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A common approach for the photoelectrochemical (PEC) splitting of water relies on the application of WO3 porous electrodes sensitized with BiVO4 acting as a visible photoanode semiconductor. In this work, we propose a new architecture of photoelectrodes consisting of supported multishell nanotubes (NTs) fabricated by a soft-template approach. These NTs are formed by a concentric layered structure of indium tin oxide (ITO), WO3, and BiVO4, together with a final thin layer of cobalt phosphate (CoPi) co-catalyst. The photoelectrode manufacturing procedure is easily implementable at a large scale and successively combines the thermal evaporation of single crystalline organic nanowires (ONWs), the magnetron sputtering deposition of ITO and WO3, and the solution dripping and electrochemical deposition of, respectively, BiVO4 and CoPi, plus the annealing in air under mild conditions. The obtained NT electrodes depict a large electrochemically active surface and outperform the efficiency of equivalent planar-layered electrodes by more than one order of magnitude. A thorough electrochemical analysis of the electrodes illuminated with blue and solar lights demonstrates that the characteristics of the WO3/BiVO4 Schottky barrier heterojunction control the NT electrode efficiency, which depended on the BiVO4 outer layer thickness and the incorporation of the CoPi electrocatalyst. These results support the high potential of the proposed soft-template methodology for the large-area fabrication of highly efficient multishell ITO/WO3/BiVO4/CoPi NT electrodes for the PEC splitting of water.

Due to the demand for renewable energies, gasses likeH2 need to be detected with sensitive, accurate and fast detectors. The US Department of Energy has made a list of requirements that H2 sensors need to fullfill of which the minimum detectable concentration (0.1%) and the reaction time (one second) are challenging for current hydrogen sensors, particularly for low-power and low-cost mass-produced sensors. This thesis covers the design and simulation of a photonic crystal nanobeam cavity sensor, using the Pt-catalyzed WO3 as a H2 sensitive material. The thicknesses of both layers show a trade-off between the minimally detectable concentration and the reaction times, resulting in a cavity with sensitivity of almost 40 nm/RIU and a Q factor varying between 5e5 and 5e4 depending on how much catalyst is required to meet the one second reaction time performance target. Based on the conservative assumptions regarding the reaction times of the sensor, the 0.1% performance target is almost achieved. This means that if in practice, any of the layer thicknesses show to be more favourable than assumed in this thesis, together with the fact that for optical sensors there is no risk of sparks, the photonic crystal nanobeam cavity as a H2 sensor shows to be a good fit for a high performance, low-cost, mass-produced H2 sensor that meets the DoE performance targets., Mechanical Engineering | Precision and Microsystems Engineering

Glycerol is an important by-product (biowaste) from biodiesel production. Transformation of glycerol into value-added compounds is critical in improving the overall efficiency of the biodiesel production. In this work, a sustainable and cleaner production of 1,3-propanediol (1,3-PDO) by vapor phase hydrogenolysis of glycerol was performed over titanium phosphate (TiP) supported catalysts by varying the Pt and WO₃ loadings (5–20 wt.%). The WO₃ promoted Pt modified TiP catalysts were prepared by a simple wet impregnation method and characterized by various analytical techniques in determining the key properties. Furthermore, the catalyst activity and stability were studied under different reaction conditions. The synergistic effects of Pt and WO₃ loadings on the final performance of the catalyst has been significant in improving the hydrogen transfer rate. Both Pt and WO₃ promotional effects is envisaged the enhanced catalytic properties in conjunction with TiP support acidity. WO₃ incorporation increased Brønsted acidity and formed strong interactions with Pt over TiP support. Both Lewis and Brønsted acid sites presented but BAS played a key role in enhancing the 1,3-PDO selectivity in a bifunctional dehydration-hydrogenation reaction mechanism of glycerol. The effect of reaction temperature, contact times and the weight hour space velocity were evaluated. Overall, under optimized reaction conditions, 2 wt.% Pt-10 wt.% WO₃/TiP catalyst displayed superior activity with a maximum glycerol conversion of ~ 85% and ~ 51% of 1,3-PDO selectivity achieved at time on stream of 4 h.

Bisphenol A (BPA) is an organic compound used in large scale at the plastics industry and as a precursor in the synthesis of polycarbonates and epoxy resins, which lead to frequent detections of BPA in surface waters. Therefore, it is necessary to develop and improve methods for BPA detection and monitoring. The electrochemical behavior of Bisphenol A at WO3 and carbon-based electrodes, like glassy carbon (GC) and multi-walled carbon nanotubes (MWCNT), were compared using cyclic voltammetry (CV). Therefore, WO3 nanoparticles were obtained by hydrothermal method and characterization was done using XRDP. The results showed that the responses of the WO3 electrode were 30 times larger compared to another examined electrode. This implies that WO3 electrode can be useful for the detection BPA in nature media.

Due to the demand for renewable energies, gasses likeH2 need to be detected with sensitive, accurate and fast detectors. The US Department of Energy has made a list of requirements that H2 sensors need to fullfill of which the minimum detectable concentration (0.1%) and the reaction time (one second) are challenging for current hydrogen sensors, particularly for low-power and low-cost mass-produced sensors. This thesis covers the design and simulation of a photonic crystal nanobeam cavity sensor, using the Pt-catalyzed WO3 as a H2 sensitive material. The thicknesses of both layers show a trade-off between the minimally detectable concentration and the reaction times, resulting in a cavity with sensitivity of almost 40 nm/RIU and a Q factor varying between 5e5 and 5e4 depending on how much catalyst is required to meet the one second reaction time performance target. Based on the conservative assumptions regarding the reaction times of the sensor, the 0.1% performance target is almost achieved. This means that if in practice, any of the layer thicknesses show to be more favourable than assumed in this thesis, together with the fact that for optical sensors there is no risk of sparks, the photonic crystal nanobeam cavity as a H2 sensor shows to be a good fit for a high performance, low-cost, mass-produced H2 sensor that meets the DoE performance targets., Mechanical Engineering | Precision and Microsystems Engineering

Vanadium redox flow batteries (VRFBs) are appealing large-scale energy storage systems due to their unique properties of independent energy/power design. The VRFBs stack design is crucial for technology deployment in power applications. Besides the design, the stack suffers from high voltage losses caused by the electrodes. The introduction of active sites into the electrode to facilitate the reaction kinetic is crucial in boosting the power rate of the VRFBs. Here, an O-rich layer has been applied onto structured graphite felt (GF) by depositing WO3 to increase the oxygen species content. The oxygen species are the active site during the positive reaction (VO2+/VO2+) in VRFB. The increased electrocatalytic activity is demonstrated by the monoclinic (m)-WO3/GF electrode that minimizes the voltage losses, yielding excellent performance results in terms of power density output and limiting current density (556 mWcm−2@800 mAcm−2). The results confirm that the m-WO3/GF electrode is a promising electrode for high-power in VRFBs, overcoming the performance-limiting issues in a positive half-reaction.

