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Artículos SCI



2020


Bio-Based Coatings for Food Metal Packaging Inspired in Biopolyester Plant Cutin


Benitez, JJ; Osbild, S; Guzman-Puyol, S; Heredia, A; Heredia-Guerrero, JA
Polymers, 12 (2020) 942
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

Metals used for food canning such as aluminum (Al), chromium-coated tin-free steel (TFS) and electrochemically tin-plated steel (ETP) were coated with a 2-3-mu m-thick layer of polyaleuritate, the polyester resulting from the self-esterification of naturally-occurring 9,10,16-trihydroxyhexadecanoic (aleuritic) acid. The kinetic of the esterification was studied by FTIR spectroscopy; additionally, the catalytic activity of the surface layer of chromium oxide on TFS and, in particular, of tin oxide on ETP, was established. The texture, gloss and wettability of coatings were characterized by AFM, UV-Vis total reflectance and static water contact angle (WCA) measurements. The resistance of the coatings to solvents was also determined and related to the fraction of unreacted polyhydroxyacid. The occurrence of an oxidative diol cleavage reaction upon preparation in air induced a structural modification of the polyaleuritate layer and conferred upon it thermal stability and resistance to solvents. The promoting effect of the tin oxide layer in such an oxidative cleavage process fosters the potential of this methodology for the design of effective long-chain polyhydroxyester coatings on ETP.


Abril, 2020 | DOI: 10.3390/polym12040942

Study of the influence of the precursors on the sensing properties of ZnO:Cu system


Ramos, A; Urbieta, A; Escalante, G; Hidalgo, P; Espinos, JP; Fernandez, P
Ceramics International, 46 (2020) 8358-8367
Nanotecnología en Superficies y Plasma

ABSTRACT

The properties of ZnO based materials for ethanol detection have been studied. Cu doped samples obtained from different precursors have been investigated. ZnO and ZnS have been used as host and Cu and CuO as dopant sources.

The sensing measurements have been mostly performed at room temperature. To monitor the effect of the presence of gas, resistivity and photoluminescence experiments with and without sensing gas have been carried out. The sensing behaviour is affected by the nature of the precursors used. For ZnO:Cu and ZnO:CuO series, a higher sensitivity is obtained at the lower gas concentrations, the better response is obtained for the sample ZnO:Cu with wt.1% of metallic copper. Strong segregation effects observed in these samples could be deleterious for the sensing properties. In the series ZnS:CuO, no segregation is observed, however the sensing behaviour is erratic and attributed to the reduction of Cu ions to the metallic state.


Abril, 2020 | DOI: 10.1016/j.ceramint.2019.12.068

Vegetable hierarchical structures as template for bone regeneration: New bio‐ceramization process for the development of a bone scaffold applied to an experimental sheep model


Filardo, G; Roffi, A; Fey, T; Fini, M; Giavaresi, G; Marcacci, M; Martinez-Fernandez, J; Martini, L; Ramirez-Rico, J; Salamanna, F; Sandri, M; Sprio, S; Tampieri, A; Kon, E
Journal of Biomedical Materials Research Part B-Applied Materials, 108 (2020) 600-611
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

Long bone defects still represent a major clinical challenge in orthopedics, with the inherent loss of function considerably impairing the quality of life of the affected patients. Thus, the purpose of this study was to assess the safety and potential of bone regeneration offered by a load‐bearing scaffold characterized by unique hierarchical architecture and high strength, with active surface facilitating new bone penetration and osseointegration in critical size bone defects. The results of this study showed the potential of bio‐ceramization processes applied to vegetable hierarchical structures for the production of new wood‐derived bone scaffolds, further improved by surface functionalization, with good biological and mechanical properties leading to successful treatment of critical size bone defects in the sheep model. Future studies are needed to evaluate if these scaffolds prototypes, as either biomaterial alone or in combination with augmentation strategies, may represent an optimal solution to enhance bone regeneration in humans.


