Obtención de combustibles solares usando fotocatalizadores a base de grafeno

Tesis por compendio[ES] En las últimas décadas se ha producido un incremento gradual en el consumo energético a escala mundial. Este aumento de las necesidades energéticas lleva asociado el consumo masivo de combustibles fósiles, principalmente petróleo y carbón, que ha tenido como consecuencia la liberación a la atmósfera de enormes cantidades de dióxido de carbono (CO2). El CO2 atmosférico, entre otros gases, se ha relacionado con el fenómeno de "efecto invernadero" responsable del calentamiento global, por lo que con el fin de evitar las dramáticas consecuencias de este fenómeno se está intentando sustituir el uso de combustibles fósiles por otros cuya huella ecológica sea neutra respecto a la emisión de CO2, cuya producción sea sostenible y que puedan ser obtenidos utilizando fuentes de energía renovables. En este sentido, la obtención fotocatalítica de combustibles solares ha sido propuesta como una de las alternativas más prometedoras en la última década. Esta se inspira en la fotosíntesis natural donde el CO2 es utilizado para generar compuestos químicos de alto valor añadido empleando luz solar como fuente de energía. Tradicionalmente los fotocatalizadores empleados han estado basados en materiales semiconductores inorgánicos, sin embargo, en los últimos años se ha apostado por el uso de otros materiales abundantes, no tóxicos y cuya producción sea sostenible, entre ellos el grafeno. En este contexto, en la presente tesis doctoral se describirá la preparación de nuevos fotocatalizadores basados en grafeno y su aplicación en la producción de combustibles solares. En concreto, se describirá la preparación de nanopartículas metálicas soportadas sobre láminas de grafeno, ya sea en forma de película nanométrica o polvo, y se estudiará su aplicación en la producción de hidrógeno a partir de agua o en la metanación de CO2.[CA] En les darreres dècades s'ha produït un increment gradual en el consum energètic a escala mundial. Aquest augment de les necessitats energètiques porta associat el consum massiu de combustibles fòssils, principalment petroli i carbó, que ha tingut com a conseqüència l'alliberament a l'atmosfera d'enormes quantitats de diòxid de carboni (CO2). El CO2 atmosfèric, entre altres gasos, s'ha relacionat amb el fenomen d'"efecte d'hivernacle" responsable del calfament global, de manera que per tal d'evitar les dramàtiques conseqüències d'aquest fenomen s'està intentant substituir l'ús de combustibles fòssils per altres amb una emprempta ecològica neutra respecte a l'emissió de CO2 i la producció dels quals siga possible mitjançant fonts d'energia renovables. En aquest sentit, l'obtenció fotocatalítica de combustibles solars ha sigut proposada com una de les alternatives més prometedores en l'última década. Aquesta s'inspira en la fotosíntesi natural on el CO2 és utilitzat per a generar composts químics d'alt valor afegit emprant llum solar com a font d'energia. Tradicionalment els fotocatalitzadors utilitzats han estat basats en materials semiconductors inorgànics, no obstant, en els últims anys s'ha apostat per l'ús d'altres materials abundants, no tòxics i sostenibles, com ara el grafé. En aquest context, en la present tesi doctoral es descriurà la preparació de nous fotocatalitzadors basats en grafé i la seua aplicació en la producció de combustibles solars. En concret, es descriurà la preparació de nanopartícules metàl·liques suportades sobre làmines de grafé, ja siga en forma de pel·lícula nanomètrica o pols, i s'estudiarà la seua aplicació en la producció d'hidrogen a partir d'aigua o en la metanació de CO2.[EN] Over the last decades there has been a gradual increase in the global energy demand. This increase in the energetic demands involves the massive consumption of fossil fuels, mainly petroleum and coal, and the emission to the atmosphere of huge amounts of carbon dioxide (CO2). The atmospheric CO2, among other gases, has been related with the "greenhouse effect" phenomenon which is responsable of the global warming. In order to avoid the dramatic consequences of this phenomenon, fossil fuels should be substituted by other sustainable ones obtained by renewable energies and whose ecological print is neutral with respect to the CO2 emissions. In this way, the photocatalytic production of fuels has been proposed as a promising alternative during the last decade. This approach is inspired by natural photosynthesis, in which CO2 is used to obtain valuable chemicals by employing solar light as a source of energy. Traditionally, inorganic semiconductor-based photocatalysts have been employed, however, in the last years there is an increasing interest in the use of other abundant, non-toxic and sustainable materials, such as graphene. In this context, the present doctoral thesis will describe the preparation of new photocatalysts based on graphene and their application in the production of solar fuels. More precisely, the thesis will describe the preparation of metallic nanoparticles supported on graphene layers, either on thin films or powder, and it will study their application in the production of hydrogen from water or in the CO2 methanation.Mateo Mateo, D. (2019). Obtención de combustibles solares usando fotocatalizadores a base de grafeno [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/121144TESISCompendi

