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2021


Dehydration of glucose to 5-Hydroxymethlyfurfural on bifunctional carbon catalysts


Bounoukta, CE; Megias-Sayago, C; Ammari, F; Ivanova, S; Monzon, A; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 286 (2021) 119938
Química de Superficies y Catálisis

ABSTRACT

The proposed study tries to reply on one important question concerning glucose dehydration: What is the role of bare or tandem Lewis/Bronsted acid sites in the reaction and which are better? A series of mono and bifunctional catalyst are designed and screened for the glucose dehydration reaction. The results clearly reveal that catalyst activity is a function of catalyst composition. The presence of Lewis sites the reaction toward first step isomerization, while the Brunsted acid dehydrate directly glucose to HMF via levoglucosane intermediate. This study proposed also a kinetic modelling of the included reactions and their contrast with the empirical observations.


Junio, 2021 | DOI: 10.1016/j.apcatb.2021.119938

IR spectroscopic insights into the coking-resistance effect of potassium on nickel-based catalyst during dry reforming of methane


Azancot, L; Bobadilla, LF; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 285 (2021) 119822
Química de Superficies y Catálisis

ABSTRACT

Dry reforming of methane (DRM) is an effective catalytic route for transforming CO2 and CH4 into valuable syngas and thus potentially attractive for mitigating the emission of environmental harmful gases. Therefore, it is crucial to develop rationally Ni-based catalysts highly resistant to coking and sintering. In this scenario, the addition of small amounts of potassium to nickel catalyst increases their resistance to coking during dry reforming of methane. Nonetheless, the specific role of potassium in these catalysts not have been fully understood and there are still important discrepancies between the different reported studies. This work provides a new approach on the anticoking nature of a K-promoted Ni catalyst by means of a combined IR spectroscopic study of in situ characterization by CO adsorption under static conditions and operando DRIFTS measurements under dynamic conditions of DRM reaction. The involved surface species formed during the reaction were elucidated by transient and steady-state operando DRIFTS studies. It was revealed that the existence of Ni-K interfacial sites favours the gasification of carbonaceous deposits towards reverse Boudouard reaction and reduces the sticking probability of CO2 dissociative adsorption. Moreover, the presence of strongly Mg-O-K basic sites leads to the formation of carbonate intermediates that are subsequently reduced into CO gaseous towards the associative mechanism by RWGS reaction. These results provide a fundamental understanding of the relevant anticoking effect of potassium on Ni-based catalysts.


Mayo, 2021 | DOI: 10.1016/j.apcatb.2020.119822

Functionalized biochars as supports for Pd/C catalysts for efficient hydrogen production from formic acid


Santos, JL; Megias-Sayago, C; Ivanova, S; Centeno, MA; Odriozola, JA
Applied Catalysis B-Environmental, 282 (2021) 119615
Química de Superficies y Catálisis

ABSTRACT

Biomass waste product was used to generate biochars as catalytic supports for selective hydrogen production from formic acid. The supports were obtained after pyrolysis in CO2 atmosphere of non-pretreated and che-mically ZnCl2 activated raw materials (vine shoot and crystalline cellulose). The support series includes materials with different textural properties and surface chemistry. The support nature and especially textural properties firstly affects significantly Pd size and dispersion and its interaction with the support and secondly influence in a great extent the catalytic behavior of the final material. The presence of prevailing mesoporous character appeared to be the most important parameter influencing formic acid dehydrogenation and overall hydrogen production.


Marzo, 2021 | DOI: 10.1016/j.apcatb.2020.119615

Structure-sensitivity of formic acid dehydrogenation reaction over additive-free Pd NPs supported on activated carbon


Santos, J.L.; Megías-Sayago, C.; Ivanova, S.; Centeno, M.A.; Odriozola, J.A.
Chemical Engineering Journal, 420 (2021) 127641
Química de Superficies y Catálisis

ABSTRACT

In this study the size-activity dependence of palladium based catalysts in formic acid dehydrogenation reaction was investigated and evaluated. A wide range of particle sizes was considered and the catalyst series were prepared upon variation of some synthetic parameters, precursor and solvent nature in particular. Synthesis method variations affect significantly Pd particle size and results in diverse activity toward hydrogen production. An optimal size was observed and explained by the diverse proportion of low and high coordinated Pd states available for different samples within the series. The evaluation of particles much bigger than 6 nm changes importantly the fraction of high and low coordination atoms and allows the clear confirmation of the importance of the presence of low coordination atoms on the surface of catalyst.