Abril, 2020 | DOI: 10.1002/jbm.b.34414

A Microstructure Insight of MTA Repair HP of Rapid Setting Capacity and Bioactive Response


Jimenez-Sanchez, MC; Segura-Egea, JJ; Diaz-Cuenca, A
Materials, 13 (2020)
Materiales para Bioingeniería y Regeneración Tisular

ABSTRACT

Mineral trioxide aggregate (MTA) is considered a bioactive endodontic material, which promotes natural mineralization at the material-tooth tissue interface. MTA Repair HP stands out because of the short setting time and the quick and effective bioactive response in vitro. The bioactivity, depens on material composition and microstructure. This work is devoted to analyze MTA Repair HP microstructural features, of both the powder precursor and set material, to get insights into the material physicochemical parameters-functionality performance relationships. Transmission electron microscopy (TEM), and field emission gun scanning electron microscopy (FEG-SEM) coupled with energy-dispersive X-ray (EDX) analyses were performed. X-ray diffraction (XRD) measurements were carried out at different times to investigate setting process. Bioactivity evaluation in vitro was carried out by soaking the processed cement disk in simulated body fluid (SBF). The presented results point out those MTA Repair HP precursor material characteristics of tricalcium silicate particles of nanometric size and high aspect ratio, which provide an elevated surface area and maximized components dispersion of calcium silicate and very reactive calcium aluminate. The MTA Repair HP precursor powder nanostructure and formulation, allows a hydration process comprising silicate hydrate structures, which are very effective to achieve both fast setting and efficient bioactive response.


Abril, 2020 | DOI: 10.3390/ma13071641

Development of a high-pressure thermobalance working under constant rate thermal analysis


Perejon, A; Sanchez-Jimenez, PE; Criado, JM; Perez-Maqueda, LA
Journal of Thermal Analysis ande Calorimetry, (2020)
Reactividad de Sólidos

ABSTRACT

A thermogravimetric instrument that works at high pressure of different gases has been designed and assembled. The instrument has been devised to work in a temperature range from room temperature to 1000 degrees C in various controlled pressures of selected gas up to 15 bar, and under conventional rising temperature and constant rate thermal analysis (CRTA) modes. CRTA method allows an intelligent control of the reaction temperature using a feedback system that monitors the mass gain or mass loss of the sample in such a way that the reaction rate is maintained constant all over the process at a preselected value. CRTA method provides a significant advantage for studying processes under high pressure as it reduces heat and mass transfer phenomena that are very relevant under these high-pressure experimental conditions. The thermal oxidation of Ni at 8 bar of pure oxygen has been used for testing the performance of the instrument under both linear heating rate and CRTA conditions.


Abril, 2020 | DOI: 10.1007/s10973-020-09644-5

Binder-free supercapacitor electrodes: Optimization of monolithic graphitized carbons by reflux acid treatment


Gomez-Martin, A; Gutierrez-Pardo, A; Martinez-Fernandez, J; Ramirez-Rico, J
Fuel Processing Technology, 199 (2020) 106279
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

The rational design of electrodes mimicking the cellular structure of natural bio-resources has been a matter of increasing interest for applications in energy storage. Due to their anisotropic and hierarchical porosity, monolithic carbon materials from natural wood precursors are appealing as electrodes for supercapacitor applications due to their interconnected channels, relatively low cost and environmentally friendly synthesis process. In this work, a liquid-phase oxidative treatment with refluxing nitric acid at 100 degrees C for 8 h was performed to enhance the surface properties of beech-derived graphitized carbons treated with an iron catalyst. Microstructural, textural and surface investigations revealed that this strategy was successful in removing amorphous carbon and in functionalizing their surfaces. The crystallinity, accessible surface area, micropore volume and surface functionality of beech-derived carbons were increased upon the reflux treatment. The resulting porous carbon materials were evaluated as binderless monolithic electrodes for supercapacitors applications in aqueous KOH electrolyte. A maximum specific capacitance of 179 F.g(-1) and a volumetric capacitance of 89 Fcm(-3) in galvanostatic charge/discharge experiments were reached. Monolithic electrodes exhibited good cycling stability, with a capacitance retention over 95% after 10,000 cycles.


