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2019


Mechanochemical combustion synthesis of vanadium carbide (VC), niobium carbide (NbC) and tantalum carbide (TaC) nanoparticles


Jalaly, M; Gotor, FJ; Sayagues, MJ
International Journal of Refractory Metals & Hard Materials, 79 (2019) 177-184
Reactividad de Sólidos

ABSTRACT

The nanoparticles of vanadium, niobium, and tantalum carbides were synthesized by a mechanically induced magnesiothermic combustion in the separate Mg/V2O5/C, Mg/Nb2O5/C, and Mg/Ta2O5/C systems. Initial materials in these systems ignited after short milling times of 10, 10, and 23 min, respectively. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM) and elemental mapping techniques were employed to characterize the combustion products. In this process, magnesium reduces initial oxides to generate elemental V/Nb/Ta to react with carbon, forming the carbide phases.


Febrero, 2019 | DOI: 10.1016/j.ijrmhm.2018.12.011

Multicycle CO2 capture activity and fluidizability of Al-based synthesized CaO sorbents


Azimi, B; Tahmasebpoor, M; Sanchez-Jimenez, PE; Perejon, A; Valverde, JM
Chemical Engineering Journal, 358 (2019) 679-690
Reactividad de Sólidos

ABSTRACT

CaO-based materials have been identified as promising sorbents for highly efficient pre-combustion and post-combustion CO2 capture in fluidized beds operated at high temperatures by means of the Calcium Looping (CaL) process. However, Ca-based sorbents suffer from a decline of the capture capacity over multiple sorption/desorption cycles, mainly due to sintering, and from a markedly heterogeneous fluidization behavior due to the strength of interparticle attractive forces as compared to particle weight. The present study is focused on the development of novel synthetic CaO/Al2O3 sorbents for CO2capture with enhanced CaL performance and fluidizability by dry mixing with flow conditioner nanopowders. The influence of initial precursors on the sorbents multicycle activity at realistic CaL conditions has been investigated. The formation of a stable Ca9Al6O18 mixed-phase during the preparation of the sorbents promotes the multicycle capture capacity. The type of Ca and Al precursors, either soluble or insoluble, can significantly affect the dispersion of this stabilizer (Ca9Al6O18) in the sorbent matrix and, consequently, may affect the carbonation activity of the materials. The sorbent prepared from soluble aluminum nitrate and calcium nitrate precursors by sol-gel method exhibits a very stable multicycle capture capacity with a capture capacity around 0.2 g of CO2/g of sorbent after 21 cycles keeping a 72% of its initial capture capacity. The fluidizability of this promising sorbent was also investigated as affected by the addition of three different flow conditioners. Fluidization experiments confirmed the positive effect of using hydrophilic alumina and hydrophobic silica nanoparticles on improving the fluidizability of the synthesized sorbents.


Febrero, 2019 | DOI: 10.1016/j.cej.2018.10.061

Catalytic Efficiency of Cu-Supported Pyrophyllite in Heterogeneous Catalytic Oxidation of Phenol


El Gaidoumi, A.; Doña-Rodríguez, J.M.; Pulido Melián, E.; González-Díaz, O.M.; Navío, J.A.; El Bali, B.; Kherbeche, A.
Arabian Journal for Science and Engineering, (2019) 1-13
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

The copper-impregnated pyrophyllite (Cu/RC) was prepared and used as catalyst in catalytic wet peroxide oxidation (CWPO) of phenol. The catalyst was prepared by impregnation of copper (2.5 wt%) into pyrophyllite-type clay and characterized by X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. The optimum operation conditions for CWPO of phenol over Cu/RC were determined by investigating the effects of pH, temperature, catalyst amount, and hydrogen peroxide concentration. Stability of the Cu/RC catalyst and toxicity of treated solution were studied, by measuring the copper concentration leached out from the catalyst and the inhibition of Vibrio fischeri bacteria bioluminescence, respectively. The probable degradation mechanism of phenol over Cu/RC was considered by HPLC analysis. The obtained results showed that Cu/RC achieved highest activity (total phenol degradation and 80% TOC reduction) and detoxification with remarkable low copper leaching concentration (0.006 mg\,L−1)mg\,L−1) at optimized conditions (pH == 3, T=50∘T=50∘C, 2 g\,L−1g\,L−1 catalyst amount, 50 mg L−1L−1phenol concentration and 7.45 mmol\,L−1mmol\,L−1 hydrogen peroxide concentration during 4 h). Meanwhile, few intermediates with low concentration were observed by the HPLC analysis for the CWPO of phenol. The Cu/RC catalyst showed a good activity after five successive runs (88% of degradation and 73% mineralization) at optimized conditions.