Photoassisted methanation using Cu2O nanoparticles supported on graphene as a photocatalyst

[EN] Photoassisted CO2 methanation can be carried out efficiently at 250 degrees C using Cu2O nanoparticles supported on few layer graphene (Cu2O/G) as a photocatalyst. The Cu2O/G photocatalyst has been prepared by chemical reduction of a Cu salt (Cu(NO3)(2)) with ethylene glycol in the presence of defective graphene obtained from the pyrolysis of alginic acid at 900 degrees C under Ar flow. Using this photocatalyst a maximum specific CH4 formation rate of 14.93 mmol g(Cu2O)(-1) h(-1) and an apparent quantum yield of 7.84% were achieved, which are among the highest reported values for the gas-phase methanation reaction at temperatures below the Sabatier reaction temperature (4350 degrees C). It was found that the most probable reaction mechanism involves photoinduced electron transfer from the Cu2O/G photocatalyst to CO2, while evidence indicates that light-induced local temperature increase and H-2 activation are negligible. The role of the temperature in the process has been studied, the available data suggesting that heating is needed to desorb the H2O formed as the product during the methanation. The most probable reaction mechanism seems to follow a dissociative pathway involving detachment of oxygen atoms from CO2.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa, grapas, and CTQ2015-69563-CO2-R1) and by the Generalitat Valenciana (Prometeo 2013014) is gratefully acknowledged. J. A. thanks the Universitat Politecnica de Valencia for a postdoctoral scholarship. D. M. also thanks the Spanish Ministry of Science for a PhD Scholarship.Mateo-Mateo, D.; Albero-Sancho, J.; García Gómez, H. (2017). Photoassisted methanation using Cu2O nanoparticles supported on graphene as a photocatalyst. Energy & Environmental Science. 10(11):2392-2400. https://doi.org/10.1039/c7ee02287eS239224001011Yuan, L., & Xu, Y.-J. (2015). 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Journal of the American Chemical Society, 136(45), 15969-15976. doi:10.1021/ja506433kXie, X., Kretschmer, K., & Wang, G. (2015). Advances in graphene-based semiconductor photocatalysts for solar energy conversion: fundamentals and materials engineering. Nanoscale, 7(32), 13278-13292. doi:10.1039/c5nr03338aLavorato, C., Primo, A., Molinari, R., & Garcia, H. (2013). N-Doped Graphene Derived from Biomass as a Visible-Light Photocatalyst for Hydrogen Generation from Water/Methanol Mixtures. Chemistry - A European Journal, 20(1), 187-194. doi:10.1002/chem.201303689Kumar, P., Mungse, H. P., Khatri, O. P., & Jain, S. L. (2015). Nitrogen-doped graphene-supported copper complex: a novel photocatalyst for CO2 reduction under visible light irradiation. RSC Advances, 5(68), 54929-54935. doi:10.1039/c5ra05319fLatorre-Sánchez, M., Esteve-Adell, I., Primo, A., & García, H. (2015). Innovative preparation of MoS2–graphene heterostructures based on alginate containing (NH4)2MoS4 and their photocatalytic activity for H2 generation. Carbon, 81, 587-596. doi:10.1016/j.carbon.2014.09.093An, X., Li, K., & Tang, J. (2014). Cu2O/Reduced Graphene Oxide Composites for the Photocatalytic Conversion of CO2. ChemSusChem, 7(4), 1086-1093. doi:10.1002/cssc.201301194Xiong, Z., Luo, Y., Zhao, Y., Zhang, J., Zheng, C., & Wu, J. C. S. (2016). Synthesis, characterization and enhanced photocatalytic CO2 reduction activity of graphene supported TiO2 nanocrystals with coexposed {001} and {101} facets. Physical Chemistry Chemical Physics, 18(19), 13186-13195. doi:10.1039/c5cp07854gXiang, Q., Cheng, B., & Yu, J. (2015). Graphene-Based Photocatalysts for Solar-Fuel Generation. Angewandte Chemie International Edition, 54(39), 11350-11366. doi:10.1002/anie.201411096Li, F., Zhang, L., Tong, J., Liu, Y., Xu, S., Cao, Y., & Cao, S. (2016). Photocatalytic CO2 conversion to methanol by Cu2O/graphene/TNA heterostructure catalyst in a visible-light-driven dual-chamber reactor. Nano Energy, 27, 320-329. doi:10.1016/j.nanoen.2016.06.056Shown, I., Hsu, H.-C., Chang, Y.-C., Lin, C.-H., Roy, P. K., Ganguly, A., … Chen, K.-H. (2014). Highly Efficient Visible Light Photocatalytic Reduction of CO2 to Hydrocarbon Fuels by Cu-Nanoparticle Decorated Graphene Oxide. Nano Letters, 14(11), 6097-6103. doi:10.1021/nl503609vLum, Y., Kwon, Y., Lobaccaro, P., Chen, L., Clark, E. L., Bell, A. T., & Ager, J. W. (2015). Trace Levels of Copper in Carbon Materials Show Significant Electrochemical CO2 Reduction Activity. ACS Catalysis, 6(1), 202-209. doi:10.1021/acscatal.5b02399Zou, J.-P., Wu, D.-D., Luo, J., Xing, Q.-J., Luo, X.-B., Dong, W.-H., … Suib, S. L. (2016). A Strategy for One-Pot Conversion of Organic Pollutants into Useful Hydrocarbons through Coupling Photodegradation of MB with Photoreduction of CO2. 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Graphene supported NiO/Ni nanoparticles as efficient photocatalyst for gas phase CO2 reduction with hydrogen