[ES] Los procesos de oxidación avanzada, caracterizados por su capacidad de generar especies con gran poder oxidante, son una de las soluciones para la eliminación de compuestos orgánicos no biodegradables en aguas residuales. Entre los procesos referidos se encuentra la llamada fotocatálisis heterogénea, donde destaca el uso de dióxido de titanio (TiO2) para la generación de, entre otras especies radicalarias, radicales hidroxilo, una de las especies más oxidantes conocidas. No obstante, una de los grandes desventajas que presenta el TiO2 es el aprovechamiento de únicamente un 9 % del espectro solar. Frente a esta problemática, en los últimos años se ha presentado el trióxido de tungsteno (VI) (WO3) como una prometedora alternativa al TiO2, gracias a la presencia de una banda prohibida estrecha, así como por la capacidad para absorber radiación en el rango del espectro visible. A pesar de estas atractivas características, el WO3 presenta una capacidad fotocatalítica limitada debido a la rápida recombinación del par electrón-hueco tras haber sido fotoexcitado. Ante esta situación, este trabajo de fin de máster se ha centrado en evitar dicha recombinación del par electrón-hueco, proponiendo dos soluciones que ayudarán eventualmente a aumentar la capacidad fotocatalítica del WO3. En primer lugar, se ha propuesto la utilización de H2O2 por su capacidad para secuestrar el electrón fotoexcitado del WO3. En segundo lugar, se ha llevado a cabo la formación de una heterounión con el WO3 y el óxido de hierro (Fe3O4) con el objetivo de hacer migrar los electrones excitados desde la banda de conducción del WO3 a la banda de conducción del Fe3O4. Con estos antecedentes, en este trabajo presentamos la síntesis de dos fotocatalizadores basados en WO3. Primero, se ha soportado WO3 sobre partículas de óxido de silicio (SiO2), lo que ha dado lugar a fotocatalizadores de tipo SiO2@WO3. Segundo, se han decorado los fotocatalizadores SiO2@WO3 previamente sintetizados con nanopartículas, [EN] Advanced oxidation processes, which are characterized by their ability to generate species with great oxidizing power, are one of the solutions for the elimination of non-biodegradable organic compounds in wastewater. One of the referred processes is heterogeneous photocatalysis, where the use of titanium dioxide (TiO2) stands out in the generation of, among other radical species, hydroxyl radicals, one of the most oxidizing species known. However, one of the biggest disadvantages of TiO2 is that it can only take advantadge of the 9 % of the solar spectrum. In order to overcome this problem, tungsten trioxide (VI) (WO3) has been proposed as a promising alternative to TiO2 in recent years, due to its narrow band-gap and its ability to absorb radiation in the visible spectrum range. Despite these attractive features, WO3 exhibits a limited photocatalytic ability due to the fast recombination of the electron-hole pair after being photoexcited. In this context, this master's thesis has focused on avoiding the mentioned recombination of the electronhole pair, proposing two solutions that will eventually help to increase WO3's photocatalytic activity. First of all, the use of H2O2 has been proposed due to its capacity to capture the photoexcited electron from WO3. Secondly, the formation of a heterojunction between WO3 and iron oxide (Fe3O4) has also been proposed, which will make the excited electrons migrate from the conduction band of WO3 to the conduction band of Fe3O4. In this regard, herein we present the synthesis of two photocatalysts based on WO3. First, WO3 has been supported on silicon oxide (SiO2) particles, leading to SiO2@WO3 type photocatalysts. Second, the previously synthesized SiO2@WO3 photocatalysts have been decorated with Fe3O4 nanoparticles, leading to SiO2@WO3@Fe3O4 photocatalysts. Subsequently, the synthesized photocatalysts have been characterized with several techniques. Finally, the photocatalytic activity of SiO2@WO3 and SiO2@WO3@Fe3O4 pho

[ES] Los procesos de oxidación avanzada, caracterizados por su capacidad de generar especies con gran poder oxidante, son una de las soluciones para la eliminación de compuestos orgánicos no biodegradables en aguas residuales. Entre los procesos referidos se encuentra la llamada fotocatálisis heterogénea, donde destaca el uso de dióxido de titanio (TiO2) para la generación de, entre otras especies radicalarias, radicales hidroxilo, una de las especies más oxidantes conocidas. No obstante, una de los grandes desventajas que presenta el TiO2 es el aprovechamiento de únicamente un 9 % del espectro solar. Frente a esta problemática, en los últimos años se ha presentado el trióxido de tungsteno (VI) (WO3) como una prometedora alternativa al TiO2, gracias a la presencia de una banda prohibida estrecha, así como por la capacidad para absorber radiación en el rango del espectro visible. A pesar de estas atractivas características, el WO3 presenta una capacidad fotocatalítica limitada debido a la rápida recombinación del par electrón-hueco tras haber sido fotoexcitado. Ante esta situación, este trabajo de fin de máster se ha centrado en evitar dicha recombinación del par electrón-hueco, proponiendo dos soluciones que ayudarán eventualmente a aumentar la capacidad fotocatalítica del WO3. En primer lugar, se ha propuesto la utilización de H2O2 por su capacidad para secuestrar el electrón fotoexcitado del WO3. En segundo lugar, se ha llevado a cabo la formación de una heterounión con el WO3 y el óxido de hierro (Fe3O4) con el objetivo de hacer migrar los electrones excitados desde la banda de conducción del WO3 a la banda de conducción del Fe3O4. Con estos antecedentes, en este trabajo presentamos la síntesis de dos fotocatalizadores basados en WO3. Primero, se ha soportado WO3 sobre partículas de óxido de silicio (SiO2), lo que ha dado lugar a fotocatalizadores de tipo SiO2@WO3. Segundo, se han decorado los fotocatalizadores SiO2@WO3 previamente sintetizados con nanopartículas, [EN] Advanced oxidation processes, which are characterized by their ability to generate species with great oxidizing power, are one of the solutions for the elimination of non-biodegradable organic compounds in wastewater. One of the referred processes is heterogeneous photocatalysis, where the use of titanium dioxide (TiO2) stands out in the generation of, among other radical species, hydroxyl radicals, one of the most oxidizing species known. However, one of the biggest disadvantages of TiO2 is that it can only take advantadge of the 9 % of the solar spectrum. In order to overcome this problem, tungsten trioxide (VI) (WO3) has been proposed as a promising alternative to TiO2 in recent years, due to its narrow band-gap and its ability to absorb radiation in the visible spectrum range. Despite these attractive features, WO3 exhibits a limited photocatalytic ability due to the fast recombination of the electron-hole pair after being photoexcited. In this context, this master's thesis has focused on avoiding the mentioned recombination of the electronhole pair, proposing two solutions that will eventually help to increase WO3's photocatalytic activity. First of all, the use of H2O2 has been proposed due to its capacity to capture the photoexcited electron from WO3. Secondly, the formation of a heterojunction between WO3 and iron oxide (Fe3O4) has also been proposed, which will make the excited electrons migrate from the conduction band of WO3 to the conduction band of Fe3O4. In this regard, herein we present the synthesis of two photocatalysts based on WO3. First, WO3 has been supported on silicon oxide (SiO2) particles, leading to SiO2@WO3 type photocatalysts. Second, the previously synthesized SiO2@WO3 photocatalysts have been decorated with Fe3O4 nanoparticles, leading to SiO2@WO3@Fe3O4 photocatalysts. Subsequently, the synthesized photocatalysts have been characterized with several techniques. Finally, the photocatalytic activity of SiO2@WO3 and SiO2@WO3@Fe3O4 pho