Febrero, 2019 | DOI: 10.1007/s13369-019-03757-2

Immobilization of Stabilized Gold Nanoparticles on Various Ceria-Based Oxides: Influence of the Protecting Agent on the Glucose Oxidation Reaction


Chenouf, M; Megias-Sayago, C; Ammari, F; Ivanova, S; Centeno, MA; Odriozola, JA
Catalysts, 9 (2019) 125
Química de Superficies y Catálisis

ABSTRACT

The influence of the protecting agent's nature on gold particle size and dispersion was studied in this work over a series of gold-based catalysts. CO and glucose oxidation were chosen as catalytic reactions to determine the catalyst's structure-activity relationship. The nature of the support appeared to be the predominant factor for the increase in activity, as the oxygen mobility was decisive for the CO oxidation in the same way that the Lewis acidity was decisive for the glucose oxidation. For the same catalyst composition, the use of montmorillonite as the stabilizing agent resulted in better catalytic performance.


Febrero, 2019 | DOI: 10.3390/catal9020125

Insight into the BiFeO3 flash sintering process by in-situ energy dispersive X-ray diffraction (ED-XRD)


Perez-Maqueda, LA; Gil-Gonzalez, E; Wassel, MA; Jha, SK; Perejon, A; Charalambous, H; Okasinski, J; Sanchez-Jimenez, PE; Tsakalakos, T
Ceramics International, 45 (2019) 2828-2834
Reactividad de Sólidos

ABSTRACT

The sintering mechanism of BiFeO3 has been investigated in-situ by energy dispersive X-ray diffraction (ED-XRD) using a high-energy white collimated X-ray beam from the Advanced Photon Source (Argonne National Laboratories). Such radiation is very penetrating thereby allowing measurements of the sample even when placed inside the flash sintering set up. Additionally, the fast ED-XRD measurements permit monitoring the flash sintering process by providing information about phase composition and sample temperature in real time. Moreover, profile scans, obtained by moving the stage vertically while recording the ED-XRD spectra, permit investigating the homogeneity of the flash for the entire length of the sample. All experiments have been complemented by ex-situ studies. It has been concluded that flash sintering of BiFeO3 is a homogeneous process without any directionality effects. Furthermore, flash sintering takes place at quite low temperatures (below the Tc ≈ 830 °C), which may be related to the high quality of the samples, as pure, highly insulating ceramics without evidence of secondary phases with a homogenous nanostructured grain size distribution are obtained by this technique. Moreover, it is also evidenced that the rapid heating of the sample does not seem to justify, at least by itself, the densification process. Therefore, it appears that the electric current should play a role in the enhanced mobility during the sintering process.


Febrero, 2019 | DOI: 10.1016/j.ceramint.2018.07.293

Environmentally Tight TiO2-SiO2 Porous 1D-Photonic Structures


Garcia-Valenzuela, A; Lopez-Santos, C; Rico, V; Alvarez, R; Palmero, A; Gonzalez-Elipe, AR
Advanced Materials Interfaces, 6 (2019) art. 1801212
Nanotecnología en Superficies y Plasma

ABSTRACT

Although thin film porosity is the basis of many optical sensors, it can be deleterious for a stable optical behavior of passive optical elements due to the condensation of water and other vapors in their pores. This paper proposes a new strategy for the magnetron sputtering (MS) fabrication of environmentally tight SiO2-TiO2 porous multilayers. Thin films of these two oxides deposited in an oblique angle configuration (MS-OAD) present a nanocolumnar and highly porous nanostructure and, as a consequence, experience significant changes in their optical properties when exposed to water vapor. Similarly, the optical properties of Bragg reflectors and Bragg microcavities made of the stacking of porous and compact SiO2 and TiO2 thin films experience reversible changes when these 1D-photonic structures are exposed to water pressure. A key finding of this work is that a very thin capping layer of SiO2 deposited on the surface of porous SiO2 films in the stack, at the interlayer between the two oxides, efficiently seals the pores making the photonic structures environmentally tight. This capping layer approach is a useful strategy to incorporate porosity as an additional parameter to design the optical behavior of planar photonic structures while preserving optical and environmental stability.


