Author: MARIANA HINOJOSA REYES
MARIANA HINOJOSA REYES (2015)
"Debido al estilo de vida de las sociedades actuales, los automóviles representan una parte inseparable de la vida diaria, sin embargo, generan altas cantidades de emisiones tales como: monóxido de carbono, hidrocarburos, compuestos orgánicos volátiles, óxidos de nitrógeno, entre otros. La emisión de CO es mayoritaria y representa un peligro para los seres vivos y ecosistemas, ya que es un producto de combustión incompleta. Una manera de contrarrestarlo es completando su oxidación a dióxido de carbono, pues este último es inofensivo, ya que existe naturalmente en la atmósfera. Una posible solución a esta problemática ambiental es el desarrollo de energías alternas a partir de recursos renovables, desde este punto de vista, el hidrógeno resulta ser la energía del futuro pues se puede obtener a partir del agua, además de que su eficiencia energética es superior a la de combustibles fósiles y el único producto de su combustión es vapor de agua. En este sentido, en esta investigación doctoral se abordaron tres reacciones: 1) oxidación de CO, 2) reacción de desplazamiento de vapor de agua (water ¿ gas shift) y 3) la ruptura de la molécula de agua (water splitting), las cuales fueron catalizadas por materiales nanoestructurados basados en dióxido de titanio modificado con níquel, cobre o hierro, a concentraciones óptimas para lograr el dopaje y/o formación de óxidos mixtos. Estos soportes, TiO2-Ni, TiO2-Cu y TiO2-Fe, además fueron modificados superficialmente con nanopartículas de oro de aproximadamente 3 nm de diámetro. El oro nanométrico se caracteriza por su alta afinidad por el monóxido de carbono y por su capacidad de actuar como trampa de electrones durante el proceso fotocatalítico. Los catalizadores Au/TiO2-Fe y Au/TiO2-Ni mostraron una alta estabilidad y actividad catalítica durante la reacción de oxidación de CO, alcanzando conversiones del 70 y 90 %, respectivamente, a temperaturas inferiores a la ambiente. Además, por espectroscopia infrarroja in situ (DRIFTS) se determinó la fuerte sinergia tanto del níquel como del hierro durante la quimisorción de CO, creando nuevos sitios de adsorción en el hierro y la especie puenteada, Ni(CO)2. Durante la purificación/producción de hidrógeno mediante la WGSR, los catalizadores Au/TiO2-Ni tuvieron un alto desempeño catalítico resultando en una conversión de CO 1.7 veces superior a los catalizadores de referencia, Au/TiO2 y Au/P25."
"Nowadays, the modern societies are based on the use of cars which are an essential part of daily life. However, these vehicles generate high amounts of emissions such as carbon monoxide, hydrocarbons, volatile organic compounds, nitrogen oxides, among others. Of all these emissions, CO is the principal pollutant and represents a hazard compound to living beings and ecosystems. One way to diminish a hazardous effect is to complete it oxidation to carbon dioxide at room temperature. A possible solution to this serious environmental problem is the generation of clean alternative energy from renewable resources. From this point of view, hydrogen is the energy of the future because can be obtained from water, and their energy efficiency is higher than that of fossil fuels and the only product of combustion is steam water. In this sense, this doctoral research is focussed in three important environmental reactions: 1) catalytic CO oxidation, 2) water – gas shift and 3) photocatalytic water splitting, which were catalyzed by nanostructured materials based on titania modified with nickel, copper or iron, at optimal concentrations to achieve doping and/or mixed oxides formation. This supports, namely TiO2-Ni, TiO2-Cu, and TiO2-Fe, also were superficially modified with gold nanoparticles about 3 nm in diameter. Nanometric gold is characterized by its high carbon monoxide affinity and its ability to act as an electron trap during the photocatalytic process. Au/TiO2-Fe and Au/TiO2-Ni catalysts show a high stability and catalytic activity during the CO oxidation reaction, achieving conversions of 70 and 90 %, respectively, at room or lower temperatures. Furthermore, the in situ infrarred spectroscopy (DRIFTS) allows to determinate a strong sinergy of both nickel and iron during the CO quimisorption. The new adsorption sites in the iron and bridged species, Ni(CO)2, are responsible for enhancing the oxidation at lower temperature. In the hydrogen purification/production by the WGSR, the Au/TiO2-Ni catalyst had a high catalytic performance, resulting in a CO conversion 1.7 times higher than the reference catalysts, Au/TiO2 and Au/P25."