[ES] La presente Tesis Doctoral tiene dos objetivos claramente diferenciados, siendo el primero de ellos la realización de un estudio de optimización de la síntesis de nanoestructuras de óxido de wolframio (WO3) mediante el uso de un diseño de experimentos, mientras que el segundo de ellos es el uso de estas nanoestructuras en la degradación fotoelectrocatalítica de 4 pesticidas organofosforados de diferentes subfamilias (diazinon, fosmet, clorfenvinfos y fenamifos). El uso del óxido de wolframio como fotocatalizador en el proceso fotoelectrocatalítico (FEC) despierta un gran interés, ya que se trata de un semiconductor con gran fotoestabilidad en electrolitos acuosos ácidos, excelente conductividad eléctrica, tiene la capacidad de absorber la parte azul del espectro visible además de la luz ultravioleta, y el borde superior de la banda de valencia es mayor que el potencial de oxidación de H2O/O2. Todo ello hace que el WO3 sea capaz de fotooxidar eficazmente una amplia gama de compuestos orgánicos. Las nanoestructuras estudiadas en la Tesis Doctoral se sintetizaron mediante anodizado electroquímico, ya que se trata de una técnica sencilla que permite un control de sus parámetros de manera fácil y efectiva, permitiendo obtener las nanoestructuras directamente sobre el propio sustrato metálico. Además, la necesidad de controlar y eliminar los contaminantes emergentes en el medio ambiente se ha vuelto cada vez más crucial durante las últimas décadas. Así, en esta Tesis se han degradado 4 pesticidas tóxicos y persistentes en el medioambiente mediante la técnica de fotoelectrocatálisis (FEC) utilizando las nanoestructuras de WO3. En esta técnica, los fenómenos electrolíticos y fotocatalíticos actúan juntos para mineralizar el contaminante orgánico. Además, la FEC está atrayendo la atención de los investigadores por su capacidad para degradar contaminantes orgánicos y transformarlos en compuestos inocuos con condiciones de trabajo no extremas. Por tanto, en el diseño de e, [CA] La present tesi doctoral té dos objectius clarament diferenciats, sent el primer la realització d'un estudi d'optimització de la síntesi de nanoestructures d'òxid de wolframi (WO3) mitjançant l'ús d'un disseny d'experiments, mentre que el segon és l'ús d'aquestes nanoestructures en la degradació fotoelectrocatalítica de quatre pesticides organofosforats de diferents subfamílies (diazinon, fosmet, clorfenvinfòs i fenamifòs). L'ús de l'òxid de wolframi com a fotocatalitzador en el procés fotoelectrocatalític (FEC) desperta un gran interès, ja que es tracta d'un semiconductor amb gran fotoestabilitat en electròlits aquosos àcids; amb una excel·lent conductivitat elèctrica; té la capacitat d'absorbir la part blava de l'espectre visible, a més de la llum ultraviolada, i la vora superior de la banda de valència és major que el potencial d'oxidació d'H2O/O2. Tot això fa que el WO3 siga capaç de fotooxidar eficaçment una àmplia gamma de compostos orgànics. Les nanoestructures estudiades en la tesi doctoral es van sintetitzar mitjançant anodització electroquímica, ja que es tracta d'una tècnica senzilla que permet un control dels seus paràmetres de manera fàcil i efectiva, i permet obtenir les nanoestructures directament sobre el mateix substrat metàl·lic. A més, la necessitat de controlar i eliminar els contaminants emergents en el medi ambient s'ha tornat cada vegada més crucial durant les últimes dècades. Així, en aquesta tesi s'han degradat quatre pesticides tòxics i persistents en el medi ambient mitjançant la tècnica de la fotoelectrocatàlisi (FEC) utilitzant les nanoestructures de WO3. En aquesta tècnica, els fenòmens electrolítics i fotocatalítics actuen junts per a mineralitzar el contaminant orgànic. La FEC està atraient l'atenció del personal investigador per la seua capacitat per a degradar contaminants orgànics i transformar-los en compostos innocus amb condicions de treball no extremes. Per tant, en el disseny d'experiments realitzat en la tesi doctoral es, [EN] This Doctoral Thesis has two clearly differentiated objectives. The first objective is to carry out an optimization study of the synthesis of tungsten oxide nanostructures (WO3) using a design of experiments. The second objective is to use of these nanostructures in the photoelectrocatalytic degradation of 4 organophosphate pesticides of different subfamilies (diazinon, phosmet, chlorfenvinphos and fenamiphos). The use of tungsten oxide as a photocatalyst in the photoelectrocatalytic (PEC) process arouses great interest, since it is a semiconductor with great photostability in acidic aqueous electrolytes, excellent electrical conductivity, it has the ability to absorb the blue part of the visible spectrum in addition to ultraviolet light, and the upper edge of the valence band is greater than the oxidation potential of H2O / O2. All this makes WO3 capable of efficiently photo-oxidizing a wide range of organic compounds. The nanostructures studied in the Doctoral Thesis were synthesized using electrochemical anodization, since it is a simple technique that permits the control their parameters easily and effectively, allowing the nanostructures to be obtained directly on the metal substrate itself. Furthermore, the need to control and eliminate emerging pollutants in the environment has become increasingly crucial over the past decades. Thus, in this Thesis, 4 toxic and persistent pesticides in the environment have been degraded by the photoelectrocatalysis (PEC) technique using the WO3 nanostructures. In this technique, the electrolytic and photocatalytic phenomena act together to mineralize the organic contaminant. PEC is attracting the attention of researchers for its ability to degrade organic pollutants and transform them into harmless compounds under non-extreme working conditions. Therefore, in the design of experiments carried out in the Doctoral Thesis, 3 variables were modified with three levels each one, therefore a 33 design was chosen. The variables

[ES] Los procesos de oxidación avanzada, caracterizados por su capacidad de generar especies con gran poder oxidante, son una de las soluciones para la eliminación de compuestos orgánicos no biodegradables en aguas residuales. Entre los procesos referidos se encuentra la llamada fotocatálisis heterogénea, donde destaca el uso de dióxido de titanio (TiO2) para la generación de, entre otras especies radicalarias, radicales hidroxilo, una de las especies más oxidantes conocidas. No obstante, una de los grandes desventajas que presenta el TiO2 es el aprovechamiento de únicamente un 9 % del espectro solar. Frente a esta problemática, en los últimos años se ha presentado el trióxido de tungsteno (VI) (WO3) como una prometedora alternativa al TiO2, gracias a la presencia de una banda prohibida estrecha, así como por la capacidad para absorber radiación en el rango del espectro visible. A pesar de estas atractivas características, el WO3 presenta una capacidad fotocatalítica limitada debido a la rápida recombinación del par electrón-hueco tras haber sido fotoexcitado. Ante esta situación, este trabajo de fin de máster se ha centrado en evitar dicha recombinación del par electrón-hueco, proponiendo dos soluciones que ayudarán eventualmente a aumentar la capacidad fotocatalítica del WO3. En primer lugar, se ha propuesto la utilización de H2O2 por su capacidad para secuestrar el electrón fotoexcitado del WO3. En segundo lugar, se ha llevado a cabo la formación de una heterounión con el WO3 y el óxido de hierro (Fe3O4) con el objetivo de hacer migrar los electrones excitados desde la banda de conducción del WO3 a la banda de conducción del Fe3O4. Con estos antecedentes, en este trabajo presentamos la síntesis de dos fotocatalizadores basados en WO3. Primero, se ha soportado WO3 sobre partículas de óxido de silicio (SiO2), lo que ha dado lugar a fotocatalizadores de tipo SiO2@WO3. Segundo, se han decorado los fotocatalizadores SiO2@WO3 previamente sintetizados con nanopartículas, [EN] Advanced oxidation processes, which are characterized by their ability to generate species with great oxidizing power, are one of the solutions for the elimination of non-biodegradable organic compounds in wastewater. One of the referred processes is heterogeneous photocatalysis, where the use of titanium dioxide (TiO2) stands out in the generation of, among other radical species, hydroxyl radicals, one of the most oxidizing species known. However, one of the biggest disadvantages of TiO2 is that it can only take advantadge of the 9 % of the solar spectrum. In order to overcome this problem, tungsten trioxide (VI) (WO3) has been proposed as a promising alternative to TiO2 in recent years, due to its narrow band-gap and its ability to absorb radiation in the visible spectrum range. Despite these attractive features, WO3 exhibits a limited photocatalytic ability due to the fast recombination of the electron-hole pair after being photoexcited. In this context, this master's thesis has focused on avoiding the mentioned recombination of the electronhole pair, proposing two solutions that will eventually help to increase WO3's photocatalytic activity. First of all, the use of H2O2 has been proposed due to its capacity to capture the photoexcited electron from WO3. Secondly, the formation of a heterojunction between WO3 and iron oxide (Fe3O4) has also been proposed, which will make the excited electrons migrate from the conduction band of WO3 to the conduction band of Fe3O4. In this regard, herein we present the synthesis of two photocatalysts based on WO3. First, WO3 has been supported on silicon oxide (SiO2) particles, leading to SiO2@WO3 type photocatalysts. Second, the previously synthesized SiO2@WO3 photocatalysts have been decorated with Fe3O4 nanoparticles, leading to SiO2@WO3@Fe3O4 photocatalysts. Subsequently, the synthesized photocatalysts have been characterized with several techniques. Finally, the photocatalytic activity of SiO2@WO3 and SiO2@WO3@Fe3O4 pho