Febrero, 2019 | DOI: 10.1002/admi.201801212

Amber, beads and social interaction in the Late Prehistory of the Iberian Peninsula: an update


Odriozola, CP; Sousa, AC; Mataloto, R; Boaventura, R; Andrade, M; Garcia, RV; Garrido-Cordero, JA; Rodriguez, E; Martinez-Blanes, JM; Aviles, MA; Daura, J; Sanz, M; Riquelme, JA
Archaeological and Anthropological Sciences, 11 (2019) 567-595

ABSTRACT

The identification of archaeological amber has been used in Iberian prehistory to evidence long-distance exchanges and engage Iberia in networks that connect western Europe with central and northern Europe, the emergence of social complexity, and the consolidation of trade networks. However, until now, no comprehensive analytical study of the Iberian amber has been produced to support any of the interpretive models currently in use. This paper approaches the analysis of Iberian Peninsula amber artefacts by considering their provenance (based on FTIR characterization), chronology, and spatial relationship with other exotica. Our work increases the number of analyzed artefacts to 156 (24%), out of the c. 647 currently known for the Iberian Peninsula. Based on these new data and a review of Murillo-Barroso and Martinon-Torres (2012), this overview outlines amber consumption patterns from the 6th to 2nd millennia BCE and demonstrates long-distance amber exchange connecting Iberia with the Mediterranean region from the Neolithic period onwards.


Febrero, 2019 | DOI: 10.1007/s12520-017-0549-7

Production of Ag-ZnO powders by hot mechanochemical processing


Guzman, D; Aguilar, C; Rojas, P; Criado, JM; Dianez, MJ; Espinoza, R; Guzman, A; Martinez, C
Transactions of nonferrous metals society of China, 29 (2019) 365-373
Reactividad de Sólidos

ABSTRACT

Ag-CdO composites are still one of the most commonly used electrical contact materials in low-voltage applications owing to their excellent electrical and mechanical properties. Nevertheless, considering the restriction on using Cd due to its toxicity, it is necessary to find alternative materials that can replace these composites. In this study, the synthesis of Ag-ZnO alloys from Ag-Zn solid solutions was investigated by hot mechanochemical processing. The hot mechanochemical processing was conducted in a modified attritor mill at 138 degrees C under flowing O-2 at 1200 cm(3)/min for 3.0 h. The microstructure and phase evolution were investigated using X-ray diffractometry, field emission gun scanning electron microscopy and transmission electron microscopy. The results suggest that it is possible to complete the oxidation of Ag-Zn solid solution by hot mechanochemical processing at a low temperature and short time. This novel synthesis route can produce Ag-ZnO composites with a homogeneous distribution of nanoscale ZnO precipitates, which is impossible to achieve using the conventional material processing methods. Considering the fact that the fundamental approach to improving electric contact material performance resides in obtaining uniform dispersion of the second-phase in the Ag matrix, this new processing route could open the possibility for Ag-ZnO composites to replace non-environmentally friendly Ag-CdO.


Febrero, 2019 | DOI: 10.1016/S1003-6326(19)64946-0

Fluorinated and Platinized Titania as Effective Materials in the Photocatalytic Treatment of Dyestuffs and Stained Wastewater Coming from Handicrafts Factories


Murcia, J.J.; Cely, A.C.; Rojas, H.A.; Hidalgo, M.C.; Navío, J.A.
Catalysts, 9 (2019) 179
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

In this study, commercial and lab-prepared TiO2 were modified by fluorination and platinum photodeposition; and the effect of these modifications over the physicochemical and photocatalytic properties of TiO2 was evaluated. It was found that F and Pt addition leads to the modification of the optical and textural properties of TiO2. The materials prepared were tested in the photocatalytic degradation of different organic dyestuffs such as methylene blue (MB) and methyl orange (MO); the degradation of commercial anilines employed in the staining of natural fibers was also evaluated. Photocatalysis was also studied in this work as an eco-friendly treatment of wastewater coming from handicrafts factories. In general it was observed that the effectiveness of the photocatalytic treatment strongly depends on the substrate to be degraded, thus, fluorinated and platinized commercial Titania (Pt-F-P25) showed the best photocatalytic performance in the MB and MO photodegradation and in contrast, in the case of the anilines the highest degradation was obtained over commercial TiO2 fluorinated (F-P25). These results can be explained by differences observed in the structure and in the adsorption of these dyestuffs over the photocatalysts surfaces. F-P25 photocatalyst also demonstrated to be the best material for the treatment of real wastewater coming from handicrafts factories.