[EN] The photocatalytic activity of NiO/Ni nanoparticles (NPs) supported on defective graphene (NiO/Ni-G) has been tested for the photoassisted CO2 reduction with H-2. NiO/Ni-G was prepared by H-2 reduction of NiCl2 adsorbed on few-layers defective G and storage under air. An optimal Ni loading of 23 wt% was found, reaching the maximum specific CH4 formation rate (642 mu mol CH4 g(Ni)(-1) h(-1) at 200 degrees C) and quantum yield of 1.98%. Under the same conditions Ni NPs supported on silica-alumina or NiO NPs exhibit notably lower specific CH4 production rates than NiO/Ni-G. It was found that H2O formed in the reaction has a detrimental influence on the photocatalytic activity and evidence supports that H2O desorption is one of the reasons why the system requires heating. Under continuous flow operation, undesirable water molecules were easier desorbed from the NiO/Ni-G photocatalyst than in the batch mode, reaching a steady specific CH4 production rate of 244.8 mu L h(-1) for 50 mg of NiO/Ni-G catalyst with a residence time of 3.1 s. Quenching experiments with electron donor of different oxidation potential (dimethylaniline, anisole and p-xylene) are compatible with a mechanism involving photoinduced charge separation.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa SEV-2016-0683, Grapas and CTQ2015-69563-CO2-R1) and by the Generalitat Valencia (Prometeo 2013-014) is gratefully acknowledged. J. A. thanks the Universitat Politecnica de Valencia for a postdoctoral scholarship. D. M. also thanks Spanish Ministry of Science for PhD Scholarship.Mateo-Mateo, D.; Albero-Sancho, J.; García Gómez, H. (2018). Graphene supported NiO/Ni nanoparticles as efficient photocatalyst for gas phase CO2 reduction with hydrogen. Applied Catalysis B Environmental. 224:563-571. https://doi.org/10.1016/j.apcatb.2017.10.071S56357122

Liquidity spillover effects of equity offerings over dual-class shares

We study the spillover effect from equity offerings over dual-class shares. Whereas, evidence has been found that a seasoned equity offering improves stock liquidity, the effect over the liquidity of different type shares of the same firm has not been explored. We use equity offerings of five Latin American countries: Brazil, Chile, Colombia, Mexico and Peru, during 1995 to 2012, because dual-class shares are widely used in the regions. In spite of the expected information asymmetry reduction, using panel data models we found a stock liquidity reduction of dual-class shares upon the offering; consistent with trading migration effects, according with the theory of inventory costs

The mechanism of photocatalytic CO2 reduction by graphene-supported Cu2O probed by sacrificial electron donors