[ES] La presente Tesis Doctoral tiene dos objetivos claramente diferenciados, siendo el primero de ellos la realización de un estudio de optimización de la síntesis de nanoestructuras de óxido de wolframio (WO3) mediante el uso de un diseño de experimentos, mientras que el segundo de ellos es el uso de estas nanoestructuras en la degradación fotoelectrocatalítica de 4 pesticidas organofosforados de diferentes subfamilias (diazinon, fosmet, clorfenvinfos y fenamifos). El uso del óxido de wolframio como fotocatalizador en el proceso fotoelectrocatalítico (FEC) despierta un gran interés, ya que se trata de un semiconductor con gran fotoestabilidad en electrolitos acuosos ácidos, excelente conductividad eléctrica, tiene la capacidad de absorber la parte azul del espectro visible además de la luz ultravioleta, y el borde superior de la banda de valencia es mayor que el potencial de oxidación de H2O/O2. Todo ello hace que el WO3 sea capaz de fotooxidar eficazmente una amplia gama de compuestos orgánicos. Las nanoestructuras estudiadas en la Tesis Doctoral se sintetizaron mediante anodizado electroquímico, ya que se trata de una técnica sencilla que permite un control de sus parámetros de manera fácil y efectiva, permitiendo obtener las nanoestructuras directamente sobre el propio sustrato metálico. Además, la necesidad de controlar y eliminar los contaminantes emergentes en el medio ambiente se ha vuelto cada vez más crucial durante las últimas décadas. Así, en esta Tesis se han degradado 4 pesticidas tóxicos y persistentes en el medioambiente mediante la técnica de fotoelectrocatálisis (FEC) utilizando las nanoestructuras de WO3. En esta técnica, los fenómenos electrolíticos y fotocatalíticos actúan juntos para mineralizar el contaminante orgánico. Además, la FEC está atrayendo la atención de los investigadores por su capacidad para degradar contaminantes orgánicos y transformarlos en compuestos inocuos con condiciones de trabajo no extremas. Por tanto, en el diseño de e, [CA] La present tesi doctoral té dos objectius clarament diferenciats, sent el primer la realització d'un estudi d'optimització de la síntesi de nanoestructures d'òxid de wolframi (WO3) mitjançant l'ús d'un disseny d'experiments, mentre que el segon és l'ús d'aquestes nanoestructures en la degradació fotoelectrocatalítica de quatre pesticides organofosforats de diferents subfamílies (diazinon, fosmet, clorfenvinfòs i fenamifòs). L'ús de l'òxid de wolframi com a fotocatalitzador en el procés fotoelectrocatalític (FEC) desperta un gran interès, ja que es tracta d'un semiconductor amb gran fotoestabilitat en electròlits aquosos àcids; amb una excel·lent conductivitat elèctrica; té la capacitat d'absorbir la part blava de l'espectre visible, a més de la llum ultraviolada, i la vora superior de la banda de valència és major que el potencial d'oxidació d'H2O/O2. Tot això fa que el WO3 siga capaç de fotooxidar eficaçment una àmplia gamma de compostos orgànics. Les nanoestructures estudiades en la tesi doctoral es van sintetitzar mitjançant anodització electroquímica, ja que es tracta d'una tècnica senzilla que permet un control dels seus paràmetres de manera fàcil i efectiva, i permet obtenir les nanoestructures directament sobre el mateix substrat metàl·lic. A més, la necessitat de controlar i eliminar els contaminants emergents en el medi ambient s'ha tornat cada vegada més crucial durant les últimes dècades. Així, en aquesta tesi s'han degradat quatre pesticides tòxics i persistents en el medi ambient mitjançant la tècnica de la fotoelectrocatàlisi (FEC) utilitzant les nanoestructures de WO3. En aquesta tècnica, els fenòmens electrolítics i fotocatalítics actuen junts per a mineralitzar el contaminant orgànic. La FEC està atraient l'atenció del personal investigador per la seua capacitat per a degradar contaminants orgànics i transformar-los en compostos innocus amb condicions de treball no extremes. Per tant, en el disseny d'experiments realitzat en la tesi doctoral es, [EN] This Doctoral Thesis has two clearly differentiated objectives. The first objective is to carry out an optimization study of the synthesis of tungsten oxide nanostructures (WO3) using a design of experiments. The second objective is to use of these nanostructures in the photoelectrocatalytic degradation of 4 organophosphate pesticides of different subfamilies (diazinon, phosmet, chlorfenvinphos and fenamiphos). The use of tungsten oxide as a photocatalyst in the photoelectrocatalytic (PEC) process arouses great interest, since it is a semiconductor with great photostability in acidic aqueous electrolytes, excellent electrical conductivity, it has the ability to absorb the blue part of the visible spectrum in addition to ultraviolet light, and the upper edge of the valence band is greater than the oxidation potential of H2O / O2. All this makes WO3 capable of efficiently photo-oxidizing a wide range of organic compounds. The nanostructures studied in the Doctoral Thesis were synthesized using electrochemical anodization, since it is a simple technique that permits the control their parameters easily and effectively, allowing the nanostructures to be obtained directly on the metal substrate itself. Furthermore, the need to control and eliminate emerging pollutants in the environment has become increasingly crucial over the past decades. Thus, in this Thesis, 4 toxic and persistent pesticides in the environment have been degraded by the photoelectrocatalysis (PEC) technique using the WO3 nanostructures. In this technique, the electrolytic and photocatalytic phenomena act together to mineralize the organic contaminant. PEC is attracting the attention of researchers for its ability to degrade organic pollutants and transform them into harmless compounds under non-extreme working conditions. Therefore, in the design of experiments carried out in the Doctoral Thesis, 3 variables were modified with three levels each one, therefore a 33 design was chosen. The variables

In this paper, we report the preparation of visible‐light active direct Z‐scheme Cu2O/WO3 nanocomposite photocatalyst by a solid‐state reaction avoiding the otherwise inevitable formation of CuWO4 phase in wet syntheses. Structure, morphology, and thermal and optical properties of prepared WO3 nanoplatelets decorated by Cu2O were investigated by XRD, Raman spectroscopy, SEM/TEM, combined thermogravimetric (TG)/differential scanning calorimetry (DSC) analysis, and UV–VIS spectroscopy. The photocatalytic performance of the prepared samples under UV and visible light was studied through monitoring discoloration of methylene blue under illumination by selected wavelengths, allowing for the distinguishing between the contributions of the two semiconductive components. Experimental results showed that the decoration of WO3 nanoplates by Cu2O nanoparticles led to an improvement in photocatalytic performance, regardless of used LED (Light‐Emitting Diode) wavelength, even at low concentrations. By using scavengers selectively blocking reactive species involved in the discoloration reaction, we determined that the Cu2O/WO3 nanocomposite exhibited the characteristics of direct Z‐scheme‐type photocatalyst. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Controlling the oxygen concentration in metal oxides is one of the most effective ways to modulate their optoelectronic properties. However, such redox control is difficult for metal oxide epitaxial films due to serious damages induced in the lattice, especially around the film/substrate interface during the large volume change upon the redox treatment. For overcoming this problem, the use of metal oxides with a stress-resistant crystal structure can be effective. Here, we show a reversible redox control in the optoelectronic properties of hexagonal tungsten oxide (h-WOx) epitaxial films with a honeycomb structure. We fabricated highly c-axis-oriented h-WOx epitaxial films on the (111) yttria-stabilized zirconia (YSZ) single-crystal substrate. Upon electro-chemical redox treatment at 300 degrees C with the application of +/- 3 V to the YSZ solid electrolyte, the oxygen content x of h-WOx was reversibly controlled in the range of 2.93 <= x <= 2.99 without inducing damage to the crystal lattice. Simultaneously, the electrical conductivity was controlled from similar to 400 S cm(-1) to an insulator, and the optical transmission at 1.5 mu m in the wavelength was controlled in the range of 35-70%. The present results would be useful for developing electrochemical optoelectronic devices based on metal oxide epitaxial films.

Solar-driven water splitting is an emerging technology with high potential to generate fuel cleanly and sustainably. In this work, we show that WO3 can be used as a cathodic electrocatalyst in combination with (Ag,Cu) InGaSe2 solar cell modules to produce hydrogen and provide electrochromic functionality to water splitting devices. This electrochromic effect can be used to monitor the charge state or performance of the catalyst for process control or for controlling the temperature and absorbed heat due to tunable optical modulation of the electrocatalyst. WO3 films coated on Ni foam, using a wide range of different sputtering conditions, were investigated as cathodic electrocatalysts for the water splitting reaction. The solar-to-hydrogen (STH) efficiency of solar-driven water electrolysis was extracted using (Ag,Cu)InGaSe2 solar cell modules with a cell band gap varied in between 1.15 and 1.25 eV with WO3 on Ni foam-based electrolyzers and yielded up to 13% STH efficiency. Electrochromic properties during water electrolysis were characterized for the WO3 films on transparent substrate (indium tin oxide). Transmittance varied between 10% and 78% and the coloration efficiency at a wavelength of 528 nm and the overpotential of 400 mV was 40 cm(2) C-1. Hydrogen ion consumption in ion intercalation for electrochromic and hydrogen gas production for water electrolysis processes was discussed.

Solar-driven water splitting is an emerging technology with high potential to generate fuel cleanly and sustainably. In this work, we show that WO3 can be used as a cathodic electrocatalyst in combination with (Ag,Cu) InGaSe2 solar cell modules to produce hydrogen and provide electrochromic functionality to water splitting devices. This electrochromic effect can be used to monitor the charge state or performance of the catalyst for process control or for controlling the temperature and absorbed heat due to tunable optical modulation of the electrocatalyst. WO3 films coated on Ni foam, using a wide range of different sputtering conditions, were investigated as cathodic electrocatalysts for the water splitting reaction. The solar-to-hydrogen (STH) efficiency of solar-driven water electrolysis was extracted using (Ag,Cu)InGaSe2 solar cell modules with a cell band gap varied in between 1.15 and 1.25 eV with WO3 on Ni foam-based electrolyzers and yielded up to 13% STH efficiency. Electrochromic properties during water electrolysis were characterized for the WO3 films on transparent substrate (indium tin oxide). Transmittance varied between 10% and 78% and the coloration efficiency at a wavelength of 528 nm and the overpotential of 400 mV was 40 cm(2) C-1. Hydrogen ion consumption in ion intercalation for electrochromic and hydrogen gas production for water electrolysis processes was discussed.