Septiembre, 2021 | DOI: 10.1016/j.cej.2020.127641

Kinetics and cyclability of limestone (CaCO3) in presence of steam during calcination in the CaL scheme for thermochemical energy storage


Arcenegui-Troya, J; Sanchez-Jimenez, PE; Perejon, A; Moreno, V; Valverde, JM; Perez-Maqueda, LA
Chemical Engineering Journal, 417 (2021) 129194
Reactividad de Sólidos

ABSTRACT

In the present work, we explore the use of steam in the CaCO3 calcination step of the Calcium Looping process devised for thermochemical energy storage (CaL-TCES). Steam produces a double benefit: firstly, it fastens calcination, allowing a reduction of the temperature needed to attain full calcination in short residence times, as those required in practice, resulting in energy savings. This behaviour is justified on the basis of a kinetics study results obtained from a non-parametric kinetic analysis, which demonstrate that the presence of steam during calcination can reduce the apparent activation energy from 175 kJ/mol to 142 kJ/mol with a steam's partial pressure of 29%. In addition, the results obtained for multicycle CaL-TCES tests show that steam alleviates the deactivation of the sorbent, which is one of the main limiting factors of this technology. This behaviour is explained in terms of the effect of steam on the microstructure of the regenerated CaO. Importantly, the values of residual conversion attained by calcining in steam are higher than those without steam.


Agosto, 2021 | DOI: 10.1016/j.cej.2021.129194

Calcination under low CO2 pressure enhances the calcium Looping performance of limestone for thermochemical energy storage


Sarrion, B; Perejon, A; Sanchez-Jimenez, PE; Amghar, N; Chacartegui, R; Valverde, JM; Perez-Maqueda, LA
Chemical Engineering Journal, 417 (2021) 127922
Reactividad de Sólidos

ABSTRACT

The Calcium Looping performance of limestone for thermochemical energy storage has been investigated under novel favorable conditions, which involve calcination at moderate temperatures under CO2 at low pressure (0.01 and 0.1 bar) and carbonation at high temperature under CO2 at atmospheric pressure. Calcining at low CO2 pressures allows to substantially reduce the temperature to achieve full calcination in short residence times. Moreover, it notably enhances CaO multicycle conversion. The highest values of conversion are obtained for limestone samples calcined under 0.01 bar CO2 at 765 degrees C. Under these conditions, the residual conversion is increased by a factor of 10 as compared to conditions involving calcination under CO2 at atmospheric pressure. The enhancement of CaO conversion is correlated to the microstructure of the CaO samples obtained after calcination. As seen from SEM, BET surface and XRD analysis, calcination under low CO2 pressure leads to a remarkable decrease of pore volume and CaO crystallite size. Consequently, CaO surface area available for carbonation in the fast reaction-controlled regime and therefore reactivity in short residence times is promoted.


Agosto, 2021 | DOI: 10.1016/j.cej.2020.127922

Patterning and control of the nanostructure in plasma thin films with acoustic waves: mechanical vs. electrical polarization effects


García-Valenzuela, A.; Fakhouri, A.; Oliva-Ramírez, M.; Rico-Gavira, V.; Rojas, T.C.; Alvarez, R.; Menzel, S.B.; Palmero, A.; Winkler, A.; González-Elipe, A.R.
Materials Horizons, 8 (2021) 515-524
Nanotecnología en Superficies y Plasma - Tribología y Protección de Superficies

