl-2-pyrazoline) and orange (rubrene) dyes homogeneously infiltrated within the host nanocolumnar SiO2film, which is formed by glancing angle deposition. Sequential physical vapor deposition at low temperatures provides the organic dyes localization within the porous nanostructure of the defect layer.

Advanced Optical Materials, 4 (2016) 1134 | DOI: 10.1002/adom.201670041

High temperature oxidation resistance of (Ti,Ta)(C,N)-based cermets

Chicardi, E; Cordoba, JM; Gotor, FJ

Cermets based on titanium-tantalum carbonitride were oxidized in static air between 800 degrees C and 1100 degrees C for 48 h. The thermogravimetric and microstructural study showed an outstanding reduction in the oxidation of more than 90% when the Ta content was increased. In cermets with low Ta content, the formation of a thin CoO/Co3O4 outer layer tends to disappear by reacting with the underlying rutile phase, which emerges at the surface. However, in cermets with higher Ta content, the formation of an external titanate layer, observed even at a low temperature, appears to prevent the oxygen diffusion and the oxidation progression. 

Corrosion Science, 102 (2016) 125-136 | DOI: 10.1016/j.corsci.2015.10.001

Kinetics of high-temperature oxidation of (Ti,Ta)(C,N)-based cermets

Chicardi, E; Cordoba, JM; Gotor, FJ

The kinetics of the high-temperature oxidation of titanium–tantalum carbonitride-based cermets with different Ti/Ta ratios was studied. Isothermal oxidation tests were conducted under static air for 48 h at temperatures between 700 °C and 1200 °C. The oxidation satisfied the parabolic kinetics, characteristic of the existence of a protective oxide layer. The apparent activation energy suggests the rate-controlling process during oxidation is the simultaneous inward and outward diffusion of oxygen and titanium, respectively, through the formed protective layer, consisting mainly of a rutile phase. A higher Ta(V) content in the rutile decreased the oxygen diffusivity due to the reduction of oxygen vacancy concentration.

Corrosion Science, 102 (2016) 168-177 | DOI: 10.1016/j.corsci.2015.10.006

Transparent polycrystalline SrREGa3O7 melilite ceramics: potential phosphors for tuneable solid state lighting

Boyer, M; Carrion, AJF; Ory, S; Becerro, AI; Villette, S; Eliseeva, SV; Petoud, S; Aballea, P; Matzen, G; Allix, M

Full and congruent crystallization from glass is applied to the SrREGa3O7 melilite family (RE = Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Y). This innovative process enables the synthesis of polycrystalline ceramics exhibiting high transparency both in the visible and near infrared regions, despite tetragonal crystal structures and micrometer scale grain sizes. Moreover, glass crystallization provides an original route to synthesize new crystalline phases which are not accessible via a classic solid state reaction, as demonstrated for SrYbGa3O7 and SrTmGa3O7. To illustrate the potential optical applications of such materials, SrGdGa3O7 transparent polycrystalline ceramics are doped with Dy3+ or Tb3+/Eu3+ in order to generate white light emission under UV excitation. It is foreseen that such transparent melilite ceramic phosphors, prepared via a cost-effective process, can be successfully used in solid state lighting devices of considerable technological interest.

Journal of Materials Chemistry C, 15 (2016) 3238-3247 | DOI: 10.1039/C6TC00633G

Solution processed high refractive index contrast distributed Bragg reflectors

Anaya, M; Rubino, A; Calvo, ME; Miguez, H

We have developed a method to alternate porous and dense dielectric films in order to build high refractive index contrast distributed Bragg reflectors (DBRs) capable of reflecting very efficiently in a targeted spectral range employing a small number of layers in the stack. Porous layers made of SiO2 nanoparticles and compact sol–gel processed TiO2 layers are sequentially deposited. The key to the preservation of porosity of every other layer during the deposition process is the use of a sacrificial layer of polystyrene that prevents the infiltration of the interstitial voids between nanoparticles with the homogeneous solution of TiO2 precursors. Our approach allows preparing a series of DBRs operating along the whole visible spectral range. Reflectance values as high as 90% are achieved from only seven layers. The particular distribution of porosity along one direction gives rise to an interesting interplay between the optical properties of the system and the vapor pressure in the surrounding atmosphere, which we foresee could be put into practice in gas sensing devices.

Journal of Materials Chemistry C, 4 (2016) 4532-4537 | DOI: 10.1039/C6TC00663A

High temperature internal friction in a Ti-46Al-1Mo-0.2Si intermetallic, comparison with creep behaviour

Castillo-Rodriguez, M; No, ML; Jimenez, JA; Ruano, OA; Juan, JS

Advanced gamma-TiAl based intermetallics Mo-bearing have been developed to obtain the fine-grained microstructure required for superplastic deformation to be used during further processing. In the present work we have studied an alloy of Ti-46.8Al-1Mo-0.2Si (at%) with two different microstructures, ascast material with a coarse grain size above 300 mu m, and the hot extruded material exhibiting a grain size smaller than 20 mu m. We have used a mechanical spectrometer especially developed for high temperature internal friction measurements to study the defect mobility processes taking place at high temperature. The internal friction spectra at different frequencies has been studied and analyzed up to 1360 K in order to characterize the relaxation processes appearing inthis temperature range. A relaxation peak, with a maximum in between 900 K and 1080 K, depending on the oscillating frequency, has been attributed to Ti-atoms diffusion by the stress-induced reorientation of Al-V-Ti-Al elastic dipoles. The high temperature background in both microstructural states, as-cast and extruded, has been analyzed, measuring the apparent activation parameters, in particular the apparent energies of E-cast(IF) = 4.4 +/- 0.05 eV and E-ext(IF) = 4.75 +/- 0.05 eV respectively. These results have been compared to those obtained on the same materials by creep deformation. We may conclude that the activation parameters obtained by internal friction analysis, are consistent with the ones measured by creep. Furthermore, the analysis of the high temperaturebackground allows establish the difference on creep resistance for both microstructural states. 

Acta Materialia, 103 (2016) 46-46 | DOI: 10.1016/j.actamat.2015.09.052

Characterization and application of a new pH sensor based on magnetron sputtered porous WO3 thin films deposited at oblique angles

Salazar, P; Garcia-Garcia, FJ; Yubero, F; Gil-Rostra, J; Gonzalez-Elipe, AR

In this communication we report about an outstanding solid-state pH sensor based on amorphous nanocolumnar porous thin film electrodes. Transparent WO3 thin films were deposited by reactive magnetron sputtering in an oblique angle configuration to enhance their porosity onto indium tin oxide (ITO) and screen printed electrodes (SPE). The potentiometric pH response of the nanoporous WO3-modified ITO electrode revealed a quasi-Nernstian behaviour, i.e. a linear working range from pH 1 to 12 with a slope of about -57.7 mV/pH. pH detection with this electrode was quite reproducible, displayed excellent anti-interference properties and a high stable response that remained unaltered over at least 3 months. Finally, a pH sensor was developed using nanoporous WO3-modified screen printed electrode (SPE) using a polypyrrole-modified Ag/AgCl electrode as internal reference electrode. This full solid state pH sensor presented a Nernstian behaviour with a slope of about -59 mV/pH and offered important analytical and operation advantages for decentralized pH measurements in different applications. 

Electrochimica Acta, 193 (2016) 24-31 | DOI: 10.1016/j.electacta.2016.02.040

Non-enzymatic Glucose electrochemical sensor made of porous NiO thin films prepared by reactive magnetron sputtering at oblique angles

Garcia-Garcia, FJ; Salazar, P; Yubero, F; Gonzalez-Elipe, AR

Porous nanostructured NiO thin films have been prepared in one step by magnetron sputtering in an oblique angle configuration (MS-OAD) and used as electrodes for the non-enzymatic detection of glucose. The films have been thoroughly characterized by different complementary techniques and their performance for the analysis of glucose in basic solutions determined by electrochemical methods. These electrodes presented four times higher sensitivity that equivalent compact thin films prepared by MS in a normal configuration and were superior in terms of sensitivity than majority of nickel based electrodes prepared by other methods. Finally, a high sensitivity towards detection of glucose in blood, insensitivity to common interferences, a long term stability and high reproducibility confirmed the good performance and reliability of these electrodes for practical analytical purposes.

Electrochimica Acta, 201 (2016) 38-44 | DOI: 10.1016/j.electacta.2016.03.193

In-situ hydrogasification/regeneration of NiAl-hydrotalcite derived catalyst in the reaction of CO2 reforming of methane: A versatile approach to catalyst recycling

Abdelsadek, Z; Sehailia, M; Halliche, D; Gonzalez-Delacruz, VM; Holgado, JP; Bachari, K; Caballero, A; Cherifi, O

A novel approach describing the in-situ regeneration of NiAl hydroalcite derived catalyst between two cycle reaction systems of CO2 reforming of methane, also known as dry reforming of methane (DRM) is described herein. The catalyst was initially prepared by co-precipitation method at pH = 11 and calcined at 450 degrees C for 6 h. The obtained material was characterized using X-ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetry (TG/ATD) and temperature programmed reduction (TPR-H-2) techniques. Following treatment of our catalyst under DRM conditions, the catalyst was subjected to in-situ hydrogasification conditions to promote regeneration followed by a second DRM cycle. An increase of 15.7% in the conversion of CH4 and 17.3% in the conversion of CO2 was attained, while the ratio of resulting H-2/CO augmented by 14%. The ratio of H-2 consumed over the course of two hours hydrogasification, to that generated over ten hours of DRM, was 9.6%. The small particle sizes of resulting Ni degrees species as well as their high stability were both key factors contributing to the increase in the amount of H-2/CO produced prior to and after regeneration. 

Journal of CO2 Utilization, 14 (2016) 98-105 | DOI: 10.1016/j.jcou.2016.03.004

Reduced graphene oxide-carboxymethylcellulose layered with platinum nanoparticles/PAMAM dendrimer/magnetic nanoparticles hybrids. Application to the preparation of enzyme electrochemical biosensors

Borisova, B; Sanchez, A; Jimenez-Falcao, S; Martin, M; Salazar, P; Parrado, C; Pingarron, JM; Villalonga, R

The assembly of a novel layer-by-layer biosensor architecture using hybrid nanomaterials is explored for the construction of an amperometric enzyme biosensors. The nanostructured sensing interface was prepared with poly(dopamine)-modified magnetic nanoparticles which were covalently coated with four-generation ethylenediamine core polyamidoamine G-4 dendrimers and further decorated with platinum nanoparticles. This nanohybrid was fully characterized and further layered on glassy carbon electrodes coated with a graphene oxide-carboxymethylcellulose hybrid nanomaterial through electrostatic interactions. The nanostructured surface was then employed as scaffold for the covalent immobilization of the enzyme xanthine oxidase through a glutaraldehyde-mediated cross-linking. The enzyme electrode allowed the amperometric detection of xanthine in the 50 nM-12 mu M range, with a high sensitivity of 140 mA/M cm(2) and low detection limit of 13 nM. The biosensor exhibited high reproducibility and repeatability, and was successfully tested for the quantification of xanthine in fish samples. 

Sensors and Actuators B-Chemical, 232 (2016) 84-90 | DOI: 10.1016/j.snb.2016.02.106

Nickel-copper bilayer nanoporous electrode prepared by physical vapor deposition at oblique angles for the non-enzymatic determination of glucose

Salazar, P; Rico, V; Gonzalez-Elipe, AR

This work presents a novel bilayer Ni/Cu porous nanostructured film electrode prepared by physical vapor deposition (PVD) in an oblique angle configuration. Scanning electron microscopy (SEM) data revealed that the film, with an approximate thickness of 200 nm, is formed by tilted nanocolumns of around 50 nm of diameter and an inclination of 30° with respect to the surface normal. X ray photoelectron spectroscopy (XPS) data confirmed a bilayer configuration with Cu and Ni located at the top and bottom parts of the film, respectively. A porosity of ca. 45–35% as determined by Rutherford back scattering (RBS) offered a large exposed area and excellent diffusion properties that, combined with a very good catalytic activity, rendered these films excellent electrodes for the quantitative determination of glucose. Under optimized working conditions of detection these electrodes presented a high sensitivity of 2.53 A M−1 cm−2 (R2: 0.999), a limit of detection of 0.23 μM and a time response of ca. 2 s. The sensors did not show any loss of response during a period of 4 months. The selectivity of the sensor was checked against various interferences, including physiological compounds, different sugars and ethanol, in all cases with excellent results. The feasibility of using of this sensor for practical applications was confirmed by successfully determining the glucose content in different commercial beverages.

Sensors and Actuators B: Chemical, 226 (2016) 436-443 | DOI: 10.1016/j.snb.2015.12.003

A hybrid silver-magnetite detector based on surface enhanced Raman scattering for differentiating organic compounds

Caro, C; Sayagues, MJ; Franco, V; Conde, A; Zaderenko, P; Gamez, F

In this work a cheap detector of organic molecules is developed. It comprises a cellulose fiber doped with a mixture of magnetite and reduced silver nanoparticles, the latter ones synthesized anew. The nanoparticles and the fiber were characterized with well-established spectroscopic, microscopic and magnetic techniques, namely infrared, UV–vis spectroscopies, vibrating sample magnetometry and electronic microscopies. The so-obtained doped-fibers were tested as surface enhanced Raman spectroscopy detector in aqueous samples with a diluted mixture of two pollutant models (rhodamine 6G and picric acid), being able to differentiate between both organic compounds. Hence, the nanoparticle-impregnated fiber is proposed as a reliable preliminary qualitative and semiquantitative test of the presence of specific organic molecules in solutions. Moreover, the magnetite nanoparticles provide the detector with a saturation magnetization value that enables the separation of the fiber from the solution with the aid of a commercial magnet.

Sensors and Actuators B: Chemical, 228 (2016) 124-133 | DOI: 10.1016/j.snb.2016.01.003

Dye-based photonic sensing systems

Aparicio, FJ; Alcaire, M; Gonzalez-Elipe, AR; Barranco, A; Holgado, M; Casquel, R; Sanza, FJ; Griol, A; Bernier, D; Dortu, F; Caceres, S; Antelius, M; Lapisa, M; Sohlstrom, H; Niklaus, F

We report on dye-based photonic sensing systems which are fabricated and packaged at wafer scale. For the first time luminescent organic nanocomposite thin-films deposited by plasma technology are integrated in photonic sensing systems as active sensing elements. The realized dye-based photonic sensors include an environmental NO2 sensor and a sunlight ultraviolet light (UV) A+B sensor. The luminescent signal from the nanocomposite thin-films responds to changes in the environment and is selectively filtered by a photonic structure consisting of a Fabry-Perot cavity. The sensors are fabricated and packaged at wafer-scale, which makes the technology viable for volume manufacturing. Prototype photonic sensor systems have been tested in real-world scenarios. 

Sensors and Actuators B: Chemical, 228 (2016) 649-657 | DOI: 10.1016/j.snb.2016.01.092

Glutamate microbiosensors based on Prussian Blue modified carbon fiber electrodes for neuroscience applications: In-vitro characterization

Salazar, P; Martin, M; O'Neill, RD; Gonzalez-Mora, JL

Herein we report a Prussian Blue modified carbon fiber electrode (CFE/PB) to be used in microbiosensors for glutamate monitoring in physiological applications as an alternative to the classical Pt and Pt-Ir transducers. Their low dimensions (∼250 μm CFE length and ∼10 μm diameter) are advantageous for measuring in living tissues. In addition, PB-modified microelectrodes allow the detection of enzyme-generated hydrogen peroxide at a low applied potential (∼0.0 V against SCE), contrasting the high potential used in many previous designs (∼0.7 V), decreasing the endogenous interference contributions. Moreover, the electrosynthesized polymer, poly-o-phenylenediamine (PoPD), was used to improve biosensor stability and selectivity. CFE/PB was conveniently characterized using impedance, Raman and XPS spectroscopies. Optimization of the fabrication procedure and analytical conditions is described, including activation of CFE/PB, enzyme enrichment, cross-linking, stabilization and anti-interference. A range of analytical parameters were also characterized such as sensitivity, limit of detection, linear range, and enzymatic loading. Finally, an optimized biosensor displaying a linear sensitivity of 135 ± 2 nA μM−1 cm−2 (n = 3), LOD of <2 μM, linear range up to 150 μM and effectively free of interference, is proposed as a suitable candidate for in-vivo glutamate monitoring in the central nervous system.

Sensors and Actuators B: Chemical, 235 (2016) 117-125 | DOI: 10.1016/j.snb.2016.05.057

Photophysical Analysis of the Formation of Organic–Inorganic Trihalide Perovskite Films: Identification and Characterization of Crystal Nucleation and Growth

Anaya, M; Galisteo-Lopez, JF; Calvo, ME; Lopez, C; Miguez, H

In this work we demonstrate that the different processes occurring during hybrid organic–inorganic lead iodide perovskite film formation can be identified and analyzed by a combined in situ analysis of their photophysical and structural properties. Our observations indicate that this approach permits unambiguously identifying the crystal nucleation and growth regimes that lead to the final material having a cubic crystallographic phase, which stabilizes to the well-known tetragonal phase upon cooling to room temperature. Strong correlation between the dynamic and static photoemission results and the temperature-dependent X-ray diffraction data allows us to provide a description and to establish an approximate time scale for each one of the stages and their evolution. The combined characterization approach herein explored yields key information about the kinetics of the process, such as the link between the evolution of the defect density during film formation, revealed by a fluctuating photoluminescence quantum yield, and the gradual changes observed in the PbI2-related precursor structure.

Journal of Physical Chemistry C, 120 (2016) 3071-3076 | DOI: 10.1021/acs.jpcc.6b00398

Determination of the Anisotropic Elastic Properties of Rocksalt Ge2Sb2Te5 by XRD, Residual Stress, and DFT

Cecchini, R; Kohary, K; Fernandez, A; Cabibbo, M; Marmier, A

The chalcogenide material Ge2Sb2Te5 is the prototype phase-change material, with widespread applications for optical media and random access memory. However, the full set of its independent elastic properties has not yet been published. In this study, we determine the elastic constants of the rocksalt Ge2Sb2Te5, experimentally by X-ray diffraction (XRD) and residual stress and computationally by density functional theory (DFT). The stiffnesses (XRD-stress/DFT) in GPa are C-11 = 41/58, C-12 = 7/8, and C-44 = 8/12, and the Zener ratio is 0.46/0.48. These values are important to understand the effect of elastic distortions and nonmelting processes on the performances of increasingly small phase change data bits.

Journal of Physical Chemistry C, 120 (2016) 5624-5629 | DOI: 10.1021/acs.jpcc.5b09867

Nitrogen Nanobubbles in a-SiOxNy Coatings: Evaluation of Its Physical Properties and Chemical Bonding State by Spatially Resolved Electron Energy-Loss Spectroscopy

Lacroix, B.; Godinho, V.; Fernández, A.

Nanoporous silicon-based materials with closed porosity filled with the sputtering gas have been recently developed by magnetron sputtering. In this work the physical properties (density and pressure) of molecular nitrogen inside closed pores in a SiOxNy coating are investigated for the first time using spatially resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope. The paper offers a detailed methodology to record and process multiple EELS spectrum images (SIs) acquired at different energy ranges and with different dwell times. An adequate extraction and quantification of the N–K edge contribution due to the molecular nitrogen inside nanopores is demonstrated. Core-loss intensity and N chemical bond state were evaluated to retrieve 2D maps revealing the stable high density of molecular nitrogen (from 40 to 70 at./nm3) in nanopores of different size (20–11 nm). This work provides new insights into the quantification of molecular N2 trapped in porous nitride matrices that could also be applied to other systems.

Journal of Physical Chemistry C, 120 (2016) 5651-5658 | DOI: 10.1021/acs.jpcc.5b09036

Gold-Based Nanomaterials for Applications in Nanomedicine

Ashraf, S; Pelaz, B; del Pino, P; Carril, M; Escudero, A; Parak, WJ; Soliman, MG; Zhang, Q; Carrillo-Carrion, C

In this review, an overview of the current state-of-the-art of gold-based nanomaterials (Au NPs) in medical applications is given. The unique properties of Au NPs, such as their tunable size, shape, and surface characteristics, optical properties, biocompatibility, low cytotoxicity, high stability, and multifunctionality potential, among others, make them highly attractive in many aspects of medicine. First, the preparation methods for various Au NPs including functionalization strategies for selective targeting are summarized. Second, recent progresses on their applications, ranging from the diagnostics to therapeutics are highlighted. Finally, the rapidly growing and promising field of gold-based theranostic nano-platforms is discussed. Considering the great body of existing information and the high speed of its renewal, we chose in this review to generalize the data that have been accumulated during the past few years for the most promising directions in the use of Au NPs in current medical research.

Light-Responsive Nanostructured Systems for Applications in Nanomedicine, 370 (2016) 169-202 | DOI: http://link.springer.com/chapter/10.1007%2F978-3-319-22942-3_6

The interaction between hybrid organic-inorganic halide perovskite and selective contacts in perovskite solar cells: an infrared spectroscopy study

Idigoras, J; Todinova, A; Sanchez-Valencia, JR; Barranco, A; Borras, A; Anta, JA

The interaction of hybrid organic-inorganic halide perovskite and selective contacts is crucial to get efficient, stable and hysteresis-free perovskite-based solar cells. In this report, we analyze the vibrational properties of methylammonium lead halide perovskites deposited on different substrates by infrared absorption (IR) measurements (4000-500 cm(-1)). The materials employed as substrates are not only characterized by different chemical natures (TiO2, ZnO and Al2O3), but also by different morphologies. For all of them, we have investigated the influence of these substrate properties on perovskite formation and its degradation by humidity. The effect of selective-hole contact (Spiro-OmeTad and P3HT) layers on the degradation rate by moisture has also been studied. Our IR results reveal the existence of a strong interaction between perovskite and all ZnO materials considered, evidenced by a shift of the peaks related to the N-H vibrational modes. The interaction even induces a morphological change in ZnO nanoparticles after perovskite deposition, pointing to an acid-base reaction that takes place through the NH3+ groups of the methylammonium cation. Our IR and X-ray diffraction results also indicate that this specific interaction favors perovskite decomposition and PbI2 formation for ZnO/perovskite films subjected to humid conditions. Although no interaction is observed for TiO2, Al2O3, and the hole selective contact, the morphology and chemical nature of both contacts appear to play an important role in the rate of degradation upon exposure to moisture.

Physical Chemistry Chemical Physics, 18 (2016) 13583-13590 | DOI: 10.1039/c6cp01265e

Combined TGA-MS kinetic analysis of multistep processes. Thermal decomposition and ceramification of polysilazane and polysiloxane preceramic polymers

Garcia-Garrido, C; Sanchez-Jimenez, PE; Perez-Maqueda, LA; Perejon, A; Criado, JM

The polymer-to-ceramic transformation kinetics of two widely employed ceramic precursors, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (TTCS) and polyureamethylvinylsilazane (CERASET), have been investigated using coupled thermogravimetry and mass spectrometry (TG-MS), Raman, XRD and FTIR. The thermally induced decomposition of the pre-ceramic polymer is the critical step in the synthesis of polymer derived ceramics (PDCs) and accurate kinetic modeling is key to attaining a complete understanding of the underlying process and to attempt any behavior predictions. However, obtaining a precise kinetic description of processes of such complexity, consisting of several largely overlapping physico-chemical processes comprising the cleavage of the starting polymeric network and the release of organic moieties, is extremely difficult. Here, by using the evolved gases detected by MS as a guide it has been possible to determine the number of steps that compose the overall process, which was subsequently resolved using a semiempirical deconvolution method based on the Frasier-Suzuki function. Such a function is more appropriate that the more usual Gaussian or Lorentzian functions since it takes into account the intrinsic asymmetry of kinetic curves. Then, the kinetic parameters of each constituent step were independently determined using both model-free and model-fitting procedures, and it was found that the processes obey mostly diffusion models which can be attributed to the diffusion of the released gases through the solid matrix. The validity of the obtained kinetic parameters was tested not only by the successful reconstruction of the original experimental curves, but also by predicting the kinetic curves of the overall processes yielded by different thermal schedules and by a mixed TTCS-CERASET precursor.

Physical Chemistry Chemical Physics, 18 (2016) 29348-29360 | DOI: 10.1039/c6cp03677e

Effect of dolomite decomposition under CO2 on its multicycle CO2 capture behaviour under calcium looping conditions

Martos, AD; Valverde, JM; Sanchez-Jimenez, PE; Perejon, A; Garcia-Garrido, C; Perez-Maqueda, LA

One of the major drawbacks that hinder the industrial competitiveness of the calcium looping (CaL) process for CO2 capture is the high temperature (∼930–950 °C) needed in practice to attain full calcination of limestone in a high CO2 partial pressure environment for short residence times as required. In this work, the multicycle CO2 capture performance of dolomite and limestone is analysed under realistic CaL conditions and using a reduced calcination temperature of 900 °C, which would serve to mitigate the energy penalty caused by integration of the CaL process into fossil fuel fired power plants. The results show that the fundamental mechanism of dolomite decomposition under CO2 has a major influence on its superior performance compared to limestone. The inert MgO grains resulting from dolomite decomposition help preserve a nanocrystalline CaO structure wherein carbonation in the solid-state diffusion controlled phase is promoted. The major role played by the dolomite decomposition mechanism under CO2 is clearly demonstrated by the multicycle CaO conversion behaviour observed for samples decomposed at different preheating rates. Limestone decomposition at slow heating rates yields a highly crystalline and poorly reactive CaCO3 structure that requires long periods to fully decarbonate and shows a severely reduced capture capacity in subsequent cycles. On the other hand, the nascent CaCO3 produced after dolomite half-decomposition consists of nanosized crystals with a fast decarbonation kinetics regardless of the preheating rate, thus fully decomposing from the very first cycle at a reduced calcination temperature into a CaO skeleton with enhanced reactivity as compared to limestone derived CaO.

Physical Chemistry Chemical Physics, 18 (2016) 16325-16336 | DOI: 10.1039/c6cp01149g

Influence of Ball Milling on CaO Crystal Growth During Limestone and Dolomite Calcination: Effect on CO2 Capture at Calcium Looping Conditions

Sanchez-Jimenez, PE; Valverde, JM; Perejon, A; de la Calle, A; Medina, S; Perez-Maqueda, LA

Under Calcium-Looping “realistic” operation conditions (high CO2 concentration and temperature), the multicycle CO2capture capacity performance of CaO derived from limestone and dolomite is inversely related to its crystallite size. Ball-milling the raw sorbents results in the formation of larger nascent CaO nanocrystals during the calcination. Constraint sintering effect due to inert compounds such as dolomitic MgO mitigates the inactivation.

Crystal Growth & Design | DOI: 10.1021/acs.cgd.6b01228

Selectivity control in oxidation of 1-tetradecanol on supported nano Au catalysts

Martinez-Gonzalez, S; Ivanova, S; Dominguez, MI; Corberan, VC

Selective oxidation of tetradecanol, a model higher fatty alcohol, on Au/CeO2-Al2O3 catalyst has been investigated to assess the factors that control selectivity. The analysis of the effect of operation conditions (temperature, run time and alcohol/metal (AIM) ratio) on catalytic performance revealed a quite complex reaction network, in which acid formation starts only after a certain level of conversion is reached. This level depends linearly on the total support surface available, indicating that it must be saturated by species generated by the reaction itself to allow acid formation to start. Addition of water to reaction medium did not modify this level, indicating that such species is not adsorbed water, as previously hypothesized, but probably spilled over hydrogen species. The resulting drastic change in the selectivity trends makes the ratio A/M a critical factor to control selectivity to aldehyde and to acid. Selectivity to ester is less sensible to operation parameters. It is noteworthy that aldehyde yields up to 27% with 90% selectivity, and acid yields up to 40% with 81% selectivity can be reached by proper selection of operation parameters.

Catalysis Today, 278 (2016) 113-119 | DOI: 10.1016/j.cattod.2016.06.019

Growth of carbonaceous nanomaterials over stainless steel foams. Effect of activation temperature

Latorre, N; Cazana, F; Sebastian, V; Royo, C; Romeo, E; Centeno, MA; Monzon, A

Some of the problems that occur during the operation of chemical reactors based of structured catalytic substrates, as monoliths, foams, membranes, cloths, fibres and other systems, are related to the preparation of long term stable coatings. Frequently, the deposition of the catalytic layer is carried out by washcoating, requiring this step a cautious attention, especially in the case of complex geometries, like of that of foams or cloths. In the case of the deposition of layers of carbonaceous materials (CNMs), an alternative route, avoiding the washcoating, it is their direct growth by catalytic decomposition light hydrocarbons (also called CCVD), over the surface of the metallic substrate. In this case, if the metallic substrate is of stainless steel, it already contains the catalytic active phases like Fe and Ni. 

In order to optimize the process of CNMs growth over structured metallic substrates, we are studying the effect of the main operational variables of the ethane decomposition reaction on stainless steel foams. In this contribution we present a study of the influence of the temperature of the activation (oxidation and reduction) stage on the type and morphology of the carbonaceous materials formed. The results obtained allow us to determine the optimal operating conditions to maximize the amount and the selectivity of the process to obtain a given type of CNM.

Catalysis Today, 273 (2016) 41-49 | DOI: 10.1016/j.cattod.2016.02.063

Impact of structured catalysts in amine oxidation under mild conditions

Latorre, N; Cazana, F; Sebastian, V; Royo, C; Romeo, E; Centeno, MA; Monzon, A

A structured graphene/graphite catalyst grown on a commercial austenitic stainless steel sheet providing a micromonolith was obtained by submitting the nude stainless steel structure to a carbon-rich atmosphere (first 300 mL/min of a reductive H-2/N-2 (1:1) flow, then to 180 mL/min of a CH4/H-2 (1:5)) at high temperature (900 degrees C) for 2 h. The preparation procedure resulted in a homogenous surface coated with a carbon-rich film as observed by EDX and SEM images. Further characterizations by Raman spectroscopy revealed characteristic Raman lines of graphene and crystalline graphite disposed in a hierarchical organization. The disposal of the obtained surface layers was also confirmed by grazing incidence X-ray diffraction. Besides this, XRD indicated the overlapping diffraction lines of graphite, cementite and M7C3 carbides. The graphene nature of the outermost layer was also confirmed by XPS. The catalytic behavior of the structured graphene/graphite catalyst was evaluated in the selective oxidation of heptylamine. At 200 degrees C it afforded a total conversion with a combined selectivity in heptanonitrile and N-heptylidene-heptylamine of 67% (10% heptanonitrile) that corresponds indeed to a very efficient system in the absence of any metal. Kinetic experiments with the scope to calculate the activation energies were also performed. 

Catalysis Today, 273 (2016) 266-272 | DOI: 10.1016/j.cattod.2016.05.001

Influence of the ionic liquid presence on the selective oxidation of glucose over molybdenum based catalysts

Megias-Sayago, C; Carrasco, CJ; Ivanova, S; Montilla, FJ; Galindo, A; Odriozola, JA

Two different approaches are proposed in this work in order to study the influence of the ionic liquid presence in the reaction of glucose oxidation by H2O2 in mild conditions. The ionic liquids are applied either as a solvent by using homogeneous Mo based catalyst, [Mo(O)(O2)2(H2O)n] complex, or by using it as an integral part of a heterogeneous catalyst, organic inorganic hybrids based on Mo Keggin structure. Both catalytic strategies resulted in acceptable glucose transformation degrees but lead to different oxidation products depending on the role of the ionic liquid. The hybrid approach restrains the number of the received products being the most selective one. A detailed study of the effect of the hybrid nature and reaction conditions is proposed in the second part of this study.

Catalysis Today, 278 (2016) 82-90 | DOI: 10.1016/j.cattod.2016.06.040

Au-supported on Fe-doped ceria solids prepared in water-in-oil microemulsions: Catalysts for CO oxidation

Laguna, OH; Centeno, MA; Boutonnet, M; Odriozola, JA

Gold catalysts were synthesized by deposition-precipitation employing Fe-doped ceria systems, previously obtained by means of the water-in-oil microemulsions methodology with different iron contents (10, 25 and 50 Fe at.%). The final catalysts were tested in the CO oxidation reaction in presence of H2. After gold deposition the crystalline structure of the supports was not altered. Moreover no XRD lines associated to gold were detected, indicating its high dispersion. Solid solution was generated in all samples, although the segregation of iron oxide was detected for the material with the highest iron loading. This phenomenon was then enhanced for the corresponding gold catalyst that also presented sintering of the gold nanoparticles.

Strong interaction between gold and the oxygen vacancies of the supports was demonstrated, as well as the promotion of the reducibility of surface Ce4+ and Fe3+species at low temperatures. A remarkable promotion of the CO conversion at lower temperatures respect to that of the supports was observed for the gold catalysts. Below 120 °C, lower the amount of iron incorporated, higher the catalytic performance of the catalyst. This behaviour is closely related not only to a high gold dispersion but also to the ability for creating additional oxygen vacancies in the support, required for the CO oxidation reaction.

Catalysis Today, 278 (2016) 140-149 | DOI: 10.1016/j.cattod.2016.05.059

On the relevant role of solids residence time on their CO2 capture performance in the Calcium Looping technology

Perejon, A; Miranda-Pizarro, J; Perez-Maqueda, LA; Valverde, JM

The multicycle CO2 capture performance of CaO derived from natural limestone and dolomite has been investigated by means of thermogravimetry under realistic Calcium-Looping conditions, which necessarily involve high CO2 concentration and high temperatures in the calcination stage and fast transitions between the carbonation and calcination stages. Natural dolomite allows reducing the calcination temperature as compared to limestone while high calcination efficiency is maintained. This could help reducing the energy penalty of the CaL process thus further enhancing the industrial competitiveness for the integration of this technology into fossil fuel power plants. Importantly, the CO2 capture capacity of the sorbents is critically affected by the solids residence time in the carbonation and calcination stages within the feasible range in practice. Thus, carbonation/calcination residence times play a critical role on the multicycle CO2 capture performance, which has been generally dismissed in previous studies. A main observation is the enhancement of carbonation in the solid-state diffusion controlled phase, which is against the commonly accepted conception that the only relevant phase in the carbonation stage is the fast reaction-controlled stage on the surface of the solids. Thus, the CO2 capture efficiency may be significantly enhanced by increasing the solids residence time in the carbonator.

Energy, 113 (2016) 160-171 | DOI: 10.1016/j.energy.2016.07.028

Multifunctional Eu-doped NaGd(MoO4)(2) nanoparticles functionalized with poly(L-lysine) for optical and MRI imaging

M. Laguna; N.O. Nuñez; V. Rodríguez; E. Cantelar, G. Stepien, M.L. García, J.M. de la Fuente; M. Ocaña

A method for the synthesis of non-aggregated and highly uniform Eu3+ doped NaGd(MoO4)(2) nanoparticles is reported for the first time. The obtained particles present tetragonal structure, ellipsoidal shape and their size can be varied by adjusting the experimental synthesis parameters. These nanoparticles, which were coated with citrate anions and functionalised with PLL, have also been developed in order to improve their colloidal stability in physiological medium (2-(N-morpholino) ethanesulfonic acid, MES). A study of the luminescent dynamics of the samples as a function of the Eu doping level has been conducted in order to find the optimum nanophosphors, whose magnetic relaxivity and cell viability have also been evaluated for the first time for this system, in order to assess their suitability as multifunctional probes for optical (in vitro) and magnetic bioimaging applications.

Dalton Transactions, 45 (2016) 16354-16365 | DOI: 10.1039/c6dt02663j

Application of Prussian Blue electrodes for amperometric detection of free chlorine in water samples using Flow Injection Analysis

Salazar, P; Martin, M; Gonzalez-Mora, JL; Gonzalez-Elipe, AR

The performance for free chlorine detection of surfactant-modified Prussian Blue screen printed carbon electrodes (SPCEs/PB-BZT) have been assessed by cyclic voltammetry and constant potential amperometry. The characterization of SPCEs/PB-BZT by X-ray photoemission, Raman and infrared spectroscopies confirmed the correct electrodeposition of the surfactant-modified PB film. These electrodes were incorporated in a Flow Injection device and the optimal working conditions determined as a function of experimental variables such as detection potential, electrolyte concentration or flow-rate. The sensor presented a linear response in the range 0–3 ppm free chlorine, with a sensitivity of 16.2 μA ppm−1 cm−2. The limit of detection (LOD) (S/N=3.3) and the limit of quantification (S/N=10) amounted to 8.25 and 24.6 ppb, respectively, adequate for controlling tap and drinking waters. To demonstrate the feasibility of using this free chlorine sensor for real applications possible interferences such as nitrate, nitrite and sulfate ions were successfully tested and discarded. Real free chlorine analysis was carried out in spiked tap water samples and commercial bleaches.

Talanta, 146 (2016) 410-416 | DOI: 10.1016/j.talanta.2015.08.072

Towards the hydrogen production by photocatalysis

Colon, G

Nowadays, problems derived from climate change urgently demand us to focus our attention on new alternatives to fossil fuels. Within this framework, the photocatalytic production of hydrogen as a clean fuel from oxygenates arises as a necessary option that must be considered. Thus, the development of highly efficient photocatalyst is crucial in order to achieve a viable technology under the industrial point of view. For this sake, it is necessary to understand the principles of photoreforming reaction. In this brief review we will revisit the different photocatalytic materials proposed in the literature highlighting on the role of different co-catalysts.

Applied Catalysis A-General, 518 (2016) 48-59 | DOI: 10.1016/j.apcata.2015.11.042

Photocatalytic Escherichia coli inactivation by means of trivalent Er3+, Y3+ doping of BiVO4 system

Adan, C; Marugan, J; Obregon, S; Colon, G

BiVO4 samples doped with different contents of Er3+ and Y3+ were prepared by a simple surfactant free hydrothermal method. X-ray diffraction reveals that the doped materials consist of a heterogeneous structure formed by a mixture of tetragonal and monoclinic phases, being found Er3+ and Y3+ co-doping clearly stabilize the tetragonal structure of BiVO4. The monoclinic BiVO4 samples shows a strong absorption in the visible light region leading to band-gap values of around 2.4eV while the tetragonal BiVO4 displays higher band-gap values of 2.9 eV. The photocatalytic activity of the catalysts was investigated for the oxidation of methanol and inactivation of Escherichia coli showing that all the BiVO4 catalysts are photocatalytically active in the oxidation of methanol and are able to inactivate more than 99.99% of bacteria not only under UV light but also under visible light irradiation. The results revealed that the co-doping of Er3+ and Y3+ into BiVO4 exhibited enhanced photocatalytic activity for methanol oxidation under simulated solar light irradiation. The inactivation of E.coli show similar results for the doped systems although in relative terms of activity the Er3+,Y3+-BiVO4 sample show a better use of the visible light, leading to a higher activity than P25-TiO2.

Applied Catalysis A-General, 526 (2015) 126-131 | DOI: 10.1016/j.apcata.2016.08.002

Permeability and mechanical integrity of porous biomorphic SiC ceramics for application as hot-gas filters

Gomez-Martin, A.; Orihuela, M. P.; Becerra, J. A.; Martinez-Fernandez, J.; Ramirez-Rico, J.

Biomorphic SiC is a biotemplated material fabricated by Si melt-infiltration of carbon preforms from wood pyrolysis. In this work, porous bioSiC ceramics from five different wood precursors, with porosities between 45 and 72% were studied for their feasibility in filtering applications.

Gas permeability and mechanical stability were investigated as a function of the microstructure of the starting wood precursor. Air-permeation performance at room temperature was measured for a range of flow rates, and the permeability constants were assessed by fitting of Forchheimer's equation to the experimental data. Darcian permeabilities were achieved in the range 10− 11–10− 12 m2, while inertial terms were in the range 10− 7–10− 8 m, showing a correlation with the average pore size and orientation of the larger channels. Regarding the mechanical stability, maximum compressive strength values were reached in the range of 3–115 MPa.

These results improve our understanding of the ways in which the microstructure influences permeability and mechanical robustness, enabling the device requirements to be tailored by selecting the wood precursor. It was also shown that these materials are promising for hot-gas filtering applications.

Materials & Design, 107 (2016) 450-460 | DOI: 10.1016/j.matdes.2016.06.060

Study by DSC and HRTEM of the aging strengthening of Cu-Ni-Zn-Al alloys

Dianez, MJ; Donoso, E; Criado, JM; Sayagues, MJ; Diaz, G; Olivares, L

The structural changes of a Cu-12 wt.% Ni-17 wt.% Zn-1.7 wt% Al alloy as a function of the aging temperature have been studied by means of Differential Scanning Calorimetry (DSC), high resolution transmission electron microscopy (HRTEM) and hardness measurements. It has been proposed a hardening mechanism that implies the crystallization of a Ll(0) Cu2NiZn phase coherent with the matrix a phase followed, firstly, by its transformation into a Ll(2) coherent phase and, secondly, by the precipitation of this phase. It has been shown that aluminum play an important role in the precipitation hardening process because Cu2NiZn precipitates are not formed by aging a ternary Cu-Ni-Zn alloy of similar composition. It has been shown by the first time that DSC could be a powerful tool for discriminating the whole set of phase transformations undergone by alloys as a function of the annealing temperature from a single heating run. 

Materials & Design, 92 (2016) 184-188 | DOI: 10.1016/j.matdes.2015.12.030

Thermal conductivity of Fe graphitized wood derived carbon

Ramirez-Rico, J; Gutierrez-Pardo, A; Martinez-Fernandez, J; Popov, VV; Orlova, TS

Graphitic porous carbon materials from pyrolysis of wood precursors were obtained by means of a nanosized Fe catalyst, and their microstructure and electrical and thermal transport properties investigated. Thermal and electrical conductivity of graphitized carbon materials increase with the pyrolysis temperature, indicating a relationship between the degree of graphitization and thus in crystallite size with transport properties in the resulting carbon scaffolds. Evaluation of the experimental results indicate that thermal conductivity is mainly through phonons and increases with the temperature in Fe-catalyzed carbons suggesting that the mean free path of phonons in the material is small and defect scattering dominates over phonon-phonon interactions in the range from room temperature to 800 °C.

Materials & Design, 99 (2016) 528-534 | DOI: 10.1016/j.matdes.2016.03.070

Ligand-Free Synthesis of Tunable Size Ln:BaGdF5 (Ln = Eu3+ and Nd3+) Nanoparticles: Luminescence, Magnetic Properties, and Biocompatibility

Becerro, AI; Gonzalez-Mancebo, D; Cantelar, E; Cusso, F; Stepien, G; de la Fuente, JM; Ocana, M

Bifunctional and highly uniform Ln:BaGdF5 (Ln = Eu3+ and Nd3+) nanoparticles have been successfully synthesized using a solvothermal method consisting of the aging at 120 degrees C of a glycerol solution containing the corresponding Lanthanide acetylacetonates and butylmethylimidazolium tetrafluoroborate. The absence of any surfactant in the synthesis process rendered hydrophilic nanospheres (with tunable diameter from 45 nm 85 nm, depending on the cations concentration of the starting solution) which are suitable for bioapplications. The particles are bifunctional because they showed both optical and magnetic properties due to the presence of the optically active lanthanides (Eu3+ in the visible and Nd3+ in the NIR regions of the electromagnetic spectrum) and the paramagnetic gadolinium ion, respectively. The luminescence decay curves of the nanospheres doped with different amounts of Eu3+ and Nd3+ have been recorded in order to determine the optimum dopant concentration in each case, which turned out to be 5% Eu3+ and 0.5% Nd3+. Likewise, proton relaxation times were measured at 1.5 T in water suspensions of the optimum particles found in the luminescence study. The values obtained suggested that both kinds of particles could be used as positive contrast agents for MRI. Finally, it was demonstrated that both the 5% Eu3+ and 0.5% Nd3+-doped BaGdF5 nanospheres showed negligible cytotoxicity for VERO cells for concentrations up to 0.25 mg mL(-1).

Langmuir, 32 (2016) 411-420 | DOI: 10.1021/acs.langmuir.5b03837

Quantitative uptake of colloidal particles by cell cultures

Feliu, N; Huhn, J; Zyuzin, MV; Ashraf, S; Valdeperez, D; Masood, A; Said, AH; Escudero, A; Pelaz, B; Gonzalez, E; Duarte, MAC; Roy, S; Chakraborty, I; Lim, ML; Sjoqvist, S; Jungebluth, P; Parak, WJ

The use of nanotechnologies involving nano-and microparticles has increased tremendously in the recent past. There are various beneficial characteristics that make particles attractive for a wide range of technologies. However, colloidal particles on the other hand can potentially be harmful for humans and environment. Today, complete understanding of the interaction of colloidal particles with biological systems still remains a challenge. Indeed, their uptake, effects, and final cell cycle including their life span fate and degradation in biological systems are not fully understood. This is mainly due to the complexity of multiple parameters which need to be taken in consideration to perform the nanosafety research. Therefore, we will provide an overview of the common denominators and ideas to achieve universal metrics to assess their safety. The review discusses aspects including how biological media could change the physicochemical properties of colloids, how colloids are endocytosed by cells, how to distinguish between internalized versus membrane-attached colloids, possible correlation of cellular uptake of colloids with their physicochemical properties, and how the colloidal stability of colloids may vary upon cell internalization. In conclusion three main statements are given. First, in typically exposure scenarios only part of the colloids associated with cells are internalized while a significant part remain outside cells attached to their membrane. For quantitative uptake studies false positive counts in the form of only adherent but not internalized colloids have to be avoided. pH sensitive fluorophores attached to the colloids, which can discriminate between acidic endosomal/lysosomal and neutral extracellular environment around colloids offer a possible solution. Second, the metrics selected for uptake studies is of utmost importance. Counting the internalized colloids by number or by volume may lead to significantly different results. Third, colloids may change their physicochemical properties along their life cycle, and appropriate characterization is required during the different stages.

Science of the Total Environment, 568 (2016) 819-828 | DOI: 10.1016/j.scitotenv.2016.05.213

Comparison of supported TiO2 catalysts in the photocatalytic degradation of NOx

Rodriguez, MJH; Melian, EP; Diaz, OG; Arana, J; Macias, M; Orive, AG; Rodriguez, JMD

A comparison is made in this study of the effectiveness of various commercial catalysts in the oxidation of NOx by heterogeneous photocatalysis. The following catalysts were considered: Aeroxide TiO2 P25, Aeroxide TiO2 P90, Hombikat UV-100, Kronos vlp7000, CristalACTIV PC105, CristalACTIV PC500, Kemira 650 and Anatasa Aldrich. All catalysts were deposited by a dip -coating technique onto borosilicate 3.3 glass plates. Optimization of catalyst load showed no significant enhancement of photoactivity, in general, above a deposited mass of 1.16 mg cm(-2). Differences between photocatalyst activity were more apparent at longer illumination times. Photoactivity decreased in the presence of humidity and differences in the adsorbed products were detected. Photocatalyst activity was strongly influenced by specific surface area, with the best results obtained by the catalysts with the largest surface area, namely the PC500, Hombikat and Kronos. Photocatalyst stability was demonstrated in successive reuse cycles. 

Journal of Molecular Catalysis A-Chemical, 413 (2016) 56-66 | DOI: 10.1016/j.molcata.2015.12.007

Nanogold mesoporous iron promoted ceria catalysts for total and preferential CO oxidation reactions

Reina, TR; Ivanova, S; Idakiev, V; Tabakova, T; Centeno, MA; Deng, QF; Yuan, ZY; Odriozola, JA

Herein, a series of highly efficient gold based catalysts supported on mesoporous CeO2-Fe2O3 mixed oxides for CO elimination reactions have been developed. The materials have been fully characterized by means of XRD, Raman and UV-vis spectroscopies among other techniques. We identify the Ce-Fe synergism as a fundamental factor controlling the catalytic performance. Our data clearly reveal that the CO oxidation activity is maximized when the electronic and structural properties of the support are carefully controlled. In this situation, fairly good catalysts for environmental applications as for example H-2 streams purification for fuel cell goals or CO abatement at room temperature can be designed. 

Journal of Molecular Catalysis A-Chemical, 414 (2016) 62-71 | DOI: 10.1016/j.molcata.2016.01.003

Modified emission of extended light emitting layers by selective coupling to collective lattice resonances

Ramezani, Mohammad; Lozano, Gabriel; Verschuuren, Marc A.; Gomez-Rivas, Jaime

We demonstrate that the coupling between light emitters in extended polymer layers and modes supported by arrays of plasmonic particles can be selectively enhanced by accurate positioning of the emitters in regions where the electric field intensity of a given mode is maximized. The enhancement, which we measure to reach up to 70%, is due to the improved spatial overlap and coupling between the optical mode and emitters. This improvement of the coupling leads to a modification of the emission spectrum and the luminous efficacy of the sample.

Physical Review B, 94 (2016) 12 | DOI: 10.1103/PhysRevB.94.125406

Cellular Viscosity in Prokaryotes and Thermal Stability of Low Molecular Weight Biomolecules

Cuecas, A; Cruces, J; Galisteo-Lopez, JF; Peng, XJ; Gonzalez, JM

Some low molecular weight biomolecules, i.e., NAD(P)H, are unstable at high temperatures. The use of these biomolecules by thermophilic microorganisms has been scarcely analyzed. Herein, NADH stability has been studied at different temperatures and viscosities. NADH decay increased at increasing temperatures. At increasing viscosities, NADH decay rates decreased. Thus, maintaining relatively high cellular viscosity in cells could result in increased stability of low molecular weight biomolecules (i.e., NADH) at high temperatures, unlike what was previously deduced from studies in diluted water solutions. Cellular viscosity was determined using a fluorescent molecular rotor in various prokaryotes covering the range from 10 to 100°C. Some mesophiles showed the capability of changing cellular viscosity depending on growth temperature. Thermophiles and extreme thermophiles presented a relatively high cellular viscosity, suggesting this strategy as a reasonable mechanism to thrive under these high temperatures. Results substantiate the capability of thermophiles and extreme thermophiles (growth range 50–80°C) to stabilize and use generally considered unstable, universal low molecular weight biomolecules. In addition, this study represents a first report, to our knowledge, on cellular viscosity measurements in prokaryotes and it shows the dependency of prokaryotic cellular viscosity on species and growth temperature.

Biophysical Journal, 111 (2016) 875–882 | DOI: 10.1016/j.bpj.2016.07.024

Nanocolumnar association and domain formation in porous thin films grown by evaporation at oblique angles

Lopez-Santos, C; Alvarez, R; Garcia-Valenzuela, A; Rico, V; Loeffler, M; Gonzalez-Elipe, AR; Palmero, A

Porous thin films grown at oblique angles by evaporation techniques are formed by tilted nanocolumnar structures which, depending on the material type and growth conditions, associate along certain preferential directions, giving rise to large domains. This arrangement, commonly denoted as bundling association, is investigated in the present work by performing fundamental experiments and growth simulations. It is proved that trapping processes of vapor species at the film surface, together with the shadowing mechanism, mediate the anisotropic widening of the nanocolumns and promote their preferential coalescence along certain directions, giving rise to domains with different shape and size. The role of these two processes is thoroughly studied in connection with the formation of these domains in materials as different as SiO2 and TiO2.

Nanotechnology, 27 (2016) 395702 | DOI: 10.1088/0957-4484/27/39/395702

TiO2-clay based nanoarchitectures for enhanced photocatalytic hydrogen production

Perez-Carvajal, J; Aranda, P; Obregon, S; Colon, G; Ruiz-Hitzky, E

New functional TiO2-clay nanoarchitectures based on layered and fibrous silicates and incorporating Pd and Pt noble metal nanoparticles (NPs) have been synthesized by applying a sol–gel methodology that involves the use of commercial organoclays. The incorporation of the noble metal NPs can be done using two different approaches: i) direct addition to the synthesis medium of a noble metal precursor (typically acetylacetonate) during the generation of the nanoarchitecture, and ii) selective photodeposition of the noble metal NPs in a post-treatment of the TiO2-clay nanoarchitecture. The resulting materials have been characterized by means of XRD, FTIR, Raman, 29Si-NMR, FE-SEM, TEM and N2 adsorption–desorption isotherms. The efficiency of these nanoarchitectures in the photocatalytic hydrogen production has been tested in the photoreforming of methanol. The higher rate in the hydrogen production corresponds to the nanoarchitectures containing Pt and TiO2 NPs derived from sepiolite.

Microporous and Mesoporous Materials, 222 (2016) 120-127 | DOI: 10.1016/j.micromeso.2015.10.007

In vitro stimulation of MC3T3-E1cells and sustained drug delivery by a hierarchical nanostructured SiO2-CaO-P2O5 scaffold

Ramiro-Gutierrez, ML; Santos-Ruiz, L; Borrego-Gonzalez, S; Becerra, J; Diaz-Cuenca, A

A hierarchical scaffold, SP1_h_HA, consisting of a biomimetic nano-hydroxyapatite surface coating growth onto a reticulated structure having a nano-organized porous texture was fabricated and functionally studied in vitro using osteoprogenitor cells. Three scaffold materials (designated as SP0_l, SP0_h and SP1_h) were also prepared through modifications of the processing variables as control materials. The scaffolds were characterized showing well-interconnected micron-sized voids and a nano (4–6 nm)-organized porosity. In order to evaluate potential local risks and performance over mammalian cells the scaffolds were studied in comparison with a commercial clinical grade scaffold material, ProOsteon® 500R. MC3T3-E1 pre-osteoblast viability was evaluated using the resazurin assay and field emission gun scanning electron microscopy (FEG-SEM), showing in all cases good proliferative response. Alkaline phosphatase (ALP) production and analysis of the differentiation marker osteocalcin (OC), both in non-osteoinductive and osteoinductive media, were assessed using colorimetric and RT-PCR methods. The implementation of the new scaffold processing variables enhanced ALP activity with respect to the SP0_l control material. The cell proliferation, ALP activity, and mRNA OC expression response to SP1_h_HA scaffold were higher than those observed after the use of ProOsteon® 500R. In addition, SP1_h_HA scaffold showed a two stage sustained release of gentamicin sulfate (GS) instead of the quick release shown by ProOsteon® 500R. These results suggest that our synthesized scaffold could be effective for antibiotic delivery and bone regeneration and a better option than ProOsteon® 500R.

Microporous and Mesoporous Materials, 229 (2016) 31-43 | DOI: 10.1016/j.micromeso.2016.04.018

Monolithic supports based on biomorphic SiC for the catalytic combustion of hydrogen

Arzac, G. M.; Ramirez-Rico, J.; Gutierrez-Pardo, A.; Jimenez de Haro, M. C.; Hufschmidt, D.; Martinez-Fernandez, J.; Fernandez, A.

Catalytic hydrogen combustion was studied with H-2/air mixtures in conditions that simulate the H-2 concentration of the exhaust gases from fuel cells (3-4% v/v H-2 in air). Pt-impregnated monoliths based on porous biomorphic SiC (bio-SiC) substrates were employed for the first time for this reaction. Capillary forces were exploited for the incipient impregnation of supports with H2PtCl6 solutions. Freeze drying permitted us to obtain a homogeneous distribution of the active phase reducing accumulation at the monolith's outer shell. The supports and catalysts were characterized from a structural and thermal point of view. Catalytic tests were performed in a homemade reactor fed with up to 1000 ml min(-1) H-2/air mixtures and a diffusional regime (non-isothermal) was achieved in the selected conditions. Catalyst loading was tested in the range of 0.25-1.5 wt% Pt and 100% conversion was achieved in all cases. Temperatures were recorded at different points of the monoliths during the reaction showing anisotropic thermal behavior for selected bio-SiC substrates. These effects are of interest for heat management applications and were explained in correlation with thermal conductivity measurements performed on the supports. Pt-impregnated monoliths were also tested in less than 100% conversion conditions (1% v/v H-2 in air) and in powder form in kinetic conditions for comparative purposes.

RSC Advances, 6 (2016) 66373-66384 | DOI: 10.1039/c6ra09127j

Aguilera, JR; Venegas, V; Oliva, JM; Sayagues, MJ; de Miguel, M; Sanchez-Alcazar, JA; Arevalo-Rodriguez, M; Zaderenko, AP

Aguilera, J. R.; Venegas, V.; Oliva, J. M.; Sayagues, M. J.; de Miguel, M.; Sanchez-Alcazar, J. A.; Arevalo-Rodriguez, M.; Zaderenko, A. P.

Tannic acid (TA) has multiple effects against cancer, being especially promising in those types that overexpress the epidermal growth factor receptor (EGFR), as TA modulates its activation and downstream signaling pathways, triggering apoptosis. Nonetheless, despite the important role of this receptor in the pathogenesis and progression of a wide variety of tumors, no TA systems targeted to this receptor have been described yet. In this work, we synthesize, characterize by physico-chemical techniques and study the cytotoxic effect and cell uptake of TA nanoparticles targeted to EGFR in both tumoral and normal human skin cells. Our nanoparticles exhibited an extremely high entrapment efficiency, and were only toxic for the tumoral cells. The uptake assay demonstrated that nanoparticles are able to enter the cells through a receptor-mediated mechanism. Furthermore, we have included fluorescent markers in these nanoparticles to combine imaging and therapeutic applications, thus building effectively a multifunctional tool for biomedicine.

 

RSC Advances, 9 (2016) 108611-108620 | DOI: 10.1039/c5ra19405a

Constant rate thermal analysis of a dehydrogenation reaction

Perejon, A; Perez-Maqueda, LA; Sanchez-Jimenez, PE; Criado, JM; Murafa, N; Subrt, J

The Constant Rate Thermal Analysis (CRTA) procedure has been employed for the first time to study the kinetics of MgH2 dehydrogenation by thermogravimetry under high vacuum. CRTA implies controlling the temperature in such a way that the decomposition rate is maintained constant all over the process, employing the mass change as the experimental signal proportional to the reaction rate. The CRTA curves present a higher resolution power to discriminate the kinetic model obeyed by the reaction in comparison with conventional heating rate curves. The combined kinetic analysis has been applied to obtain the kinetic parameters, which show that MgH2 decomposition under high vacuum obeys first-order kinetics (F1). It has been proposed that the dehydrogenation of MgH2 under high vacuum takes place by instantaneous nucleation in the border line of the bidimensional crystallites followed by the growth of the nuclei.

RSC Advances, 6 (2016) 81454-81460 | DOI: 10.1039/C6RA10157G

Use of steel slag for CO2 capture under realistic calcium-looping conditions

Miranda-Pizarro, J; Perejon, A; Valverde, JM; Sanchez-Jimenez, PE; Perez-Maqueda, LA

In this study, CaO derived from steel slag pretreated with diluted acetic acid has been tested as a dry sorbent for CO2 capture under realistic Ca-Looping (CaL) conditions, which necessarily implies calcination under high CO2 partial pressure and fast transitions between carbonation and calcination stages. The multicycle capture performance of the sorbent has been investigated by varying the precalcination time, carbonation/calcination residence times and with the introduction of a recarbonation stage. Results show that the sorbent can be regenerated in very short residence times at 900 °C under high CO2 partial pressure, thus reducing the calciner temperature by about 30–50 °C when compared to limestone. Although the introduction of a recarbonation stage to reactivate the sorbent, as suggested in previous studies for limestone, results in a slightly enhanced capture capacity, the sorbent performance can be significantly improved if the main role of the solid-state diffusion-controlled carbonation is not dismissed. Thus, a notable enhancement of the capture capacity is achieved when the carbonation residence time is prolonged beyond just a few minutes, which suggests a critical effect of solids residence time in the carbonator on the CO2 capture efficiency of the CaL process when integrated into a power plant.

RSC Advances, 6 (2016) 37656-37663 | DOI: 10.1039/C6RA03210A

Ripening and recrystallization of NaCl nanocrystals in humid conditions

Oliva-Ramirez, M; Macias-Montero, M; Borras, A; Gonzalez-Elipe, AR

This study shows that Ostwald ripening, a universal mechanism responsible for the increase of crystal size during precipitation from solutions, can be meditated by ion diffusion through condensed monolayers of water that connect separated nanocrystals. In an environmental electron microscope we have observed "in situ" the time evolution of the number, shape, size and crystallographic texture of NaCl nanoparticles deposited by electron beam evaporation at oblique angles. Analysis of NaCl nanoparticles before and after water vapor condensation has evidenced that the size of nanocrystals is not the unique driving force inducing nanoparticle ripening and recrystallization, but the faceting of their crystalline habits and the amorphisation degree of the initially deposited nuclei also play important roles. These findings have implications for other crystallization and nucleation processes and can be of relevance for rock weathering and related phenomena.

RSC Advances, 6 (2016) 3778-3782 | DOI: 10.1039/C5RA22425J

Tailor-made preparation of Co-C, Co-B, and Co catalytic thin films using magnetron sputtering: insights into structure-composition and activation effects for catalyzed NaBH4 hydrolysis

Paladini, M; Godinho, V; Arzac, GM; de Haro, MCJ; Beltran, AM; Fernandez, A

The magnetron sputtering (MS) methodology is a powerful tool for tailor-made fabrication of Co-based thin film catalysts with controlled microstructures and compositions for sodium borohydride (SBH) hydrolysis. In particular, Co-C catalysts were tested in this reaction and compared to Co-B and Co catalyst coatings. The microstructural and chemical analyses by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), Rutherford back scattering (RBS) and X-ray photoelectron spectroscopy (XPS) were used to characterize a complete library of thin film catalysts. Pure Co materials were characterized by their nanocrystalline microstructure, and grain refinement was achieved via an increase in the deposition pressure. The incorporation of boron or carbon via co-deposition results in amorphization and dispersion of the active metallic Co phase. The composition can be tuned while keeping a controlled microstructure, and a comparison of activity at 25 degrees C was performed on catalysts deposited on Ni foam substrates. A comparison of the initial activities showed that the Co-B samples were more active than the Co-C samples because of electronic effects. However, a strong activation was found for the Co-C catalysts after the first use. This effect was dependent upon the incorporation of cobalt boride (CoxB) species on the catalysts' surface, as shown by XPS. After the first several uses, the activity of the Co-C samples (values up to 2495 mL min(-1) g(catalyst)(-1)) were as high as that of fresh Co-B, and the surface composition of both the catalysts was similar. This activation was not observed for the pure Co and was very weak for the Co-B catalysts. The use of polymeric (PTFE) substrates (flexible membranes) illustrated the versatility of the methodology to obtain catalytic membranes and allowed for a TEM microstructural analysis at the nanoscale. Catalytic activities at 60 degrees C were as high as 16.7 and 20 L min(-1) g(Co)(-1) for the Co-C and Co-B membranes, respectively. We determined the optimized conditions to increase the catalytic activity of Co-based coatings prepared via magnetron sputtering.

RSC Advances, 6 (2016) 108611-108620 | DOI: 10.1039/c6ra23171c

Timing of calcium nitrate addition affects morphology, dispersity and composition of bioactive glass nanoparticles

Zheng, K; Taccardi, N; Beltran, AM; Sui, BY; Zhou, T; Marthala, VRR; Hartmann, M; Boccaccini, AR

Bioactive glass nanoparticles (BGN) are promising materials for a number of biomedical applications. Many parameters related to the synthesis of BGN using sol–gel methods can affect their characteristics. In this study, the influence of timing of calcium nitrate (calcium precursor) addition during processing on BGN characteristics was investigated. The results showed that the addition timing could affect the morphology, dispersity and composition of BGN. With delayed addition of calcium nitrate, larger, more regular and better dispersed BGN could be synthesized while the gap between nominal and actual compositions of BGN was widened. However, the addition timing had no significant influence on structural characteristics, as BGN with different addition-timing of calcium nitrate exhibited similar infrared spectra and amorphous nature. The results also suggested that monodispersed BGN could be synthesized by carefully controlling the addition of calcium nitrate. The synthesized monodispersed BGN could release Si and Ca ions continuously for up to at least 14 days. They also showed in vitro bioactivity and non-cytotoxicity towards rat bone marrow-derived mesenchymal stem cells (rBMSCs). In conclusion, the timing of calcium precursor addition is an essential parameter to be considered when producing BGN which should exhibit monodisperse characteristics for biomedical applications.

RSC Advances, 6 (2016) 95101-95111 | DOI: 10.1039/C6RA05548F

Intensification of hydrogen production by methanol steam reforming

Sanz, O; Velasco, I; Perez-Miqueo, I; Poyato, R; Odriozola, JA; Montes, M

This paper studies the methanol steam reforming intensification to enhance the hydrogen production in a multi-channel block type micro-reformer. The effects of operating parameters such as reforming temperature, space velocity and catalyst layer thickness on reforming performance are investigated. For optimized design and operating conditions, the 8 cm(3) reformer unit produced 170 LH2/h containing on dry basis 75.0% H-2, 23.5% CO2, 0.06% CH3OH and 1.44% CO at 648 K allowing the production of 218-255 Win a commercial PEMFC with 80% hydrogen utilization. This study shows that high methanol conversion can be achieved with high Pd/ZnO catalyst loading at 648 K with very low CO content (<1.5%) in the outlet stream. 

International Journal Hydrogen Energy, 41 (2016) 5250-5259 | DOI: 10.1016/j.ijhydene.2016.01.084

Portable IR dye laser optofluidic microresonator as a temperature and chemical sensor

Lahoz, F; Martin, IR; Gil-Rostra, J; Oliva-Ramirez, M; Yubero, F; Gonzalez-Elipe, AR

A compact and portable optofluidic microresonator has been fabricated and characterized. It is based on a Fabry-Perot microcavity consisting essentially of two tailored dichroic Bragg mirrors prepared by reactive magnetron sputtering deposition. The microresonator has been filled with an ethanol solution of Nile-Blue dye. Infrared laser emission has been measured with a pump threshold as low as 0.12 MW/cm2 and an external energy conversion efficiency of 41%. The application of the device as a temperature and a chemical sensor is demonstrated. Small temperature variations as well as small amount of water concentrations in the liquid laser medium are detected as a shift of the resonant laser modes.

Optics Express, 24 (2016) 14383-14392 | DOI: 10.1364/OE.24.014383

Pre-prosthetic use of poly(lactic-co-glycolic acid) membranes treated with oxygen plasma and TiO2 nanocomposite particles for guided bone regeneration processes

Castillo-Dali, G; Castillo-Oyague, R; Terriza, A; Saffar, JL; Batista-Cruzado, A; Lynch, CD; Sloan, AJ; Gutierrez-Perez, JL; Torres-Lagares, D

Objectives: Guided bone regeneration (GBR) processes are frequently necessary to achieve appropriate substrates before the restoration of edentulous areas. This study aimed to evaluate the bone regeneration reliability of a new poly-lactic-co-glycolic acid (PLGA) membrane after treatment with oxygen plasma (PO2) and titanium dioxide (TiO2) composite nanoparticles. 

Methods: Circumferential bone defects (diameter: 10 mm; depth: 3 mm) were created on the parietal bones of eight experimentation rabbits and were randomly covered with control membranes (Group 1: PLGA) or experimental membranes (Group 2: PLGA/PO2/TiO2). The animals were euthanized two months afterwards, and a morphologic study was then performed under microscope using ROI (region of interest) colour analysis. Percentage of new bone formation, length of mineralised bone formed in the grown defects, concentration of osteoclasts, and intensity of osteosynthetic activity were assessed. Comparisons among the groups and with the original bone tissue were made using the Kruskal-Wallis test. The level of significance was set in advance at a = 0.05. 

Results: The experimental group recorded higher values for new bone formation, mineralised bone length, and osteoclast concentration; this group also registered the highest osteosynthetic activity. Bone layers in advanced formation stages and low proportions of immature tissue were observed in the study group. 

Journal of Dentistry, 47 (2016) 71-79 | DOI: 10.1016/j.jdent.2016.01.015

Effect of Nickel and Magnesium on the Electrochemical Behavior of AA 1050 Alloys in Nitric Acid Solution

Garcia-Garcia, FJ; Skeldon, P; Thompson, GE

The study investigates the influence of nickel and magnesium additions to AA 1050 aluminum alloy on the electrochemical behavior of the alloy in nitric acid solution under conditions relevant to the lithographic and electronic industries. Magnesium and nickel additions are of interest, since they can improve the alloy properties for the printing process by improving reverse bending fatigue strength and thermal softening resistance, while nickel may provide uniform pitting during electrograining. Scanning electron microscopy was used to characterize the resulting surface morphologies. The addition of nickel led to an increase in the pitting and corrosion potentials; additionally, it reduced the rate of dissolution of intermetallic particles during anodic polarization and increased the rate of aluminum dissolution during cathodic polarization. In contrast, the addition of magnesium had negligible influence on the open circuit and pitting behaviors, since the magnesium is retained in solid solution and has negligible influence on the cathodic behavior of intermetallic particles, which dominate the corrosion behavior.

Journal of the Electrochemical Society, 163 (9) (2016) C593-C601 | DOI: 10.1149/2.1181609jes

The calorimetric analysis as a tool for studying the aging hardening mechanism of a Cu-10wt%Ni-5.5wt%Sn alloy

Dianez, MJ; Donoso, E; Sayagues, MJ; Perejon, A; Sanchez-Jimenez, PE; Perez-Maqueda, LA; Criado, JM

The transformations of a Cu-10wt%Ni-5.5wt%Sn alloy as a function of the aging time in the range from room temperature up to 600 degrees C have been followed by Differential Scanning Calorimetry (DSC). The results obtained have shown that this alloy undergone two overlapping exothermic phase transitions with DSC peaks at 208 degrees C and 305 degrees C, respectively, followed by an endothermic phase transformation with a DSC peak at 526 degrees C. The structural analysis by TEM, ED, EDX and XRD of the intermediates phases previously discriminated by DSC suggests that the first exothermic peak is associated to the spinodal decomposition of the sample, while the second one is associated to the segregation of a DO22 (Cu-x-Ni1-x)(3)Sn tetragonal phase coherent with the alpha-Cu structure of the starting alloy. The endothermic peak has been associated to the precipitation of cubic DO3 nanocrystals from the DO22 phase previously formed. The microhardness measurements carried out in combination with the structural characterization demonstrate that the aging hardening of the alloy under study is exclusively due to the formation of the coherent DO22 phase. The DO22/DO3 transition leads to a dramatic drop of the hardness of the alloy.