Solar-driven water splitting is an emerging technology with high potential to generate fuel cleanly and sustainably. In this work, we show that WO3 can be used as a cathodic electrocatalyst in combination with (Ag,Cu) InGaSe2 solar cell modules to produce hydrogen and provide electrochromic functionality to water splitting devices. This electrochromic effect can be used to monitor the charge state or performance of the catalyst for process control or for controlling the temperature and absorbed heat due to tunable optical modulation of the electrocatalyst. WO3 films coated on Ni foam, using a wide range of different sputtering conditions, were investigated as cathodic electrocatalysts for the water splitting reaction. The solar-to-hydrogen (STH) efficiency of solar-driven water electrolysis was extracted using (Ag,Cu)InGaSe2 solar cell modules with a cell band gap varied in between 1.15 and 1.25 eV with WO3 on Ni foam-based electrolyzers and yielded up to 13% STH efficiency. Electrochromic properties during water electrolysis were characterized for the WO3 films on transparent substrate (indium tin oxide). Transmittance varied between 10% and 78% and the coloration efficiency at a wavelength of 528 nm and the overpotential of 400 mV was 40 cm(2) C-1. Hydrogen ion consumption in ion intercalation for electrochromic and hydrogen gas production for water electrolysis processes was discussed.

Controlling the oxygen concentration in metal oxides is one of the most effective ways to modulate their optoelectronic properties. However, such redox control is difficult for metal oxide epitaxial films due to serious damages induced in the lattice, especially around the film/substrate interface during the large volume change upon the redox treatment. For overcoming this problem, the use of metal oxides with a stress-resistant crystal structure can be effective. Here, we show a reversible redox control in the optoelectronic properties of hexagonal tungsten oxide (h-WOx) epitaxial films with a honeycomb structure. We fabricated highly c-axis-oriented h-WOx epitaxial films on the (111) yttria-stabilized zirconia (YSZ) single-crystal substrate. Upon electro-chemical redox treatment at 300 degrees C with the application of +/- 3 V to the YSZ solid electrolyte, the oxygen content x of h-WOx was reversibly controlled in the range of 2.93 <= x <= 2.99 without inducing damage to the crystal lattice. Simultaneously, the electrical conductivity was controlled from similar to 400 S cm(-1) to an insulator, and the optical transmission at 1.5 mu m in the wavelength was controlled in the range of 35-70%. The present results would be useful for developing electrochemical optoelectronic devices based on metal oxide epitaxial films.

This paper demonstrates, for the first time, synthesis of uniform and crystalline WO3 mesopomus fibers with a diameter of approximate to 1 mu m via centrifugal spinning. This was achieved by using a stable aqueous precursor solution based on ammonium metatungstate (AMT, (NH4)6H(2)W(12)O(40)center dot xH(2)O)) and polyvinyl pyrrolidone (PVP, (C6H9NO)(n)). Annealing at 300 degrees C for 1 h followed by an additional annealing at 500 degrees C for 6 h was conducted to obtain crystalline WO3 fibers. The resulting centrifugally spun WO3 fibers possess approx. 1.4-4 times enhancement in photocatalytic activity under UV (k = 0.0205 min(-1)) and VIS (k = 0.0109 min(-1)) light irradiation compared to that of electrospun WO3 fibers and commercially available WO3 nanoparticles. This is due to the increased specific surface area of the centrifugally spun WO3 fibers (S-BET = 22.3 m(2)/g) compared to electrospun WO3 fibers (S-BET = 7.4 m(2)/g) and WO3 nanoparticles (S-BET = 6.4 m(2)/g). On the other hand, optical properties of all tested materials (including optical band gap) were nearly the same.

This paper demonstrates, for the first time, synthesis of uniform and crystalline WO3 mesopomus fibers with a diameter of approximate to 1 mu m via centrifugal spinning. This was achieved by using a stable aqueous precursor solution based on ammonium metatungstate (AMT, (NH4)6H(2)W(12)O(40)center dot xH(2)O)) and polyvinyl pyrrolidone (PVP, (C6H9NO)(n)). Annealing at 300 degrees C for 1 h followed by an additional annealing at 500 degrees C for 6 h was conducted to obtain crystalline WO3 fibers. The resulting centrifugally spun WO3 fibers possess approx. 1.4-4 times enhancement in photocatalytic activity under UV (k = 0.0205 min(-1)) and VIS (k = 0.0109 min(-1)) light irradiation compared to that of electrospun WO3 fibers and commercially available WO3 nanoparticles. This is due to the increased specific surface area of the centrifugally spun WO3 fibers (S-BET = 22.3 m(2)/g) compared to electrospun WO3 fibers (S-BET = 7.4 m(2)/g) and WO3 nanoparticles (S-BET = 6.4 m(2)/g). On the other hand, optical properties of all tested materials (including optical band gap) were nearly the same.

Solar-driven water splitting is an emerging technology with high potential to generate fuel cleanly and sustainably. In this work, we show that WO3 can be used as a cathodic electrocatalyst in combination with (Ag,Cu) InGaSe2 solar cell modules to produce hydrogen and provide electrochromic functionality to water splitting devices. This electrochromic effect can be used to monitor the charge state or performance of the catalyst for process control or for controlling the temperature and absorbed heat due to tunable optical modulation of the electrocatalyst. WO3 films coated on Ni foam, using a wide range of different sputtering conditions, were investigated as cathodic electrocatalysts for the water splitting reaction. The solar-to-hydrogen (STH) efficiency of solar-driven water electrolysis was extracted using (Ag,Cu)InGaSe2 solar cell modules with a cell band gap varied in between 1.15 and 1.25 eV with WO3 on Ni foam-based electrolyzers and yielded up to 13% STH efficiency. Electrochromic properties during water electrolysis were characterized for the WO3 films on transparent substrate (indium tin oxide). Transmittance varied between 10% and 78% and the coloration efficiency at a wavelength of 528 nm and the overpotential of 400 mV was 40 cm(2) C-1. Hydrogen ion consumption in ion intercalation for electrochromic and hydrogen gas production for water electrolysis processes was discussed.

Controlling the oxygen concentration in metal oxides is one of the most effective ways to modulate their optoelectronic properties. However, such redox control is difficult for metal oxide epitaxial films due to serious damages induced in the lattice, especially around the film/substrate interface during the large volume change upon the redox treatment. For overcoming this problem, the use of metal oxides with a stress-resistant crystal structure can be effective. Here, we show a reversible redox control in the optoelectronic properties of hexagonal tungsten oxide (h-WOx) epitaxial films with a honeycomb structure. We fabricated highly c-axis-oriented h-WOx epitaxial films on the (111) yttria-stabilized zirconia (YSZ) single-crystal substrate. Upon electro-chemical redox treatment at 300 degrees C with the application of +/- 3 V to the YSZ solid electrolyte, the oxygen content x of h-WOx was reversibly controlled in the range of 2.93 <= x <= 2.99 without inducing damage to the crystal lattice. Simultaneously, the electrical conductivity was controlled from similar to 400 S cm(-1) to an insulator, and the optical transmission at 1.5 mu m in the wavelength was controlled in the range of 35-70%. The present results would be useful for developing electrochemical optoelectronic devices based on metal oxide epitaxial films.

This paper demonstrates, for the first time, synthesis of uniform and crystalline WO3 mesopomus fibers with a diameter of approximate to 1 mu m via centrifugal spinning. This was achieved by using a stable aqueous precursor solution based on ammonium metatungstate (AMT, (NH4)6H(2)W(12)O(40)center dot xH(2)O)) and polyvinyl pyrrolidone (PVP, (C6H9NO)(n)). Annealing at 300 degrees C for 1 h followed by an additional annealing at 500 degrees C for 6 h was conducted to obtain crystalline WO3 fibers. The resulting centrifugally spun WO3 fibers possess approx. 1.4-4 times enhancement in photocatalytic activity under UV (k = 0.0205 min(-1)) and VIS (k = 0.0109 min(-1)) light irradiation compared to that of electrospun WO3 fibers and commercially available WO3 nanoparticles. This is due to the increased specific surface area of the centrifugally spun WO3 fibers (S-BET = 22.3 m(2)/g) compared to electrospun WO3 fibers (S-BET = 7.4 m(2)/g) and WO3 nanoparticles (S-BET = 6.4 m(2)/g). On the other hand, optical properties of all tested materials (including optical band gap) were nearly the same.