Marzo, 2020 | DOI: 10.1016/j.fuproc.2019.106279

Optical Responses of Localized and Extended Modes in a Mesoporous Layer on Plasmonic Array to Isopropanol Vapor


Murai, S; Cabello-Olmo, E; Kamakura, R; Calvo, ME; Lozano, G; Atsumi, T; Miguez, H; Tanaka, K
Journal of Physical Chemistry C, 124 (2020) 5772-5779
Materiales Ópticos Multifuncionales

ABSTRACT

Mesoporous silica features open and accessible pores that can intake substances from the outside. The combination of mesoporous silica with plasmonic nanostructures represents an interesting platform for an optical sensor based on the dependence of plasmonic modes on the refractive index of the medium in which metallic nanoparticles are embedded. However, so far only a limited number of plasmonic nanostructures are combined with mesoporous silica, including random dispersion of metallic nanoparticles and flat metallic thin films. In this study, we make a mesoporous silica layer on an aluminum nanocylinder array. Such plasmonic arrangements support both localized surface plasmon resonances (LSPRs) and extended modes which are the result of the hybridization of LSPRs and photonic modes extending into the mesoporous layer. We investigate in situ optical reflectance of this system under controlled pressure of isopropanol vapor. Upon exposure, the capillary condensation in the mesopores results in a gradual spectral shift of the reflectance. Our analysis demonstrates that such shifts depend largely on the nature of the modes; that is, the extended modes show larger shifts compared to localized ones. Our materials represent a useful platform for the field of environmental sensing.


Marzo, 2020 | DOI: 10.1021/acs.jpcc.9b10999

Optical interference effects on the Casimir-Lifshitz force in multilayer structures


Esteso, V; Carretero-Palacios, S; Miguez, H
Physical Review A, 101 (2020) 033815
Materiales Ópticos Multifuncionales

ABSTRACT

The Casimir-Lifshitz force F(C-L) between planar objects when one of them is stratified at the nanoscale is herein investigated. Layering results in optical interference effects that give rise to a modification of the optical losses, which, as stated by the fluctuation-dissipation theorem, should affect the Casimir-Lifshitz interaction. On these grounds, we demonstrate that, by nanostructuring the same volume of dielectric materials in diverse multilayer configurations, it is possible to access F(C-L) of attractive or repulsive nature, even getting canceled, at specific separation distances.


Marzo, 2020 | DOI: 10.1103/PhysRevA.101.033815

Potentialization of bentonite properties as support in acid catalysts


Amaya, J; Bobadilla, L; Azancot, L; Centeno, M; Moreno, S; Molina, R
Materials Research Bulletin, 123 (2020) 110728
Química de Superficies y Catálisis

ABSTRACT

Enhancement of the main physicochemical properties of a natural bentonite was carried out by means of modifications using surfactant, reflux, microwave treatment and, subsequently, the incorporation of AlZr and AlCe species. The evolution of the main changes in each modification stage was evaluated by means of X-ray diffraction, N-2 sortometry, scanning microscopy (SEM), NH3-TPD, NH3-DRIFTS and CO adsorption at low temperature. For the evaluation of the catalytic behavior, the dehydration-dehydrogenation reactions of 2-propanol and hydro-conversion of decane were used; both of which generate, in addition, information regarding the acidic properties of the materials. The correlation of the number, type and acid strength with the catalytic behavior, allowed establishing the effect produced by both the delamination method and the nature of the incorporated cation. This generated tools that allow controlling the physicochemical properties, and more specifically, the enhancement of the acidity of new supports based on this type of natural clay mineral.