Journal of Alloys and Compounds, 688 (2016) 288-294 | DOI: 10.1016/j.jallcom.2016.07.021

Non-Enzymatic Glucose Sensors Based on Nickel Nanoporous Thin Films Prepared by Physical Vapor Deposition at Oblique Angles for Beverage Industry Applications

Salazar, P; Rico, V; Gonzalez-Elipe, AR

Nickel nanoporous thin films deposited on Indium tin oxide conductive plates have been prepared by physical vapor deposition in an oblique angle configuration. The scanning electron microscopy characterization of these films revealed a microstructure formed by tilted nanocolumns of ca. 40-60 nm of diameter inclined by ca. 26 degrees with respect to the normal. These highly porous films had ca. 30% of void space and provided a large exposed area and outstanding diffusion properties for sensor applications. X-ray diffraction analysis confirmed the deposition of metallic nickel, while Raman and X-ray photoelectron spectroscopies demonstrated that electrochemically treated films presented an oxi/hydroxide outer layer that is the active phase for glucose sensing. The activated electrodes had a high sensitivity (2.05 A M-1 cm(-2)), an excellent coefficient of determination (R-2: 0.999), an outstanding reproducibility (3.2%) and a detection limit of 0.34 mu M. Their glucose selectivity was excellent with regard to common electroactive interferences and other sugars found in agro-alimentary products. Tests carried out with commercial beverages proved the reliability of these electrodes for glucose analysis in real conditions.

Journal of the Electrochemical Society, 163 (14) (2016) B704-B709 | DOI: 10.1149/2.1241614jes

Magnesium hydride for energy storage applications: The kinetics of dehydrogenation under different working conditions

Perejon, A; Sanchez-Jimenez, PE; Criado, JM; Perez-Maqueda, LA

A new approach to the kinetics of magnesium hydride dehydrogenation is considered. A model able to predict the dehydrogenation under different experimental conditions has been proposed. A new combined kinetic analysis method, which considers the thermodynamic of the process according to the microreversibility principle, has been used for performing the kinetic analysis of data obtained under different thermal schedules at hydrogen pressures ranging from high vacuum up to 20 bar. 
The kinetic analysis shows that the dehydrogenation mechanism of magnesium hydride depends on the experimental conditions. Thus, the reaction follows a first order kinetics, equivalent to an Avarmi-Erofeev kinetic model with an Avrami coefficient equal to 1, when carried out under high vacuum, while a mechanism of tridimensional growth of nuclei previously formed (A3) is followed under hydrogen pressure. An explanation of the change of mechanism is given. It has been shown that the activation energy is closed to the Mg-H bond breaking energy independently of the hydrogen pressure surrounding the sample, which suggests that the breaking of this bond would be the rate limiting step of the process. The reliability of the calculated kinetic parameters is tested by comparing simulated and experimental curves.

Journal of Alloys and Compounds, 681 (2016) 571-579 | DOI: 10.1016/j.jallcom.2016.04.191

Au/CeO2 Catalysts: Structure and CO Oxidation Activity

Centeno, MA; Reina, TR; Ivanova, S; Laguna, OH; Odriozola, JA

In this comprehensive review, the main aspects of using Au/CeO2 catalysts in oxidation reactions are considered. The influence of the preparation methods and synthetic parameters, as well as the characteristics of the ceria support (presence of doping cations, oxygen vacancies concentration, surface area, redox properties, etc.) in the dispersion and chemical state of gold are revised. The proposed review provides a detailed analysis of the literature data concerning the state of the art and the applications of gold–ceria systems in oxidation reactions.

Catalysts, 6 (2016) 158 | DOI: 10.3390/catal6100158

Nickel catalyst with outstanding activity in the DRM reaction prepared by high temperature calcination treatment

Smolakova, L; Kout, M; Capek, L; Rodriguez-Gomez, A; Gonzalez-Delacruz, VM; Hromadko, L; Caballero, A

The catalytic performance of some Ni-Ce/Al2O3 catalytic systems (11 wt.% Ni and 3 wt.% Ce) were checked after being submitted to different calcination and reduction treatments. It was found that, the reduced Ni-Ce/Al2O3 catalysts were more active and stable in the dry reforming reaction of methane than thecorresponding not-reduced catalysts. This high activity was initially connected with the smaller size of pre-reduced Ni species, which at the same time leads on to the formation of filamentous carbon. The best overall performance was obtained for the reduced catalyst after being calcined at 1000 degrees C. This catalyst presents a very high stability, a low level of carbon formation, maintaining the nickel particle size constant during reaction. Surprisingly, although its reduction degree is only 12% at 750 degrees C, its catalytic activity is similar to the full reduced catalysts. So, the small number of reduced metallic particles of this catalyst shows a very high activity, much higher than the other catalysts.

International Journal of Hydrogen Energy, 41 (2016) 8459-8469 | DOI: 10.1016/j.ijhydene.2016.03.161

Metallization of ceramic substrates by laser induced decomposition of coordination complexes

Rico, V; Lopez-Gascon, C; Espinos, JP; Lahoz, R; Laguna, M; Gonzalez-Elipe, AR; de la Fuente, GF

This work describes an in-situ Nd:YAG laser-assisted coating method to modify industrial glazed ceramic surfaces. The method makes use of a Cu polymer coordination complex, transformed via 1064 nm continuos wave (cw) laser irradiation, into a lustre-type glassy coating covering the ceramic substrate. The obtained coatings, with typical thicknesses ranging between 4 and 14 μm, become integrated onto the ceramic glaze via a sharp interface, as found by SEM observation. Diffuse Reflectance UV-vis spectroscopy shows that the lustre effect arises from surface plasmon resonant effects associated to the formation of nanometric size Cu particles dispersed throughout the glaze coating. This was confirmed by XPS analysis and other techniques showing that the laser decomposition treatment induces the redox transformation of the Cu (II) complexes, present in the original precursor, into reduced Cu (0) nanoparticles.

Journal of the European Ceramic Society, 36 ( | DOI: 10.1016/j.jeurceramsoc.2016.04.016

Flue gas adsorption by single-wall carbon nanotubes: A Monte Carlo study

Romero-Hermida, MI; Romero-Enrique, JM; Morales-Florez, V; Esquivias, L

Adsorption of flue gases by single-wall carbon nanotubes (SWCNT) has been studied by means ofMonte Carlo simulations. The flue gas is modeled as a ternary mixture of N2, CO2, and O2, emulating realistic compositions of the emissions from power plants. The adsorbed flue gas is in equilibrium with a bulk gas characterized by temperature T, pressure p, and mixture composition. We have considered different SWCNTs with different chiralities and diameters in a range between 7 and 20 Å. Our results show that the CO2 adsorption properties depend mainly on the bulk flue gas thermodynamic conditions and the SWCNT diameter. Narrow SWCNTs with diameter around 7 Å show high CO2 adsorptioncapacity and selectivity, but they decrease abruptly as the SWCNT diameter is increased. For wideSWCNT, CO2 adsorption capacity and selectivity, much smaller in value than for the narrow case, decrease mildly with the SWCNT diameter. In the intermediate range of SWCNT diameters, the CO2adsorption properties may show a peculiar behavior, which depend strongly on the bulk flue gas conditions. Thus, for high bulk CO2 concentrations and low temperatures, the CO2 adsorption capacity remains high in a wide range of SWCNT diameters, although the corresponding selectivity is moderate. We correlate these findings with the microscopic structure of the adsorbed gas inside the SWCNTs.

Journal of Chemical Physics, 145 (2016) | DOI: 10.1063/1.4961023

A novel 3D absorption correction method for quantitative EDX-STEM tomography

Burdet, P; Saghi, Z; Filippin, AN; Borras, A; Midgley, PA

This paper presents a novel 3D method to correct for absorption in energy dispersive X-ray (EDX) microanalysis of heterogeneous samples of unknown structure and composition. By using STEM-based tomography coupled with EDX, an initial 3D reconstruction is used to extract the location of generated X-rays as well as the X-ray path through the sample to the surface. The absorption correction needed to retrieve the generated X-ray intensity is then calculated voxel-by-voxel estimating the different compositions encountered by the X-ray. The method is applied to a core/shell nanowire containing carbon and oxygen, two elements generating highly absorbed low energy X-rays. Absorption is shown to cause major reconstruction artefacts, in the form of an incomplete recovery of the oxide and an erroneous presence of carbon in the shell. By applying the correction method, these artefacts are greatly reduced. The accuracy of the method is assessed using reference X-ray lines with low absorption.

Ultramicroscopy, 160 (2016) 118-129 | DOI: 10.1016/j.ultramic.2015.09.012

Luminescent Rare-earth-based Nanoparticles: A Summarized Overview of their Synthesis, Functionalization, and Applications

Escudero, A; Carrillo-Carrion, C; Zyuzin, MV; Parak, WJ

Rare-earth-based nanoparticles are currently attracting wide research interest in material science, physics, chemistry, medicine, and biology due to their optical properties, their stability, and novel applications. We present in this review a summarized overview of the general and recent developments in their synthesis and functionalization. Their luminescent properties are also discussed, including the latest advances in the enhancement of their emission luminescence. Some of their more relevant and novel biomedical, analytical, and optoelectronic applications are also commented on.

Topics in current chemistry, 374 (2016) Article number 48 | DOI: 10.1007/s41061-016-0049-8

High-Temperature Deformation Mechanisms in Monolithic 3YTZP and 3YTZP Containing Single-Walled Carbon Nanotubes

Castillo-Rodriguez, M; Munoz, A; Dominguez-Rodriguez, A

Monolithic 3YTZP and 3YTZP containing 2.5 vol% of single-walled carbon nanotubes (SWCNT) were fabricated by Spark Plasma Sintering (SPS) at 1250 degrees C. Microstructural characterization of the as-fabricated 3YTZP/SWCNTs composite shows a homogeneous CNTs dispersion throughout the ceramic matrix. The specimens have been crept at temperatures between 1100 degrees C and 1200 degrees C in order to investigate the influence of the SWCNTs addition on high-temperature deformation mechanisms in zirconia. Slightly higher stress exponent values are found for 3YTZP/SWCNTs nanocomposites (n similar to 2.5) compared to monolithic 3YTZP (n similar to 2.0). However, the activation energy in 3YTZP (Q=715 +/- 60kJ/mol) experiences a reduction of about 25% by the addition of 2.5vol% of SWCNTs (Q=540 +/- 40kJ/mol). Scanning electron microscopy studies indicate that there is no microstructural evolution in crept specimens, and Raman spectroscopy measurements show that SWCNTs preserved their integrity during the creep tests. All these results seem to indicate that the high-temperature deformation mechanism is grain-boundary sliding (GBS) accommodated by grain-boundary diffusion, which is influenced by yttrium segregation and the presence of SWCNTs at the grain boundary.

Journal of The American Ceramic Society, 99 (2016) 286-292 | DOI: 10.1111/jace.13974

Nanostructured Ti thin films by magnetron sputtering at oblique angles

Alvarez, R; Garcia-Martin, JM; Garcia-Valenzuela, A; Macias-Montero, M; Ferrer, FJ; Santiso, J; Rico, V; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A

The growth of Ti thin films by the magnetron sputtering technique at oblique angles and at room temperature is analysed from both experimental and theoretical points of view. Unlike other materials deposited in similar conditions, the nanostructure development of the Ti layers exhibits an anomalous behaviour when varying both the angle of incidence of the deposition flux and the deposition pressure. At low pressures, a sharp transition from compact to isolated, vertically aligned, nanocolumns is obtained when the angle of incidence surpasses a critical threshold. Remarkably, this transition also occurs when solely increasing the deposition pressure under certain conditions. By the characterization of the Ti layers, the realization of fundamental experiments and the use of a simple growth model, we demonstrate that surface mobilization processes associated to a highly directed momentum distribution and the relatively high kinetic energy of sputtered atoms are responsible for this behaviour.

Journal of Physics D-Applied Physics, 49 (2016) 045303 | DOI: 10.1088/0022-3727/49/4/045303

Nanoindentation and scratch resistance of multilayered TiO2-SiO2 coatings with different nanocolumnar structures deposited by PV-OAD

Roa, JJ; Rico, V; Oliva-Ramirez, M; Gonzalez-Elipe, AR; Jimenez-Pique, E

This paper presents a study of the mechanical properties and an evaluation of damage mechanisms of nanocolumnar TiO2-SiO2 multilayer coatings prepared by physical vapour oblique angle deposition at different configurations (slanted, zigzag or chiral) and two zenithal evaporation angles (70 degrees or 85 degrees). The characterization at micro-and nanometric length scales of the mechanical properties of the multilayers has been carried out by nanoindentation and nanoscratch tests, while the morphological evaluation of the surface and sub-surface damages produced with a sharp indenter and the adhesive and/or cohesive failures between coating and substrate have been investigated by field emission scanning electron microscopy and focused ion beam, respectively. The obtained results have shown that the main processing parameters controlling the mechanical response of the different multilayers is the zenithal angle of deposition and the number of layers in the multilayer stack, while the coating architecture had only a minor effect on the mechanical response. This analysis also revealed a higher resistance to scratch testing and a brittle failure behaviour for the low zenithal angle coatings as compared with the high angle ones.

Journal of Physics D-Applied Physics, 49 (2016) 13 | DOI: 10.1088/0022-3727/49/13/135104

Biodegradable polyester films from renewable aleuritic acid: surface modifications induced by melt-polycondensation in air

Benitez, JJ; Heredia-Guerrero, JA; de Vargas-Parody, MI; Cruz-Carrillo, MA; Morales-Florez, V; de la Rosa-Fox, N; Heredia, A

Good water barrier properties and biocompatibility of long-chain biopolyesters like cutin and suberin have inspired the design of synthetic mimetic materials. Most of these biopolymers are made from esterified mid-chain functionalized.-long chain hydroxyacids. Aleuritic (9,10,16-trihydroxypalmitic) acid is such a polyhydroxylated fatty acid and is also the major constituent of natural lac resin, a relatively abundant and renewable resource. Insoluble and thermostable films have been prepared from aleuritic acid by melt-condensation polymerization in air without catalysts, an easy and attractive procedure for large scale production. Intended to be used as a protective coating, the barrier's performance is expected to be conditioned by physical and chemical modifications induced by oxygen on the air-exposed side. Hence, the chemical composition, texture, mechanical behavior, hydrophobicity, chemical resistance and biodegradation of the film surface have been studied by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM), nanoindentation and water contact angle (WCA). It has been demonstrated that the occurrence of side oxidation reactions conditions the surface physical and chemical properties of these polyhydroxyester films. Additionally, the addition of palmitic acid to reduce the presence of hydrophilic free hydroxyl groups was found to have a strong influence on these parameters.

Journal of Physics D-Applied Physics, 49 (2016) 175601 | DOI: 10.1088/0022-3727/49/17/175601

Thermal conductivity of porous biomorphic SiC derived from wood precursors

Gomez-Martin, A; Orihuela, MP; Ramirez-Rico, J; Chacartegui, R; Martinez-Fernandez, J

Biomorphic SiC is a SiC/Si composite made by the reactive infiltration of molten silicon by capillarity into a carbon preform from high-temperature pyrolysis of a wood porous precursor. When excess silicon is removed, a hierarchically porous SiC material with highly interconnected porosity is obtained. By choosing different wood precursors, different pore size distributions can be obtained thus tailoring the resulting properties. 

We study the thermal conductivity of porous biomorphic SiC from five different precursors, including a recycled wood product, in order to determine the microstructure-conductivity correlation. Here, we remove the excess of silicon by a high temperature capillary extraction-evaporation method. We used the laser flash technique to measure thermal diffusivity in the range similar to 300 K to 973 K, in order to determine the thermal conductivity. Thermal conductivities in the range 4-88 W/m K were achieved. The temperature, porosity, pore shape and orientation, and the treatment used to remove the remaining silicon all have a significant impact in the resulting thermal conductivity. We explain this influence in a first approximation in terms of a geometrical model.

Ceramics International, 42 (2016) 16220-16229 | DOI: 10.1016/j.ceramint.2016.07.151

Active metal brazing of silicon nitride ceramics using a Cu-based alloy and refractory metal interlayers

Fernandez, JM; Asthana, R; Singh, M; Valera, FM

Silicon nitride/silicon nitride joints with refractory metal (W and Mo) interlayers were vacuum brazed using an active braze, Cu-ABA (Cu-3Si-2Al-2.25Ti, wt%), and two interlayer arrangements in a double-lap offset configuration: Si3N4/Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si3N4 and Si3N4/Cu-ABA /Si3N4. Titanium segregated at the Si3N4/Cu-ABA and Mo/Cu-ABA interfaces, but not at the W/Cu-ABA interface. The room-temperature compression-shear strength values of Si3N4/Cu-ABA/Si3N4 and Si3N4/Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si3N4 joints were 118 +/- 24 MPa and 22 +/- 5 MPa, respectively. Elevated-temperature compression tests showed that Si3N4/Cu-ABA/Si3N4 joints had strength of 31 +/- 6 MPa at 1023 K and 17 +/- 3 MPa at 1073 K. Likewise, Si3N4/Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si3N4 joints had strength of 19 +/- 4 MPa at 1023 K and 13 +/- 3 MPa at 1073 K. Knoop microhardness profiles revealed hardness gradients across the joints. The effect of joint microstructure and test configuration on the mechanical behavior is discussed.

Ceramics International, 42 (2016) 5447-5454 | DOI: 10.1016/j.ceramint.2015.12.087

Recycling of construction and demolition waste generated by building infrastructure for the production of glassy materials

Dominguez, A; Dominguez, MI; Ivanova, S; Centeno, MA; Odriozola, JA

The use of waste materials generated by construction and demolition industry to yield valuable glassy materials, i.e. enamel for glazed ceramic tiles and cellular glasses is presented in this study. Both types of materials are produced by one-step treatment at moderate temperatures after simple waste chemical composition adjust. The enamels are manufactured directly from the initial waste powder by melting, while the expanded materials result from mixing of the vitreous material obtained after waste vitrification with an adequate foaming agent and posterior thermal treatment. Through the manuscript the feasibility of one step production of second generation profit materials is discussed in order to help achieving sustainable development and environmental protection.

Ceramics International, 42 (2016) 17217-175223 | DOI: 10.1016/j.ceramint.2016.06.157

Electrical properties of reduced 3YTZP ceramics consolidated by spark plasma sintering

Poyato, R; Macias-Delgadoa, J; Garcia-Valenzuela, A; Gonzalez-Romero, RL; Munoz, A; Dominguez-Rodriguez, A

3 mol% Yttria doped zirconia ceramics were consolidated by spark plasma sintering (SPS) at two sintering temperatures with the aim of achieving two different reduction levels. Microstructural characterization of the ceramics was performed by scanning electron microscopy (SEM). Electrical properties were investigated by means of impedance spectroscopy from room temperature up to 500 degrees C. The two ceramics presented a remarkably different electrical behavior. The effect of the extra electrons introduced by reduction during SPS on both the bulk and the grain boundary conductivity was analyzed and discussed.

Ceramics International, 42 (2016) 6713-6719 | DOI: 10.1016/j.ceramint.2016.01.040

Assessment of the performance of commonly used DFT functionals vs. MP2 in the study of IL-Water, IL-Ethanol and IL-(H2O)(3) clusters

López-López, A., Ayala, R.

We present a comparative study of the accuracy of different DFT approaches vs. MP2 for evaluating ionic liquids (ILs) + cosolvent. Namely, we are interested in [XBmim] + cosolvent (X being Cl-, BF4-, PF6-, and CH3SO3- anions and cosolvent being water or ethanol) and [XBmim] + (H2O)(3) clusters. In this study the B3LYP, B3LYP-D3, M06, M06-2X and M06-HF functionals with Pople and Dunning basis sets are considered. We find that the influence of the basis sets is a factor to take into consideration. As already seen for weakly bonded systems when the basis set quality is low the uncorrected counterpoise (unCP) or averaging counterpoise (averCP) energies must be used due to cancellation errors. Besides, the inclusion of extra diffuse functions and polarization is also required specially in the case of ILs interacting with water clusters. The B3LYP functional does not reproduce either the structure or the interaction energies for ILs + H2O and ILs + EtOH aggregates, the energetic discrepancies being more significant than the structural ones. Among the dispersive corrected functionals, M06-2X results resemble to a great extent the reference data when the unCP interaction energies are considered for both water and ethanol. In turn, M06 and B3LYP-D3 functionals are the best option for ILs containing polar and non-polar anions, respectively, whether the averCP interactions energies are taking into consideration. From the structural point of view, B3LYP and M06 functionals describe more open structures whereas B3LYP-D3, M06-2X and M06-HF structures resemble quite well MP2 results. When the number of water molecules increases the H bonding motif gains importance and the effect depends on the underlying functional. Only M06-2X and M06-HF behaviour is similar to that observed for one water molecule. This is important because to describe ILs-cosolvent solutions is not only necessary to take into account the ILs-cosolvent interactions but also the cosolvent-cosolvent ones in the ensemble of the system.

Journal of Molecular Liquids, 220 (2016) | DOI: 10.1016/j.molliq.2016.05.037

Stoichiometric Control of SiOx Thin Films Grown by Reactive Magnetron Sputtering at Oblique Angles

Garcia-Valenzuela, A; Alvarez, R; Lopez-Santos, C; Ferrer, FJ; Rico, V; Guillen, E; Alcon-Camas, M; Escobar-Galindo, R; Gonzalez-Elipe, AR; Palmero, A

The deposition of SiOx (x <= 2) compound thin films by the reactive magnetron sputtering technique at oblique angles is studied from both theoretical and experimental points of view. A simple mathematical formula that links the film stoichiometry and the deposition conditions is deduced. Numerous experiments have been carried out to test this formula at different deposition pressures and oblique angle geometries obtaining a fairly good agreement in all studied conditions. It is found that, at low deposition pressures, the proportion of oxygen with respect to silicon in the film increases a factor of similar to 5 when solely tilting the film substrate with respect to the target, whereas at high pressures the film stoichiometry depends very weakly on the tilt angle. This behavior is explained by considering the fundamental processes mediating the growth of the film by this technique.

Plasma Processes and Polymers, 13 (2016) 1242-1248 | DOI: 10.1002/ppap.201600077

Highly Porous ZnO Thin Films and 1D Nanostructures by Remote Plasma Processing of Zn-Phthalocyanine

Alcaire, M; Filippin, AN; Macias-Montero, M; Sanchez-Valencia, JR; Rojas, TC; Mora-Boza, A; Lopez-Santos, C; Espinos, JP; Barranco, A; Borras, A

In this paper the fabrication of highly porous 1D nanostructures by a vacuum and plasma etching combined protocol is presented. Zn-phthalocyanine (ZnPc) is utilized as a solid precursor to form the ZnO. First the ZnPc is sublimated in low argon pressure. Depending on the substrate temperature and microstructure, polycrystalline films or single crystal ZnPc nanowires are grown. These starting materials are then subjected to a remote plasma oxidizing treatment. Experimental parameters such as substrate position, plasma power, treatment duration, and substrate temperature determine the microstructure and properties of the final ZnO nanostructures. The article gathers an in depth study of the obtained porous nanostructured films following scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), UV-Vis transmittance, and fluorescence spectroscopies.

Plasma Processes and Polymers, 13 (2016) 287-297 | DOI: 10.1002/ppap.201500133

High-Rate Deposition of Stoichiometric Compounds by Reactive Magnetron Sputtering at Oblique Angles

Rafael Alvarez, Aurelio Garcia-Valenzuela, Carmen Lopez-Santos, Francisco J. Ferrer, Victor Rico, Elena Guillen, Mercedes Alcon-Camas, Ramon Escobar-Galindo, Agustin R. Gonzalez-Elipe, Alberto Palmero

Target poisoning in reactive magnetron sputtering deposition of thin films is an undesired phenomenon, well known for causing a drastic fall of the process efficiency. We demonstrate that when this technique is operated at oblique angles, films with composition raging from pure metallic to stoichiometric compound can be grown in non-poisoned conditions, thus avoiding most of the associated drawbacks. We have employed amorphous TiOx, although the presented results can be easily extrapolated to other materials and conditions. It is found that the proposed method improves 400% the growth rate of TiO2 thin films.

Plasma Processes and Polymers, 13 (2016) 571-576 | DOI: 10.1002/ppap.201600019

Cathode and ion-luminescence of Eu:ZnO thin films prepared by reactive magnetron sputtering and plasma decomposition of non-volatile precursors

Gil-Rostra, J; Ferrer, FJ; Martin, IR; Gonzalez-Elipe, AR; Yubero, F

This paper reports the luminescent behavior of Eu:ZnO thin films prepared by an one-step procedure that combines reactive magnetron sputtering deposition of ZnO with the plasma activated decomposition of a non-volatile acetylacetonate precursor of Eu sublimated in an effusion cell. Chemical composition and microstructure of the Eu:ZnO thin films have been characterized by several methods and their photo-, cathode- and ion-luminescent properties studied as a function of Eu concentration. The high transparency and well controlled optical properties of the films have demonstrated to be ideal for the development of cathode- and ion- luminescence sensors.

Journal of Luminescence, 178 (2016) 139-146 | DOI: 10.1016/j.jlumin.2016.01.034

A new approach to the determination of the synthetic or natural origin of red pigments through spectroscopic analysis

Franquelo, ML; Perez-Rodriguez, JL

This work suggests a way of differentiation between the natural or synthetic origin of inorganic materials that were historically used in the Cultural Heritage field. An exhaustive review of different reported procedures of synthesis of pigments was conducted, as well as a review of the accompanying minerals in case of natural pigments. The natural or synthetic origin of the pigments studied in this work was performed through the characterization of the accompanying minerals, in the case of the natural pigments, or the trace elements that are present as part of synthesis by-products or washing/purifying reagents and/or reactants that have only been partly removed in the final steps of these processes. This work characterized red pigments due to their wide variety, complexity and possibility of use in different mixtures. The following pigments were studied: cinnabar-vermilion, red lead and iron pigments. Also mixtures of these pigments between them and with red lake were also studied. Natural cinnabar was accompanied by silicon oxide (opal, chalcedony or quartz), calcite, clay minerals and, sometimes, pyrite. K together with S indicated a synthetic pigment (vermilion) obtained through the wet method. Nevertheless, K has not been found in layers containing only vermilion in our samples. The presence of Sn in some cases indicated vermilion that came from the dry process. K from the synthesis always appeared in the red lead pigment. The red natural ochre was confirmed by presence of clay minerals and iron. It should be said that Ca and S, and sometimes Al and K, were usually found in Mars red pigment. The presence of Al and Ca allowed the identification of carmine lake.

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 166 (2016) 103-111 | DOI: 10.1016/j.saa.2016.04.054

Correlation between chemical and mineralogical characteristics and permeability of phyllite clays using multivariate statistical analysis

Garzon, E; Romero, E; Sanchez-Soto, PJ

Phyllite clays are applied as a layer on a surface to be waterproofed and subsequently compacted. For this purpose, phyllite clays deposits can be grouped by their chemical and mineralogical characteristics, and these characteristics can be connected with their properties, mainly permeability, in order to select those deposits with the lowest permeability values. Several deposits of phyllite clays in the provinces of Almeria and Granada (SE Spain) have been studied. The results of applying a multivariate statistical analysis (MVA) to the chemical data analysed from 52 samples determined by XRF, mineralogical analysis by XRD and permeability are reported. Permeability, a characteristic physical property of phyllite clays, was calculated using the results for experimental nitrogen gas adsorption and nitrogen adsorption-desorption permeability dependence. According to the results, permeability values differentiated two groups, i.e. group 1 and group 2, with two subgroups in the latter. The influence of chemical as well as mineralogical characteristics on the permeability values of this set of phyllite clays was demonstrated using a multiple linear regression model. Two regression equations were deduced to describe the relationship between adsorption and desorption permeability values, which support this correlation. This was an indication of the statistical significance of each chemical and mineralogical variable, as it was added to the model. The statistical tests of the residuals suggested that there was no serious autocorrelation in the residuals. 

Applied Clay Science, 129 (2016) 92-101 | DOI: 10.1016/j.clay.2016.05.008

Ceramics from clays and by-product from biodiesel production: Processing, properties and microstructural characterization

Martinez-Martinez, S; Perez-Villarejo, L; Eliche-Quesada, D; Carrasco-Hurtado, B; Sanchez-Soto, PJ; Angelopoulos, GN

The production of biodiesel generates a by-product called glycerine which contains glycerol that cannot be reintegrated into the same manufacturing process. The ceramic bricks are an interesting option to set in their structure a wide range of by-products and residues materials and composites, sometimes serving only as a reservoir for the inert residue, and other, having a positive effect on the ceramic material or process. In the present work, the incorporation of this waste in raw clays has been studied. The raw materials: clay and glycerine was characterized by XRD, XRF, CNHS analysis, higher heating value and thermal analysis and after, using conventional moulding and sintering processing methods to prepare clay-glycerine composites, the influence of the amount of waste added to clay has been evaluated. To do this, percentages of glycerine were added to the clay from 5% to 20% and evaluated by a series of technological properties such as compressive strength, absorption and suction of water, bulk density, the study of porosity generated by adsorption-desorption isotherms of N-2, thermal conductivity and finally by the compressive strength after freezing-thaw, it was considered as the maximum permissible rate of addition of glycerol 10-15% in weight, because higher additions have a strong effect on the properties of the obtained materials such as compression strength and bulk density which descending dramatically due to the large amount of porosity generated as reflected by high values of absorption and suction experiments. It was concluded that adding 5% glycerol to the ceramic paste generated plasticity in clay to achieve be moulded, with values of compressive strength of 84 MPa while gets to reduce the density apparent by almost.

Applied Clay Science, 121 (2016) 119-126 | DOI: 10.1016/j.day.2015.12.003

Effect of lime on stabilization of phyllite clays

Garzon, E; Cano, M; O'Kelly, BC; Sanchez-Soto, PJ

This paper represents a new advance in the study of engineering properties and material applications of phyllite clays. Considering their potential use as construction materials for structures subjected to low stress levels, this laboratory research investigated the stabilization and improvement in engineering properties of a Spanish phyllite clay achieved by the addition of 3, 5 and 7 wt.% lime. Geotechnical properties investigated include the consistency limits, compaction, California Bearing Ratio, swelling potential and water-permeability. The phyllite clay–lime mixtures had good compaction properties and very to extremely low permeability-coefficient values, with a semi-logarithmic correlation between increasing permeability and increasing proportion of lime additive. The addition of 3 wt.% lime was sufficient to reach the index of capacity amble specified in the Sheet of Technical General Prescriptions for Works of Roads and Bridges PG–3 (Spanish Highways Agency, 2008), significantly reducing the plasticity index value, with the compacted mixture undergoing no swelling under soakage. The required pavement thicknesses for the raw phyllite–clay material and the phyllite clay–lime mixtures are compared and discussed. Potential applications for phyllite clay–lime mixtures include for pavements/road subgrade, earth construction, building materials and for impermeabilization purposes.

Applied Clay Science, 123 (2016) 329-334 | DOI: 10.1016/j.clay.2016.01.042

On the Multicycle Activity of Natural Limestone/Dolomite for Thermochemical Energy Storage of Concentrated Solar Power

Sarrion, B; Valverde, JM; Perejon, A; Perez-Maqueda, L; Sanchez-Jimenez, PE

Cheap, efficient, and non-toxic energy storage technologies are urgently needed to handle the rapidly increasing penetration of intermittent renewable energies into the grid. This work explores the use of limestone and dolomite for energy storage in concentrated solar power (CSP) plants by means of the calcium looping (CaL) process based on the multicycle carbonation/calcination of CaO. An efficient integration of the CaL process into CSP plants involves high temperature carbonation and calcination at moderate temperatures in a close CO2 cycle for power generation. These conditions differ from those of the CaL process for CO2 capture, which lead to CaO deactivation as extensively reported in recent years. In contrast, we show that limestone- and dolomite-derived CaO give rise to a high residual conversion at CaL-CSP conditions and in short residence times, which would facilitate the development of a competitive and clean CSP technology with permanent energy storage.

Energy Technology, 4 (2016) 1013-1019 | DOI: 10.1002/ente.201600068

Confinement and surface effects on the physical properties of rhombohedral-shape hematite (alpha-Fe2O3) nanocrystals

Luna, C; Cuan-Guerra, AD; Barriga-Castro, ED; Nunez, NO; Mendoza-Resendez, R

Morphological, microstructural and vibrational properties of hematite (alpha-Fe2O3) nanocrystals with a rhombohedral shape and rounded edges, obtained by forced hydrolysis of iron(III) solutions under a fast nucleation, have been investigated in detail as a function of aging time. These studies allowed us to propose a detailed formation mechanism and revealed that these nanocrystals are composed of four {104} side facets, two {110} faces at the edges of the long diagonal of the nanocrystals and two {-441} facets as the top and bottom faces. Also, the presence of nanoscopic pores and fissures was evidenced. The vibrational bands of such nanocrystals were shifted to lower frequencies in comparison with bulk hematite ones as the nanocrystal size was reduced due to phonon confinement effects. Also, the indirect and direct transition band gaps displayed interesting dependences on the aging time arising from quantum confinementand surface effects 

Materials Research Bulletin, 80 (2016) 44-52 | DOI: 10.1016/j.materresbull.2016.03.029

In-situ Raman spectroscopy study of Ru/TiO2 catalyst in the selective methanation of CO

Martinez Tejada, LM; Munoz, A; Centeno, MA; Odriozola, JA

Raman spectroscopic technique has been used to characterize a Ru/TiO2 catalyst and to follow in situ their structural changes during the CO selective methanation reaction (S-MET). For a better comprehension of the catalytic mechanism, the in-situ Raman study of the catalysts activation (reduction) process, the isolated CO and CO2 methanation reactions and the effect of the composition of the reactive stream (H2O and CO2 presence) have been carried out. Raman spectroscopy evidences that the catalyst is composed by islands of TiO2-RuO2 solid solutions, constituting Ru-TiO2 interphases in the form of RuxTi1-xO2 rutile type solid solutions. The activation procedure with H-2 at 300 degrees C promotes the reduction of the RuO2-TiO2 islands generating Ru-o-Ti3+ centers. The spectroscopic changes are in agreement with the strong increase in chemical reactivity as increasing the carbonaceous intermediates observed. The selective methanation of CO proceeds after their adsorption on these Ru-o-Ti3+ active centers and subsequent C?O dissociation throughout the formation of CHx/CnHx/CnHxO/CHx?CO species. These intermediates are transformed into CH4 by a combination of hydrogenation reactions. The formation of carbonaceous species during the methanation of CO and CO2 suggests that the CO presence is required to promote the CO2 methanation. Similar carbonaceous species are detected when the selective CO methanation is carried out with water in the stream. However, the activation of the catalysts occurs at much lower temperatures, and the carbon oxidation is favored by the oxidative effect of water.

Journal of Raman Spectroscopy, 47 (2016) 189-197 | DOI: 10.1002/jrs.4774

Ru-Ni Catalyst in the Combined Dry-Steam Reforming of Methane: The Importance in the Metal Order Addition

Alvarez, MA; Centeno, MA; Odriozola, JA

Biogas is one of the main biomass-energy resources. Its use for syngas production with a H-2/CO ratio close to two would have huge environmental, social and economic impact in the actual energetic scenario. However, the use of dry reforming, where the two main components are transformed into syngas, does not allow the desired H-2/CO ratio. For this reason, the addition of water is proposed. The process was performed with two Ru-Ni catalysts where the metal order in the impregnation process was varied. The catalysts were prepared either by simultaneous or consecutive impregnation of the active phases and its catalytic performance in the combined dry-steam reforming of methane was tested. The catalysts were characterized by XRF, XRD, S-BET, TPR-H-2 and Raman spectroscopy. The existence of a strong Ni-Ru interaction is evidenced by Raman spectroscopy and TPR-H-2 in the sample synthesized by the simultaneous impregnation. Concerning the catalytic activity, this sample presents the highest CH4 and CO2 conversion values in the entire composition rate and the lowest amount of carbon deposits after reaction. After pulse, and reactivity tests it was concluded that the higher Ni-Ru interaction displayed by the catalyst synthesized by the simultaneous impregnation, enhances the carbon gasification.

Topics in Catalysis, 59 (2016) 303-313 | DOI: 10.1007/s11244-015-0426-5

Synthesis and characterization of CuInS2 nanocrystalline semiconductor prepared by high-energy milling

Dutkova, E; Sayagues, MJ; Briancin, J; Zorkovska, A; Bujnakova, Z; Kovac, J; Kovac, J; Balaz, P; Ficeriova, J

Nanocrystalline CuInS2 particles have been synthesized from copper, indium, and sulfur powders by high-energy milling in a planetary mill in an argon atmosphere. Structural characterization of the prepared nanoparticles, including phase identification, Raman spectroscopy, specific surface area measurement, and particle size analysis were performed. The optical properties were studied using UV-Vis absorption and photoluminescence (PL) spectroscopy. The production of CuInS2 (JCPDS 027-0159) particles with a crystallite size of about 17.5-23.5 nm was confirmed by X-ray diffraction. The crystal structure has a tetragonal body-centered symmetry belonging to the I-42d space group. The Raman spectra also proved the formation of pure CuInS2 nanoparticles. TEM and HRTEM measurements revealed the presence of nanoparticles of different dimensions (10-20 nm) and their tendency to form agglomerates. The nanoparticles tend to agglomerate due to their large specific surface area. The average size of the synthesized particles was determined by photon cross-correlation spectroscopy to be in the range of 330-530 nm (bimodal size distribution). The band gap of the CuInS2 particles is 2 eV which is wider than that in bulk materials. The decrease in size leads to the blue-shift of the PL spectra. Therefore, CuInS2 nanoparticles are promising candidates for optical applications, and they have high potential in solar energy conversion.

Journal of Materials Science, 51 (2016) 1978-1984 | DOI: 10.1007/s10853-015-9507-x

Stress measurement using area detectors: a theoretical and experimental comparison of different methods in ferritic steel using a portable X-ray apparatus

Ramirez-Rico, J; Lee, SY; Ling, JJ; Noyan, IC

Using area detectors for stress determination by diffraction methods in a single exposure greatly simplifies the measurement process and permits the design of portable systems without complex sample cradles or moving parts. An additional advantage is the ability to see the entire or a large fraction of the Debye ring and thus determine texture and grain size effects before analysis. The two methods most commonly used to obtain stress from a single Debye ring are the so-called cosαcos⁡αand full-ring fitting methods, which employ least-squares procedures to determine the stress from the distortion of a Debye ring by probing a set of scattering vector simultaneously. The widely applied sin2ψsin2⁡ψ method, in contrast, requires sample rotations to probe a different subset of scattering vector orientations. In this paper, we first present a description of the different methods under the same formalism and using a unified set of coordinates that are suited to area detectors normal to the incident beam, highlighting the similarities and differences between them. We further characterize these methods by means of in situ measurements in carbon steel tube samples, using a portable detector in reflection geometry. We show that, in the absence of plastic flow, the different methods yield basically the same results and are equivalent. An analysis of possible sources of errors and their impact in the final stress values is also presented.

Journal of Materials Science, 51 (2016) 5343-5355 | DOI: 10.1007/s10853-016-9837-3

Sliding wear resistance of porous biomorphic sic ceramics

Lopez-Robledo, MJ; Gomez-Martin, A; Ramirez-Rico, J; Martinez-Fernandez, J

Porous biomorphic SiC ceramics were fabricated from four different wood precursors, three natural woods and one recycled wood product, by reactive infiltration of molten silicon into a carbon preform obtained from wood pyrolysis. Sliding wear resistance when sliding against a Si3N4 ball in air was studied. Tribological experiments were done with a pin-on-disk apparatus, under normal loads of 1 and 2 N, at a sliding velocity of 100 mm/s. The wear properties and the volume fraction of porosity were correlated. A commercial sintered SiC ceramic was also tested for comparison. The measured values of friction coefficient were in the range reported in literature for monolithic SiC ceramics under similar dry contact conditions. Two concurrent wear mechanisms are taking place: abrasion from the SiC debris and soft ploughing. The presence of an oxide tribolayer was assessed using energy dispersive X-ray analysis. Wear rates were found to scale with the composite porosity.

International Journal of Refractory Metals and Hard Materials, 59 (2016) 26-31 | DOI: 10.1016/j.ijrmhm.2016.05.004

Mechanochemically synthesized nanocrystalline ternary CuInSe2 chalcogenide semiconductor

Dutkova, E; Sayagues, MJ; Kovac, J; Kovac, J; Bujnakova, Z; Briancin, J; Zorkovska, A; Balaz, P; Ficeriova, J

The synthesis of nanocrystalline ternary CuInSe2 particles prepared by high-energy milling in a planetary mill in an argon atmosphere from copper, indium and selenium was reported. CuInSe2 particles crystallize in the tetragonal structure with the crystallite size of about 30.5 nm. The Raman spectrum of CuInSe2 nanoparticles shows a strong peak at 176 cm−1 corresponds to the A1 phonon mode of tetragonal CuInSe2 chalcopyrite. HRTEM measurements also revealed the presence of nanocrystals with the size of 10–20 nm with the tendency to form agglomerates. The optical absorption study shows that nanoparticles have direct optical band gap energy of 1.8 eV. The quantum size effect of the particles was confirmed also by PL measurement.

Materials Letters, 173 (2016) 182-186 | DOI: 10.1016/j.matlet.2016.03.051

Enhancement of dielectric barrier layer properties by sol-gel and PECVD stacks

Lopez-Lopez, C; Menendez, MF; Menendez, LA; Menendez, A; Sanchez, P; Alba, MD; Sanchez-Cortezon, E; Delgado-Sanchez, JM

Thin-film PV modules grown on flexible, light weight, thermally stable and low cost substrates such as stainless steel foil, are an attractive product for solar market applications. When metal foils are used as substrate, it is essential to deposit a dielectric barrier layer to isolate electrically and chemically the thin-film solar cells from the substrate. In this work, SiOx stacks deposited on ‘rough’ stainless steel by a combination of a new sol-gel formulation and a Plasma Enhanced Chemical Vapor Deposition (PECVD) deposition step are reported as a suitable dielectric barrier layer candidate. Using these SiOx multilayers, a smooth and homogeneous film was achieved. X-ray diffraction (XRD) analysis showed that back contact of the solar cell (based on Molybdenum) is not affected by the presence of the barrier layer. Moreover, according to X-ray photoelectron spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS) measurements, this approach led to excellent barrier layer properties against the diffusion of impurities from the stainless steel. A complete electrical characterization of these dielectric barrier layers was also carried out showing good electrical insulation.

Surface and Coatings Technology, 305 (2016) 36-40 | DOI: 10.1016/j.surfcoat.2016.07.085

Structure, electrochemical properties and functionalization of amorphous CN films deposited by femtosecond pulsed laser ablation

Maddi, C; Bourquard, F; Tite, T; Loir, AS; Donnet, C; Garrelie, F; Barnier, V; Wolski, K; Fortgang, P; Zehani, N; Braiek, M; Lagarde, F; Chaix, C; Jaffrezic-Renault, N; Rojas, TC; Sanchez-Lopez, JC

Amorphous carbon nitride (a-C:N) material has attracted much attention in research and development Recently, it has become a more promising electrode material than conventional carbon based electrodes in electrochemical and biosensor applications. Nitrogen containing amorphous carbon (a-C:N) thin films have been synthesized by femtosecond pulsed laser deposition (fs-PLD) coupled with plasma assistance through Direct Current (DC) bias power supply. During the deposition process, various nitrogen pressures (0 to 10 Pa) and DC bias (0 to -350 V) were used in order to explore a wide range of nitrogen content into the films. The structure and chemical composition of the films have been studied by using Raman spectroscopy, electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM). Increasing the nitrogen pressure or adding a DC bias induced an increase of the N content, up to 21 at%. Nitrogen content increase induces a higher sp(2) character of the film. However DC bias has been found to increase the film structural disorder, which was detrimental to the electrochemical properties. Indeed the electrochemical measurements, investigated by cyclic voltammetry (CV), demonstrated that a-C:N film with moderate nitrogen content (10 at.%) exhibited the best behavior, in terms of reversibility and electron transfer kinetics. Electrochemical grafting from diazonium salts was successfully achieved on this film, with a surface coverage of covalently bonded molecules close to the dense packed monolayer of ferrocene molecules. Such a film may be a promising electrode material in electrochemical detection of electroactive pollutants on bare film, and of biopathogen molecules after surface grafting of the specific affinity receptor. 

Diamond and Related Materials,65 (2016) | DOI: 10.1016/j.diamond.2016.01.001

Effect of temperature variations on equilibrium distances in levitating parallel dielectric plates interacting through Casimir forces

Esteso, V; Carretero-Palacios, S; Miguez, H

We study at thermal equilibrium the effect of temperature deviations around room temperature on the equilibrium distance (d(eq)) at which thin films made of Teflon, silica, or polystyrene immersed in glycerol levitate over a silicon substrate due to the balance of Casimir, gravity, and buoyancy forces. We find that the equilibrium nature (stable or unstable) of d(eq) is preserved under temperature changes, and provide simple rules to predict whether the new equilibrium position will occur closer to or further from the substrate at the new temperature. These rules depend on the static permittivities of all materials comprised in the system (epsilon((m))(0)) and the equilibrium nature of d(eq). Our designed dielectric configuration is excellent for experimental observation of thermal effects on the Casimir force indirectly detected through the tunable equilibrium distances (with slab thickness and material properties) in levitation mode.

Journal of Applied Physics, 119 (2016) 144301 | DOI: 10.1063/1.4945428

Quantitative analysis of Ni 2p photoemission in NiO and Ni diluted in a SiO2 matrix

Pauly, N; Yubero, F; Garcia-Garcia, FJ; Tougaard, S

In X-ray excited photoelectron emission (XPS), besides the initial excitation process, the shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface (including bulk and surface effects) and to intrinsic excitations due to the sudden creation of the static core hole. To make an accurate quantitative interpretation of features observed in XPS, these effects must be included in the theoretical description of the emitted photoelectron spectra. It was previously shown [N. Pauly, S. Tougaard, F. Yubero, Surf. Sci. 620 (2014) 17] that these three effects can be calculated by means of the QUEELS-XPS software (Quantitative analysis of Electron Energy Losses at Surfaces for XPS) in terms of effective energy-differential inelastic electron scattering cross-sections. The only input needed to calculate these cross-sections is the energy loss function of the media which is determined from analysis of Reflection Electron Energy Loss Spectra (REELS). The full XPS spectrum is then modeled by convoluting this energy loss cross-section with the primary excitation spectrum that accounts for all effects which are part of the initial photo-excitation process, i.e. lifetime broadening, spin-orbit coupling, and multiplet splitting. In this paper we apply the previously presented procedure to the study of Ni 2p photoemission in NiO and Ni diluted in a SiO2 matrix (Ni:SiO2), samples being prepared by reactive magnetron sputtering at room temperature. We observe a significant difference between the corresponding Ni 2p primary excitation spectra. The procedure allows quantifying the relative intensity of the c3d(9)L, c3d(10)L(2), and c3d(8) final states contributing to the Ni 2p photoemission spectra of the Ni2+ species in the oxide matrices. Especially, the intensity ratio in NiO between the non-local and local contributions to the 3d(9)L configuration is determined to be 2.5. Moreover the relative intensity ratio of the c3d(9)L/c3d(10)L(2)/c3d(8) configurations is found to be 1.0/0.83/0.11 for both the NiO and Ni:SiO2 samples. 

Surface Science, 644 (2016) 46-52 | DOI: 10.1016/j.susc.2015.09.012

The role of carbon overlayers on Pt-based catalysts for H-2-cleanup by CO-PROX

Romero-Sarria, F; Garcia-Dali, S; Palma, S; Jimenez-Barrera, EM; Oliviero, L; Bazin, P; Odriozola, JA

In this work, we analyze the effect of the activation method on the catalytic activity of Pt-based catalysts supported on alumina in the PROX reaction. For this, model Pt/Al2O3 catalysts with variable amounts of acetic acid were prepared and their thermal evolution studied by FTIR spectroscopy. From the analysis of the nature of the platinum surface upon acetic acid decomposition and the gas phase evolved products, we have demonstrated the formation of partially hydrogenated carbon overlayers that tailor the activity of Pt-based catalysts in the PROX reaction. 

Surface Science, 648 (2016) 84-91 | DOI: 10.1016/j.susc.2015.12.017

Liquid-phase oxidation with hydrogen peroxide of benzyl alcohol and xylenes on Ca-10(PO4)(6)(OH)(2) - CaWO4

Dominguez, MI; Cojocaru, B; Tudorache, M; Odriozola, JA; Centeno, MA; Parvulescu, VI

A W-containing apatite (W/HAp) catalyst was prepared following a hydrothermal synthesis route and served as a model catalyst. Crystallographic analysis indicated that the resulting material contained hydroxyapatite, Ca10-3xWx(PO4)(6)(OH)(2), W-hydroxyapatite, calcium tungstate, CaWO4, and tricalcium phosphate, Ca-3(PO4)(2). The catalyst was investigated in liquid phase oxidation of benzyl alcohol and xylenes using hydrogen peroxide as an oxidant. For comparison, commercial calcium phosphate, hydroxyapatite and CaWO4 were tested in the same reaction. Calcium phosphate and hydroxyapatite appeared as inactive and decomposed hydrogen peroxide non-selectively. A moderate activity but low hydrogen peroxide efficiency was observed for the CaWO4 phase. In contrast, the W/HAp catalyst showed a reasonable activity and a better hydrogen peroxide efficiency in the oxidation of benzyl alcohol and xylenes. This new W/HAp catalyst showed, after six cycles, losses of the activity below 15% compared to the fresh catalyst with no effect on the selectivity. It is noteworthy that ICP-OES analyses showed no tungsten leaching that is the main advantage of this catalyst. 

Comptes Rendus Chimie, 19 (2016) 1156-1165 | DOI: 10.1016/j.crci.2015.10.013

Deposition of silica protected luminescent layers of Eu:GdVO4 nanoparticles assisted by atmospheric pressure plasma jet

Moretti, E; Pizzol, G; Fantin, M; Enrichi, F; Scopece, P; Nunez, NO; Ocana, M; Benedetti, A; Polizzi, S

Eu:GdVO4 nanophosphors with an average size of 60 nm, synthesized by a facile solvothermal method, were deposited on monocrystalline silicon wafers by a spray-coating technique with artworks anti-counterfeiting applications in mind. Atmospheric pressure plasma jet (APPJ) was used to deposit a silica-based layer on top of the nanometric luminescent layer, in order to improve its adhesion to the substrate and to protect it from the environment. The nanophosphors were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Coating composition was investigated by Fourier transform infrared spectroscopy (FT-IR) and its morphology was characterized by scanning electron microscopy (FEG-SEM). The film thickness was evaluated by means of ellipsometry and adhesion was estimated by a peeling test. Luminescent properties of the nanophosphors deposited and fixed on silicon wafers were also measured. The whole layer resulted well-adhered to the silicon substrate, transparent and undetectable in the presence of visible light, but easily activated by UV light source.

Thin Solid Films, 598 (2016) 88-94 | DOI: 10.1016/j.tsf.2015.11.061

Disorder-order phase transformation in a fluorite-related oxide thin film: In-situ X-ray diffraction and modelling of the residual stress effects

Gaboriaud, RJ; Paumier, F; Lacroix, B

This work is focused on the transformation of the disordered fluorite cubic-F phase to the ordered cubic-C bixbyite phase, induced by isothermal annealing as a function of the residual stresses resulting from different concentrations of microstructural defects in the yttrium oxide, Y2O3. 

This transformation was studied using in-situ X-ray diffraction and was modelled using Kolmogorov-Johnson-Mehl-Avrami (KJMA) analysis. The degree of the disorder of the oxygen network was associated with the residual stress, which was a key parameter for the stability and the kinetics of the transition of the different phases that were present in the thin oxide film. When the degree of disorder/residual stress level is high, this transition, which occurs at a rather low temperature (300 degrees C), is interpreted as a transformation of phases that occurs by a complete recrystallization via the nucleation and growth of a new cubic-C structure. Using the KJMA model, we determined the activation energy of the transformation process, which indicates that this transition occurs via a one-dimensional diffusion process. Thus, we present the analysis and modelling of the stress state. When the disorder/residual stress level was low, a transition to the quasi-perfect ordered cubic-C structure of the yttrium oxide appeared at a rather high temperature (800 degrees C), which is interpreted as a classic recovery mechanism of the cubic-C structure.

Thin Solid Films, 601 (2016) 84-88 | DOI: 10.1016/j.tsf.2015.08.030

Surface functionalizing of a lipid nanosystem to promote brain targeting: step-by-step design and physico-chemical characterization

Cozar-Bernal, MJ; Garcia-Esteban, E; Sanchez-Soto, PJ; Rabasco, AM; Gonzalez-Rodriguez, ML

The use of lipid nanosystems as drug delivery to the central nervous system may be advantageous over the current strategies. The aim of this study was to develop and characterize functionalized liposomes for treatment of brain diseases. The covalent method of coupling IgG to liposomes via the derivatized lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-[4-(p-maleimidophenyl)butyramide](MPB-PE) was investigated. Optimized coupling conditions are shown to result in the efficient conjugation of IgG to liposomes containing low concentrations of MPB-PE (3/1 SH:IgG). The qualitative analysis has shown that after the extrusion process, more homogeneous populations of vesicles have been obtained with a nanometric size suitable to be effective to further anchor the protein. Negative values of zeta potential demonstrate that they are stable systems. Lyophilization was used to maintain the stability of the formulation. These very interesting results encourage further investigations to formulate peptide- and protein-loaded immunoliposomes, making targeting of liposomes as an attractive approach for brain drug delivery.

Pharmaceutical Development and Technology, 21 (2016) 823-831 | DOI: 10.3109/10837450.2015.1063651

Surface functionalization of a lipid nanosystem to promote brain targeting: step-by-step design and physico-chemical characterization

Cózar-Bernal, MJ; García-Esteban, E; Sánchez-Soto, PJ; Rabasco, AM; González-Rodríguez, ML

The use of lipid nanosystems as drug delivery to the central nervous system may be advantageous over the current strategies. The aim of this study was to develop and characterize functionalized liposomes for treatment of brain diseases. The covalent method of coupling IgG to liposomes via the derivatized lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-[4-(p-maleimidophenyl)butyramide](MPB-PE) was investigated. Optimized coupling conditions are shown to result in the efficient conjugation of IgG to liposomes containing low concentrations of MPB-PE (3/1 SH:IgG). The qualitative analysis has shown that after the extrusion process, more homogeneous populations of vesicles have been obtained with a nanometric size suitable to be effective to further anchor the protein. Negative values of zeta potential demonstrate that they are stable systems. Lyophilization was used to maintain the stability of the formulation. These very interesting results encourage further investigations to formulate peptide- and protein-loaded immunoliposomes, making targeting of liposomes as an attractive approach for brain drug delivery.

Pharmaceutical Development and Technology, 21 (7) (2016) 823-831 | DOI: 10.3109/10837450.2015.1063651

An innovative combination of non-invasive UV–Visible-FORS, XRD and XRF techniques to study Roman wall paintings from Seville, Spain

Garofano, Isabel; Luis Perez-Rodriguez, Jose; Dolores Robador, Maria; Duran, Adrian

This study attempts to establish the advantages and limitations of the combined use of portable UV–Vis-FORS and XRF-XRD portable equipment for the non-invasive characterisation of pigments from Roman wall paintings from Seville, Spain, dated to the first and second century AD. XRD revealed the presence of calcite, dolomite and aragonite, indicating the colour white. Egyptian blue was identified using FORS and XRF, and additional information was obtained with XRD. For the colour green, FORS and mainly FTIR and colorimetry enabled the distinction between glauconite and celadonite, although other techniques were necessary to classify all components of the green areas by determining the presence of cuprorivaite, chlorite and chromium. For the colours yellow and red, the presence of goethite, yellow ochre, cinnabar and haematite was confirmed using FORS and XRF in some cases; the results were corroborated by XRD. Chromatic characterisation and the values of inflection points of FORS spectra enabled a better differentiation between reddish colours (orange, brown, purple and pink). The XRD and XRF techniques revealed that violet was created by mixing red haematite and Egyptian blue and slight variations in FORS spectra confirmed this.

Journal of Cultural Heritage, 22 (2016) 1028-1039 | DOI: 10.1016/j.culher.2016.07.002

Effects of electronic and nuclear stopping power on disorder induced in GaN under swift heavy ion irradiation

Moisy, F; Sall, M; Grygiel, C; Balanzat, E; Boisserie, M; Lacroix, B; Simon, P; Monnet, I

Wurtzite GaN epilayers, grown on the c-plane of sapphire substrate, have been irradiated with swift heavy ions at different energies and fluences, and thereafter studied by Raman scattering spectroscopy, UV–visible spectroscopy and transmission electron microscopy. Raman spectra show strong structural modifications in the GaN layer. Indeed, in addition to the broadening of the allowed modes, a large continuum and three new modes at approximately 200 cm−1, 300 cm−1 and 670 cm−1 appear after irradiation attributed to disorder-activated Raman scattering. In this case, spectra are driven by the phonon density of states of the material due to the loss of translation symmetry of the lattice induced by defects. It was shown qualitatively that both electronic excitations and elastic collisions play an important role in the disorder induced by irradiation. UV–visible spectra reveal an absorption band at 2.8 eV which is linked to the new mode at 300 cm−1observed in irradiated Raman spectra and comes from Ga-vacancies. These color centers are produced by elastic collisions (without any visible effect of electronic excitations).

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 381 (2016) 39-44 | DOI: 10.1016/j.nimb.2016.05.024

The Structure and Chemical Composition of Wall Paintings From Islamic and Christian Times in the Seville Alcazar

Robador, MD; De Viguerie, L; Perez-Rodriguez, JL; Rousseliere, H; Walter, P; Castaing, J

Wall paintings from the Islamic epoch (10th to 12th centuries) and the Christian monarchy (14th to 16th centuries) have been recovered in discarded materials and on walls after reconstruction works in the Seville Alcazar. These paintings have spent centuries underground or under a plaster coat. Portable X-ray fluorescence (XRF) and combined XRF/X-ray diffraction (XRD) were employed in situ, as well as scanning electron microscopy (SEM-EDX), grazing angle incidence XRD and micro-Raman spectroscopy, on cross-section samples to fully characterize the materials in the wall paintings. Using these methods, the fresco technique was demonstrated, and many kinds of pigments were identified in accordance with the various periods of the history of the Alcazar, thus assessing the authenticity of all the wall paintings studied here.

Archaeometry, 58 (2016) 255-270 | DOI: 10.1111/arcm.12218

Fabrication and characterization of CeO2 pellets for simulation of nuclear fuel

Garcia-Ostos, C; Rodriguez-Ortiz, JA; Arevalo, C; Cobos, J; Gotor, FJ; Torres, Y

Cerium Oxide, CeO2, has been shown as a surrogate material to understand irradiated Mixed Oxide (MOX) based matrix fuel for nuclear power plants due to its similar structure, chemical and mechanical properties. In this work, CeO2 pellets with controlled porosity have been developed through conventional powder-metallurgy process. Influence of the main processing parameters (binder content, compaction pressure, sintering temperature and sintering time) on porosity and volumetric contraction values has been studied. Microstructure and physical properties of sintered compacts have also been characterized through several techniques. Mechanical properties such as dynamic Young's modulus, hardness and fracture toughness have been determined and connected to powder-metallurgy parameters. Simulation of nuclear fuel after reactor utilization with radial gradient porosity is proposed.

Nuclear Engineering and Design, 298 (2016) 160-167 | DOI: 10.1016/j.nucengdes.2015.12.026

Microstructure, elastic, and inelastic properties of biomorphic carbons carbonized using a Fe-containing catalyst

Orlova, TS; Kardashev, BK; Smirnov, BI; Gutierrez-Pardo, A; Ramirez-Rico, J

The microstructure and amplitude dependences of the Young’s modulus E and internal friction (logarithmic decrement δ), and microplastic properties of biocarbon matrices BE-C(Fe) obtained by beech tree carbonization at temperatures Tcarb = 850–1600°C in the presence of an iron-containing catalyst are studied. By X-ray diffraction analysis and transmission electron microscopy, it is shown that the use of Fe-catalyst during carbonization with Tcarb ≥ 1000°C leads to the appearance of a bulk graphite phase in the form of nanoscale bulk graphite inclusions in a quasi-amorphous matrix, whose volume fraction and size increase with Tcarb. The correlation of the obtained dependences E(Тcarb) and δ(Tcarb) with microstructure evolution with increasing Тcarb is revealed. It is found that E is mainly defined by a crystalline phase fraction in the amorphous matrix, i.e., a nanocrystalline phase at Тcarb < 1150°C and a bulk graphite phase at Tcarb > 1300°C. Maximum values E = 10–12 GPa are achieved for samples with Тcarb ≈ 1150 and 1600°C. It is shown that the microplasticity manifest itself only in biocarbons with Tcarb ≥ 1300°C (upon reaching a significant volume of the graphite phase); in this case, the conditional microyield stress decreases with increasing total volume of introduced mesoporosity (free surface area).

Physics of the Solid State, 58 (2016) 2481-2487 | DOI: 10.1134/S1063783416120234

Thermal conductivity of partially graphitized biocarbon obtained by carbonization of medium-density fiberboard in the presence of a Ni-based catalyst

Orlova, TS; Parfen'eva, LS; Smirnov, BI; Gutierrez-Pardo, A; Ramirez-Rico, J

The thermal conductivity k and resistivity rho of biocarbon matrices, prepared by carbonizing medium-density fiberboard at T (carb) = 850 and 1500A degrees C in the presence of a Ni-based catalyst (samples MDF-C( Ni)) and without a catalyst (samples MDF-C), have been measured for the first time in the temperature range of 5-300 K. X-ray diffraction analysis has revealed that the bulk graphite phase arises only at T (carb) = 1500A degrees C. It has been shown that the temperature dependences of the thermal conductivity of samples MDFC- 850 and MDF-C-850(Ni) in the range of 80-300 K are to each other and follow the law of k(T) similar to T (1.65), but the use of the Ni-catalyst leads to an increase in the thermal conductivity by a factor of approximately 1.5, due to the formation of a greater fraction of the nanocrystalline phase in the presence of the Ni-catalyst at T (carb) = 850A degrees C. In biocarbon MDF-C-1500 prepared without a catalyst, the dependence is k(T) similar to T (1.65), and it is controlled by the nanocrystalline phase. In MDF-C-1500(Ni), the bulk graphite phase formed increases the thermal conductivity by a factor of 1.5-2 compared to the thermal conductivity of MDF-C-1500 in the entire temperature range of 5-300 K; k(T = 300 K) reaches the values of similar to 10 W m(-1) K-1, characteristic of biocarbon obtained without a catalyst only at high temperatures of T (carb) = 2400A degrees C. It has been shown that MDF-C-1500(Ni) in the temperature range of 40aEuro'300 K is characterized by the dependence, k(T) similar to T (1.3), which can be described in terms of the model of partially graphitized biocarbon as a composite of an amorphous matrix with spherical inclusions of the graphite phase.

Physics of the Solid State, 58 (2016) 208-214 | DOI: 10.1134/S1063783416010236

Strength and microplasticity of biocarbons prepared by carbonization in the presence of a catalyst

Shpeizman, VV; Orlova, TS; Smirnov, BI; Gutierrez-Pardo, A; Ramirez-Rico, J

The microdeformation has been investigated under uniaxial compression of beech-derived biocarbons partially graphitized during carbonization in the presence of a Ni- or Fe-containing catalyst. The strength and ultimate fracture strain have been determined at different temperatures of carbonization of the samples in the absence or in the presence of a catalyst. It has been shown using high-precision interferometry that the deformation of biocarbon samples under uniaxial loading occurs through jumps (in magnitude and rate of deformation) with axial displacements in the nanometer and micrometer ranges. The use of a catalyst leads to a decrease in the size of nanometer-scale jumps and in the number of micrometer-scale jumps. The standard deviations of the strain rate on loading steps from the smooth average dependence of the strain rate on the displacement have been calculated for micrometer-scale jumps. A similar characteristic for nanometer- scale jumps has been determined from the distortion of the shape of beats in the primary interferogram. It has been shown that the variation in the standard deviation of the strain rate with a change in the carbonization temperature is similar to the corresponding dependence of the ultimate fracture strain.

Physics of the Solid State, 58 (2016) 703-710 | DOI: 10.1134/S1063783416040223

Obtention of Li3xLa2/3−xTiO3 ceramics from amorphous nanopowders by spark plasma sintering

Leyet, Y.; Guerrero, F.; Anglada-Rivera, J.; Martinez, I.; Amorin, H.; Romaguera-Barcelay, Y.; Poyato, R.; Gallardo-Lopez, A.

In this work, Li3xLa2/3-xTiO3 powder with nominal lithium content (x = 0.08) was synthesized by mechano synthesis method. Spark plasma sintering (SPS) was employed to prepare lithium lanthanum titanium oxide solid-state ceramic. The techniques of X-ray diffraction, high resolution scanning electron microscopy, and Raman spectroscopy were used to characterize the composition and microstructure of samples. The results showed that fine-grained ceramics with relative density of 95.5% were obtained by sintering the oxide powders at 1100 degrees C for only 5min.

Ferroelectrics, 498 (2016) 62-66 | DOI: 10.1080/00150193.2016.1167538

Preparation of calcium carbonate as nanoparticles from inorganic precursors and sucrose as additive with potential application as biomaterial

Takabait, F; Mahtout, L; Villarejo, LP; Hurtado, BC; Soto, PJS

En esta comunicación se presentan unos primeros resultados de interés relevante sobre la obtención de carbonato de calcio precipitado como nanopartículas de los polimorfos vaterita y calcita. Se parte de precursores inorgánicos, nitrato de calcio tetrahidratado y bicarbonato de sodio, en presencia de sacarosa empleada como aditivo orgánico en disolución acuosa. Las fases cristalinas formadas se estudian mediante difracción de rayos X con un método cuantitativo y la morfología de las partículas obtenidas, mediante microscopia electrónica de barrido. Cuando no se emplea el aditivo orgánico se consigue la precipitación de calcita, polimorfo más estable termodinámicamente, como fase nanocristalina predominante (83%) mezclada con vaterita. Con una alta concentración del aditivo (67%) se obtiene vaterita como fase mayoritaria (> 98%). La utilización del aditivo en distinta proporción produce la formación de los 2 polimorfos de carbonato de calcio, siendo vaterita la fase predominante. La morfología de las partículas obtenidas muestra la formación de partículas nanoesféricas uniformes con contornos irregulares que se asocian a vaterita, así como partículas romboédricas de calcita cuando está presente, con potencial interés por su biocompatibilidad para su aplicación como biomateriales en implantes óseos.

Boletin de la Sociedad Española de Cerámcia y Vidrio, 55 (2016) 179-184 | DOI: 10.1016/j.bsecv.2016.01.006

Influence of tin additions on the precipitation processes in a Cu-Ni-Zn alloys

Donoso, EC; Dianez, MJ; Criado, JM; Espinoza, R; Mosquera, E

Influence of tin additions on the precipitation processes in a Cu-Ni-Zn alloys. The influence of 1.1 wt% tin additions on the precipitation hardening of Cu-11 wt% Ni-20 wt% Zn alloy was studied by Differential Scanning Calorimetry (DSC), microhardeness measurements and High Resolution Transmission Electron Microscopy (HRTEM). The calorimetric curves, in the range of temperatures analyzed, show the presence of two exothermic reactions in the ternary alloy, associated to the short-range-order development assisted by migration of excess vacancies. On the other hand, one exothermic and one endothermic reaction are observed in the quaternary alloy, associated to the formation and dissolution of Cu2NiZn precipitates, respectively. It has been show that an addition of 1.1% tin plays an important role in the formation of Cu2NiZn precipitates, responsible for the precipitation hardening of the ternary alloy.

Revista de Metalurgia, 52 (2016) e060 | DOI: 10.3989/revmetalm.060

Characterization and Validation of a-Si Magnetron-Sputtered Thin Films as Solid He Targets with High Stability for Nuclear Reactions

Godinho, V; Ferrer, FJ; Fernandez, B; Caballero-Hernandez, J; Gomez-Camacho, J; Fernandez, A

In this work, we present our magnetron sputtering based methodology to produce amorphous silicon coatings with closed porosity, as a strategy to fabricate solid helium targets, in the form of supported or self-supported thin films, for nuclear reactions. We show how by changing the He working pressure it is possible to obtain highly porous homogeneous structures incorporating different He amounts. These porous coatings (a-Si: He) are very reproducible from run to run, and the high He amount incorporated makes them excellent candidates for solid He targets. The possibility of producing self-supported films is illustrated here, and its potential use in inverse kinematics experiments with radioactive beams is shown through the dispersion in forward geometry of a stable Li-6 beam. Also the elastic scattering cross-sections for proton from helium were determined using an a-Si: He coating. The results agree well with the ones reported in the literature. These two examples validate our coatings as good candidates to be used as solid He targets in nuclear reactions. The stability of He inside the coatings, fundamental for its use as solid He targets, was investigated, both over time and after irradiation. The coatings proved to be very stable, and the amount of He inside the pores remains unaltered at least 2 years after deposition and after high irradiation fluence (5 x 10(17) particles/cm(2); with a dose rate of 5 x 10(12) particles/(cm(2) s)).