ABSTRACT

Nanostructuration and 2D patterning of thin films are common strategies to fabricate biomimetic surfaces and components for microfluidic, microelectronic or photonic applications. This work presents the fundamentals of a surface nanotechnology procedure for laterally tailoring the nanostructure and crystalline structure of thin films that are plasma deposited onto acoustically excited piezoelectric substrates. Using magnetron sputtering as plasma technique and TiO2 as case example, it is demonstrated that the deposited films depict a sub-millimetre 2D pattern that, characterized by large lateral differences in nanostructure, density (up to 50%), thickness, and physical properties between porous and dense zones, reproduces the wave features distribution of the generated acoustic waves (AW). Simulation modelling of the AW propagation and deposition experiments carried out without plasma and under alternative experimental conditions reveal that patterning is not driven by the collision of ad-species with mechanically excited lattice atoms of the substrate, but emerges from their interaction with plasma sheath ions locally accelerated by the AW-induced electrical polarization field developed at the substrate surface and growing film. The possibilities of the AW activation as a general approach for the tailored control of nanostructure, pattern size, and properties of thin films are demonstrated through the systematic variation of deposition conditions and the adjustment of AW operating parameters.


Febrero, 2021 | DOI: 10.1039/D0MH01540G

Photocatalytic oxidation of pollutants in gas-phase via Ag3PO4-based semiconductor photocatalysts: Recent progress, new trends, and future perspectives


Y. Naciri; A. Hsini; A. Bouziani; R. Djellabi; Z. Ajmal; M. Laabd; J.A. Navío; A. Mills; C.L. Bianchi; H.Li; B. Bakiz; A. Albourine
Critical Reviews in Environmental Science and Technology,
Fotocatálisis Heterogénea: Aplicaciones

ABSTRACT

Air pollution has become a significant challenge for both developing and developed nations. due to its close association with numerous fatal diseases such as cancer, respiratory, heart attack, and brain stroke. Over recent years, heterogeneous semiconductor photocatalysis has emerged as an effective approach to air remediation due to the ease of scale-up, ready application in the field, use of solar light and ready availability of a number of different effective photocatalysts. To date, most work in this area has been conducted using UV-absorbing photocatalysts, such as TiO2 and ZnO; However, recent studies have revealed Ag3PO4 as an attractive, visible-light-absorbing alternative, with a bandgap of 2.43 eV. In particular, this material has been shown to be an excellent photocatalyst for the removal of many types of pollutants in the gas phase. However, the widespread application of Ag3PO4 is restricted due to its tendency to undergo photoanodic corrosion and the poor reducing power of its photogenerated conductance band electrons, which are unable to reduce O2 to superoxide •O2 −. These limitations are critically evaluated in this review. In addition, recent studies on the modification of Ag3PO4 via combination with the conventional heterojunctions or Z-scheme junctions, as well as the photocatalytic mechanistic pathways for enhanced gas-pollutants removal, are summarized and discussed. Finally, an overview is given on the future developments that are required in order to overcome these challenges and so stimulate further research into this promising field.


Febrero, 2021 | DOI: 10.1080/10643389.2021.1877977

Ni/YMnO3 perovskite catalyst for CO2 methanation


Gonzalez-Castano, M; de Miguel, JCN; Penkova, A; Centeno, MA; Odriozola, JA; Arellano-Garcia, H
Applied Materials Today, 23 (2021) 101055
Química de Superficies y Catálisis

ABSTRACT

This work proposes an innovative Ni catalyst supported over YMnO3 perovskite as a promising catalytic system for CO2 methanation reaction. Under reductive conditions, the attendance of Mn redox couples within the layered perovskite structure promotes the constitution of sub-stoichiometric YMnO3-x units which, by means of the flexible YMnO3-x reorganization capacity, results in boosted anionic mobility's. The competitive turnover frequencies (20.1 and 17.0 s(-1) at 400 degrees C under dry- and steamed- CO2 methanation conditions) displayed by Ni/YMnO3 system were related to the synergism between strongly interacting Ni particles with partially reduced YMnO3-x perovskites. The optimal Ni dispersions, for which no relevant signs of sintering issues were discerned, combined to effective role of oxygen vacancies towards the dissociative activation of CO2 molecules enabled highly active and stable catalytic behaviours with no evidence of cooking phenomena. On evaluating the water presence within CO2 methanation feedstock's, the deprived catalytic behaviour was fundamentally associated to depleted oxygen vacancies concentrations and promoted WGS side reactions.