Marzo, 2020 | DOI: 10.1016/j.materresbull.2019.110728

Influence of the Test Configuration and Temperature on the Mechanical Behaviour of WC-Co


Gonzalez, LM; Chicardi, E; Gotor, FJ; Bermejo, R; Llanes, L; Torres, Y
Metals, 10 (2020) 322
Reactividad de Sólidos

ABSTRACT

In this work, the effect of the test configuration and temperature on the mechanical behaviour of cemented carbides (WC-Co) with different carbide grain sizes (d(WC)) and cobalt volume fractions (V-Co), implying different binder mean free paths (lambda (Co)), was studied. The mechanical strength was measured at 600 degrees C with bar-shaped specimens subjected to uniaxial four-point bending (4PB) tests and with disc specimens subjected to biaxial ball-on-three-balls (B3B) tests. The results were analysed within the frame of the Weibull theory and compared with strength measurements performed at room temperature under the same loading conditions. A mechanical degradation greater than 30% was observed when the samples were tested at 600 degrees C due to oxidation phenomena, but higher Weibull moduli were obtained as a result of narrower defect size distributions. A fractographic analysis was conducted with broken specimens from each test configuration. The number of fragments (N-f) and the macroscopic fracture surface were related to the flexural strength and fracture toughness of WC-Co. For a given number of fragments, higher mechanical strength values were always obtained for WC-Co grades with higher K-Ic. The observed differences were discussed based on a linear elastic fracture mechanics (LEFM) model, taking into account the effect of the temperature and microstructure of the cemented carbides on the mechanical strength.


Marzo, 2020 | DOI: 10.3390/met10030322

Pt–TiO2–Nb2O5 heterojunction as effective photocatalyst for the degradation of diclofenac and ketoprofen


Sacco, O.l; Murcia, J.J.; Lara, A.E.; Hernández-Laverde, M.; Rojas, H.; Navío, J.A.; Hidalgo, M.C.; Vaiano, V.
Materials Science in Semiconductor Processing, 107 (2020) 104839
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

Pt–TiO2–Nb2O5 heterojunction was synthetized and studied for the photocatalytic removal of diclofenac (DCF) and ketoprofen (KTF) under UV light irradiation. The physical-chemical properties of the prepared catalysts were analysed by different characterization techniques revealing that the lowest platinum nanoparticle size and the better metal distribution was observed in Pt–TiO2–Nb2O5 sample. The Pt–TiO2–Nb2O5 heterojunction possessed the best photocatalytic activity toward both the photodegradation and mineralization of the two selected pollutants. The optimal photocatalyst showed a DCF and KTF mineralization rate of 0.0555 and 0.0746 min−1, respectively, which were higher than those of Pt–TiO2 (0.0321 min−1 for DCF and 0.0597 min−1 for KTF). The experiments driven to analyse the effects of free radical capture showed that ·OH, ·O2− and h+ have a primary role in reactive during the photocatalytic reaction. The improved photocatalytic performances of the Pt–TiO2–Nb2O5 heterojunction could be argue by a direct Z-scheme mechanism in which the Pt0 nanoparticles could act as a bridge between TiO2 and Nb2O5, improving the electron-hole separation and, ultimately, enhancing the photocatalytic removal rate of both DCF and KTF.


Marzo, 2020 | DOI: 10.1016/j.mssp.2019.104839

Role of particle size on the multicycle calcium looping activity of limestone for thermochemical energy storage


Duran-Martin, JD; Jimenez, PES; Valverde, JM; Perejon, A; Arcenegui-Troya, J; Trinanes, PG; Maqueda, LAP
Journal of Advanced Research, 22 (2020) 67-76
Reactividad de Sólidos

ABSTRACT

The calcium looping process, based on the reversible reaction between CaCO3 and CaO, is recently attracting a great deal of interest as a promising thermochemical energy storage system to be integrated in Concentrated Solar Power plants (CaL-CSP). The main drawbacks of the system are the incomplete conversion of CaO and its sintering-induced deactivation. In this work, the influence of particle size in these deactivation mechanisms has been assessed by performing experimental multicycle tests using standard limestone particles of well-defined and narrow particle size distributions. The results indicate that CaO multicycle conversion benefits from the use of small particles mainly when the calcination is carried out in helium at low temperature. Yet, the enhancement is only significant for particles below 15 μm. On the other hand, the strong sintering induced by calcining in CO2 at high temperatures makes particle size much less relevant for the multicycle performance. Finally, SEM imaging reveals that the mechanism responsible for the loss of activity is mainly pore-plugging when calcination is performed in helium, whereas extensive loss of surface area due to sintering is responsible for the deactivation when calcination is carried out in CO2 at high temperature.