ACS Omega, 1 (2016) 1229-1238 | DOI: 10.1021/acsomega.6b00270

Plasmonic Nanoparticles as Light-Harvesting Enhancers in Perovskite Solar Cells: A User’s Guide

Carretero-Palacios, S.; Jiménez-Solano, A.; Míguez, H.

In this Perspective we discuss the implications of employing metal particles of different shape, size, and composition as absorption enhancers in methylammonium lead iodide perovskite solar cells, with the aim of establishing some guidelines for the future development of plasmonic resonance-based photovoltaic devices. Hybrid perovskites present an extraordinarily high absorption coefficient which, as we show here, makes it difficult to extrapolate concepts and designs that are applied to other solution-processed photovoltaic materials. In addition, the variability of the optical constants attained from perovskite films of seemingly similar composition further complicates the analysis. We demonstrate that, by means of rigorous design, it is possible to provide a realistic prediction of the magnitude of the absorption enhancement that can be reached for perovskite films embedding metal particles. On the basis of this, we foresee that localized surface plasmon effects will provide a means to attain highly efficient perovskite solar cells using films that are thinner than those usually employed, hence facilitating collection of photocarriers and significantly reducing the amount of potentially toxic lead present in the device.

ACS Energy Letters, (2016) 323-331 | DOI: 10.1021/acsenergylett.6b00138

Highly Efficient Perovskite Solar Cells with Tunable Structural Color

W. Zhang, M. Anaya, G. Lozano, M.E. Calvo, M.B. Johnston, H. Míguez, H.J. Snaith

The performance of perovskite solar cells has been progressing over the past few years and efficiency is likely to continue to increase. However, a negative aspect for the integration of perovskite solar cells in the built environment is that the color gamut available in these materials is very limited and does not cover the green-to-blue region of the visible spectrum, which has been a big selling point for organic photovoltaics. Here, we integrate a porous photonic crystal (PC) scaffold within the photoactive layer of an opaque perovskite solar cell following a bottom-up approach employing inexpensive and scalable liquid processing techniques. The photovoltaic devices presented herein show high efficiency with tunable color across the visible spectrum. This now imbues the perovskite solar cells with highly desirable properties for cladding in the built environment and encourages design of sustainable colorful buildings and iridescent electric vehicles as future power generation sources.

Nano Letters, 15 (2015) 1698-1702 | DOI: 10.1021/nl504349z

Sonogashira Cross-Coupling and Homocoupling on a Silver Surface: Chlorobenzene and Phenylacetylene on Ag(100)

Sanchez-Sanchez, C; Orozco, N; Holgado, JP; Beaumont, SK; Kyriakou, G; Watson, DJ; Gonzalez-Elipe, AR; Feria, L; Sanz, JF; Lambert, RM

Scanning tunneling microscopy, temperature-programmed reaction, near-edge X-ray absorption fine structure spectroscopy, and density functional theory calculations were used to study the adsorption and reactions of phenylacetylene and chlorobenzene on Ag(100). In the absence of solvent molecules and additives, these molecules underwent homocoupling and Sonogashira cross-coupling in an unambiguously heterogeneous mode. Of particular interest is the use of silver, previously unexplored, and chlorobenzene—normally regarded as relatively inert in such reactions. Both molecules adopt an essentially flat-lying conformation for which the observed and calculated adsorption energies are in reasonable agreement. Their magnitudes indicate that in both cases adsorption is predominantly due to dispersion forces for which interaction nevertheless leads to chemical activation and reaction. Both adsorbates exhibited pronounced island formation, thought to limit chemical activity under the conditions used and posited to occur at island boundaries, as was indeed observed in the case of phenylacetylene. The implications of these findings for the development of practical catalytic systems are considered.

Journal of the American Chemical Society, 137 (2015) 940-947 | DOI: 10.1021/ja5115584

Theory and Practice: Bulk Synthesis of C3B and its H2- and Li-Storage Capacity

King, TC; Matthews, PD; Glass, H; Cormack, JA; Holgado, JP; Leskes, M; Griffin, JM; Scherman, OA; Barker, PD; Grey, CP; Dutton, SE; Lambert, RM; Tustin, G; Alavi, A; Wright, DS

Previous theoretical studies of C3B have suggested that boron-doped graphite is a promising H2- and Li-storage material, with large maximum capacities. These characteristics could lead to exciting applications as a lightweight H2-storage material for automotive engines and as an anode in a new generation of batteries. However, for these applications to be realized a synthetic route to bulk C3B must be developed. Here we show the thermolysis of a single-source precursor (1,3-(BBr2)2C6H4) to produce graphitic C3B, thus allowing the characteristics of this elusive material to be tested for the first time. C3B was found to be compositionally uniform but turbostratically disordered. Contrary to theoretical expectations, the H2- and Li-storage capacities are lower than anticipated, results that can partially be explained by the disordered nature of the material. This work suggests that to model the properties of graphitic materials more realistically, the possibility of disorder must be considered.

Angewandte Chemie International Edition, 54 (2015) 5919-5923 | DOI: 10.1002/anie.201412200

Environmental Effects on the Photophysics of Organic-Inorganic Halide Perovskites

Galisteo-Lopez, JF; Anaya, M; Calvo, ME; Miguez, H

The photophysical properties of films of organic-inorganic lead halide perovskites under different ambient conditions are herein reported. We demonstrate that their luminescent properties are determined by the interplay between photoinduced activation and darkening processes, which strongly depend on the atmosphere surrounding the samples. We have isolated oxygen and moisture as the key elements in each process, activation and darkening, both of which involve the interaction with photogenerated carriers. These findings show that environmental factors play a key role in the performance of lead halide perovskites as efficient luminescent materials.

Journal of Physical Chemistry Letters, 6 (2015) 2200-2205 | DOI: 10.1021/acs.jpclett.5b00785

Optical Description of Mesostructured Organic-Inorganic Halide Perovskite Solar Cells

Anaya, M; Lozano, G; Calvo, ME; Zhang, W; Johnston, MB; Snaith, HJ; Miguez, H

Herein we describe both theoretically and experimentally the optical response of solution-processed organic–inorganic halide perovskite solar cells based on mesostructured scaffolds. We develop a rigorous theoretical model using a method based on the propagation of waves in layered media, which allows visualizing the way in which light is spatially distributed across the device and serves to quantify the fraction of light absorbed by each medium comprising the cell. The discrimination between productive and parasitic absorption yields an accurate determination of the internal quantum efficiency. State-of-the-art devices integrating mesoporous scaffolds infiltrated with perovskite are manufactured and characterized to support the calculations. This combined experimental and theoretical analysis provides a rational understanding of the optical behavior of perovskite cells and can be beneficial for the judicious design of devices with improved performance. Notably, our model justifies the presence of a solid perovskite capping layer in all of the highest efficiency perovskite solar cells based on thinner mesoporous scaffolds.

Journal of Physical Chemistry Letters, 6 (2015) 48-53 | DOI: 10.1021/jz502351s

Synergy between gold and oxygen vacancies in gold supported on Zr-doped ceria catalysts for the CO oxidation

Laguna, OH; Perez, A; Centeno, MA; Odriozola, JA

The CO oxidation activity of 1 wt.% gold catalysts prepared by deposition-precipitation on a series of ceria doped with Zr supports was studied. The supports (10, 25 and 50 Zr at.%) were synthesized by a pseudo sol-gel method through the thermal decomposition of the corresponding metallic propionates. All the prepared solids were characterized by means of XRF, BET, XRD, Raman spectroscopy, SEM, and H-2-TPR. Solid solution was obtained in all mixed systems, while the segregation of different Ce-Zr oxides was observed for the solid with the 50 Zr at.%. The oxygen vacancies population and the amount of easier reducible Ce4+ species in the solids increase with the Zr content. No major textural or structural modifications were detected after gold deposition, although a strong Au-support interaction was generated. Such interaction is strongly influenced by the nucleation of gold deposits on the oxygen vacancies and consequently the amount of Zr inserted in the ceria network also determines the dispersion of gold. The presence of gold eases the surface reduction at lower temperatures, and as higher the amount of Zr in the gold catalysts, higher the CO conversion at low temperatures, probably due to the enhancement of the electronic transfer at the surface of the catalysts. 

Applied Catalysis B-Environmental, 176 (2015) 385-395 | DOI: 10.1016/j.apcatb.2015.04.019

Evolution of H-2 photoproduction with Cu content on CuOx-TiO2 composite catalysts prepared by a microemulsion method

Kubacka, A; Munoz-Batista, MJ; Fernandez-Garcia, M; Obregon, S; Colon, G

Copper oxides in contact with anatase correspond to promising materials with high activity in the photo-production of hydrogen by aqueous reforming of alcohols. By a single pot microemulsion method we obtained a series of Cu-Ti composite systems with controlled copper content in the 0-25 wt.% range. The scanning of such a wide range of composition led to the discovery of two well differentiated maxima in the photo-reaction performance. These maxima present rather high and relatively similar reaction rates and photonic efficiencies but are ascribed to the presence of different copper species. A multi-technique analysis of the materials indicates that the maxima obtained comes from optimizing different steps of the reaction; while the first would be connected with a positive effect on anatase charge handling performance the second seems exclusively related to electron capture by surface copper species.

Applied Catalysis B: Environmental, 163 (2015) 214-222 | DOI: 10.1016/j.apcatb.2014.08.005

Synthesis and application of layered titanates in the photocatalytic degradation of phenol

Ivanova, S; Penkova, A; Hidalgo, MD; Navio, JA; Romero-Sarria, F; Centeno, MA; Odriozola, JA

This study proposes a direct synthetic route to single titanate sheets through the mild and versatile conditions of the “chimie douce”. The stages of the production include the complexation of the titanium alkoxide precursor by benzoic acid, the formation of titanium oxo-clusters and their controlled transformation into single sheet titanates during the hydrolysis stage. The resulted material appears to be an excellent precursor for self-organized TiO2 nanotubes formation which presents an excellent activity as photocatalyst in the photo-degradation of phenol.

Applied Catalysis B: Environmental, 163 (2015) 23-29 | DOI: 10.1016/j.apcatb.2014.07.048

Study of the phenol photocatalytic degradation over TiO2 modified by sulfation, fluorination, and platinum nanoparticles photodeposition

Murcia, JJ; Hidalgo, MC; Navio, JA; Arana, J; Dona-Rodriguez, JM

In this work, titanium dioxide has been modified by sulfation, fluorination and simultaneous Pt nanoparticles deposition; the influence of these treatments on the photocatalytic activity of this oxide has been studied. A complete characterization study was carried out and it was observed that sulfation, fluorination and metallization were important factors influencing the TiO2 properties. The photocatalytic activity of the materials prepared was evaluated in the phenol degradation and it was found that TiO2fluorination significantly increased the phenol photodegradation rate, compared with bare TiO2, sulfated TiO2 or the commercial TiO2 Degussa P25. It was also found that Pt photodeposition on sulphated TiO2 notably increased the photocatalytic activity of this oxide, while Pt on fluorinated TiO2 did not modify significantly the phenol photodegradation rate.

Applied Catalysis B: Environmental, 179 (2015) 305-312 | DOI: 10.1016/j.apcatb.2015.05.040

Cu–TiO2 systems for the photocatalytic H2 production: Influence of structural and surface support features

Obregon, S; Munoz-Batista, MJ; Fernandez-Garcia, M; Kubacka, A; Colon, G

The influence of different TiO2 supports on the Cu active species has been studied. It was found that the photocatalytic H2 evolution is highly affected by the structural and electronic features of surface Cu species. Thus, metal dispersion and oxidation state appears strongly conditioned by the structural and surface properties of the TiO2 support. We have examined three TiO2 supports prepared by different synthetic methods; sol–gel, hydrothermal and microemulsion. In addition, we have induced structural and surface modifications by sulfate pretreatment over freshly prepared TiO2 precursors and subsequent calcination. Notably different copper dispersion and oxidation state is obtained by using these different TiO2 supports. From the wide structural and surface analysis of the catalysts we are able to propose that the occurrence of highly disperse Cu2+ species, the sample surface area as well as the crystallinity of the TiO2 support are directly related to the photocatalytic activity for H2 production reaction.

Applied Catalysis B: Environmental, 179 (2015) 468-478 | DOI: 10.1016/j.apcatb.2015.05.043

Fine Tuning the Emission Properties of Nanoemitters in Multilayered Structures by Deterministic Control of their Local Photonic Environment

Alberto Jiménez-Solano, Juan Francisco Galisteo-López and Hernán Míguez

Deterministic control on the dynamics of organic nanoemitters is achieved through precise control of its photonic environment. Resonators are fabricated by a combination of spin- and dip-coating techniques, which allows placement of the emitters at different positions within the sample, thus acting as a probe of the local density of states.

Small, 11 (2015) 2727-2732 | DOI: 10.1002/smll.201402898

Nanocolumnar 1-dimensional TiO2 photoanodes deposited by PVD-OAD for perovskite solar cell fabrication

Javier Ramos, F.; Oliva-Ramirez, Manuel; Nazeeruddin, Mohammad Khaja; Graetzel, Michael; Gonzalez-Elipe, Agustin R.; Ahmad, Shahzada

Perovskite solar cells have attracted increasing interest among the photovoltaic community in the last few years owing to their unique properties and high efficiency. In the present work, we report the fabrication of perovskite solar cells based on highly ordered 1-dimensional porous TiO2 photoanodes, which are uniform on a large area. These nanocolumnar porous TiO2 photoanodes were deposited by physical vapor deposition in an oblique angle configuration (PVD-OAD) by varying the zenithal angle between the target and the substrate normal. Perovskite infiltration into these 1-dimensional nanocolumnar structures was homogeneous through the entire thickness of the porous layer as revealed by secondary ion mass spectroscopy studies. The fabricated solar cells, with an optimized thickness of the photoanode and with industrially accepted methods, will pave the way for easy implementation on a large scale.

Journal of Materials Chemistry A, 3 (2015) 13291-13298 | DOI: 10.1039/c5ta02238j

Full solution processed mesostructured optical resonators integrating colloidal semiconductor quantum dots

Calvo, ME; Hidalgo, N; Schierholz, R; Kovacs, A; Fernandez, A; Bellino, MG; Soler-Illia, GJAA; Miguez, H

Herein we show a solution based synthetic pathway to obtain a resonant optical cavity with embedded colloidal semiconductor quantum dots (CSQDs). The optical cavity pore network, surrounded by two dense Bragg mirrors, was designed ad hoc to selectively host the quantum dots, while uncontrolled infiltration of those in the rest of the layered structure was prevented. Coupling between the optical resonant modes of the host and the natural emission of the embedded nanoparticles gives rise to the fine tuning of the luminescence spectrum extracted from the ensemble. Our approach overcomes, without the need for an encapsulating agent and exclusively by solution processing, the difficulties that arise from the low thermal and chemical stability of the CSQDs. It opens the route to achieving precise control over their location and hence over the spectral properties of light emitted by these widely employed nanomaterials. Furthermore, as the porosity of the cavity is preserved after infiltration, the system remains responsive to environmental changes, which provides an added value to the proposed structure.

Nanoscale, 7 (2015) 16583-16589 | DOI: 10.1039/C5NR03977K

Sunlight Absorption Engineering for Thermophotovoltaics: Contributions from the Optical Design

Miguez, H

Nowadays, solar thermophotovoltaic systems constitute a platform in which sophisticated optical material designs are put into practice with the aim of achieving the long sought after dream of developing an efficient energy conversion device based on this concept. Recent advances demonstrate that higher efficiencies are at reach using photonic nanostructures amenable to mass production and scale-up.

ChemSusChem, 8 (2015) 786-788 | DOI: 10.1002/cssc.201403361

Design and realization of transparent solar modules based on luminescent solar concentrators integrating nanostructured photonic crystals

Jimenez-Solano, A; Delgado-Sanchez, JM; Calvo, ME; Miranda-Munoz, JM; Lozano, G; Sancho, D; Sanchez-Cortezon, E; Miguez, H

Herein, we present a prototype of a photovoltaic module that combines a luminescent solar concentrator integrating one-dimensional photonic crystals and in-plane CuInGaSe2 (CIGS) solar cells. Highly uniform and wide-area nanostructured multilayers with photonic crystal properties were deposited by a cost-efficient and scalable liquid processing amenable to large-scale fabrication. Their role is to both maximize light absorption in the targeted spectral range, determined by the fluorophore employed, and minimize losses caused by emission at angles within the escape cone of the planar concentrator. From a structural perspective, the porous nature of the layers facilitates the integration with the thermoplastic polymers typically used to encapsulate and seal these modules. Judicious design of the module geometry, as well as of the optical properties of the dielectric mirrors employed, allows optimizing light guiding and hence photovoltaic performance while preserving a great deal of transparency. Optimized in-plane designs like the one herein proposed are of relevance for building integrated photovoltaics, as ease of fabrication, long-term stability and improved performance are simultaneously achieved.

Progress in Photovoltaics, 23 (2015) 1785-1792 | DOI: 10.1002/pip.2621

H-2 oxidation as criterion for PrOx catalyst selection: Examples based on Au-Co-O-x-supported systems

Reina, TR; Megias-Sayago, C; Florez, AP; Ivanova, S; Centeno, MA; Odriozola, JA

A new approach for understanding PrOx reaction over gold catalysts is proposed in this work. The competition between H-2 and CO oxidation has been studied over a series of Au/MOx/Al2O3 (M = Ce and Co) catalysts in simulated post-reforming gas stream, containing H2O and CO2 for H-2 cleanup goals. The catalysts' behavior is correlated to their oxygen storage capacity, redox behavior, and oxidation ability. The estimation of the reaction rates reveals that in these solids the H-2 combustion, the selectivity limiting factor in the PrOx process, is mainly controlled by the support and not by the gold presence. The possible use of the hydrogen oxidation reaction as a catalyst selection criterion is discussed. 

Journal of Catalysis, 326 (2015) 161-171 | DOI: 10.1016/j.jcat.2015.03.015

Anisotropic In-Plane Conductivity and Dichroic Gold Plasmon Resonance in Plasma-Assisted ITO Thin Films e-Beam-Evaporated at Oblique Angles

Parra-Barranco, Julian; Garcia-Garcia, Francisco J.; Rico, Victor; Borras, Ana; Lopez-Santos, Carmen; Frutos, Fabian; Barranco, Angel; Gonzalez-Elipe, Agustin R.

ITO thin films have been prepared by electron beam evaporation at oblique angles (OA), directly and while assisting their growth with a downstream plasma. The films microstructure, characterized by scanning electron microscopy, atomic force microscopy, and glancing incidence small-angle X-ray scattering, consisted of tilted and separated nanostructures. In the plasma assisted films, the tilting angle decreased and the nanocolumns became associated in the form of bundles along the direction perpendicular to the flux of evaporated material. The annealed films presented different in-depth and sheet resistivity as confirmed by scanning conductivity measurements taken for the individual nanocolumns. In addition, for the plasma-assisted thin films, two different sheet resistance values were determined by measuring along the nanocolumn bundles or the perpendicular to it. This in-plane anisotropy induces the electrochemical deposition of elongated gold nanostructures. The obtained Au-ITO composite thin films were characterized by anisotropic plasmon resonance absorption and a dichroic behavior when examined with linearly polarized light.

ACS Applied Materials & Interfaces, 7 (2015) 10993-11001 | DOI: 10.1021/acsami.5b02197

Fabrication of Optical Multi layer Devices from Porous Silicon Coatings with Closed Porosity by Magnetron Sputtering

Caballero-Hernandez, Jaime; Godinho, Vanda; Lacroix, Bertrand; Jimenez de Haro, Maria C.; Jamon, Damien; Fernandez, Asuncion

The fabrication of single-material photonic-multilayer devices is explored using a new methodology to produce porous silicon layers by magnetron sputtering. Our bottom-up methodology produces highly stable amorphous porous silicon films with a controlled refractive index using magnetron sputtering and incorporating a large amount of deposition gas inside the closed pores. The influence of the substrate bias on the formation of the closed porosity was explored here for the first time when He was used as the deposition gas. We successfully simulated, designed, and characterized Bragg reflectors and an optical microcavity that integrates these porous layers. The sharp interfaces between the dense and porous layers combined with the adequate control of the refractive index and thickness allowed for excellent agreement between the simulation and the experiments. The versatility of the magnetron sputtering technique allowed for the preparation of these structures for a wide range of substrates such as polymers while also taking advantage of the oblique angle deposition to prepare Bragg reflectors with a controlled lateral gradient in the stop band wavelengths.

ACS Applied Materials & Interfaces, 7 (2015) 13880-13897 | DOI: 10.1021/acsami.5b02356

Laser Treatment of Ag@ZnO Nanorods as Long-Life-Span SERS Surfaces

Macias-Montero, M; Pelaez, RJ; Rico, VJ; Saghi, Z; Midgley, P; Afonso, CN; Gonzalez-Elipe, AR; Borras, A

UV nanosecond laser pulses have been used to produce a unique surface nanostructuration of Ag@ZnO supported nanorods (NRs). The NRs were fabricated by plasma enhanced chemical vapor deposition (PECVD) at low temperature applying a silver layer as promoter. The irradiation of these structures with single nanosecond pulses of an ArF laser produces the melting and reshaping of the end of the NRs that aggregate in the form of bundles terminated by melted ZnO spherical particles. Well-defined silver nanoparticles (NPs), formed by phase separation at the surface of these melted ZnO particles, give rise to a broad plasmonic response consistent with their anisotropic shape. Surface enhanced Raman scattering (SERS) in the as-prepared Ag@ZnO NRs arrays was proved by using a Rhodamine 6G (Rh6G) chromophore as standard analyte. The surface modifications induced by laser treatment improve the stability of this system as SERS substrate while preserving its activity.

ACS Applied Materials & Interfaces, 7 (2015) 2331-2339 | DOI: 10.1021/am506622x

Self-lubricity of WSex nanocomposite coatings

S. Dominguez-Meister; M. Conte; A. Igartua; T.C. Rojas; J.C. Sánchez-López

Transition metal chalcogenides with lamellar structure are known for their use in tribological applications although limited to vacuum due to their easy degradation in the presence of oxygen and/or moisture. Here we present a tailored WSex coating with low friction (0.07) and low wear rates (3 × 10–7 mm3 Nm–1) even in ambient air. To understand the low friction behavior and lower chemical reactivity a tribological study is carried out in a high-vacuum tribometer under variable pressure (atmospheric pressure to 1 × 10–8 mbar). A detailed investigation of the film nanostructure and composition by advanced transmission electron microscopy techniques with nanoscale resolution determined that the topmost layer is formed by nanocrystals of WSe2 embedded in an amorphous matrix richer in W, a-W(Se). After the friction test, an increased crystalline order and orientation of WSe2 lamellas along the sliding direction were observed in the interfacial region. On the basis of high angle annular dark field, scanning transmission electron microscopy, and energy dispersive X-ray analysis, the release of W atoms from the interstitial basal planes of the a-W(Se) phase is proposed. These W atoms reaching the surface, play a sacrificial role preventing the lubricant WSe2 phase from oxidation. The increase of the WSe2 crystalline order and the buffer effect of W capturing oxygen atoms would explain the enhanced chemical and tribological response of this designed nanocomposite material.

ACS Applied Materials & Interfaces, 7 (2015) 7979-7986 | DOI: 10.1021/am508939s

Effect of catalytic graphitization on the electrochemical behavior of wood derived carbons for use in supercapacitors

Gutierrez-Pardo, A; Ramirez-Rico, J; Cabezas-Rodriguez, R; Martinez-Fernandez, J

Porous graphitic carbons were successfully obtained from wood precursors through pyrolysis using a transition metal as catalyst. Once the catalyst is removed, the resulting material mimics the microstructure of the wood and presents high surface area, open and interconnected porosity and large pore volume, high crystallinity and good electrical conductivity, making these carbons interesting for electrochemical devices. Carbons obtained were studied as electrodes for supercapacitors in half cell experiments, obtaining high capacitance values in a basic media (up to 133 F g−1 at current densities of 20 mA g−1 and 35 F g−1 at current densities of 1 A g−1). Long-cycling experiments showed excellent stability of the electrodes with no reduction of the initial capacitance values after 1000 cycles in voltammetry.

Journal of Power Sources, 278 (2015) 18-26 | DOI: 10.1016/j.jpowsour.2014.12.030

Plasma reforming of methane in a tunable ferroelectric packed-bed dielectric barrier discharge reactor

Montoro-Damas, AM; Brey, JJ; Rodriguez, MA; Gonzalez-Elipe, AR; Cotrino, J

In a tunable circular parallel plate dielectric barrier discharge reactor with pellets of a ferroelectric material separating the electrodes we investigate the plasma reforming of methane trying to maximize both the reaction yield and the energetic efficiency of the process. The geometrical configuration of the reactor (gap between electrodes, active electrode area) and the ferroelectric pellet size have been systematically varied to determine their influence on the process efficiency. The comparison between wet (with H2O as reactant), oxidative (with O2), and dry (with CO2) reforming reactions reveals a higher efficiency for the former with CO + H2 as main reaction products. The maximum energetic efficiency EE, defined as the produced number of litres of H2 per kWh, found for optimized working conditions at low-level applied power is higher than the up to date best-known results. A comprehensive discussion of the influence of the different parameters affecting the reaction yield is carried out.

Journal of Power Sources, 296 (2015) 268-275 | DOI: 10.1016/j.jpowsour.2015.07.038

Nanocolumnar coatings with selective behavior towards osteoblast and Staphylococcus aureus proliferation

Izquierdo-Barba, Isabel; Miguel Garcia-Martin, Jose; Alvarez, Rafael; Palmero, Alberto; Esteban, Jaime; Perez-Jorge, Concepcion; Arcos, Daniel; Vallet-Regi, Maria

Bacterial colonization and biofilm formation on orthopedic implants is one of the worst scenarios in orthopedic surgery, in terms of both patient prognosis and healthcare costs. Tailoring the surfaces of implants at the nanoscale to actively promote bone bonding while avoiding bacterial colonization represents an interesting challenge to achieving better clinical outcomes. Herein, a Ti6Al4V alloy of medical grade has been coated with Ti nanostructures employing the glancing angle deposition technique by magnetron sputtering. The resulting surfaces have a high density of nanocolumnar structures, which exhibit strongly impaired bacterial adhesion that inhibits biofilm formation, while osteoblasts exhibit good cell response with similar behavior to the initial substrates. These results are discussed on the basis of a "lotus leaf effect" induced by the surface nanostructures and the different sizes and biological characteristics of osteoblasts and Staphylococcus aureus.

Acta Biomaterialia, 15 (2015) 20-28 | DOI: 10.1016/j.actbio.2014.12.023

Biocompatible Films with Tailored Spectral Response for Prevention of DNA Damage in Skin Cells

Nunez-Lozano, R; Pimentel, B; Castro-Smirnov, JR; Calvo, ME; Miguez, H; de la Cueva-Mendez, G

A hybrid nanostructured organic–in­organic biocompatible film capable of efficiently blocking a preselected range of ultraviolet light is designed to match the genotoxic action spectrum of human epithelial cells. This stack protects cultured human skin cells from UV-induced DNA lesions. As the shielding mechanism relies exclusively on reflection, the secondary effects due to absorption harmful radiation are prevented

Advanced Healthcare Materials, 4 (2015) 1944-1948 | DOI: 10.1002/adhm.201500223

Ca-looping for postcombustion CO2 capture: A comparative analysis on the performances of dolomite and limestone

Valverde, JM; Sanchez-Jimenez, PE; Perez-Maqueda, LA

The low cost and wide availability of natural limestone (CaCO3) is at the basis of the industrial competitiveness of the Ca-looping (CaL) technology for postcombustion CO2 capture as already demonstrated by similar to 1 Mw(t) scale pilot projects. A major focus of studies oriented towards further improving the efficiency of the CaL technology is how to prevent the gradual loss of capture capacity of limestone derived CaO as the number of carbonation/calcination cycles is increased. Natural dolomite (MgCa(CO3)(2)) has been proposed as an alternative sorbent precursor to limestone. Yet, carbonation of MgO is not thermodynamically favorable at CaL conditions, which may hinder the capture performance of dolomite. In the work described in this paper we carried out a thermogravimetric analysis on the multicyclic capture performance of natural dolomite under realistic regeneration conditions necessarily implying high calcination temperature, high CO2 concentration and fast transitions between the carbonation and calcination stages. Our study demonstrates that the sorbent derived from dolomite has a greater capture capacity as compared to limestone. SEM analysis shows that MgO grains in the decomposed dolomite are resistant to sintering under severe calcination conditions and segregate from CaO acting as a thermally stable support which mitigates the multicyclic loss of CaO conversion. Moreover, full decomposition of dolomite is achieved at significantly lower calcination temperatures as compared to limestone, which would help improving further the industrial competitiveness of the technology. 

Applied Energy, 138 (2015) 202-215 | DOI: 10.1016/j.apenergy.2014.10.087

An Optically Controlled Microscale Elevator Using Plasmonic Janus Particles

Nedev, S; Carretero-Palacios, S; Kuhler, P; Lohmuller, T; Urban, AS; Anderson, LJE; Feldmann, J

In this article, we report how Janus particles, composed of a silica sphere with a gold half-shell, can be not only stably trapped by optical tweezers but also displaced controllably along the axis of the laser beam through a complex interplay between optical and thermal forces. Scattering forces orient the asymmetric particle, while strong absorption on the metal side induces a thermal gradient, resulting in particle motion. An increase in the laser power leads to an upward motion of the particle, while a decrease leads to a downward motion. We study this reversible axial displacement, including a hysteretic jump in the particle position that is a result of the complex pattern of a tightly focused laser beam structure above the focal plane. As a first application we simultaneously trap a spherical gold nanoparticle and show that we can control the distance between the two particles inside the trap. This photonic micron-scale “elevator” is a promising tool for thermal force studies, remote sensing, and optical and thermal micromanipulation experiments.

ACS Photonics, 2 (2015) 491-496 | DOI: 10.1021/ph500371z

Hydration and carbolenation reactions of calcium oxide by weathering: Kinetics and changes in the nanostructure

Morales-Florez, V; Santos, A; Romero-Hermida, I; Esquivias, L

The weathering reactions of hydration and carbonation of nanostructured calcium oxide with atmospheric moisture and carbon dioxide have been characterized. This work is the first-to-date combined kinetic and nanostructural research on CaO oriented to two key processes for different systems, i.e. hardening of construction materials and carbon mineral sequestration. The evolution of the precipitated crystalline phases was monitored by X-ray diffraction and thermogravimetry, along with structural characterization by nitrogen physisorption, electron microscopy and small-angle scattering. Complete hydration of the samples was always found prior to the onset of carbon sequestration, which depended on the nanostructure of the samples. Hence, carbonation started after 300 h of weathering for samples with a specific surface area of 40 m(2)/g, whereas carbonation of the samples with 20 m(2)/g occurred after 550 h. Full carbonation from atmospheric CO2 (100% efficiency) was obtained in all cases. This combined research was completed by developing an empirical description of the weathering reactions in terms of a two-process Random Pore Model. Finally, this work aimed to determine the role of the nanostructure of samples based on industrial wastes as one of the most important factors for developing efficient carbon sequestration technologies.

Chemical Engineering Journal, 265 (2015) 194-200 | DOI: 10.1016/j.cej.2014.12.062

Toughening of complete solid solution cermets by graphite addition

Chicardi, E; Torres, Y; Sayagues, MJ; Medri, V; Melandri, C; Cordoba, JM; Gotor, FJ

(Ti0.95Ta0.05)(C0.5N0.5)-Co complete solid solution cermets (CSCs) were developed by a mechanochemical synthesis process and a pressureless sintering method. The effect of different percentages of graphite used as a sintering additive on the nature of the binder phase and the mechanical properties of the cermets was investigated. Microstructural and mechanical characterisations were carried out by X-ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Vickers hardness, indentation fracture toughness and nanoindentation. The addition of graphite modified the carbon activity during sintering, reducing the dissolution of carbonitride ceramic particles into the molten binder. The amount of Ti and Ta remaining in the binder after sintering gradually decreased as the amount of graphite added increased, which induced a change in the nature of the binder phase. When no graphite was added, the binder consisted of the brittle TixTa1−xCo2 intermetallic phase. With the increase in the amount of graphite added, the formation of more ductile phases, such as TixTa1−xCo3 and α-Co, was observed, causing a significant improvement in the toughness of the cermets.

Chemical Engineering Journal, 267 (2015) 297-305 | DOI: 10.1016/j.cej.2015.01.022

Uranium immobilization by FEBEX bentonite and steel barriers in hydrothermal conditions

Villa-Alfageme, M; Hurtado, S; El Mrabet, S; Pazos, MC; Castro, MA; Alba, MD

FEBEX clay is considered a reference material in engineered barriers for safe storage of nuclear waste and uranium is a minor component of high-level radioactive waste (HLRW) and a main component of the spent nuclear fuel (SNF). Here, the kinetics of reaction of uranium with FEBEX was investigated in addition to the uranium immobilisation ability and the structural analysis of the reaction products. Hydrothermal treatments were accomplished with UO22+ and tetravalent actinide simulator ZrO2+, also present in HLRW. The quantification of the reaction was performed through gamma spectrometry of uranium. Two mechanisms for UO22+ retention by FEBEX were detected: adsorption and formation of stable and insoluble new phases. The structural analyses performed using ZrO2+, confirmed the uranium adsorption and the presence of new phases, ZrO2 and Zr(SiO4), that emphasise the existence of a chemical reaction with the bentonite. The analysis of the velocity of reaction uranium-clay minerals revealed temperature dependence. An exponential fitting suggested that the removal of uranium from solution at temperatures over 200 °C could be completed in less than a year. For lower temperatures, several years are needed. Milliequivalents of UO22+ immobilised by the clay depended on temperature and time and were over cation exchange capacity (CEC) of FEBEX even at 100 °C (reaching 600% of CEC). The reaction with steel, also temperature dependent, was finally analysed. At 200 °C 40–70% of uranium reacted with steel. But only 30–15% reacted at 300 °C and 100 °C. The reactions provide a stable immobilisation mechanism for uranium even when its sorption and swelling capacities fail. Our experiments will be of particular interest for very deep borehole disposals were higher temperatures and pressures are expected.

Chemical Engineering Journal, 269 (2015) 279-287 | DOI: 10.1016/j.cej.2015.01.134

Microreactors technology for hydrogen purification: Effect of the catalytic layer thickness on CuOx/CeO2-coated microchannel reactors for the PROX reaction

Laguna, O. H.; Castano, M. Gonzalez; Centeno, M. A.; Odriozola, J. A.

Two blocks of microreactors composed by 100 microchannels and coated, respectively, with 150 and 300 mg of a CuOx/CeO2 catalyst, were prepared and tested in the preferential oxidation of CO in presence of H2 (PROX). The deposition of different amount of catalyst resulted in different catalytic layer thicknesses thus modifying the catalytic performances of the microreactor. The evaluation of the main reaction variables (the space velocity, the O2-to-CO ratio and the presence of H2O and/or CO2 in the stream) was performed over both microreactors and compared to that of the parent powder catalyst. The least loaded microreactor, with a coating thickness around 10 μm, presented the highest CO conversion and selectivity levels at temperatures below 160 °C. This result evidences (i) the improvement of the catalytic performances got by the structuration of the powder catalyst and (ii) the importance of the selection of the adequate thickness of the catalytic layer on the microreactor, which have not to exceed and optimal value. An adequate coating thickness allows minimizing the mass and heat transport limitations, thus resulting in the enhancement of the catalytic performance during the PROX reaction.

Chemical Engineering Journal, 271 (2015) 45-52 | DOI: 10.1016/j.cej.2015.04.023

Water splitting performance of Er3+-doped YVO4 prepared from a layered K3V5O14 precursor

Obregon, S; Colon, G

Erbium-doped YVO4 have been synthesized by means of a simple solution method having good photo activities under UV-like excitation for the water splitting half reactions. From the structural and morphological characterization it has been stated that the presence of Er3+ induces the promotion of luminescence. Moreover the incorporation of erbium clearly affects to the morphology YVO4 leading to 200 nm size well-defined spindle-like particles. The improved photocatalytic performance might be associated to a better electron–hole separation mechanism, probably due to the slight increase of band-gap value. The obtained photoactivities for H2 and O2 evolution reactions make this material a promising candidate for water splitting reactions.

Chemical Engineering Journal, 262 (2015) 29-33 | DOI: 10.1016/j.cej.2014.09.073

Enhancement of stability and photoactivity of TiO2 coatings on annular glass reactors to remove emerging pollutants from waters

Espino-Estevez, MR; Fernandez-Rodriguez, C; Gonzalez-Diaz, OM; Navio, JA; Fernandez-Hevia, D; Dona-Rodriguez, JM

TiO2 coatings of highly photoactive lab-made titania were prepared on the outer wall of the inner tube of a glass tubular reactor by dip-coating method. The effect of decreasing the size of the aggregates to improve adhesion and photoactivity of the coatings to degrade phenol, diclofenac and isoproturon was also investigated. Chemical disaggregation of the TiO2 particles resulted in a lower aggregate size, between 0.1 and 1 μm, than mechanical disaggregation, between 1 and 10 μm. The results of the adhesion tape test showed that either milling of aggregate material with a planetary mill or chemical stabilization of the particles were necessary to obtain TiO2 coatings on glass tube with acceptable quality to be used in water treatment applications. SEM images showed that coatings prepared after milling the TiO2 suspension were more homogeneous without surface aggregates. The degree of adhesion of the coatings after increasing the roughness of the support by abrasive blasting was also evaluated. Adhesion to the substrate was slightly lower when using the modified support. The photoactivity results showed that the coatings prepared after wet milling of catalyst during 30 min and after chemical disaggregation were more efficient in terms of degradation and mineralization when using phenol as model molecule. Subsequent studies with two emerging pollutants, diclofenac and isoproturon, also showed enhanced efficiency of these coatings. The reusability of the TiO2 coatings was also evaluated and a promising photocatalytic performance was observed with a very low variation of the decay rate after five consecutive usages.

Chemical Engineering Journal, 279 (2015) 488-497 | DOI: 10.1016/j.cej.2015.05.038

Electrochemical activation of an oblique angle deposited Cu catalyst film for H-2 production

Gonzalez-Cobos, J; Rico, VJ; Gonzalez-Elipe, AR; Valverde, JL; de Lucas-Consuegra, A

A novel Cu catalyst film was prepared by oblique angle physical vapour deposition (OAD) on a K-βAl2O3 solid electrolyte (alkaline ionic conductor) for catalytic/electrocatalytic purposes. This technique allowed us to obtain a highly porous and electrically conductive Cu catalyst electrode which was tested in the partial oxidation of methanol (POM) reaction for H2 production and its catalytic activity was in situ enhanced via electrochemical promotion of catalysis (EPOC). The electropromotional effect was reversible and reproducible, and allowed us to increase both hydrogen and methyl formate production rates by almost three times under optimal promotion conditions (320 °C, 2.2 × 10−7 mol of K+ transferred). The observed promotional effect was attributed to a decrease in the Cu catalyst work function as a consequence of the controlled migration of electropositive K+ ions which favoured the chemisorption of electron acceptor molecules (O2) at the expense of the electron donor ones (CH3OH). Under the reaction conditions these ions formed some kinds of potassium surface compounds as demonstrated by SEM, EDX and XPS post-reaction characterization analyses. The obtained results demonstrate the interest of the used catalyst-electrode preparation technique for the electrochemical activation of non-noble metal catalyst films.

Catalysis Science & Technology, 5 (2015) 2203-2214 | DOI: 10.1039/c4cy01524j

Ultra-fast and energy-efficient sintering of ceramics by electric current concentration

Zapata-Solvas, E; Gomez-Garcia, D; Dominguez-Rodriguez, A; Todd, RI

Electric current activated/assisted sintering (ECAS) techniques, such as electrical discharge sintering (EDS) or resistive sintering (RS), have been intensively investigated for longer than 50 years. In this work, a novel system including an electrically insulated graphite die for Spark Plasma Sintering (SPS) is described, which allows the sintering of any refractory ceramic material in less than 1 minute starting from room temperature with heating rates higher than 2000°C/min and an energy consumption up to 100 times lower than with SPS. The system alternates or combines direct resistive sintering (DRS) and indirect resistive sintering (IRS). Electrical insulation of the die has been achieved through the insertion of a film made of alumina fibers between the graphite die and the graphite punches, which are protected from the alumina fiber film by a graphite foil. This system localized the electric current directly through the sample (conductive materials) as in DRS and EDS, or through the thin graphite foil (non-conductive materials) as in IRS, and is the first system capable of being used under EDS or RS conditions independently combining current concentration/localization phenomena.

Scientific Reports, 5 (2015) art n. 8513 | DOI: 10.1038/srep08513

Adaptable Ultraviolet Reflecting Polymeric Multilayer Coatings of High Refractive Index Contrast

Smirnov, JRC; Ito, M; Calvo, ME; Lopez-Lopez, C; Jimenez-Solano, A; Galisteo-Lopez, JF; Zavala-Rivera, P; Tanaka, K; Sivaniah, E; Miguez, H

A synthetic route is demonstrated to build purely polymeric nanostructured multilayer coatings, adaptable to arbitrary surfaces, and capable of efficiently blocking by reflection a targeted and tunable ultraviolet (UV) range. Reflection properties are determined by optical interference between UV light beams reflected at the interfaces between polystyrene layers of different porosity and hence refractive index. As no dopant absorber intervenes in the shielding effect, polymer degradation effects are prevented. Alternated porosity results from the modulation of photochemical effects at the few tens of nanometers length scale, combined with the collective osmotic shock induced during the processing of the precursor diblock copolymer film. Experimental evidence of the application of this method to coat rough surfaces with smooth and conformal UV protecting films is provided.

Advanced Optical Materials, 3 (2015) 1633-1639 | DOI: 10.1002/adom.201500209

Flexible Distributed Bragg Reflectors from Nanocolumnar Templates

Calvo, ME; Gonzalez-Garcia, L; Parra-Barranco, J; Barranco, A; Jimenez-Solano, A; Gonzalez-Elipe, AR; Miguez, H

A flexible distributed Bragg reflector is made by the infiltration of a nanocolumnar array with polydimethyl siloxane oligomers. The high optical reflectance displayed by the final material is a direct consequence of the high refractive index contrast of the columnar layers whereas the structural stability is due to the polymer properties.

Advanced Optical Materials, 3 (2015) 171-175 | DOI: 10.1002/adom.201400338

Structural, Optical, and Electrical Characterization of Yttrium-Substituted BiFeO3 Ceramics Prepared by Mechanical Activation

Perejon, A; Gil-Gonzalez, E; Sanchez-Jimenez, PE; Criado, JM; Perez-Maqueda, LA

Ceramics of Bi1-xYxFeO3 solid solutions (x = 0.02, 0.07, and 0.10) have been prepared by mechanical activation followed by sintering. The effect of yttrium content on the structural, electrical, and optical properties of the materials has been studied. Thus, single-phase solid solutions with rhombohedral R3c structure have been achieved for x = 0.02 and 0.07, while for x = 0.10 the main R3c phase has been detected together with a small amount of the orthorhombic Pbnm phase. Multiferroic properties of the samples, studied by differential scanning calorimetry (DSC), showed that both T-N and T-C (temperatures of the antiferromagnetic paramagnetic and ferroelectric-paraelectric transitions, respectively) decrease with increasing yttrium content. The nature of the ferroelectric paraelectric transition has been studied by temperature-dependent X-ray diffraction (XRD), which revealed rhombohedral R3c to orthorhombic Pbnm phase transitions for x = 0.07 and 0.10. On the other hand, for x = 0.02 the high-temperature phase was indexed as Pnma. Optical properties of the samples, as studied by diffuse reflectance spectroscopy, showed low optical band gap that decreases with increasing yttrium content. Prepared ceramics were highly insulating at room temperature and electrically homogeneous, as assayed by impedance spectroscopy, and the conductivity increased with x.

Inorganic Chemistry, 54 (2015) 9876-9884 | DOI: 10.1021/acs.inorgchem.5b01654

New Copper wide range nanosensor electrode prepared by physical vapor deposition at oblique angles for the non-enzimatic determination of glucose

Salazar, P; Rico, V; Rodriguez-Amaro, R; Espinos, JP; Gonzalez-Elipe, AR

In this work a novel Cu nanostructured electrode is presented. Cu tilted nanocolumnar and porous thin films have been prepared by physical vapor deposition (PVD) in an oblique angle configuration and characterized by different techniques. Cyclic voltammetry and amperometry were used to study the sensing ability of the copper films deposited on ITO to quantitatively determine glucose and to optimize the experimental conditions of detection. Scanning electron microscopy data revealed that the film microstructure consists of tilted nanocolumns of around 70 nm of diameter and an inclination of 65° with respect to the surface normal that extend through the total thickness of the layer of ca. 300 nm. X ray photoelectron spectroscopy and Raman, used to determine the oxidation state of Cu, revealed that an oxy/hydroxide external layer formed around the nanocolumns is the active phase responsible for the electrocatalytic detection of glucose. Under optimized conditions, the CuO/Cu nanoporous/ITO electrode presented a sensitivity of 1.41 A mol dm−3 cm−2 (R2:0.999) with a limit of detection of 0.36 μmol dm−3 and a reproducibility of 3.42%.The selectivity of the proposed sensor was checked against various interferences, including physiological compounds, different sugars and ethanol, thereby showing excellent anti-interference properties. The CuO/Cu nanoporous/ITO electrode was also used successfully to determine glucose in blood samples showing a performance comparable to that of a commercial glucometer. An extended working range covering from 1 to 5 × 10−3 mol dm−3 was determined for these sensor films which, in this way, could be applied for different analytical purposes including agro industrial liquids.

Electrochimica Acta, 169 (2015) 195-201 | DOI: 10.1016/j.electacta.2015.04.092

A novel and improved surfactant-modified Prussian Blue electrode for amperometric detection of free chlorine in water

Salazar, Pedro; Martin, Miriam; Garcia-Garcia, Francisco J.; Luis Gonzalez-Mora, Jose; Gonzalez-Elipe, Agustin R.

A surfactant-modified Prussian Blue (PB) electrochemical sensor has been developed. Benzethonium was used to assist the electrodeposition of PB onto a glassy carbon electrode (GCE). The surface coverage ( [View the MathML source] ) was 7.75 × 10−8 mol cm−2, five times higher than the value obtained in the absence of surfactant, and the film thickness of ca. 123 nm. SEM, EDX, Raman were used to characterize the electrodes while their electrochemical analysis proved a superior performance for the surfactant modified PB film. Cyclic voltammetry and amperometry were used to study the sensor ability to detect chlorine, and the main experimental variables were optimized. Under optimized conditions, the sensor presented a sensitivity of 12 μA ppm−1 cm−2, a linear range from 9 ppb to 10 ppm and a reproducibility of 4.2%. For the first time, we proved the sensor performance for real applications. Thus, chlorine was determined in tap water and the obtained concentrations validated with a standard colorimetric method. The obtained results showed that our sensor is highly performant and reliable for applications involving determinations of environmental residual chlorine.

Sensors and Actuators B: Chemical, 213 (2015) 116-123 | DOI: 10.1016/j.snb.2015.02.092

Rapid Legionella pneumophila determination based on a disposable core–shell Fe3O4@poly(dopamine) magnetic nanoparticles immunoplatform

Martin, M; Salazar, P; Jimenez, C; Lecuona, M; Ramos, MJ; Ode, J; Alcoba, J; Roche, R; Villalonga, R; Campuzano, S; Pingarron, JM; Gonzalez-Mora, JL

A novel amperometric magnetoimmunoassay, based on the use of core–shell magnetic nanoparticles and screen-printed carbon electrodes, was developed for the selective determination of Legionella pneumophila SG1. A specific capture antibody (Ab) was linked to the poly(dopamine)–modified magnetic nanoparticles (MNPs@pDA-Ab) and incubated with bacteria. The captured bacteria were sandwiched using the antibody labeled with horseradish peroxidase (Ab-HRP), and the resulting MNPs@pDA-Ab-Legionella neumophila-Ab-HRP were captured by a magnetic field on the electrode surface. The amperometric response measured at −0.15 V vs. Ag pseudo-reference electrode of the SPCE after the addition of H2O2 in the presence of hydroquinone (HQ) was used as transduction signal. The achieved limit of detection, without pre-concentration or pre-enrichment steps, was 104 Colony Forming Units (CFUs) mL−1. The method showed a good selectivity and the MNPs@pDA-Ab exhibited a good stability during 30 days. The possibility of detecting L. pneumophila at 10 CFU mL−1 level in less than 3 h, after performing a membrane-based preconcentration step, was also demonstrated.

Analytica Chimica Acta, 887 (2015) 51-58 | DOI: 10.1016/j.aca.2015.05.048

Physiological Degradation Mechanisms of PLGA Membrane Films under Oxygen Plasma Treatment

Lopez-Santos, C; Terriza, A; Portoles, J; Yubero, F; Gonzalez-Elipe, AR

Degradation under simulated physiological conditions of poly(lactic-co-glycolic) (PLGA) copolymer membrane films subjected to an oxygen plasma treatment compared to its “as prepared” state has been studied by gas cluster ion beam assisted X-ray photoelectron spectroscopy for chemical depth profiling analysis. This investigation is complemented with atomic force microscopy, weight loss measurements, and visual inspection of the films at the different stages of the degradation process. The obtained results show that the carbon functional groups of the PLGA membrane films undergo a heterogeneous hydrolytic degradation to different rates depending on the plasma pretreatment. The content of glycolic groups (GA) in untreated PLGA samples immersed for 3 weeks in a phosphate-buffered saline solution decreased at the surface, whereas the ratio between glycolic and lactic units (LA) did not vary in the inner regions (∼400 nm depth) of the degraded membrane films. By contrast, oxygen plasma pretreatment enhances the degradation efficiency and causes that both lactic and glycolic functional components decreased at the surface and in the interior of the film, although with less prevalence for the lactic units that present a comparatively higher resistance to degradation.

Journal fo Physical Chemistry C, 119 (2015) 20446–20452 | DOI: 10.1021/acs.jpcc.5b05011

Limestone Calcination Nearby Equilibrium: Kinetics, CaO Crystal Structure, Sintering and Reactivity

Valverde, JM; Sanchez-Jimenez, PE; Perez-Maqueda, LA

In this work, we analyze limestone calcination kinetics at environmental conditions involving a CO2 partial pressure P close to the equilibrium pressure Peq by means of in situ X-ray diffraction (XRD) and thermogravimetric (TG) analyses. In contrast with previous empirical observations carried out mostly at conditions far from equilibrium (P/Peq ≪ 1), our results show that the decarbonation rate decreases as the temperature in increased while P/Peq is kept constant, which is explained from a reaction mechanism including desorption of CO2 and the exothermic structural transformation from metastable CaO* nanocrystals to the stable CaO form. The crystal structure and sintering of nascent CaO during calcination has been investigated from in situ XRD analysis, physisorption analysis, and scanning electron microscopy (SEM), which shows that the ratio of the size of polycrystalline CaO grains to crystallite size increases linearly with the CO2 partial pressure in the calcination atmosphere. For high CO2 partial pressures, the size of CaO grains reaches a maximum value of around 1 μm, which leads to a residual surface area of about 1 m2/g, whereas in the limit P → 0 grain size and crystallite size (of the order of 10 nm) would coincide. Accordingly, sintering in the presence of CO2 would be triggered by the agglomeration of CaO crystals enhanced by CO2adsorption, which increases the surface energy. The carbonation reactivity of CaO resulting from calcination scales proportionally to its surface area and is not determined by a growth of the CaO exposed surface along a preferred crystallographic direction wherein carbonation would be unfavorable as suggested in recent works.

Journal of Physical Chemistry C, 119 (2015) 1523-1541 | DOI: 10.1021/jp508745u

Absorption Enhancement in Organic-Inorganic Halide Perovskite Films with Embedded Plasmonic Gold Nanoparticles

Carretero-Palacios, S; Calvo, ME; Miguez, H

We report on the numerical analysis of solar absorption enhancement in organic-inorganic halide perovskite films embedding plasmonic gold nanoparticles. The effect of particle size and concentration is analyzed in realistic systems in which random particle location within the perovskite film and the eventual formation of dimers are also taken into account. We find a maximum integrated solar absorption enhancement of similar to 10% in perovskite films of 200 nm thickness and similar to 6% in 300 nm films, with spheres of radii 60 and 90 nm, respectively, in volume concentrations of around 10% in both cases. We show that the presence of dimers boosts the absorption enhancement up to,similar to 12% in the thinnest films considered. Absorption reinforcement arises from a double contribution of plasmonic near-field and scattering effects, whose respective weight can be discriminated and evaluated from the simulations.

Journal of Physical Chemistry C, 119 (2015) 18635-18640 | DOI: 10.1021/acs.jpcc.5b06473

"In Operando" X-ray Absorption Spectroscopy Analysis of Structural Changes During Electrochemical Cycling of WO3 and WxSiyOz Amorphous Electrochromic Thin Film Cathodes

Garcia-Garcia, FJ; Gil-Rostra, J; Yubero, F; Espinos, JP; Gonzalez-Elipe, AR; Chaboy, J

This work reports a X-ray absorption spectroscopy (XAS) study under in operando conditions of the structural and chemical changes undergone by WO3 and WxSiyOz thin films used as electrochromic cathodes. The electrochromic films were prepared by magnetron sputtering deposition at oblique angles and then characterized by a large variety of techniques. The voltammograms and chronoamperometric diagrams in both aqueous and organic electrolyte media revealed a total reversibility of the electrochromic behavior, a low response time, and a high coloration efficiency for the two types of thin films. The in operando X-ray absorption study of the films working in aqueous solutions revealed that when they were electrochemically cycled the average WO distances reversibly varied by a Delta d of 0.06 and 0.08 angstrom for, respectively, WO3 and WxSiyOz. These changes are discussed by assuming the reduction of W6+ cations and the transformation of W-O double bonds into single WO bond structures during the electrochemical cycling of the films.

Journal of Physical Chemistry C, 119 (2015) 644-652 | DOI: 10.1021/jp508377v

Nanolevitation Phenomena in Real Plane-Parallel Systems Due to the Balance between Casimir and Gravity Forces

Esteso, V; Carretero-Palacios, S; Miguez, H

We report on the theoretical analysis of equilibrium distances in real plane-parallel systems under the influence of Casimir and gravity forces at thermal equilibrium. Due to the balance between these forces, thin films of Teflon, silica, or polystyrene in a single-layer configuration and immersed in glycerol stand over a silicon substrate at certain stable or unstable positions depending on the material and the slab thickness. Hybrid systems containing silica and polystyrene, materials which display Casimir forces and equilibrium distances of opposite nature when considered individually, are analyzed in either bilayer arrangements or as composite systems made of a homogeneous matrix with small inclusions inside. For each configuration, equilibrium distances and their stability can be adjusted by fine-tuning of the volume occupied by each material. We find the specific conditions under which nanolevitation of realistic films should be observed. Our results indicate that thin films of real materials in plane-parallel configurations can be used to control suspension or stiction phenomena at the nanoscale.

Journal of Physical Chemistry C, 119 (2015) 5663-5670 | DOI: 10.1021/jp511851z

Oxodiperoxomolybdenum complex immobilized onto ionic liquid modified SBA-15 as an effective catalysis for sulfide oxidation to sulfoxides using hydrogen peroxide

Carrasco, Carlos J.; Montilla, Francisco; Bobadilla, Luis; Ivanova, Svetlana; Antonio Odriozola, Jose; Galindo, Agustin

A supported ionic-liquid-phase (SILP) was prepared by the reaction of 1-methyl-3-(3-(triethoxysilyl) propyl)-1H-imidazol-3-ium chloride with a mesoporous SBA-15 silica and then an oxodiperoxomolybdenum complex was immobilized onto the obtained SILP. The resulting material, identified as SBA-15 + ImCl+ MoO5, was characterized by solid state NMR (H-1, C-13 and Si-29), and their textural and thermogravimetric properties were determined. The SBA-15 + ImCl+ MoO5 material was investigated as catalyst for the oxidation of methylphenylsulfide, as model reaction, with aqueous hydrogen peroxide as oxidant at room temperature. The presence of the molybdenum species was crucial for achieving good conversions and methanol was selected as the best solvent (conversion of 95% and selectivity toward sulfoxide 98%). The optimized reaction conditions were applied for the oxidation of several selected sulfides. In general, good catalytic activity and selectivity to sulfoxide were obtained and, remarkably, the selectivity toward sulfoxide is higher than those observed in the study of the same process carried out in [C(4)min][PF6] (C(4)mim = 1-buty1-3-methylimidazolium) and catalyzed by a molecular molybdenum complex, under the same reaction conditions. The importance of the IL-functionalization in the SBA-15 material was evidenced by recycling experiments. The SBA-15 + ImCl+ MoO5 catalyst was used for the sulfoxidation of the methylphenylsulfide substrate for ten reaction cycles without a significant change in conversion, selectivity to sulfoxide and molybdenum content.

Catalysis Today, 255 (2015) 102-108 | DOI: 10.1016/j.cattod.2014.10.053

Photocatalytic activity of bismuth vanadates under UV-A and visible light irradiation: Inactivation of Escherichia coli vs oxidation of methanol

Adan, C; Marugan, J; Obregon, S; Colon, G

Four bismuth vanadates have been synthesized by using two different precipitating agents (NH3 and triethylamine) following a hydrothermal treatment at 100 °C for 2 h and at 140 °C for 20 h. Then, solids were characterized by X-ray diffraction, BET surface area, UV–vis spectroscopy and scanning microscopy techniques. The characterization of the synthesized materials showed a well crystallized scheelite monoclinic structure with different morphologies. All materials display optimum light absorption properties for visible light photocatalytic applications. The photocatalytic activity of the catalysts was investigated for the inactivation of Escherichia coli bacteria and the oxidation of methanol under UV–vis and visible light irradiation sources. Main results demonstrate that BiVO4 are photocatalytically active in the oxidation of methanol and are able to inactivate bacteria below the detection level. The activity of the catalyst decreases when using visible light, especially for methanol oxidation, pointing out differences in the reaction mechanism. In contrast with bacteria, whose interaction with the catalyst is limited to the external surface, methanol molecules can access the whole material surface.

Catalysis Today, 240 (2015) 93-99 | DOI: 10.1016/j.cattod.2014.03.059

Role of ruthenium on the catalytic properties of CeZr and CeZrCo mixed oxides for glycerol steam reforming reaction toward H2 production

Martinez, LM; Araque, M; Centeno, MA; Roger, AC

The effect of ruthenium on the physico-chemical properties of CeZr and CeZrCo mixed oxides for H2production by glycerol steam reforming reaction has been studied. The combination of in situ Raman spectroscopy under both reductive and oxidative conditions, H2/O2 pulses and XRD, Raman, BET analysis, H2-TPR and TPD-TPO analyses contributed to the determination of the structural and textural properties, redox behavior, re-oxidation capacity and resistance to carbon deposition of the synthesized catalysts. The results show that the catalytic activity is improved by the (positive) cooperative and complementary effect between cobalt and ruthenium that favors the selectivity toward the steam reforming, selective to H2, with respect to the unselective thermal decomposition of glycerol. Ruthenium stabilizes the cobalt cations inserted in the fluorite structure preventing its rejection as Co3O4; and provides the necessary hydrogen to reduce Ce4+. The combination cobalt–ruthenium modifies positively the redoxproperties of the catalysts, increases the re-oxidation capacity (OSC) and promotes the gasification of the carbon deposits. Under the reaction conditions, the decrease in glycerol conversion came along with a change of selectivity. The formation of H2 and CO2 were strongly decreased, while the formation of CO, C2H4 and condensable products (mainly hydroxyacetone) increase. The differences in the catalytic stability and activity of the catalysts are related to the capability of the catalysts to activate H2O under the reaction conditions, favoring the steam reforming reaction over the thermal decomposition.

Catalysis Today, 242 (2015) 80-90 | DOI: 10.1016/j.cattod.2014.07.034

Boosting the activity of a Au/CeO2/Al2O3 catalyst for the WGS reaction

Reina, T. R.; Ivanova, S.; Centeno, M. A.; Odriozola, J. A.

Herein a strategy to design highly efficient Au/CeO2/Al2O3 based WGS catalysts is proposed. The inclusion of transition metals, namely Fe, Cu and Zn as CeO2 dopant is considered. All the promoters successfully increased the WGS performance of the undoped sample. The activity improvement can be correlated to structural and/or redox features induced by the dopants. The comparative characterization of the doped samples by means of XRD, Raman spectroscopy and OSC evaluation permits an accurate understanding of the boosted WGS activity arising from the Ce-promoter interaction. This study establishes distinction among both, structural and redox sources of promotion and provides a useful strategy to develop highly active Au/CeO2 based catalysts for the WGS reaction.

Catalysis Today, 253 (2015) 149-154 | DOI: 10.1016/j.cattod.2015.01.041

STEM-in-SEM high resolution imaging of gold nanoparticles and bivalve tissues in bioaccumulation experiments

C.A. García-Negrete; M.C. Jiménez de Haro; J. Blasco; M. Soto; A. Fernández

The methodology termed scanning transmission electron microscopy in scanning electron microscopy (STEM-in-SEM) has been used in this work to study the uptake of citrate stabilized gold nanoparticles (AuNPs) (average particle sizes of 23.5 ± 4.0 nm) into tissue samples uponin vitro exposure of the dissected gills of the Ruditapes philippinarum marine bivalve to the nanoparticle suspensions. The STEM-in-SEM methodology has been optimized for achieving optimum resolution under SEM low voltage operating conditions (20–30 kV). Based on scanning microscope assessments and resolution testing (SMART), resolutions well below 10 nm were appropriately achieved by working at magnifications over 100k×, with experimental sample thickness between 300 and 200 nm. These relatively thick slices appear to be stable under the beam and help avoid NP displacement during cutting. We herein show that both localizing of the internalized nanoparticles and imaging of ultrastructural disturbances in gill tissues are strongly accessible due to the improved resolution, even at sample thicknesses higher than those normally employed in standard TEM techniques at higher voltages. Ultrastructural imaging of bio-nano features in bioaccumulation experiments have been demonstrated in this study.

Analyst, 140 (2015) 3082-3089 | DOI: 10.1039/C4AN01643B

Boosting the visible-light photoactivity of Bi2WO6 using acidic carbon additives

Carmona, RJ; Velasco, LF; Hidalgo, MC; Navio, JA; Ania, CO

We have explored the role of the physicohemical properties of carbon materials as additives to bismuth tungstate on its structure, optical properties, and photocatalytic activity for the degradation of rhodamine B under visible light. For this purpose, C/Bi2WO6 hybrid composites were prepared following two different routes: (i) physical mixture of the catalyst components, and (ii) one-pot hydrothermal synthesis of the semiconductor in the presence of the carbon additive. Three carbons with different properties were selected as additives: biomass-derived activated carbon, carbon nanotubes and carbon spheres obtained from polysaccharides. Data has shown the outstanding role of the acidic/basic nature of the carbon additive, and of the synthetic method on the photocatalytic performance of the resulting composites. For a given additive, the degradation rate of RhB is greatly improved for the catalysts prepared through a one-step hydrothermal synthesis, where there is low shielding effect of the carbon matrix. Carbon additives of acidic nature boost the surface acidity of the hybrid photocatalyst, thereby enhancing the photodegradation of RhB under visible light via a coupled mechanism (photosensitization, semiconductor photocatalysis and carbon-photon mediated reactions).

Applied Catalysis A-General, 505 (2015) 467-477 | DOI: 10.1016/j.apcata.2015.05.011

Mono and bimetallic Cu-Ni structured catalysts for the water gas shift reaction

O. Arbeláez, T.R. Reina, S. Ivanova, F. Bustamante, A.L. Villa, M.A. Centeno, J.A. Odriozola

The water-gas shift (WGS) reaction over structured Cu, Ni, and bimetallic Cu-Ni supported on active carbon (AC) catalysts was investigated. The structured catalysts were prepared in pellets form and applied in the medium range WGS reaction. A good activity in the 180–350 °C temperature range was registered being the bimetallic Cu-Ni:2-1/AC catalyst the best catalyst. The presence of Cu mitigates the methanation activity of Ni favoring the shift process. In addition the active carbon gasification reaction was not observed for the Cu-containing catalyst converting the active carbon in a very convenient support for the WGS reaction. The stability of the bimetallic Cu-Ni:2-1/AC catalyst under continuous operation conditions, as well as its tolerance towards start/stop cycles was also evaluated.

Applied Catalysis A-General, 497 (2015) 1-9 | DOI: 10.1016/j.apcata.2015.02.041

A comparative study of Bi2WO6, CeO2, and TiO2 as catalysts for selective photo-oxidation of alcohols to carbonyl compounds

Lopez-Tenllado, FJ; Murcia-Lopez, S; Gomez, DM; Marinas, A; Marinas, JM; Urbano, FJ; Navio, JA; Hidalgo, MC; Gatica, JM

Several semiconductors based on ceria or bismuth tungstate were tested for selective oxidation of alcohols to carbonyl compounds in a search for photocatalysts more selective than TiO2. Gas-phase selective photo-oxidation of propan-2-ol to acetone and liquid-phase transformation of 2-buten-1-ol (crotyl alcohol) to 2-butenal (crotonaldehyde) were studied as test reactions. In both processes the highest selectivities were achieved with Bi2WO6-based solids. Further studies on crotyl alcohol transformation evidenced the lower adsorption of the aldehyde on these systems which could minimize the decrease in crotyl alcohol yield observed for TiO2 or CeO2 at high conversions. Incorporation of titania (5% molar) to the Bi2WO6 system increased the reaction rate significantly whereas the aldehyde yield remained high. 

Applied Catalysis A-General, 505 (2015) 375-381 | DOI: 10.1016/j.apcata.2015.08.013

On the origin of the photocatalytic activity improvement of BIVO4 through rare earth tridoping

Obregon, S; Colon, G

Rare earth (Tm3+/Er3+,Yb3+,Y3+) tri-doped BiVO4 have been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of methylene blue and O-2 evolution reactions. The improved photocatalytic performance has been attained by multiple approach of the overall photocatalytic mechanism. From the structural and morphological characterization it has been stated that the presence of Y3+ induces the stabilization of the tetragonal phase probably due to its substitutional incorporation in the BiVO4 lattice. Moreover, the extensive doping with rare earth ions such as Yb3+ and Er3+/Tm3+ t-BiVO4 evidenced that important structural, electronic changes as well as the luminescence properties were also exalted. Ternary doping clearly prompts the higher photocatalytic activities. A more packed tetragonal structure in conjunction leading to improved charge carriers mobility, with the observed visible and NIR photoactivities of t-BiVO4 could be the responsible of the improved photocatalytic activity under solar-like irradiation.

Applied Catalysis A-General, 501 (2015) 56-62 | DOI: 10.1016/j.apcata.2015.04.032

Glycerol steam reforming on bimetallic NiSn/CeO2-MgO-Al2O3 catalysts: Influence of the support, reaction parameters and deactivation/regeneration processes

Bobadilla, LP; Penkova, A; Alvarez, A; Dominguez, MI; Romero-Sarria, F; Centeno, MA; Odriozola, JA

NiSn bimetallic catalysts supported over Al2O3 modified with different promoter (Mg and/or Ce) were prepared and characterized by powder X-ray diffraction (XRD), N2 sorptometry, and temperature programmed reduction (TPR). Hydrogen production by glycerol steam reforming over these catalysts was investigated. Among the catalysts, NiSn/AlMgCe catalyst shows the highest hydrogen yield as well as the best stability during the reaction. The effect of reaction temperature, water/glycerol molar ratio and space velocity on the glycerol steam reforming over NiSn/AlMgCe were also investigated. Finally, it was verified that the catalyst can be regenerated by oxidation of carbonaceous deposits.

Applied Catalysis A: General, 492 (2015) 38-47 | DOI: 10.1016/j.apcata.2014.12.029

High-temperature deformation of fully-dense fine-grained boron carbide ceramics: Experimental facts and modeling

Moshtaghioun, BM; Garcia, DG; Rodriguez, AD

Boron carbide ceramics are the hardest material in Nature after diamond and the cubic phase of boron nitride. Due to this fact, their room-temperature fracture properties are the object of intense research. Paradoxically, high-temperature deformation is essentially unknown, because very high temperatures and stresses are necessarily required and high-quality specimens have not been available until recently. In this paper, the high-temperature compressive creep of fine-grained boron carbide polycrystals is reported. The breakdown of the classical power-law for high-temperature plasticity in ceramics is found. An analytical model is proposed. The model assumes that deformation is produced by dislocation glide. However, since the formation of twins is energetically favorable in this material and they act as strong barriers for dislocation glide, their motion turns to become progressively more difficult as elongation proceeds. The combination of increasing twin barriers and dislocations in mutual interaction is proposed to be the mechanism for high-temperature plasticity in this material. The model is validated with the experimental results. Final elongation of boron carbide specimens is reported to be over 100%, although this material cannot be described as a superplastic ceramic. 