Febrero, 2019 | DOI: 10.3390/catal9020179

Holmium doped fiber thermal sensing based on an optofluidic Fabry-Perot microresonator


Lahoz, F; Martin, IR; Soler-Carracedo, K; Caceres, JM; Gil-Rostra, J; Yubero, F
Journal of Luminescence, 206 (2019) 492-497
Nanotecnología en Superficies y Plasma

ABSTRACT

An optical temperature sensor suitable for label free liquid sensing has been designed and characterized. The sensor combines the photochemical stability of rare earth doped glasses and the high sensitivity of interferometric resonators. It is formed by a planar Eabry-Perot (FP) microcavity filled with the liquid to be monitored. A Ho3+ doped tapered optical fiber has been placed inside the microcavity surrounded by the fluid medium. An external laser is focused on the optical fiber inside the cavity to induce the luminescence of the Ho3+ ions, which couples to the FP optical resonances. The spectral position of the FP resonances is highly sensitive to the refractive index of the cavity medium. A second laser is co-aligned with the first one to locally heat the liquid medium around the optical fiber. An average blue shift of the FP resonances around 32 pm/degrees C is measured. The limit of detection of the laser induced heating of the liquid medium is about 0.3 degrees C in the biological temperature range. Alternatively, a hot-plate is used to heat the system. Interestingly, a red shift of the FP modes is observed with 75 pm/degrees C dependence and 0.12 degrees C limit of detection features.


Febrero, 2019 | DOI: 10.1016/j.jlumin.2018.10.103

Mechanism of Photoluminescence Intermittency in Organic-Inorganic Perovskite Nanocrystals


Galisteo-Lopez, JF; Calvo, ME; Rojas, TC; Miguez, H
ACS Applied Materials & Interfaces, 11 (4) (2019) 6344-6349
Materiales Ópticos Multifuncionales

ABSTRACT

Lead halide perovskite nanocrystals have demonstrated their potential as active materials for optoelectronic applications over the past few years. Nevertheless, one issue that hampers their applicability has to do with the observation of photoluminescence intermittency, commonly referred to as "blinking", as in their inorganic counterparts. Such behavior, reported for structures well above the quantum confinement regime, has been discussed to be strongly related to the presence of charge carrier traps. In this work, we analyze the characteristics of this intermittency and explore the dependence on the surrounding atmosphere, showing evidence for the critical role played by the presence of oxygen. We discuss a possible mechanism in which a constant creation/annihilation of halide-related carrier traps takes place under light irradiation, with the dominant rate being determined by the atmosphere.


Febrero, 2019 | DOI: 10.1021/acsami.8b17122

An innovative approach for micro/nano structuring plasma polymer films


Thiry, D; Vinx, N; Aparicio, FJ; Moerman, D; Lazzaroni, R; Cossement, D; Snyders, R
Thin Solid Films, 672 (2019) 26-32
Nanotecnología en Superficies y Plasma

ABSTRACT

This work aims at presenting an innovative method for tailoring the morphology of functionalized plasma polymer films (PPF). The approach is based on the formation of a plasma polymer bilayer system in which the two layers differ by their chemical composition and cross-linking degree. As a case study, propanethiol-based plasma polymer films have been investigated. As revealed by a much higher S/C ratio than in the propanethiol precursor (i.e. 0.83 vs 0.33), it has been demonstrated that the bottom layer contains a large fraction of trapped sulfur-based molecules (e.g. H2S). When further covered by a denser PPF formed at higher energetic conditions, a three-dimensional morphological reorganization takes place giving rise to the micro/nano structuration of the organic material. The shape, the dimensions as well as the density of the generated structures are found to depend on the thickness of both coatings involved in the bilayer structure, offering a great flexibility for surface engineering. Annealing experiments unambiguously confirm the major role played by the sulfur-based trapped molecules for inducing the reshaping process. The whole set of data clearly paves the way for the development of an innovative approach for finely tailoring the morphology of functionalized PPF at the micro/nano scale.