Controlling the oxygen concentration in metal oxides is one of the most effective ways to modulate their optoelectronic properties. However, such redox control is difficult for metal oxide epitaxial films due to serious damages induced in the lattice, especially around the film/substrate interface during the large volume change upon the redox treatment. For overcoming this problem, the use of metal oxides with a stress-resistant crystal structure can be effective. Here, we show a reversible redox control in the optoelectronic properties of hexagonal tungsten oxide (h-WOx) epitaxial films with a honeycomb structure. We fabricated highly c-axis-oriented h-WOx epitaxial films on the (111) yttria-stabilized zirconia (YSZ) single-crystal substrate. Upon electro-chemical redox treatment at 300 degrees C with the application of +/- 3 V to the YSZ solid electrolyte, the oxygen content x of h-WOx was reversibly controlled in the range of 2.93 <= x <= 2.99 without inducing damage to the crystal lattice. Simultaneously, the electrical conductivity was controlled from similar to 400 S cm(-1) to an insulator, and the optical transmission at 1.5 mu m in the wavelength was controlled in the range of 35-70%. The present results would be useful for developing electrochemical optoelectronic devices based on metal oxide epitaxial films.

In this paper, we report the preparation of visible‐light active direct Z‐scheme Cu2O/WO3 nanocomposite photocatalyst by a solid‐state reaction avoiding the otherwise inevitable formation of CuWO4 phase in wet syntheses. Structure, morphology, and thermal and optical properties of prepared WO3 nanoplatelets decorated by Cu2O were investigated by XRD, Raman spectroscopy, SEM/TEM, combined thermogravimetric (TG)/differential scanning calorimetry (DSC) analysis, and UV–VIS spectroscopy. The photocatalytic performance of the prepared samples under UV and visible light was studied through monitoring discoloration of methylene blue under illumination by selected wavelengths, allowing for the distinguishing between the contributions of the two semiconductive components. Experimental results showed that the decoration of WO3 nanoplates by Cu2O nanoparticles led to an improvement in photocatalytic performance, regardless of used LED (Light‐Emitting Diode) wavelength, even at low concentrations. By using scavengers selectively blocking reactive species involved in the discoloration reaction, we determined that the Cu2O/WO3 nanocomposite exhibited the characteristics of direct Z‐scheme‐type photocatalyst. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

The paper reports and comments the results of several electron spin resonance investigations, performed on semiconductor oxides for gas sensing. The main aspects, related to the comparison between spectroscopic and electric data, are concerning on (i) the role of the oxide defects in interacting with the gas atmosphere; (ii) the origin of the sensing enhancement, which follows the doping of the oxide by transition metal ions; and (iii) the effects of different particle morphology and of the controlled particle shape on the sensing functionality. The electron spin resonance results have been associated, when possible, to those deriving from X-ray photoelectron spectroscopy, in order to investigate the electronic configuration of the transition metal centers. Special emphasis has been deserved to the oxide synthesis procedures, in several cases well related to the electrical response. The data have been drawn from several studies, performed in different time periods, and have been compared to suggest a possible common interpretation of the sensing mechanism, based on either electronic or morphological properties.

Solar-driven water splitting is an emerging technology with high potential to generate fuel cleanly and sustainably. In this work, we show that WO3 can be used as a cathodic electrocatalyst in combination with (Ag,Cu) InGaSe2 solar cell modules to produce hydrogen and provide electrochromic functionality to water splitting devices. This electrochromic effect can be used to monitor the charge state or performance of the catalyst for process control or for controlling the temperature and absorbed heat due to tunable optical modulation of the electrocatalyst. WO3 films coated on Ni foam, using a wide range of different sputtering conditions, were investigated as cathodic electrocatalysts for the water splitting reaction. The solar-to-hydrogen (STH) efficiency of solar-driven water electrolysis was extracted using (Ag,Cu)InGaSe2 solar cell modules with a cell band gap varied in between 1.15 and 1.25 eV with WO3 on Ni foam-based electrolyzers and yielded up to 13% STH efficiency. Electrochromic properties during water electrolysis were characterized for the WO3 films on transparent substrate (indium tin oxide). Transmittance varied between 10% and 78% and the coloration efficiency at a wavelength of 528 nm and the overpotential of 400 mV was 40 cm(2) C-1. Hydrogen ion consumption in ion intercalation for electrochromic and hydrogen gas production for water electrolysis processes was discussed.

The influence of different milling conditions obtained using two high-energy mills on hydrogen desorption from MgH2-WO3 composites was investigated. The morphology, particle and crystallite size were studied as a function of milling speed, vial's volume, and ball-to-powder ratio. The vial's fill level, the number, and type of milling balls and additive's content kept constant. Changes in morphology and microstructure were correlated to desorption properties of materials. Higher milling speed reduced particle size but, there is no significant crystallite size reduction. On the other hand, additive distribution is similar regardless of the energy input. It has been noticed that different energy input on milling blend, which is the result of combined effects of above-mentioned factors, reflects on desorption temperature but not on the kinetics of desorption. In fact, desorption mechanism changes from 2D to 3D growth with constant nucleation rate, despite obtained changes in microstructure or chemical composition of the material. © 2019 Hydrogen Energy Publications LLC

There are active oxygen species that contribute to oxidative coupling or the partial oxidation during the oxidative dehydrogenation of methane when using solid oxide catalysts, and those species have not been definitively identified. In the present study, we clarify which of the active oxygen species affect the oxidative dehydrogenation of methane by employing photo-catalysts such as TiO2 or WO3, which generate active oxygen from UV-LED irradiation conditions under an oxygen flow. These photo-catalysts were studied in combination with Sm2O3, which is a methane oxidation coupling catalyst. For this purpose, we constructed a reaction system that could directly irradiate UV-LED to a solid catalyst via a normal fixed-bed continuous-flow reactor operated at atmospheric pressure. Binary catalysts prepared from TiO2 or WO3 were either supported on or kneaded with Sm2O3 in the present study. UV-LED irradiation clearly improved the partial oxidation from methane to CO and/or slightly improved the oxidative coupling route from methane to ethylene when binary catalysts consisting of Sm2O3 and TiO2 are used, while negligible UV-LED effects were detected when using Sm2O3 and WO3. These results indicate that with UV-LED irradiation the active oxygen of O2− from TiO2 certainly contributes to the activation of methane during the oxidative dehydrogenation of methane when using Sm2O3, while the active oxygen of H2O2 from WO3 under the same conditions afforded only negligible effects on the activation of methane.

In this work, PdOx-CuOx co-loaded porous WO3 microspheres were synthesized with varying loading levels by ultrasonic spray pyrolysis (USP) using polymethyl methacrylate (PMMA) microspheres as a vehicle template. The as-prepared sensing materials and their fabricated sensor properties were characterized by X-ray analysis, nitrogen adsorption, and electron microscopy. The gas-sensing properties were studied toward methyl mercaptan (CH3SH), hydrogen sulfide (H2S), dimethyl sulfide (CH3SCH3), nitric oxide (NO), nitrogen dioxide (NO2), methane (CH4), ethanol (C2H5OH), and acetone (C3H6O) at 0.5 ppm under atmospheric conditions with different operating temperatures ranging from 100 to 400 °C. The results showed that the CH3SH response of USP-made WO3 microspheres was collaboratively enhanced by the creation of pores in the microsphere and co-loading of CuOx and PdOx at low operating temperatures (≤200 °C). More importantly, the CH3SH selectivity against H2S was significantly improved and high selectivity against CH3SCH3, NO, NO2, CH4, C2H5OH, and CH3COCH3 were upheld by the incorporation of PdOx to CuOx-loaded WO3 sensors. Therefore, the co-loading of PdOx-CuOx on porous WO3 structures could be promising strategies to achieve highly selective and sensitive CH3SH sensors, which would be practically useful for specific applications including biomedical and periodontal diagnoses., ACS Applied Materials & Interfaces, 12(37), pp.41728-41739; 2020

WO3 is one of the most popular materials for visible-light photocatalysts. However, its conduction band minimum is too low for water reduction. Here, we found that WO3 can assist water reduction by using visible light in a CuCl2 aqueous solution. Photoirradiation of WO3 in CuCl2 reduces Cu2+ to form indissoluble CuCl adducts, and as-produced CuCl/WO3 was active for H2 evolution under UV-light. This composite has very low reactivity under visible light (>400 nm), but visible-light assisted H2 evolution was observed with simultaneous irradiation with UV light: the activity was increased ∼1.7 fold. Transient absorption measurements revealed that Z-schematic recombination initially takes place between photogenerated electrons in WO3 and holes in CuCl. As a result, the lifetime of electrons in CuCl was increased, enhancing H2 evolution. These results demonstrate that inactive narrow-band gap materials can be used to enhance the activity of wide-band gap materials under sunlight illumination.