Materials & Design, 88 (2015) 287-293 | DOI: 10.1016/j.matdes.2015.08.134

Self-Assembling of Tetradecylammonium Chain on Swelling High Charge Micas (Na-Mica-3 and Na-Mica-2): Effect of Alkylammonium Concentration and Mica Layer Charge

Pazos, MC; Cota, A; Osuna, FJ; Pavon, E; Alba, MD

A family of tetradecylammonium micas is synthesized using synthetic swelling micas with high layer charge (NanSi8-nAln,Mg6F4O20 center dot XH2O, where n = 2 and 3) exchanged with tetradecylammonium cations. The molecular arrangement of the surfactant is,elucidated on the basis of XRD patterns and DTA. The ordering conformation of the surfactant molecules into the interlayer space of Micas is investigated by IR/FT, C-13, Al-27, and Si-29 MAS NMR. The structural arrangement of the tetradecylammonium cation in the interlayer space of high-charge micas is more sensitive to the effect of the mica layer charge at high concentration. The surfactant arrangement is found to follow the bilayer-paraffin model for all values of layer charge and surfactant concentration. However, at initial concentration below the mica CEC, a lateral monolayer is also observed. The amount of ordered conformation all-trans is directly proportional to the layer charge and surfactant concentration.

Langmuir, 31 (2015) 4394-4401 | DOI: 10.1021/acs.langmuir.5b00224

Ultraviolet Pretreatment of Titanium Dioxide and Tin-Doped Indium Oxide Surfaces as a Promoter of the Adsorption of Organic Molecules in Dry Deposition Processes: Light Patterning of Organic Nanowires

Oulad-Zian, Y; Sanchez-Valencia, JR; Parra-Barranco, J; Hamad, S; Espinos, JP; Barranco, A; Ferrer, J; Coll, M; Borras, A

In this article we present the preactivation of TiO2 and ITO by UV irradiation under ambient conditions as a tool to enhance the incorporation of organic molecules on these oxides by evaporation at low pressures. The deposition of p-stacked molecules on TiO2 and ITO at controlled substrate temperature and in the presence of Ar is thoroughly followed by SEM, UV-vis, XRD, RBS, and photoluminescence spectroscopy, and the effect is exploited for the patterning formation of small-molecule organic nanowires (ONWs). X-ray photoelectron spectroscopy (XPS) in situ experiments and molecular dynamics simulations add critical information to fully elucidate the mechanism behind the increase in the number of adsorption centers for the organic molecules. Finally, the formation of hybrid organic/inorganic semiconductors is also explored as a result of the controlled vacuum sublimation of organic molecules on the open thin film microstructure of mesoporous TiO2.

Langmuir, 31 (2015) 8294-8302 | DOI: 10.1021/acs.langmuir.5b01572

A novel two-steps solvothermal synthesis of nanosized BiPO4 with enhanced photocatalytic activity

Zhang, YF; Sillanpaa, M; Obregon, S; Colon, G

Nano-sized BiPO4 has been successfully synthesized via a novel designed two-steps solvothermal route using ethylene glycol as solvent. Comparing with traditional hydrothermal method, the novel approach could readily prepare BiPO4 with shorter time. The photocatalytic activity of prepared BiPO4 has been tested via degradation of methylene blue (MB) under light irradiation. The experimental results show that the BiPO4 prepared by novel route had enhanced photocatalytic activity and the synthetic parameters also impact the reaction rate meaningfully. Finally, the obtained samples have been widely characterized by means of powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy (SEM), UV–vis diffuse reflectance spectra (DRS) and Fourier transformed infrared (FTIR) spectra. BiPO4 prepared by this novel approach have a particles size below 100 nm, which is a big improvement by comparing with previous works (few micrometer). The effect of EG during the formation of BiPO4 has been discussed and a possible formation mechanism is proposed.
 

Journal of Molecular Catalysis A-Chemical, 402 (2015) 92-99 | DOI: 10.1016/j.molcata.2015.03.011

Core-shell polydopamine magnetic nanoparticles as sorbent in micro-dispersive solid-phase extraction for the determination of estrogenic compounds in water samples prior to high-performance liquid chromatography-mass spectrometry analysis

Socas-Rodriguez, B; Hernandez-Borges, J; Salazar, P; Martin, M; Rodriguez-Delgado, MA

In this work, core-shell Fe3O4@poly(dopamine) magnetic nanoparticles (m-NPs) were prepared and characterized in our laboratory and applied as sorbents for the magnetic-micro solid phase extraction (m-mu SPE) of twelve estrogenic compounds of interest (i.e. 17 alpha-estradiol, 17 beta-estradiol, estrone, hexestrol, 17 alpha-ethynylestradiol, diethylstibestrol, dienestrol, zearalenone, alpha-zearalanol,beta-zearalanol, alpha-zearalenol and beta-zearalenol) from different water samples. Separation, determination and quantification were achieved by high-performance liquid chromatography coupled to ion trap mass spectrometry with electrospray ionization. NPs@poly(dopamine) were synthesized by a chemical coprecipitation procedure and characterized by different surface characterization techniques (X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, transmission and scanning electron microscopy, infrared and Raman spectroscopy, vibrating sample magnetometry, microelectrophoresis and adsorption/desorption isotherms). Parameters affecting the extraction efficiency of m-mu SPE (i.e. polymerization time, pH of the sample, extraction and elution conditions) were studied and optimized. The methodology was validated for Milli-Q, mineral, tap and wastewater using 2-methoxyestradiol as internal standard, obtaining recoveries ranging from 70 to 119% with relative standard deviation values lower than 20% and limits of quantification in the range 0.02-1.1 mu g/L.

Journal of Chromatography A, 1397 (2015) 1-10 | DOI: 10.1016/j.chroma.2015.04.010

Morphological changes on graphene nanoplatelets induced during dispersion into an epoxy resin by different methods

Moriche, R; Prolongo, SG; Sanchez, M; Jimenez-Suarez, A; Sayagues, MJ; Urena, A

A structural analysis demonstrating how the manufacturing method of graphene nanoplatelets (GNPs) into a polymer matrix can strongly modify the GNPs morphology and, consequently, their properties, was carried out. Three different methods based on sonication and high shear forces were used to elucidate defects induction and possible size diminution. Manufacturing methods including high shear forces caused the extension of the GNPs while sonication induces wrinkling of the sheets. Residual stresses are induced in the nanoplatelets structure showing an increase in the Raman intensities ratios I-D/I-G and I-D/I-G when a major cycles number of calendering are applied.

Composites Part B-Engineering, 72 (2015) 199-205 | DOI: 10.1016/j.compositesb.2014.12.012

BaGa4O7, a new A3BC10O20 crystalline phase: synthesis, structural determination and luminescence properties

Boyer, Marina; Veron, Emmanuel; Becerro, Ana Isabel; Porcher, Florence; Suchomel, Matthew R.; Matzen, Guy; Allix, Mathieu

The synthesis, structural determination and luminescence properties of a new barium gallate, BaGa4O7, are reported. This crystalline material can uniquely be obtained by direct cooling from the molten state. The crystallographic structure was determined using a combination of electron, synchrotron and neutron powder diffraction data. BaGa4O7 crystallizes in the monoclinic I2/mspace group with a = 15.0688(1) Å, b = 11.7091(1) Å, c = 5.1429(2) Å and β = 91.0452(2)° and can be described as an original member of the A3BC10O20 family. Atypical for this A3BC10O20structural framework, BaGa4O7 is found to contain exclusively divalent and trivalent cations. In order to maintain overall electroneutrality, disordered defect-type partial substitution of gallium and oxygen ions on barium sites occurs within the pentagonal channels of BaGa4O7. Thanks to the flexibility of this structural framework, BaGa4O7 can be heavily doped with europium and thus is shown to exhibit strong orange-red luminescence emission at 618 nm under 393 nm excitation.

CrystEngComm, 17 (2015) 6127-6135 | DOI: 10.1039/C5CE01101A

Effective photoreduction of a nitroaromatic environmental endocrine disruptor by AgNPs functionalized on nanocrystalline TiO2

Hernandez-Gordillo, A; Obregon, S; Paraguay-Delgadod, F; Rodriguez-Gonzalez, V

Unprecedented photoactivity of silver nanoparticles photodeposited on nanocrystalline TiO2 for the efficient reduction of 4-nitrophenol at room temperature is reported. The use of Na2SO3 as a harmless scavenger agent for the reduction of a nitroaromatic endocrine disruptor yields a valuable 4-aminophenol reagent.

RSC Advances, 5 (2015) 15194-15197 | DOI: 10.1039/c5ra00094g

A new model of the carbonator reactor in the calcium looping technology for post-combustion CO2 capture

Ortiz, C; Chacartegui, R; Valverde, JM; Becerra, JA; Perez-Maqueda, LA

The Ca-Looping (CaL) process is considered as a promising technology for CO2 post-combustion capture in power generation plants yielding a minor penalty on plant performance as compared with other capture technologies such as conventional amine-based capture systems. This manuscript presents a new carbonator reactor model based on lab-scale multicyclic CaO conversion results, which take into account realistic CaO regeneration conditions that necessarily involve calcination under high CO2 partial pressure and high temperature. Under these conditions, CaO conversion in the diffusion controlled stage is a relevant contribution to the carbonation degree during typical residence times. The main novelty of the model proposed in the present work is the consideration of the capture efficiency in the diffusion controlled phase of carbonation. It is demonstrated that increasing the residence time by a few minutes in the carbonator yields a significant improvement of the capture efficiency. Model predictions are shown to agree with experimental results retrieved from pilot-scale tests. The new model allows a more accurate evaluation and prediction of carbonator’s performance over a wider range of residence times. The results obtained may be relevant for the optimization of CaL operation parameters to be used in real power plants.

Fuel, 160 (2015) 328-338 | DOI: 10.1016/j.fuel.2015.07.095

STEM-EELS analysis reveals stable highdensity He in nanopores of amorphous silicon coatings deposited by magnetron sputtering

Schierholz, Roland; Lacroix, Bertrand; Godinho, Vanda; Caballero-Hernandez, Jaime; Duchamp, Martial; Fernandez, Asuncion

A broad interest has been showed recently on the study of nanostructuring of thin films and surfaces obtained by low-energy He plasma treatments and He incorporation via magnetron sputtering. In this paper spatially resolved electron energy-loss spectroscopy in a scanning transmission electron microscope is used to locate and characterize the He state in nanoporous amorphous silicon coatings deposited by magnetron sputtering. A dedicated MATLAB program was developed to quantify the helium density inside individual pores based on the energy position shift or peak intensity of the He K-edge. A good agreement was observed between the high density (~35–60 at nm−3) and pressure (0.3–1.0 GPa) values obtained in nanoscale analysis and the values derived from macroscopic measurements (the composition obtained by proton backscattering spectroscopy coupled to the macroscopic porosity estimated from ellipsometry). This work provides new insights into these novel porous coatings, providing evidence of high-density He located inside the pores and validating the methodology applied here to characterize the formation of pores filled with the helium process gas during deposition. A similar stabilization of condensed He bubbles has been previously demonstrated by high-energy He ion implantation in metals and is newly demonstrated here using a widely employed methodology, magnetron sputtering, for achieving coatings with a high density of homogeneously distributed pores and He storage capacities as high as 21 at%.

Nanotechnology, 26 (2015) 075703 | DOI: 10.1088/0957-4484/26/7/075703

Single-step fabrication process of 1-D photonic crystals coupled to nanocolumnar TiO2 layers to improve DSC efficiency

Gonzalez-Garcia, L; Colodrero, S; Miguez, H; Gonzalez-Elipe, AR

The present work proposes the use of a TiO2 electrode coupled to a one-dimensional photonic crystal (1DPC), all formed by the sequential deposition of nanocolumnar thin films by physical vapor oblique angle deposition (PV-OAD), to enhance the optical and electrical performance of DSCs while transparency is preserved. We demonstrate that this approach allows building an architecture combining a non-dispersive 3 µm of TiO2 electrode and 1 µm TiO2-SiO2 1DPC, both columnar, in a single-step process. The incorporation of the photonic structure is responsible for a rise of 30% in photovoltaic efficiency, as compared with a transparent cell with a single TiO2 electrode. Detailed analysis of the spectral dependence of the photocurrent demonstrates that the 1DPC improves light harvesting efficiency by both back reflection and optical cavity modes confinement within the TiO2 films, thus increasing the overall performance of the cell.

Optics Express, 23 (2015) A1642-A1650 | DOI: 10.1364/OE.23.0A1642

Active vacuum brazing of CNT films to metal substrates for superior electron field emission performance

Longtin, R; Sanchez-Valencia, JR; Shorubalko, I; Furrer, R; Hack, E; Elsener, H; Groning, O; Greenwood, P; Rupesinghe, N; Teo, K; Leinenbach, C; Groning, P

The joining of macroscopic films of vertically aligned multiwalled carbon nanotubes (CNTs) to titanium substrates is demonstrated by active vacuum brazing at 820 degrees C with a Ag-Cu-Ti alloy and at 880 degrees C with a Cu-Sn-Ti-Zr alloy. The brazing methodology was elaborated in order to enable the production of highly electrically and thermally conductive CNT/metal substrate contacts. The interfacial electrical resistances of the joints were measured to be as low as 0.35 Omega. The improved interfacial transport properties in the brazed films lead to superior electron fieldemission properties when compared to the as-grown films. An emission current of 150 mu A was drawn from the brazed nanotubes at an applied electric field of 0.6 V mu m(-1). The improvement in electron field-emission is mainly attributed to the reduction of the contact resistance between the nanotubes and the substrate. The joints have high re-melting temperatures up to the solidus temperatures of the alloys; far greater than what is achievable with standard solders, thus expanding the application potential of CNT films to high-current and high-power applications where substantial frictional or resistive heating is expected.

Science and Technology of Advanced Materials, 16 (2015) 015005 (11 pp) | DOI: 10.1088/1468-6996/16/1/015005

Synthesis temperature effect on Na-Mica-4 crystallinity and heteroatom distribution

Naranjo, M; Castro, MA; Cota, A; Osuna, FJ; Pavon, E; Alba, MD

The discovery of swelling brittle mica, Na-Mica-4, has been one of the most significant advances in the pursuit for a material with high ion-exchange capacity. For technical applications, the control of the phase evolution during the synthesis is crucial. The main aim of this study was to investigate the effect of Na-Mica-4 synthesis temperature on the crystalline phase evolution, Si–Al distribution in the tetrahedral sheet, the Al occupancy between tetrahedral and octahedral sites and their effects on the interlayer space composition. The synthesis temperature range between 600 °C and 900 °C was explored. At low temperature (600 °C), the precursors were transformed in a low-charged swelling 2:1 phyllosilicate, saponite type, which was progressively aluminum enriched with temperature. The high-charged swelling mica was completely formed at 700 °C, although a minor anhydrous contribution remained up to 850 °C. Up to 800 °C, silicates and fluorides secondary phases were detected as a minor contribution.

Microporous and Mesoporous Materials, 204 (2015) 282-288 | DOI: 10.1016/j.micromeso.2014.11.026

Quick synthesis, functionalization and properties of uniform, luminescent LuPO4-based nanoparticles

Becerro, AI; Ocana, M

The aim of this study was to find a surfactant-free method for the synthesis of uniform Eu:LuPO4nanophosphors which are able to form stable colloidal suspensions in aqueous media. Uniform, ovoid Eu-doped LuPO4 fluorescent nanoparticles were obtained after aging for 30 minutes at 180 °C a butylene glycol solution containing, exclusively, lutetium acetate, europium acetate and H3PO4. XRD and digital diffraction patterns of HRTEM images suggested that the particles were single crystalline in nature with the c-axis of the unit cell parallel to the long particle axis. The luminescence study revealed that the optimum doping level was 5 molar%. The latter particles (85 nm × 40 nm dimensions) were functionalized with polyacrylic acid and their colloidal stability in two different biological buffers was demonstrated to persist for at least 15 days.

RSC Advances, 44 (2015) 34517-34524 | DOI: 10.1039/C5RA05305F

The role of silver nanoparticles functionalized on TiO2 for photocatalytic disinfection of harmful algae

Lee, Soo-Wohn; Obregon, S.; Rodriguez-Gonzalez, V.

Silver loaded TiO2 samples were prepared by photodeposition of different amounts of Ag+ ions over commercial titanium dioxide (Evonik TiO2 P25) in aqueous media without the presence of sacrificial agents. The obtained photocatalysts were characterized by several techniques such as X-ray powder diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) in order to correlate the effect of the silver amount on the photocatalytic properties of the final nanocomposite. The effect of the silver nanoparticles on the photocatalytic behaviour of TiO2 was evaluated by means of the photodegradation of methyl orange dye and the inactivation of noxious algae Tetraselmis suecicaand Amphidium carterae under continuous exposure of low power irradiation UV-light. The sample with 1.5% wt of silver nanoparticles showed the highest photocatalytic elimination of the azo dye and both algae types. According to the results, the cells were deformed during the photocatalytic process by the attack of highly reactive species such as hydroxyl radicals, H2O2 and superoxide ions generated on the TiO2 surface. The algae cells were not regenerated by themselves after the photocatalytic process due the high degree of fragmentation that they suffered during the light irradiation.

RSC Advances, 5 (2015) 44470-44475 | DOI: 10.1039/C5RA08313C

Island-type growth of Au–Pt heterodimers: direct visualization of misfit dislocations and strain-relief mechanisms

Garcia-Negrete, CA; Knappett, BR; Schmidt, FP; Rojas, TC; Wheatley, AEH; Hofer, F; Fernandez, A

Structural and analytical characterization related to the formation mechanism of Au–Pt heterodimers from polyhedral Pt nanocrystals is reported. The observation of specific lattice strain effects and the emergence of misfit dislocations point to the relevance of the Stranski–Krastanov growth mode as a means of explaining the previously reported dimerisation reaction between Au and Pt. Two size-dependent strain relief mechanisms were identified. For dimers grown from 4.7 nm seeds, the mechanism is related to bulk lattice strain accumulation at {111} planes along with lattice relaxation effects on other crystalline planes. However, for dimers grown from 11.2 nm seed sizes, the formation of misfit dislocations proved to be a highly efficient mechanism by which to release interface mismatch strain. Nanoscale chemical mapping at Au–Pt interfaces also revealed Au–Pt alloying to be unlikely under the mild temperature conditions employed in this work for Au–Pt heterodimer synthesis.

RSC Advances, 5 (2015) 55262-55268 | DOI: 10.1039/C5RA09808D

Synergistic strategies for the preparation of highly efficient dye-sensitized solar cells on plastic substrates: combination of chemical and physical sintering

Li, Y; Yoo, K; Lee, DK; Kim, JY; Son, HJ; Kim, JH; Lee, CH; Miguez, H; Ko, MJ

Preparation of well-interconnected TiO2 electrodes at low temperature is critical for the fabrication of highly efficient dye-sensitized solar cells (DSCs) on plastic substrates. Herein we explore a synergistic approach using a combination of chemical and physical sintering. We formulate a binder-free TiO2 paste based on “nanoglue” as the chemical sintering agent, and use it to construct a photoelectrode on plastic by low-temperature physical compression to further improve the connectivity of TiO2 films. We systematically investigated the factors affecting the photovoltaic performance and found the conditions to achieve electron diffusion lengths as long as 25 μm and charge collection efficiencies as high as 95%, as electrochemical impedance spectroscopy measurements indicate. We apply this approach to obtain a DSC deposited on plastic displaying 6.4% power conversion efficiency based on commercial P25 titania particles.

RSC Advances, 5 (2015) 76795-76803 | DOI: 10.1039/C5RA10290A

Porous, robust highly conducting Ni-YSZ thin film anodes prepared by magnetron sputtering at oblique angles for application as anodes and buffer layers in solid oxide fuel cells

Garcia-Garcia, Francisco J.; Yubero, Francisco; Gonzalez-Elipe, Agustin R.; Balomenou, Stella P.; Tsiplakides, Dimitris; Petrakopoulou, Ioanna; Lambert, Richard M.

Uniform, highly porous, columnar thin films incorporating YSZ and NiO prepared by magnetron sputtering with deposition at glancing incidence exhibited stoichiometries close to that of the Y-Zr-Ni sputter target. Characterization by means of SEM, XRD, XPS and RBS revealed that the uniformly distributed nickel component in the as-deposited films consisted of NiO, and that the YSZ component was essentially amorphous. Annealing such films at 850 degrees C in hydrogen resulted in crystallization of the YSZ phase with preservation of the columnar morphology, while the NiO underwent reduction to metallic Ni, which partially segregated to the film surface. The hydrogen-annealed thin film anodes exhibited high conductivity, comparable to that of conventionally-prepared anodes, in both hydrogen and hydrogen/water mixtures at temperatures relevant to SOFC operation. They were also robust against strain-induced separation from the substrate under limited thermal cycling in both oxidizing and reducing atmospheres and are promising candidates for use as anodes in their own right and as strain-accommodating buffer layers between conventional anodes and the electrolyte for use in SOFC applications.

Inernational Journal of Hydrogen Energy, 40 (2015) 7382-7387 | DOI: 10.1016/j.ijhydene.2015.04.001

Catalytic screening of Au/CeO2-MOx/Al2O3 catalysts (M = La, Ni, Cu, Fe, Cr, Y) in the CO-PrOx reaction

Reina, TR; Ivanova, S; Centeno, MA; Odriozola, JA

In this work, a series of Au/CeO2-MOx/Al2O3 catalysts has been prepared and evaluated in the PrOx reaction. Within the series of dopants Fe and Cu containing samples enhanced the catalytic performance of the parent Au/CeO2/Al2O3 catalyst being copper the most efficient promoter. For both samples an enhanced oxygen storage capacity (OSC) is registered and accounts for the high CO oxidation activity. More particularly, the Au/CeO2-CuOx/Al2O3 catalyst successfully withstands the inclusion of water in the PrOx stream and presents good results in terms of CO elimination. However to achieve a good selectivity toward, CO2 formation properly adjusting of the reaction parameters, such as oxygen concentration and space velocity is needed. Within the whole screened series the Cu-containing catalyst can be considered as the most interesting alternative for H-2 clean-up applications.

International Journal of Hydrogen Energy, 40 (2015) 1782-1788 | DOI: 10.1016/j.ijhydene.2014.11.141

Hydrogen production through sodium borohydride ethanolysis

Arzac, GM; Fernandez, A

In this work, sodium borohydride (SB) ethanolysis was explored for the first time as a method to generate hydrogen for Polymer Exchange Membrane Fuel Cells. Ethanolysis by-product was characterized by Fourier Transform Infrared Spectroscopy, X-Ray Diffraction, and Nuclear Magnetic Resonance. Metal and acid catalysts were tested. RuCl3 center dot 3H(2)O was the best metal catalyst. Acetic acid was selected for the study because of its effectiveness, low cost and relative greenness. The maximum gravimetric hydrogen density obtained was 2.1% wt. The addition of water produces an increase in hydrogen generation rate and a decrease in conversion. The use of ethanol-methanol mixtures produces an increase in reaction rates in absence of catalyst. As a proof of concept the reaction was performed in a small reactor which operates by the addition of ethanolic acetic acid solutions to solid SB (in the form of granules). The reactor produces stable and constant hydrogen generation in the range of 20-80 ml min(-1) during 1 h at constant temperature (around 27-35 degrees.

International Journal of Hydrogen Energy, 40 (2015) 5326-5332 | DOI: 10.1016/j.ijhydene.2015.01.115

Synthesis of a nanosilica supported CO2 sorbent in a fluidized bed reactor

Soria-Hoyo, C; Valverde, JM; van Ommen, JR; Sanchez-Jimenez, PE; Perez-Maqueda, LA; Sayagues, MJ

CaO has been deposited on a nanosilica powder matrix by a procedure based on atomic layer deposition (ALD) in a fluidized bed reactor at atmospheric pressure following a potentially scalable process. In previous works ALD in gas fluidized bed has been mostly performed under reduced pressure, which hampers scaling-up the production technology. The material synthesized in the present work is tested as CO2 solid sorbent at calcium looping conditions. Multicyclic thermogravimetric analysis (TGA) shows that the nanosilica support stabilizes the capture capacity of CaO. EDX-STEM analysis illustrates the presence of Ca well distributed on the surface of the SiO2 nanoparticles.

Applied Surface Science, 328 (2015) 548-553 | DOI: 10.1016/j.apsusc.2014.12.106

High N-content a-C:N films elaborated by femtosecond PLD with plasma assistance

Maddi, C; Donnet, C; Loir, AS; Tite, T; Barnier, V; Rojas, TC; Sanchez-Lopez, JC; Wolski, K; Garrelie, F

Amorphous carbon nitride (a-C:N) thin films are a interesting class of carbon-based electrode materials. Therefore, synthesis and characterization of these materials have found lot of interest in environmental analytical microsystems. Herein, we report the nitrogen-doped amorphous carbon thin film elaboration by femtosecond pulsed laser deposition (fs-PLD) both with and without a plasma assistance. The chemical composition and atomic bonding configuration of the films were investigated by multi-wavelength (MW) Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS). The highest nitrogen content, 28 at.%, was obtained with plasma assistance. The I(D)/I(G) ratio and the G peak position increased as a function of nitrogen concentration, whereas the dispersion and full width at half maximum (FWHM) of G peak decreased. This indicates more ordered graphitic like structures in the films both in terms of topological and structural, depending on the nitrogen content. EELS investigations were correlated with MW Raman results. The interpretation of XPS spectra of carbon nitride films remains a challenge. Plasma assisted PLD in the femtosecond regime led to a significant high nitrogen concentration, which is highlighted on the basis of collisional processes in the carbon plasma plume interacting with the nitrogen plasma.

Applied Surface Science, 332 (2015) 346-353 | DOI: 10.1016/j.apsusc.2015.01.123

Optical properties of zirconium oxynitride films: The effect of composition, electronic and crystalline structures

Carvalho, P; Borges, J; Rodrigues, MS; Barradas, NP; Alves, E; Espinos, JP; Gonzalez-Elipe, AR; Cunha, L; Marques, L; Vasilevskiy, MI; Vaz, F

This work is devoted to the investigation of zirconium oxynitride (ZrOxNy) films with varied optical responses prompted by the variations in their compositional and structural properties. The films were prepared by dc reactive magnetron sputtering of Zr, using Ar and a reactive gas mixture of N-2 + O-2 ( 17:3). The colour of the films changed from metallic-like, very bright yellow-pale and golden yellow, for low gas flows to red-brownish for intermediate gas flows. Associated to this colour change there was a significant decrease of brightness. With further increase of the reactive gas flow, the colour of the samples changed from red-brownish to dark blue or even to interference colourations. The variations in composition disclosed the existence of four different zones, which were found to be closely related with the variations in the crystalline structure. XRD analysis revealed the change from a B1 NaCl face-centred cubic zirconium nitride-type phase for films prepared with low reactive gas flows, towards a poorly crystallized over-stoichiometric nitride phase, which may be similar to that of Zr3N4 with some probable oxygen inclusions within nitrogen positions, for films prepared with intermediate reactive gas flows. For high reactive gas flows, the films developed an oxynitride-type phase, similar to that of gamma-Zr2ON2 with some oxygen atoms occupying some of the nitrogen positions, evolving to a ZrO2 monoclinic type structure within the zone where films were prepared with relatively high reactive gas flows. The analysis carried out by reflected electron energy loss spectroscopy (REELS) revealed a continuous depopulation of the d-band and an opening of an energy gap between the valence band (2p) and the Fermi level close to 5 eV. The ZrN-based coatings (zone land II) presented intrinsic colourations, with a decrease in brightness and a colour change from bright yellow to golden yellow, red brownish and dark blue. Associated to these changes, there was also a shift of the reflectivity minimum to lower energies, with the increase of the non-metallic content. The samples lying in the two last zones (zone III, oxynitride and zone IV, oxide films) revealed a typical semi-transparent-optical behaviour showing interference-like colourations only due to the complete depopulation of the d band at the Fermi level. The samples lying in these zones presented also an increase of the optical bandgap from 2 to 3.6 eV. 

Applied Surface Science, 358 (2015) 660-669 | DOI: 10.1016/j.apsusc.2015.09.129

Role of Y in the oxidation resistance of CrAlYN coatings

Dominguez-Meister, S; El Mrabet, S; Escobar-Galindo, R; Mariscal, A; de Haro, CJ; Justo, A; Brizuela, M; Rojas, TC; Sanchez-Lopez, JC

CrAlYN coatings with different aluminum (4–12 at.%) and yttrium (2–5 at.%) contents are deposited by d.c. reactive magnetron sputtering on silicon and M2 steel substrates using metallic targets and Ar/N2 mixtures. The influence of the nanostructure and chemical elemental distribution on the oxidation resistance after heating in air at 1000 °C is studied by means of cross-sectional scanning electron microscopy (X-SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and glow discharge optical emission spectroscopy (GD-OES). The sequential exposure to the metallic targets during the synthesis leads to a multilayer structure where concentration of metallic elements (Cr, Al and Y) is changing periodically. A good oxidation resistance is observed when Al- and Y-rich regions are separated by well-defined CrN layers, maintaining crystalline coherence along the columnar structure. This protective behavior is independent of the type of substrate and corresponds to the formation of a thin mixed (Al, Cr)-oxide scale that protects the film underneath. The GD-OES and XRD analysis have demonstrated that Y acts as a reactive element, blocking the Fe and C atoms diffusion from the steel and favoring higher Al/Cr ratio in the passivation layer after heating. The coating with Y content around 4 at.% exhibited the best performance with a thinner oxide scale, a delay in the CrN decomposition and transformation to Cr2N, and a more effective Fe and C blocking.

Applied Surface Science, 363 (2015) 504-511 | DOI: 10.1016/j.apsusc.2015.06.099

Pectin-Lipid Self-Assembly: Influence on the Formation of Polyhydroxy Fatty Acids Nanoparticles

Guzman-Puyol, Susana; Jesus Benitez, Jose; Dominguez, Eva; Bayer, Ilker Sefik; Cingolani, Roberto; Athanassiou, Athanassia; Heredia, Antonio; Heredia-Guerrero, Jose Alejandro

Nanoparticles, named cutinsomes, have been prepared from aleuritic (9,10,16-trihidroxipalmitic) acid and tomato fruit cutin monomers (a mixture of mainly 9(10), 16-dihydroxypalmitic acid (85%, w/w) and 16-hydroxyhexadecanoic acid (7.5%, w/w)) with pectin in aqueous solution. The process of formation of the nanoparticles of aleuritic acid plus pectin has been monitored by UV-Vis spectrophotometry, while their chemical and morphological characterization was analyzed by ATR-FTIR, TEM, and non-contact AFM. The structure of these nanoparticles can be described as a lipid core with a pectin shell. Pectin facilitated the formation of nanoparticles, by inducing their aggregation in branched chains and favoring the condensation between lipid monomers. Also, pectin determined the self-assembly of cutinsomes on highly ordered pyrolytic graphite (HOPG) surfaces, causing their opening and forming interconnected structures. In the case of cutin monomers, the nanoparticles are fused, and the condensation of the hydroxy fatty acids is strongly affected by the presence of the polysaccharide. The interaction of pectin with polyhydroxylated fatty acids could be related to an initial step in the formation of the plant biopolyester cutin.

Plos One, 10 (2015) e0124639 | DOI: 10.1371/journal.pone.0124639

Template-free synthesis and luminescent properties of hollow Ln:YOF (Ln = Eu or Er plus Yb) microspheres

Martinez-Castro, E; Garcia-Sevillano, J; Cusso, F; Ocana, M

A method for the synthesis of hollow lanthanide doped yttrium oxyfluoride (YOF) spheres in the micrometer size range with cubic structure based on the pyrolysis at 600 degrees C of liquid aerosols generated from aqueous solutions containing the corresponding rare earth chlorides and trifluoroacetic acid has been developed. This procedure, which has been used for the first time for the synthesis of YFO based materials, is simpler and advantageous when compared with other methods usually employed for the production of hollow spheres since it does not require the use of sacrificial templates. In addition, it is continuous, which is desirable because of practical reasons. The procedure is also suitable for doping the YOF spheres with europium cations resulting in down converting red phosphors when activated with UV light, or for co-doping with both Er3+ and Yb3+ giving rise to up-converting phosphors, which emit intense red light under near infrared (NIR) irradiation. Because of their optical properties and hollow architecture, the developed materials may find applications in optoelectronic devices and biotechnology. 

Journal of Alloys and Compounds, 619 (2015) 44-51 | DOI: 10.1016/j.jallcom.2014.09.023

Ni-CeO2/C Catalysts with Enhanced OSC for the WGS Reaction

Pastor-Perez, L; Ramirez Reina, T; Ivanova, S; Centeno, MA; Odriozola, JA; Sepulveda-Escribano, A

In this work, the WGS performance of a conventional Ni/CeO2 bulk catalyst is compared to that of a carbon-supported Ni-CeO2 catalyst. The carbon-supported sample resulted to be much more active than the bulk one. The higher activity of the Ni-CeO2/C catalyst is associated to its oxygen storage capacity, a parameter that strongly influences the WGS behavior. The stability of the carbon-supported catalyst under realistic operation conditions is also a subject of this paper. In summary, our study represents an approach towards a new generation of Ni-ceria based catalyst for the pure hydrogen production via WGS. The dispersion of ceria nanoparticles on an activated carbon support drives to improved catalytic skills with a considerable reduction of the amount of ceria in the catalyst formulation.

Catalysts, 5 (2015) 298-309 | DOI: 10.3390/catal5010298

Preparation of phase pure, dense fine grained ceramics by conventional and spark plasma sintering of La-substituted BiFeO3 nanoparticles

Perejon, Antonio; Sanchez-Jimenez, Pedro E.; Poyato, Rosalia; Maso, Nahum; West, Anthony R.; Criado, Jose M.; Perez-Maqueda, Luis A.

High density ceramics of the system Bi1-xLaxFeO3, 0 <= x <= 0.15, have been prepared starting from nanoparticles obtained by mechanosynthesis. The ceramics have been sintered conventionally at 850 degrees C and by spark plasma sintering (SPS). Sintering conditions have been optimized to obtain single phase ceramics, and the microstructure of the ceramics has been compared. Ceramics prepared conventionally present grain sizes from 5 mu m to less than 1 mu m, whereas grain sizes by SPS are in the range from 50 to 100 nm, which demonstrates that it is possible to obtain nanostructured ceramics of La-substituted BiFeO3 using mechanosynthesis followed by SPS at low temperature (625-650 degrees C). The as-prepared SPS ceramics show low resistivity, indicating some reduction in the samples. However, after an oxidative anneal in air, ceramics are highly insulating at room temperature and electrically homogeneous. The high quality of the ceramics has also been demonstrated by XRD, EDX, Raman and DSC.

Journal of the European Ceramic Society, 35 (2015) 2283-2293 | DOI: 10.1016/j.jeurceramsoc.2015.01.030

Mechanical and electrical properties of low SWNT content 3YTZP composites

Poyato, R; Macias-Delgado, J; Garcia-Valenzuela, A; Gallardo-Lopez, A; Morales-Rodriguez, A; Munoz, A; Dominguez-Rodriguez, A

Fully dense 3 mol% Y2O3-ZrO2 (3YTZP) composites with low single wall carbon nanotube content (0.5, 1 and 1.5 vol% SWNT) were prepared by colloidal processing and spark plasma sintering (SPS). SWNT were distributed at ceramic grain boundaries and also into agglomerates. Characterization of SWNT agglomerates indicated that increase in SWNT vol% does not imply an increase in agglomeration. SWNT agglomerate density was related to the evolution of hardness and fracture toughness with SWNT vol%. Electrical properties of the composites were characterized in a wide temperature range, and percolation threshold was estimated. A model allowing separation of the individual SWNT bundles contribution to resistance from the resistance due to junctions between bundles was proposed for composites with a percolating SWNT network.

Journal of the European Ceramic Society, 35 (2015) 2351-2359 | DOI: 10.1016/j.jeurceramsoc.2015.02.022

Ceramics from the Alcazar Palace in Seville (Spain) dated between the 11th and 15th centuries: Compositions, technological features and degradation processes

Garofano, I; Robador, MD; Perez-Rodriguez, JL; Castaing, J; Pacheco, C; Duran, A

For the purpose of chemical characterization, a selection of 29 ceramic fragments from the 11th to 15th century has been made from materials excavated in the Seville Alcazar Palace. The PIXE elemental analysis results indicated that the ceramic bodies can be divided into four groups. The XRD identification of the phases present in the bodies revealed differences in the firing temperatures. The PIXE analysis of the glazes revealed variable PbO and SnO2 contents. The latter component was not detected in all the glazes. Cu, Co, Mn, Fe and Sb elements were associated with green, blue, black and yellow colours, respectively. Some glazes were covered by iridescent layers constituted by lead carbonate and phosphates due to alteration of the glazes. It was also possible to detail the microstructure and composition of the ultimate surface layers responsible for the lustre effect observed in two of the ceramic samples using PIXE and Rutherford backscattering spectrometry (RBS).

Journal of the European Ceramic Society, 35 (2015) 4307-4319 | DOI: 10.1016/j.jeurceramsoc.2015.07.033

Biotribological behavior of Ag–ZrCxN1−x coatings against UHMWPE for joint prostheses devices

Calderon, SV; Sanchez-Lopez, JC; Cavaleiro, A; Carvalho, S

This study aims to evaluate the structural, mechanical and tribological properties of zirconium carbonitrides (ZrCxN1−x) coatings with embedded silver nanoparticles, produced with the intention of achieving a material with enhanced multi-functional properties, including mechanical strength, corrosion resistance, tribological performance and antibacterial behavior suitable for their use in joint prostheses. The coatings were deposited by direct current (DC) reactive magnetron sputtering onto 316 L stainless steel, changing the silver content from 0 to 20 at% by modifying the current density applied to the targets. Different nitrogen and acetylene gas fluxes were used as reactive gases. The coatings revealed different mixtures of crystalline ZrCxN1−x, silver nanoparticles and amorphous carbon phases. The hardness of the films was found to be mainly controlled by the ratio between the hard (ZrCxN1−x) and soft (Ag and amorphous carbon) phases in the films, fluctuating between 7.4 and 20.4 GPa. The coefficient of friction, measured against ultra-high molecular weight polyethylene (UHMWPE) in Hank’s balanced salt solution with 10 g L−1albumin, is governed by the surface roughness and hardness. The UHMWPE wear rates were in the same order of magnitude (between 1.4 and 2.0×10−6 mm3 N−1 m−1), justified by the effect of the protective layer of albumin formed during the tests. The small differences were due to the hydrophobic/hydrophilic character of the surface, as well as to the silver content.

Journal of the Mechanical Behavior of Biomedical Materials, 41 (2015) 83-91 | DOI: 10.1016/j.jmbbm.2014.09.028

Removing the effects of the "dark matter" in tomography

Gontard, Lionel C.

Electron tomography (ET) using different imaging modes has been progressively consolidating its position as a key tool in materials science. The fidelity of a tomographic reconstruction, or tomogram, is affected by several experimental factors. Most often, an unrealistic cloud of intensity that does not correspond to a real material phase of the specimen ("dark matter") blurs the tomograms and enhances artefacts arising from the missing wedge (MW). Here we show that by simple preprocessing of the background level of any tomographic tilt series, it is possible to minimise the negative effects of that "dark matter". Iterative reconstruction algorithms converge better, leading to tomograms with fewer streaking artefacts from the MW, more contrast, and increased accuracy. The conclusions are valid irrespective of the imaging mode used, and the methodology improves the segmentation and visualisation of tomograms of both crystalline and amorphous materials. We show examples of HAADF STEM and BF TEM tomography.

Ultramicroscopy, 154 (2015) 64-72 | DOI: 10.1016/j.ultramic.2015.03.017

Efficient synthesis of ammonia from N-2 and H-2 alone in a ferroelectric packed-bed DBD reactor

Gomez-Ramirez, A; Cotrino, J; Lambert, RM; Gonzalez-Elipe, AR

A detailed study of ammonia synthesis from hydrogen and nitrogen in a planar dielectric barrier discharge (DBD) reactor was carried out. Electrical parameters were systematically varied, including applied voltage and frequency, electrode gap, and type of ferroelectric material (BaTiO3 versus PZT). For selected operating conditions, power consumption and plasma electron density were estimated from Lissajous diagrams and by application of the Bolsig + model, respectively. Optical emission spectroscopy was used to follow the evolution of plasma species (NH*, N*, N-2(+) and N-2*) as a function of applied voltage with both types of ferroelectric material. PZT gave both greater energy efficiency and higher ammonia yield than BaTiO3: 0.9 g NH3 kWh(-1) and 2.7% single pass N-2 conversion, respectively. This performance is substantially superior to previously published findings on DBD synthesis of NH3 from N-2 and H-2 alone. The influence of electrical working parameters, the beneficial effect of PZT and the importance of controlling reactant residence time are rationalized in a reaction model that takes account of the principal process variables

Plasma Sources Science and Technology, 24 (2015) 065011 | DOI: 10.1088/0963-0252/24/6/065011

New Insights on the Kinetic Analysis of Isothermal Data: The Independence of the Activation Energy from the Assumed Kinetic Model

Sanchez-Jimenez, PE; Perejon, A; Perez-Maqueda, LA; Criado, JM

Isothermal experiments are widely employed to study the kinetics of solid-state reactions or processes to extract essential kinetic information needed for modeling the processes at an industrial scale. The kinetic analysis of isothermal data requires finding or assuming a kinetic function that can properly fit the evolution of the reaction rate with time, so that the resulting parameters, i.e., the activation energy and pre-exponential factor, can be considered reliable. In the present work, we demonstrate using both simulated and experimental data that the kinetic analysis of a set of isothermal plots obtained at different temperatures, considering a single-step solid-state reaction, necessarily leads to the real activation energy, regardless the mathematical function selected for performing the kinetic analysis. This makes irrelevant the election of the kinetic function used to fit the experimental data and greatly facilitates the estimation of the activation energy for any single process.

Energy & Fuels, 29 (2015) 392-397 | DOI: 10.1021/ef502269r

Influence of the Processing Route on the Carbon Nanotubes Dispersion and Creep Resistance of 3YTZP/SWCNTs Nanocomposites

Castillo-Rodriguez, M; Munoz, A; Morales-Rodriguez, A; Poyato, R; Gallardo-Lopez, A; Dominguez-Rodriguez, A

3YTZP matrix composites containing 2.5 vol% of single-walled carbon nanotubes (SWCNT) were fabricated by Spark Plasma Sintering (SPS) at 1250°C, following different processing routines with the aim of optimizing the SWCNTs dispersion throughout the ceramic matrix. Microstructural characterization of the as-fabricated samples has been performed by means of scanning electron microscopy (SEM). The specimens have been crept at 1200°C to correlate creep resistance and SWCNTs distribution. There are no creep experimental results on these nanocomposites reported in literature. Mechanical results show that the incorporation of SWCNTs into a 3YTZP matrix produces an increase in the strain rate at high temperature with respect to monolithic zirconia. The creep resistance of these nanocomposites decreases with the improvement of the SWCNTs dispersion, where a smaller SWCNTs agglomerate size and consequently a higher concentration of carbon nanotubes surrounding the 3YTZP grain boundaries is found. This fact indicates that SWCNTs act as a lubricant making grain-boundary sliding easier during deformation of these composites.

Journal of the American Ceramic Society, 98 (2015) 645-653 | DOI: 10.1111/jace.13348

Microstructure and impedance spectroscopy of 3YTZP/SWNT ceramic nanocomposites

Poyato, R; Macias-Delgado, J; Gallardo-Lopez, A; Munoz, A; Dominguez-Rodriguez, A

This work provides new insights on microstructure and electrical properties of 3 mol% Y2O3-ZrO2 (3YTZP) composites with 0.5, 1, and 1.5 vol% single walled carbon nanotubes (SWNTs). The composites were spark plasma sintered (SPS) in identical conditions at 1250 degrees C from powder prepared by two different processing routines, with the aim of optimizing the SWNTs dispersion throughout the ceramic matrix. High densification and submicrometric grain size were achieved in all the composites. Electrical properties of the composites were characterized in a wide temperature range, and modeling of the impedance properties was approached by means of an equivalent circuit that allows separation of the individual SWNT bundles contribution to resistance from the resistance due to junctions between bundles. Effects of the homogeneous distribution of SWNTs at the ceramic grain boundaries on the crystalline phases, percolation threshold, total conductivity and evolution of junctions' resistivity with temperature were analyzed and discussed. 

Ceramics International, 41 (2015) 12861-12868 | DOI: 10.1016/j.ceramint.2015.06.123

Mechanically induced self-propagating reaction of vanadium carbonitride

Roldan, MA; Alcala, MD; Real, C

Vanadium carbonitrides (VCxN1-x) were prepared via mechanosynthesis from mixtures of elemental vanadium and carbon with different V/C atomic ratios under a nitrogen atmosphere using a high-energy ball mill. We obtained the full composition range of carbonitrides at room temperature. The products were characterized using X-ray diffraction, scanning electron microscopy and electron energy loss spectroscopy. The results showed particle-sized products with high sinterability and very high microhardness.

Ceramics International, 41 (2015) 4688-4695 | DOI: 10.1016/j.ceramint.2014.12.016

Modulating Low Energy Ion Plasma Fluxes for the Growth of Nanoporous Thin Films

Alvarez, Rafael; Lopez-Santos, Carmen; Ferrer, Francisco J.; Rico, Victor; Cotrino, Jose; Gonzalez-Elipe, Agustin R.; Palmero, Alberto

The growth of nanoporous layers by plasma-assisted deposition techniques is strongly mediated by the ion fluxes in the reactor. To analyze their influence we have deposited different nanostructured thin films by the magnetron sputtering technique at oblique angles, modulating the ion fluxes in the plasma by tuning the frequency of the electromagnetic signal from pure DC to 160 kHz DC pulsed mode. In the DC case, ions possess energies below 5 eV and do not induce noticeable changes in the film structure. However, when the signal is pulsed, ions with energies up to 40 eV impinge on the film, decreasing the porosity of the layers and tilting down the porous/nanocolumnar structures. As a result, we demonstrate that the overall porosity of the layers and the tilt angle of the columns can be tailored as two independent morphological quantities.

Plasma Processes and Polymers, 12 (2015) 719-724 | DOI: 10.1002/ppap.201400209

Uniform Poly(acrylic acid)-Functionalized Lanthanide-Doped LaVO4 Nanophosphors with High Colloidal Stability and Biocompatibility

Nunez, NO; Zambrano, P; Garcia-Sevillano, J; Cantelar, E; Rivera-Fernandez, S; de la Fuente, JM; Ocana, M

Ln-doped (Ln = Eu or Nd) LaVO4 nanoparticles functionalized with poly(acrylic acid) (PAA) were prepared from lanthanide and vanadate precursors in the presence of PAA by a simple one-pot method that consists of a homogeneous precipitation reaction in ethylene glycol/water at a moderate temperature (120 degrees C). The size of the nanoparticles could be modified in the 40-70 nm range by adjusting the amount of PAA added. The effects of the Eu and Nd contents of these nanomaterials on theirs optical properties (emission intensity and lifetime) were also analyzed to find the optimum nanophosphors. Finally, the nanoparticles showed negligible cytotoxicity for Vero cells at concentrations up to 0.05 mgmL(-1) and a high colloidal stability in physiological buffer solutions; therefore, they satisfy the most important requirements for in vitro biotechnological applications.

European Journal of Inorganic Chemistry, 27 (2015) 4546-4554 | DOI: 10.1002/ejic.201500265

Biosynthesis of silver fine particles and particles decorated with nanoparticles using the extract of Illicium verum (star anise) seeds

Luna, Carlos; Chavez, V. H. G.; Diaz Barriga-Castro, Enrique; Nunez, Nuria O.; Mendoza-Resendez, Raquel

Given the upsurge of new technologies based on nanomaterials, the development of sustainable methods to obtain functional nanostructures has become an imperative task. In this matter, several recent researches have shown that the biodegradable natural antioxidants of several plant extracts can be used simultaneously as reducing and stabilizing agents in the wet chemical synthesis of metallic nanoparticles, opening new opportunities to design greener synthesis. However, the challenge of these new techniques is to produce stable colloidal nanoparticles with controlled particle uniformity, size, shape and aggregation state, in similar manner than the well-established synthetic methods. In the present work, colloidal metallic silver nanoparticles have been synthesized using silver nitrate and extracts of Illicium verum (star anise) seeds at room temperature in a facile one-step procedure. The resulting products were colloidal suspensions of two populations of silver nanoparticles, one of them with particle sizes of few nanometers and the other with particles of tens of nm. Strikingly, the variation of the AgNO3/extract weight ratio in the reaction medium yielded to the variation of the spatial distribution of the nanoparticles: high AgNO3/extract concentration ratios yielded to randomly dispersed particles, whereas for lower AgNO3/extract ratios, the biggest particles appeared coated with the finest nanoparticles.-This biosynthesized colloidal system, with controlled particle aggregation states, presents plasmonic and SERS properties with potential applications in molecular sensors and nanophotonic devices. 

Spectrochimica Acta Part A-Molecular and Biomolecular Spectroscopy, 141 (2015) 43-50 | DOI: 10.1016/j.saa.2014.12.076

Valorization and inertization of galvanic sludge waste in clay bricks

Perez-Villarejo, L; Martinez-Martinez, S; Carrasco-Hurtado, B; Eliche-Quesada, D; Urena-Nieto, C; Sanchez-Soto, PJ

Galvanic sludge wastes (GSW) are produced by the physico-chemical treatments of wastewater generated by electroplating plants. These materials have a significant potential for the production of clay ceramic bricks. This paper focuses on the viability of the inertization of heavy metals from GSW mixed with clays. The original materials were obtained by mixing three types of raw clay (red, yellow and black) in equal parts with GSW. These mixtures were characterized by XRD, XRF, and chemical elemental analysis CHNS. The dosage of GSW in the clay–GSW bricks was up to 5 wt.%. The bricks were then manufactured using conventional processes. The influence of the amount of GSW was evaluated after firing the clay–GSW composites at 950 °C for 1 h. The engineering properties of the fired samples, such as density, water absorption, open porosity, water suction and compressive strength, with and without the GSW, were determined. The incorporation of GSW into the clay mix clearly decreased the linear shrinkage and bulk density of the bricks in comparison with the fired clay used as a control. These GSW–clay composites also showed lower open porosity. According to the results obtained for the bulk density of the bricks, samples with GSW addition showed slightly lower values of open porosity than clay bodies, indicating that the GSW–clay samples had slightly higher closed porosity values. This was also shown by SEM. The open porosity, SEM and pore size distribution tests indicated that the porosity generated by the addition of GSW was mainly closed and, therefore, GSW bricks had excellent mechanical properties. The environmental risks of the incorporation of GSW, rich in heavy metals (Cr, Zn, Ni and others), to a clay matrix were evaluated by leaching tests of the fired products. The results indicated a successful inertization of the pollutants.

Applied Clay Science, 105-106 (2015) 89-99 | DOI: 10.1016/j.clay.2014.12.022

Phyllite clay-cement composites having improved engineering properties and material applications

Garzon, E; Cano, M; O'Kelly, BC; Sanchez-Soto, PJ

Phyllite clays contain clay minerals (chlorite, illite and mixed-layer illite smectite), quartz and feldspars. In this experimental laboratory study, new composites of phyllite clay and cement (5, 7 and 9 wt.%) were prepared and tested to determine their Atterberg limits, dry density and optimum water content for modified Proctor (MP) compaction, California Bearing ratio, swelling potential after soakage in water, unconfined compressive strength (UCS) and water-permeability coefficient. From the mixes investigated, the composite with 5 wt.% cement was deemed most suitable for certain construction material applications, having a plasticity index of 10.5%, maximum dry density of 2.17 Mg/m3 and optimum water content of 8% for MP compaction (undergoing no swelling under soakage), a UCS of 0.74 MPa, and a very low permeability coefficient value of 7.4 × 10− 11 m/s. Potential material applications for these new composites include for building construction, roofs, and flexible pavements.

Applied Clay Science, 114 (2015) 229-233 | DOI: 10.1016/j.clay.2015.06.006

An improved method for determining the external specific surface area and the plasticity index of clayey samples based on a simplified method for non-swelling fine-grained soils

Garzon, E; Sanchez-Soto, PJ

Previous studies have used the clay content of soils for estimating the specific surface areas and different correlations have been found, including plasticity-value correlations. Based on several assumptions, Dolinar (2012) proposed a simplified method for determining the external specific surface area of non-swelling fine-grained soils. An equation relates the external specific surface area (BET-nitrogen) with percentage of clay fraction (< 2 μm), determined by hydrometer method, and plasticity index (Atterberg).

In this work, based on that simplified method, the authors have developed an improved method for determining the external specific surface area of fine-grained clay samples. Instead of percentage of clay fraction, it was proposed to use the clay mineral content estimated by XRD methods. From an analysis of previous Dolinars results, the calculated and measured values of external specific surface area were studied for a group of non-swelling and fine-grained soil samples (Dolinar's samples), five non-swelling clayey samples and data samples from the literature. Additionally, an estimation of the plasticity index (Atterberg) has been also considered in this improved method. Both these methods, simplified and improved, were tested and compared using all these samples. It demonstrated the practical application of both these methods for an estimation of external specific surface area and plasticity index. However, in the present research two models were considered to determine the specific surface areas (BET and Langmuir) and the influence of several sources of errors in these predictions was discussed. The predictions were found more accurate when specific surface area from Langmuir's model is considered. It is concluded that the present research will be useful for the prediction of external specific surface area and plasticity index of non-swelling clayey materials and to dispose of theoretical practical relationships between clay mineralogy and geotechnical properties of valuable interest.

Applied Clay Science, 115 (2015) 97-107 | DOI: 10.1016/j.clay.2015.07.015

Green pigments of Roman mural paintings from Seville Alcazar

Perez-Rodriguez, JL; de Haro, MDJ; Siguenza, B; Martinez-Blanes, JM

We report here a study of 30 fragments of green wall paintings from Roman times found in the Patio de Banderas excavation in Seville Alcazar. The sample characterisation was realised using optical microscopy, colourimetry, infrared and micro-Raman spectroscopy, X-ray diffraction, and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. The study of these pigments is important because it can help determine the source or the pictorial technique used. The samples studied in this work have been divided into two groups, according to the composition of their green pigments. In the first group, celadonite has been characterised as the primary component of the green colour; chlorite was also detected. Particles constituted by chromium accompanied by aluminium, iron and zinc were found in all studied samples of this group. Chlorite and chromium oxide could also be responsible for the green colour. The presence of chromium suggested the presence of green colour pigment from Verona. In the second group, a mixture of celadonite and glauconite was detected and could be responsible for the green colour observed. The addition of refracting material such as Egyptian blue was also used. A mixture of Egyptian green and Egyptian blue together with celadonite and glauconite was also found. Four classes of intonaco were recognised and classified based upon the composition of the aggregates.

Applied Clay Science, 116 (2015) 211-219 | DOI: 10.1016/j.clay.2015.03.016

Impact of hydrothermal treatment of FEBEX and MX80 bentonites in water, HNO3 and Lu(NO3)(3) media: Implications for radioactive waste control

Osuna, FJ; Chain, P; Cota, A; Pavon, E; Alba, MD

Engineered barriers of deep geological repositories (DGR) are commonly constructed with bentonite. FEBEX and MX80 bentonites have been selected by different countries as reference materials for the sealing of repositories; however, their chemical reactivity with high-level long-lived radioactive wastes (HLRW) under subcritical conditions had not been explored before. The hydrothermal stability in neutral and acid media and chemical reactivity in contact with an actinide analogous compound were both studied. The long-range and short-range structural changes were analyzed by X-ray diffraction, nuclear magnetic resonance and scanning electron microscopy. Both bentonites have exhibited a good stability in neutral and acid media and have generated a new phase immobilizing the actinide analogous compound. The extent of the chemical reaction is higher in MX80 bentonite than in FEBEX bentonite. 

Applied Clay Science, 118 (2015) 48-55 | DOI: 10.1016/j.clay.2015.08.036

Viability of adding gypsum and calcite for remediation of metal-contaminated soil: laboratory and pilot plant scales

Gonzalez-Nunez, R; Alba, MD; Vidal, M; Rigol, A

The effect of adding waste materials (gypsum and calcite) for the remediation of a soil contaminated by pyritic minerals was examined. Materials were characterised in terms of their acid neutralisation capacity (ANC), sorption capacity and structural components. Their effect on the contaminant leaching in soil + material mixtures over a wide range of pH was also evaluated. Results at laboratory and pilot plant scales were compared to account for the potential variability in the material efficiency when applied at larger scale. The use of gypsum permitted its valorisation, although calcite was a more effective amendment because its addition led to a greater increase in the pH and acid neutralisation capacity, and thus in the sorption capacity in the resulting soil + material mixture. In the same way, when the combination of gypsum + calcite was added to the soil, it led to an increase in the pH from 2.5 to 6.9 and in the ANC from −86 to 1,513 meq/kg. As a result, the concentration of extractable heavy metals and As was reduced, and they were successfully immobilised both at laboratory and at pilot plant scales. Thus, the use of these materials induced a significant reduction in the contaminant mobility and permitted the valorisation of waste materials.

International Journal of Environmental Science and Technology, 12 (2015) 2697-2710 | DOI: 10.1007/s13762-014-0671-3

Nanoindentation of (Ti,Ta)(C,N)-Co cermets prepared by methods of mechanochemistry

Hvizdos, Pavol; Balko, Jan; Manuel Cordoba, Jose; Chicardi, Ernesto

Four materials TixTa(1 - x)C(0.5)N(0.5)-20%Co of two chemical compositions (x = 0.9 and 0.95) and two high energy milling methods (one stage and two stage milling) have been prepared. Nano-hardness and elastic modulus for microstructure as a whole and for individual constituent phases (matrix and carbide grains) were obtained by instrumented indentation. Individual targeted indentations as well as grid nanoindentation technique were used to discern the individual constituents' properties. Maximum loads of 20 mN for individual phases and 300 mN for composite microstructure were applied. Materials with higher amount of Ti had larger grains but the milling procedure had stronger influence on the grain size. The two step milling resulted in finer microstructures but with a much wider grain size distribution. Final composite mechanical properties, however, were very similar. Hardness and indentation elasticity modulus of all materials were comparable within the errors of measurement.

International Journal of Refractory Metals & Hard Materials, 49 (2015) 219-224 | DOI: 10.1016/j.ijrmhm.2014.07.038

Sliding wear resistance of sintered SiC-fiber bonded ceramics

Vera, MC; Ramirez-Rico, J; Martinez-Fernandez, J; Singh, M

Advanced SiC-based ceramics and fiber reinforced composites are interesting materials for a wide variety of applications involving sliding wear conditions because of their excellent thermomechanical properties. The microstructure and wear resistance of sintered SiC fiber bonded ceramics (SA Tyrannohex) were studied. The material is composed of SiC-fibers in two orientations, with polygonal cross sections and cores having higher carbon content than their surroundings, as observed with SEM. A thin layer of C exists between the fibers. This layer has been found to be a turbostratic-layered structure oriented parallel to the fiber surface. XRD shows that the material is highly crystalline and composed mostly of β-SiC. Unlubricated wear behavior of the SA-Tyrannohex material when sliding against a Si3N4 ball in air at room temperature was evaluated. Experiments were performed using a pin on disk apparatus, under different normal loads of 2, 5 and 10 N at sliding speeds of 25, 50, 100 mm/s. A decrease of the friction coefficient with load was found due to the presence of the turbostratic carbon layer between the fibers. Wear rates of the order of 100 mm3/MJ were obtained, independently of sliding speed. Microfracture of the fibers is the main wear mechanism.

International Journal of Refractory Metals & Hard Materials, 49 (2015) 232-239 | DOI: 10.1016/j.ijrmhm.2014.06.020

Sliding wear resistance of biomorphic SiC ceramics

Vera, MC; Ramirez-Rico, J; Martinez-Fernandez, J; Singh, M

Biomorphic SiC ceramics were fabricated from four different wood precursors and their Knoop hardness and sliding wear resistance when sliding against a Si3N4 ball in air were studied. Tribological experiments were performed using a pin on disk apparatus, under normal loads of 2 and 5 N, at a sliding speed of 100 mm/s. The effects of specimen porosity and microstructure on measured wear were evaluated. A commercial sintered silicon carbide ceramic was also tested for comparison. Small differences in friction coefficient comparable to monolithic SiC ceramics were obtained. Several concurrent wear mechanisms are taking place: microfracture, plastic deformation in the Si phase and oxidation of the Si and/or SiC phase. The presence of an oxide tribolayer was assessed using fluorescence microscopy. Wear rates were found to scale with SiC content and depend on residual porosity in the composite.

International Journal of Refractory Metals & Hard Materials, 49 (2015) 327-333 | DOI: 10.1016/j.ijrmhm.2014.07.004

Photocatalytic reduction of CO2 over platinised Bi2WO6-based materials

Murcia-Lopez, S; Vaiano, V; Hidalgo, MC; Navio, JA; Sannino, D

The photocatalytic reduction of CO2 with H2O to produce CH4 in the gas phase was carried out in the presence of two Bi2WO6-based materials. For this purpose, single Bi2WO6 and a coupled Bi2WO6-TiO2 system were synthesised and metallised with Pt, through a Pt photodeposition method. Then, the samples were characterised and the photocatalytic activity was evaluated in a continuous fluidised-bed reactor irradiated with UV light. Single Bi2WO6 presents an interesting behaviour under H2O rich conditions. In particular, the metallisation improves the material's performance for CH4 formation, while the TiO2 addition to Bi2WO6 increases the CH4 yield only at low H2O/CO2 ratio. The Bi2WO6-TiO2 system metallised with a Pt photocatalyst displayed the highest CH4 yield among all the prepared photocatalysts. The stability of the system can be enhanced through the addition of a blue phosphor to the reactant mixture, especially under H2O rich conditions.

Photochemical & Photobiological Sciences, 14 (2015) 678-685 | DOI: 10.1039/c4pp00407h

Up-conversion in Er3+/Yb3+ co-doped LaPO4 submicron-sized spheres

Garcia-Sevillano, J.; Cantelar, E.; Cusso, F.; Ocana, M.

Er3+/Yb3+ co-doped materials have been extensively used for imaging in biomedical applications using either visible up-converted (UC) or near-infrared (NIR) emissions. The UC spectrum is composed mainly by two Erbium emissions in the green (2H11/2:4S3/2 → 4I15/2) and red (4F9/2 → 4I15/2) spectral range, while the NIR spectrum includes Er3+ (λ ∼ 1.5 μm, 4I13/2 → 4I15/2) and Er3+/Yb3+ (λ ∼ 980 nm, 2F5/2 → 2F7/2(Yb3+):4I11/2 → 4I15/2 (Er3+)) transitions; which relative intensities are dependent on several physical parameters. In the present work, we present the preparation and optical characterization of Er3+/Yb3+ co-doped LaPO4 submicron-sized spheres. The luminescence (CW and pulsed) characteristics, after different post-annealing treatments, are studied. It is found that such treatments strongly increment the emission efficiency, possibly due to the suppression of residual impurities. After calcination at 1100 °C the material behaves as an excellent UC and NIR–NIR wavelength converter.

Optical Materials, 41 (2015) 104-107 | DOI: 10.1016/j.optmat.2014.10.022

Tribocorrosion behavior of TiBxCy/a-C nanocomposite coating in strong oxidant disinfectant solutions

Gracia-Escosa, E; Garcia, I; Sanchez-Lopez, JC; Abad, MD; Mariscal, A; Arenas, MA; de Damborenea, J; Conde, A

Corrosion and tribocorrosion studies of a TiBxCy/a-C coating deposited on AISI 316L steel have been performed in an aqueous solution of 026 vol.% acetic, 0.16 vol.% peracetic and 0.18 vol.% hydrogen peroxide (commercial product Oxonia I vol.%). The corrosion current density of the TiBxCy/a-C coating ranges on the same order as bare steel but with a significantly decreasing friction (0.1 vs. 0.6) and wear rate (similar to 10 times lower). The compact microstructure of the coating hinders the access of the aggressive electrolyte to the substrate, preventing the onset of the corrosion attack, while maintaining an excellent tribological behavior in strong oxidant solutions.

Surface & Coatings Technology, 263 (2015) 78-85 | DOI: 10.1016/j.surfcoat.2014.12.047

Direct observation of doping incorporation pathways in self-catalytic GaMnAs

Kasama, T.; Thuvander, M.; Siusys, A.; Gontard, L. C.; Kovacs, A.; Yazdi, S.; Duchamp, M.; Gustafsson, A.; Dunin-Borkowski, R. E.; Sadowski, J.

Doping mechanisms of Mn in GaAs nanowires (NWs) that have been grown self-catalytically at 600 °C by molecular beam epitaxy (MBE) are investigated using advanced electron microscopy techniques and atom probe tomography. Mn is found to be incorporated primarily in the form of non-magnetic tetragonal Ga0.82Mn0.18 nanocrystals in Ga catalyst droplets at the ends of the NWs, while trace amounts of Mn (22 ± 4 at. ppm) are also distributed randomly in the NW bodies without forming clusters or precipitates. The nanocrystals are likely to form after switching off the reaction in the MBE chamber, since they are partially embedded in neck regions of the NWs. The Ga0.82Mn0.18 nanocrystals and the low Mn concentration in the NW bodies are insufficient to induce a ferromagnetic phase transition, suggesting that it is difficult to have high Mn contents in GaAs even in 1-D NW growth via the vapor-liquid-solid process.

Journal of Applied Physics, 118 (2015) 054302 | DOI: 10.1063/1.4927623

Structural and chemical reactivity modifications of a cobalt perovskite induced by Sr-substitution. An in situ XAS study

Hueso, JL; Holgado, JP; Pereniguez, R; Gonzalez-DelaCruz, VM; Caballero, A

LaCoO3 and La0.5Sr0.5O3O3-delta perovskites have been studied by in situ Co K-edge XAS. Although the partial substitution of La(III) by Sr(II) species induces an important increase in the catalytic oxidation activity and modifies the electronic state of the perovskite, no changes could be detected in the oxidation state of cobalt atoms. So, maintaining the electroneutrality of the perovskite requires the generation of oxygen vacancies in the network. The presence of these vacancies explains that the substituted perovskite is now much more reducible than the original LaCoO3 perovskite. As detected by in situ XAS, after a consecutive reduction and oxidation treatment, the original crystalline structure of the LaCoO3 perovskite is maintained, although in a more disordered state, which is not the case for the Sr doped perovskite. So, the La0.5Sr0.5CoO3-delta perovskite submitted to the same hydrogen reduction treatment produces metallic cobalt, while as determined by in situ XAS spectroscopy the subsequent oxidation treatment yields a Co(III) oxide phase with spinel structure. Surprisingly, no Co(II) species are detected in this new spinel phase. 

Materials Chemistry and Physics, 151 (2015) 29-33 | DOI: 10.1016/j.matchemphys.2014.11.015

Uniform, luminescent Eu: LuF3 nanoparticles

Becerro, AI; Gonzalez-Mancebo, D; Ocana, M

A simple procedure for the synthesis of orthorhombic, uniform, LuF3 particles with two different morphologies (rhombus- and cocoon-like) and nanometer and sub-micrometer size, respectively, is reported. The method consists in the aging, at 120 °C for 2 h, a solution containing [BMIM]BF4 ionic liquid (0.5 mL) and lutetium acetate (in the case of the rhombi) or lutetium nitrate (in the case of the cocoons) (0.02 M) in ethylene glycol (total volume 10 mL). This synthesis method was also adequate for the synthesis of Eu3+-doped LuF3 particles of both morphologies, whose luminescence properties were investigated in detail. The experimental observations reported herein suggest that these materials are suitable phosphors for optoelectronic as well as in vitro biotechnological applications.

Journal of Nanoparticle Research, 17 (2015) 58 | DOI: 10.1007/s11051-015-2874-z

Free-Base Carboxyphenyl Porphyrin Films Using a TiO2 Columnar Matrix: Characterization and Application as NO2 Sensors

Roales, Javier; Pedrosa, Jose M.; Guillen, Maria G.; Lopes-Costa, Tania; Castillero, Pedro; Barranco, Angel; Gonzalez-Elipe, Agustin R.

The anchoring effect on free-base carboxyphenyl porphyrin films using TiO2 microstructured columns as a host matrix and its influence on NO2 sensing have been studied in this work. Three porphyrins have been used: 5-(4-carboxyphenyl)10,15,20-triphenyl-21H,23H-porphyrin (MCTPP); 5,10,15,20-tetrakis(4-carboxyphenyl)-21H,23H-porphyrin (p-TCPP); and 5,10,15,20-tetrakis(3-carboxyphenyl)-21H,23H-porphyrin (m-TCPP). The analysis of UV-Vis spectra of MCTPP/TiO2, p-TCPP/TiO2 and m-TCPP/TiO2 composite films has revealed that m-TCPP/TiO2 films are the most stable, showing less aggregation than the other porphyrins. IR spectroscopy has shown that m-TCPP is bound to TiO2 through its four carboxylic acid groups, while p-TCPP is anchored by only one or two of these groups. MCTPP can only be bound by one carboxylic acid. Consequently, the binding of p-TCPP and MCTPP to the substrate allows them to form aggregates, whereas the more fixed anchoring of m-TCPP reduces this effect. The exposure of MCTPP/TiO2, p-TCPP/TiO2 and m-TCPP/TiO2 films to NO2 has resulted in important changes in their UV-Vis spectra, revealing good sensing capabilities in all cases. The improved stability of films made with m-TCPP suggests this molecule as the best candidate among our set of porphyrins for the fabrication of NO2 sensors. Moreover, their concentration-dependent responses upon exposure to low concentrations of NO2 confirm the potential of m-TCPP as a NO2 sensor.