Junio, 2021 | DOI: 10.1016/j.apmt.2021.101055

Enhanced Directional Light Extraction from Patterned Rare-Earth Phosphor Films


Cabello-Olmo, E; Molet, P; Mihi, A; Lozano, G; Miguez, H
Advanced Optical Materials, 9 (2021) 2001611
Materiales Ópticos Multifuncionales

ABSTRACT

The combination of light‐emitting diodes (LEDs) and rare earth (RE) phosphors as color‐converting layers comprises the basis of solid‐state lighting. Indeed, most LED lamps include a photoluminescent coating made of phosphor material, i.e., crystalline matrix suitably doped with RE elements, to produce white light from a blue or ultraviolet LED chip. Transparent phosphor‐based films constitute starting materials for new refined emitters that allow different photonic designs to be implemented. Among the different photonic strategies typically employed to tune or enhance emission, surface texturing has proved its versatility and feasibility in a wide range of materials and devices. However, most of the nanofabrication techniques cannot be applied to RE phosphors directly because of their chemical stability or because of their cost. The first monolithic patterned structure of down‐shifting nanophosphors with square arrays of nanoholes with different lattice parameters is reported in this study. It is shown that a low‐cost soft‐nanolithography procedure can be applied to red‐emitting nanophosphors (GdVO4:Eu3+ nanocrystals) to tune their emission properties, attaining a twofold directional enhancement of the emitted light at predesigned emission wavelengths in specific directions.


Enero, 2021 | DOI: 10.1002/adom.202001611

The Complex Interplay of Lead Halide Perovskites with Their Surroundings


Galisteo-Lopez, JF; Calvo, ME; Miguez, H
Advanced Optical Materials, (2021) 2100133
Materiales Ópticos Multifuncionales

ABSTRACT

Photoexcitation of lead halide perovskites induces a restructuration of the material that simultaneously enhances its emission properties and triggers its degradation. These concomitant processes are strongly dependent on the surroundings of the perovskite, both while and after being processed, underlining the relevance the environment and the interfacial design have in the stability and performance of these materials and the devices based on them. This shocking observation reveals that when subjected to external illumination, lead halide perovskites undergo a number of photophysical processes that strongly modify their structure and thus their optoelectronic properties. Such photoinduced instability stems from a defective structure directly linked to the low-temperature and solution-processed fabrication routes generally employed to build perovskite solar cells with efficiencies comparable to state-of-the-art values. On the other hand, these same inexpensive and unsophisticated procedures make this material a promising component in energy conversion devices. Here, an analysis is provided regarding the different impact on the perovskite structure, hence on its optoelectronic performance, that the interaction with its surroundings has, providing specific examples that highlight this interplay, describing the kind of modification it induces, and listing the related effects on the optoelectronic properties that should be accounted for when characterizing them.


Marzo, 2021 | DOI: 10.1002/adom.202100133

Anisotropic Resistivity Surfaces Produced in ITO Films by Laser-Induced Nanoscale Self-organization


Lopez-Santos, C; Puerto, D; Siegel, J; Macias-Montero, M; Florian, C; Gil-Rostra, J; Lopez-Flores, V; Borras, A; Gonzalez-Elipe, AR; Solis, J
Advanced Optical Materials, 9 (2021) 2001086
Nanotecnología en Superficies y Plasma

ABSTRACT

Highly anisotropic resistivity surfaces are produced in indium tin oxide (ITO) films by nanoscale self-organization upon irradiation with a fs-laser beam operating at 1030 nm. Anisotropy is caused by the formation of laser-induced periodic surface structures (LIPSS) extended over cm-sized regions. Two types of optimized structures are observed. At high fluence, nearly complete ablation at the valleys of the LIPSS and strong ablation at their ridges lead to an insulating structure in the direction transverse to the LIPSS and conductive in the longitudinal one. A strong diminution of In content in the remaining material is then observed, leading to a longitudinal resistivity rho(L) approximate to 1.0 omega center dot cm. At a lower fluence, the material at the LIPSS ridges remains essentially unmodified while partial ablation is observed at the valleys. The structures show a longitudinal conductivity two times higher than the transverse one, and a resistivity similar to that of the pristine ITO film (rho approximate to 5 x 10(-4) omega center dot cm). A thorough characterization of these transparent structures is presented and discussed. The compositional changes induced as laser pulses accumulate, condition the LIPSS evolution and thus the result of the structuring process. Strategies to further improve the achieved anisotropic resistivity results are also provided.