WO3 is one of the most popular materials for visible-light photocatalysts. However, its conduction band minimum is too low for water reduction. Here, we found that WO3 can assist water reduction by using visible light in a CuCl2 aqueous solution. Photoirradiation of WO3 in CuCl2 reduces Cu2+ to form indissoluble CuCl adducts, and as-produced CuCl/WO3 was active for H2 evolution under UV-light. This composite has very low reactivity under visible light (>400 nm), but visible-light assisted H2 evolution was observed with simultaneous irradiation with UV light: the activity was increased ∼1.7 fold. Transient absorption measurements revealed that Z-schematic recombination initially takes place between photogenerated electrons in WO3 and holes in CuCl. As a result, the lifetime of electrons in CuCl was increased, enhancing H2 evolution. These results demonstrate that inactive narrow-band gap materials can be used to enhance the activity of wide-band gap materials under sunlight illumination.

The influence of different milling conditions obtained using two high-energy mills on hydrogen desorption from MgH2-WO3 composites was investigated. The morphology, particle and crystallite size were studied as a function of milling speed, vial's volume, and ball-to-powder ratio. The vial's fill level, the number, and type of milling balls and additive's content kept constant. Changes in morphology and microstructure were correlated to desorption properties of materials. Higher milling speed reduced particle size but, there is no significant crystallite size reduction. On the other hand, additive distribution is similar regardless of the energy input. It has been noticed that different energy input on milling blend, which is the result of combined effects of above-mentioned factors, reflects on desorption temperature but not on the kinetics of desorption. In fact, desorption mechanism changes from 2D to 3D growth with constant nucleation rate, despite obtained changes in microstructure or chemical composition of the material. © 2019 Hydrogen Energy Publications LLC

© The Royal Society of Chemistry 2020. Photocatalytic reduction of CO2into solar fuels is regarded as one of the most promising approaches to address the issues of global warming and the energy crisis. The promotion of spatial charge separation and transfer through crystal facet engineering could be conducive to improved photocatalytic activity. In this study, one-dimensional (1D) WO3nanowires with a {110} dominant facet (WO3-110) and two-dimensional (2D) WO3nanosheets with a {001} dominant facet (WO3-001) coupled with CuO nanoparticles are fabricated by a facile method and used for CO2photoreduction. Its composition and structural characterizations suggest that the WO3-CuO hybrid features good contact between the WO3and CuO nanostructures. Under light irradiation, the WO3and WO3-CuO nanostructures are able to photoreduce CO2into CH4. Notably, the prepared WO3-CuO nanohybrids with different exposed facets show improved CO2reduction capability compared to pure WO3and CuO. The heterojunction interface between the WO3photocatalyst and the CuO cocatalyst through p-n contact can facilitate electron-hole pair separation and accordingly results in enhanced photocatalytic performance. With the assistance of the CuO cocatalyst, the {110} facet WO3-CuO hybrid displays superior photoreduction capability compared to the {001} facet WO3-CuO, which is attributed to the difference in the crystal facets in the heterostructure. The {110} facet WO3nanowires have a more negative conduction band edge, contributing to the higher reduction capacity of this sample. On the other hand, it is shown that faster charge carrier transfer efficiency would enable more photoinduced electrons to participate in CO2photoreduction, especially with the involvement of the nanoparticulate CuO cocatalyst. This work provides guidance for designing a hetero-photocatalyst-cocatalyst system through crystal facet engineering.

© The Royal Society of Chemistry 2020. Photocatalytic reduction of CO2into solar fuels is regarded as one of the most promising approaches to address the issues of global warming and the energy crisis. The promotion of spatial charge separation and transfer through crystal facet engineering could be conducive to improved photocatalytic activity. In this study, one-dimensional (1D) WO3nanowires with a {110} dominant facet (WO3-110) and two-dimensional (2D) WO3nanosheets with a {001} dominant facet (WO3-001) coupled with CuO nanoparticles are fabricated by a facile method and used for CO2photoreduction. Its composition and structural characterizations suggest that the WO3-CuO hybrid features good contact between the WO3and CuO nanostructures. Under light irradiation, the WO3and WO3-CuO nanostructures are able to photoreduce CO2into CH4. Notably, the prepared WO3-CuO nanohybrids with different exposed facets show improved CO2reduction capability compared to pure WO3and CuO. The heterojunction interface between the WO3photocatalyst and the CuO cocatalyst through p-n contact can facilitate electron-hole pair separation and accordingly results in enhanced photocatalytic performance. With the assistance of the CuO cocatalyst, the {110} facet WO3-CuO hybrid displays superior photoreduction capability compared to the {001} facet WO3-CuO, which is attributed to the difference in the crystal facets in the heterostructure. The {110} facet WO3nanowires have a more negative conduction band edge, contributing to the higher reduction capacity of this sample. On the other hand, it is shown that faster charge carrier transfer efficiency would enable more photoinduced electrons to participate in CO2photoreduction, especially with the involvement of the nanoparticulate CuO cocatalyst. This work provides guidance for designing a hetero-photocatalyst-cocatalyst system through crystal facet engineering.

A suspended AlGaN/GaN high electron mobility transistor (HEMT) sensor with a tungsten trioxide (WO 3 ) nanofilm modified gate was microfabricated and characterized for ppm-level acetone gas detection. The sensor featured a suspended circular membrane structure and an integrated microheater to select the optimum working temperature. High working temperature (300°C) increased the sensitivity to up to 25.7% and drain current change I DS to 0.31 mA for 1000-ppm acetone in dry air. The transient characteristics of the sensor exhibited stable operation and good repeatability at different temperatures. For 1000-ppm acetone concentration, the measured response and recovery times reduced from 148 and 656 to 48 and 320 s as the temperature increased from 210 °C to 300 °C. The sensitivity to 1000-ppm acetone gas was significantly greater than the sensitivity to ethanol, ammonia, and CO gases, showing low cross-sensitivity. These results demonstrate a promising step toward the realization of an acetone sensor based on the suspended AlGaN/GaN HEMTs., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Electronic Components, Technology and Materials

type:Journal Article, Hydrogen bond based visible-light-response heterojunction photocatalyst Melam/WO3 (MW) has been fabricated for the first time by facile planetary milling treatment. Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric (TG) analysis reveal the formation of hydrogen bonds (NH···O) between melam and WO3. As compared to WO3, the MW not only complete decomposes acetaldehyde, but also shows 10 times and 12 times higher photocatalytic activity for photo-degradation of 2-propanol and photo-generation of H2O2, respectively, under the visible-light irradiation. X-ray photoelectron spectroscopy suggests that the potential difference between N and O (N+H⋯O−) in the heterojunction provides the driving force for the charge transfer from WO3 to melam. Furthermore, hydrogen bonds offer an ultrafast electron pathway for heterojunction. This study demonstrates that hydrogen bond based heterojunction could be a promising approach for developing a new photocatalyst with efficient visible-light photocatalytic activity., source:https://doi.org/10.1016/j.apcatb.2016.12.069

A suspended AlGaN/GaN high electron mobility transistor (HEMT) sensor with a tungsten trioxide (WO 3 ) nanofilm modified gate was microfabricated and characterized for ppm-level acetone gas detection. The sensor featured a suspended circular membrane structure and an integrated microheater to select the optimum working temperature. High working temperature (300°C) increased the sensitivity to up to 25.7% and drain current change I DS to 0.31 mA for 1000-ppm acetone in dry air. The transient characteristics of the sensor exhibited stable operation and good repeatability at different temperatures. For 1000-ppm acetone concentration, the measured response and recovery times reduced from 148 and 656 to 48 and 320 s as the temperature increased from 210 °C to 300 °C. The sensitivity to 1000-ppm acetone gas was significantly greater than the sensitivity to ethanol, ammonia, and CO gases, showing low cross-sensitivity. These results demonstrate a promising step toward the realization of an acetone sensor based on the suspended AlGaN/GaN HEMTs., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Electronic Components, Technology and Materials