Febrero, 2019 | DOI: 10.1016/j.tsf.2018.12.050

Highly Efficient Transparent Nanophosphor Films for Tunable White-Light-Emitting Layered Coatings


Geng, DL; Lozano, G; Miguez, H
ACS Applied Materials & Interfaces, 11 (4) (2019) 4219-4225
Materiales Ópticos Multifuncionales

ABSTRACT

Bright luminescence in rare-earth (RE) nanocrystals, the so-called nanophosphors, is generally achieved by choosing a host that enables an effective excitation of the RE activator through charge or energy transfer. Although tungstate, molybdate, or vanadate compounds provide the aforementioned transfer, a comparative analysis of the efficiency of such emitters remains elusive. Herein, we perform a combined structural and optical analysis, which reveals that the tetragonal GdVO4 matrix gives rise to the highest efficiency among the different transparent nanophosphor films compared. Then, we demonstrate that by a sequential stacking of optical quality layers made of Eu3+- and Dy3+-doped nanocrystals, it is possible to attain highly transparent white-light-emitting coatings of tunable shade with photoluminescence quantum yields above 35%. Layering provides a precise dynamic tuning of the chromaticity based on the photoexcitation wavelength dependence of the emission of the nanophosphor ensemble without altering the chemical composition of the emitters or degrading their efficiency. The total extinction of the incoming radiation along with the high quantum yields achieved makes these thin-layered phosphors one of the most efficient transparent white converter coatings ever developed.


Enero, 2019 | DOI: 10.1021/acsami.8b17368

Influence of Al and Y content on the oxidation resistance of CrAlYN protective coatings for high temperature applications: New insights about the Y role


Rojas, TC; Dominguez-Meister, S; Brizuela, M; Sanchez-Lopez, JC
Journal of Alloys and Compounds, 777 (2019) 1172-1181
Tribología y Protección de Superficies

ABSTRACT

CrAlYN hard coatings with two different average Al contents: similar to 16 at.% and similar to 25 at.%, and Y concentration varying between 1.2 and 5.7 at.% were deposited by direct current reactive magnetron co-sputtering of mixed Cr-Al and Y targets on commercial M2 steel substrates. The samples were heated to 1000 degrees C in air during 2 h to study their oxidation resistance and thermal stability. The Y content is critical and the coatings present different behaviour depending on the Al content. The best oxidation resistance and thermal stability are obtained for the coating with similar to 16 at.% Al and 3.4 at.% Y. The initial film microstructure and the cubic phase (fcc-CrAlN) were retained, and a thin (Cr,Al)(2)O-3 oxide protective scale was formed. At lower Y content (1.2 at.%) iron, from the substrate crosses the coating, while a higher content (4.6 at.%) avoided the iron diffusion at the expense of a thicker oxide scale with new oxide phases. The coatings with higher Al content (similar to 25 at. %) were not thermally stable at 1000 degrees C. A good oxidation resistance was obtained for 2.6 at.% of Y although new phases (hcp-AlN and Cr-Fe) were formed. Higher amount of yttrium (similar to 5.7 at. %) led to the complete oxidation of the coating. 


Enero, 2019 | DOI: 10.1016/j.jallcom.2018.09.280

Coupling of Ag2CO3 to an optimized ZnO photocatalyst: Advantages vs. disadvantages


P. Sánchez-Cid; C. Jaramillo-Páez; J.A. Navío; A.N. Martín-Gómez; M.C. Hidalgo
Journal of Photochemistry and Photobiology A: Chemistry, 369 (2019) 119-132
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