MARIANA HINOJOSA REYES (2011)
"Actualmente, una de las principales causas de la contaminación atmosférica es la emisión de compuestos orgánicos volátiles (COVs). Para reducir la contaminación por COVs, se han estudiado varias tecnologías de tratamiento; entre estas destacan los sistemas biológicos y fisicoquímicos, así como los procesos de oxidación. En este trabajo se aprovechan las ventajas de un sistema híbrido empleando un proceso de oxidación avanzada (POA) como sistema de pretratamiento acoplado a un sistema biológico para así tener mayores capacidades de eliminación (CE) y eficiencias de remoción (ER) utilizando etilbenceno (EB) como modelo de COV. Los procesos fotocatalíticos se realizaron a longitudes de onda de 254 y 365 nm empleando los catalizadores P25-Degussa, TiO2, TiO2-In 1%, TiO2-In 5%; los cuales fueron preparados por dopaje sol-gel (In 1 y 5% w/w, respectivamente) y caracterizados mediante espectroscopia FT-IR, Raman y UV-Vis de reflectancia difusa, difracción de rayos X y fisisorción de nitrógeno. Además, se hicieron las respectivas fotólisis como experimento control. Los materiales fueron soportados en perlita, manejando concentraciones de entrada de EB de 1.5 g/m3 y tiempos de residencia de 60 s. La concentración de EB fue cuantificada mediante CG-FID. Por otro lado, la biofiltración se realizó en un reactor de lecho fijo utilizando perlita como soporte y un consorcio bacteriano tomado de suelos contaminados con hidrocarburos de alto peso molecular. El periodo de operación fue de 100 días, con concentraciones de entrada de EB entre 1.50 y 1.75 g/m3 con un tiempo de residencia de 60 s. Se cuantificó EB y CO2 mediante CG-FID y CG-TCD, respectivamente. Debido a su velocidad de degradación (30.5 ng/gmin) y CE de 19.2 g/m3h (ER 21.9%), el sistema TiO2-In 1%/365 nm fue elegido como sistema de pretratamiento. Mientras tanto, en el biofiltro se obtuvo una CE de 60 g/m3h (ER 40%). El sistema acoplado operó durante 15 días a una concentración de entrada de 3.5 g/m3 de y un tiempo de residencia de 60 s para EB, mostrando una CE total de 150 g/m3h (ER 75%). Los resultados anteriores muestran que la tecnología híbrida utilizada en el presente trabajo puede ser prometedora para mejorar la degradación de COVs. No obstante, es necesario optimizar parámetros como tiempo de residencia, humedad de la corriente de entrada, entre otros, para incrementar las CE y ER."