Low power consumption, low limits of detection, and low cost are the compelling demands in the world of gas sensors development that motivate the search for new materials. Recently, gas sensors based on organic-inorganic nanocomposite materials have attracted much attention due to their high performance and low working temperatures in comparison with the commercial sensors for Hydrogen sulfide (H₃S) gas. The development of H₂S gas sensors is vital because H₂S is one of the major air pollutants produced in large quantities in petroleum/natural gas drilling and refining. H₂S gas is extremely toxic, corrosive, and potentially lethal at low concentrations. The focus of this thesis project was to fabricate new gas sensors with high sensitivity and low working temperatures to reduce power consumption. The aim of this work is basically to develop H₂S gas sensors with enhanced flexibility, low operating temperature, and high sensitivity and selectivity. The proposed sensor is fabricated based on the integration of nanotechnology and conducting polymer technology. Indeed, the sensor is fabricated using metal oxide semiconducting nanoparticles (NPs) such as Tungsten Oxide (WO₃) and Copper Oxide (CuO), embedded in a newly developed organic polymer (Chitosan) with controllable conductivity. The metal oxide nanoparticles are mixed with the organic solution at certain concentrations to produce the sensing elements membranes using the casting method. The electrical and gas sensing properties of the organic-inorganic hybrid membranes formed by the casted doped solution have been investigated. The results of this study show that the proposed sensors possess very good sensing properties and a reasonable average response time, which is in good agreement with previously reported work in the field of H₂S gas sensing applications. The best response of all the sensors to H₂S gas was obtained at 40°C

Electrochromic materials have attracted the interest of researchers over the last several decades. They are able to change their color upon the application of a voltage. Tungsten oxide (WO3) and titanium oxide (TiO2) are the conventional electrochromic materials and have been studied most, due to their good electrochromic properties and electrochemical stability. Hence the research in this thesis is mainly based on tungsten oxide and titanium oxide electrochromic materials. By adjusting the precursor, nanostructured electrochromic materials were prepared on the substrates with improved electrochromic properties. A thin film of hexagonal WO3 nanowires was grown directly onto a bare fluorine-doped tin oxide glass (FTO) without the assistance of a WO3 seed layer via a facile and low-cost solvothermal method. Compared with the WO3 film synthesized with a seed layer, a faster switching time, higher coloration efficiency and more stable cycling were achieved due to direct nanowire contact with the substrate. In order to improve the contact between the WO3 and FTO, and therefore increase the stability of the electrode, it was annealed under N2 and the cycling life increased by almost a factor of 10. Hierarchical WO3 nanotree-like structures were grown from nanowires by a two-step non-seeded solvothermal technique on FTO. A study of the growth process revealed that the nanotrunks formed before the nanobranches grew, with the trunks orientated along the (002) plane of the hexagonal phase WO3, while the branches were orientated along the (100) and (200) planes. An electrochromic film prepared with WO3 nanotrees are expected to have a large active surface area, which enabled a large optical modulation of 74.7% at 630 nm at the low potential of -0.2 V, fast switching speeds of 2.64 s and 7.28 s for bleaching and coloration, respectively, and a high coloration efficiency of 75.35 cm2 C-1. A nanocomposite TiO2 film was prepared by decorating a rutile TiO2 nanorod (TiO2 NR) array

Transition metal dichalcogenide (TMD) materials crystalize in a layered structure with a stoichiometry MX₂ where M is a transition metal (Mo, W, Tc, Re, V, Nb, Ta, Ti, Zr, Hf) and X is a chalcogen (S, Se, Te). While there is a strong covalent bond between the chalcogen and the metal atoms in each 2-dimensional (2D) sheet, the bulk 3-dimensional crystals are held together by weak van der Waals forces acting on the adjacent 2D sheets allowing for micromechanical and liquid phase exfoliation into nanostructures composed of either a single layer or a few layers. Since the electronic band structure depends not only on the chemistry but also on the number of layers, a whole new range of metal, semimetal and semiconductor materials may be achieved. These properties, among many other advantages (e.g. tunable band structure, high mobility of carriers, easy intercalation with ions), make TMDs appealing and timely for applications in solar cells and photodetectors, heterogeneous catalysis, electrocatalytic electrodes, energy storage and in (electro) chemical sensing. Motivated by the anticipated fascinating properties of TMDs, this research work focuses on the synthesis, characterization and application of a novel hybrid WS₂ nanomaterial. While the original goal of the research work was to develop a simple method to synthesize WS₂ nanowires, it became clear that instead of nanowires a hybrid nanowire-nanoflake (NW-NF) structure could be synthesized by a simple thermal sulfurization of hydrothermally grown WO₃ nanowires. The structure, morphology and composition of the new materials were analyzed by X-ray diffraction, Raman spectroscopy, electron microscopy and X-ray photoelectron spectroscopy. Temperature dependent electrical measurements carried out on random networks of the nanostructures showed nonlinear characteristics and a negative temperature coefficient of resistance indicating that the hybrids were semiconducting. Resistive gas sensors were prepared and expos, Tiivistelmä Siirtymämetallidikalkogenidistä (transition metal dichalcogenide, TMD) olevat materiaalit kiteytyvät kerroksittaisiksi rakenteiksi, joiden stoikiometria on MX₂, missä M on siirtymämetalli (Mo, W, Tc, Re, V, Nb, Ta, Ti, Zr, Hf) ja X on kalkogeeni (S, Se, Te). 2-ulotteisessa (2D) tasossa kalkogeenin ja metallin välillä on voimakas kovalenttinen sidos, mutta suuremmassa kolmiulotteisessa kiteessä viereisiä tasoja sitoo toisiinsa vain heikot van der Waals-voimat, jolloin tasot on mahdollista erottaa mikromekaanisesti ja nestefaasikuorinnalla yksittäisiksi tai muutamasta kerroksesta koostuvaksi nanorakenteeksi. Koska elektronivyörakenne ei riipu ainoastaan kemiallisesta koostumuksesta vaan myös kerrosten lukumäärästä, voidaan muodostaa täysin uusia metallisia, puolimetallisia tai puolijohdemateriaaleja. Nämä ominaisuudet monien muiden lisäksi (esim. räätälöity vyörakenne, korkeanliikkuvuuden varauksen kuljettajat, helppo ionien interkelaatio) tekevät TMD-materiaaleista kiinnostavia ja ajankohtaisia aurinkokennoihin, valokennoihin, heterogeeniseen katalyysiin, sähkökatalyyttisiin elektrodeihin, energiavarastoihin ja sähkökemiallisiin antureihin. TDM-materiaalien oletettavasti kiehtovien ominaisuuksien motivoimana tämä tutkimus keskittyy uusien hybridi-WS₂-nanomateriaalien synteesiin, karakterisoimiseen ja sovellutuksiin. Tutkimuksen alkuperäinen tavoite oli kehittää yksinkertainen menetelmä WS₂-nanolankojen syntetisoimiseksi, mutta kävi ilmi että nanolankojen sijaan syntyi nanolanka-nanohiutale -hybridirakenne (nanowire-nanoflake, NW-NF), kun hydrotermisesti kasvatettuja WO₃-nanolankoja rikitettiin termisesti. Näiden uusien materiaalien rakenne, morfologia ja koostumus on analysoitu röntgendiffraktiolla, Raman-spekstrokopialla, elektronimikroskoopilla ja röntgenfotoelektronispektroskopialla. Valikoimattomista nanorakenteista koostuvien verkostojen lämpötilasta riippuvien sähköisten ominaisuuksien mittaukset osoittavat epälineaarisia piirteitä ja negatiivinen r

Degradation of electrochromic thin films under extended charge insertion and extraction is a technically important phenomenon for which no in-depth understanding is currently on hand. Here, we report on an explorative study of sputter-deposited WO3 films in a Li-ion-conducting electrolyte by use of cyclic voltammetry, in situ optical transmittance, and impedance spectroscopy. A cycling-dependent decrease of the charge capacity could be accurately modeled by a power-law function, and impedance spectroscopy gave evidence for anomalous diffusion as well as a higher charge transfer resistance during deintercalation than during intercalation. Thus, a consistent conceptual picture emerged for the degradation dynamics; it includes the growth of an interfacial barrier layer and also embraces anomalous diffusion coupled with dispersive power-law chemical kinetics.

Tungsten trioxide (WO3) thin films were grown by matrix assisted pulsed laser evaporation (MAPLE) and pulsed laser deposition (PLD), and their properties were investigated for electrochromic applications. The structure, morphology and optical properties of these MAPLE and PLD grown from monoclinic WO3 nano-sized particles WO3 thin films were also studied. A KrF* excimer (λ=248 nm, ζFWHM=25 ns) laser source was used in all experiments. The films were studied by atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) and Fourier transform infrared spectroscopy (FTIR). Cyclic voltammetry measurements were also performed in glove box with Ar atmosphere towards Li electrode, and the coloring and bleaching states were investigated. The morpho-structural investigations disclosed the synthesis of single-phase monoclinic WO3 films consisting of crystalline nano-grains embedded in an amorphous matrix. All thin films showed good electrochromic properties - strong coloration and fast and full bleaching. The effect was observed for many cycles, the strong coloration and full bleaching being preserved. These results are promising for future application of MAPLE and PLD deposited WO3 thin films in the development of electrochromic devices.