Sensors, 15 (2015) 11118-11132 | DOI: 10.3390/s150511118

Polyester Films Obtained by Noncatalyzed Melt-Condensation Polymerization of Aleuritic (9,10,16-Trihydroxyhexadecanoic) Acid in Air

Benitez, JJ; Heredia-Guerrero, JA; Guzman-Puyol, S; Dominguez, E; Heredia, A

To mimic nontoxic and fully biodegradable biopolymers like the plant cutin, polyester films from a natural occurring fatty polyhydroxyacid like aleuritic (9,10,16-trihydroxyhexadecanoic) acid have been prepared by noncatalyzed melt-polycondensation at moderate temperature (150 degrees C) directly in air. The course of the reaction has been followed by infrared spectroscopy, C-13 magic angle spinning nuclear magnetic resonance spectroscopy, differential scanning calorimetry and X-ray diffraction and well differentiated stages are observed. First, a high conversion esterification reaction leads to an amorphous rubbery, infusible, and insoluble material whose structure is made out of ester linkages mostly involving primary hydroxyls and partially branched by minor esterification with secondary ones. Following the esterification stage, the cleavage of vicinal secondary hydroxyls and further oxidation to carboxylic acid is observed at the near surface region of films. New carboxylic groups created also undergo esterification and generate cross-linking points within the polymer structure. Additionally, and despite the harsh preparation conditions used, very little additional side reaction like peroxidation and dehydration are observed. Results demonstrate the feasibility of polyester films fabrication from a reference fatty polyhydroxyacid like aleuritic acid by noncatalyzed melt-polycondensation directly in air. The methodology can potentially be extended to similar natural occurring hydroxyacids to obtain films and coatings to be used, for instance, as nontoxic and biodegradable food packaging material.

Journal of Applied Polymer, 132 (2015) Art. 41328 | DOI: 10.1002/app.41328

Transmission electron microscopy of thiol-capped Au clusters on C: Structure and electron irradiation effects

Lionel C. Gontard, Rafal E. Dunin-Borkowski

High-resolution transmission electron microscopy is used to study interactions between thiol-capped Au clusters and amorphous C support films. The morphologies of the clusters are found to depend both on their size and on the local structure of the underlying C. When the C is amorphous, larger Au clusters are crystalline, while smaller clusters are typically disordered. When the C is graphitic, the Au particles adopt either elongated shapes that maximize their contact with the edge of the C film or planar arrays when they contain few Au atoms. We demonstrate the influence of electron beam irradiation on the structure, shape and stability of the Au clusters, as well as on the formation of holes bounded by terraces of graphitic lamellae in the underlying C.

Micron | DOI: 10.1016/j.micron.2014.12.001

Photocatalytic propylene epoxidation on Bi2WO6-based photocatalysts

Murcia-Lopez, S.; Vaiano, V.; Sannino, D.; Hidalgo, M. C.; Navio, J. A.

The photocatalytic epoxidation of propylene (PR) with molecular oxygen was carried out in a fluidized-bed reactor with several Bi2WO6-based materials under UV-A illumination. Three different photocatalysts were tested: one of single Bi2WO6 and two of coupled Bi2WO6-TiO2 heterostructures, thus showing that a mixed system of Bi2WO6 with commercial TiO2 Degussa-P25 leads to the best combination of conversion and PO selectivity. Then, direct support on glass spheres and silica gel was made, being a good alternative for improving the Bi2WO6 performance. Additionally, several reaction conditions of temperature and PR to O-2 feed ratio were studied.

Research on Chemical Intermediates, 41 (2015) 4199-4212 | DOI: 10.1007/s11164-013-1523-3

Amperometric magnetobiosensors using poly(dopamine)-modified Fe3O4 magnetic nanoparticles for the detection of phenolic compounds

Martin, M; Salazar, P; Campuzano, S; Villalonga, R; Pingarron, JM; Gonzalez-Mora, JL

The synthesis of poly(dopamine)-modified magnetic nanoparticles (MNPs) and their application in preparing electrochemical enzyme biosensors that are useful to detect phenolic compounds is reported in this work. MNPs of about 16 nm were synthesized by a co-precipitation method and conveniently modified with poly(dopamine). Non-modified and modified MNPs were characterized using X-ray photoelectron spectroscopy (XPS), Raman and infrared spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). Horseradish peroxidase (HRP) was covalently immobilized onto the surface of the poly(dopamine)-modified MNPs via Michael addition and/or Schiff base formation and used to construct a biosensor for phenolic compounds by capturing the HRP-modified-nanoparticles onto the surface of a magnetic-modified glassy carbon electrode (GCE). Cyclic voltammetry and amperometry were used to study the electrochemical and analytical properties of the biosensor using hydroquinone (HQ) as a redox probe. Among the different phenolic compounds studied, the biosensor exhibited higher sensitivity for HQ, 1.38 A M−1 cm−2, with limits of detection and quantification of 0.3 and 1.86 μM, respectively. The analytical biosensor performance for HQ and 2-aminophenol compared advantageously with those of previous phenolic biosensors reported in the literature.

Analytical Methods, 7 (2015) 8801-8808 | DOI: 10.1039/C5AY01996F

Ionic liquid immobilization on carbon nanofibers and zeolites: Catalyst design for the liquid-phase toluene chlorination

Losch, Pit; Martinez Pascual, Antonio; Boltz, Marilyne; Ivanova, Svetlana; Louis, Benoit; Montilla, Francisco; Antonio Odriozola, Jose

The environmental-friendly chlorination reaction of toluene by trichloroisocyanuric acid (TCCA, C3N3O3Cl3) was investigated applying immobilized ionic liquids (ILs) on different supports. Ionic liquids were grafted either on carbon nanofibers (CNF) or encapsulated in zeolites. Their influence on the chlorination activity as well as on the selectivity in different chlorinated products was studied. An unusually high selectivity toward meta-chlorotoluene was achieved, up to 36%. Hence, the selectivity could be tuned to produce either expected ortho-/para-chlorotoluene or meta-chlorotoluene with a proper support choice. 

Comptes Rendus Chimie, 18 (2015) 324-329 | DOI: 10.1016/j.crci.2014.06.006

Applications of sample-controlled thermal analysis (SCTA) to kinetic analysis and synthesis of materials

Perez-Maqueda, L. A.; Criado, J. M.; Sanchez-Jimenez, P. E.; Dianez, M. J.

The advantages of the sample-controlled thermal analysis (SCTA) for both the kinetic analysis of solid-state reactions and the synthesis of materials are reviewed. This method implies an intelligent control of the temperature by the solid-state reaction under study in such a way that the reaction rate as a function of the time fits a profile previously defined by the user. It has been shown that SCTA has important advantages for discriminating the kinetic model of solid-state reactions as compared with conventional rising temperature methods. Moreover, the advantages of SCTA methods for synthesising materials with controlled texture and structure are analysed.

Journal of Thermal Analysis and Calorimetry, 120 (2015) 45-51 | DOI: 10.1007/s10973-014-4176-6

Study of coatings by thermal analysis in a monument built with calcarenite

Luisa Franquelo, Maria; Dolores Robador, Maria; Luis Perez-Rodriguez, Jose

In this research, characterization of materials either added during restoration or formed by environmental contamination in the Seville City Hall, built with calcarenite stone, was investigated by thermal methods. Three different mortars for restoration have been characterized: (a) lime micro-mortar for internal consolidation of mortar itself, (b) mortar for reconstruction of deteriorated areas and (c) mortar with Portland cement. Acrylate polymer as consolidant and protection used was characterized. Addition of gypsum or “white cement” has been also applied in the restoration. Altered materials as black crusts constituted by gypsum, calcite and organic compound were determined by thermal analysis. Patina with high concentration of hydrated calcium oxalate, and the transformation mechanism of calcium oxalate into calcium carbonate and formation of calcium oxide produced by decomposition of the calcite were also characterized in the studied monument by thermal analysis. The patina with hydrated calcium oxalate produced by high biological activity was also studied.

Journal of Thermal Analysis and Calorimetry, 121 (2015) 195-201 | DOI: 10.1007/s10973-015-4432-4

Microstructure of mixed oxide thin films prepared by magnetron sputtering at oblique angles

Gil-Rostra, J; Garcia-Garcia, FJ; Ferrer, FJ; Gonzalez-Elipe, AR; Yubero, F

Several mixed oxide thin film series of samples (Si–Co–O, Si–Ni–O, Si–W–O) have been prepared by reactive magnetron sputtering at oblique angle geometries. The paper focuses on the description of microstructure of the films as a function of their stoichiometry. It is found that for identical process parameters (gas mixture, pressure, magnetron-substrate distance, incidence angle of the vapour flux, etc.) the tilt angle of the developed columnar microstructure and the film porosity is strongly dependent on the stoichiometry of the films. The results are discussed in the framework of several theoretical models on this topic.

Thin Solid Films, 591 (2015) 330-335 | DOI: 10.1016/j.tsf.2015.01.058

"In situ" XPS studies of laser-induced surface nitridation and oxidation of tantalum

Lahoz, R; Espinos, JP; Yubero, F; Gonzalez-Elipe, AR; de la Fuente, GF

This work studies the nitridation of Ta by laser irradiation by means of x-ray photoelectron spectroscopy. The study has been carried out under "in situ" conditions by controlling the nitrogen partial pressure, the presence of traces of oxygen, and the irradiance of the laser. It is found that a thin layer of Ta2O5 is directly obtained when irradiating in the presence of oxygen, while a Ta3N5 surface compound and some minor contributions of nonstoichiometric phases are formed in the presence of nitrogen. For O-2:N-2 mixtures at 0.1 Pa, preferential nitride formation occurs up to a ratio of 1:4, while Ta2O5 starts to be predominant for ratios above this value. The air stability of the tantalum nitride layer formed by laser irradiation and the surface topography of the irradiated metal are also studied. The possible factors determining this behavior are discussed.

Journal of Materials Research, 30 (2015) 2967-2976 | DOI: 10.1557/jmr.2015.190

Facile Synthesis of Decahedral Particles of Anatase TiO2 with Exposed {001} Facets

Perales-Martinez, IA; Rodriguez-Gonzalez, V; Obregon-Alfaro, S; Lee, SW

This paper reports a facile synthesis of decahedral particles of anatase TiO2 dominated by {101} and {001} faces. The decahedral particles has been enhanced by means a microwave-assisted hydrothermal method using TiF4 as a titanium precursor and HF as capping agent to promote oriented growth and formation of {001} faces in only 4 h. The prepared samples were characterized by scanning electron microscopy, high resolution of transmission electron microscopy and X-ray diffraction. The morphology of anatase TiO2 particles is consisted of near-perfect-truncated-bipyramid-shape. Reaction time is a key factor to obtain truncated-bipyramid-shaped particles with sharp and well-defined edges. Reaction times longer than 4 h induce irregular particles. Decahedral anatase TiO2 particles are truncated bypiramid crystals which have eight {101} and two {001} facets at top/bottom surfaces. The average size of decahedral anatase TiO2 particles are similar to 250 nm for the samples obtained without applying the microwave irradiation and similar to 350 nm for reaction 4 h.

Journal of Nanoscience and Nanotechnology, 15 (2015) 7351-7356 | DOI: 10.1166/jnn.2015.10578

Photocatalytic Properties of TiO2 Thin Films Modified with Ag and Pt Nanoparticles Deposited by Gas Flow Sputtering

Maicu, M; Gloss, D; Frach, P; Hecker, D; Gerlach, G; Cordoba, JM

In this work, a gas flow sputtering (GFS) process which allows the production and deposition of metal nanoparticles (NPs) in a vacuum environment is described. Aim of the study is to prove the potential of this technology for the fabrication of new TiO2 films with enhanced photocatalytic properties. For this purpose, Ag and Pt NPs have been produced and deposited on photocatalytic float glass coated with TiO2 thin films by magnetron sputtering. The influence of the process parameters and of the metal amount on the final properties of the particles (quantity, size, size distribution, oxidation state etc.,) was widely investigated. Moreover, the effect of the NPs on the photocatalytic activity of the resulting materials was evaluated for the case of the decomposition of stearic acid (SA) during UV-A irradiation. The reduction of the water contact angle (WCA) during the irradiation period was measured in order to test the photo-induced super-hydrophilicity (PSH).

Journal of Nanoscience and Nanotechnology, 15 (2015) 6478-6486 | DOI: 10.1166/jnn.2015.10873

In Situ Synthesis of a ZrB2-Based Composite Powder Using a Mechanochemical Reaction for the Zircon/Magnesium/Boron Oxide/Graphite System

Jalaly, M; Bafghi, MSS; Tamizifar, M; Gotor, FJ

A ZrSiO4/B2O3/Mg/C system was used to synthesize a ZrB2-based composite through a high-energy ball milling process. As a result of the milling process, a mechanically induced self-sustaining reaction (MSR) was achieved in this system. A composite powder of ZrB2-SiC-ZrC was prepared in situ by a magnesiothermic reduction with an ignition time of approximately 6min. The mechanism for the formation of the product was investigated by studying the relevant subreactions, the stoichiometric amount of B2O3, and thermal analysis.

International Journal of Applied Ceramic Technology, 12 (2015) 551-559 | DOI: 10.1111/ijac.12202

Atomic scale characterization of SiO2/4H-SiC interfaces in MOSFETs devices

Beltran, AM; Duguay, S; Strenger, C; Bauer, AJ; Cristiano, F; Schamm-Chardon, S

The breakthrough of 4H-SiC MOSFETs is stemmed mainly due to the mobility degradation in their channel in spite of the good physical intrinsic material properties. Here, two different n-channel 4H-SiC MOSFETs are characterized in order to analyze the elemental composition at the SiC/SiO2 interface and its relationship to their electrical properties. Elemental distribution analyses performed by EELS reveal the existence of a transition layer between the SiC and the SiO2 regions of the same width for both MOSFETs despite a factor of nearly two between their electron mobility. Additional 3D compositional mapping by atom probe tomography corroborates these results, particularly the absence of an anomalous carbon distribution around the SiC/SiO2interface.

Solid State Communications, 221 (2015) 28-32 | DOI: 10.1016/j.ssc.2015.08.017

Long-Chain Polyhydroxyesters from Natural Occurring Aleuritic Acid as Potential Material for Food Packaging

Benitez, JJ; Heredia-Guerrero, JA; Guzman-Puyol, S; Dominguez, E; Heredia, A

Fatty polyhydroxyesters (C≥16) are present in nature as barrier polymers like cutin in some protective tissues of higher plants. The mimicry of these biopolymers is regarded as a strategy to design nontoxic and fully biodegradable food packaging films and coatings. To obtain cutin inspired materials we have used a natural occurring polyhydroxylated monomer like aleuritic (9,10,16-trihydroxypalmitic) acid and a direct and scalable synthesis route consisting in the noncatalyzed melt-condensation polymerization in air. To reduce the number of hydroxyl groups and to increase hydrophobicity, palmitic acid has been used as a capping agent. Aleuritic-palmitic polyhydroxyesteres films have been obtained and characterized.

Soft Materials, 13 (2015) 5-11 | DOI: 10.1080/1539445X.2014.993476

Effect of magnesium and titanium on the cathodic behaviour of aluminium in nitric acid

Garcia-Garcia, FJ, Chiu, TY, Skeldon, P, Thompson, GE

Cathodic polarization of aluminium and Al-0.18wt.%Mg and Al-0.08wt.% Ti alloys in 0.24moldm(-3) nitric acid solution at 38 degrees C has been employed to assist understanding of the roles of alloying elements in electrograining. The findings indicate that additions of magnesium and titanium to aluminium accelerate the corrosion of the substrate under the alkalization caused by the cathodic reactions. The accelerated dissolution and the consequent formation of hydrated alumina result in a decreased net cathodic current density in potentiostatic and potentiodynamic polarization conditions relative to the behaviour of aluminium. 

Surface and Interface Analysis, 47 (2015) 30-36 | DOI: 10.1002/sia.5640

Specific features of the electrical properties in partially graphitized porous biocarbons of beech wood

Popov, VV; Orlova, TS; Gutierrez-Pardo, A; Ramirez-Rico, J

The electrical and galvanomagnetic properties of partially graphitized highly porous bioC(Ni) biocarbon matrices produced by pyrolysis (carbonization) of beech wood at temperatures T (carb) = 850-1600A degrees C in the presence of a Ni-containing catalyst have been studied in comparison with their microstructural features. The temperature dependences of the resistivity, the magnetoresistance, and the Hall coefficient have been measured in the temperature range of 4.2-300 K in magnetic fields to 28 kOe. It has been shown that an additional graphite phase introduction into samples with T (carb) a parts per thousand yen 1000A degrees C results in an increase in the carrier mobility by a factor of 2-3, whereas the carrier (hole) concentration remains within similar to 10(20) cm(-3), as in biocarbons obtained without catalyst. An analysis of experimental data has demonstrated that the features of the conductivity and magnetoresistance of these samples are described by quantum corrections related to their structural features, i.e., the formation of a globular graphite phase of nano- and submicrometer sizes in the amorphous matrix. The quantum corrections to the conductivity decrease with increasing carbonization temperature, which indicates an increase in the degree of structure ordering and is in good agreement with microstructural data.

Physics of the solid state, 57 (2015) 1746-1751 | DOI: 10.1134/S1063783415090280

Microstructure, elastic and inelastic properties of partially graphitized biomorphic carbons

Orlova, TS; Kardashev, BK; Smirnov, BI; Gutierrez-Pardo, A; Ramirez-Rico, J; Martinez-Fernandez, J

The microstructural characteristics and amplitude dependences of the Young's modulus E and internal friction (logarithmic decrement delta) of biocarbon matrices prepared by beech wood carbonization at temperatures T (carb) = 850-1600A degrees C in the presence of a nickel-containing catalyst have been studied. Using X-ray diffraction and electron microscopy, it has been shown that the use of a nickel catalyst during carbonization results in a partial graphitization of biocarbons at T (carb) a parts per thousand yen 1000A degrees C: the graphite phase is formed as 50- to 100-nm globules at T (carb) = 1000A degrees C and as 0.5- to 3.0-mu m globules at T (carb) = 1600A degrees C. It has been found that the measured dependences E(T (carb)) and delta(T (carb)) contain three characteristic ranges of variations in the Young's modulus and logarithmic decrement with a change in the carbonization temperature: E increases and delta decreases in the ranges T (carb) < 1000A degrees C and T (carb) > 1300A degrees C; in the range 1000 < T (carb) < 1300A degrees C, E sharply decreases and delta increases. The observed behavior of E(T (carb)) and delta(T (carb)) for biocarbons carbonized in the presence of nickel correlates with the evolution of their microstructure. The largest values of E are obtained for samples with T (carb) = 1000 and 1600A degrees C. However, the samples with T (carb) = 1600A degrees C exhibit a higher susceptibility to microplasticity due to the presence of a globular graphite phase that is significantly larger in size and total volume.

Physics of the Solid State, 57 (2015) 586-591 | DOI: 10.1134/S106378341503018X

Simultaneous Production of CH4 and H-2 from Photocatalytic Reforming of Glucose Aqueous Solution on Sulfated Pd-TiO2 Catalysts

Vaiano, V; Iervolino, G; Sarno, G; Sannino, D; Rizzo, L; Mesa, JJM; Hidalgo, MC; Navio, JA

In this work, the simultaneous production of CH4 and H-2 from photocatalytic reforming of glucose aqueous solution on Pd-TiO2 catalysts under UV light irradiation by Light-Emitting Diodes (LED) was investigated. The Pd-TiO2 catalysts were prepared by the photodeposition method. The Pd content was in the range 0.5-2 wt% and a photodeposition time in the range 15-120 min was used. Pd-TiO2 powders were extensively characterized by X-Ray Diffraction (XRD), SBET, X-Ray Fluorescence spectrometry (XRF), UV-Vis Diffuse Reflectance Spectra (UV-Vis DRS), TEM and X-Ray Photoelectron Spectroscopy (XPS). It was found that the lower Pd loading (0.5 wt%) and 120 min of photodeposition time allowed us to obtain homogeneously distributed metal nanoparticles of small size; it was also observed that the increase in the metal loading and deposition time led to increasing the Pd-0 species effectively deposited on the sulfated TiO2 surface. Particle size and the oxidation state of the palladium were the main factors influencing the photocatalytic activity and selectivity. The presence of palladium on the sulfated titania surface enhanced the H-2 and CH4 production. In fact, on the catalyst with 0.5 wt% Pd loading and 120 min of photodeposition time, H-2 production of about 26 lmol was obtained after 3 h of irradiation time, higher than that obtained with titania without Pd (about 8.5 lmol). The same result was obtained for the methane production. The initial pH of the solution strongly affected the selectivity of the system. In more acidic conditions, the production of H-2 was enhanced, while the CH4 formation was higher under alkaline conditions.

Oil & Gas Science and Technology-Revue D IFP Energies Nouvelles, 70 (2015) 891-902 | DOI: 10.2516/ogst/2014062

Dye sensitized solar cells as optically random photovoltaic media

Galvez, FE; Barnes, PRF; Halme, J; Miguez, H

In order to enhance optical absorption, light trapping by multiple scattering is commonly achieved in dye sensitized solar cells by adding particles of a different sort. Herein we propose a theoretical method to find the structural parameters (particle number density and size) that optimize the conversion efficiency of electrodes of different thicknesses containing spherical inclusions of diverse composition. Our work provides a theoretical framework in which the response of solar cells containing diffuse scattering particles can be rationalized. Optical simulations are performed by combining a Monte Carlo approach with Mie theory, in which the angular distribution of scattered light is accounted for. Several types of scattering centers, such as anatase, gold and silver particles, as well as cavities, are considered and their effect compared. Estimates of photovoltaic performance, insight into the physical mechanisms responsible for the observed enhancements, and guidelines to improve the cell design are provided. We discuss the results in terms of light transport in weakly disordered optical media and find that the observed variations between the optimum scattering configurations attained for different electrode thicknesses can be understood as the result of the randomization of the light propagation direction at different depths within the active layer. A primary conclusion of our study is that photovoltaic performance is optimised when the scattering properties of the film are adjusted so that the distance over which incident photons are randomized is comparable to the thickness of the film. This simple relationship could also be used as a design rule to attain the optimum optical design in other photovoltaic materials.

Energy & Environmental Science, 6 (2014) 1260-1266 | DOI: 10.1039/C3EE42587H

Low Temperature Production of Formaldehyde from Carbon Dioxide and Ethane by Plasma-Assisted Catalysis in a Ferroelectrically Moderated Dielectric Barrier Discharge Reactor

Gomez-Ramirez, A; Rico, VJ; Cotrino, J; Gonzalez-Elipe, A; Lambert, RM

Plasma-assisted catalysis of the reaction between CO2 and C2H6 in a single-pass, ferroelectrically moderated dielectric barrier discharge reactor has been studied at near ambient temperature as a function of physicochemical and electrical reaction variables. The presence of small amounts of a vanadia/alumina catalyst dispersed on the BaTiO3 ferroelectric markedly enhanced the production of formaldehyde, the focus of this work. A maximum HCOH selectivity of 11.4% (defined with respect to the number of ethane carbon atoms consumed) at 100% ethane conversion was achieved, the other products being CO, H2O, H2, CH4 and a small amount of C3H8. N2O was also an effective partial oxidant (HCOH selectivity 8.9%) whereas use of O2 led to complete combustion, behavior that may be rationalized in terms of the electron impact excitation cross sections of the three oxidants. Control experiments with the coproducts CH4 and C3H8 showed that these species were not intermediates in HCOH formation from C2H6. Analysis of reactor performance as a function of discharge characteristics revealed that formaldehyde formation was strongly favored at low frequencies where the zero-current fraction of the duty cycle was greatest, the implication being that plasma processes also acted to destroy previously formed products. A tentative reaction mechanism is proposed that accounts for the broad features of formaldehyde production.

ACS Catalysis, 4 (2014) 402-408 | DOI: 10.1021/cs4008528

Active Site Considerations on the Photocatalytic H-2 Evolution Performance of Cu-Doped TiO2 Obtained by Different Doping Methods

Valero, JM; Obregon, S; Colon, G

A photocatalytic H2 evolution reaction was performed over copper doped TiO2. The influence of sulfate pretreatment over fresh TiO2 support and the Cu doping method has been evaluated. Wide structural and surface characterization of catalysts was carried out in order to establish a correlation between the effect of sulfuric acid treatment and the further Cu-TiO2photocatalytic properties. Notably a different copper dispersion and oxidation state is obtained by different metal decoration methods. From the structural and surface analysis of the catalysts we have stated that the occurrence of highly disperse and reducible Cu2+ species is directly related to the photocatalytic activity for the H2 production reaction. Highly active materials have been obtained from a chemical reduction method leading to 18 mmol·h–1·g–1for 3 mol % copper loading.

ACS Catalysis, 4 (2014) 3320-3329 | DOI: 10.1021/cs500865y

Biomechanical properties of the tomato (Solanum lycopersicum) fruit cuticle during development are modulated by changes in the relative amounts of its components

Espana, L; Heredia-Guerrero, JA; Segado, P; Benitez, JJ; Heredia, A; Dominguez, E

Keywords:
attenuated total reflectance–Fourier transform infrared (ATR-FTIR);biomechanics;cuticle;cutin;flavonoids;tomato (Solanum lycopersicum) fruit


Summary

- In this study, growth-dependent changes in the mechanical properties of the tomato (Solanum lycopersicum) cuticle during fruit development were investigated in two cultivars with different patterns of cuticle growth and accumulation.

- The mechanical properties were determined in uniaxial tensile tests using strips of isolated cuticles. Changes in the functional groups of the cuticle chemical components were analysed by attenuated total reflectance–Fourier transform infrared (ATR-FTIR).

- The early stages of fruit growth are characterized by an elastic cuticle, and viscoelastic behaviour only appeared at the beginning of cell enlargement. Changes in the cutin:polysaccharide ratio during development affected the strength required to achieve viscoelastic deformation. The increase in stiffness and decrease in extensibility during ripening, related to flavonoid accumulation, were accompanied by an increase in cutin depolymerization as a result of a reduction in the overall number of ester bonds.

- Quantitative changes in cuticle components influence the elastic/viscoelastic behaviour of the cuticle. The cutin:polysaccharide ratio modulates the stress required to permanently deform the cuticle and allow cell enlargement. Flavonoids stiffen the elastic phase and reduce permanent viscoelastic deformation. Ripening is accompanied by a chemical cleavage of cutin ester bonds. An infrared (IR) band related to phenolic accumulation can be used to monitor changes in the cutin esterification index.

New Phytologist, 202 (3) (2014) 790-802 | DOI: 10.1111/nph.12727

Production of hydrogen by water photo-splitting over commercial and synthesised Au/TiO2 catalysts

Mendez, JAO; Lopez, CR; Melian, EP; Diaz, OG; Rodriguez, JMD; Hevia, DF; Macias, M

H2 production from methanol/water photo-splitting was compared using various commercial photocatalysts (Evonik P25 (P25), Hombikat UV-100 (HB) and Kronos vlp7000 (KR)) and others synthesised with a sol–gel-hydrothermal (HT) process and a sol–gel method followed by calcination (SG400 and SG750). All photocatalysts had been surface modified with Au at different concentrations, from 0.2 to 6.0 wt.%, using the photodeposition method. A complete characterisation study of the different photocatalysts was performed (BET, XRD, TEM, SEM-EDX, FTIR, UV–vis Reflectance Diffuse Spectra and aggregate size). The experiments were conducted for 3.5 h using 1 g L−1 of photocatalyst with methanol (25 vol.%) as sacrificial agent. In addition to H2 generation, production of the main intermediates, formaldehyde and formic acid, and of CO2 was also evaluated. The commercial photocatalyst KR at 0.8 wt.% Au had the highest H2 production of all the photocatalysts studied with 1542.9 μmol h−1. Of the photocatalysts synthesised by our group, SG750 at Au loading of 2.0 wt.% gave the highest H2 production of 723.1 μmol h−1. The SG750 photocatalyst at Au loading of 2.0 wt.% also had the highest H2 production yield per unit of surface area at 45.5 μmol g h−1 m−2.

Applied Catalysis B: Environmental, 147 (2014) 439-452 | DOI: 10.1016/j.apcatb.2013.09.029

Improved H2 production of Pt-TiO2/g-C3N4-MnOx composites by an efficient handling of photogenerated charge pairs

Obregon, S; Colon, G

Pt-TiO2/g-C3N4-MnOx hybrid structures are synthesized by means of a simple impregnation method of Pt-TiO2 and g-C3N4-MnOx. From the wide structural and surface characterization we have stated that TiO2/g-C3N4 composites are formed by an effective covering of g-C3N4 by TiO2. The modification of composite by Pt and/or MnOx leads to improved photoactivities for phenol degradation reaction. Moreover, enhanced photoactivities have been obtained for composites systems for H2 evolution reaction. The notably photocatalytic performance obtained was related with the efficient separation of charge pairs in this hybrid heterostructure.

Applied Catalysis B: Environmental, 144 (2014) 775-782 | DOI: 10.1016/j.apcatb.2013.07.034

Effect of gold on a NiLaO3 perovskite catalyst for methane steam reforming

Palma, S; Bobadilla, LF; Corrales, A; Ivanova, S; Romero-Sarria, F; Centeno, MA; Odriozola, JA

The effect of gold addition to a supported Ni SRM catalyst has been studied in this work in order to determine the influence of gold on both the amount and type of carbon species formed during the reaction. The structure of the support, a mixed La–Al perovskite, determines the catalyst reducibility and Ni particle size. Gold addition affects the metal particle size increasing metal dispersion on increasing the gold content. Therefore, although gold blocks step Ni sites, the more active sites for Csingle bondH activation, and increases electron density on nickel, the higher dispersion results in an apparently higher activity upon gold addition. Moreover, gold addition increases the catalyst stability by decreasing the rate of growth of carbon nanotubes.

Applied Catalysis B: Environmental, 144 (2014) 846-854 | DOI: 10.1016/j.apcatb.2013.07.055

Correlation study between photo-degradation and surface adsorption properties of phenol and methyl orange on TiO2 Vs platinum-supported TiO2

Murcia, JJ; Hidalgo, MC; Navio, JA; Arana, J; Dona-Rodriguez, JM

Adsorption of phenol and methyl orange on the surface of TiO2 and Pt–TiO2 photocatalysts was investigated by FT-IR spectroscopy. It was found that platinum plays an important role in the adsorption properties of the studied substrates on TiO2. Platinum deposits modified the phenol-photocatalyst interaction providing new adsorption sites on TiO2 surface. On Pt–TiO2 photocatalysts, phenol mainly interacts via formation of adsorbed phenolates species. It was also found that the adsorption of methyl orange on titania and Pt–TiO2 photocatalysts occurs via interaction of the azo group with surface Ti4+. Pt photodeposition significantly increases the TiO2 photoreactivity in phenol and methyl orange photo-degradation; however, this increase depends on the properties of the Pt deposits. Moreover, it was observed that platinum content is the main factor determining the substrate-photocatalyst interaction and therefore the Pt–TiO2 photocatalytic performance.

Applied Catalysis B: Environmental, 150-151 (2014) 107-115 | DOI: 10.1016/j.apcatb.2013.12.010

In situ XAS study of an improved natural phosphate catalyst for hydrogen production by reforming of methane

Abba, MO; Gonzalez-DelaCruz, VM; Colon, G; Sebti, S; Caballero, A

Some nickel catalysts supported on natural phosphate (NP) have been tested for the dry methane reforming reaction. Although the original impregnated 15%Ni/NP catalyst has no activity at all, the modification of the support by mechano-chemical and/or acid treatment strongly improved the catalytic performance, yielding a series of very active and stable catalysts. The chemical and physical characterization by X-ray diffraction (XRD), temperature programmed reduction (TPR), in situ X-ray absorption spectroscopy (XAS) and other techniques have shown that these treatments mainly modify the interaction between the nickel phase and the support surface. The nickel ions occupy calcium position in the surface of the phosphate phase, which stabilizes and improves the dispersion of nickel species. The final reduced catalysts present a much better dispersed metallic phase interacting with the NP surface, which has been identified as responsible for the observed outstanding catalytic performances.

Applied Catalysis B: Environmental, 150-151 (2014) 459-465 | DOI: 10.1016/j.apcatb.2013.12.031

Could an efficient WGS catalyst be useful in the CO-PrOx reaction?

Reina, TR; Papadopoulou, E; Palma, S; Ivanova, S; Centeno, MA; Ioannides, T; Odriozola, JA

This work presents an evaluation of a high performance series of water gas shift (WGS) catalysts in the preferential CO oxidation reaction (PrOx) in order to examine the applicability of the same catalyst for both processes as a first step for coupling both reactions in a single process. Gold based catalysts are applied in an extensive study of the CO-PrOx reaction parameters, such as λ, WHSV, CO concentration and [H2O]/[CO2] ratio in order to obtain the best activity/selectivity balance. CO and H2 oxidation reactions were treated separately in order to establish the degree of CO/H2 oxidation competition. Additionally the catalysts behavior in the CO-PrOx parallel reactions such a WGS and RWGS have been also carried out to analyze their effect on product composition.

Applied Catalysis B: Environmental, 150-151 (2014) 554-563 | DOI: 10.1016/j.apcatb.2014.01.001

Excellent photocatalytic activity of Yb3+, Er3+ co-doped BiVO4 photocatalyst

Obregon, S.; Colon, G.

Ytterbium-Erbium co-doped BiVO4 have been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Methylene Blue and O2 evolution reactions. From the structural and morphological characterization it has been stated that the presence of Yb3+ and Er3+ induces the stabilization of the tetragonal phase probably due to its substitutional incorporation in the BiVO4 lattice. The occurrence of the Yb3+,Er3+ co-doped monoclinic-tetragonal BiVO4 heterostructure induces the higher photocatalytic activities. The best photocatalytic performance was attained for the sample with 1:4 Er3+:Yb3+ ratio. The observed NIR photoactivity clearly denotes the occurrence of an up-conversion mechanism involved in the overall photocatalytic process.

Applied Catalysis B: Environmental, 152-153 (2014) 328-334 | DOI: 10.1016/j.apcatb.2014.01.054

Heterostructured Er3+ doped BiVO4 with exceptional photocatalytic performance by cooperative electronic and luminescence sensitization mechanism

Obregon, S; Colon, G

Er-BiVO4 has been synthesized by means of mw-assisted hydrothermal method having good photoactivity under sun-like excitation. It is stated that the precursor addition sequence plays a critical role which determine the further structural feature of BiVO4. From the structural and morphological characterization, it can be demonstrated that the presence of Er3+ would induce the stabilization of the tetragonal phase probably due to the formation of tetragonal-ErVO4 seeds previous to BiVO4 formation. The best photocatalytic performance is attained for the sample with 0.75 at% Er3+ content. At this dopant loading a mixture of tetragonal and monoclinic phase (70% tetragonal) is obtained. The dramatic increase in the photocatalytic activity for 0.75 at% Er-BiVO4 is related to the occurrence of such heterostructure. For this system, the MB degradation rate constant appears drastically higher as bare m-BiVO4. Furthermore, activities of photocatalysts for visible-light-driven O2 evolution have been evaluated, demonstrating that the photocatalytic activity of this Er-doped system (O2 evolution rate, 1014 μmol g−1 h−1) is 20 times as that of undoped m-BiVO4 (O2 evolution rate, 54 μmol g−1 h−1). From the obtained results, the cooperative conjunction of electronic and luminescence mechanism involved in the reaction is proposed to be the origin of the enhanced photocatalytic efficiencies of such systems.

Applied Catalysis B: Environmental, 158-159 (2014) 242-249 | DOI: 10.1016/j.apcatb.2014.04.029

Supported Co catalysts prepared as thin films by magnetron sputtering for sodium borohydride and ammonia borane hydrolysis

Paladini, M; Arzac, GM; Godinho, V; De Haro, MCJ; Fernandez, A

Supported Co catalysts were prepared for sodium borohydride and ammonia borane hydrolysis by magnetron sputtering for the first time under different conditions. Ni foam was selected as support. Deposition conditions (time, pressure, and power) were varied to improve catalytic activity. A decrease in deposition power from 200 to 50 W, leads to a decrease in crystallite and column size and a higher activity of catalysts. The increase in deposition pressure from 1.5 × 10−2 to 4.5 × 10−2 mbar produces same effect but in this case the enhancement in activity is higher because amorphous materials were obtained. The highest activity for SB hydrolysis was 2650 ml min−1 gcat−1 for the 50 W Co 4.5 (4 h) sample (Ea = 60 ± 2 kJ mol−1). For AB hydrolysis activity for the 50 W Co 3.2 (4 h) sample was similar. Durability of the thin films was tested for both reactions upon cycling (14 cycles). Diluted acid washing was effective to recover the activity for sodium borohydride reaction but not for ammonia borane hydrolysis. The strong Co–NH3 interactions explain the non-efficiency of the acid washing.

Applied Catalysis B: Environmental, 158-159 (2014) 400-409 | DOI: 10.1016/j.apcatb.2014.04.047

Tailor-made directional emission in nanoimprinted plasmonic-based light-emitting devices

Lozano, G; Grzela, G; Verschuuren, MA; Ramezani, M; Rivas, JG

We demonstrate an enhanced and tailor-made directional emission of light-emitting devices using nanoimprinted hexagonal arrays of aluminum nanoparticles. Fourier microscopy reveals that the, luminescence of the device is not only determined by the material properties of the organic dye molecules but is also strongly influenced by the coherent scattering resulting from periodically arranged metal nanoparticles. Emitters can couple to lattice-induced hybrid plasmonic-photonic modes sustained by plasmonic arrays. Such modes enhance the spatial coherence of an emitting layer, allowing the efficient beaming of the emission along narrow angular and spectral ranges. We show that tailoring the separation of the nanoparticles in the array yields an accurate angular distribution of the emission. This combination of large-area metal nanostructures fabricated by nanoimprint lithography and light-emitting devices is beneficial for the design and optimization of solid-state lighting systems.

Nanoscale, 6 (2014) 9223-9229 | DOI: 10.1039/c4nr01391c

Shape-defined nanodimers by tailored heterometallic epitaxy

Garcia-Negrete, Carlos A; Rojas, Teresa C; Knappett, Benjamin R; Jefferson, David A; Wheatley, Andrew E H; Fernandez, Asuncion

The systematic construction of heterogeneous nanoparticles composed of two distinct metal domains (Au and Pt) and exhibiting a broad range of morphologically defined shapes is reported. It is demonstrated that careful Au overgrowth on Pt nanocrystal seeds with shapes mainly corresponding to cubeoctahedra, octahedra and octapods can lead to heterometallic systems whose intrinsic structures result from specific epitaxial relationships such as {111} + {111}, {200} + {200} and {220} + {220}. Comprehensive analysis shows also that nanoparticles grown from octahedral seeds can be seen as comprising of four Au tetrahedral subunits and one Pt octahedral unit in a cyclic arrangement that is similar to the corresponding one in decahedral gold nanoparticles. However, in the present case, the multi-component system is characterized by a broken five-fold rotational symmetry about the [011] axis. This set of bimetallic dimers could provide new platforms for fuel cell catalysts and plasmonic devices.

Nanoscale, 6 (2014) 11090-11097 | DOI: 10.1039/C4NR01815J

Pt vs. Au in water-gas shift reaction

Castano, MG; Reina, TR; Ivanova, S; Centeno, MA; Odriozola, JA

This work presents a comparison of the gold- and platinum-based catalysts behavior in the water–gas shift (WGS) reaction. The influence of the support, e.g., its composition and electronic properties, studied in detail by means of UV–Vis spectroscopy, of the metal nature and dispersion and of the stream composition has been evaluated. The catalytic performance of the samples is directly correlated with the electronic properties modification as a function of metal and/or support. Both metals present high activity in the selected reaction although in a different operation temperature window.

Journal of Catalysis, 314 (2014) 1-9 | DOI: 10.1016/j.jcat.2014.03.014

Direct evidence of Lowenstein's rule violation in swelling high-charge micas

Pavon, E; Osuna, FJ; Alba, MD; Delevoye, L

The structure of high-charged micas, Na-n-micas (n = 2 and 4), a family of synthetic silicates with a wide range of applications, was investigated through the use of 17O solid-state NMR at natural abundance in order to preserve quantitative spectral information. The use of a very high-field and highly sensitive probehead, together with 17O NMR literature data allowed for the detection of an isolated signal at 26 ppm, assigned partially to AlOAl, as evidence of the violation of Lowenstein's rule for Na-4-mica.

Chemical Communications, 53 (2014) 6984-6986 | DOI: 10.1039/C4CC01632G

Bending Induced Self-Organized Switchable Gratings on Polymeric Substrates

Parra-Barranco, J; Oliva-Ramirez, M; Gonzalez-Garcia, L; Alcaire, M; Macias-Montero, M; Borras, A; Frutos, F; Gonzalez-Elipe, AR; Barranco, A

We present a straightforward procedure of self-surface patterning with potential applications as large area gratings, invisible labeling, optomechanical transducers, or smart windows. The methodology is based in the formation of parallel micrometric crack patterns when polydimethylsiloxane foils coated with tilted nanocolumnar SiO2 thin films are manually bent. The SiO2 thin films are grown by glancing angle deposition at room temperature. The results indicate that crack spacing is controlled by the film nanostructure independently of the film thickness and bending curvature. They also show that the in-plane microstructural anisotropy of the SiO2 films due to column association perpendicular to the growth direction determines the anisotropic formation of parallel cracks along two main axes. These self-organized patterned foils are completely transparent and work as customized reversible diffraction gratings under mechanical activation.

ACS Applied Materials & Interfaces, 6 (2014) 11924-11931 | DOI: 10.1021/am5037687

Ceramic Barrier Layers for Flexible Thin Film Solar Cells on Metallic Substrates: A Laboratory Scale Study for Process Optimization and Barrier Layer Properties

Delgado-Sanchez, JM; Guilera, N; Francesch, L; Alba, MD; Lopez, L; Sanchez, E

Flexible thin film solar cells are an alternative to both utility-scale and building integrated photovoltaic installations. The fabrication of these devices over electrically conducting low-cost foils requires the deposition of dielectric barrier layers to flatten the substrate surface, provide electrical isolation between the substrate and the device, and avoid the diffusion of metal impurities during the relatively high temperatures required to deposit the rest of the solar cell device layers. The typical roughness of low-cost stainless-steel foils is in the hundred-nanometer range, which is comparable or larger than the thin film layers comprising the device and this may result in electrical shunts that decrease solar cell performance. This manuscript assesses the properties of different single-layer and bilayer structures containing ceramics inks formulations based on Al2O3, AlN, or Si3N4 nanoparticles and deposited over stainless-steel foils using a rotogravure printing process. The best control of the substrate roughness was achieved for bilayers of Al2O3 or AlN with mixed particle size, which reduced the roughness and prevented the diffusion of metals impurities but AlN bilayers exhibited as well the best electrical insulation properties.

ACS Applied Materials & Interfaces, 6 (2014) 18543-18549 | DOI: 10.1021/am504923z

A General Perspective of the Characterization and Quantification of Nanoparticles: Imaging, Spectroscopic, and Separation Techniques

Lapresta-Fernandez, A; Salinas-Castillo, A; de la Llana, SA; Costa-Fernandez, JM; Dominguez-Meister, S; Cecchini, R; Capitan-Vallvey, LF; Moreno-Bondi, MC; Marco, MP; Sanchez-Lopez, JC; Anderson, IS

This article gives an overview of the different techniques used to identify, characterize, and quantify engineered nanoparticles (ENPs). The state-of-the-art of the field is summarized, and the different characterization techniques have been grouped according to the information they can provide. In addition, some selected applications are highlighted for each technique. The classification of the techniques has been carried out according to the main physical and chemical properties of the nanoparticles such as morphology, size, polydispersity characteristics, structural information, and elemental composition. Microscopy techniques including optical, electron and X-ray microscopy, and separation techniques with and without hyphenated detection systems are discussed. For each of these groups, a brief description of the techniques, specific features, and concepts, as well as several examples, are described.

Critical Reviews in Solid State and Materials Sciences, 39 (2014) 423-458 | DOI: 10.1080/10408436.2014.899890

Chemical and electrical properties of LSM cathodes prepared by mechanosynthesis

Moriche, R.; Marrero-López, D.; Gotor, F.J.; Sayagués, M.J.

Mechanosynthesis of La1−xSrxMnO3 (x = 0, 0.25, 0.5, 0.75 and 1) was carried out at room temperature from stoichiometric mixtures of La2O3, Mn2O3 and SrO, obtaining monophasic powders with the perovskite structure. Physical properties of these materials and their chemical compatibility with the electrolyte yttria stabilized zirconia (YSZ), which depend strongly on the La/Sr ratio, were evaluated to corroborate availability to be implemented as cathode material in solid oxide fuel cells (SOFCs). Electrical conductivity values in air ranged between 100 and 400 S cm−1 in the temperature range of 25–850 °C. Samples presented low reactivity with YSZ in the working temperature range (600–1000 °C) maintaining the grain size small enough to preserve the catalytic activity for oxygen reduction.

Journal of Power Sources, 252 (2014) 43-50 | DOI: 10.1016/j.jpowsour.2013.11.093

Impregnation of carbon black for the examination of colloids using TEM

Gontard, LC; Knappett, BR; Wheatley, AEH; Chang, SLY; Fernandez, A

Nanoparticles are frequently synthesised as colloids, dispersed in solvents such as water, hexane or ethanol. For their characterisation by transmission electron microscopy (TEM), a drop of colloid is typically deposited on a carbon support and the solvent allowed to evaporate. However, this method of supporting the nanoparticles reduces the visibility of fine atomic details, particularly for carbonaceous species, due to interference from the 2-dimensional carbon support at most viewing angles. We propose here the impregnation of a 3 dimensional carbon black matrix that has been previously deposited on a carbon film as an alternative means of supporting colloidal nanoparticles, and show examples of the application of this method to advanced TEM techniques in the analysis of monometallic, core@shell and hybrid nanoparticles with carbon-based shells.

Nanoparticles represent one of the most studied structures in nanotechnology and nanoscience because of the wide range of applications arising from their unique optical, physical and chemical properties [1]. Often they have core@shell structures, or are coated with organic molecules. Nanoparticle functionality is largely affected by the specific configuration of the outer surface atoms. For example, in heterogeneous catalysis activity and selectivity are mostly determined by the type of atomic defects present at the surface of metallic nanoparticles, and in the field of biomedicine the surface coating of hybrid (inorganic core@organic shell) nanoparticles regulates their stability, solubility and targeting.

Nanoparticles are frequently synthesised using solution techniques that yield colloids, i.e., a solid–liquid mixture containing solid particles that are dispersed to various degrees in a liquid medium; most frequently water, ethanol or hexane. Colloid characterisation generally employs a variety of techniques to establish understanding and control over nanoparticle synthesis and properties. Electron microscopy in transmission mode (TEM) and in scanning transmission mode (STEM) are widely used for particle characterisation, and advances in these techniques mean that it is now routinely possible to resolve single atoms at the surfaces of nanoparticles using aberration-corrected microscopes, to elucidate the three-dimensional shapes of nanoparticles using electron tomography, and to enhance the contrast in very low density materials (e.g., carbonaceous materials) using electron holography [2] and [3]. However, the significant potential of these (S)TEM techniques is ultimately limited by the sample and the techniques available for sample preparation.

Typically, examination by (S)TEM requires that a nanoparticulate sample be prepared by depositing a drop of colloid on a thin, electron-transparent support. It is usual that an amorphous carbon film, silicon nitride film or graphene layers deposited on a copper grid constitute the support [4]. Crucially, these sample preparation techniques suffer from the major limitation that the contrast from the support often shadows atomic details at the particle surface. Moreover, it has been established that the thinnest supports can degrade under electron-beam irradiation, affecting particle stability [5], and also that hydrocarbon contamination can be an issue [6]. The most widely used commercially available TEM support is holey carbon, which comprises of a perforated carbon thin film. In this case, sample preparation aims to locate at least some of the nanoparticles of interest at the edges of the perforations. However, the concave nature of the holes means that solvent contaminants tend to accumulate preferentially at these sites. Moreover, if the TEM sample holder is tilted a particle attached to the edge of a hole is very likely to be shadowed by the carbon film. Taken together, these drawbacks significantly limit the application of techniques such as electron tomography [6].

We propose here a method of circumventing some of these fundamental problems by developing a technique for mounting nanoparticulate samples using a carbon matrix that is inspired by the way samples used in electrocatalysis are prepared [7]. Fig. 1 shows an image of a typical Pt-based electrocatalyst supported on carbon black as used in proton-electron membrane fuels cells, and which consists of Pt nanoparticles formed by calcination of a carbon black impregnated with a solution of salt precursor. Carbon black is a low-grade form of graphite, which is composed of nanocrystallites and no long-range order [8]. In Fig. 1 the carbon black is Vulcan XC-72R, which is widely used as a catalyst support in fuel cells because it provides high electrical conductivity, good reactant gas access, adequate water handling and good corrosion resistance, whilst allowing high dispersion of the particles. In electrocatalyst samples it is common to find particles, like the 5 nm Pt particle shown in Fig. 1, attached strongly to the surface of the support and viewed edge-on against a vacuum so as to provide optimal conditions for high-resolution TEM (HRTEM). Fig. 1B is a quantitative phase image of a Pt particle obtained from a defocus series of 20 images at intervals of 5 nm acquired in a FEGTEM JEOL 2020 at 200 kV with spherical aberration of −30 μm and applying the exit-wave restoration technique [2]. The contrast between details of the particle finestructure is very high compared to conventional HRTEM images, and details such as the presence of monoatomic carbon ribbons surrounding the particle can be seen.

Carbon, 76 (2014) 464-468 | DOI: 10.1016/j.carbon.2014.05.006

Effect of the type of acid used in the synthesis of titania–silica mixed oxides on their photocatalytic properties

Llano, B; Hidalgo, MC; Rios, LA; Navio, JA

TiO2–SiO2 mixed oxides were synthesized by the sol–gel technique using three different acids, i.e., acetic, sulfuric, or chlorhydric acid. Their photocatalytic behavior was evaluated on the phenol oxidation in liquid phase and correlated with the characterization results. It was found that the kind of acid used during the preparation strongly influences the phase composition and stability of the TiO2 phases incorporated in the silica structure as well as the photocatalytic activity. In all cases, silica introduced a dispersive effect that stabilized the TiO2 crystalline phases upon calcination at 700 °C. SO42− and CH3COO− ions stabilized the anatase phase at high calcination temperatures (700 °C) leading to samples with the highest photoactivities. Cl− ions induced the formation of traces of rutile and brookite resulting in a lower photoactivity. The highest photoactivity was achieved with the catalyst synthesized with acetic acid and calcined at 700 °C (TS1-700-ace). The photocatalytic performance of this material was even better than that obtained with the commercial catalyst Degussa P-25.

Applied Catalysis B: Environmental, 150-151 (2014) 389-395 | DOI: 10.1016/j.apcatb.2013.12.039

Nanosilica supported CaO: A regenerable and mechanically hard CO2 sorbent at Ca-looping conditions

Sanchez-Jimenez, PE; Perez-Maqueda, LA; Valverde, JM

This work presents a CO2 sorbent that may be synthesized from low-cost and widely available materials following a simple method basically consisting of impregnation of a nanostructured silica support with a saturated solution of calcium nitrate. In a first impregnation stage, the use of a stoichiometric CaO/SiO2 ratio serves to produce a calcium silicate matrix after calcination. This calcium silicate matrix acts as a thermally stable and mechanically hard support for CaO deposited on it by further impregnation. The CaO-impregnated sorbent exhibits a stable CaO conversion at Ca-looping conditions whose value depends on the CaO wt% deposited on the calcium silicate matrix, which can be increased by successive reimpregnations. A 10 wt% CaO impregnated sorbent reaches a stable conversion above 0.6 whereas the stable conversion of a 30 wt% CaO impregnated sorbent is around 0.3, which is much larger than the residual conversion of CaO derived from natural limestone (between 0.07 and 0.08). Moreover, particle size distribution measurements of samples predispersed in a liquid and subjected to high energy ultrasonic waves indicate that the CaO-impregnated sorbent has a relatively high mechanical strength as compared to limestone derived CaO.

Applied Energy, 118 (2014) 92-99 | DOI: 10.1016/j.apenergy.2013.12.024

Role of precalcination and regeneration conditions on postcombustion CO2 capture in the Ca-looping technology

Valverde, JM; Sanchez-Jimenez, PE; Perez-Maqueda, LA

The Ca-looping (CaL) technology is already recognized as a potentially viable method to capture CO2 from postcombustion gas in coal fired power plants. In this process, CO2 is chemisorbed by CaO solid particles derived from precalcination of cheap and widely available natural limestone. The partially carbonated solids are regenerated by calcination under high CO2 concentration. Novel CaL concepts are proposed to further improve the efficiency of the technology such as the introduction of a recarbonation reactor in between the carbonation and calcination stages to mitigate the progressive deactivation of the regenerated CaO. Process simulations aimed at retrieving optimum design parameters and operating conditions to scale-up the technology yield results critically dependent on the multicyclic sorbent performance. Nevertheless, technical limitations usually preclude lab-scale tests from mimicking realistic CaL conditions necessarily involving high CO2 concentration for sorbent regeneration and quick transitions between carbonation and calcination. In this work, a lab-scale experimental analysis is reported on the CaO multicyclic conversion at CaL conditions closely resembling those to be expected in practice. The results presented evidence a relevant role of precalcination conditions. Precalcination in air leads to a strongly adverse effect on the activity of the sorbent regenerated under high CO2 concentration, which is further hindered if a recarbonation stage is introduced. On the other hand, sorbent deactivation is mitigated if precalcination is carried out at conditions similar to those used for sorbent regeneration. In this case, recarbonation helps lessening the loss of multicyclic conversion, which is further enhanced by the synergistic combination with heat pretreatment. Moreover, the present study shows that the kinetics of carbonation is strongly dependent on precalcination and regeneration conditions. The diffusion controlled carbonation phase and recarbonation are intensified if the sorbent is precalcined and regenerated under high CO2 concentration whereas the reaction controlled carbonation phase is notably hampered.

Applied Energy, 136 (2014) 347-356 | DOI: 10.1016/j.apenergy.2014.09.052

Calcium-looping for post-combustion CO2 capture. On the adverse effect of sorbent regeneration under CO2

Valverde, JM; Sanchez-Jimenez, PE; Perez-Maqueda, LA

The multicyclic carbonation/calcination (c/c) of CaO solid particles at high temperature is at the basis of the recently emerged Calcium-looping (CaL) technology, which has been shown to be potentially suitable for achieving high and sustainable post-combustion CO2 capture efficiency. Despite the success of pilot plant projects at the MWth scale, a matter of concern for scaling-up the CaL technology to a commercial level (to the GWth scale) is that the CaO carbonation reactivity can be recovered only partially when the sorbent is regenerated by calcination at high temperatures (around 950 °C) as required by the CO2 high concentration in the calciner. In order to reactivate the sorbent, a novel CaL concept has been proposed wherein a recarbonator reactor operated at high temperature/high CO2 concentration leads to further carbonation of the solids before entering into the calciner for regeneration. Multicyclic thermogravimetric analysis (TGA) tests demonstrate the feasibility of recarbonation to reactivate the sorbent regenerated at high calcination temperatures yet at unrealistically low CO2 partial pressure mainly because of technical limitations concerning low heating/cooling rates. We report results from multicyclic c/c and carbonation/recarbonation/calcination (c/r/c) TGA tests at high heating/coling rates and in which the sorbent is regenerated in a dry atmosphere at high CO2 partial pressure. It is shown that at these conditions there is a drastic drop of CaO conversion to a very small residual value in just a few cycles. Moreover, the introduction of a recarbonation stage has actually an adverse effect. Arguably, CaCO3 decomposition in a CO2 rich atmosphere is ruled by CO2 dynamic adsorption/desorption in reactive CaO (1 1 1) surfaces as suggested by theoretical studies, which would preclude the growth of the regenerated CaO crystal structure along these reactive surfaces, and this effect would be intensified by recarbonation. Nevertheless, the presence of H2O in the calciner, which is also adsorbed/desorbed dynamically in CaO reactive planes, would shield CO2 adsorption/desorption thus mitigating the deeply detrimental effect of CO2 on the carbonation reactivity of the regenerated CaO structure. Oxy-combustion, which produces a significant amount of H2O, is currently used in pilot-scale plants to raise the temperature in the calciner. Auxiliary techniques are being explored to help heating the partially carbonated solids since oxyxombustion represents an important penalty to the CaL technology. Our study suggests that steam injection would be necessary in a dry calciner environment to avoid a sharp loss of CaO conversion if the sorbent is regenerated at high CO2 partial pressure.

Applied Energy, 126 (2014) 161-171 | DOI: 10.1016/j.apenergy.2014.03.081

Improved O-2 evolution from a water splitting reaction over Er3+ and Y3+ co-doped tetragonal BiVO4

Obregon, S; Colon, G

Erbium–yttrium co-doped BiVO4 with a tetragonal structure is synthesized by means of a surfactant free hydrothermal method. The studied photocatalyst shows good photoactivity under sun-like excitation for the degradation of methylene blue (MB) and for O2 evolution. From structural and morphological characterization, it has been stated that the presence of lanthanides induces the stabilization of the tetragonal phase. This is probably due to the substitutional occupation that occurs in the BiVO4 lattice. The photocatalytic performance under visible-NIR radiation clearly evidences the occurrence of an up-conversion process involved in the overall photo-electronic mechanism. The tetragonal phase Er0.0075,Y0.03–Bi0.9625VO4 system gives the highest O2 evolution rate (425 μmol g−1 h−1) under sun-like excitation, being 8 times higher than that attained for m-BiVO4 (53 μmol g−1 h−1).

Catalysis Science & Technology, 4 (2014) 2042-2050 | DOI: 10.1039/C4CY00050A

Tuning the transmittance and the electrochromic behavior of CoxSiyOz thin films prepared by magnetron sputtering at glancing angle

Gil-Rostra, J; Garcia-Garcia, F; Yubero, F; Gonzalez-Elipe, AR

This work reports the synthesis and the characterization of amorphous CoxSiyOz thin films prepared by magnetron sputtering from a single cathode. Porous layers with outstanding electrochromic properties are obtained at room temperature in one step by performing the deposition at a glancing angle configuration. The electrochromic behavior of these layers in a basic aqueous medium was dependent on the Co/Si ratio in the films and in all cases was characterized by a fast response, a high coloration efficiency and a complete reversibility after several hundred cycles. A characteristic feature of these electrochromic layers is that, for a similar thickness, the range of transmittance modulation can be tuned by changing the Co/Si ratio in the films and, specifically for films with a high concentration of silicon, to change their aspect from an almost transparent to a full colored state.

Solar Energy Materials and Solar Cells, 123 (2014) 130-138 | DOI: 10.1016/j.solmat.2013.12.020

Relevant Influence of Limestone Crystallinity on CO2 Capture in The Ca-Looping Technology at Realistic Calcination Conditions

Valverde, JM; Sanchez-Jimenez, PE; Perez-Maqueda, LA

We analyze the role of limestone crystallinity on its CO2 capture performance when subjected to carbonation/calcination cycles at conditions mimicking the Ca-looping (CaL) technology for postcombustion CO2 capture. The behavior of raw and pretreated limestones (milled and thermally annealed) is investigated by means of thermogravimetric analysis (TGA) tests under realistic sorbent regeneration conditions, which necessarily involve high CO2 partial pressure in the calciner and quick heating rates. The pretreatments applied lead to contrasting effects on the solid crystal structure and, therefore, on its resistance to solid-state diffusion. Our results show that decarbonation at high CO2 partial pressure is notably promoted by decreasing solid crystallinity. CaO regeneration is fully achieved under high CO2 partial pressure at 900 °C in short residence times for the milled limestone whereas complete regeneration for raw limestone requires a minimum calcination temperature of about 950 °C. Such a reduction of the calcination temperature and the consequent mitigation of multicyclic capture capacity decay would serve to enhance the efficiency of the CaL technology. On the other hand, the results of our study suggest that the use of highly crystalline limestones would be detrimental since excessively high calcination temperatures should be required to attain full decarbonation at realistic conditions.

Environmental Science & Technology, 48 (2014) 9882-9889 | DOI: 10.1021/es5014505

Role of crystal structure on CO2 capture by limestone derived CaO subjected to carbonation/recarbonation/calcination cycles at Ca-looping conditions

Valverde, JM; Sanchez-Jimenez, PE; Perez-Maqueda, LA; Quintanilla, MAS; Perez-Vaquero, J

Large scale pilot plants are currently demonstrating the feasibility of the Calcium-looping (CaL) technology built on the multicyclic calcination/carbonation of natural limestone for post-combustion and precombustion CO2 capture. Yet, limestone derived CaO exhibits a drop of conversion when subjected to multiple carbonation/calcination cycles, which lessens the efficiency of the technology. In this paper we analyze a novel CaL concept recently proposed to mitigate this drawback based on the introduction of an intermediate stage wherein carbonation is intensified at high temperature and high CO2 partial pressure. It is shown that carbonation in this stage is mainly driven by solid-state diffusion, which is determined by the solid's crystal structure. Accordingly, a reduction of crystallinity by ball milling, which favors diffusion, serves to promote recarbonation. Conversely, thermal annealing, which enhances crystallinity, hinders recarbonation. An initial fast phase has been identified in the recarbonation stage along which the rate of carbonation is also a function of the crystal structure indicating a relevant role of surface diffusion. This is consistent with a recently proposed mechanism for nucleation of CaCO3 on the CaO surface in islands with a critical size determined by surface diffusion. A further issue analyzed has been the effects of pretreatment and cycling on the mechanical strength of the material, whose fragility hampers the CaL process efficiency. Particle size distribution of samples dispersed in a liquid and subjected to high energy ultrasonic irradiation indicate that milling promotes friability whereas thermal annealing enhances the resistance of the particles to fragmentation even though pretreatment effects become blurred after cycling. Our study demonstrates that recarbonation conditions and crystal-structure controlled diffusion are important parameters to be considered in order to assess the efficiency of CO2 capture in the novel CaL concept.

Applied Energy, 125 (2014) 264-275 | DOI: 10.1016/j.apenergy.2014.03.065

Bifunctional, Monodisperse BiPO4-Based Nanostars: Photocatalytic Activity and Luminescent Applications

Becerro, AI; Criado, J; Gontard, LC; Obregon, S; Fernandez, A; Colon, G; Ocana, M

Monodisperse, monoclinic BiPO4 nanostars have been synthesized by a homogeneous precipitation reaction at 120 °C through controlled release of Bi3+ cations from a Bi–citrate chelate, in a mixture of glycerol and ethylene glycol, using H3PO4 as the phosphate source. The set of experimental conditions necessary to obtain uniform nanoparticles is very restrictive, as the change in either the polyol ratio or the reactant concentrations led to ill-defined and/or aggregated particles. The morphology of the particles consists of a starlike, hierarchical structure formed by the ordered arrangement of nanorod bundles. Transmission electron tomography has revealed that the nanostars are not spherical but flattened particles. Likewise, Fourier transform infrared spectroscopy and thermogravimetry have shown that the synthesized nanostars are functionalized with citrate groups. The mechanism of formation of the nanostars has been analyzed to explain their morphological features. The as-synthesized BiPO4 nanostars exhibit an efficient photocatalytic performance for the degradation of Rhodamine B. Finally, it has been demonstrated that the stars can be Eu3+-doped up to 2 mol % without any change in the particle morphology or symmetry, and the doped samples show emission in the orange-red region of the visible spectrum after ultraviolet excitation. These experimental observations make this material a suitable phosphor for biotechnological applications.

Crystal Growth & Design, 14 (2014) 3319-3326 | DOI: 10.1021/cg500208h

The Mitigation Effect of Synthetic Polymers on Initiation Reactivity of CL-20: Physical Models and Chemical Pathways of Thermolysis

Yan, QL; Zeman, S; Jimenez, PES; Zhang, TL; Perez-Maqueda, LA; Elbeih, A

In this paper, the thermal decomposition physical models of different CL-20 polymorph crystals and their polymer bonded explosives (PBXs) bonded by polymeric matrices using polyisobutylene (PIB), acrylonitrile butadiene rubber (NBR), styrene butadiene rubber (SBR), Viton A, and Fluorel binders are obtained and used to predict the temperature profiles of constant rate decomposition. The physical models are further supported by the detailed decomposition pathways simulated by a reactive molecular dynamics (ReaxFF-lg) code. It has been shown that both ε-CL-20 and α-CL-20 decompose in the form of γ-CL-20, resulting in close activation energy (169 kJ mol–1) and physical model (first-order autoaccelerated model, AC1). Fluoropolymers could change the decomposition mechanism of ε-CL-20 from the “first-order autocatalytic” model to a “three-dimensional nucleation and growth” model (A3), while the polymer matrices of Formex P1, Semtex, and C4 could change ε-CL-20 decomposition from a single-step process to a multistep one with different activation energies and physical models. Compared to fluoropolymers, PIB, SBR and NBR may make ε-CL-20 undergo more complete N–NO2 scission before collapse of the cage structure. This is likely the main reason why those polymer bases could greatly mitigate the decomposition process of ε-CL-20 from a single step to a multistep, resulting in lower impact sensitivity, whereas fluoropolymers have only a little effect on that. For ε-CL-20 and its PBXs, the impact sensitivity depends not only on the heat built-up period of their decomposition, but also on the probability of hotspot generation (defects in solid crystals and interfaces) especially when it decomposes in a solid state.

Journal of Physical Chemistry C, 118 (2014) 22881-22895 | DOI: 10.1021/jp505955n

Thermal Stability of Multiferroic BiFeO3: Kinetic Nature of the beta-gamma Transition and Peritectic Decomposition

Perejon, A; Sanchez-Jimenez, PE; Criado, JM; Perez-Maqueda, LA

The thermal stability of BiFeO3 prepared by mechanosynthesis and sintered at 850 °C has been studied by DSC as a function of the atmosphere and temperature. It has been found that neither the phase transitions nor the thermal stability of BiFeO3 is affected by the atmosphere in which the heating process is performed. The material is unstable above the α–β transition (TC) and slowly decomposes to produce Bi2O3 and Bi2Fe4O9. The kinetics of this slow process has been studied by performing heating–cooling DSC cycles, concluding it follows an Avrami–Erofeev nucleation and growth kinetic model. The β–γ transition and the peritectic decomposition of BiFeO3 overlap and are kinetically controlled. The kinetics of this complex process has been studied for the first time employing a new kinetic analysis procedure implying the deconvolution and subsequent analysis of the individual contributing stages. Thus, it has been demonstrated that the decomposition of BiFeO3 is accelerated when the sample is heated above the β–γ transition and both processes also follow Avrami–Erofeev kinetic models.

Journal of Physical Chemistry C, 118 (2014) 26387-26395 | DOI: 10.1021/jp507831j

Interaction of Hydrated Cations with Mica-n (n = 2, 3 and 4) Surface

Pavon, E; Castro, MA; Cota, A; Osuna, FJ; Pazos, MC; Alba, MD

High charged swelling micas, with layer charge between 2 and 4, have been found to readily swell with water, and complete cation exchange (CEC) can be achieved. Because of their high CEC, applications like radioactive cation fixation or removal of heavy metal cations from wastewater were proposed. Their applicability can be controlled by the location of the interlayer cation in a confined space with a high electric field. In synthetic brittle micas, the interlayer cation has a low water coordination number; therefore, their coordination sphere would be completed by the basal oxygen of the tetrahedral layer as inner-sphere complexes (ISC). However, no direct evidence of these complexes formation in brittle micas has been reported yet. In this contribution, we mainly focus on the understanding the mechanisms that provoke the formation of ISC in high charge swelling micas, Mica-n. A whole series of cations (X) were used to explore the influence of the charge and size of the interlayer cation. Three brittle swelling micas, Mica-n (n = 4, 3 and 2), were selected in order to analyze the influence of the layer charge in the formation of ISC. The contribution of the ISC has been analyzed thorough the evolution of the 060 reflection and the changes in the short-range order of the tetrahedral cations will be followed 29Si and 27Al MAS NMR. The results showed that ISC was favored in X-Mica-4 and that provoked a high distortion angle between the Si–Al tetrahedra. When the content of aluminum decreases, the electrostatic forces between the layers are relaxed, and the hydrated cations did not interact so strongly with the tetrahedral sheet, having the opportunity to complete their hydration sphere.