With the aim of improving the photocatalytic properties of a previously optimized zinc oxide photocatalyst, the effect of the incorporation of different amounts of Ag2CO3 on the aforementioned ZnO has been studied. For this purpose we report the synthesis, by means of simple precipitation procedures, of bare ZnO and Ag2CO3 samples as well as the coupled materials ZnO/Ag2CO3 (X) (where X = 1%, 2%, 4% and 5% in molar percentages). Both, single and coupled materials have been characterized by different techniques (XRD, XRF, N2-absorption, SEM, TEM, UV–vis/DRS and XPS). To assess the advantages or disadvantages that Ag2CO3 addition could have over the optimized ZnO, the photocatalytic properties have been established by following the photo-degradation of selected toxic molecules, both in the UV and in the visible, as well as using complementary techniques of liquid medium analyses (TOC and Atomic Emission Spectrometry with plasma ICP). Three selected substrates were chosen: Rhodamine B (RhB) as a dye, and phenol and caffeine as colourless recalcitrant toxic molecules.
Our results suggest that although the use of Ag2CO3 could be beneficial to implement the optical absorption towards the visible region, however, other effects have to be bore in mind, such as the photo-corrosion of Ag2CO3 and the chemical structure of the chosen substrate, to elucidate whether the addition of Ag2CO3 has beneficial or detrimental effects on the photocatalytic properties of the coupled ZnO/Ag2CO3 materials.


Enero, 2019 | DOI: 10.1016/j.jphotochem.2018.10.024

Influence of framework and interlayer on the colloidal stability of design swelling high-charged micas


Osuna, FJ; Cota, A; Fernandez, MA; Pavon, E; Sanchez, RMT; Alba, MD
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 561 (2019) 32-38
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

Stability of colloidal clay minerals dispersion of fundamental in many industrial processes. Therefore, surface charge of the synthetic swelling high-charged mica family, Na-Mica-n (n = 2 or 4, n is the total layer charge) were investigated to study its colloidal dispersion stability as a function of the framework and interlayer space composition. Na-Mica-n (n = 2 or 4) micas were synthesized and functionalized with ethylammonium, mercaptoethylammonium or octadecylammonium. Their zeta-potential evolutions as a function of solution pH were correlated with their structural, compositional and morphological characteristics. The results have shown that the total charge of swelling high charged micas, Mica-n, didn´t affect significantly their colloidal dispersion stability, the interlayer composition and interlayer cation arrangement were the main factors of colloidal behaviour. The synthesis and functionalization of those synthetic micas can be tuned for their optimal use.


Enero, 2019 | DOI: 10.1016/j.colsurfa.2018.09.086

Synthesis and Characterization of ZnO-ZrO2 Nanocomposites for Photocatalytic Degradation and Mineralization of Phenol


Lopez, MCU; Lemus, MAA; Hidalgo, MC; Gonzalez, RL; Owen, PQ; Oros-Ruiz, S; Lopez, SAU; Acosta, J
Journal of Nanomaterials (2019) art. 1015876, 12 pages
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

ZnO-ZrO2 nanocomposites using zinc (II) acetylacetonate and different ZnO contents (13, 25, 50, and 75% mol) were synthesized through sol-gel method. The synthesis process was strongly related to nanocomposite properties especially on their structural composition. The obtained ZnO-ZrO2 nanomaterials presented tetragonal crystalline structure for zirconia whereas hexagonal one was formed in ZnO. Raman spectroscopy and XRD patterns confirmed the formation of tetragonal zirconia whereas inhibition of monoclinic structure was observed. Addition of ZnO affected the pore size distribution of the composite, and the measured specific surface areas were from 10 m2/g (for pure ZnO) to 46 m2/g (pristine ZrO2). Eg values of ZrO2 were modified by ZnO addition, since calculated values using Kubelka-Munk’s function varied from 4.73 to 3.76 eV. The morphology and size of the nanomaterials investigated by electron microscopy showed formation of nanorods for ZnO with sizes ranging from 50 nm to 300 nm while zirconia was formed by smaller particles (less than 50 nm). The main advantage of using the nanocomposite for photocatalytic degradation of phenol was the mineralization degree, since 75ZnO-ZrO2 nanocomposite surpassed mineralization reached by pure ZnO and also inhibited formation of undesirable intermediates.