Marzo, 2020 | DOI: 10.1016/j.jare.2019.10.008

An insight on the design of mercapto functionalized swelling brittle micas


Osuna, FJ; Pavon, E; Alba, MD
Journal of Colloid and Interface Science, 561 (2020) 533-541
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

Surface modification of natural clay minerals with reagents containing metal chelating groups has great environmental value. The functionalization by adsorption or grafting guarantees a durable immobilization of the reactive organic groups, preventing their leaching when they are used in liquid media. The aim of this research was the designed mercapto functionalization of swelling brittle micas, Na-Mn, thorough both chemical and physical mechanisms. Na-Mn were functionalized with 2-mercaptoethylammonium (MEA), 2,3-dimercapto-1-propanol (BAL) and (3-mercaptopropyl)trimethoxysilane (MPTMS). The thiol concentration on swelling brittle micas is higher than the observed value for others adsorbents. The cation exchange reaction with MEA and one-step grafting with MPTMS in acid medium are the most efficient mercapto functionalization mechanism.


Marzo, 2020 | DOI: 10.1016/j.jcis.2019.11.028

Development by Mechanochemistry of La0.8Sr0.2Ga0.8Mg0.2O2.8 Electrolyte for SOFCs


Garcia-Garcia, FJ; Tang, YQ; Gotor, FJ; Sayagues, MJ
Materials, 13 (2020)
Reactividad de Sólidos

ABSTRACT

In this work, a mechanochemical process using high-energy milling conditions was employed to synthesize La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) powders from the corresponding stoichiometric amounts of La2O3, SrO, Ga2O3, and MgO in a short time. After 60 min of milling, the desired final product was obtained without the need for any subsequent annealing treatment. A half solid oxide fuel cell (SOFC) was then developed using LSGM as an electrolyte and La0.8Sr0.2MnO3 (LSM) as an electrode, both obtained by mechanochemistry. The characterization by X-ray diffraction of as-prepared powders showed that LSGM and LSM present a perovskite structure and pseudo-cubic symmetry. The thermal and chemical stability between the electrolyte (LSGM) and the electrode (LSM) were analyzed by dynamic X-ray diffraction as a function of temperature. The electrolyte (LSGM) is thermally stable up to 800 and from 900 °C, where the secondary phases of LaSrGa3O7 and LaSrGaO4 appear. The best sintering temperature for the electrolyte is 1400 °C, since at this temperature, LaSrGaO4 disappears and the percentage of LaSrGa3O7 is minimized. The electrolyte is chemically compatible with the electrode up to 800 °C. The powder sample of the electrolyte (LSGM) at 1400 °C observed by HRTEM indicates that the cubic symmetry Pm-3m is preserved. The SOFC was constructed using the brush-painting technique; the electrode–electrolyte interface characterized by SEM presented good adhesion at 800 °C. The electrical properties of the electrolyte and the half-cell were analyzed by complex impedance spectroscopy. It was found that LSGM is a good candidate to be used as an electrolyte in SOFC, with an Ea value of 0.9 eV, and the LSM sample is a good candidate to be used as cathode


Marzo, 2020 | DOI: 10.3390/ma13061366

Platinum nanoparticles stabilized by N-heterocyclic thiones. Synthesis and catalytic activity in mono- and di-hydroboration of alkynes


Moraes, LCC; Figueiredo, RCC; Espinos, JPP; Vattier, F; Franconetti, A; Jaime, C; Lacroix, B; Rojo, J; Lara, P; Conejero, S
Nanoscale, 12 (2020) 6821-6831
Nanotecnología en Superficies y Plasma