[EN] Cu2O nanoparticles of 5 nm average size have been adsorbed (1.74 wt% loading) on defective graphene (Cu2O/G) previously obtained by the pyrolysis of alginic acid sodium salt. The Cu2O crystal phase was determined by XRD. XPS shows that the external layers of the Cu2O nanoparticles are constituted mainly of Cu+ although a certain percentage of CuII+ was also present. Cu2O/G is a photocatalyst for the CO2 reduction to methane in the presence of sacrificial agents, and the rate of CH4 production depends on the oxidation potential of the electron donor. This relationship supports a mechanism involving photo-induced charge separation with the generation of electrons and holes. The highest CH4 formation rate upon UV-Vis irradiation of Cu2O/G with a 300 W Xe lamp was achieved for dimethylaniline reaching 326 mu mol CH4 per g per h. The spectral response of the Cu2O photocatalyst shows, however, that the response of the photocatalyst is mainly due to UV irradiation, indicating that light absorption at the low Cu2O loading on the Cu2O/G photocatalyst occurs mainly on the graphene component.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa SEV2016-0683, GRAPAS, and CTQ2015-69563-CO2-R1) and the Generalitat Valenciana (Prometeo 2015-083) is gratefully acknowledged. J. A. thanks the Universitat Politecnica de Valencia for a postdoctoral scholarship. D. M. also thanks the Spanish Ministry of Science for the PhD scholarship.Mateo-Mateo, D.; Asiri, AM.; Albero-Sancho, J.; García Gómez, H. (2018). The mechanism of photocatalytic CO2 reduction by graphene-supported Cu2O probed by sacrificial electron donors. Photochemical & Photobiological Sciences. 17(6):829-834. https://doi.org/10.1039/c7pp00442gS82983417

Design of reconfigurable RF circuits for self compensation

In this paper we will show how a combination of design choices allows for the design of a PVT robust RF front-end with minimum area, power and nominal specifications penalty.Peer ReviewedPostprint (published version

La Leyenda como recurso didáctico en el segundo internivel de Educación Primaria

Con este trabajo pretendo dar a conocer la importancia de la literatura infantil, especialmente de las leyendas, para conseguir el desarrollo de la creatividad del alumnado. Intento, además, inculcar la importancia de la leyenda como recurso didáctico y acercar a la población en edad escolar a la tradición oral ya que esta ha perdido la importancia que merece dentro de nuestra sociedad. El trabajo tiene dos partes, una teórica centrada en definir y explicar aspectos relacionados con la literatura infantil y las leyendas. Otra práctica, que consta de una exposición de un proyecto creativo aplicado en el aula durante el periodo de prácticas. En ésta se revisan aspectos relacionados con la elaboración del proyecto y otros relacionados con su aplicación, como son los resultados del análisis de los datos obtenidos tras su desarrollo.Grado en Educación Primari

Plan de Acción Local en los Valles de Sedano, Valdelucio y Rudrón (Burgos) basado en el aprovechamiento del sector forestal y fundamentado en la participación de la sociedad

El presente proyecto de fin de Máster busca conformar un Plan de Desarrollo Rural en los valles de Sedano, valdelucio y Rudrón co el objetivo de dinamizar su tejido socioeconómico. Para ello se realizará un diagnóstico territorial, demográfico, económico, social e infraestructural de la zona objeto de estudio. Posteriormente se utilizará la metodología de la participación pública para comprender y analizar las necesidades de los pobladores de la zona, en base a esas necesidades y percepciones se elaborará un Plan de acción con líneas estratégicas, programas y proyectos y posteriormente un plan de seguimiento y un plan de información y comunicación.Departamento de Producción Vegetal y Recursos ForestalesMáster en Ingeniería de Monte

Die Wahrheit hinter dem Schweigen. Der Konflikt und das Leiden dreier Generationen in Alexandra Senffts Schweigen tut weh: Eine deutsche Familiengeschichte

Trabajo de fin de Grado. Grado en Estudios Alemanes. Curso académico 2019-2020[GE]Die folgende Arbeit will anhand des biographischen Werkes Schweigen tut weh: Eine deutsche Familiengeschichte von Alexandra Senfft zeigen, wie sich die Vermittlunsgprozesse des familiären Gedächtnisses über den Nationalsozialismus in der Literatur nach 1990 widerspiegeln. Dabei spielen Trauma, Schweigen und Loyalität eine grundlegende Rolle im familiären Gedächtnis, verhindern die Aufdeckung der Wahrheit der nationalsozialistischen Vergangenheit der Familie und verursachen das Unglück der Mutter der Autorin.[ES]El siguiente trabajo quiere mostrar cómo son reflejados los procesos de transmisión de la memoria familiar sobre el nacionalsocialismo en la literatura posterior a 1990 usando como base la obra de carácter biográfico Schweigen tut weh: Eine deutsche Familiengeschichte de Alexandra Senfft, en la que el trauma, el silencio y la lealtad jugarán un papel fundamental en la memoria familiar, que impedirán destapar la verdad del pasado nacionalsocialista familiar y serán causantes de las desgracias de la madre de la autora

Nuevos lenguajes en el repertorio guitarrístico

Este artículo quiere ser un acercamiento a un repertorio más vanguardista y menos conocido para el público. Durante la presentación de estas obras, se abordará también el uso de algunas de las técnicas extendidas utilizadas por los compositores, que, ya sea por novedosas o por una original forma de anotarlas, se consideran de interés