Enero, 2019 | DOI: 10.1155/2019/1015876

Flexible nanophosphor films doped with Mie resonators for enhanced out-coupling of the emission


Miranda-Munoz, JM; Geng, DL; Calvo, ME; Lozano, G; Miguez, H
Journal of Materials Chemistry C, 7 (2019) 267-274
Materiales Ópticos Multifuncionales

ABSTRACT

Herein, we present a general method to prepare self-standing flexible photoluminescent coatings of controlled opacity for integration into light-emitting diodes (LEDs) employing cost-effective solution-processing methods. From colloidal suspensions of nano-sized phosphors, we fabricate light-emitting transparent films that can be doped with spherical scatterers, which act as Mie resonators that trigger a controlled photoluminescence enhancement, evidenced by the reduction of the guided light along the layer. This results in an enhanced emission compared to that extracted from a bare phosphor layer. We show not only that emission is visible under ultraviolet-LED illumination for both rigid and flexible versions of the coatings, but we also prove the feasibility of the integration of these flexible conversion layers into such devices. We believe these results can contribute to develop more efficient and cost-effective illumination sources by providing efficient and easy-to-handle conversion layers susceptible to excitation by LEDs emitting at wavelengths in the near UV region.


Enero, 2019 | DOI:

Isotope Labelling for Reaction Mechanism Analysis in DBD Plasma Processes


Navascues, P; Obrero-Perez, JM; Cotrino, J; Gonzalez-Elipe, AR; Gomez-Ramirez, A
Catalysts, 9(1) (2019) 45
Nanotecnología en Superficies y Plasma

ABSTRACT

Dielectric barrier discharge (DBD) plasmas and plasma catalysis are becoming an alternative procedure to activate various gas phase reactions. A low-temperature and normal operating pressure are the main advantages of these processes, but a limited energy efficiency and little selectivity control hinder their practical implementation. In this work, we propose the use of isotope labelling to retrieve information about the intermediate reactions that may intervene during the DBD processes contributing to a decrease in their energy efficiency. The results are shown for the wet reforming reaction of methane, using D2O instead of H2O as reactant, and for the ammonia synthesis, using NH3/D-2/N-2 mixtures. In the two cases, it was found that a significant amount of outlet gas molecules, either reactants or products, have deuterium in their structure (e.g., HD for hydrogen, CDxHy for methane, or NDxHy for ammonia). From the analysis of the evolution of the labelled molecules as a function of power, useful information has been obtained about the exchange events of H by D atoms (or vice versa) between the plasma intermediate species. An evaluation of the number of these events revealed a significant progression with the plasma power, a tendency that is recognized to be detrimental for the energy efficiency of reactant to product transformation. The labelling technique is proposed as a useful approach for the analysis of plasma reaction mechanisms.


Enero, 2019 | DOI: 10.3390/catal9010045

Enhancing Luminescence and X-ray Absorption Capacity of Eu3+:LaF3 Nanoparticles by Bi3+ Codoping


Mancebo, DG; Becerro, AI; Corral, A; Moros, M; Balcerzyk, M; de la Fuente, JM; Ocana, M
ACS Omega, 4 (2019) 765-774
Materiales Coloidales

ABSTRACT

Bi3+ codoping has been proposed in this work with a twofold objective, namely, enhancing the luminescence emission of Eu3+:LaF3 nanoparticles (NPs) and increasing their X-ray attenuation capacity, with the purpose of obtaining a bimodal bioprobe for luminescence bioimaging and X-ray computed tomography. The synthesis method, reported here for the first time for LaF3 particles, allowed obtaining uniform, nonaggregated NPs using a homogeneous precipitation in polyol medium at room temperature in just 2 h. The simplicity of the synthesis method allows the large-scale production of NPs. LaF3 NPs with different Eu3+ contents were first synthesized to find the critical Eu3+ concentration, producing the highest emission intensity. This concentration was subsequently used to fabricate Bi3+-Eu3+-codoped LaF3 NPs using the same method. The emission intensity of the codoped NPs increased in more than one order of magnitude, thanks to the possibility of excitation through the Bi3+. Eu3+ energy-transfer band. The luminescence properties of the codoped NPs were analyzed in detail to find the mechanism responsible for the emission enhancement. Finally, it was demonstrated that the high atomic number of Bi3+, higher than that of lanthanides, was an added value of the material because it increased its X-ray attenuation capacity. In summary, the LaF3 NPs codoped with Eu3+ and Bi3+ presented in this work are promising candidates as a bimodal bioprobe for luminescence bioimaging and X-ray computed tomography.


Enero, 2019 | DOI: 10.1021/acsomega.8b03160

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