ABSTRACT

N-Heterocyclic Thiones (NHT) proved to be efficient ligands for the stabilization of small platinum nanoparticles (1.3-1.7 nm), synthesized by decomposition of [Pt(dba)(2)], under a H-2 atmosphere, in the presence of variable sub-stoichiometric amounts of the NHT. Full characterization by means of TEM, HR-TEM, NMR, ICP, TGA and XPS have been carried out, providing information about the nature of the metal nanoparticles and the interaction of the NHT ligands to the metal surface. Importantly, DFT calculations indicate that some NHT ligands interact with the metal through the C & xe001;C double bond of the imidazole fragment in addition to the sulfur atom, thus providing additional stabilization to the nanoparticles. According to XPS, TGA and ICP techniques, the surface coverage by the ligand increases by decreasing the size of the substituents on the nitrogen atom. The platinum nanoparticles have been used as catalyst in the hydroboration of alkynes. The most active system is that with a less covered surface area lacking an interaction of the ligand by means of the C & xe001;C double bond. This catalyst hydroborates alkynes with excellent selectivities towards the monoborylated anti-Markovnikov product (vinyl-boronate) when one equiv. of borane is used. Very interestingly, aliphatic alkynes undergo a second hydroborylation process leading to the corresponding 1,1- and 1,2-diboroylated species with good selectivities towards the former.


Marzo, 2020 | DOI: 10.1039/d0nr00251h

Localized surface plasmon effects on the photophysics of perovskite thin films embedding metal nanoparticles


Bayles, A; Carretero-Palacios, S; Calio, L; Lozano, G; Calvo, ME; Miguez, H
Journal of Materials Chemistry C, 8 (2020) 916-921
Materiales Ópticos Multifuncionales

ABSTRACT

Herein we provide direct experimental evidence that proves that the photophysical properties of thin methylammonium lead iodide perovskite films are significantly enhanced by localized surface plasmon resonances (SPRs). Observations are well supported by rigorous calculations that prove that improved light harvesting can be unequivocally attributed to plasmonic scattering and near field reinforcement effects around silver nanoparticles embedded within the semiconductor layer. Adequate design of the localized SPR allows raising the absorptance of a 300 nm thick film at well-defined spectral regions while minimizing the parasitic absorption from the metallic inclusions. Measured enhancements can be as large as 80% at specific wavelengths and 20% when integrated over the whole range at which SPR occurs, in agreement with theoretical estimations. Simultaneously, the characteristic quenching effect that the vicinity of metals has on the photoluminescence of semiconductors is largely compensated for by the combined effect of the enhanced photoexcitation and the higher local density of photon states occurring at SPR frequencies, with a two fold increase of the perovskite photoemission efficiency being measured.


Marzo, 2020 | DOI: 10.1039/c9tc05785d

Optofluidic liquid sensing on electromicrofluidic devices


Oliva-Ramirez, M; Wang, SL; Rico-Gavira, V; Lopez-Santos, C; Fan, SK; Gonzalez-Elipe, AR
Materials Research Express, 7 (2020) 036407
Nanotecnología en Superficies y Plasma

ABSTRACT

Electromicrofluidic (EMF) devices are used to handle and move tiny amounts of liquids by electrical actuation, including electrowetting-on-dielectric (EWOD) and dielectrophoresis (DEP). Monitoring the liquid characteristics in one of these devices requires suitable sensing transducers incorporated within the microfluidic structure. In the present work, we describe the incorporation of an optofluidic photonic transducer in an EMF device to monitor the refractive index of a liquid during its manipulation. The incorporated transducer consists of a responsive porous Bragg Microcavity (BM) deposited via physical vapor oblique angle deposition. Besides reporting the manufacturing procedure of the sensing-EMF device combining liquid handling and monitoring, the performance of the BM is verified by infiltrating several liquids dripped on its surface and comparing the responses with those of liquid droplets electrically moved from the delivery part of the chip to the BM location. This study proved that modified EMF devices can incorporate photonic structures to analyze very low liquid volumes (similar to 0.2 mu L) during its handling.