Enero, 2021 | DOI: 10.1002/adom.202001086

The Role of the Atmosphere on the Photophysics of Ligand-Free Lead-Halide Perovskite Nanocrystals


Moran-Pedroso, M; Rubino, A; Calvo, ME; Espinos, JP; Galisteo-Lopez, JF; Miguez, H
Advanced Optical Materials, (2021) 2100605
Materiales Ópticos Multifuncionales

ABSTRACT

Lead halide perovskite (LHP) nanocrystals (NCs) have gained attention over the past decade due to their outstanding optoelectronic properties, making them a suitable material for efficient photovoltaic and light emitting devices. Due to its soft nature, these nanostructures undergo strong structural changes upon irradiation, where these light-induced processes are strongly influenced by the environment. Since most processing routes for LHP NCs are based on colloidal approaches, the role of factors such as stabilizing ligands or solvents is usually hard to disentangle from the interaction of external radiation with the perovskite material. Employing a recently proposed synthetic approach, where ligand-free NCs can be grown within metal-oxide-based insulating nanoporous matrices, it has been feasible to perform a clean study of the effect of the surrounding atmosphere on the photophysical properties of perovskite NCs, avoiding the interference of protective capping layers or solvents. Simultaneous light-induced photo-activation and darkening processes are monitored and disentangled, and their relation with bulk and surface processes, respectively, demonstrated.


Junio, 2021 | DOI: 10.1002/adom.202100605

Structural Evolution in Iron-Catalyzed Graphitization of Hard Carbons


Gomez-Martin, A; Schnepp, Z; Ramirez-Rico, J
Chemistry of Materials, 33 (2021) 3087-3097
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

Despite the recent interest in catalytic graphitization to obtain graphite-like materials from hard-carbon sources, many aspects of its mechanism are still poorly unknown. We performed a series of in situ experiments to study phase transformations during graphitization of a hard-carbon precursor using an iron catalyst at temperatures up to 1100 degrees C and ex situ total scattering experiments up to 2000 degrees C to study the structural evolution of the resulting graphitized carbon. Our results show that upon heating and cooling, iron undergoes a series of reductions to form hematite, magnetite, and wustite before forming a carbide that later decomposes into metallic iron and additional graphite and that the graphitization fraction increases with increasing peak temperature. Structural development with temperature results in decreasing sheet curvature and increased stacking, along with a decrease in turbostratic disorder up to 1600 degrees C. Higher graphitization temperatures result in larger graphitic domains without further ordering of the graphene sheets. Our results have implications for the synthesis of novel biomass-derived carbon materials with enhanced crystallinity.


Mayo, 2021 | DOI: 10.1021/acs.chemmater.0c04385

Swelling layered minerals applications: A solid state NMR overview


Pavon, E; Alba, MD
Progress in Nuclear Magnetic Resonance Spectroscopy, 124 (2021) 99-128
Materiales y Procesos Catalíticos de Interés Ambiental y Energético

ABSTRACT

Swelling layered clay minerals form an important sub-group of the phyllosilicate family. They are characterized by their ability to expand or contract in the presence or absence of water. This property makes them useful for a variety of applications, ranging from environmental technologies to heteroge-neous catalysis, and including pharmaceutical and industrial applications. Solid State Nuclear Magnetic Resonance (SS-NMR) has been extensively applied in the characterization of these materials, providing useful information on their dynamics and structure that is inaccessible using other characterization methods such as X-ray diffraction. In this review, we present the key contributions of SS-NMR to the understanding of the mechanisms that govern some of the main applications associated to swelling clay minerals. The article is divided in two parts. The first part presents SS-NMR conventional applications to layered clay minerals, while the second part comprises an in-depth review of the information that SS-NMR can provide about the different properties of swelling layered clay minerals.