Journal of Physical Chemistry C, 118 (2014) 2115-2121 | DOI: 10.1021/jp4110695

Oxygen Optical Sensing in Gas and Liquids with Nanostructured ZnO Thin Films Based on Exciton Emission Detection

Sanchez-Valencia, JR; Alcaire, M; Romero-Gomez, P; Macias-Montero, M; Aparicio, FJ; Borras, A; Gonzalez-Elipe, AR; Barranco, A

Transparent nanocolumnar porous ZnO thin films have been prepared by plasma-enhanced chemical vapor deposition. By controlling the H-2/O-2 ratio in the plasma gas, the deposition conditions were optimized to obtain an intense exciton emission at around 381 nm and virtually no luminescence in the visible region associated with electronic states in the gap. The intensity of the exciton band varied significantly and reversibly with the partial pressure of oxygen in the environment. This behavior and its variations with temperature and water vapor sustain the use of these thin films as photonic sensors of oxygen. Further experiments in liquid water show that fluorescence intensity also varies with the amount of dissolved oxygen even for concentrations lower than 0.02 mg/L where commercial oxygen galvanic sensors show limited sensitivity. These results and the use of ZnO as photonic sensor of oxygen are discussed by assuming a classical mechanism involving the photoactivated adsorption of oxygen when this oxide is irradiated with UV light during its fluorescence interrogation.

Journal of Physical Chemistry C, 118 (2014) 9852-9859 | DOI: 10.1021/jp5026027

The Flexible Surface Revisited: Adsorbate-Induced Reconstruction, Homocoupling, and Sonogashira Cross-Coupling on the Au(100) Surface

Sanchez-Sanchez, C; Yubero, F; Gonzalez-Elipe, AR; Feria, L; Sanz, JF; Lambert, RM

Phenylacetylene (PA) and iodobenzene (IB) are prototypical reactants in Sonogashira cross-coupling. Their adsorption behavior and reactivity on the Au(100) surface were studied by STM, temperature-programmed desorption and reaction, and DFT calculations that included the effect of dispersion forces. The two species exhibited very different behavior. Thus, even at 200 K, PA rearranged Au surface atoms so as to lift the hex reconstruction and adsorb in 4-fold-symmetric islands on the unreconstructed 100 surface. On the other hand, IB adsorbed on the reconstructed hex surface, again as islands, forming three different coexisting close-packed structures. The DFT results are in good accord with these findings, demonstrating the strong preference of PA and IB for the (100) and hex surfaces, respectively. Moreover, the calculated adsorption energies were in satisfactory agreement with values estimated from the desorption data. Adsorbed separately, both PA and IB underwent homocoupling yielding diphenyl diacetylene and biphenyl, respectively; in the former case, reaction appeared to originate at island boundaries. On the well-annealed surface, coadsorbed PA and IB behaved independently, generating only products of homocoupling. However, on the Ar+ roughened surface, Sonogashira cross-coupling also occurred, yielding diphenyl acetylene. These findings are discussed in terms of the island-forming propensity of the reactants, amplified by the labile nature of the Au 100 surface under adsorption and the marked preference of the two reactants for different substrate structures, factors that act to inhibit the formation of a mixed adlayer and suppress reactivity. The implications for the behavior of practical Au nanoparticle catalysts are considered.

Journal of Physical Chemistry C, 118 (2014) 11677-11684 | DOI: 10.1021/jp501321u

New Single-Phase, White-Light-Emitting Phosphors Based on delta-Gd2Si2O7 for Solid-State Lighting

Fernandez-Carrion, AJ; Ocana, M; Garcia-Sevillano, J; Cantelar, E; Becerro, AI

Two new white-light (WL)-emitting phosphors (δ-Gd2Si2O7:Dy and δ-Gd2Si2O7:Eu,Tb) have been synthesized by the sol–gel method. The Gd-Ln3+ (Ln3+= Dy3+, Tb3+, Eu3+) energy-transfer band has been used to excite both phosphors, which provides an enhancement of the Ln3+ emissions. First, WL was generated from δ-Gd2Si2O7:xDy thanks to the particular ratio of the blue and yellow emissions observed in all three compositions, which had chromatic coordinates of x = 0.30, y = 0.33 and CCT values of between 7077 and 6721 K. The decay curves of the main transitions of Dy3+ showed a maximum lifetime value for δ-Gd2Si2O7:0.5%Dy, which is, therefore, the most efficient doping level. Second, a broad spectral range, single-phase, WL-emitting phosphor was generated by codoping δ-Gd2Si2O7 with Tb3+ and Eu3+. The composition δ-Gd2Si2O7:0.3%Eu3+;0.8%Tb3+ showed CIE coordinates well inside the ideal WL region of the CIE diagram and a CCT value of 5828 K. The single-phase WL-emitting phosphors presented in this paper are promising materials to be used in white solid-state lighting systems and field-emission displays due to the advantages provided both by Gd3+ ions and by the high thermal and chemical stabilities of the rare earth disilicate matrix.

Journal of Physical Chemistry C, 118 (2014) 18035-18043 | DOI: 10.1021/jp505524g

Luminescent 3-hydroxyflavone nanocomposites with a tuneable refractive index for photonics and UV detection by plasma assisted vacuum deposition

Aparicio, FJ; Alcaire, M; Borras, A; Gonzalez, JC; Lopez-Arbeloa, F; Blaszczyk-Lezak, I; Gonzalez-Elipe, AR; Barranco, A

Luminescent organic-thin-films transparent in the visible region have been synthesized by a plasma assisted vacuum deposition method. The films have been developed for their implementation in photonic devices and for UV detection. They consist of a plasma polymeric matrix that incorporates 3-hydroxyflavone molecules characterized by absorption of UV radiation and emission of green light. The present work studies in detail the properties and synthesis of this kind of transparent and luminescent material. The samples were characterized by X-ray photoemission (XPS), infrared (FT-IR) and secondary ion mass (ToF-SIMS) spectroscopies; and their optical properties were analysed by UV-Vis absorption, fluorescence and ellipsometry (VASE) spectroscopies. The key factors controlling the optical and luminescent properties of the films are also discussed. Indeed, our experimental results show how the optical properties of the films can be adjusted for their integration in photonic devices. Moreover, time resolved and steady state fluorescence analyses, including quantum yield determination, indicate that the fluorescence efficiency is a function of the deposition parameters. An outstanding property of these materials is that, even for high UV absorption values (i.e. large layer thickness and/or dye concentration), the emitted light is not reabsorbed by the film. Such highly UV absorbent and green emitting films can be used as UV photodetectors with a detection threshold smaller than 10 mu W cm(-2), a value similar to the limit of some commercial UV photodetectors. Based on these properties, the use of the films as visual tags for the detection of solar UV irradiation is proposed.

Journal of Materials Chemistry C, 2 (2014) 6561-6573 | DOI: 10.1039/c4tc00294f

Single phase, electrically insulating, multiferroic La-substituted BiFeO3 prepared by mechanosynthesis

Perejon, A; Sanchez-Jimenez, PE; Perez-Maqueda, LA; Criado, JM; de Paz, JR; Saez-Puche, R; Maso, N; West, AR

Single phase, electrically insulating samples of Bi1−xLaxFeO3 solid solutions have been prepared by mechanosynthesis over the whole compositional range for the first time. Lanthanum substitution influenced the kinetics of the mechanochemical reaction and crystallite size of the products. For 0 ≤ x ≤ 0.15, an increase in the La content produced a significant decrease in the weight-normalized cumulative kinetic energy required to obtain the final product and an increase in the resulting crystallite size. Larger La contents did not affect either the reactivity or the crystallite size. The effect of x on the structure has been identified. Samples in the ranges x ≤ 0.15 and x ≥ 0.45 gave single phase solid solutions with R3c and Pnma space groups, respectively, while for the intermediate range, a non-centrosymetric Pn21a(00γ)s00 super structure was obtained. For 0 ≤ x ≤ 0.30, differential scanning calorimetry showed two endothermic effects corresponding to the Néel temperature (TN, antiferromagnetic–paramagnetic transition) and the Curie temperature (TC, ferroelectric–paraelectric transition), demonstrating their multiferroic character. Compositions with a larger La content only showedTN. Dilatometric and permittivity measurements confirmed the results obtained by DSC for the ferroelectric–paraelectric transition. The composition dependence of TN and TC showed that, at low x, TN < TC, but a cross-over, or isoferroic transition occurred at x [[similar]] 0.28, when TN = TC = 386 °C. Ceramics with 0 ≤ x ≤ 0.15 were highly insulating at room temperature with a resistivity, extrapolated from the Arrhenius plots, of [[similar]] 7 × 1016 to 8 × 1014 Ω cm and an activation energy [[similar]] 1.14–1.20 eV. Magnetization of the samples improved with La substitution.

Journal of Materials Chemistry C, 2 (2014) 8398-8411 | DOI: 10.1039/C4TC01426J

Viability of Au/CeO2-ZnO/Al2O3 Catalysts for Pure Hydrogen Production by the Water-Gas Shift Reaction

Reina, TR; Ivanova, S; Delgado, JJ; Ivanov, I; Idakiev, V; Tabakova, T; Centeno, MA; Odriozola, JA

The production of H2 pure enough for use in fuel cells requires the development of very efficient catalysts for the water–gas shift reaction. Herein, a series of gold catalysts supported on ZnO-promoted CeO2–Al2O3 are presented as interesting systems for the purification of H2 streams through the water–gas shift reaction. The addition of ZnO remarkably promotes the activity of an Au/CeO2/Al2O3 catalyst. This increase in activity is mainly associated with the enhanced oxygen storage capacity exhibited for the Zn-containing solids. High activity and good stability and resistance towards start-up–shut-down situations was found, which makes these catalysts a promising alternative for CO clean-up applications.

ChemCatChem, 6 (2014) 1401-1409 | DOI: 10.1002/cctc.201300992

The effect of polymer matrices on the thermal hazard properties of RDX-based PBXs by using model-free and combined kinetic analysis

Yan, QL; Zeman, S; Jimenez, PES; Zhao, FQ; Perez-Maqueda, LA; Malek, J

In this paper, the decomposition reaction models and thermal hazard properties of 1,3,5-trinitro-1,3,5-triazinane (RDX) and its PBXs bonded by Formex P1, Semtex 1A, C4, Viton A and Fluorel polymer matrices have been investigated based on isoconversional and combined kinetic analysis methods. The established kinetic triplets are used to predict the constant decomposition rate temperature profiles, the critical radius for thermal explosion and isothermal behavior at a temperature of 82 C. It has been found that the effect of the polymer matrices on the decomposition mechanism of RDX is significant resulting in very different reaction models. The Formex P1, Semtex and C4 could make decomposition process of RDX follow a phase boundary controlled reaction mechanism, whereas the Viton A and Fluorel make its reaction model shifts to a two dimensional Avrami-Erofeev nucleation and growth model. According to isothermal simulations, the threshold cook-off time until loss of functionality at 82 degrees C for RDX-C4 and RDX-FM is less than 500 days, while it is more than 700 days for the others. Unlike simulated isothermal curves, when considering the charge properties and heat of decomposition, RDX-FM and RDX-C4 are better than RDX-SE in storage safety at arbitrary surrounding temperature.

Journal of Hazardous Materials, 271 (2014) 185-195 | DOI: 10.1016/j.jhazmat.2014.02:019

Panchromatic porous specular back reflectors for efficient transparent dye solar cells

Lopez-Lopez, C; Colodrero, S; Miguez, H

A panchromatic specular reflector based dye solar cell is presented herein. Photovoltaic performance of this novel design is compared to that of cells in which standard diffuse scattering layers are integrated. The capability of the proposed multilayer structures to both emulate the broad band reflection of diffuse scattering layers of standard thickness (around 5 microns) and give rise to similarly high light harvesting and power conversion efficiencies, yet preserving the transparency of the device, is demonstrated. Such white light reflectors are comprised of stacks of different porous optical multilayers, each one displaying a strong reflection in a complementary spectral range, and are designed to leave transmittance unaltered in a narrow red-frequency range in which the sensitized electrode shows negligible absorption, thus allowing us to see through the cell. The reflectance bandwidth achieved is three times as broad as the largest bandwidth previously achieved using any photonic structure integrated into a dye solar cell.

Physical Chemistry Chemical Physics, 16 (2014) 663-668 | DOI: 10.1039/C3CP53939C

Morphological and structural behavior of TiO2 nanoparticles in the presence of WO3: crystallization of the oxide composite system

Kubacka, A; Iglesias-Juez, A; di Michiel, M; Becerro, AI; Fernandez-Garcia, M

Composite TiO2-WO3 oxide materials were prepared by a single pot microemulsion method and studied during calcination treatments under dry air in order to analyze the influence of tungsten on the behavior of the dominant titania component. To this end, the surface and bulk morphological and structural evolution of the solid precursors was studied using X-ray diffraction and infrared spectroscopy. In the calcination process, differences in the dominant titania component behavior appeared as a function of the W/Ti atomic ratio of the precursor. First, the crystallization of the anatase phase is affected by tungsten through an effect on the primary particle size growth. Furthermore, such an effect also influences the anatase to rutile phase transformation. The study provides evidence that the W-Ti interaction develops differently for a low/high W/Ti atomic ratio below/above 0.25 affecting fundamentally the above-mentioned anatase primary particle size growth process and the subsequent formation of the rutile phase and showing that addition of tungsten provides a way to control morphology and phase behavior in anatase-based oxide complex materials.

Physical Chemistry Chemical Physics, 16 (2014) 19540-19549 | DOI: 10.1039/c4cp02181a

New Bio-Ceramization Processes Applied to Vegetable Hierarchical Structures for Bone Regeneration: An Experimental Model in Sheep

Filardo, G; Kon, E; Tampieri, A; Cabezas-Rodriguez, R; Di Martino, A; Fini, M; Giavaresi, G; Lelli, M; Martinez-Fernandez, J; Martini, L; Ramirez-Rico, J; Salamanna, F; Sandri, M; Sprio, S; Marcacci, M

Bone loss is still a major problem in orthopedics. The purpose of this experimental study is to evaluate the safety and regenerative potential of a new scaffold based on a bio-ceramization process for bone regeneration in long diaphyseal defects in a sheep model. The scaffold was obtained by transformation of wood pieces into porous biomorphic silicon carbide (BioSiC®). The process enabled the maintenance of the original wood microstructure, thus exhibiting hierarchically organized porosity and high mechanical strength. To improve cell adhesion and osseointegration, the external surface of the hollow cylinder was made more bioactive by electrodeposition of a uniform layer of collagen fibers that were mineralized with biomimetic hydroxyapatite, whereas the internal part was filled with a bio-hybrid HA/collagen composite. The final scaffold was then implanted in the metatarsus of 15 crossbred (Merinos-Sarda) adult sheep, divided into 3 groups: scaffold alone, scaffold with platelet-rich plasma (PRP) augmentation, and scaffold with bone marrow stromal cells (BMSCs) added during implantation. Radiological analysis was performed at 4, 8, 12 weeks, and 4 months, when animals were sacrificed for the final radiological, histological, and histomorphometric evaluation. In all tested treatments, these analyses highlighted the presence of newly formed bone at the bone scaffolds' interface. Although a lack of substantial effect of PRP was demonstrated, the scaffold+BMSC augmentation showed the highest value of bone-to-implant contact and new bone growth inside the scaffold. The findings of this study suggest the potential of bio-ceramization processes applied to vegetable hierarchical structures for the production of wood-derived bone scaffolds, and document a suitable augmentation procedure in enhancing bone regeneration, particularly when combined with BMSCs.

Tissue Engineering Part A, 20 (2014) 763-773 | DOI: 10.1089/ten.tea.2013.0108

Long-term high temperature oxidation of CrAl(Y)N coatings in steam atmosphere

Mato, S; Alcala, G; Brizuela, M; Galindo, RE; Perez, FJ; Sanchez-Lopez, JC

The oxidation resistance of CrAl(Y)N coatings deposited by reactive magnetron sputtering on P92 steel substrates was tested at 650 °C in 100% steam atmosphere up to 2000 h of oxidation. Mass gain measurements and characterisation of coatings and scales after oxidation show the enhanced oxidation resistance provided by the coatings with respect to that of the substrate. The dominant influence of the film microstructure developed due to the presence of an adhesion interlayer of CrN at the coating/substrate interface over Y additions is evidenced. The best performance is achieved by a CrAlN dense coating of around 6 μm without adhesion interlayer.

Corrosion Science, 80 (2014) 453-460 | DOI: 10.1016/j.corsci.2013.11.066

Enhanced oxidation resistance of Ti(C,N)-based cermets containing Ta

Chicardi, E; Gotor, FJ; Cordoba, JM

(TixTa1−x)(C0.5N0.5)–Co-based cermets with various Ta contents (x = 0, 0.01, 0.05, 0.1 and 0.2) were oxidized at 900 °C for 48 h in static air. A parabolic rate law, which is indicative of the formation of a protective oxide layer, was observed for all samples. The multi-layered oxide scale and the internal oxidation region that formed as the oxidation progressed toward the interior of the cermet specimens were characterized using XRD, SEM and EDS. The enhanced oxidation resistance achieved in cermets composed by a hard component with stoichiometry Ti0.95Ta0.05C0.5N0.5 may satisfy the optimal requirements for many applications in the field of cutting tools.

Corrosion Science, 84 (2014) 11-20 | DOI: 10.1016/j.corsci.2014.03.007

Exalted photocatalytic activity of tetragonal BiVO4 by Er3+ doping through a luminescence cooperative mechanism

Obregon, S; Lee, SW; Colon, G

Er-doped BiVO4 are synthesized by means of a surfactant free microwave assisted hydrothermal method having good photoactivities under sun-like excitation for the degradation of methylene blue. From the structural and morphological characterization, it has been stated that the presence of Er3+ induces a slight stabilization of the tetragonal phase, probably due to its incorporation in the BiVO4 lattice. The best photocatalytic performances were attained for the samples with Er3+ content higher than 3 at%. The occurrence of the Er3+ doped tetragonal BiVO4 clearly induces higher photocatalytic activities. The existence of a luminescence process has been related with the enhanced photoactivity observed.

Dalton Transactions, 43 (2014) 311-316 | DOI: 10.1039/C3DT51923F

A study of the optical properties of metal-doped polyoxotitanium cages and the relationship to metal-doped titania

Lv, YK; Cheng, J; Matthews, PD; Holgado, JP; Willkomm, J; Leskes, M; Steiner, A; Fenske, D; King, TC; Wood, PT; Gan, LH; Lambert, RM; Wright, DS

To what extent the presence of transition metal ions can affect the optical properties of structurally well-defined, metal-doped polyoxotitanium (POT) cages is a key question in respect to how closely these species model technologically important metal-doped TiO2. This also has direct implications to the potential applications of these organically-soluble inorganic cages as photocatalytic redox systems in chemical transformations. Measurement of the band gaps of the series of closely related polyoxotitanium cages [MnTi14(OEt)28O14(OH)2] (1), [FeTi14(OEt)28O14(OH)2] (2) and [GaTi14(OEt)28O15(OH)] (3), containing interstitial Mn(II), Fe(II) and Ga(III) dopant ions, shows that transition metal doping alone does not lower the band gaps below that of TiO2 or the corresponding metal-doped TiO2. Instead, the band gaps of these cages are within the range of values found previously for transition metal-doped TiO2 nanoparticles. The low band gaps previously reported for 1 and for a recently reported related Mn-doped POT cage appear to be the result of low band gap impurities (most likely amorphous Mn-doped TiO2).

Dalton Transactions, 43 (2014) 8679-8689 | DOI: 10.1039/C4DT00555D

Multidirectional Light-Harvesting Enhancement in Dye Solar Cells by Surface Patterning

Lopez-Lopez, C; Colodrero, S; Jimenez-Solano, A; Lozano, G; Ortiz, R; Calvo, ME; Miguez, H

One dimensional gratings patterned on the surface of nanocrystalline titania electrodes are used as a light harvesting strategy to improve the overall performance of dye solar cells under both frontal and rear illumination conditions. A soft-lithography-based micromoulding approach is employed to replicate a periodic surface relief pattern onto the surface of the electrode, which is later sensitized with a dye. As the patterned surface acts as an optical grating both in reflection and transmission modes, its effect is to increase the light path of diffracted beams within the absorbing layer when it is irradiated either from the electrode or the counter electrode for a broad range of angles of incidence on each surface. Full optical and photovoltaic characterization demonstrates not only the optical quality of the patterned surfaces but also the multidirectional character of the enhancement of light harvesting and conversion efficiency. The approach herein presented thus permits to preserve the operation of the cell when irradiated from its two faces while increasing its overall power conversion efficiency. This feature is a key advantage over other light harvesting efficiency enhancing methods, such as the deposition of a back diffuse scattering layer, in which the performance of the cell under illumination from one of its sides is enlarged at the expense of reducing the output under reverse irradiation conditions.

Advanced Optical Materials, 2 (2014) 879-884 | DOI: 10.1002/adom.201400160

Synthesis and luminescence of uniform europium-doped bismuth fluoride and bismuth oxyfluoride particles with different morphologies

A. Escudero; E. Moretti; M. Ocaña

Facile synthesis routes have been developed for the preparation of uniform cubic bismuth fluoride and bismuth oxyfluoride particles. The synthesis methods are based on homogeneous precipitation reactions at 120 °C in solutions of bismuth nitrate and sodium tetrafluoroborate precursors in polyol-based solvents. Both the nature of the solvent and the heating modes (conventional or microwave-assisted heating) have a remarkable effect on the morphology and crystallinity of the resulting particles. Thus, polycrystalline spheres of α-BiF3 with a mean diameter ranging from 1.2 to 2 μm could be obtained by heating solutions with the appropriate reagent concentrations in a mixture of ethylene glycol and glycerol (1 : 1 by volume) using a conventional oven, whereas octahedral single crystals of α-BiOyF3−2y with mean edges ranging from 250 nm to 920 nm precipitated when using a diethylene glycol–water mixture (8 : 2 in volume) as solvent and a microwave reactor for heating. To explain these different morphological and structural features, the mechanism of formation of such particles was investigated. Both kinds of particles were also doped with Eu3+, and both the morphological and luminescence properties of the resulting materials were evaluated. It was found that the luminescence intensity of the europium-doped α-BiOyF3−2y nanoparticles was higher than that of the europium-doped α-BiF3 sub-micrometric spheres, which was associated with the higher crystallinity of the former. Moreover, the presence of oxygen in the europium-doped α-BiOyF3−2y samples permits the excitation of the europium cations through an Eu–O energy transfer process, which results in a much higher luminescence intensity with respect to that corresponding to the direct excitation of the europium cations. Finally, the effect of the amount of dopant on the luminescence properties of the phosphors was also evaluated.

CrysEngComm, 16 (2014) 3274-3283 | DOI: 10.1039/C3CE42462F

Infrared and Raman spectroscopic features of plant cuticles: a review

Heredia-Guerrero, JA; Benitez, JJ; Dominguez, E; Bayer, IS; Cingolani, R; Athanassiou, A; Heredia, A

The cuticle is one of the most important plant barriers. It is an external and continuous lipid membrane that covers the surface of epidermal cells and whose main function is to prevent the massive loss of water. The spectroscopic characterization of the plant cuticle and its components (cutin, cutan, waxes, polysaccharides and phenolics) by infrared and Raman spectroscopies has provided significant advances in the knowledge of the functional groups present in the cuticular matrix and on their structural role, interaction and macromolecular arrangement. Additionally, these spectroscopies have been used in the study of cuticle interaction with exogenous molecules, degradation, distribution of components within the cuticle matrix, changes during growth and development and characterization of fossil plants.

Frontiers in Plant Science, 25 (2014) | DOI: 10.3389/fpls.2014.00305

Metallic structured catalysts: Influence of the substrate on the catalytic activity

Dominguez, MI; Perez, A; Centeno, MA; Odriozola, JA

In order to study the influence of the metallic substrate on the catalytic activity of structured micromonolithic catalysts, a CuOx/CeO2 catalyst was deposited on different oxidized or enameled metallic micromonoliths and tested in the PROX reaction under ideal and realistic conditions. The obtained results show as both activity and selectivity depend on the nature of the alloy and the nature of the interphase between the metal substrate and the catalyst layer. In oxidized micromonoliths, diffusion of Cr and Fe has been observed. For enameled micromonoliths, together with that diffusion, the interaction of the glass-ceramic interphase with the reactive gas streams resulted in the partial hydrolysis of this layer leading to diffusion toward the catalyst surface of the hydrolysis products, namely Na, Ca and Si cations. In some cases, the alteration of the surface composition favors the spreading of the copper active phase. As a result, it must be concluded that the metallic substrates are not spectators, at least in the PROX reaction, playing a fundamental role in the performances of the catalytic devices.

Applied Catalysis A-General, 478 (2014) 45-57 | DOI: 10.1016/j.apcata.2014.03.028

Heterogeneous selective oxidation of fatty alcohols: Oxidation of 1-tetradecanol as a model substrate

Corberan, VC; Gomez-Aviles, A; Martinez-Gonzalez, S; Ivanova, S; Dominguez, MI; Gonzalez-Perez, ME

Selective oxidation of fatty alcohols, i.e., linear long-chain alkanols, has been scarcely investigated to date, despite its potential application in high value chemical's production. We report for the first time the liquid phase heterogeneous oxidation of 1-tetradecanol, used as a model molecule for fatty alcohols, according to green chemistry principles by using a Au/CeO2-Al2O3 catalyst and O-2 as oxidant at normal pressure. High selectivity to tetradecanal (ca. 80%) or to tetradecanoic acid (60-70%) are reached at medium conversion (up to 38%), depending on the reaction conditions used. Comparison with similar tests of 1-octanol oxidation shows that the increase of the carbon chain length decreases the alcohol conversion and the formation of ester, probably due to a greater steric effect.

Catalysis Today, 238 (2014) 49-53 | DOI: 10.1016/j.cattod.2014.03.033

A ternary Er3+-BiVO4/TiO2 complex heterostructure with excellent photocatalytic performance

Obregon, S; Colon, G

Ternary erbium doped BiVO4/TiO2 complexes are synthesized by means of a simple impregnation method with good photoactivities under sun-like excitation for the degradation of phenol. From the structural and morphological characterization it has been stated that the presence of Er3+ induces a slight stabilization of the tetragonal phase probably due to its incorporation in the BiVO4 lattice. Therefore a ternary heterostructured material has been obtained. The best photocatalytic performance was attained for the samples with 1 wt% of Er3+-doped BiVO4 content with respect to TiO2. The occurrence of a complex structural mixture with the adequate band position leads to effective charge pair separation which induces higher photocatalytic activities.

RSC Advances, 4 (2014) 20765-20771 | DOI: 10.1039/C3RA46603E

Synthesis of antibacterial silver-based nanodisks and dendritic structures mediated by royal jelly

Mendoza-Resendez, R; Gomez-Trevino, A; Barriga-Castro, ED; Nunez, NO; Luna, C

 

The one-step preparation of silver nanoparticles and dendritic structures mediated by aqueous royal jelly solutions has been investigated for the first time. It has been found that royal jelly (RJ) is a complex organic matrix that can be simultaneously used as a reducing and stabilizing agent in the chemical synthesis of colloidal silver-based nanostructures from aqueous AgNO3 solutions, without the requirement of additional reagents or heating sources to initiate the oxidation–reduction reactions. The resulting product consisted of very fine single-crystal disks of Ag and silver 4,4′-dimethyldiazoaminobenzene (a triazenic compound). Both kinds of particles tended to coalesce and form supramolecular dendritic structures, the AgNO3/RJ weight ratio chosen in the synthesis being a key parameter to control the crystal growth and the microstructural properties of the Ag nanodisks. Data obtained from Fourier transform infrared and Raman spectroscopy analysis indicated that these nanostructures are coated by RJ biomolecules (residues of proteins and carbohydrates). In vitro biological assays showed that these nanostructures exhibit a promising enhanced antibacterial activity against both Gram-positive and Gram-negative bacteria.

RSC Advances, 4 (2014) 1650-1658 | DOI: 10.1039/C3RA45680C

Anchoring effect on (tetra)carboxyphenyl porphyrin/TiO2 composite films for VOC optical detection

Roales, J; Pedrosa, JM; Cano, M; Guillen, MG; Lopes-Costa, T; Castillero, P; Barranco, A; Gonzalez-Elipe, AR

The optical gas sensing properties of Zn-(II)-5,10,15,20-tetra(3-carboxyphenyl)porphyrin (m-ZnTCPP) and Zn-(II)-5,10,15,20-tetra(4-carboxyphenyl)porphyrin (p-ZnTCPP) bound to microcolumnar TiO2 thin films have been compared and explained in terms of their different molecular structure and anchoring to the titania surface. This different binding has been confirmed by specular reflectance FTIR revealing that m-ZnTCPP is bound by its four carboxylic groups in contrast to p-ZnTCPP where two or three of these groups remain unanchored. As a consequence, the Soret band of the para derivative is blue shifted with respect to the solution, indicating H aggregation, while m-ZnTCPP remained in its monomeric form due to the planar anchoring by the four COOH groups to the titania matrix that would avoid porphyrin aggregation. The sensing performance of the two systems has been assessed by analyzing the spectral changes in their UV-visible spectra under exposure to six volatile organic compounds. Although the highly porous and non-dispersive TiO2 matrix allow good sensing ability in both cases, the response of the m-ZnTCPP/TiO2 composite has been found to be more intense and faster than that of p-ZnTCPP. Moreover, the use of identification patterns also indicates that the meta derivative achieves a more selective recognition of the selected analytes. This improvement in the sensing capabilities of m-ZnTCPP has been attributed to the absence of aggregation between adjacent macrocycles.

RSC Advances, 4 (2014) 1974-1981 | DOI: 10.1039/C3RA42443J

Surface Oxygen Vacancies in Gold Based Catalysts for CO Oxidation

Romero-Sarria, F; Plata, JJ; Laguna, OH; Marquez, AM; Centeno, MA; Sanz, JF; Odriozola, JA

Experimental catalytic activity measurements, Diffuse Reflectance Infrared Fourier Spectroscopy, and Density Functional Theory calculations are used to investigate the role and dynamics of surface oxygen vacancies in the CO oxidation with O2 catalyzed by Au nanoparticles supported on a Y-doped TiO2 catalyst. Catalytic activity measurements show that the CO conversion is improved in a second cycle of reaction if the reactive flow is composed by CO and O2 (and inert) while if water is present in the flow, the catalyst shows a similar behaviour in two successive cycles. DRIFTS-MS studies indicate the occurrence of two simultaneous phenomena during the first cycle in dry conditions: the surface is dehydroxylated and a band at 2194 cm-1 increases (proportionally to the number of surface oxygen vacancies). Theoretical calculations were conducted in order to explain these observations. On one hand, the calculations show that there is a competition between gold nanoparticles and OH to occupy the surface oxygen vacancies and that the adsorption energy of gold on these sites increases as the surface is being dehydroxylated. On another hand, these results evidence that a strong electronic transfer from the surface to the O2 molecule is produced after its adsorption on the Au/TiO2 perimeter interface (activation step), leaving the gold particle in a high oxidation state. This explains the appearance of a band at a wavenumber unusually high for the CO adsorbed on oxidized gold particles (2194 cm-1) when O2 is present in the reactive flow. These simultaneous phenomena indicate that a gold redispersion on the surface occurs under reactive flow in dry conditions generating small gold particles very actives at low temperature. This fact is notably favoured by the presence of surface oxygen vacancies that improve the surface dynamics. The obtained results suggest that the reaction mechanism proceeds through the formation of a peroxo-like complex formed after the electronic transfer from the surface to the gas molecule.

RSC Advances, 4 (2014) 13145-13152 | DOI: 10.1039/c3ra46662k

Chemistry, nanostructure and magnetic properties of Co-Ru-B-O nanoalloys

Arzac, GM; Rojas, TC; Gontard, LC; Chinchilla, LE; Otal, E; Crespo, P; Fernandez, A

In our previous works, Co–B–O and Co–Ru–B–O ultrafine powders with variable Ru content (xRu) were studied as catalysts for hydrogen generation through sodium borohydride hydrolysis. These materials have shown a complex nanostructure in which small Co–Ru metallic nanoparticles are embedded in an amorphous matrix formed by Co–Ru–B–O based phases and B2O3. Catalytic activity was correlated to nanostructure, surface and bulk composition. However, some questions related to these materials remain unanswered and are studied in this work. Aspects such as: 3D morphology, metal nanoparticle size, chemical and electronic information on the nanoscale (composition and oxidation states), and the study of the formation or not of a CoxRu1−x alloy or solid solution are investigated and discussed using XAS (X-ray Absorption Spectroscopy) and Scanning Transmission Electron Microscopy (STEM) techniques. Also magnetic behavior of the series is studied for the first time and the structure–performance relationships discussed. All Co-containing samples exhibited ferromagnetic behavior up to room temperature while the Ru–B–O sample is diamagnetic. For the xRu = 0.13 sample, an enhancement in the Hc (coercitive field) and Ms (saturation magnetization) is produced with respect to the monometallic Co–B–O material. However this effect is not observed for samples with higher Ru content. The presence of the CoxB-rich (cobalt boride) amorphous ferromagnetic matrix, very small metal nanoparticles (Co and CoxRu(1−x)) embedded in the matrix, and the antiferromagnetic CoO phase (for the higher Ru content sample, xRu = 0.7), explain the magnetic behavior of the series.

RSC Advances, 4 (2014) 46576-46586 | DOI:

On the formation of the porous structure in nanostructured a-Si coatings deposited by dc magnetron sputtering at oblique angles

Godinho, V; Moskovkin, P; Alvarez, R; Caballero-Hernandez, J; Schierholz, R; Bera, B; Demarche, J; Palmero, A; Fernandez, A; Lucas, S

The formation of the porous structure in dc magnetron sputtered amorphous silicon thin films at low temperatures is studied when using helium and/or argon as the processing gas. In each case, a-Si thin films were simultaneously grown at two different locations in the reactor which led to the assembly of different porous structures. The set of four fabricated samples has been analyzed at the microstructural level to elucidate the characteristics of the porous structure under the different deposition conditions. With the help of a growth model, we conclude that the chemical nature of the sputter gas not only affects the sputtering mechanism of Si atoms from the target and their subsequent transport in the gaseous/plasma phase towards the film, but also the pore formation mechanism and dynamics. When Ar is used, pores emerge as a direct result of the shadowing processes of Si atoms, in agreement with Thornton's structure zone model. The introduction of He produces, in addition to the shadowing effects, a new process where a degree of mobility results in the coarsening of small pores. Our results also highlight the influence of the composition of sputtering gas and tilt angles (for oblique angle deposition) on the formation of open and/or occluded porosity.

Nanotechnology, 25 (2014) 355705 | DOI: 10.1088/0957-4484/25/35/355705

Enhanced activity of clays and its crucial role for the activity in ethylene polymerization

Camejo-Abreu, C; Tabernero, V; Alba, MD; Cuenca, T; Terreros, P

This paper presents a study of the effects of different treatments on the polymerization activity of modified clays as cocatalysts. To achieve this goal, an intercalating cation was introduced into two smectites and these clays were then modified with trimethyl aluminium. The results for ethylene polymerization, when a zirconocene complex was used as catalyst, and the structure analysis, allow us to obtain interesting deductions about the generation mode of the active species. All active materials employed as support activators presented aluminium in a pentahedral environment together with acidic hydrogen atoms. These two features were detected only after TMA treatment and they seem to be crucial elements in active cocatalyst generation. Moreover, a material without structural aluminium displayed the best activity pointing to the new aluminium species generated in the solid matrix as the determining factor for the activity. We proposed a synergic effect between Lewis acid aluminium centres and acidic Bronsted protons that generate the SiOHAl groups that activate the zirconium compound.

Journal of Molecular Catalysis A-Chemical, 393 (2014) 96-104 | DOI: 10.1016/j.molcata.2014.05.030

Multicyclic conversion of limestone at Ca-looping conditions: The role of solid-sate diffusion controlled carbonation

Sanchez-Jimenez, PE; Valverde, JM; Perez-Maqueda, LA

Limestone derived CaO conversion when subjected to multiple carbonation/calcination cycles is a subject of interest currently fueled by several industrial applications of the so-called Ca-looping (CaL) technology. The multicyclic CaO conversion at Ca-looping conditions exhibits two main features as demonstrated by thermogravimetric analysis (TGA). On one hand, carbonation occurs by two well differentiated phases: a first kinetically-driven fast phase and a subsequent much slower solid-state diffusion controlled phase. On the other, carbonation in the fast phase usually shows a drastic decay with the cycle number along the first carbonation/calcination cycles. This trend can be reversed by means of heat pretreatment, which induces a marked loss of fast conversion in the first carbonation but enhances diffusion of CO2 in the solid. Upon decarbonation the regenerated CaO skeleton displays an increased conversion in the fast carbonation phase of the next cycle, a phenomenon which has been referred to as reactivation. Nonetheless, sorbent reactivation is hampered by looping carbonation/calcination conditions as those to be likely found in practice such as carbonation stages characterized by low CO2 concentrations and short duration and calcination stages at high temperatures in a CO2 enriched atmosphere, which causes a sintering and loss of activity of the regenerated CaO skeleton. We analyze in this work sorbent reactivation as affected by heat pretreatment and carbonation/calcination conditions. Aimed at shedding light on the role played by these conditions on reactivation we look separately at the multicyclic evolution of conversion in the kinetic and diffusive phases. Generally, the evolution of multicyclic conversion after the first cycle can be described by a balance between the surface area gain due to diffusive carbonation and the surface area loss as caused by sintering in the calcination stage. A significant gain of relative surface area after the first cycle, which is favored by harshening the heat pretreatment conditions, leads however to a marked decay of it during subsequent cycles, which precludes reactivation for an extended interval of cycles. On the other hand, sorbent grinding, if performed before heat pretreatment, leads to a less marked but more sustainable reactivation along the cycles. A novel observation reported in our work is that pretreatment of limestone in a CO2 atmosphere leads upon a subsequent quick decarbonation to a CaO skeleton with extraordinarily enhanced reactivity in the kinetically-driven carbonation phase and with a high resistance to solid-state diffusion, which can be attributed to annealing of the crystal structure as reported by independent studies.

Fuel, 127 (2014) 131-140 | DOI: 10.1016/j.fuel.2013.09.064

High and stable CO2 capture capacity of natural limestone at Ca-looping conditions by heat pretreatment and recarbonation synergy

Valverde, JM; Sanchez-Jimenez, PE; Perez-Maqueda, LA

The Ca-looping (CaL) process, based on the multicyclic carbonation/calcination of limestone derived CaO, has emerged recently as a potentially economically advantageous technology to achieve sustainable postcombustion and precombustion CO2 capture efficiencies. Yet, a drawback that hinders the efficiency of the CaL process is the drastic drop of limestone capture capacity as the number of carbonation/calcination cycles is increased. Precalcination of limestone at high temperatures for a prolonged period of time has been proposed as a potential technique to reactivate the sorbent, which is however precluded by regeneration temperatures above 850 degrees C and low CO2 concentrations in the carbonator to be found in the practical situation. Under these conditions, heat pretreatment leads to a stable yet very small CaO conversion. On the other hand, the introduction of a recarbonation stage between the ordinary carbonation and calcination stages has been shown to decelerate the rate of sorbent activity decay even though this favorable effect is not noticeable up to a number of above 10-15 cycles. The present manuscript demonstrates that the synergetic action of heat pretreatment and recarbonation yields a high and stable value for the multicyclic conversion of limestone derived CaO. It is foreseen that recarbonation of heat pretreated limestone would lead to a reduction of process costs especially in the case of precombustion applications. Even though sorbent purging will always be needed because of ash accumulation and sul-phation in postcombustion CO2 capture applications, the stable and high multicyclic CaO conversion achieved by the combination of these techniques would make it necessary to a lesser extent.

Fuel, 123 (2014) 79-85 | DOI: 10.1016/j.fuel.2014.01.045

Gold supported on CuOx/CeO2 catalyst for the purification of hydrogen by the CO preferential oxidation reaction (PROX)

Laguna, OH; Hernandez, WY; Arzamendi, G; Gandia, LM; Centeno, MA; Odriozola, JA

Hydrogen produced from the conversion of hydrocarbons or alcohols contains variable amounts of CO that should be removed for some applications such as feeding low-temperature polymer electrolyte membrane fuel cells (PEMFCs). The CO preferential oxidation reaction (PROX) is particularly well-suited for hydrogen purification for portable and on-board applications. In this work, the synthesis and characterization by XRF, BET, XRD, Raman spectroscopy and H2-TPR of a gold catalyst supported on a copper−cerium mixed oxide (AuCeCu) for the PROX reaction are presented. The comparison of this catalyst with the copper–cerium mixed oxide (CeCu) revealed that the experimental procedure used for the deposition of gold gave rise to the loss of reducible material by copper lixiviation. However, the AuCeCu solid was more active for CO oxidation at low temperature. A kinetic study has been carried over the AuCeCu catalyst for the PROX reaction and compared with that of the CeCu catalyst. The main difference between the models affected the contribution of the CO adsorption term. This fact may be related to the surface electronic activity produced by the interaction of the cationic species in the AuCeCu solid, able to create more active sites for the CO adsorption and activation in the presence of gold.

Fuel, 134 (2014) 9-20 | DOI: 10.1016/j.fuel.2013.10.072

Analysis on the mechanical strength of WC-Co cemented carbides under uniaxial and biaxial bending

Torres, Y; Bermejo, R; Gotor, FJ; Chicardi, E; Llanes, L

The mechanical strength of three WC-Co grades was determined and compared under uniaxial and biaxial bending. Uniaxial four-point bending was conducted on bar-shaped specimens; biaxial testing was performed on discs using the ball-on-three-balls (B3B) method. Strength results were analysed within the frame of the Weibull theory. Differences in characteristic strength between uniaxial and biaxial bending were explained as an effect of the effective surface tested in each case. A higher Weibull modulus was obtained in one grade, independent of the testing method, which was related to its higher fracture toughness. The use and validity of the B3B biaxial test to determine the strength distribution of cemented carbides is discussed.

Materials & Design, 55 (2014) 851-856 | DOI: 10.1016/j.matdes.2013.10.051

Effect of tantalum content on the microstructure and mechanical behavior of cermets based on (TixTa1−x)(C0.5N0.5) solid solutions

Chicardi, E; Torres, Y; Cordoba, JM; Hvizdos, P; Gotor, FJ

Titanium–tantalum carbonitride, (Ti, Ta)(C, N), based cermets with different Ti and Ta contents were prepared using a mechanically induced self-sustaining reaction and then densified using a pressureless sintering process. Complete microstructural and mechanical characterizations were performed on the materials, which revealed that the size of the carbonitride ceramic particle was significantly reduced when the Ta content was increased. The flexural strength and fracture toughness were measured using the ball on three balls test and the indentation microfracture test, respectively. The strength profile was analyzed under the framework of Weibull theory. The change in the mechanical properties as a function of the Ta content was correlated with the normalized microstructural parameters, such as the binder mean free path. The decrease in toughness and flexural strength was attributed to the presence of intermetallic compounds in the binder phase, which was also corroborated by the nanoindentation tests.

Materials & Design, 53 (2014) 435-444 | DOI: 10.1016/j.matdes.2013.07.039

Processing and characterisation of cermet/hardmetal laminates with strong interfaces

Gotor, FJ; Bermejo, R; Cordoba, JM; Chicardi, E; Medri, V; Fabbriche, DD; Torres, Y

Cemented carbides and cermets are potential materials for high speed machining tools. However, cemented carbides are not chemically stable at high temperature and cermets present poor fracture toughness. Novel cermet/hardmetal multilayer systems show a huge potential for this intended application. It would be possible to achieve the right balance of the required thermomechanical properties using cermet as temperature protective outer layers and hardmetal as reinforcement layers. In this work, preliminary results on the microstructural and mechanical characterisation of a multilayer TiCxN1−x–Co/WC–Co composite densified by hot pressing are presented, with special attention to the properties of the interface. Microstructural observations revealed the existence of strong bonding interfaces between cermet and hardmetal layers due to chemical interaction during the sintering process. As a consequence, owing to the different coefficient of thermal expansion between cermet and hardmetal, a tensile and compressive biaxial residual stress of σres,Cermet ≈ +260 ± 50 MPa and σres,WC–Co ≈ −350 ± 70 MPa was estimated in the corresponding layers. Microindentation cracks introduced in the cermet layers (the less toughness material) and propagated transversely to the layers were arrested at the interface, showing the combined effect of toughness and compressive stresses on crack shielding.

Materials & Design, 58 (2014) 226-233 | DOI: 10.1016/j.matdes.2014.01.076

A new route of synthesis of Na-Mica-4 from sodalite

Naranjo, M; Castro, MA; Cota, A; Pavon, E; Pazos, MC; Alba, MD

Synthesis of Na-Mica-4 has been achieved by a “mix and calcine” method using sodalite and magnesium fluoride as the only precursors. Previous research found sodalite as a key intermediate reaction product in the formation of Na-Mica-4 when the NaCl melt method was employed. Similarities in structure, chemical composition and cation distribution in products using the proposed method and the NaCl melt method are described and suggest that Na-Mica-4 is a very stable product. The use of sodalite as precursor provokes microporous formation in the final mica. The absence of excess Na leads to a lower particle size and to the presence of less impurity in the calcined product. Different sodalites could be used in the synthesis of different Na-Mica-4 with presumably different physicochemical properties.

Microporous and Mesoporous Materials, 188 (2014) 176-180 | DOI: 10.1016/j.micromeso.2013.12.004

Characterization of thermally stable gamma alumina fibres biomimicking sisal

Benitez-Guerrero, M; Perez-Maqueda, LA; Sanchez-Jimenez, PE; Pascual-Cosp, J

Mesoporous gamma alumina fibres of high surface area, stable up to 1000 °C, were synthesized by bioreplica technique using sisal fibres as templates. Alumina formation during pyrolysis and calcination of fibres infiltrated with aluminium chloride solution has been studied, paying special attention to the interaction between the precursor and sisal fibres, using several experimental techniques such as ATR-FTIR, coupled TG-FTIR and thermo-XRD analysis. The morphology and microstructure of the resulting alumina fibres were characterized using SEM and TEM. The crystallographic analysis of the alumina sample performed by electron and X-ray diffraction suggests that fibres are constituted by η and γ-Al2O3 crystallites, whose chemical structure was confirmed by ATR-FTIR and Al27-MAS-NMR. The specific surface area and porosity of ceramic fibres were determined by N2 and CO2 adsorption–desorption measurements. Resulting alumina fibres retain high specific surface areas of 200 and 150 m2/g even after calcination at 1000 °C for 15 h in dry air and for 4 h in wet air, respectively.

Microporous and Mesoporous Materials, 185 (2014) 167-178 | DOI: 10.1016/j.micromeso.2013.11.012

Mechanisms of Electron Transport and Recombination in ZnO Nanostructures for Dye-Sensitized Solar Cells

Vega-Poot, AG; Macias-Montero, M; Idigoras, J; Borras, A; Barranco, A; Gonzalez-Elipe, AR; Lizama-Tzec, FI; Oskam, G; Anta, JA

ZnO is an attractive material for applications in dye-sensitized solar cells and related devices. This material has excellent electron-transport properties in the bulk but its electron diffusion coefficient is much smaller in mesoporous films. In this work the electron-transport properties of two different kinds of dye-sensitized ZnO nanostructures are investigated by small-perturbation electrochemical techniques. For nanoparticulate ZnO photoanodes prepared via a wet-chemistry technique, the diffusion coefficient is found to reproduce the typical behavior predicted by the multiple-trapping and the hopping models, with an exponential increase with respect to the applied bias. In contrast, in ZnO nanostructured thin films of controlled texture and crystallinity prepared via a plasma chemical vapor deposition method, the diffusion coefficient is found to be independent of the electrochemical bias. This observation suggests a different transport mechanism not controlled by trapping and electron accumulation. In spite of the quite different transport features, the recombination kinetics, the electron-collection efficiency and the photoconversion efficiency are very similar for both kinds of photoanodes, an observation that indicates that surface properties rather than electron transport is the main efficiency-determining factor in solar cells based on ZnO nanostructured photoanodes.

Chemphyschem, 15 (2014) 1088-1097 | DOI: 10.1002/cphc.201301068

Quinone-Rich Poly(dopamine) Magnetic Nanoparticles for Biosensor Applications

Martin, M; Orive, AG; Lorenzo-Luis, P; Creus, AH; Gonzalez-Mora, JL; Salazar, P

Novel core-shell quinone-rich poly(dopamine)–magnetic nanoparticles (MNPs) were prepared by using an in situ polymerization method. Catechol groups were oxidized to quinone by using a thermal treatment. MNPs were characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, magnetic force microscopy, UV/Vis, Fourier-transform infrared spectroscopy, and electrochemical techniques. The hybrid nanomaterial showed an average core diameter of 17 nm and a polymer-film thickness of 2 nm. The core-shell nanoparticles showed high reactivity and were used as solid supports for the covalent immobilization of glucose oxidase (Gox) through Schiff base formation and Michael addition. The amount of Gox immobilized onto the nanoparticle surface was almost twice that of the nonoxidized film. The resulting biofunctionalized MNPs were used to construct an amperometric biosensor for glucose. The enzyme biosensor has a sensitivity of 8.7 mA m−1 cm−2, a low limit of detection (0.02 mm), and high stability for 45 days. Finally, the biosensor was used to determine glucose in blood samples and was checked against a commercial glucometer.

ChemPhysChem, 15 (2014) 3742-3752 | DOI: 10.1002/cphc.201402417

Perovskite Solar Cells Based on Nanocolumnar PlasmaDeposited ZnO Thin Films

Ramos, FJ; Lopez-Santos, MC; Guillen, E; Nazeeruddin, MK; Gratzel, M; Gonzalez-Elipe, AR; Ahmad, S

ZnO thin films having a nanocolumnar microstructure are grown by plasma-enhanced chemical vapor deposition at 423 K on pre-treated fluorine-doped tin oxide (FTO) substrates. The films consist of c-axis-oriented wurtzite ZnO nanocolumns with well-defined microstructure and crystallinity. By sensitizing CH3NH3PbI3 on these photoanodes a power conversion of 4.8 % is obtained for solid-state solar cells. Poly(triarylamine) is found to be less effective when used as the hole-transport material, compared to 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD), while the higher annealing temperature of the perovskite leads to a better infiltration in the nanocolumnar structure and an enhancement of the cell efficiency.

Chemphyschem, 15 (2014) 1148-1153 | DOI: 10.1002/cphc.201301215

Reticulated bioactive scaffolds with improved textural properties for bone tissue engineering: Nanostructured surfaces and porosity

Ramiro-Gutierrez, ML; Will, J; Boccaccini, AR; Diaz-Cuenca, A

Organised nanoporous SBA-15 type silica precursor (SP) particulate material has been processed into three-dimensional macroporous, reticulated structures using a novel strategy consisting of blending increasing percentages of SP with a SiO2-CaO-P2O5 (80Si15Ca5P) mesoporous bioactive glass (MBG) sol. The procedure successfully produced consolidated and functionally competent open-cell scaffolds while preserving the nanoporous order of the SP. Scaffolds were prepared using four different (MBG)/(SP) ratios. These structures were then characterized using field emission gun scanning electron microscopy, X-ray diffraction (XRD), nitrogen adsorption-desorption measurements, and compressive strength testing. Open-cell interconnected structures with dual macro (150-500 mu m) and nano (4-6 nm)-organised porosity were produced. Both the textural and mechanical properties were found to improve with increasing SBA-15 content. The in vitro bioactive response using simulated body fluid confirmed high reactivity for all prepared scaffolds. In addition, the SBA-15 containing scaffolds exhibited a superior ability to delay the pH-triggered lysozyme release with antibiotic activity. (C) 2013 Wiley Periodicals, Inc.

Journal of Biomedical Materials Research Part A, 102 (2014) 2982-2992 | DOI: 10.1002/jbm.a.34968

Influence of the acid–base properties over NiSn/MgO–Al2O3 catalysts in the hydrogen production from glycerol steam reforming

Bobadilla, LF; Penkova, A; Romero-Sarria, F; Centeno, MA; Odriozola, JA

In this work we have investigated the hydrogen production from glycerol steam reforming. The effect of the acid-base properties was evaluated using four catalysts based in an alloy Ni-Sn as active phase supported over (Upsilon)-Al2O3 with different content in MgO, varying between 0 and 30 wt.% The incorporation of MgO results in the formation of MgAl2O4 spinel, which modifies the acid-base properties of the catalyst. Addition of MgO favored the glycerol conversion into gas, and the catalyst loaded with 10 wt.% MgO exhibited better catalytic performance and higher stability. A blank test with quartz was performed indicating that pyrolysis of glycerol takes place in the quartz.

International Journal of Hydrogen Energy, 39 (2014) 5704-5712 | DOI: 10.1016/j.ijhydene.2014.01.136

Understanding the Role of the Cosolvent in the Zeolite Template Function of Imidazolium-Based Ionic Liquid

Ayala, R; Ivanova, S; Blanes, JMM; Romero-Sarria, F; Odriozola, JA

In this work, a study for understanding the role played by [ClBmim], [BF4Bmim], [PF6Bmim], and [CH3SO3Bmim] ionic liquids (ILs) in the synthesis of zeolites is presented. The use of [ClBmim] and [CH3SO3Bmim] ILs, as reported earlier [ Chem. Eur. J. 2013, 19, 2122] led to the formation of MFI or BEA type zeolites. Contrary, [BF4Bmim] and [PF6Bmim] ILs did not succeed in organizing the Si–Al network into a zeolite structure. To try to explain these results, a series of quantum mechanical calculations considering monomers ([XBmim]) and dimers ([XBmim]2) by themselves and plus cosolvent (water or ethanol) were carried out, where X ≡ Cl–, BF4–, PF6–, or CH3SO3–. Our attention was focused on the similarities and differences among the two types of cosolvents and the relation between the structure and the multiple factors defining the interactions among the ILs and the cosolvent. Although a specific pattern based on local structures explaining the different behavior of these ILs as a zeolite structuring template was not found, the calculated interaction energies involving the Cl– and CH3SO3– anions were very close and larger than those for BF4– and PF6– species. These differences in energy can be used as an argument to describe their different behavior as structure directing agents. Moreover, the topology of the cosolvent is also an ingredient to take into account for a proper understanding of the results.

Journal of Physical Chemistry B, 118 (2014) 3650–3660 | DOI: 10.1021/jp410260g

The Use of Fluorocarbons to Mitigate the Oxygen Dependence of Glucose Microbiosensors for Neuroscience Applications

Martin, M; O'Neill, RD; Gonzalez-Mora, JL; Salazar, P

First-generation amperometric glucose biosensors are the most commonly used method for glucose monitoring in neuroscience. Nevertheless, biosensors of this genre suffer from the so-called "oxygen deficit". This problem is particularly acute when the oxygen concentration is low, as is the case in brain extracellular fluid. In the present work we use different fluorocarbons, such as Nafion and H700, to mitigate the oxygen deficit. These fluorocarbon-derived materials display a remarkable solubility for oxygen, and are able to act as oxygen reservoirs supporting the enzymatic reaction. Different biosensor configurations are presented, evaluating their sensitivity, linear range and oxygen dependence. Optimized Nafion- and H700-modified biosensors displayed a remarkable oxygen tolerance, with K-M(O-2) values as low as 11 and 4 mu mol L-1, respectively, and an appropriate sensitivity for in-vivo applications. Finally, in-vivo data are reported in order to illustrate the application of such devices in neuroscience applications.

Journal of The Electrochemical Society, 161 (2014) H689-H695 | DOI: 10.1149/2.1071410jes

Enhanced general analytical equation for the kinetics of the thermal degradation of poly(lactic acid)/montmorillonite nanocomposites driven by random scission

Carrasco, F; Perez-Maqueda, LA; Santana, OO; Maspoch, ML

An enhanced general analytical equation has been developed in order to evaluate the kinetic parameters of the thermal degradation of nanocomposites, composed of poly(lactic acid) (PLA) and organo-modified montmorillonite (OMMT) nanoparticles. This improvement has consisted of replacing the n-order conversion function by a modified form of the Sestak–Berggren equation f(α) = c (1 − α)nαm that led to a better adjustment of experimental data and also adequately represented the conventional mechanisms for solid-state processes. The kinetic parameters so obtained have been compared to those determined by conventional differential and isoconversional methods. Given that the thermal degradation of PLA has been argued to be caused by random chain scission reactions of ester groups, the conversion function f(α) = L (L − 1)x(1 − x)L−1, corresponding to a random scission mechanism, has been tested. Once optimized the kinetic model, the thermal degradation kinetics of nanocomposites (0.5 and 2.5% of OMMT) was compared to that of the polymer matrix. Moreover, the thermal stability of nanocomposites was tested and compared to that of the polymer matrix.

Polymer Degradation and Stability, 101 (2014) 52-59 | DOI: 10.1016/j.polymdegradstab.2014.01.014

Improvement of the thermal stability of branched poly(lactic acid) obtained by reactive extrusion

Carrasco, F; Cailloux, J; Sanchez-Jimenez, PE; Maspoch, ML

One-step reactive extrusion-calendering process (REX-calendering) has been used in order to obtain sheets of 1 mm from poly(lactic acid) modified with a styrene-acrylic multifunctional oligomeric agent. In a preliminary internal mixer study, torque versus time has been monitored in order to ascertain chain extender ratios and reaction time. Once all the parameters were optimized, reactive extrusion experiments have been performed. An enhanced general analytical equation has been developed in order to evaluate the kinetic parameters of the thermal degradation of PLA sheets manufactured by reactive extrusion. This improvement has consisted of replacing the n-order conversion function by a modified form of the Sestak–Berggren equation f(α) = c (1 − α)nαm that led to a better adjustment of experimental data and also adequately represented the conventional mechanisms for solid-state processes. The kinetic parameters so obtained have been compared to those determined by conventional differential methods and n-order reaction kinetics. Given that the thermal degradation of PLA has been argued to be caused by random chain scission reactions of ester groups, the conversion function f(α) = 2 (α1/2 − α), corresponding to a random scission mechanism for L = 2 (as well as other functions for L values up to 8), has been tested. Once optimized the kinetic model, the thermal degradation kinetics of sheets obtained by REX-calendering process was compared to that of conventional sheets and polymer matrix.

Polymer Degradation and Stability, 104 (2014) 40-49 | DOI: 10.1016/j.polymdegradstab.2014.03.026

The role of boron oxide and carbon amounts in the mechanosynthesis of ZrB2–SiC–ZrC nanocomposite via a self-sustaining reaction in the zircon/magnesium/boron oxide/graphite system

Jalaly, M; Bafghi, MS; Tamizifar, M; Gotor, FJ

Herein, ZrSiO4/B2O3/Mg/C system was used to synthesize a ZrB2-based composite by means of a high energy ball milling process. A mechanically induced self-sustaining reaction was achieved in this system. A nanocomposite powder of ZrB2–SiC–ZrC was prepared with an ignition time of approximately 6 min of milling. The role of the stoichiometric amounts of B2O3 and carbon was investigated to clarify the governing mechanism for the formation of the product.

Journal of Alloys and Compounds, 598 (2014) 113-119 | DOI: 10.1016/j.jallcom.2014.02.033

Structure determination and electronic structure of Cu3Au0.5N

Soto, G; Ponce, I; Moreno, MG; Yubero, F; De la Cruz, W

This study investigated the formation of a Cu3Au-nitride alloy using both experimental and computational methods. The alloy was produced as thin film by sputtering a Cu3Au target in a nitrogen atmosphere. The films were characterized for structure and composition by spectroscopic and diffraction techniques. The structure was established by Rietveld and ab inito methods. The structure is cubic and of the Fm3m space group, with a composition close to Cu6AuN2. Relative to the Cu3N structure, the Cu atoms occupy the faces, Au the half corners, and N the centers. The compound is a narrow-gap semiconductor with a positive hall coefficient that could be used for infrared detection.

Journal of Alloys and Compounds, 594 (2014) 48-51 | DOI: 10.1016/j.jallcom.2014.01.113

An investigation on the formation mechanism of nano ZrB2 powder by a magnesiothermic reaction

Jalaly, M; Bafghi, MS; Tamizifar, M; Gotor, FJ

Nanocrystalline zirconium diboride (ZrB2) powder was produced by mechanochemistry from the magnesiothermic reduction in the Mg/ZrO2/B2O3 system. The use of high-energy milling conditions was essential to induce a mechanically induced self-sustaining reaction (MSR) and significantly reduce the milling time required for complete conversion. Under these conditions, it was found that the ignition time for ZrB2 formation was only about a few minutes. In this study, the mechanism for the formation of ZrB2 in this system was determined by studying the relevant sub-reactions, the effect of stoichiometry, and the thermal behavior of the system.

Journal of Alloys and Compounds, 588 (2014) 36-41 | DOI: 10.1016/j.jallcom.2013.11.050

Spinodal decomposition and precipitation in Cu–Cr nanocomposite

Sheibani, S; Heshmati-Manesh, S; Ataie, A; Caballero, A; Criado, JM

In this study, spinodal decomposition and precipitation mechanism of mechanically alloyed supersaturated Cu–3wt.%Cr and Cu–5wt.%Cr solid solutions was investigated under nonisothermal aging. Decomposition mechanism and kinetics were studied using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques. Also, the microstructure was characterized by transmission electron microscopy (TEM). Effect of Al2O3 reinforcement on the aging kinetics was also evaluated. It was found that Cu–3wt.%Cr and Cu–5wt.%Cr solid solutions undergo spinodal decomposition at initial stages of ageing. However, decomposition mechanism was changed to nucleation and growth by the aging progress. The aging kinetics for the Cu–Cr/Al2O3 composition appeared to be slightly faster than that for Cu–Cr, since the ageing activation energy is decreased in presence of Al2O3 nano-particles. This behavior is probably due to the higher dislocation density and other structural defects previously produced during ball milling. A detailed comparison of the DSC results with those obtained by TEM, showing good consistency, has been presented. The average size of Cr-rich precipitates was about 10 nm in the copper matrix.

Journal of Alloys and Compounds, 587 (2014) 670-676 | DOI: 10.1016/j.jallcom.2013.11.019

Effect of high SWNT content on the room temperature mechanical properties of fully dense 3YTZP/SWNT composites

Poyato, R; Gallardo-Lopez, A; Gutierrez-Mora, F; Morales-Rodriguez, A; Munoz, A; Dominguez-Rodriguez, A

This paper is devoted to correlate the microstructure and room temperature mechanical properties of single-wall carbon nanotube (SWNT) reinforced 3 mol% yttria stabilized tetragonal zirconia with high SWNT content (2.5, 5 and 10 vol%). Fully dense composites were prepared by using a combination of aqueous colloidal powder processing and Spark Plasma Sintering. SWNTs were located at the ceramic grain boundaries and they were not damaged during the sintering process. The weak interfacial bonding between SWNTs and ceramic grains together with the detachment of SWNTs within thick bundles have been pointed out as responsible for the decrease of hardness and fracture toughness of the composites in comparison with the monolithic 3YTZP ceramic.

Journal of the European Ceramic Society, 34 (2014) 1571-1579 | DOI: 10.1016/j.jeurceramsoc.2013.12.024

Additive-free superhard B4C with ultrafine-grained dense microstructures

Moshtaghioun, BM; Cumbrera, FL; Ortiz, AL; Castillo-Rodriguez, M; Gomez-Garcia, D

A unique combination of high-energy ball-milling, annealing, and spark-plasma sintering has been used to process superhard B4C ceramics with ultrafine-grained, dense microstructures from commercially available powders, without sintering additives. It was found that the ultrafine powder prepared by high-energy ball-milling is hardly at all sinterable, but that B2O3 removal by gentle annealing in Ar provides the desired sinterability. A parametric study was also conducted to elucidate the role of the temperature (1600–1800 °C), time (1–9 min), and heating ramp (100 or 200 °C/min) in the densification and grain growth, and thus to identify optimal spark-plasma sintering conditions (i.e., 1700 °C for 3 min with 100 °C/min) to densify completely (>98.5%) the B4C ceramics with retention of ultrafine grains (∼370 nm). Super-high hardness of ∼38 GPa without relevant loss of toughness (∼3 MPa m1/2) was thus achieved, attributable to the smaller grain size and to the transgranular fracture mode of the B4C ceramics.

Journal of the European Ceramic Society, 34 (2014) 841-848 | DOI: 10.1016/j.jeurceramsoc.2013.10.006

High temperature internal friction measurements of 3YTZP zirconia polycrystals. High temperature background and creep

Simas, P; Castillo-Rodriguez, M; No, ML; De-Bernardi, S; Gomez-Garcia, D; Dominguez-Rodriguez, A; Juan, JS

This work focuses on the high-temperature mechanic properties of a 3 mol% yttria zirconia polycrystals (3YTZP), fabricated by hot-pressureless sintering. Systematic measurements of mechanical loss as a function of temperature and frequency were performed. An analytical method, based on the generalized Maxwell rheological model, has been used to analyze the high temperature internal friction background (HTB). This method has been previously applied to intermetallic compounds but never to ceramics, except in a preliminary study performed on fine grain and nanocrystalline zirconia. The HTB increases exponentially and its analysis provides an apparent activation enthalpy which correlates well with that obtained from creep experiments. This fact shows on the one hand the plausibility of applying the generalized Maxwell model to ceramics, and on the other hand indicates the possibility of using mechanical spectroscopy as a complementary helpful technique to investigate the high temperature deformation mechanism of materials.

Journal of the European Ceramic Society, 34 (2014) 3859-3863 | DOI: 10.1016/j.jeurceramsoc.2014.05.016

Improvement of Vickers hardness measurement on SWNT/Al2O3 composites consolidated by spark plasma sintering

Rodriguez, AM; Lopez, AG; Fernandez-Serrano, A; Poyato, R; Munoz, A; Dominguez-Rodriguez, A

Dense alumina composites with different carbon nanotube content were prepared by colloidal processing and consolidated by Spark Plasma Sintering (SPS). Single-wall carbon nanotubes (SWNTs) were distributed at grain boundaries and also into agglomerates homogeneously dispersed. Carrying out Vickers hardness tests on the cross-section surfaces instead of top (or bottom) surfaces has shown a noticeable increase in the reliability of the hardness measurements. This improvement has been mainly attributed to the different morphology of carbon nanotube agglomerates, which however does not seem to affect the Vickers hardness value. Composites with lower SWNT content maintain the Vickers hardness of monolithic alumina, whereas it significantly decreases for the rest of compositions. The decreasing trend with increasing SWNT content has been explained by the presence of higher SWNT quantities at grain boundaries. Based on the results obtained, a method for optimizing Vickers hardness tests performance on SWNT/Al2O3 composites sintered by SPS is proposed.

Journal of the European Ceramic Society, 34 (2014) 3801-3809 | DOI: 10.1016/j.jeurceramsoc.2014.05.048

Effect of La2O3 addition on long-term oxidation kinetics of ZrB2-SiC and HfB2-SiC ultra-high temperature ceramics

Zapata-Solvas, E; Jayaseelan, DD; Brown, PM; Lee, WE

Long-term oxidation kinetics of SiC-reinforced UHTCs and La2O3-doped UHTCs over an intermediate temperature range (1400-1600 degrees C) reveal partially protective behavior for the former characterized by an oxidation kinetic exponent 1 < n < 2. In addition, unstable oxidation behavior was observed in HfB2-based UHTCs due to the presence of SiC agglomerates. On the other hand, La2O3-doped UHTCs were found to be protective over the whole temperature range studied (n = 2), in particular at 1600 degrees C, where oxidation kinetic exponents as high as 8 were observed as a consequence of formation of new oxidation protective particles, MeOxCy, where Me is Zr, Hf or Si. Adsorption of oxygen-containing species formed protective MeOxCy), phases, which enhanced the thermal stability of the oxide scale as well as providing protection against oxidation for long exposure times at 1600 degrees C.

Journal of European Ceramic Society, 34 (2014) 3535-3548 | DOI: 10.1016/j.jeurceramsoc.2014.06.004

One-Step Synthesis and Polyacrylic Acid Functionalization of Multifunctional Europium-Doped NaGdF4 Nanoparticles with Selected Size for Optical and MRI Imaging

Nunez, NO; Garcia, M; Garcia-Sevillano, J; Rivera-Fernandez, S; de la Fuente, JM; Ocana, M

Multifunctional Eu:NaGdF4 nanospheres functionalized with polyacrylic acid (PAA) polymer have been prepared for the first time by a simple one-pot method that consists of a homogeneous precipitation reaction at 120 °C. The size of the nanospheres, which were polycrystalline and crystallized into a hexagonal structure, could be altered in the 60–95 nm range by adjusting the amount of polyacrylic acid added. The effects of Eu content and particle size of these nanomaterials on their optical properties (emission intensity and lifetime) as well as on their relaxivity (r1 and r2) values were also analyzed to find the optimum system for optical bioimaging and as a positive contrast agent for magnetic resonance imaging (MRI) applications. Finally, such optimum nanoparticles showed negligible cytotoxicity for Vero cells for concentrations up to 0.5 mg mL–1 and a high colloidal stability in 2-morpholinoethanesulfonic acid solutions, thereby satisfying the most important requirements for their use in biotechnological applications.