Marzo, 2020 | DOI: 10.1088/2053-1591/ab7fdf

Preparation of ZnFe2O4/ZnO composite: Effect of operational parameters for photocatalytic degradation of dyes under UV and visible illumination


Zouhier, M.; Tanji, K.; Navio, J.A.; Hidalgo, M.C.; Jaramillo-Páez, C.; Kherbeche, A.
Journal of Photochemistry and Photobiology A: Chemistry, 390 (2020) 112305
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

An ZnFe2O4/ZnO composite catalyst was prepared by solution combustion method. In this study, one nominal molar percentage of iron was used in the synthesis, corresponding to 20 % molar relative to ZnO. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray Fluorescence (XRF), Scanning Electronic Microscopy (SEM), Transmission Electronic Microscopy (TEM) and Ultraviolet-visible (UV–vis) diffuse spectroscopy (DRS). The photocatalytic activities of the catalysts were investigated based on the degradation of two dyes, methylene blue (MB) and remazol brilliant blue (RBB), in aqueous solution under both UV and visible light illumination respectively. It was found that the composite had a good photocatalytic activity at basic pH by using 1 g/L of catalyst under UV illumination for both MB and RBB. Under visible illumination, while pristine ZnO showed no activity, the composite exhibited an excellent visible efficiency, reaching up to an 80 % conversion of the initial dye concentrations in 2 h. The enhancement of the visible photocatalytic activity of Fe/ZnO sample with respect to pristine ZnO is attributed to the formation of ZnFe2O4 coupled with ZnO, having a narrow band gap value that contributes to the absorption of visible photons with an improved separation path for the photo-generated carriers.


Marzo, 2020 | DOI: 10.1016/j.jphotochem.2019.112305

Positron annihilation analysis of nanopores and growth mechanism of oblique angle evaporated TiO2 and SiO2 thin films and multilayers


Garcia-Valenzuela, A; Butterling, M; Liedke, MO; Hirschmann, E; Trinh, TT; Attallah, AG; Wagner, A; Alvarez, R; Gil-Rostra, J; Rico, V; Palmero, A; Gonzalez-Elipe, AR
Microporous and Mesoporous Materials, 295 (2020) 109968
Nanotecnología en Superficies y Plasma

ABSTRACT

The nano-porosity embedded into the tilted and separated nanocolumns characteristic of the microstructure of evaporated thin films at oblique angles has been critically assessed by various variants of the positron annihilation spectroscopy. This technique represents a powerful tool for the analysis of porosity, defects and internal interfaces of materials, and has been applied to different as-deposited SiO2 and TiO2 thin films as well as SiO2/TiO2 multilayers prepared by electron beam evaporation at 70 and 85 zenithal angles. It is shown that, under same deposition conditions, the concentration of internal nano-pores in SiO2 is higher than in TiO2 nanocolumns, while the situation is closer to this latter in TiO2/SiO2 multilayers. These features have been compared with the predictions of a Monte Carlo simulation of the film growth and explained by considering the influence of the chemical composition on the growth mechanism and, ultimately, on the structure of the films.


Marzo, 2020 | DOI: 10.1016/j.micromeso.2019.109968

Synthesis of Mn2+-doped ZnS by a mechanically induced self-sustaining reaction


Aviles, MA; Cordoba, JM; Sayagues, MJ; Gotor, FJ
Journal of Materials Science, 55 (2020) 1603-1613
Reactividad de Sólidos

ABSTRACT

The mechanochemical process denoted as a mechanically induced self-sustaining reaction was successfully applied in obtaining Mn-doped ZnS samples with Mn content between 0 and 5 mol%. The process consists in milling Zn/Mn/S powder elemental mixtures with the appropriate stoichiometry, which promotes after approximately 80 min the induction of a combustion reaction. The doping level was properly adjusted by controlling the atomic ratio of the starting mixture. A complete characterization of samples was carried out, including X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction, energy-dispersive X-ray spectroscopy, Raman spectroscopy, diffuse reflectance UV-Vis spectroscopy and emission and excitation photoluminescence measurements. A wurtzite structure, in which Mn2+ replaces Zn2+, was obtained with a nanometric character. The photoluminescence of samples showed the characteristic (Mn2+T1)-T-4-(6)A(1) emission that was highly dependent on the doping level. The maximum luminescence efficiency through the ZnS excitation was found for a doping value of 1 mol%. The photoluminescence showed virtually no contribution from the host emission, which confirmed that samples were properly doped.


Febrero, 2020 | DOI: 10.1007/s10853-019-04138-8

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