Junio, 2021 | DOI: 10.1016/j.pnmrs.2021.04.001

Waterproof-breathable films from multi-branched fluorinated cellulose esters


Tedeschi, G; Guzman-Puyol, S; Ceseracciu, L; Benitez, JJ; Goldoni, L; Koschella, A; Heinze, T; Cavallo, G; Dichiarante, V; Terraneo, G; Athanassiou, A; Metrangolo, P; Heredia-Guerrero, JA
Carbohydrate Polymers, 271 (2021) 118031
Materiales de Diseño para la Energía y Medioambiente

ABSTRACT

Cellulose ester films were prepared by esterification of cellulose with a multibranched fluorinated carboxylic acid, "BRFA" (BRanched Fluorinated Acid), at different anhydroglucose unit:BRFA molar ratios (i.e., 1:0, 10:1, 5:1, and 1:1). Morphological and optical analyses showed that cellulose-BRFA materials at molar ratios 10:1 and 5:1 formed flat and transparent films, while the one at 1:1 M ratio formed rough and translucent films. Degrees of substitution (DS) of 0.06, 0.09, and 0.23 were calculated by NMR for the samples at molar ratios 10:1, 5:1, and 1:1, respectively. ATR-FTIR spectroscopy confirmed the esterification. DSC thermograms showed a single glass transition, typical of amorphous polymers, at -11 degrees C. The presence of BRFA groups shifted the mechanical behavior from rigid to ductile and soft with increasing DS. Wettability was similar to standard fluoropolymers such as PTFE and PVDF. Finally, breathability and water uptake were characterized and found comparable to materials typically used in textiles.


Noviembre, 2021 | DOI: 10.1016/j.carbpol.2021.118031

Solid-State Dewetting of Gold on Stochastically Periodic SiO2 Nanocolumns Prepared by Oblique Angle Deposition


Oliva-Ramirez, M; Wang, D; Flock, D; Rico, V; Gonzalez-Elipe, AR; Schaaf, P
ACS Applied Materials & Interfaces, 13 (2021) 11385-11395
Nanotecnología en Superficies y Plasma

ABSTRACT

Solid-state dewetting (SSD) on patterned substrates is a straightforward method for fabricating ordered arrays of metallic nanoparticles on surfaces. However, a drawback of this procedure is that the patterning of substrates usually requires time-consuming and expensive two-dimensional (2D) fabrication methods. Nanostructured thin films deposited by oblique angle deposition (OAD) present at the surface a form of stochastically arranged periodic bundles of nanocolumns that might act as a patterned template for fabricating arrays of nanoparticles by SSD. In this work, we explore this concept and investigate the effect of three different types of OAD SiO2 thin films on the SSD of Au deposited on their surface. We demonstrate that the size and spatial distribution of the particles can be tailored through the surface morphology of these OAD film substrates. It has been found that the SSD of the evaporated Au layer gives rise to a bimodal size distribution of particles. A majority of them appeared as mesoparticles with sizes.100 nm and the rest as nanoparticles with similar to 10 nm, respectively, located either on top of the nanocolumns following their lateral distribution (i.e., resulting from a patterning effect) or incorporated inside the open mesopores existing among them. Moreover, on the SiO2-OAD thin films where interconnected nanocolumnar bundles arrange in the form of discrete motifs, the patterning effect gave rise to the formation of approximately one Au mesoparticle per motif, which is one of the assets of patterned SSD. The morphological, optical (i.e., plasmon resonance), and crystalline structural characteristics of Au mesoparticles suggest that the interplay between a discontinuous nanocolumnar surface acting as a template and the poor adhesion of Au onto SiO2 are key factors for the observed template effect controlling the SSD on the surface of OAD thin films.


Marzo, 2021 | DOI: 10.1021/acsami.0c19327

Form Birefringence in Resonant Transducers for the Selective Monitoring of VOCs under Ambient Conditions


Oliva-Ramirez, Manuel; Lopez-Santos, Carmen; Berthon, Hermine; Goven, Mathilde; Portoles, Jose; Gil-Rostra, Jorge; Gonzalez-Elipe, Agustin R.; Yubero, Francisco
ACS Applied Materials & Interfaces, 13 (2021) 19148-19158
Nanotecnología en Superficies y Plasma