European Journal of Inorganic Chemistry, 35 (2014) 6075-6084 | DOI: 10.1002/ejic.201402690

Effect of Heat Pretreatment/Recarbonation in the Ca-Looping Process at Realistic Calcination Conditions

Valverde, JM; Sanchez-Jimenez, PE; Perez-Maqueda, LA

Even though an increasing number of pilot-scale plants are demonstrating the potential efficiency of the Ca-looping technology to capture CO2 at a commercial level, a still standing matter of concern is the loss of carbonation reactivity of the regenerated CaO by calcination, which is expected to be particularly marked at realistic conditions necessarily implying a high CO2 partial pressure in the calciner. In this work, we address the effect of previously reported strategies for sorbent reactivation, namely heat pretreatment and the introduction of a recarbonation stage before regeneration. Both techniques, either combined or separately, are shown to favor the carbonation reactivity, albeit CaO regeneration is usually carried out at low CO2 partial pressure in lab-scale tests. Novel results reported in this paper show the opposite when the sorbent is regenerated by calcination at high CO2 concentration, which is arguably due to the diverse mechanisms that rule decarbonation depending on the CO2 concentration in the calciner atmosphere. Dynamic and reversible adsorption/desorption of CO2 is thought to govern decarbonation during calcination at high CO2 partial pressure, which would be hindered by the introduction of a recarbonation stage before carbonation. Moreover, carbonation in the fast phase is severely hampered as a result of the marked loss of reactivity of the surface of CaO regenerated under high CO2 partial pressure. On the other hand, heat pretreatment and harsh calcination conditions lead to a notable enhancement of diffusion, which would favor the process efficiency. In these conditions, diffusion controlled carbonation becomes a significant contribution to CaO conversion, which is notably increased by prolonging the carbonation stage. Heat pretreatment allows also reducing the calcination temperature at high CO2 partial pressure while still achieving full decarbonation in short residence times.

Energy & Fuels, 27 (2014) 4062-4067 | DOI: 10.1021/ef5007325

Influence of thickness and coatings morphology in the antimicrobial performance of zinc oxide coatings

Carvalho, P; Sampaio, P; Azevedo, S; Vaz, C; Espinos, JP; Teixeira, V; Carneiro, JO

In this research work, the production of undoped and silver (Ag) doped zinc oxide (ZnO) thin films for food-packaging applications were developed. The main goal was to determine the influence of coatings morphology and thickness on the antimicrobial performance of the produced samples. The ZnO based thin films were deposited on PET (Polyethylene terephthalate) substrates by means of DC reactive magnetron sputtering. The thin films were characterized by optical spectroscopy, X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Scanning Electron Microscopy (SEM). The antimicrobial performance of the undoped and Ag-doped ZnO thin films was also evaluated. The results attained have shown that all the deposited zinc oxide and Ag-doped ZnO coatings present columnar morphology with V-shaped columns. The increase of ZnO coatings thickness until 200 nm increases the active surface area of the columns. The thinner samples (50 and 100 nm) present a less pronounced antibacterial activity than the thickest ones (200–600 nm). Regarding Ag-doped ZnO thin films, it was verified that increasing the silver content decreases the growth rate of Escherichia coli and decreases the amount of bacteria cells present at the end of the experiment

Applied Surface Science, 307 (2014) 548-557 | DOI: 10.1016/j.apsusc.2014.04.072

Pyridine adsorption on NiSn/MgO-Al2O3: An FTIR spectroscopic study of surface acidity

Penkova, A; Bobadilla, LF; Romero-Sarria, F; Centeno, MA; Odriozola, JA

The acid-base properties of MgO-Al2O3 supports and NiSn/MgO-Al2O3 catalysts were evaluated by IR spectroscopy using pyridine as a probe molecule. The results indicate that only Lewis acid sites were detected on the surface of the supports as well as on the catalysts. Nevertheless, Bronsted acid sites were not detected. In the support without MgO three kinds of coordinatively unsaturated acid sites were detected: Al3+ cations occupying octahedral, tetrahedral and tetrahedral with cationic vacancy in the neighbourhood. The last sites appear as the strongest. Moreover, they are able to activate the pyridine molecules leading to the formation of an intermediate ce-pyridone complex. When MgO or NiO were added to the alumina, the number and strength of the Lewis acid sites decreased and significant changes were observed in the tetrahedral sites with adjoining cation vacancies. The incorporation of the Mg2+ cations into the alumina's structure takes place on the vacant tetrahedral positions, forming spinel MgAl2O4. As a result, the fraction of tetrahedral sites with adjoining cationic vacancy diminished and the intermediate ce-pyridone complex in the support with the highest MgO loading was hardly detected. The addition of Ni2+ cations leads to the filling of the free octahedral positions, resulting in the formation of a NiAl2O4 spinel structure and the thermal stability of the ce-pyridone species decreases. In the catalysts, the progressive reduction of the number and strength of the Lewis acid sites is due to a competitive formation of the two types of MgAl2O4 and NiAl2O4 spinels. In the catalyst NiSn/30MgO-Al2O3 no cationic vacancies were detected and the surface reaction with ce-pyridone formation did not occur. 

Applied Surface Science, 317 (2014) 241-251 | DOI: 10.1016/j.apsusc.2014.08.093

Osteoblasts Interaction with PLGA Membranes Functionalized with Titanium Film Nanolayer by PECVD. In vitro Assessment of Surface Influence on Cell Adhesion during Initial Cell to Material Interaction

Terriza, A; Vilches-Perez, JI; Gonzalez-Caballero, JL; de la Orden, E; Yubero, F; Barranco, A; Gonzalez-Elipe, AR; Vilches, J; Salido, M

New biomaterials for Guided Bone Regeneration (GBR), both resorbable and non-resorbable, are being developed to stimulate bone tissue formation. Thus, the in vitro study of cell behavior towards material surface properties turns a prerequisite to assess both biocompatibility and bioactivity of any material intended to be used for clinical purposes. For this purpose, we have developed in vitro studies on normal human osteoblasts (HOB®) HOB® osteoblasts grown on a resorbable Poly (lactide-co-glycolide) (PLGA) membrane foil functionalized by a very thin film (around 15 nm) of TiO2 (i.e., TiO2/PLGA membranes), designed to be used as barrier membrane. To avoid any alteration of the membranes, the titanium films were deposited at room temperature in one step by plasma enhanced chemical vapour deposition. Characterization of the functionalized membranes proved that the thin titanium layer completely covers the PLGA foils that remains practically unmodified in their interior after the deposition process and stands the standard sterilization protocols. Both morphological changes and cytoskeletal reorganization, together with the focal adhesion development observed in HOB osteoblasts, significantly related to TiO2 treated PLGA in which the Ti deposition method described has revealed to be a valuable tool to increase bioactivity of PLGA membranes, by combining cell nanotopography cues with the incorporation of bioactive factors.

Materials, 7(3) (2014) 1687-1708 | DOI: 10.3390/ma7031687

Fully stable numerical calculations for finite one-dimensional structures: Mapping the transfer matrix method

Luque-Raigon, JM; Halme, J; Miguez, H

We design a fully stable numerical solution of the Maxwell's equations with the transfer matrix method (TMM) to understand the interaction between an electromagnetic field and a finite, one-dimensional, non-periodic structure. Such an exact solution can be tailored from a conventional solution by choosing an adequate transformation between its reference systems, which induces a mapping between its associated TMMs. The paper demonstrates theoretically the numerical stability of the TMM for the exact solution within the framework of Maxwell's equations, but the same formalism can efficiently be applied to resolve other classical or quantum linear wave-propagation interaction in one, two, and three dimensions. This is because the formalism is exclusively built up for an in depth analysis of the TMM's symmetries.

Journal of Quantitative Spectroscopy and Radiative Transfer, 134 (2014) 9-20 | DOI: 10.1016/j.jqsrt.2013.10.007

Influence of the synthesis parameter on the interlayer and framework structure of lamellar octadecyltrimethylammonium kanemite

Corredor, JI; Cota, A; Pavon, E; Osuna, FJ; Alba, MD

Inorganic–organic nanostructures, used as host materials for selective adsorption of functional molecules and as mesostructured material precursors, can be constructed by the interlayer modification of inorganic layered materials with surfactants. The formation mechanism is mainly determined by the surfactant assemblies in the 2D limited space. In this paper, a detailed structural analysis of the lamellar mesophases prepared from kanemite, a lamellar silicate, and octadecyltrimethylammonium (ODTMA) under various conditions was reported. The adsorbed amount of ODTMA and the long and short range structural orders were explored by TGA, XRD, IR/FT and MAS NMR spectroscopies. The results revealed that ODTMA molecules were efficiently intercalated in the interlayer space of kanemite and, in all synthesis conditions, an ordered lamellar structure was obtained. The ODTMA adsorption in kanemite caused changes not only in the interlayer space but also in the silicate framework, where five-member rings were formed. The characteristics of the final products were influenced by the synthesis conditions, although the separation mode, filtration or centrifugation, was not relevant. Therefore, the adsorption conditions of ODTMA in kanemite will contribute to the design of novel layered materials with potential environmental and technological use.

Applied Clay Science, 95 (2014) 9-17 | DOI: 10.1016/j.clay.2014.02.030

Quantification and comparison of the reaction properties of FEBEX and MX-80 clays with saponite: Europium immobilisers under subcritical conditions

Villa-Alfageme, M; Hurtado, S; Castro, MA; El Mrabet, S; Orta, MM; Pazos, MC; Alba, MD

The evaluation of the retention mechanisms in FEBEX and MX-80 bentonites, selected as reference materials to construct engineered barriers, carries major implications in the safe storage of immobilisation capacity through a recently discovered chemical retention mechanism and the structural analysis of the reaction products. Hydrothermal treatments were accomplished with immobilisation capacity through a recently discovered chemical retention mechanism and the structural analysis of the reaction products. Hydrothermal treatments were accomplished with Eu(NO3)3 (151Eu and 153Eu, with 52.2% 153Eu) and spiked with radioactive 152Eu for the quantification of the reactions. Results were compared with saponite as the reference smectite. The strong dependence of the reaction parameters with temperature and time was quantified and the reaction velocity was evaluated. The velocity follows these trends: 240 days are needed for the total retention of europium for temperatures over 200 °C; below 150 °C, significantly longer reaction times, on the order of three years, are required to complete the reaction. Clays do not influence velocity rates, but the retention capacity of bentonites remains lower than for saponite. At 300 °C, the milliequivalents retained by the three clays are consistently over CEC. The structural analyses reveal not only adsorption of europium but also the presence of Eu(OH)3 precipitation and Eu2SiO3 confirming the existence of a chemical reaction.

Applied Clay Science, 101 (2014) 10-15 | DOI: 10.1016/j.clay.2014.08.012

c- C4F8 Plasmas for the Deposition of Fluorinated Carbon Films

Terriza, A; Macias-Montero, M; Lopez-Santos, MC; Yubero, F; Cotrino, J; Gonzalez-Elipe, AR

Highly fluorinated polymeric (CFX), fluorine containing diamond-like carbon (F-DLC) and, for comparison, diamond-like carbon (DLC) films have been plasma deposited in a RF parallel plate reactor by using c-C4F8 as fluorine precursor and different mixtures of argon, C2H2, and H2. Plasmas have been characterized by optical emission spectroscopy, mass spectrometry, and Langmuir probe measurements. Differences in the film composition and structure have been related with the type of species formed in the plasma and with the self-bias potential developed at the deposition electrode. Additional experiments using CF4 have confirmed that the formation in the plasmas of neutral or ionized CxFy species with x > 2 is a critical factor for the synthesis of fluorine rich films.

Plasma Processes and Polymers, 11 (2014) 289-299 | DOI: 10.1002/ppap.201300129

Plasma Deposition of Superhydrophobic Ag@ TiO2 Core@ shell Nanorods on Processable Substrates

Macias-Montero, M; Borras, A; Romero-Gomez, P; Cotrino, J; Frutos, F; Gonzalez-Elipe, AR

This work reports the low temperature plasma formation of Ag@TiO2 nanorods (NRs) on processable substrates. The layers have been analyzed by electron microscopy and secondary ion mass spectroscopy. The NRs morphologies suggest that the plasma sheath, the high mobility of the silver and the incoming direction of the precursor moieties are key factors determining their shape, dimensions, and tilting orientation. Both amorphous and anatase Ag@TiO2 NRs surfaces are superhydrophobic, and turn into superhydrophilic by irradiation with UV light. This wetting behavior is discussed by considering the water penetration in the inter-NR space during the light-mediated transformation.

Plasma Process and Polymers, 11 (2014) 164-174 | DOI: 10.1002/ppap.201300112

On the Deposition Rates of Magnetron Sputtered Thin Films at Oblique Angles

Alvarez, R; Garcia-Martin, JM; Lopez-Santos, MC; Rico, V; Ferrer, FJ; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A

We describe here the deposition of thin films using magnetron sputtering at oblique angles. General relations between the deposition rates of the films and experimental parameters, such as gas pressure or substrate tilt angles, are deduced and experimentally tested. The model also permits the direct determination of the thermalization mean free path of the sputtered particles in the plasma gas, a key parameter defining the balance between ballistic and diffusive flows in the deposition reactor. The good agreement between experimental and calculated results supports the validity of our description, which becomes a useful tool to explain the main features of the magnetron sputtering deposition of thin films at oblique angles.

Plasma Processes and Polymers, 11 (2014) 571-576 | DOI: 10.1002/ppap.201300201

Hardness and flexural strength of single-walled carbon nanotube/alumina composites

Gallardo-Lopez, A; Poyato, R; Morales-Rodriguez, A; Fernandez-Serrano, A; Munoz, A; Dominguez-Rodriguez, A

This work adds new experimental facts on room temperature hardness and flexural strength of alumina and composites with 1, 2, 5 and 10 vol% single-walled carbon nanotubes (SWNT) with similar grain size. Monolithic Al2O3 and composites were spark plasma sintered (SPS) in identical conditions at 1300 A degrees C, achieving high density, submicrometric grain size and a reasonably homogeneous distribution of SWNT along grain boundaries for all compositions with residual agglomerates. Vickers hardness values comparable to monolithic alumina were obtained for composites with low (1 vol%) SWNT content, though they decreased for higher concentrations, attributed to the fact that SWNT constitute a softer phase. Three-point bending flexural strength also decreased with increasing SWNT content. Correlation between experimental results and microstructural analysis by electron microscopy indicates that although SWNT agglomerates have often been blamed for detrimental effects on the mechanical properties of these composites, they are not the main cause for the reported decay in flexural strength.

Journal of Materials Science, 20 (2014) 7116-7123 | DOI: 10.1007/s10853-014-8419-5

Characterization of porous graphitic monoliths from pyrolyzed wood

Gutierrez-Pardo, A; Ramirez-Rico, J; de Arellano-Lopez, AR; Martinez-Fernandez, J

Porous graphitic carbons were obtained from wood precursors using Ni as a graphitization catalyst during pyrolysis. The structure of the resulting material retains that of the original wood precursors with highly aligned, hierarchical porosity. Thermal characterization was performed by means of thermogravimetry and differential scanning calorimetry, and the onset temperature for graphitization was determined to be similar to 900 A degrees C. Structural and microstructural characterization was performed by means of electron microscopy, electron and x-ray diffraction, and Raman spectroscopy. The effect of maximum pyrolysis temperature on the degree of graphitization was assessed. No significant temperature effect was detected by means of Raman scattering in the range of 1000-1400 A degrees C, but at temperatures over the melting point of the catalyst, the formation of graphite grains with long-range order was detected.

Journal of Materials Science, 49 (2014) 7688-7696 | DOI: 0.1007/s10853-014-8477-8

Phase assembly and electrical conductivity of spark plasma sintered CeO2-ZrO2 ceramics

Poyato, R; Cruz, SA; Cumbrera, FL; Moreno, B; Chinarro, E; Odriozola, JA

Cex Zr1−x O2 (x = 0.10, 0.16 and 0.33) nanocrystalline powders were obtained by a two-step synthesis technique and sintered by spark plasma sintering (SPS). As consequence of the reduction of Ce4+ to Ce3+ species by carbon in the graphite environment in SPS, phase assemblies including tetragonal, monoclinic and pyrochlore phases were generated in the ceramics during the sintering process. The electrical conductivity was highly dependent on phase assembly and atmosphere (N2, H2 and O2). A significant decrease in the activation energy was noticed in the ceramics with high pyrochlore content when measuring the conductivity in H2 atmosphere, consequence of the strong reduction promoted in these ceramics during the measurement. Equal conduction behavior with similar activation energy was observed in all the ceramics when measuring in O2 atmosphere.

Journal of Materials Science, 49 (2014) 6353-6362 | DOI: 10.1007/s10853-014-8361-6

Wall paintings studied using Raman spectroscopy: A comparative study between various assays of cross sections and external layers

Perez-Rodriguez, JL; Robador, MD; Centeno, MA; Siguenza, B; Duran, A

This work describes a comparative study between in situ applications of portable Raman spectroscopy and direct laboratory measurements using micro-Raman spectroscopy on the surface of small samples and of cross sections. The study was performed using wall paintings from different sites of the Alcazar of Seville.

Little information was obtained using a portable Raman spectrometer due to the presence of an acrylic polymer, calcium oxalate, calcite and gypsum that was formed or deposited on the surface. The pigments responsible for different colours, except cinnabar, were not detected by the micro-Raman spectroscopy study of the surface of small samples taken from the wall paintings due to the presence of surface contaminants.

The pigments and plaster were characterised using cross sections. The black colour consisted of carbon black. The red layers were formed by cinnabar and white lead or by iron oxides. The green and white colours were composed of green emerald or atacamite and calcite, respectively. Pb3O4 has also been characterised. The white layers (plaster) located under the colour layers consisted of calcite, quartz and feldspars. The fresco technique was used to create the wall paintings.

A wall painting located on a gypsum layer was also studied. The Naples yellow in this wall painting was not characterised due to the presence of glue and oils.

This study showed the advantage of studying cross sections to completely characterise the pigments and plaster in the studied wall paintings.

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 120 (2014) 602-609 | DOI: 10.1016/j.saa.2013.10.052

Self-propagating combustion synthesis via an MSR process: An efficient and simple method to prepare (Ti, Zr, Hf)B2–Al2O3 powder nanocomposites

Sayagues, MJ; Aviles, MA; Cordoba, JM; Gotor, FJ

The synthesis of (Ti1 − xZrx)B2–Al2O3, (Ti1 − xHfx)B2–Al2O3 and (Zr1 − xHfx)B2–Al2O3 (x = 0, 0.5 and 1) powder nanocomposites via a mechanochemical method using TiO2, ZrO2, HfO2, HBO2 and Al as the raw materials was investigated. The formation of the nanocomposites proceeds via a mechanically-induced self-sustaining reaction (MSR) process that involves several simultaneous reactions. The aluminothermic reductions of the TMO2 and HBO2 produce Al2O3 and transition metal and boron elements, which in turn react to yield the diboride phase. The ignition of the complex combustion reaction occurred after a short milling time (15–30 min), instantly transforming most of the reactants into products. The sample composition was marked by the stoichiometry of the combustion reaction, and the resulting nanocomposites were analysed using XRD, ED, SEM, TEM and EDX techniques. The X-ray results confirmed the biphasic character of the prepared composite powder (TMB2 and Al2O3 structures); minor amounts of the Zr and Hf oxides were also observed. The achieved microstructure was characterised by the agglomeration of Al2O3 nanocrystallites and diboride crystals with a diffraction domain size ranging between 100 and 300 nm.

Powder Technology, 256 (2014) 244-250 | DOI: 10.1016/j.powtec.2014.02.031

Mechanical and phase stability of TiBC coatings up to 1000 degrees C

Abad, MD; Veldhuis, SC; Endrino, JL; Beake, BD; Garcia-Luis, A; Brizuela, M; Sanchez-Lopez, JC

TiBC coatings with different phase compositions (nanocrystalline TiBxCy or TiB2 phases mixed or not with amorphous carbon, a-C) were prepared by magnetron sputtering. These coatings were comparatively studied in terms of phase stability after thermal annealing at 250, 500, 750, and 1000 °C in argon using Raman and x-ray absorption near-edge spectroscopy techniques. The main differences were observed at temperatures above 500 °C when oxidation processes occur and the mechanical properties deteriorate. At 1000 °C, the samples were fully oxidized forming a-C, TiO2, and B2O3 as final products. Higher hardness and reduced indentation modulus values and better tribological properties were observed at 750 °C for nanocomposite structures including amorphous carbon and ternary TiBxCy phases. This behavior is attributed to a protective effect associated with the a-C phase which is achieved by the encapsulation of the nanocrystals in the coating and the better hard/lubricant phase ratio associated with this type of coating.

Journal of Vacuum Science & Technology A, 32 (2014) 021508 | DOI: 10.1116/1.4861365

Thermal properties of La2O3-doped ZrB2- and HfB2-based ultra-high temperature ceramics

Zapata-Solvas, E; Jayaseelan, DD; Brown, PM; Lee, WE

Thermal properties of La2O3-doped ZrB2- and HfB2-based ultra high temperature ceramics (UHTCs) have been measured at temperatures from room temperature to 2000 °C and compared with SiC-doped ZrB2- and HfB2-based UHTCs and monolithic ZrB2 and HfB2. Thermal conductivities of La2O3-doped UHTCs remain constant around 55–60 W/mK from 1500 °C to 1900 °C while SiC-doped UHTCs showed a trend to decreasing values over this range.

Journal of the European Ceramic Society, 33 (2013) 3467-3472 | DOI: 10.1016/j.jeurceramsoc.2013.06.009

Study and restoration of the Seville City Hall facade

Robador, MD; Arroyo, F; Perez-Rodriguez, JL

Before restoring the Seville City Hall façade, a study of the original materials and the compounds added or formed was performed. The stone is fine-grained carbonate rock. Gypsum and mortars were used to restore stone fragments. A black crust was also found the wall was covered with an acrylic resin. A layer of lime on the surface was also detected. The restoration was intended to preserve the artistic quality and uniqueness of this building. The cleaning, reinforcing and innovatively consolidating and protecting the stone using suitable materials similar to those used in the original construction are described in this study.

Construction and Building Materials, 53 (2014) 370-380 | DOI: 10.1016/j.conbuildmat.2013.11.088

CdSe@ZnS nanocomposites prepared by a mechanochemical route: No release of Cd2+ ions and negligible in vitro cytotoxicity

Balaz, P; Sayagues, MJ; Balaz, M; Zorkovska, A; Hronec, P; Kovac, J; Kovac, J; Dutkova, E; Mojzisova, G; Mojzis, J

CdSe@ZnS nanocomposites have been prepared by a two-step solid state mechanochemical synthesis. CdSe prepared from Cd and Se elements in the first step was mixed with zinc acetate and sodium sulphide in the second step of milling to prepare a CdSe@ZnS nanocomposite. In the third step, the obtained nanocomposite was coated with l-cysteine to prepare a biocompatible system. The crystallite size of the new type of nanocomposite was 20–35 nm for cubic CdSe and 3–8 nm for hexagonal ZnS as calculated from XRD, TEM and SEM data. The synthesised samples show good crystallinity and have been tested for dissolution and cytotoxicity. The dissolution of cadmium from CdSe@ZnS was less than 0.05 μg mL−1, whereas a value of 0.8 μg mL−1 was measured for CdSe alone. The binding of ZnS with CdSe in the nanocomposite practically eliminated the release of cadmium into solution. As a consequence, a very low cytotoxic activity has been evidenced for CdSe@ZnS. The nanocomposites coated with l-cysteine have a great potential as fluorescent labels in biomedical engineering.

Materials Research Bulletin, 49 (2014) 302-309 | DOI: 10.1016/j.materresbull.2013.08.070

Competitive effect of the metallic canister and clay barrier on the sorption of Eu3+ under subcritical conditions

El Mrabet, S; Castro, MA; Hurtado, S; Orta, MM; Pazos, MC; Villa-Alfageme, M; Alba, MD

An in depth knowledge and understanding of high activity radionuclide (HLRW) immobilization processes on the materials composing the engineered barrier (clay and metallic canister) is required to ensure the safety and the long-term performance of radioactive waste disposal procedures. Therefore, the aim of this study was to understand the mechanisms involved in the retention of Eu3+ by two components of the multibarrier system, the bentonite barrier and the canister. As such, a comparative study of the interaction of trivalent Eu3+, used to simulate trivalent actinides, with both bentonite and a metallic canister has been undertaken in this work. To this end, we designed a minireactor into which the bentonite was introduced and compacted. The minireactor-bentonite system was then submitted to a hydrothermal reaction with a 7.9 × 10−2 M solution of Eu3+ at 300 °C for 4.5 days. SEM and XRD results revealed that both bentonite and the container were involved in the immobilization of europium by the formation of insoluble europium silicate phases. The presence of europium silicate adsorbed on the surface of the metallic canister indicates the competitive effect of both components of the engineered barrier (bentonite and metallic canister) in HLRW immobilization. These results suggested that the canister could play a role in the HLRW immobilization even during its corrosion process.

Applied Geochemistry, 40 (2014) 25-31 | DOI: j.apgeochem.2013.10.014

Chromium removal on chitosan-based sorbents - An EXAFS/XANES investigation of mechanism

Vieira, RS; Meneghetti, E; Baroni, P; Guibal, E; de la Cruz, VMG; Caballero, A; Rodriguez-Castellon, E; Beppu, MM

Chitosan is known to be a good sorbent for metal-containing ions as the presence of amino groups and hydroxyl functions act as effective binding sites. Its crosslinking, employing glutaraldehyde or epichlorohydrin, may change the sorption properties (sorption capacity or diffusion properties) of this biopolymer, since the available functional groups are different in each case. X-ray absorption spectroscopy (XAS), including extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES), Fourier-transformed infrared spectroscopy with attenuated total reflectance device (FTIR-ATR) was used along with speciation diagrams, in order to identify the binding groups involved in chromate sorption and its mechanisms. In pristine chitosan and epichlorohydrin-crosslinked chitosan membranes, amino groups are most likely responsible for adsorption, although the contribution of hydroxyl groups cannot be excluded (especially for metal-sorbent stabilization). In this case, when adsorbed about 70% of chromate ions remain in the Cr(VI) oxidation state. In the case of glutaraldehyde-crosslinked membranes, the functional groups involved are different. Carbonyl groups and imino bonds – resulting from the reaction of the crosslinking agent and amino groups – may be involved in the adsorption mechanism. Additionally, a higher fraction of chromate anions, around 44% are reduced to Cr(III) oxidation state in loaded sorbent. The presence of free aldehyde groups may explain this partial reduction.

Materials Chemistry and Physics, 146 (2014) 412-417 | DOI: 10.1016/j.matchemphys.2014.03.046

Scission kinetic model for the prediction of polymer pyrolysis curves from chain structure

Perez-Maqueda, LA; Sanchez-Jimenez, PE; Perejon, A; Garcia-Garrido, C; Criado, JM; Benitez-Guerrero, M

There is a significant interest in correlating polymer structure with thermal degradation behavior. Thus, polymer pyrolysis curves could be predicted from the chemical structure of the polymer. Recent proposals correlate the kinetic temperature function directly with the chemical structure of the polymer by means of the dissociation energy while assuming a semi-empirical first order model for the reaction fraction function. However, a first order model lacks physical meaning and produces significant deviations of the predicted curves, mostly under isothermal conditions. Thus, in this work, an upgrade of the method is proposed by using a new random scission kinetic model. The newly proposed kinetic equation has been checked by fitting the experimental data reported by different authors for the thermal pyrolysis of polystyrene. It has been demonstrated that it accounts for the experimental data of polymer degradation under different heating schedules with considerably higher precision than the previously assumed first order kinetics.

Polymer Testing, 37 (2014) 1-5 | DOI: 10.1016/j.polymertesting.2014.04.004

Comparison of thermal behavior of natural and hot-washed sisal fibers based on their main components: Cellulose, xylan and lignin. TG-FTIR analysis of volatile products

Benitez-Guerrero, M; Lopez-Beceiro, J; Sanchez-Jimenez, PE; Pascual-Cosp, J

This paper presents in a comprehensive way the thermal behavior of natural and hot-washed sisal fibers, based on the fundamental components of lignocellulosic materials: cellulose, xylan and lignin. The research highlights the influence exerted on the thermal stability of sisal fibers by other constituents such as non-cellulosic polysaccharides (NCP) and mineral matter.

Thermal changes were investigated by thermal X-ray diffraction (TXRD), analyzing the crystallinity index (%Ic) of cellulosic samples, and by simultaneous thermogravimetric and differential thermal analysis coupled with Fourier-transformed infrared spectrometry (TG/DTA-FTIR), which allowed to examine the evolution of the main volatile compounds evolved during the degradation under inert and oxidizing atmospheres. The work demonstrates the potential of this technique to elucidate different steps during the thermal decomposition of sisal, providing extensible results to other lignocellulosic fibers, through the analysis of the evolution of CO2, CO, H2O, CH4, acetic acid, formic acid, methanol, formaldehyde and 2-butanone, and comparing it with the volatile products from pyrolysis of the biomass components. The hydroxyacetaldehyde detected during pyrolysis of sisal is indicative of an alternative route to that of levoglucosan, generated during cellulose pyrolysis.

Hot-washing at 75 °C mostly extracts non-cellulosic components of low decomposition temperature, and reduces the range of temperature in which sisal decomposition occurs, causing a retard in the pyrolysis stage and increasing TbNCP and TbCEL, temperatures at the maximum mass loss rate of non-cellulosic polysaccharides and cellulose decompositions, respectively. However, enriching sisal fibers in cellulose produces a decrease of TbCEL under an oxidizing atmosphere, and furthermore, a delay of the combustion process, displacing TbCOM to higher temperatures.

The results and findings of the paper would help further understanding of thermal processes where Agave fibers are involved, as the decomposition of their composites.

Thermochimica Acta, 581 (2014) 70-86 | DOI: 10.1016/j.tca.2014.02.013

On the kinetic and thermodynamic electron temperatures in non-thermal plasmas

Alvarez, R; Cotrino, J; Palmero, A

The framework to describe the out-of-equilibrium free electrons in cold plasmas is developed assuming the electron entropy is defined through the Boltzmann H-theorem. Our theory explains why the Saha-Boltzmann relation among higher-lying excited states by means of the electron kinetic temperature is fulfilled, even when free electrons are far from equilibrium. The thermodynamic electron temperature, pressure and chemical potential have been introduced through the derivatives of the electron entropy. It is demonstrated that under usual conditions in cold plasmas, e.g. when the electron distribution function possesses the Maxwellian, Druyvestein or Kappa functional forms, kinetic and thermodynamic electron temperatures yield the same value.

EPL (Europhysic Letters), 105 (2014) | DOI: 10.1209/0295-5075/105/15001

Tribological comparison of different C-based coatings in lubricated and unlubricated conditions

Ciarsolo, I; Fernandez, X; de Gopegui, UR; Zubizarreta, C; Abad, MD; Mariscal, A; Caretti, I; Jimenez, I; Sanchez-Lopez, JC

The use of carbon-based coatings (hydrogenated and non-hydrogenated DLC, doped and alloyed-DLC) is of wide interest due to its applications in mechanical components submitted to friction and wear including sliding parts in automotive engines. A tribological comparative analysis using a reciprocating (SRV) tester in lubricated and unlubricated conditions with a 4-stroke motor oil has been carried out on six currently relevant state-of-the-art coatings (namely WC/a-C, TiBC/a-C and TiC/a-C:H nanocomposites, Ti-doped DLC, BCN film and a crystalline monolithic TiC film as reference). The quantification of the fraction of the sp(2)-bonded matrix has been done by fitting of C 1s XPS peak and the mechanical properties evaluated by nanoindentation. The comparative analysis has allowed us to identify the capabilities of each system depending on the testing conditions and the possible synergies as a function of the chemical composition and film nature. Under lubricated harsh conditions (max. contact pressure 1.7 GPa) only coatings displaying hardness superior to 20 GPa could stand the sliding motion without failure. At lower contact pressures, a significant fraction of sp(2) carbon (>= 75%) is advantageous for reducing wear in boundary lubrication. WC/a-C, BCN and Ti-DLC films showed the best tribological response in dry sliding conditions. This fundamental information would be of relevance for assisting engineers in selecting best partnership for lubrication systems. 

Surface and Coatings Technology, 257 (2014) 278-285 | DOI: 10.1016/j.surfcoat.2014.07.068

Effect of clays and metal containers in retaining Sm3+ and ZrO2+ and the process of reversibility

El Mrabet, S; Castro, MA; Hurtado, S; Orta, MM; Pazos, MC; Villa-Alfageme, M; Alba, MD

Knowledge and understanding about radionuclides retention processes on the materials composing the engineered barrier (clay mineral and metallic container waste) are required to ensure the safety and the long-term performance of radioactive waste disposal. Therefore, the present study focuses on the competitiveness of clay and the metallic container in the process of adsorption/desorption of the radionuclides simulators of Am3+ and UO22+. For this purpose, a comparative study of the interaction of samarium (chosen as chemical analog for trivalent americium) and zirconyl (as simulator of uranyl and tetravalent actinides) with both FEBEX bentonite and metallic container, under subcritical conditions, was carried out. The results revealed that the AISI-316L steel container, chemical composition detailed in Table 1, immobilized the high-radioactive waste (HRW), even during the corrosion process. The ZrO2+ was irreversibly adsorbed on the minireactor surface. In the case of samarium SEM/EDX analysis revealed the formation of an insoluble phase of samarium silicate on the container surface. There was no evidence of samarium diffusion through the metallic container. Samarium remained adsorbed by the container also after desorption experiment with water. Therefore, steel canister is actively involved in the HRW immobilization.

American Mineralogist, 99 (4) (2014) 696-703 | DOI: 10.2138/am.2014.4665

Properties of mechanochemically synthesized nanocrystalline Bi2S3 particles

Dutkova, E; Sayagues, MJ; Zorkovska, A; Real, C; Balaz, P; Satka, A; Kovac, J

Nanocrystalline Bi2S3 particles have been synthesized from Bi and S powders by high-energy milling in a planetary mill. Structural and microstructural characterization of the prepared particles, including phase identification, specific surface area measurement and particle size analysis has been carried out. The optical properties were measured by spectroscopic methods and the structural stability up to 500 °C was studied by thermal analysis. The production of orthorhombic Bi2S3 with crystallite size of about 26 nm was confirmed by X-ray diffraction. The nanocrystals tend to agglomerate due to their large specific surface area. Accordingly, the average hydrodynamic diameter of the mechanochemically synthesized particles is 198 nm. EDS analysis shows that the synthesized material is pure Bi2S3. The band gap of the Bi2S3 nanoparticles is 4.5 eV which is wider than that in bulk materials. The nanoparticles exhibit good luminescent properties with a peak centered at 490 and 390 nm. Differential scanning calorimetry curves exhibit a broad exothermic peak between 200 and 300 °C, suggesting recovery processes. This interpretation is supported by X-ray diffraction measurements that indicate a 10-fold increase of the crystallite size to about 230 nm. The controlled mechanochemical synthesis of Bi2S3 nanoparticles at ambient temperature and atmospheric pressure remains a great challenge.

Materials Science in Semiconductor Processing, 27 (2014) 267-272 | DOI: 10.1016/j.mssp.2014.05.057

The growth of cobalt oxides on HOPG and SiO2 surfaces: A comparative study

Diaz-Fernandez, D; Mendez, J; Bomati-Miguel, O; Yubero, F; Mossanek, RJO; Abbate, M; Dominguez-Canizares, G; Gutierrez, A; Tougaard, S; Soriano, L

The growth of cobalt oxides by reactive thermal evaporation of metallic cobalt on highly oriented pyrolytic graphite (HOPG) and SiO2 (X cut quartz surface), in an oxygen atmosphere at room temperature, has been chemically and morphologically studied by means of X-ray photoelectron spectroscopy and atomic force microscopy. The chemical analysis, which also includes cluster calculations, reveals that for the early deposition stages on both substrates, Co2 + species are stabilized at the surface up to a coverage which depends on the substrate. Further coverages lead to the formation of the spinel oxide Co3O4. The results are discussed in terms of the dependence of the surface energy on the size of the CoO deposited moieties. On the other hand, it has been found that the initial way of growth of cobalt oxides on HOPG is of Stranski–Krastanov mode whereas on SiO2 the growth is of Volmer–Weber mode. The differences in the growth morphology have been discussed in terms of the surface diffusivity of the CoO deposits on the substrates.

Surface Science, 624 (2014) 145-153 | DOI: 10.1016/j.susc.2014.02.007

LMM Auger primary excitation spectra of copper

Pauly, N; Tougaard, S; Yubero, F

The shape and intensity of measured Auger peaks are strongly affected by extrinsic excitations due to electron transport out of the surface and to intrinsic excitations induced by the sudden creation of the two static core holes. Following a method developed for XPS in a previous work [N. Pauly, S. Tougaard, F. Yubero, Surf. Sci. 620 (2014) 17], we have calculated the effective energy-differential inelastic electron scattering cross-sections, including the effects of the surface and of the two core holes, within the dielectric response theory by means of the QUEELS-XPS software (QUantitative analysis of Electron Energy Losses at Surfaces for XPS). The Auger spectra are then modeled by convoluting this energy loss cross section with the primary excitation spectrum that accounts for all effects which are part of the initial Auger process, i.e. L–S coupling and vacancy satellite effects. The shape of this primary excitation spectrum is fitted to get close agreement between the theoretical and the experimental spectra obtained from X-ray excited Auger electron spectroscopy (XAES). We have performed these calculations of XAES spectra for various LMM Auger transitions of pure Cu (L3M45M45, L3M23M45, L3M23M23 and L2M45M45 transitions). We compare the resulting primary excitation spectra with theoretical results published in the literature and obtain reasonable quantitative agreement. In particular, we extract from experimental spectra quantitative intensities due to Coster–Kronig, shake-off and shake-up processes relative to the intensity from the “normal” Auger process.

Surface Science, 630 (2014) 294-299 | DOI: 10.1016/j.susc.2014.08.029

A Nanoscale Characterization with Electron Microscopy of Multilayered CrAlYN Coatings: A Singular Functional Nanostructure

Rojas, TC; Dominguez-Meister, S; Brizuela, M; Garcia-Luis, A; Fernandez, A; Sanchez-Lopez, JC

A combination of transmission electron microscopy techniques and spatially resolved microanalysis is used to investigate the nanostructure, constituting phases, and chemical elemental distribution in CrAlYN multilayered coatings. The location of the metallic elements and their chemical state are needed to understand their functional properties. Samples were prepared with variable Al (4-12 at%) and Y (2-5 at%) contents by direct current reactive magnetron sputtering on silicon substrates using metallic targets and Ar/N-2 mixtures under different deposition parameters (power applied to the target and rotation speed of the sample holder). The changes produced in the nanostructure and chemical distribution were investigated. Nanoscale resolution electron microscopy analysis has shown that these coatings present a singular nanostructure formed by multilayers containing at a certain periodicity nanovoids filled with molecular nitrogen. Spatially resolved energy dispersive spectroscopy and electron energy loss elemental mappings and profiles showed that the chromium, aluminum, and yttrium atoms are distributed in a sequential way following the position of the targets inside the deposition chamber. Analysis of the different atomic distribution and phases formed at the nanoscale is discussed depending on the deposition parameters.

Microscoy and Microanalysis, 20 (2014) 14-24 | DOI: 10.1017/S1431927613013962

Tomographic Heating Holder for In Situ TEM: Study of Pt/C and PtPd/Al2O3 Catalysts as a Function of Temperature

Gontard, LC; Dunin-Borkowski, RE; Fernandez, A; Ozkaya, D; Kasama, T

A tomographic heating holder for transmission electron microscopy that can be used to study supported catalysts at temperatures of up to similar to 1,500 degrees C is described. The specimen is placed in direct thermal contact with a tungsten filament that is oriented perpendicular to the axis of the holder without using a support film, allowing tomographic image acquisition at high specimen tilt angles with minimum optical shadowing. We use the holder to illustrate the evolution of the active phases of Pt nanoparticles on carbon black and PtPd nanoparticles on gamma-alumina with temperature. Particle size distributions and changes in active surface area are quantified from tilt series of images acquired after subjecting the specimens to increasing temperatures. The porosity of the alumina support and the sintering mechanisms of the catalysts are shown to depend on distance from the heating filament.

Microscoy and Microanalysis, 20 (2014) 982-990 | DOI: 10.1017/S1431927614000373

Transmission electron microscopy of unstained hybrid Au nanoparticles capped with PPAA (plasma-poly-allylamine): Structure and electron irradiation effects

Gontard, LC; Fernandez, A; Dunin-Borkowski, RE; Kasama, T; Lozano-Perez, S; Lucas, S

Hybrid (organic shell–inorganic core) nanoparticles have important applications in nanomedicine. Although the inorganic components of hybrid nanoparticles can be characterized readily using conventional transmission electron microscopy (TEM) techniques, the structural and chemical arrangement of the organic molecular components remains largely unknown. Here, we apply TEM to the physico-chemical characterization of Au nanoparticles that are coated with plasma-polymerized-allylamine, an organic compound with the formula C3H5NH2. We discuss the use of energy-filtered TEM in the low-energy-loss range as a contrast enhancement mechanism for imaging the organic shells of such particles. We also study electron-beam-induced crystallization and amorphization of the shells and the formation of graphitic-like layers that contain both C and N. The resistance of the samples to irradiation by high-energy electrons, which is relevant for optical tuning and for understanding the degree to which such hybrid nanostructures are stable in the presence of biomedical radiation, is also discussed.

Micron, 67 (2014) 1-9 | DOI: 10.1016/j.micron.2014.06.004

Tribological behaviour at high temperature of hard CrAlN coatings doped with Y or Zr

Sanchez-Lopez, JC; Contreras, A; Dominguez-Meister, S; Garcia-Luis, A; Brizuela, M

The tribological properties of CrAlN, CrAlYN and CrAlZrN coatings deposited by direct current reactive magnetron sputtering are studied by means of pin-on-disc experiments at room temperature, 300, 500 and 650 °C using alumina balls as counterparts. The influence of the metallic composition (Al, Y and Zr) on the friction, wear properties and oxidation resistance is studied by means of scanning electron microscopy, energy dispersive X-ray analysis and Raman analysis of the contact region after the friction tests. The results obtained allow us to classify the tribological behaviour of the CrAl(Y,Zr)N coatings into three groups according to the nature of the dopant and aluminium content. The sliding wear mechanism is characterized by the formation of an overcoat rich in chromium and aluminium oxides whose particular composition is determined by the initial chemical characteristics of the coating and the testing temperature. The fraction of Cr2O3 becomes more significant as the Al content decreases and the temperature increases. The addition of Y, and particularly Zr, favours the preferential formation of Cr2O3 versus CrO2 leading to a reduction of friction and wear of the counterpart. Conversely, the tribological behaviour of pure CrAlN coatings is characterized by higher friction but lower film wear rates as a result of higher hardness and major presence of aluminium oxides on the coating surface.

Thin Solid Films, 550 (2014) 413-420 | DOI: 10.1016/j.tsf.2013.10.041

Nanoindentation of nanocolumnar TiO2 thin films with single and stacked zig-zag layers

Jimenez-Pique, E; Gonzalez-Garcia, L; Rico, VJ; Gonzalez-Elipe, AR

This paper reports a systematic analysis of the mechanical properties of nanocolumnar TiO2 thin films prepared by evaporation at a glancing geometry. A systematic study of the mechanical properties is carried out by comparing the hardness and the Young's modulus determined by nanoindentation for thin films prepared at different deposition angles and characterized by a tilted nanocolumnar structure and others where the nanocolumns are perpendicular to the substrate or are arranged as zig-zag stacked layers. A correlation between mechanical properties and glazing angle geometry is proposed. Differences in the results are discussed in view of the cross section images obtained by focused ion beam and of the deformed areas. Zig-zagged layers present lower values of hardness and Young's modulus due to the collapse of the angles of the columns, but at the same time this configuration impedes the appearance of fracture or delamination, as observed for tilted columns.

Thin Solid Films, 550 (2014) 444-449 | DOI: 10.1016/j.tsf.2013.10.022

Biomimetic polymers of plant cutin: an approach from molecular modeling

San-Miguel, MA; Oviedo, J; Heredia-Guerrero, JA; Heredia, A; Benitez, JJ

Biomimetics of materials is based on adopting and reproducing a model in nature with a well-defined functionality optimized through evolution. An example is barrier polymers that protect living tissues from the environment. The protecting layer of fruits, leaves, and non-lignified stems is the plant cuticle. The cuticle is a complex system in which the cutin is the main component. Cutin is a biopolyester made of polyhydroxylated carboxylic acids of 16 and 18 carbon atoms. The biosynthesis of cutin in plants is not well understood yet, but a direct chemical route involving the self-assembly of either molecules or molecular aggregates has been proposed. In this work, we present a combined study using experimental and simulation techniques on self-assembled layers of monomers selectively functionalized with hydroxyl groups. Our results demonstrate that the number and position of the hydroxyl groups are critical for the interaction between single molecules and the further rearrangement. Also, the presence of lateral hydroxyl groups reinforces lateral interactions and favors the bi-dimensional growth (2D), while terminal hydroxyl groups facilitate the formation of a second layer caused by head–tail interactions. The balance of 2D/3D growth is fundamental for the plant to create a protecting layer both large enough in 2D and thick enough in 3D.

Journal of Molecular Modeling, 20 (2014) 2329 | DOI: 10.1007/s00894-014-2329-y

Mechanochemical Processing of CaCu3Ti4O12 with Giant Dielectric Properties

Espinoza-Gonzalez, R; Vega, E; Tamayo, R; Criado, JM; Dianez, MJ

The dielectric properties of CaCu3Ti4O12 (CCTO) ceramic prepared by mechanochemical synthesis (MCS) were investigated. The effect on dielectric properties of ball-to-powder weight ratio and milling time was investigated and compared to the behavior of CCTO prepared by conventional solid state reaction (CSSR). CCTO ceramic was partially obtained after 6h of the milling process, while complete transformation was obtained during the sintering step of milled powders. It was shown that the dielectric properties of CCTO processed by MCS are dramatically improved compared with samples prepared by CSSR.

Materials and Manufacturing Processes, 29 (2014) 1179-1183 | DOI: 10.1080/10426914.2014.921702

Osteoconductive Potential of Barrier NanoSiO(2) PLGA Membranes Functionalized by Plasma Enhanced Chemical Vapour Deposition

Terriza, A; Vilches-Perez, JI; de la Orden, E; Yubero, F; Gonzalez-Caballero, JL; Gonzalez-Elipe, AR; Vilches, J; Salido, M

The possibility of tailoring membrane surfaces with osteoconductive potential, in particular in biodegradable devices, to create modified biomaterials that stimulate osteoblast response should make them more suitable for clinical use, hopefully enhancing bone regeneration. Bioactive inorganic materials, such as silica, have been suggested to improve the bioactivity of synthetic biopolymers. An in vitro study on HOB human osteoblasts was performed to assess biocompatibility and bioactivity of SiO2 functionalized poly(lactide-co-glycolide) (PLGA) membranes, prior to clinical use. A 15 nm SiO2 layer was deposited by plasma enhanced chemical vapour deposition (PECVD), onto a resorbable PLGA membrane. Samples were characterized by X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and infrared spectroscopy (FT-IR). HOB cells were seeded on sterilized test surfaces where cell morphology, spreading, actin cytoskeletal organization, and focal adhesion expression were assessed. As proved by the FT-IR analysis of samples, the deposition by PECVD of the SiO2 onto the PLGA membrane did not alter the composition and other characteristics of the organic membrane. A temporal and spatial reorganization of cytoskeleton and focal adhesions and morphological changes in response to SiO2 nanolayer were identified in our model. The novedous SiO2 deposition method is compatible with the standard sterilization protocols and reveals as a valuable tool to increase bioactivity of resorbable PLGA membranes.

BioMed Research International, 2014 (2014) 253590 | DOI: 10.1155/2014/253590

Materials characteristics of Roman and Arabic mortars and stuccoes from The Patio de Banderas in the Real Alcazar of Seville (SPAIN)

Garofano, I; Robador, MD; Duran, A

This study discusses the materials and traditional knowledge used in the manufacture and application of lime mortars and stuccoes by Romans and Arabs in Seville (southern Iberian Peninsula). All of the samples studied contain calcite as a binder, combined with aggregates based on river sand from the filling materials of the Guadalquivir River's depression, located in the vicinity of the Real Alcazar Palace in Seville, Spain, where the artefacts were discovered. The Romans used high-quality production technology, as evidenced by the careful selection of raw materials as well as by the adequate binder-to-aggregate ratio and the elevated homogeneity of the mortars and stuccoes. The suitable distribution of aggregates resulted in higher density values for Roman fragments than for Arabic ones. Results derived from Arabic samples suggest a decline in technology manufacture over time. This work provides useful information, particularly regarding the Roman and Arabic periods in the Iberian Peninsula. The analytical techniques employed in this study were X-ray diffraction (XRD), X-ray fluorescence (XRF)—using conventional and portable systems, scanning electron microscopy (SEM), petrographic microscopy, differential thermal analysis/thermogravimetry (DTA/TG), particle-size analysis and mercury intrusion porosimetry.

Archaeometry, 56 (2014) 541-561 | DOI: 10.1111/arcm.12041

Nanocolumnar growth of thin films deposited at oblique angles: Beyond the tangent rule

Alvarez, R; Lopez-Santos, C; Parra-Barranco, J; Rico, V; Barranco, A; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A

The growth of nanostructured physical vapor deposited thin films at oblique angles is becoming a hot topic for the development of a large variety of applications. Up to now, empirical relations, such as the so-called tangent rule, have been uncritically applied to account for the development of the nanostructure of these thin films even when they do not accurately reproduce most experimental results. In the present paper, the growth of thin films at oblique angles is analyzed under the premises of a recently proposed surface trapping mechanism. The authors demonstrate that this process mediates the effective shadowing area and determines the relation between the incident angle of the deposition flux and the tilt angle of the columnar thin film nanostructures. The analysis of experimental data for a large variety of materials obtained in our laboratory and taken from the literature supports the existence of a connection between the surface trapping efficiency and the metallic character of the deposited materials. The implications of these predictive conclusions for the development of new applications based on oblique angle deposited thin films are discussed.

Journal of Vacuum Science & Technology B, 32 (2014) 041802 | DOI: 10.1116/1.4882877

Calcium silicates synthesised from industrial residues with the ability for CO2 sequestration

Morales-Florez, V; Santos, A; Lopez, A; Morina, I; Esquivias, L

This work explored several synthesis routes to obtain calcium silicates from different calcium-rich and silica-rich industrial residues. Larnite, wollastonite and calcium silicate chloride were successfully synthesised with moderate heat treatments below standard temperatures. These procedures help to not only conserve natural resources, but also to reduce the energy requirements and CO2 emissions. In addition, these silicates have been successfully tested as carbon dioxide sequesters, to enhance the viability of CO2 mineral sequestration technologies using calcium-rich industrial by-products as sequestration agents. Two different carbon sequestration experiments were performed under ambient conditions. Static experiments revealed carbonation efficiencies close to 100% and real-time resolved experiments characterised the dynamic behaviour and ability of these samples to reduce the CO2 concentration within a mixture of gases. The CO2 concentration was reduced up to 70%, with a carbon fixation dynamic ratio of 3.2mgCO(2) per g of sequestration agent and minute. Our results confirm the suitability of the proposed synthesis routes to synthesise different calcium silicates recycling industrial residues, being therefore energetically more efficient and environmentally friendly procedures for the cement industry.

Waste Management & Research, 32 (2014) 1178-1185 | DOI: 10.1177/0734242X14542148

Study of the early stages of growth of Co oxides on oxide substrates

Diaz-Fernandez, D; Mendez, J; Yubero, F; Dominguez-Canizares, G; Gutierrez, A; Soriano, L

The growth of Cobalt oxides by reactive thermal evaporation of metallic Cobalt in an oxygen atmosphere on a series of oxide substrates, namely SiO2, Al2O3 and MgO, has been chemically and morphologically studied by means of XPS and atomic force microscopy (AFM). The XPS results reveal that cobalt oxide grows as CoO (Co2+) for coverages up to some tens of equivalent monolayers on all substrates. For larger coverages, the formation of the spinel oxide Co3O4 has been observed. AFM and XPS quantification allowed us to determine the way of growth of CoO on all substrates, being of Volmer-Weber (i.e. islands) mode for SiO2, whereas for Al2O3 and MgO, the growth follows the Frank-van der Merwe (i.e. layer-by-layer) mode. The results are discussed in terms of the mismatch of the lattice parameters of the CoO adsorbates with the substrates

Surface and Interface Analysis, 46 (2014) 975-979 | DOI: 10.1002/sia.5366

Interpretation of electron Rutherford backscattering spectrometry for hydrogen quantification

Alvarez, R; Yubero, F

In the last few years, several papers have appeared showing the capabilities of electron Rutherford backscattering spectrometry (eRBS) to quantify the H content at surfaces. The basis of the H detection in this technique relies on the difference in recoil energy of the incident electrons depending on the mass of the atoms located at the surface that act as scatter centers. In this paper, we address the interpretation of eRBS spectra of hydrogen containing surfaces. The aim is to compare the naive single elastic scattering approximation with a more realistic description of eRBS spectra including multiple elastic scattering using the HQ-eRBS (hydrogen quantification eRBS) software based on a Monte Carlo algorithm. It is concluded that multiple elastic scattering is a significant contribution to experimentally measured eRBS spectra of a polyethylene surface. It induces significant broadening of the distribution of the maximum elastic scattering angle along the electron trajectories contributing to the measured spectra. However, it has weak effect in the energy distribution of the collected electrons (about 10% overestimation of the H content in the particular case of a polyethylene surface with respect to the corresponding ratio of elastic scattering cross sections).

Surface and Interface Analysis, 46 (2014) 812-816 | DOI: 10.1002/sia.5486

Modeling of X-ray photoelectron spectra: surface and core hole effects

Pauly, N; Tougaard, S; Yubero, F

The shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface and by intrinsic excitations induced by the sudden creation of the static core hole. Besides, elastic electron scattering may also be important. These effects should be included in the theoretical description of the emitted photoelectron peaks. To investigate the importance of surface and core hole effects relative to elastic scattering effect, we have calculated full XPS spectra for the Cu 2p emissions of Cu and CuO with the simulation of electron spectra for surface analysis (SESSA) software and with a convolution procedure using the differential inelastic electron scattering cross-section obtained with the quantitative analysis of electron energy loss in XPS (QUEELS-XPS) software. Surface and core hole effects are included in QUEELS-XPS but absent in SESSA while elastic electron scattering effects are included in SESSA but absent in QUEELS-XPS. Our results show that the shape of the XPS spectra are strongly modified because of surface and core hole effects, especially for energy losses smaller than about 20eV.

Surface and Interface Analysis, 46 (2014) 920-923 | DOI: 10.1002/sia.5372

Promoting effect of Ce and Mg cations in Ni/Al catalysts prepared from hydrotalcites for the dry reforming of methane

Djebarri, B; Gonzalez-Delacruz, VM; Halliche, D; Bachari, K; Saadi, A; Caballero, A; Holgado, JP; Cherifi, O

Several catalytic systems containing Ni/Mg/Al/Ce were synthesized from nitrates of Ni2+, Mg2+, Al3+ and Ce3+ cations with M2+/M3+ = 2 ratios by means of the carbonate co-precipitation method and subsequent calcination at 800 A degrees C. Atomic absorption spectroscopy, X-ray diffraction (XRD), FT-IR spectroscopy, BET, temperature programmed reduction and scanning electron microscopy were used in order to describe the structural, morphological and surface characteristics of the solids completely. The effect of substitution/incorporation of Al by Ce and/or Mg on NiAl sample was studied. XRD analyses confirm that on Al-containing samples (NiAl, NiMgAl), the formation of the precursors layered double hydroxide structure. On the other hand, on cerium containing samples (NiCe, NiMgCe), poorly resolved diffractograms were observed what can be explained by the large radius of cerium. The catalysts were evaluated in the reaction of CO2 reforming of methane at 750 A degrees C. NiCe and NiMgAl catalysts exhibit higher activity and a H-2/CO ratio of almost 1. NiAl and NiMgCe samples showed lower conversions and a CH4/CO2 ratio < 1, indicating the occurrence of reverse water gas shift reaction.

Reaction Kinetics, Mechanisms and Catalysis, 111 (2014) 259-275 | DOI: 10.1007/s11144-013-0646-2

Comparative Study of Micro- and Nano-structured Coatings for High-Temperature Oxidation in Steam Atmospheres

Perez, FJ; Castaneda, SI; Hierro, MP; Galindo, RE; Sanchez-Lopez, JC; Mato, S

For many high-temperature applications, coatings are applied in order to protect structural materials against a wide range of different environments: oxidation, metal dusting, sulphidation, molten salts, steam, etc. The resistance achieved by the use of different kind of coatings, such as functionally graded material coatings, has been optimized with the latest designs. In the case of supercritical steam turbines, many attempts have been made in terms of micro-structural coatings design, mainly based on aluminides, and other diffusion coating systems in order to consider alternatives, nano-structured coatings based on Cr and Al compositions and deposited by a physical vapor deposition technique, were assessed to high-temperature oxidation resistance in steam environments. The oxidation kinetics where analyzed for up to 2,000 h at 650 °C by means of gravimetric measurements. The evaporation behavior was also analyzed by thermogravimetric-mass spectrometry. Excellent results where observed for some of the nano-structured coatings tested. Those results where compared to results obtained for micro-structured coatings. Based on that comparison, it was deduced that the nano-structured coatings have a potential application as protective systems in high-temperature steam environments.

Oxidation of Metals, 81 (2014) 227-236 | DOI: 10.1007/s11085-013-9447-2

Simultaneous quantification of light elements in thin films deposited on Si substrates using proton EBS (Elastic Backscattering Spectroscopy)

Ferrer, FJ; Alcaire, M; Caballero-Hernandez, J; Garcia-Garcia, FJ; Gil-Rostra, J; Terriza, A; Godinho, V; Garcia-Lopez, J; Barranco, A; Fernandez-Camacho, A

Quantification of light elements content in thin films is an important and difficult issue in many technological fields such as polymeric functional thin films, organic thin film devices, biomaterials, and doped semiconducting structures.

Light elements are difficult to detect with techniques based on X-ray emission, such as energy dispersive analysis of X-rays (EDAX). Other techniques, like X-ray photoelectron spectroscopy (XPS), can easily quantify the content of light elements within a surface but often these surface measurements are not representative of the lights elements global composition of the thin film. Standard Rutherford backscattering spectroscopy (RBS), using alpha particles as probe projectiles, is not a good option to measure light elements deposited on heavier substrates composed of heavier elements like Si or glass. Nuclear Reaction Analysis (NRA) offers a good quantification method, but most of the nuclear reactions used are selective for the quantification of only one element, so several reactions and analysis are necessary to measure different elements.

In this study, Elastic Backscattering Spectroscopy (EBS) using proton beams of 2.0 MeV simultaneously quantified different light elements (helium, carbon, nitrogen, oxygen, and fluorine) contained in thin films supported on silicon substrates. The capabilities of the proposed quantification method are illustrated with examples of the analysis for a series of thin film samples: amorphous silicon with helium bubbles, fluorinated silica, fluorinated diamond-like carbon and organic thin films. It is shown that this simple and versatile procedure allows the simultaneous quantification of light elements in thin films with thicknesses in the 200–500 nm range and contents lower than 10 at.%.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 332 (2014) 449-453 | DOI: 10.1016/j.nimb.2014.02.124

Detecting single-electron events in TEM using low-cost electronics and a silicon strip sensor

Gontard, LC; Moldovan, G; Carmona-Galn, R; Lin, C; Kirkland, AI

There is great interest in developing novel position-sensitive direct detectors for transmission electron microscopy (TEM) that do not rely in the conversion of electrons into photons. Direct imaging improves contrast and efficiency and allows the operation of the microscope at lower energies and at lower doses without loss in resolution, which is especially important for studying soft materials and biological samples. We investigate the feasibility of employing a silicon strip detector as an imaging detector for TEM. This device, routinely used in high-energy particle physics, can detect small variations in electric current associated with the impact of a single charged particle. The main advantages of using this type of sensor for direct imaging in TEM are its intrinsic radiation hardness and large detection area. Here, we detail design, simulation, fabrication and tests in a TEM of the front-end electronics developed using low-cost discrete components and discuss the limitations and applications of this technology for TEM.

Microscopy, 63(2) (2014) 119-130 | DOI: 10.1093/jmicro/dft051

Mineralogical Characterization of the Polychrome in Cultural Heritage Artifacts (Antiquity to Date) from Southern Spain Using Micro-Raman Spectroscopy and Complementary Techniques

Perez-Rodriguez, JL; Duran, A

This work reports on the use of micro-Raman spectroscopy for the characterization of materials used for producing the polychrome in cultural heritage artifacts from southern Spain. The micro-Raman technique was applied for the characterization of several types of artworks or for cross-sections from these works, which were produced along different historical epochs. This technique was demonstrated to be valuable for the characterization of compounds, which were all detected within the artworks studied. The identification of all of these compounds by micro-Raman was confirmed by other complementary techniques, such as micro-X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy.

Spectroscopy Letters: An International Journal for Rapid Communication, 47 (2014) 223-237 | DOI: 10.1080/00387010.2013.791857

Effect of carbonization temperature on the microplasticity of wood-derived biocarbon

Shpeizman, VV; Orlova, TS; Kardashev, BK; Smirnov, BI; Gutierrez-Pardo, A; Ramirez-Rico, J

The uniaxial compression strength under stepped loading and the 325-nm-stepped deformation rate of biocarbon samples obtained by carbonization of beech wood at different temperatures in the 600–1600°C range have been measured using high-precision interferometry. It has been shown that the strength depends on the content of nanocrystalline phase in biocarbon. The magnitude of deformation jumps at micro- and nanometer levels and their variation with a change in the structure of the material and loading time have been determined. For micro- and nanometer-scale jumps, standard deviations of the differences between the experimentally measured deformation rate at loading steps and its magnitude at the smoothed fitting curve have been calculated, and the correlation of the error with the deformation prior to destruction has been shown. The results obtained have been compared with the previously published data on measurements of the elastic properties and internal friction of these materials.

Physics of the Solid State, 56 (2014) 538-545 | DOI: 10.1134/S1063783414030305

Thermal conductivity at the amorphous-nanocrystalline phase transition in beech wood biocarbon

Parfen'eva, LS; Orlova, TS; Smirnov, BI; Smirnov, IA; Misiorek, H; Jezowski, A; Ramirez-Rico, J

High-porosity samples of beech wood biocarbon (BE-C) were prepared by pyrolysis at carbonization temperatures T carb = 650, 1300, and 1600°C, and their resistivity ρ and thermal conductivity κ were studied in the 5–300 and 80–300 K temperature intervals. The experimental results obtained were evaluated by invoking X-ray diffraction data and information on the temperature dependences ρ(T) and κ(T) for BE-C samples prepared at T carb = 800, 1000, and 2400°C, which were collected by the authors earlier. An analysis of the κ(T carb) behavior led to the conclusion that the samples under study undergo an amorphous-nanocrystalline phase transition in the interval 800°C < T carb < 1000°C. Evaluation of the electronic component of the thermal conductivity revealed that the Lorentz number of the sample prepared at T carb = 2400°C exceeds by far the classical Sommerfeld value, which is characteristic of metals and highly degenerate semiconductors.

Physica of the Solid State, 56 (2014) 1071-1080 | DOI: 10.1134/S1063783414050229

Mechanochemically synthesized nanocrystalline Sb2S3 particles

Dutkova, E; Sayagues, MJ; Real, C; Zorkovska, A; Balaz, P; Satka, A; Kovac, J; Ficeriova, J

Nanocrystalline Sb2S3 particles have been synthesized from Sb and S powders by high-energy milling in a planetary mill using argon protective atmosphere. X-ray diffraction, particle size analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, electron diffraction, high resolution transmission electron microscopy, UV-VIS, and differential scanning calorimetry methods for characterization of the prepared particles were applied. The powder X-ray diffraction pattern shows that Sb2S3 nanocrystals belong to the orthorhombic phase with calculated crystallite size of about 36 nm. The nanocrystalline Sb2S3 particles are constituted by randomly distributed crystalline nanodomains (20 nm) and then these particles are forming aggregates. The monomodal distribution of Sb2S3 particles with the average hydrodynamic parameter 210 nm was obtained. The quantification of energy dispersive X-ray spectroscopy analysis peaks give an atomic ratio of 2:3 for Sb:S. The optical band gap determined from the absorption spectrum is 4.9 eV, indicating a considerable blue shift relative to the bulk Sb2S3. Differential scanning calorimetry curves exhibit a broad exothermic peak between 200 and 300°C, suggesting recovery processes. This interpretation is supported by X-ray diffraction measurements that indicate a 23-fold increase of the crystallite size to about 827 nm as a consequence of application of high temperature process. The controlled mechanochemical synthesis of Sb2S3nanoparticles at ambient temperature and atmospheric pressure remains a great challenge.

Acta Physica Polonica A, 126 (2014) 943-946 | DOI: 10.12693/APhysPolA.126.943

Technological Proposals for Recycling Industrial Wastes for Environmental Applications

Romero-Hermida, I; Morales-Florez, V; Santos, A; Villena, A; Esquivias, L

A two-fold objective is proposed for this research: removing hazardous and unpleasant wastes and mitigating the emissions of green house gasses in the atmosphere. Thus, the first aim of this work is to identify, characterize and recycle industrial wastes with high contents of calcium or sodium. This involves synthesizing materials with the ability for CO2 sequestration as preliminary work for designing industrial processes, which involve a reduction of CO2 emissions. In this regard, phosphogypsum from the fertilizer industry and liquid wastes from the green olive and bauxite industries have been considered as precursors. Following a very simple procedure, Ca-bearing phosphogypsum wastes are mixed with Na-bearing liquid wastes in order to obtain a harmless liquid phase and an active solid phase, which may act as a carbon sequestration agent. In this way, wastes, which are unable to fix CO2 by themselves, can be successfully turned into effective CO2 sinks. The CO2 sequestration efficiency and the CO2 fixation power of the procedure based on these wastes are assessed.

Minerals, 4 (2014) 746-757 | DOI: 10.3390/min4030746

Nanometer-Scale Precision Tuning of 3D Photonic Crystals Made Possible Using Polyelectrolytes with Controlled Short Chain Length and Narrow Polydispersity

Wang, Z; Calvo, ME; Masson, G; Arsenault, AC; Peiris, F; Mamak, M; Miguez, H; Manners, I; Ozin, GA

Nanometer-scale tuning of the optical properties of prefabricated photonic crystals is achieved via layer-by-layer assembly of polyelectrolytes in the interstitial spaces of the photonic lattice. The key to the approach is using polyelectrolytes with controlled short chain lengths. This ensures they do not block the air voids, thereby maintaining uniform coating and thus precise and reproducible optical 

Advanced Materials Interfaces, 1 (2014) Art. 1300051 | DOI: 10.1002/admi.201300051

Hallmarks of mechanochemistry: from nanoparticles to technology

Balaz, P; Achimovicova, M; Balaz, M; Billik, P; Cherkezova-Zheleva, Z; Criado, JM; Delogu, F; Dutkova, E; Gaffet, E; Gotor, FJ; Kumar, R; Mitov, I; Rojac, T; Senna, M; Streletskii, A; Wieczorek-Ciurowa, K

The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

Chemical Society Reviews, 42 (2013) 7571-7637 | DOI: 10.1039/C3CS35468G

Tuning Dichroic Plasmon Resonance Modes of Gold Nanoparticles in Optical Thin Films

Gonzalez-Garcia, L; Parra-Barranco, J; Sanchez-Valencia, JR; Ferrer, J; Garcia-Gutierrez, MC; Barranco, A; Gonzalez-Elipe, AR

A simple method is presented to tune the gold surface plasmon resonance (SPR) modes by growing anisotropic nanoparticles into transparent SiO2 thin films prepared by glancing angle deposition. In this type of composite film, the anisotropy of the gold nanoparticles, proved by gracing incidence small angle X-ray scattering, is determined by the tilted nanocolumnar structure of the SiO2 host and yields a strong film dichroism evidenced by a change from an intense colored to a nearly transparent aspect depending on light polarization and/or sample orientation. The formation in these films of lithographic non-dichroic SPR patterns by nanosecond laser writing demonstrates the potentialities of this procedure to develop novel optical encryption or anti-counterfeiting structures either at micrometer- or macroscales.

Advanced Functional Materials, 23 (2013) 1655-1663 | DOI: 10.1002/adfm.201201900

Angular response of photonic crystal based dye sensitized solar cells

López López, C.; Colodrero, S.; Calvo, M.E. and Míguez, H.

Herein we report an experimental analysis of the performance of photonic crystal based dye solar cells (PC-DSCs) as the incident light angle moves away from the normal with respect to the cell surface. Nanoparticle multilayers operating at different wavelength ranges were coupled to the working electrode of a dye solar cell for this study. The interplay between optical and photovoltaic properties with the incident light angle is discussed. We demonstrate that an efficiency enhancement is attained for PC-DSCs at all angles measured, and that rational design of the photonic crystal back mirror leads to a reduction of the photocurrent losses related to the tilt angle of the cell, usually labeled as cosine losses. Angular variations of the cell transparency are also reported and discussed. These angular properties are relevant to the application of these solar devices in building integrated photovoltaics as potential window modules.

Energy & Environmental Science, 6 (2013) 1260-1266 | DOI: 10.1039/C3EE23609A

Tuning of Cell–Biomaterial Anchorage for Tissue Regeneration

Leal-Egana, Aldo; Diaz-Cuenca, Aranzazu; Boccaccini, Aldo R

Which mechanisms mediate cell attachment to biomaterials? What role does the surface charge or wettability play on cell–material anchorage? What are the currently investigated strategies to modify cell–matrix adherence spatiotemporally? Considering the development of scaffolds made of biocompatible materials to temporarily replace the structure and/or function of the extracellular matrix, focus is given to the analysis of the specific (i.e., cell adhesive peptide sequences) and unspecific (i.e., surface charge, wettability) mechanisms mediating cell-matrix interactions. Furthermore, because natural tissue regeneration is characterized by the dynamic attachment/detachment of different cell populations, the design of advanced scaffolds for tissue engineering, based in the spatiotemporal tuning of cell–matrix anchorage is discussed.