ABSTRACT

In this work, we have developed a new kind of nanocolumnar birefringent Bragg microcavity (BBM) that, tailored by oblique angle deposition, behaves as a selective transducer of volatile organic compounds (VOCs). Unlike the atomic lattice origin of birefringence in anisotropic single crystals, in the BBM, it stems from an anisotropic self-organization at the nanoscale of the voids and structural elements of the layers. The optical adsorption isotherms recorded upon exposure of these nanostructured systems to water vapor and VOCs have revealed a rich yet unexplored phenomenology linked to their optical activity that provides both capacity for vapor identification and partial pressure determination. This photonic response has been reproduced with a theoretical model accounting for the evolution of the form birefringence of the individual layers upon vapor condensation in nanopores and internanocolumnar voids. BBMs that repel water vapor but are accessible to VOCs have been also developed through grafting of their internal surfaces with perfluorooctyltriethoxysilane molecules. These nanostructured photonic systems are proposed for the development of transducers that, operating under environmental conditions, may respond specifically to VOCs without any influence by the degree of humidity of the medium.


Abril, 2021 | DOI: 10.1021/acsami.1c02499

Highly Versatile Upconverting Oxyfluoride-Based Nanophosphor Films


Ngo, TT; Cabello-Olmo, E; Arroyo, E; Becerro, AI; Ocana, M; Lozano, G; Miguez, H
ACS Applied Materials & Interfaces, 13 (2021) 30051-30060
Materiales Ópticos Multifuncionales - Materiales Coloidales

ABSTRACT

Fluoride-based compounds doped with rare-earth cations are the preferred choice of materials to achieve efficient upconversion, of interest for a plethora of applications ranging from bioimaging to energy harvesting. Herein, we demonstrate a simple route to fabricate bright upconverting films that are transparent, self-standing, flexible, and emit different colors. Starting from the solvothermal synthesis of uniform and colloidally stable yttrium fluoride nanoparticles doped with Yb3+ and Er3+, Ho3+, or Tm3+, we find the experimental conditions to process the nanophosphors as optical quality films of controlled thickness between few hundreds of nanometers and several micrometers. A thorough analysis of both structural and photophysical properties of films annealed at different temperatures reveals a tradeoff between the oxidation of the matrix, which transitions through an oxyfluoride crystal phase, and the efficiency of the upconversion photoluminescence process. It represents a significant step forward in the understanding of the fundamental properties of upconverting materials and can be leveraged for the optimization of upconversion systems in general. We prove bright multicolor upconversion photoluminescence in oxyfluoride-based phosphor transparent films upon excitation with a 980 nm laser for both rigid and flexible versions of the layers, being possible to use the latter to coat surfaces of arbitrary shape. Our results pave the way toward the development of upconverting coatings that can be conveniently integrated in applications that demand a large degree of versatility.


Junio, 2021 | DOI: 10.1021/acsami.1c07012

Active sites and optimization of mixed copper-cobalt oxide anodes for anion exchange membrane water electrolysis


Lopez-Fernandez, E; Gil-Rostra, J; Escudero, C; Villar-Garcia, IJ; Yubero, F; Consuegra, AD; Gonzalez-Elipe, AR
Journal of Power Sources, 485 (2021) 229217
Nanotecnología en Superficies y Plasma

ABSTRACT

The optimization of the catalysts incorporated to the electrodes for anion exchange membrane water electmlysers is a key issue to maximize their performance through the improvement of the oxygen evolution reaction (OER) yield. In this work, we show that the modification of the microstructure and the chemical properties of a mixed copper-cobalt oxide anode may contribute to increase the activity of this reaction. For this purpose, the OER has been systematically studied, either in a half cell or in a membrane electrode assembly configuration, as a function of the load and agglomeration degree of the catalysts used as electrodes, as prepared on a carbon paper support by magnetron sputtering deposition in an oblique angle configuration. Chemical analysis by X-ray absorption spectroscopy and electrochemical analysis by cyclic voltammetry and impedance spectroscopy have shown that cobalt-copper mixed oxide catalysts with a 1.8 Co/Cu atomic ratio and about one micron equivalent thickness maximizes the cell performance. The chemical, structural and microstructural factors controlling the final behaviour of these anodes and accounting for this maximization of the reaction yield are discussed on the basis of these characterization results and as a function of preparation variables of the electrodes and operating conditions of the cell.


Febrero, 2021 | DOI: 10.1016/j.jpowsour.2020.229217

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