Advanced Materials, 25 (2013) 4049-4057 | DOI: 10.1002/adma.201301227

Resonant Photocurrent Generation in Dye-Sensitized Periodically Nanostructured Photoconductors by Optical Field Confinement Effects

Anaya, M; Calvo, ME; Luque-Raigon, JM; Miguez, H

Herein we show experimental evidence of resonant photocurrent generation in dye-sensitized periodically nanostructured photoconductors, which is achieved by spectral matching of the sensitizer absorption band to different types of localized photon modes present in either periodic or broken symmetry structures. Results are explained in terms of the calculated spatial distribution of the electric field intensity within the configurations under analysis.

Journal of the American Chemical Society, 135 (2013) 7803-7806 | DOI: 10.1021/ja401096k

Selective UV Reflecting Mirrors Based on Nanoparticle Multilayers

Smirnov, JRC; Calvo, ME; Miguez, H

A new type of nanostructured selective ultraviolet (UV) reflecting mirror is presented. Periodic porous multilayers with photonic crystal properties are built by spin-coating-assisted layer-by-layer deposition of colloidal suspensions of nanoparticles of ZrO2 and SiO2 (electronic band gap at λ < 220 nm). These optical filters are designed to block well-defined wavelength ranges of the UVA, UVB, and UVC regions of the electromagnetic spectrum while preserving transparency in the visible. The shielding against those spectral regions arises exclusively from optical interference phenomena and depends only on the number of stacked layers and the refractive index contrast between them. In addition, it is shown that the accessible pore network of the as-deposited multilayer allows preparing thin, flexible, self-standing, transferable, and adaptable selective UV filters by polymer infiltration, without significantly losing reflectance intensity, i.e., preserving the dielectric contrast. These films offer a degree of protection comparable to that of traditional ones, without any foreseeable unwanted secondary effects, such as photodegradation, increase of local temperature or, as is the case for organic absorbers, generation of free radicals, all of which are caused by light absorption.

Advanced Functional Materials, 23 (2013) 2805-2811 | DOI: 10.1002/adfm.201202587

Vertically Aligned Hybrid Core/Shell Semiconductor Nanowires for Photonics Applications

Macias-Montero, M; Filippin, AN; Saghi, Z; Aparicio, FJ; Barranco, A; Espinos, JP; Frutos, F; Gonzalez-Elipe, AR; Borras, A

A family of 1D organic/inorganic core/shell materials formed by an inner organic nanowire (ONW) conformally covered with an inorganic wide band gap semiconductor (ZnO or TiO2) layer is presented. The developed procedure is a two-steps vacuum methodology involving the formation of supported single crystal small-molecule nanowires by physical vapor deposition and plasma enhance chemical vapor deposition (PECVD) of the inorganic shell. Critical characteristics of the last technique are the possibilities of low temperature and remote configuration deposition. Additionally, an initial step has to be included in order to create nucleation centers for the growth of the ONWs. The procedure and its general character in terms of the variability in organic core and inorganic shells composition and the applicability of the technique to different substrates are presented. The formation of the inorganic shell with no damage of the organic core single-crystalline structure is demonstrated by high resolution transmission electron microscopy. The vertical alignment of the hybrid nanostructure is achieved thanks to the interaction of the 1D organic nanostructured surfaces and the glow discharge during the deposition of the inorganic shell by PECVD. The optical properties of these core/shell NWs are studied by fluorescence spectroscopy and microscopy, and their application as nanoscale waveguides in the 550–750 nm range addressed.

Advanced Functional Materiales, 23 (2013) 5981-5989 | DOI: 10.1002/adfm.201301120

Perfectly Transparent Sr3Al2O6 Polycrystalline Ceramic Elaborated from Glass Crystallization

Alahrache, S; Al Saghir, K; Chenu, S; Veron, E; Meneses, DD; Becerro, AI; Ocana, M; Moretti, F; Patton, G; Dujardin, C; Cusso, F; Guin, JP; Nivard, M; Sangleboeuf, JC; Matzen, G; Allix, M

The highly visible and infrared (up to 6 mu m) transparent Sr3Al2O6 polycrystalline ceramic was obtained by full crystallization of the corresponding glass composition. The glass synthesis and the direct congruent crystallization processes are described, and the material transparency is discussed in light of its microstructure. This new transparent ceramic exhibits a high density (i.e., complete absence of porosity) and micrometer-scale crystallites with very thin grain boundaries. These microstructural characteristics, inherent to the preparation method, minimize light scattering and demonstrate the advantages of this synthesis route compared to the high-pressure process used for the few reported transparent polycrystalline materials. This Sr3Al2O6 ceramic shows a H = 10.5 GPa hardness, a E-r = 150 GPa reduced elasticity modulus, and a 9.6 x 10(-6) K-1 thermal expansion coefficient. Such a transparent strontium aluminate ceramic opens the way to a wide range of applications, especially photonics when doped by various doping agents. As examples, the luminescence of Sr3Al2O6:Eu3+ and Sr3Al2O6:Er3+, which show strong emissions in the visible and infrared ranges, respectively, is presented. Moreover, the Sr3Al2O6:Ce3+ material was found to exhibit scintillation properties under X-ray excitation. Interestingly, the analogous Sr3Ga2O6 transparent polycrystalline ceramic material could equally be prepared using the same elaboration method, although its hygroscopicity prevents the preservation of its high transparency under normal conditions. The establishment of the key factors for the transparency of this economical and innovative synthesis method should enable the prediction of new classes of technologically relevant transparent ceramics.

Chemistry of Materials, 25 (2013) 4017-4024 | DOI: 10.1021/cm401953d

Competing Misfit Relaxation Mechanisms in Epitaxial Correlated Oxides

Sandiumenge, F; Santiso, J; Balcells, L; Konstantinovic, Z; Roqueta, J; Pomar, A; Espinos, JP; Martinez, B

Strain engineering of functional properties in epitaxial thin films of strongly correlated oxides exhibiting octahedral-framework structures is hindered by the lack of adequate misfit relaxation models. Here we present unreported experimental evidence of a four-stage hierarchical development of octahedral-framework perturbations resulting from a progressive imbalance between electronic, elastic, and octahedral tilting energies in La0.7Sr0.3MnO3 epitaxial thin films grown on SrTiO3 substrates. Electronic softening of the Mn-O bonds near the substrate leads to the formation of an interfacial layer clamped to the substrate with strongly degraded magnetotransport properties, i.e., the so-called dead layer, while rigid octahedral tilts become relevant at advanced growth stages without significant effects on charge transport and magnetic ordering.

Physical Review Letters, 110 (2013) 107206 | DOI: 10.1103/PhysRevLett.110.107206

Promotional effect of the base metal on bimetallic Au-Ni/CeO2 catalysts prepared from core-shell nanoparticles

Holgado, JP; Ternero, F; Gonzalez-delaCruz, VM; Caballero, A

A set of three catalysts (a Au–Ni bimetallic and their corresponding Au and Ni monometallics) has been prepared by impregnation of previously prepared suspensions of monodisperse metallic particles to ensure the precise control of their physicochemical characteristics (size and composition). The Au–Ni/CeO2 bimetallic catalysts present better reactivity toward CO oxidation than monometallic Au/CeO2 and Ni/CeO2 prepared under identical conditions. “operando-like” characterization of Ni and Au atoms into the bimetallic particles using, among other techniques, ambient-pressure photoelectron spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy has allowed us to determine that under oxidative conditions the samples present a Au@NiO core–shell distribution, where Ni surface atoms are affected by an electronic effect from inner Au atoms.

ACS Catalysis, 3 (2013) 2169-2180 | DOI: 10.1021/cs400293b

Characterisation of Co@Fe3O4 core@shell nanoparticles using advanced electron microscopy

Knappett, BR; Abdulkin, P; Ringe, E; Jefferson, DA; Lozano-Perez, S; Rojas, TC; Fernandez, A; Wheatley, AEH

Cobalt nanoparticles were synthesised via the thermal decomposition of Co2(CO)8 and were coated in iron oxide using Fe(CO)5. While previous work focused on the subsequent thermal alloying of these nanoparticles, this study fully elucidates their composition and core@shell structure. State-of-the-art electron microscopy and statistical data processing enabled chemical mapping of individual particles through the acquisition of energy-filtered transmission electron microscopy (EFTEM) images and detailed electron energy loss spectroscopy (EELS) analysis. Multivariate statistical analysis (MSA) has been used to greatly improve the quality of elemental mapping data from core@shell nanoparticles. Results from a combination of spatially resolved microanalysis reveal the shell as Fe3O4 and show that the core is composed of oxidatively stable metallic Co. For the first time, a region of lower atom density between the particle core and shell has been observed and identified as a trapped carbon residue attributable to the organic capping agents present in the initial Co nanoparticle synthesis.

Nanoscale, 5 (2013) 5765-5772 | DOI: 10.1039/C3NR33789H

High temperature plasticity in yttria stabilised tetragonal zirconia polycrystals (Y-TZP)

Dominguez-Rodriguez, A; Gomez-Garcia, D; Wakai, F

The literature data on the superplastic deformation of high purity yttria stabilised tetragonal zirconia polycrystals is reviewed in detail. It is shown that, based on the existence of a threshold stress, the single mechanism of grain boundary sliding (GBS) accommodated by diffusional processes can explain the superplasticity of these materials over all the ranges of temperature, stress, grain size, and surrounding atmosphere that have been studied. The origin of the threshold stress and its quantitative dependence on temperature and grain size is explained in terms of the segregation of yttrium atoms at the grain boundaries. A new model for GBS accommodated by lattice or grain-boundary diffusion is presented which can explain the transition of the stress exponent from 2 to 1.

International Materials Reviews, 58 (2013) 399-417 | DOI: 10.1179/1743280413Y.0000000018

A single-source route to bulk samples of C3N and the co-evolution of graphitic carbon microspheres

King, TC; Matthews, PD; Holgado, JP; Jefferson, DA; Lambert, RM; Alavi, A; Wright, DS

The thermolysis of commercially available m-phenylenediamine (1,3-(NH2)2C6H4) at 800 °C under a static vacuum in a sealed quartz tube provides the first bulk synthesis of C3N, whose properties have only been predicted theoretically previously. Hollow carbon microspheres (CMSs) which do not contain significant nitrogen doping (1–3 μm diameter) are co-produced in the reaction and readily separated from the C3N flakes. The separate C3N flakes and CMSs have been characterized by electron microscopy, X-ray spectroscopy and X-ray diffraction. These studies show that the samples of C3N and CMSs both possess multi-layered turbostratic graphitic structures. A new mechanism for the template-free assembly of CMSs is proposed on the basis of electron microscopy that involves bubble evolution from a static carbonized layer.

Carbon, 64 (2013) 6-10 | DOI: 10.1016/j.carbon.2013.04.043

High-performance Er3+–TiO2 system: Dual up-conversion and electronic role of the lanthanide

Obregon, S; Kubacka, A; Fernandez-Garcia, M; Colon, G

Erbium-doped TiO2 materials are synthesized by means of a surfactant-free hydrothermal method having good photoactivities for the liquid-phase degradation of phenol and MB and the gas phase of toluene. From the structural and morphological characterization, it has been stated that the presence of Er3+ induces a progressive anatase cell expansion due to its incorporation in the TiO2 lattice. The best photocatalytic performance was attained for the samples with 2 at% of Er3+ irrespective of the chemical degradation reaction essayed. From activity and optical studies under different irradiation excitation conditions, a dual-type mechanism is proposed to be at the origin of the photocatalytic activity enhancement. On one hand, the improvement observed under UV irradiation occurs by the effective charge separation promoted by Er3+ species which would act as electron scavenger. Besides, the up-conversion luminescence process of Er3+ allows profiting the NIR range of the lamp and transferring energy in the UV range to the TiO2. The dual action of Er ions located at anatase networks will open up a wide roadway for the developing of an integral solar active photocatalyst.

Journal of Catalysis, 299 (2013) 298-306 | DOI: 10.1016/j.jcat.2012.12.021

In situ FT-IR study of the adsorption and photocatalytic oxidation of ethanol over sulfated and metallized TiO2

Murcia, JJ; Hidalgo, MC; Navio, JA; Arana, J; Dona-Rodriguez, JM

TiO2 Degussa P25, TiO2 prepared by sol–gel submitted to sulfation pre-treatment and some metallized catalysts obtained by photodeposition of Au or Pt over the sulfated TiO2, were evaluated in the reaction of ethanol photo-oxidation. FT-IR spectroscopy was used to investigate the surface features of the photocatalysts, identifying adsorbed species and following the evolution of intermediate products in the ethanol photo-oxidation reaction. Nature of surface acidity in terms of Brönsted and Lewis centers was also studied.

Results showed that sulfation pre-treatment and metallization were important factors influencing the selectivity. Acetaldehyde was the main oxidation product on sulfated TiO2; in the case of P25 also acetates production was observed. The photodeposition of metals had a detrimental effect on the selectivity to acetaldehyde; on metallized catalysts the formation of stable secondary intermediates was detected.

Based on these findings, a reaction pathway for the ethanol photo-oxidation over the different photocatalysts, via acetaldehyde or via acetate formation is proposed.

Applied Catalysis B: Environmental, 142-143 (2013) 205-213 | DOI: 10.1016/j.apcatb.2013.05.022

Erbium doped TiO2–Bi2WO6 heterostructure with improved photocatalytic activity under sun-like irradiation

Obregon, S; Colon, G

Erbium doped TiO2–Bi2WO6 have been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Rhodamine B. From the structural and morphological characterization it has been stated that the presence of Er3+ induces a progressive russelite cell contraction due to its incorporation in the Bi2WO6 lattice in substitutional sites. The best photocatalytic performance was attained for the samples with 1 at% of Er. From the study of the photocatalytic activity under different irradiation conditions it can be inferred that Er3+ presence induces a significant improvement of the photoactivity in the UV range. The evolution of band-gap values seems to be similarly related with the reaction rate progression. Thus, the higher band-gap values in lower Er doped systems would be the cause of a better electron hole separation under UV irradiation.

Applied Catalysis B: Environmental, 140-141 (2013) 299-305 | DOI: 10.1016/j.apcatb.2013.04.014

Liquids Analysis with Optofluidic Bragg Microcavities

Oliva-Ramirez, M; Gonzalez-Garcia, L; Parra-Barranco, J; Yubero, F; Barranco, A; Gonzalez-Elipe, AR

Porous Bragg microcavities formed by stacking a series of porous nanocolumnar layers with alternate low (SiO2) and high (TiO2) refractive index materials have been prepared by physical vapor deposition at glancing angles (GLAD). By strictly controlling the porosity and refractive index of the individual films, as well as the relative orientation of the nanocolumns from one layer to the next, very porous and nondispersive high optical quality microcavities have been manufactured. These photonic structures have been implemented into responsive devices to characterize liquids, mixtures of liquids, or solutions flowing through them. The large displacements observed in the optical spectral features (Bragg reflector gap and resonant peak) of the photonic structures have been quantitatively correlated by optical modeling with the refractive index of the circulating liquids. Experiments carried out with different glucose and NaCl solutions and mixtures of water plus glycerol illustrate the potentialities of these materials to serve as optofluidic devices to determine the concentration of solutions or the proportion of two phases in a liquid mixture.

ACS Applied Materials & Interfaces, 5 (2013) 6743-650 | DOI: 10.1021/am401685r

Preferential oxidation of CO in excess H2 over CuO/CeO2 catalysts: Characterization and performance as a function of the exposed face present in the CeO2 support

Gamarra, D; Camara, AL; Monte, M; Rasmussen, SB; Chinchilla, LE; Hungria, AB; Munuera, G; Gyorffy, N; Schay, Z; Corberan, VC; Conesa, JC; Martinez-Arias, A

A series of oxidised copper-cerium nanostructured catalysts prepared by impregnation of copper over ceria supports synthesized by different methods (hydrothermal with varying preparation parameters, microemulsion/precipitation), in order to achieve different specific morphologies (nanocubes, nanorods and nanospheres), have been examined with respect to their catalytic properties for preferential oxidation of CO in excess H2 (CO-PROX). The catalysts have been characterized in detail by XRD, Raman, SBET measurement, HREM, XPS, TPR and EPR, which allows establishing a model of structural characteristics of the catalysts. The characterization results have been correlated with analysis of CO-PROX catalytic properties by means of catalytic activity measurements complemented by operando-DRIFTS. Structural dependence of the CO oxidation reaction on the dispersed copper oxide entities as a function of the exposed face present at the surface of the different ceria supports is revealed. An important overall enhancement of the CO-PROX performance is detected for the sample supported on ceria nanocubes which is proposed to be a consequence of the interaction between copper oxide and (1 0 0) faces of the ceria support.

Applied Catalysis B: Environmental, 130-131 (2013) 224-238 | DOI: 10.1016/j.apcatb.2012.11.008

Multiple Zeolite Structures from One Ionic Liquid Template

Blanes, JMM; Szyja, BM; Romero-Sarria, F; Centeno, MA; Hensen, EJM; Odriozola, JA; Ivanova, S

This study reports the use of 1-butyl-3-methyl imidazolium methanesulfonate ionic liquid as a template in the synthesis of zeolites. It is found that the silicon source determines the formation of beta (BEA), mordenite framework inverted (MFI), or analcime (ANA) zeolites. Depending on this source, different preorganized complexes are obtained that drive the formation of the different zeolite structures. In the presence of ethanol, the ionic liquid form preorganized complexes that drive the formation of MFI. In its absence, BEA is obtained. Whereas, the large amount of sodium present when using sodium metasilicate leads to ANA formation. A molecular simulation study of the relative stability of the template-framework system and location of the template provides further insight into the mechanism of synthesis.

Chemistry-A European Journal, 19 (2013) 2122-2130 | DOI: 10.1002/chem.201202556

Constant rate thermal analysis for enhancing the long-term CO2 capture of CaO at Ca-looping conditions

Valverde, JM; Sanchez-Jimenez, PE; Perejon, A; Perez-Maqueda, LA

Experimental results are reported on the (Ca-looping) multicyclic CO2 capture of CaO and nanosilica/CaO composites derived from Ca(OH)2 and nanosilica/Ca(OH)2 dry mixtures subjected in situ to linear and constant rate thermal analysis (CRTA) preheating programs in either air or air/CO2 atmospheres. By means of CRTA preheating the rates of the reactions taking place during pretreatment are kept at a constant and small value along the entire process. In agreement with a pore skeleton model, previously proposed in the literature for explaining the behavior of natural limestones thermally pretreated, our results suggest that air/CO2-CRTA pretreatment yields a thermally stable hard skeleton of poorly reactive CaO on which a soft skeleton of reactive CaO would be supported. The sorbent subjected to this preheating program exhibits a reactivation in the very first carbonation/calcination cycles, after which CaO conversion decays slowly with the cycle number. In contrast, linearly or air-CRTA preheated sorbents show a significant decrease of CaO conversion within the first cycles. In the latter case, CaO multicyclic conversion fits well to a model where it is assumed that the progressive reduction of surface area as the number of carbonation/calcination cycles is increased obeys to sintering of the preheated sorbent skeleton as it is subjected to repeated calcinations during cycling. In the former case, CaO conversion data conforms to the prediction by a model in which the loss of surface area is mainly due to sintering of a nascent CaO soft skeleton regenerated in the diffusive carbonation phase, which is enhanced by the air/CO2-CRTA pretreatment. As regards the effect of nanosilica, the results indicate that it slows down CaO sintering during pretreatment, which hinders the development of a stable CaO skeleton thus hampering reactivation and stabilization of conversion. On the other hand, as CaO sintering is also lessened during looping calcination, nanosilica is useful to increase the absolute values of CaO conversion.

Applied Energy, 108 (2013) 108-120 | DOI: 10.1016/j.apenergy.2013.03.013

Colored and Transparent Oxide Thin Films Prepared by Magnetron Sputtering: The Glass Blower Approach

Gil-Rostra, J; Chaboy, J; Yubero, F; Vilajoana, A; Gonzalez-Elipe, AR

This work describes the reactive magnetron sputtering processing at room temperature of several mixed oxide MxSiyOz thin films (M: Fe, Ni, Co, Mo, W, Cu) intended for optical, coloring, and aesthetic applications. Specific colors can be selected by adjusting the plasma gas composition and the Si–M ratio in the magnetron target. The microstructure and chemistry of the films are characterized by a large variety of techniques including X-ray photoemission spectroscopy, X-ray absorption spectroscopy (XAS), and infrared spectroscopy, while their optical properties are characterized by UV–vis transmission and reflection analysis. Particularly, XAS analysis of the M cations in the amorphous thin films has provided valuable information about their chemical state and local structure. It is concluded that the M cations are randomly distributed within the SiO2 matrix and that both the M concentration and its chemical state are the key parameters to control the final color of the films.

ACS Applied Materials & Interfaces, 5 (2013) 1967-1976 | DOI: 10.1021/am302778h

Solution Properties of the System ZrSiO4–HfSiO4: A Computational and Experimental Study

Cota, Agustin; Burton, Benjamin P.; Chain, Pablo; Pavon, Esperanza; Alba, Maria D.

ZrSiO4 and HfSiO4 are of considerable interest because of their low thermal expansions, thermal conductivities, and the optical properties of HfSiO4. In addition, silicate phases of both are studied as model radioactive waste disposal materials. Previous first principles calculations reported near ideal mixing in the Zr1–xHfxSiO4 system, with a very weak propensity for phase separation. Density functional theory (DFT)/cluster-expansion first principles calculations presented in this work indicate near ideal mixing with a very weak propensity for ordering. Zr1–xHfxSiO4 samples (x = 0, 0.25, 0.5, 0.75, and 1.0) were synthesized from intimate stoichiometric mixtures of constituent-oxides and annealing at 1823 K for 20 days in a platinum crucible. Samples were characterized by X-ray diffraction (XRD; Rietveld analysis) and 29Si MAS NMR. The XRD data exhibited a pronounced negative deviation from Vegard’s law in the excess volume of mixing, and the 29Si MAS NMR spectra also suggest nonideal mixing. Given the very weak energetics that favor cation ordering, it is clear that there must be some other cause(s) for the observed deviations from ideal mixing behavior.

Journal of Physical Chemistry C, 117 (2013) 10013-10019 | DOI: 10.1021/jp401539g

Monoclinic–Tetragonal Heterostructured BiVO4 by Yttrium Doping with Improved Photocatalytic Activity

Usai, S; Obregon, S; Becerro, AI; Colon, G

Yttrium-doped BiVO4 has been synthesized by means of a surfactant free hydrothermal method having good photoactivities under sun-like excitation for the degradation of Methylene Blue (MB). From the structural and morphological characterization it has been stated that the presence of Y3+ induces the progressive stabilization of the tetragonal phase and the slight higher surface area values. By following the tetragonal cell parameters, the substitutional incorporation of Y3+ into the BiVO4 tetragonal lattice might be considered. Best photocatalytic performances were attained for the samples with Y3+ content of 3.0 at. % for which the MB degradation rate constant appears 2-fold higher. Furthermore, photoactivities for visible-light-driven O2 evolution demonstrate that the photocatalytic performance of the best Y-doped system (initial rate of O2 evolution, 285 μmol g–1 h–1) was more than 5 times that of undoped m-BiVO4 (initial rate of O2 evolution, 53 μmol g–1 h–1). The occurrence of Y3+ doping and a monoclinic–tetragonal heterostructured BiVO4 system induces the higher photocatalytic activities. PL analysis provides a clear evidence of the lower charge carriers recombination in heterostructured yttrium-doped systems.

Journal of Physical Chemistry C, 117 (2013) 24479-24484 | DOI: 10.1021/jp409170y

Crystal Structures and Photoluminescence across the La2Si2O7–Ho2Si2O7 System

Fernandez-Carrion, AJ; Allix, M; Ocana, M; Garcia-Sevillano, J; Cusso, F; Fitch, AN; Suard, E; Becerro, AI

The La2Si2O7−Ho2Si2O7 system displays a solid solubility region of G-(La,Ho)2Si2O7 which extends to the La0.6Ho1.4Si2O7 composition. Compositions richer in Ho3+ show a two-phase domain (G+δ), while δ-(La,Ho)2Si2O7 is the stable phase for Ho3+ contents higher than La0.2Ho1.8Si2O7. A preferential occupation of Ho for the RE2 site of the G-unit cell is observed. Luminescence measurements have shown that the lifetimes remain unchanged in the range 0.5% < [Ho3+] < 10%, and only above this value does concentration quenching become operative.

Inorganic Chemistry, 52 (2013) 13469-13479 | DOI: 10.1021/ic401867c

Crystal Structure and Luminescent Properties of Eu3+-Doped A-La2Si2O7 Tetragonal Phase Stabilized by Spray Pyrolysis Synthesis

Fernandez-Carrion, Alberto J.; Ocana, Manuel; Florian, Pierre; Garcia-Sevillano, Jorge; Cantelar, Eugenio; Fitch, Andrew N.; Suchomel, Matthew R.; Becerro, Ana I.

Pure A-La2Si2O7 powder has been synthesized through a spray pyrolysis method followed by calcination at 1100 degrees C for 15 h. The crystallographic structure, refined from the synchrotron powder diffraction pattern of the sample, showed tetragonal symmetry with space group P4(1), a = 6.83565(1) angstrom, and c = 24.84133(1) angstrom. The Si-29 and La-139 NMR spectra have been described here for the first time in the literature and could be simulated with four Si and four La resonances, respectively, in good agreement with the presence of four Si and four La crystallographic sites in the unit cell. The same synthesis method was 2 successful for the synthesis of Eu3+-doped A-La2Si2O7 (%Eu = 3-40). The analysis of the unit cell volumes indicated that Eu3+ replaces La3+ in the unit cell for all Eu3+ substitution levels investigated. However, anomalous diffraction data indicated that the La/Eu substitution mechanism was not homogeneous, but Eu much prefers to occupy the RE3 sites. The Eu-doped A-La2Si2O7 phosphors thus synthesized exhibited a strong orange-red luminescence after excitation at 393 nm. Lifetime measurements indicated that the optimum phosphor was that with an Eu3+ content of 20%, which showed a lifetime of 2.3 ms. The quantum yield of the latter was found to be 12% at 393 nm excitation. These experimental observations together with the high purity of the phase obtained by the proposed spray pyrolysis method make this material an excellent phosphor for optoelectronic applications.

Journal of Physical Chemistry C, 117 (2013) 20876-20886 | DOI: 10.1021/jp407172z

Synthesis and Properties of Multifunctional Tetragonal Eu:GdPO4 Nanocubes for Optical and Magnetic Resonance Imaging Applications

Rodriguez-Liviano, S; Becerro, AI; Alcantara, D; Grazu, V; de la Fuente, JM; Ocana, M

A simple and fast (7 min) procedure for synthesis of gadolinium phosphate nanocubes (edge = 75 nm) based on the microwave-assisted heating at 120 °C of gadolinium acetylacetonate and phosphoric acid solutions in buthylene glycol is reported. These nanocubes were highly crystalline and crystallized into a tetragonal structure, which has not been ever reported for pure gadolinium phosphate. Determination of such crystal structure has been carried out here for the first time in the literature by means of powder X-ray diffraction. The developed synthesis procedure was also successful for preparation of multifunctional europium(III)-doped the gadolinium phosphate nanocubes, which were nontoxic for cells and exhibited strong red luminescence under UV illumination and high transverse relaxivity (r2) values. These properties confer them potential applications as biolabels for in vitro optical imaging and as negative contrast agent for magnetic resonance imaging.

Inorganic Chemistry, 52 (2013) 647-654 | DOI: 10.1021/ic3016996

Impact of Ce–Fe synergism on the catalytic behaviour of Au/CeO2–FeOx/Al2O3 for pure H2 production

Reina, TR; Ivanova, S; Idakiev, V; Delgado, JJ; Ivanov, I; Tabakova, T; Centeno, MA; Odriozola, JA

In this work the development of a series of gold catalysts, essentially based on γ-alumina promoted with a small superficial fraction of Ce–Fe mixed oxides, is reported. The catalytic behaviour is evaluated in the water gas shift reaction. The formation of a Ce–Fe solid solution is evidenced by XRD and related to the catalytic activity where the importance of the Ce–Fe interaction is demonstrated. The best catalyst reached CO conversions very close to the equilibrium limit. A long-term stability test is performed and the loss of activity is observed and attributed to reaction intermediates. Almost complete recovery of the initial conversion is achieved after oxidation treatment, suggesting that the problem of stability could be overcome by a suitable change in the reaction parameters thus leading to a highly efficient catalyst for future applications in H2 production and clean-up.

Catalysis Science & Technology, 3 (2013) 779-787 | DOI: 10.1039/C2CY20537H

A Novel 3D Architecture of GdPO4 Nanophosphors: Multicolored and White Light Emission

Becerro, AI; Rodriguez-Liviano, S; Fernandez-Carrion, AJ; Ocaña, M

Homogeneous monoclinic GdPO4 particles composed of three intersecting lance-shaped crystals forming a penetration twin have been synthesized following a very restrictive, simple, and fast (10 min) method consisting of the hydrothermal reaction of gadolinium acetylacetonate with H3PO4 in a mixture of ethylene glycol and water at 180 °C. Slightly increasing the amount of water in the solvent mixture leads to hexagonal rodlike GdPO4·0.5H2O nanoparticles, whereas the variation of the Gd source, PO4 source, aging temperature, and polyol type gave rise to heterogeneous particles. The synthesis procedure is also suitable for the preparation of Eu3+-, Tb3+-, and Dy3+-doped GdPO4 particles with the same morphology and crystalline structure as the undoped materials. The effect of the doping level on the luminescent properties of the twinlike nanophosphors was evaluated, finding optimum doping levels of 5, 5, and 1% for the Eu3+-, Tb3+-, and Dy3+-doped materials, respectively. The twinlike GdPO4 nanophosphors were found to be more efficient than the rodlike GdPO4 ones in terms of emission intensity. Finally, a solid-state single-phase white-light-emitting nanophosphor has been fabricated for the first time in this system by triply doping the GdPO4 twined particles with appropriate concentrations of Eu3+, Tb3+, and Dy3+ and exciting through the Gd–Ln energy-transfer band at 273 nm. In addition to this energy transfer band, other energy charge transfer processes among the three dopants (Eu3+, Tb3+, and Dy3+) have been observed in the triply doped material.

Crystal Growth & Design, 55 (2013) 454-460 | DOI: 10.1021/cg301023k

Ionic Liquid Mediated Synthesis and Surface Modification of Multifunctional Mesoporous Eu:GdF3 Nanoparticles for Biomedical Applications

Rodriguez-Liviano, S; Nunez, NO; Rivera-Fernandez, S; de la Fuente, JM; Ocana, M

A procedure for the synthesis of multifunctional europium(III)-doped gadolinium(III) fluoride (Eu:GdF3) nanoparticles (85 nm) with quasispherical shape by precipitation at 120 °C from diethylene glycol solutions containing lanthanide chlorides and an ionic liquid (1-Butyl, 2-methylimidazolium tetrafluoroborate) as fluoride source has been developed. These nanoparticles were polycrystalline and crystallized into a hexagonal structure, which is unusual for GdF3. They were also mesoporous (pore size = 3.5 Å), having a rather high BET surface area (75 m2 g–1). The luminescent and magnetic (relaxivity) properties of the Eu:GdF3 nanoparticles have been also evaluated in order to assess their potentiality as “in vitro” optical biolabels and contrast agent for magnetic resonance imaging. Finally, a procedure for their functionalization with aspartic-dextran polymers is also reported. The functionalized Eu:GdF3 nanoparticles presented negligible toxicity for Vero cells, which make them suitable for biotecnological applications.

Langmuir, 29 (2013) 3411-3418 | DOI: 10.1021/la4001076

Microwave-Assisted Synthesis of Biocompatible Europium-Doped Calcium Hydroxyapatite and Fluoroapatite Luminescent Nanospindles Functionalized with Poly(acrylic acid)

Escudero, A; Calvo, ME; Rivera-Fernandez, S; de la Fuente, JM; Ocana, M

Europium-doped calcium hydroxyapatite and fluoroapatite nanophosphors functionalized with poly(acrylic acid) (PAA) have been synthesized through a one-pot microwave-assisted hydrothermal method from aqueous basic solutions containing calcium nitrate, sodium phosphate monobasic, and PAA, as well as sodium fluoride in the case of the fluoroapatite particles. In both cases a spindlelike morphology was obtained, resulting from an aggregation process of smaller subunits which also gave rise to high specific surface area. The size of the nanospindles was 191 (32) × 40 (5) nm for calcium hydroxyapatite and 152 (24) × 38 (6) nm for calcium fluoroapatite. The luminescent nanoparticles showed the typical red luminescence of Eu3+, which was more efficient for the fluoroapatite particles than for the hydroxyapatite. This is attributed to the presence of OH– quenchers in the latter. The nanophosphors showed negligible toxicity for Vero cells. Both PAA-functionalized nanophosphors showed a very high (up to at least 1 week) colloidal stability in 2-(N-morpholino)ethanesulfonic acid (MES) at pH 6.5, which is a commonly used buffer for physiological pH. All these features make both kinds of apatite-based nanoparticles promising tools for biomedical applications, such as luminescent biolabels and tracking devices in drug delivery systems.

Langmuir, 29 (2013) | DOI: 10.1021/la304534f

Arsenic sorption by nanocrystalline magnetite: An example of environmentally promising interface with geosphere

Bujnakova, Z; Balaz, P; Zorkovska, A; Sayagues, MJ; Kovac, J; Timko, M

In this paper, the sorption of arsenic onto nanocrystalline magnetite mineral Fe3O4 was studied in a model system. Nanocrystalline magnetite was produced by mechanical activation in a planetary ball mill from natural microcrystalline magnetite. As a consequence of milling, the specific surface area increased from 0.1 m2/g to 11.9 m2/g and the surface site concentration enhanced from 2.2 sites/nm2 to 8.4 sites/nm2. These changes in surface properties of magnetite lead to the enhancement of arsenic removal from model system. The best sorption ability was achieved with magnetite sample activated for 90 min. In this case the sample was able to absorb around 4 mg/g. The structural changes of magnetite were also observed and the new hematite phase was detected after 120 min of milling. A good correlation between the decreasing particle size, increasing specific surface area and reduction of saturation magnetization was found. In desorption study, KOH and NaOH were found as the best eluents where more than 70% of arsenic was released back into the solution. The principal novelty of the paper is that mineral magnetite, truly one nature's gift can be used after “smart” milling (mechanical activation) as an effective arsenic sorbent.

Journal of Hazardous Materials, 262 (2013) 1204-1212 | DOI: 10.1016/j.jhazmat.2013.03.007

Gold(III) stabilized over ionic liquids grafted on MCM-41 for highly efficient three-component coupling reactions

Bobadilla, LF; Blasco, T; Odriozola, JA

Two alkoxysilyl-modified ionic liquids (ILs) have been synthesized and further grafted onto mesoporous silica, MCM-41; these ionic liquids were used for dispersing AuCl3 catalysts that activate C–H bonds as required for the synthesis of propargylamines by coupling alkyne, aldehyde and amine (A3 coupling) species. 29Si NMR experiments demonstrate the formation of covalent bonds between alkoxysilyl-modified Bmim IL and the MCM-41 surface through silanol groups. The catalytic activities of Au(III)-supported MCM-41 and Au(III) homogeneous catalysts are lower than those obtained for the IL functionalized Au–MCM-41 solids when the same gold loading is considered. An interaction between Au(III) species and the IL is proposed for explaining the stabilization of gold(III) species. However, successive reaction cycles result in a decrease in the catalytic activity that has been explained on the basis of gold leaching.

Physical Chemistry Chemical Physics, 39 (2013) 16927-16934 | DOI: 10.1039/C3CP52924J

CO2 multicyclic capture of pretreated/doped CaO in the Ca-looping process. Theory and experiments

Valverde, JM; Sanchez-Jimenez, PE; Perejon, A; Perez-Maqueda, LA

We study in this paper the conversion of CaO-based CO2 sorbents when subjected to repeated carbonation–calcination cycles with a focus on thermally pretreated/doped sorbents. Analytical equations are derived to describe the evolution of conversion with the cycle number from a unifying model based on the balance between surface area loss due to sintering in the looping-calcination stage and surface area regeneration as a consequence of solid-state diffusion during the looping-carbonation stage. Multicyclic CaO conversion is governed by the evolution of surface area loss/regeneration that strongly depends on the initial state of the pore skeleton. In the case of thermally pretreated sorbents, the initial pore skeleton is highly sintered and regeneration is relevant, whereas for nonpretreated sorbents the initial pore skeleton is soft and regeneration is negligible. Experimental results are obtained for sorbents subjected to a preheating controlled rate thermal analysis (CRTA) program. By applying this preheating program in a CO2 enriched atmosphere, CaO can be subjected to a rapid carbonation followed by a slow rate controlled decarbonation, which yields a highly sintered skeleton displaying a small conversion in the first cycle and self-reactivation in the next ones. Conversely, carbonation of the sorbent at a slow controlled rate enhances CO2 solid-state diffusion, which gives rise, after a quick decarbonation, to a highly porous skeleton. In this case, CaO conversion in the first cycle is very large but it decays abruptly in subsequent cycles. Data for CaO conversion retrieved from the literature and from further experimental measurements performed in our work are analyzed as influenced by a variety of experimental variables such as preheating temperature program, preheating exposition time, atmosphere composition, presence of additives, and carbonation–calcination conditions. Conversion data are well fitted by the proposed model equations, which are of help for a quantitative interpretation of the effect of experimental conditions on the multicyclic sorbent performance as a function of sintering/regeneration parameters inferred from the fittings and allow foreseeing the critical conditions to promote reactivation. The peculiar behavior of some pretreated sorbents, showing a maximum conversion in a small number of cycles, is explained in light of the model.

Physical Chemistry Chemical Physics, 15 (2013) 11775-11793 | DOI: 10.1039/C3CP50480H

Spectroscopic properties of electrochemically populated electronic states in nanostructured TiO2 films: anatase versus rutile

Berger, T; Anta, JA; Morales-Florez, V

A thorough characterization of nanostructured materials under application-relevant conditions is a prerequisite for elucidating the interplay between their physicochemical nature and their functional properties in practical applications. Here, we use a spectroelectrochemical approach to study the population of electronic states in different types of nanostructured anatase and rutile TiO2 films in contact with an aqueous electrolyte. The spectroscopic properties of the two polymorphs were addressed under Fermi level control in the energy range between the fundamental absorption threshold and the onset of lattice absorption (3.3–0.1 eV). The results evidence the establishment of an equilibrium between localized Ti3+ centers absorbing in the vis/NIR and shallow (e−)(H+) traps absorbing in the MIR upon electron accumulation in anatase electrodes. The absence of the MIR-active (e−)(H+) traps on all rutile electrodes points to a crystal structure-dependent electron population in the films.

Physical Chemistry Chemical Physics, 15 (2013) 13790-13795 | DOI: 10.1039/C3CP52324A

Surface modified Eu:GdVO4 nanocrystals for optical and MRI imaging

Nunez, Nuria O.; Rivera, Sara; Alcantara, David; de la Fuente, Jesus M.; Garcia-Sevillano, Jorge; Ocana, Manuel

A facile solvothermal route has been developed for the preparation of europium doped gadolinium orthovanadate nanoparticles ([similar]70 nm) with tetragonal structure, based on a homogenous precipitation reaction at 120 °C from rare earth precursors (yttrium nitrate and europium nitrate) and sodium orthovanadate solutions using an ethylene glycol–water mixture as the solvent. The effects of the doping level on the luminescence properties were evaluated in order to find the optimum nanophosphors. These nanocrystals were successfully functionalized with amino (two step process) and carboxylate (one-pot process) groups provided by amino-dextran polymers (AMD) and polyacrylic acid (PAA), respectively. It was found that while the luminescent properties of both kinds of functionalized systems were similar, the colloidal stability of the PAA-modified sample was higher, because of which, it was selected to study their cytotoxicity and magnetic properties (relaxivity and phantom analyses) to assess their potentiality as multifunctional probes for both “in vitro” optical biolabels and negative contrast agents for magnetic resonance imaging.

Dalton Transactions, 42 (2013) 10725-10734 | DOI: 10.1039/C3DT50676B

Spark plasma sintering of TixTa1−xC0.5N0.5-based cermets: Effects of processing conditions on chemistry, microstructure and mechanical properties

Cordoba, Jose M.; Chicardi, Ernesto; Poyato, Rosalia; Gotor, Francisco J.; Medri, Valentina; Guicciardi, Stefano; Melandri, Cesare

Nanometric powdered TixTa1−xC0.5N0.5-based cermets were fabricated using a mechanically induced self-sustaining reaction and consolidated by spark plasma sintering. Highly dense cermets were obtained, and their chemistry, microstructure and mechanical properties were characterised by X-ray diffraction, scanning electron microscopy, image analysis, microindentation and nanoindentation. The microhardness was found to depend directly on the contiguity and size of the ceramic hard particles. The samples synthesised at the lowest temperature (1150 °C) exhibited more homogeneous microstructures and smaller ceramic particles and the best combination of microhardness and fracture toughness.

Chemical Engineering Journal, 230 (2013) 558-566 | DOI: 10.1016/j.cej.2013.06.104

Behaviour of Au-citrate nanoparticles in seawater and accumulation in bivalves at environmentally relevant concentrations

Garcia-Negrete, C. A.; Blasco, J.; Volland, M.; Rojas, T. C.; Hampel, M.; Lapresta-Fernandez, A.; Jimenez de Haro, M. C.; Soto, M.; Fernandez, A.

The degree of aggregation and/or coalescence of Au-citrate nanoparticles (AuNPs, mean size 21.5 ± 2.9 nm), after delivery in simulated seawater, are shown to be concentration-dependent. At low concentrations no coalescence and only limited aggregation of primary particles were found. Experiments were performed in which the marine bivalve (Ruditapes philippinarum) was exposed to AuNPs or dissolved Au and subsequently, bivalve tissues were studied by Scanning and Transmission Electron Microscopy and chemical analyses. We show that the bivalve accumulates gold in both cases within either the digestive gland or gill tissues, in different concentrations (including values of predicted environmental relevance). After 28 days of exposure, electron-dense deposits (corresponding to AuNPs, as proven by X-ray microanalysis) were observed in the heterolysosomes of the digestive gland cells. Although non-measurable solubility of AuNPs in seawater was found, evidence is presented of the toxicity produced by Au3+ dissolved species (chloroauric acid solutions) and its relevance is discussed.

Environmental Pollution, 174 (2013) 134-141 | DOI: 10.1016/j.envpol.2012.11.014

A low-temperature single-source route to an efficient broad-band cerium(III) photocatalyst using a bimetallic polyoxotitanium cage

Lv, YK; Yao, MM; Holgado, JP; Roth, T; Steiner, A; Gan, LH; Lambert, RM; Wright, DS

Aqueous hydrolysis of a series of cerium-containing polyoxotitanium cages gives Ce(III)-doped TiO2 [TiO2(Ce)] or TiO2-supported Ce(III)2Ti2O7, depending on the starting Ti : Ce ratio of the precursor. TiO2-supported Ce2Ti2O7 exhibits superior photocatalytic activity to the Ce-doped TiO2 materials and unusual broad-band absorption behaviour across the visible and near-infrared regions.

RSC Advances, 3 (2013) 13659-13662 | DOI: 10.1039/C3RA41524D

Synthesis of metallic silver nanoparticles and silver organometallic nanodisks mediated by extracts of Capsicum annuum var. aviculare (piquin) fruits

Mendoza-Resendez, R; Nunez, NO; Barriga-Castro, ED; Luna, C

Silver-based nanostructures were prepared through reduction/oxidation reactions of aqueous silver nitrate solutions mediated by extracts of red fruits of the piquin pepper (Capsicum annuum var. aviculare) at room temperature. Detailed morphological and microstructural studies using X-ray diffraction, conventional and high-resolution transmission electron microscopy and selected area electron diffraction revealed that the product was constituted by three kinds of nanoparticles. One of them was composed of twinned metallic silver nanoparticles with a size of few nanometers. Other kind of particles was ultrafine disk-like single crystals of silver 4,4′-dimethyldiazoaminobenzene, being in our best knowledge the first time that this compound is reported in the form of nanoparticles. Both kinds of nanoparticles experienced processes of self-assembly and subsequent grain growth to form the third kind of nanoparticles. Such resulting nanostructures are monocrystalline and flattened metallic silver nanoparticles that have diameters around tens of nanometers, the [112] direction perpendicular to the particle plane, and are coated by a surface organometallic layer and residues of biomolecules. The ultraviolet-visible spectrum of the biosynthesized product showed a surface plasmon resonance (SPR) extinction band with an absorbance maximum at around 400 nm, thereby confirming the presence of fine Ag particles. Studies carried out by Fourier transform infrared spectroscopy indicated that the principal active compounds responsible of the reduction of the Ag ions are proteins and capsaicin (through the amino groups) and phenolic compounds (through hydroxyl groups).

RSC Advances, 43 (2013) 20765-20771 | DOI: 10.1039/C3RA43524E

On the different photocatalytic performance of BiVO4 catalysts for Methylene Blue and Rhodamine B degradation

Obregon, S; Colon, G

BiVO4 hierarchical structures were synthesized by means of a surfactant free hydrothermal method having good photoactivities for the degradation of Methylene Blue and Rhodamine B under UV–vis irradiation. From the structural and morphological characterization it has been stated that BiVO4 present the monoclinic crystalline phase with different morphologies depending on the pH value. For Methylene Blue the photodegradation rate is strongly affected by the crystallite size and higher (0 0 4) facet exposition. On the contrary, for Rhodamine B, the ζ-potential of the surface clearly determines the photocatalytic performance of BiVO4 catalyst.

Journal of Molecular Catalysis A: Chemical, 376 (2013) 40-47 | DOI: 10.1016/j.molcata.2013.04.012

Enhanced reactivity and related optical changes of Ag nanoparticles on amorphous Al2O3 supports

Pelaez, RJ; Castelo, A; Afonso, CN; Borras, A; Espinos, JP; Riedel, S; Leiderer, P; Boneberg, J

Pairs of samples containing Ag nanoparticles (NPs) of different dimensions have been produced under the same conditions but on different substrates, namely standard glass slides and a thin layer of amorphous aluminum oxide (a-Al2O3) on-glass. Upon storage in ambient conditions (air and room temperature) the color of samples changed and a blue-shift and damping of the surface plasmon resonance was observed. The changes are weaker for the samples on-glass and tend to saturate after 12 months. In contrast, the changes for the samples on a-Al2O3 appear to be still progressing after 25 months. While x-ray photoelectron spectroscopy shows a slight sulfurization and negligible oxidation of the Ag for the on-glass samples upon 25 months aging, it shows that Ag is strongly oxidized for the on a-Al2O3 samples and sulfurization is negligible. Both optical and chemical results are consistent with the production of a shell at the expense of a reduction of the metal core dimensions, the latter being responsible for the blue-shift and related to the small (<10 nm initial diameter) of the NPs. The enhanced reactivity of the Ag NPs on the a-Al2O3 supports goes along with specific morphological changes of the Ag NPs and the observation of nitrogen.

Nanotechnology, 24 (2013) 365702 | DOI: 10.1088/0957-4484/24/36/365702

Laser induced enhancement of dichroism in supported silver nanoparticles deposited by evaporation at glancing angles

Filippin, AN; Borras, A; Rico, VJ; Frutos, F; Gonzalez-Elipe, AR

Silver nanoparticles (NPs) depicting well defined surface plasmon resonance (SPR) absorption were deposited on flat substrates by physical vapor deposition in a glancing angle configuration. The particles were characterized by scanning electron microscopy and atomic force microscopy and their optical properties examined by UV–vis absorption spectroscopy using linearly polarized light. It was found that, depending on the amount of deposited silver and the evaporation angle, part of the 'as-prepared' samples present NPs characterized by an anisotropic shape and a polarization dependent SPR absorption and different colors when using polarized white light at 0° and 90°. Low-power irradiation of these materials with an infrared Nd-YAG nanosecond laser in ambient conditions produced an enhancement in such dichroism. At higher powers, the dichroism was lost and the SPR bands shifted to lower wavelengths as a result of the reshaping of the silver NPs in the form of spheres. The possible factors contributing to the observed changes in dichroism are discussed.

Nanotechnology, 24 (2013) 045301 | DOI: 10.1088/0957-4484/24/4/045301

Growth regimes of porous gold thin films deposited by magnetron sputtering at oblique incidence: from compact to columnar microstructures

Alvarez, R; Garcia-Martin, JM; Macias-Montero, M; Gonzalez-Garcia, L; Gonzalez, JC; Rico, V; Perlich, J; Cotrino, J; Gonzalez-Elipe, AR; Palmero, A

Growth regimes of gold thin films deposited by magnetron sputtering at oblique angles and low temperatures are studied from both theoretical and experimental points of view. Thin films were deposited in a broad range of experimental conditions by varying the substrate tilt angle and background pressure, and were analyzed by field emission scanning electron microscopy and grazing-incidence small-angle x-ray scattering techniques. Results indicate that the morphological features of the films strongly depend on the experimental conditions, but can be categorized within four generic microstructures, each of them defined by a different bulk geometrical pattern, pore percolation depth and connectivity. With the help of a growth model, a microstructure phase diagram has been constructed where the main features of the films are depicted as a function of experimentally controllable quantities, finding a good agreement with the experimental results in all the studied cases.

Nanotechnology, 24 (2013) 045604 | DOI: 10.1088/0957-4484/24/4/045604

A new bottom-up methodology to produce silicon layers with a closed porosity nanostructure and reduced refractive index

Godinho, V; Caballero-Hernandez, J; Jamon, D; Rojas, TC; Schierholz, R; Garcia-Lopez, J; Ferrer, FJ; Fernandez, A

A new approach is presented to produce amorphous porous silicon coatings (a-pSi) with closed porosity by magnetron sputtering of a silicon target. It is shown how the use of He as the process gas at moderated power (50–150 W RF) promotes the formation of closed nanometric pores during the growth of the silicon films. The use of oblique-angle deposition demonstrates the possibility of aligning and orientating the pores in one direction. The control of the deposition power allows the control of the pore size distribution. The films have been characterized by a variety of techniques, including scanning and transmission electron microscopy, electron energy loss spectroscopy, Rutherford back scattering and x-ray photoelectron spectroscopy, showing the incorporation of He into the films (most probably inside the closed pores) and limited surface oxidation of the silicon coating. The ellipsometry measurements show a significant decrease in the refractive index of porous coatings (n500 nm = 3.75) in comparison to dense coatings (n500 nm = 4.75). The capability of the method to prepare coatings with a tailored refractive index is therefore demonstrated. The versatility of the methodology is shown in this paper by preparing intrinsic or doped silicon and also depositing (under DC or RF discharge) a-pSi films on a variety of substrates, including flexible materials, with good chemical and mechanical stability. The fabrication of multilayers of silicon films of controlled refractive index in a simple (one-target chamber) deposition methodology is also presented.

Nanotechnology, 24 (2013) 275604 | DOI: 10.1088/0957-4484/24/27/275604

Evaluation of rare earth on layered silicates under subcritical conditions: Effect of the framework and interlayer space composition

Chain, P; Cota, A; El Mrabet, S; Pavon, E; Pazos, MC; Alba, MD

Clay-based minerals are considered to be an important component in backfill barriers due to both their ability to seal and adsorb radioactive waste and to interact chemically with it under subcritical conditions. Herein, we describe a systematic study of the properties of layered silicates that could affect their hydrothermal reactivity, namely type of layers, octahedral occupancy, origin and total amount of the layer charge, and nature of the interlayer cation. The silicates studied were selected on the basis of their different characteristics associated with these properties and were treated hydrothermally at 300 °C for 48 h in a 7.3 · 10− 2 M Lu(NO3)3 · 3.6H2O solution. The final products were analyzed by X-ray diffraction and solid-state NMR spectroscopy. All the layered silicates studied were found to be able to generate a Lu2Si2O7 phase after hydrothermal treatment under subcritical conditions, thereby confirming the participation of a chemical mechanism of the clay barrier generating phases being stables with temperature and pH conditions. However, the extent of this reaction depends to a large extent on the physicochemical properties of the framework and the interlayer space composition, such as the presence or absence of an octahedral sheet, the degree of occupancy of this sheet, and the origin and total layer charge. Therefore, this study allows tuning the clay mineral framework characteristic that favors the rare earth cations (as trivalent actinide simulator) immobilization.

Chemical Geology, 347 (2013) 208-216 | DOI: 10.1016/j.chemgeo.2013.03.006

Role of activated carbon on the increased photocatalytic activity of AC/Bi2WO6 coupled materials

Murcia-López, S; Navío, J.A.; Hidalgo, M.C.

The photocatalytic activities of several Bi2WO6 and TiO2/Bi2WO6 materials with different activated carbon (AC) contents were studied for Rhodamine B (RhB) (and Phenol) photodegradation under UV–vis and vis illumination. A wide characterization of the materials was carried out. The addition of AC strongly affected the Bi2WO6 morphology although not the crystalline phase. Even in the material with the lowest AC content (2 wt% nominal content) a structure with hierarchical porosity was formed. AC presence increased the initial reaction rates in the degradation of RhB. An important improvement in the photoactivity under both UV–vis and vis illumination conditions was obtained with the lowest AC content (2 wt%) when compared to the pristine material Bi2WO6 or to the systems with higher AC additions. AC/TiO2/Bi2WO6 materials were also improved in comparison to the TiO2/Bi2WO6 heterostructure without carbon. The improvement cannot be only ascribed to adsorption capability and surface area effects. A mechanism explaining the role of AC on the photocatalytic activity improvement is proposed.

Applied Catalysis A: General, 466 (2013) 51-59 | DOI: 10.1016/j.apcata.2013.06.022

Surface properties of anatase TiO2 nanowire films grown from a fluoride-containing solution

Berger, T; Anta, JA; Morales-Florez, V

Controlling the surface chemistry of nucleating seeds during wet-chemical synthesis allows for the preparation of morphologically well-defined nanostructures. Synthesis conditions play a key role in the surface properties, which directly affect the functional properties of the material. Therefore, it is important to establish post-synthesis treatments to facilitate the optimization of surface properties with respect to a specific application, without losing the morphological peculiarity of the nanostructure. We studied the surface properties of highly crystalline and porous anatase TiO2 nanowire (NW) electrodes, grown by chemical-bath deposition in fluoride-containing solutions, using a combined electrochemical and spectroscopic approach. As-deposited films showed low capacity for catechol adsorption and a poor photoelectrocatalytic activity for water oxidation. Mild thermal annealing at 200 °C resulted in a significant improvement of the electrode photoelectrocatalytic activity, whereas the bulk properties of the NWs (crystal structure, band-gap energy) remained unchanged. Enhancement of the functional properties of the material is discussed on the basis of adsorption capacity and electronic properties. The temperature-induced decrease of recombination centers, along with the concomitant increase of adsorption and reaction sites upon thermal annealing are called to be responsible for such improved performance.

Chemphyschem, 14 (2013) 1676-1685 | DOI: 10.1002/cphc.201300024

Influence of the O2/CO ratio and the presence of H2O and CO2 in the feed-stream during the preferential oxidation of CO (PROX) over a CuOx/CeO2-coated microchannel reactor

Laguna, OH; Dominguez, MI; Oraa, S; Navajas, A; Arzamendi, G; Gandia, LM; Centeno, MA; Montes, M; Odriozola, JA

The catalytic performance of a CuOx/CeO2 powder catalyst and that of a microchannel reactor or microreactor (MR) coated with the same solid was determined and compared. The catalytic activity measurements were carried out with varying O2/CO molar ratios in the feed-stream. In addition, the influence of the presence of CO2 and H2O in the reaction mixture was studied. Some discrepancies were observed between the performances of the powder catalyst and the MR depending on the O2/CO ratio. The MR presented a very good performance with a superior selectivity for CO conversion. This behaviour was due to a more efficient heat removal in the case of the MR that inhibited the H2 oxidation reaction and the r-WGS. The isothermicity of the microreactor during the process was demonstrated through the monitoring of the MR inlet and outlet temperatures.

Concerning the presence of CO2 or H2O in the feed-stream, both compounds gave rise to a decrease of the CO conversion. The negative effect on the catalytic performance was more marked when both compounds were fed together, although the principal inhibitor effect was associated to the CO2. This seems to be related with the formation of stable carbonates at the catalyst surface.

Catalysis Today, 203 (2013) 182-187 | DOI: 10.1016/j.cattod.2012.04.021

Preferential oxidation of CO over Au/CuOx–CeO2 catalyst in microstructured reactors studied through CFD simulations

Uriz, I; Arzamendi, G; Dieguez, PM; Laguna, OH; Centeno, MA; Odriozola, JA; Gandia, LM

A computational fluid dynamics (CFD) simulation study of the preferential oxidation of CO (CO-PROX) in microstructured reactors consisting in square and semicircular microchannels coated with an Au/CuOx–CeO2 catalyst is presented. The CO content of the feed stream was set at 1 vol.%. A parametric sensitivity analysis has been performed under isothermal conditions revealing that an optimal reaction temperature exists that leads to a minimum CO content at the microreactor exit. The influence of the space velocity, CO2 concentration and oxygen-to-CO molar ratio in the feed stream (λ), catalyst loading, and microchannel characteristic dimension (d) on the microreactor performance has been investigated. Under suitable conditions, the CO concentration can be reduced below 10 ppm at relatively low temperatures within the 155–175 °C range. A negative effect of the increase of d from 0.35 mm to 2.8 mm on the CO removal efficiency has been found and attributed to a more detrimental effect of the mass transport limitations on the oxidation of CO than that of H2. Non-isothermal CFD simulations have been performed to investigate the cooling of the CO-PROX reactor with air or a fuel cell anode off gas surrogate in parallel microchannels. Due to the very rapid heat transfer allowed by the microreactor and the strong influence of the reaction temperature on the exit CO concentration, a careful control of the coolant flow rate and inlet temperature is required for proper reactor operation. The microreactor behavior is virtually isothermal.

Catalysis Today, 216 (2013) 283-291 | DOI: 10.1016/j.cattod.2013.04.023

Effect of the alloy on micro-structured reactors for methanol steam reforming

Echave, FJ; Sanz, O; Velasco, I; Odriozola, JA; Montes, M

Micro-monoliths and foams made of aluminium, Fecralloy® and brass were studied as substrates for structured systems for methanol steam reforming (MSR). All the alloys exhibited very adherent oxide layer produced by pre-treatment to improve the adhesion between substrate and catalyst. 2.5% Pd/ZnO catalyst was prepared and deposited on structured substrates. Both, good catalyst adhesion and stable catalytic performance were achieved in the case of brass micro-monoliths. The Fecralloy® and aluminium substrates reacted with the catalytic active components resulting in catalyst modification. The aluminium based substrates promoted dimethyl ether (DME) formation. Aluminium foam produced better performance than aluminium micro-monoliths that could be related to improved mass and heat transfer properties in foams.

Catalysis Today, 213 (2013) 145-154 | DOI: 10.1016/j.cattod.2013.02.027

Cyclohexane photocatalytic oxidation on Pt/TiO2 catalysts

Murcia, JJ; Hidalgo, MC; Navio, JA; Vaiano, V; Sannino, D; Ciambelli, P

Gas-solid heterogeneous photocatalytic oxidation (PCO) of cyclohexane in humidified air over TiO2 and Pt/TiO2 catalyst was studied.

Pt/TiO2 photocatalysts were synthesized by photodeposition method at different Pt loadings (0.5–2 wt.%). The addition of 0.5 wt.% Pt does not significantly modify the TiO2 properties. The increase in Pt loading induces to an aggregation of metallic particles on TiO2 surface.

The cyclohexane PCO was performed in a fluidized bed photoreactor at 60 and 100 °C. Pure TiO2 was more active than 1 and 2 wt.% Pt/TiO2 samples at 60 °C. Nevertheless, the conversion level increases with temperature on Pt/TiO2 photocatalysts. The cyclohexane was mineralized into CO2, water and low amount of CO. A beneficial effect of Pt addition was found, since total CO2 selectivity was obtained. The Pt/TiO2 photocatalysts prepared by photodeposition provide the total cyclohexane PCO without CO production. Photocatalysts deactivation was not observed in any performed test. Evidence of an opportune tuning of temperature is highlighted.

Catalysis Today, 209 (2013) 164-169 | DOI: 10.1016/j.cattod.2012.11.018

In situ characterization of iron-promoted ceria–alumina gold catalysts during the water-gas shift reaction

Reina, TR; Xu, WQ; Ivanova, S; Centeno, MA; Hanson, J; Rodriguez, JA; Odriozola, JA

In this work an in situ XRD and XANES study of two gold catalysts supported on iron-promoted ceria–alumina carriers was carried out during the water-gas shift reaction (WGS). The first catalyst, Au/CeO2–FeOx/Al2O3, was prepared using a commercial alumina support in order to obtain a Ce–Fe oxide solid solution and in the second one, Au/FeOx/CeO2–Al2O3, an iron oxide monolayer was deposited onto a ceria–alumina commercial support to promote its redox properties. Catalytic activities in the WGS were remarkably different for both systems. The catalytic activity of the Au/CeO2–FeOx/Al2O3 catalyst was higher than the one shown by the Au/FeOx/CeO2–Al2O3 catalyst that resulted active at much higher temperatures. In situ XRD demonstrates the formation of magnetite (Fe3O4) during the WGS reaction and the presence of big gold particles, ca. 21 nm in diameter, in the low-activity system. This in contrast to the high-activity system that shows undetectable gold nanoparticles and the absence of diffraction peaks corresponding to magnetite during the WGS. The data obtained using in situ XANES states that Ce4+ species undergo reduction to Ce3+during the WGS for both catalysts, and also confirms that in the high-activity catalyst iron is just present as Fe3+ species while in the low-activity catalyst Fe3+ and Fe2+ coexist, resulting in iron spinel observed by XRD. These results allow us conclude that the Au/CeO2–Fe2O3/Al2O3 catalyst is a suitable catalyst for WGS when avoiding the formation of magnetite, in such a case Fe3+ species favors reduction and water splitting increasing the catalytic activity in the WGS reaction.

Catalysis Today, 205 (2013) 41-48 | DOI: 10.1016/j.cattod.2012.08.004

Studies of isothermal crystallisation kinetics of sunflower hard stearin-based confectionery fats

Bootello, MA; Hartel, RW; Levin, M; Martinez-Blanes, JM; Real, C; Garces, R; Martinez-Force, E; Salas, JJ

The crystallisation and polymorphic properties of three sunflower hard stearins (SHSs) and cocoa butter equivalents (CBEs) formulated by blending SHSs and palm mid fraction (PMF) were studied and compared with those from cocoa butter (CB), to explore their possibilities as confectionery fats. The isothermal crystallisation kinetics of these fats were examined by pNMR and DSC at three different temperatures. All samples studied displayed a two-step crystallisation profile that could be fitted to an exponential-Gompertz equation. Stop-and-return DSC studies showed that SHSs and CBEs exhibited different crystallisation mechanisms according to their triacylglycerol composition, with a quick formation of metastable crystals, followed by a polymorphic transition to the more stable β or β′ forms. X-ray diffraction (XRD) was used to investigate the polymorphic forms of tempered SHSs and CBEs in the long term. In all cases the resulting fats displayed short spacing patterns associated with β polymorphism. These formulations based on SHSs and PMF met all the requirements to be considered as CBEs; therefore they could be used as an alternative to traditional confectionery fats.

Food Chemistry, 139 (2013) 184-195 | DOI: 10.1016/j.foodchem.2012.11.141

Thermal conductivity of wood-derived graphite and copper–graphite composites produced via electrodeposition

Johnson, MT; Childers, AS; Ramirez-Rico, J; Wang, H; Faber, KT

The thermal conductivity of wood-derived graphite and graphite/copper composites was studied both experimentally and using finite element analysis. The unique, naturally-derived, anisotropic porosity inherent to wood-derived carbon makes standard porosity-based approximations for thermal conductivity poor estimators. For this reason, a finite element technique which uses sample microstructure as model input was utilized to determine the conductivity of the carbon phase independent of porosity. Similar modeling techniques were also applied to carbon/copper composite microstructures and predicted conductivities compared well to those determined via experiment.

Composites Part A: Applied Science and Manufaturing, 63 (2013) 182-189 | DOI: 10.1016/j.compositesa.2013.06.009

Evidence of nanograin cluster coalescence in spark plasma sintered α-Al2O3

Morales-Rodriguez, A; Poyato, R; Gallardo-Lopez, A; Munoz, A; Dominguez-Rodriguez, A

The aim of this study is to elucidate the coarsening kinetics involved during densification of fine-grained pure α-alumina by spark plasma sintering. Low temperature and short dwell time sintering conditions were used to preserve the nanocrystalline structure of the starting commercial powder (about 50 nm). Notwithstanding the above, submicron grain coarsened microstructures have been developed. The microstructure evolution of alumina under different sintering conditions points to a nanograin rotation densification mechanism as being responsible for the fast grain growth observed.

Scripta Materialia, 69 (2013) 529-532 | DOI: 10.1016/j.scriptamat.2013.06.019

In situ imaging and strain determination during fracture in a SiC/SiC ceramic matrix composite

Ramirez-Rico, J; Stolzenburg, F; Almer, JD; Routbort, JL; Singh, D; Faber, KT

A combined imaging and microdiffraction technique using high-energy synchrotron X-rays is described and used to reveal microstructure, damage and strain evolution around notches in SiC/SiC composites. This technique allows for monitoring the material for cracks while loading and mapping the strain distribution in fibers and matrix with a resolution of tens of microns. We show that at current resolutions this technique is capable of measuring the strain distribution near crack tips in ceramic matrix composites and observe load transfer effects.

Scripta Materialia, 69 (2013) 497-500 | DOI: 10.1016/j.scriptamat.2013.05.032

Solvent-Controlled Synthesis and Luminescence Properties of Uniform Eu:YVO4 Nanophosphors with Different Morphologies

Nunez, N; Sabek, J; Garcia-Sevillano, J; Cantelar, E; Escudero, A; Ocana, M

A facile solvothermal route has been developed for the preparation of tetragonal europium-doped yttrium orthovanadate nanoparticles (Eu:YVO4) and is based on a homogeneous precipitation reaction at 120 °C from solutions of rare earth precursors (yttrium acetylacetonate and europium nitrate) and sodium orthovanadate in ethylene glycol or ethylene glycol/water mixtures. The nature of the solvent has a dramatic effect on the morphology and crystallinity of the resulting nanoparticles. Polycrystalline nanoellipsoids (130 × 60 nm) were obtained in pure ethylene glycol, whereas quasispherical nanoparticles (100 nm) with monocrystalline character precipitated in ethylene glycol/water (7:3 by volume) mixtures. To explain these different morphological and structural features, the mechanism of particles formation was investigated. The effects of the doping level on the luminescence properties (emission spectra and luminescence lifetime) were also evaluated to find the optimum nanophosphors. Finally, it is shown that the luminescent efficiency of the quasispherical nanoparticles was higher than that of the nanoellipsoids; this can be related to differences in crystallinity and in impurity content.

European Journal of Inorganic Chemistry, 8 (2013) 1301-1309 | DOI: 10.1002/ejic.201201016

Reversible reactions of Ni and Pd hydroxo pincer complexes [( iPrPCP)M-OH] with CO2: Solid-state study of the decarboxylation of the monomeric bicarbonate complexes [(i PrPCP)M-OCOOH] (M = Ni, Pd)

Martinez-Prieto, LM; Real, C; Avila, E; Alvarez, E; Palma, P; Campora, J

Monomeric Ni and Pd hydroxides stabilized by the iPrPCP pincer ligand react with CO2 to give labile terminal bicarbonate complexes that readily lose CO2 and water to give binuclear carbonate complexes. Differential scanning calorimetry (DSC) has been used to monitor the decomposition of both bicarcabonates in the solid state. When the carbonate complexes are heated under reflux in thf in the presence of water, full decarboxylation takes place, restoring the starting hydroxides and demonstrating that CO2 insertion is a fully reversible process. The decarboxylation of the nickel carbonate complex is completed more readily, suggesting that the reaction of the Pd hydroxide with CO2 is more favourable than that of its nickel counterpart. This is supported by DFT calculations, which also shows that CO2 insertion takes place through a concerted Lipscomb-type mechanism. Monomeric Ni and Pd hydroxides stabilized by the iPrPCP pincer ligand react with CO2 to give labile terminal hydrogen carbonate complexes that readily lose CO2 and water to give binuclear carbonate complexes.

European Journal of Inorganic Chemistry, 32 (2013) 5555-5566 | DOI: 10.1002/ejic.201300995

Steam reforming of methanol over supported Ni and Ni–Sn nanoparticles

Bobadilla, LF; Palma, S; Ivanova, S; Dominguez, MI; Romero-Sarria, F; Centeno, MA; Odriozola, JA

The influence of the synthesis method and Sn addition on Ni/CeO2–MgO–Al2O3 catalyst is correlated to its catalytic behavior in the reaction of methanol steam reforming. The catalysts prepared by impregnation method are compared to samples obtained by deposition of previously obtained nanoparticles by the polyol method. X-ray diffraction (XRD), specific surface