"Nowadays, emissions of volatile organic compounds (VOCs) are one of the main sources of atmospheric pollution. In order to decrease VOCs pollution, several outstanding technologies have been studied; such as biological and physicochemical system, and oxidation processes as well. In the present project we take advantage of the benefits of a hybrid system that uses an advanced oxidation process (AOP) as pretreatment process and is coupled up to a biological system and therefore attain better elimination capacity (EC) and removal efficiency (RE), using ethylbenzene (EB) like as VOC model. The photocatalytic processes were performed at wavelengths of 254 and 365 nm, using P25-Degussa, TiO2, TiO2-In 1%, TiO2-In 5% catalysts, which were doped (In 1 and 5% w/w, respectively) by employing sol-gel method and characterized by FTIR, UV-Vis DR and Raman spectroscopy, X-ray diffraction, and nitrogen physisorption. In addition, the respective photolysis were used as standard. Materials were supported on pearlite with EB inlet concentration of 1.50 g/m3 and
residence time of 60 s. EB concentration was quantified by GC-FID. On the other hand, biofiltration was performed in a fixed bed reactor using pearlite as supporting material, and a bacterial consortium that was taken from high-molecular-weight hydrocarbon-contaminated soils. The operating time was 100 days, with EB inlet concentrations in the range of 1.50-1.75 g/m3, and residence time of 60 s. EB and
CO2 were quantified by GC-FID and GC-TCD, respectively. Due to its degradation rate (30.5 ng/gmin) and EC of 19.2 g/m3h (RE 21.9%), the TiO2-In 1%/365 nm was selected for being the pretreatment system. Meanwhile, the biofilter had a EC of 60 g/m3h (RE 40%). The coupled system operated during 15 days with an EB inlet concentration of 3.5 g/m3, and residence time of 60 s, resulting in a total EC of 150 g/m3h (RE 75%). These results show that the hybrid technology described herein is promising for VOCs degradation. However, paramenters such as residence time and humidity of input current should be optimized in order to increase EC and RE."
Sistema Acoplado Biofiltración Procesos de Oxidación avanzada Etilbenceno CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO CIENCIAS DE LA ATMÓSFERA CONTAMINACIÓN ATMOSFÉRICA
Doped indium–TiO2 mesoporous photocatalysts were synthesized by a controlled sol–gel process. The catalysts were characterized by XRD, N2 physisorption, UV–Vis-DRS, Photoluminescence and Raman spectroscopies. The indium–TiO2 semiconductors were immobilized on perlite granules by a simple coating method and examined by SEM-EDS. Photocatalytic activity of the In–TiO2/perlite materials was evaluated by the decomposition of ethylbenzene in moist air in a plug-flow photoreactor with a concentric cylindrical configuration, under 254 or 365 nm irradiation. Ethylbenzene was substantially decomposed by oxidation in an air steam flowing over the In-doped coated/perlite granules. The decomposition rate of ethylbenzene may be attributed to the presence of indium, which can increase surface phenomena and sensitize the response of the semiconductors to the 365 nm UV irradiation. The materials with indium
content show enhanced decomposition rates in contrast to the undoped materials. The study indicates that the immobilized In–TiO2/perlite photocatalysts may be a practical way to decompose volatile organic compounds in a stream of moist gas.
"In this work, we explore the hydrogen production via the water splitting process on Rh-WO3 photocatalysts supported on nanotubes of TiO2. H2 production tests were performed in a 2-propanol-water solution. The support (titanate nanotubes, NT) was obtained, first, by the sol-gel method followed by the hydrothermal method. The surface of the titanate nanotubes was decorated with nanoparticles of rhodium and tungsten by applying microwave irradiation. The photocatalysts were characterized by XRD, HR-TEM, UV-vis, SBET, H2-TPR and XPS. For the photocatalytic tests, we employed two photocatalysts with 0.3 and 0.5 wt.% of Rh on WO3/TiO2 (3 wt.% of WO3) under UV-A light radiation at 365 nm and visible light at 450 nm. We found that 56 ?mol h?1 of hydrogen were produced by photolysis. The support (NT) produced 59 ?mol h?1 of hydrogen. The addition of 3 wt.% of WO3 to the nanotubes increased slightly the H2 production (66 ?mol h?1). However, a promotional effect was observed when rhodium was added to the 3WO3/NT photocatalysts. In fact, the highest hydrogen production was obtained on the 0.5Rh-3WO3/NT photocatalyst (234 ?mol h?1), even after seven cycles of 8 h. We suggest that Rh acts as co-catalyst of the WO3 during the water splitting process. A diagram for the density of states, based on the UV-vis and XPS results, is proposed."
"Cu-TiO2 photocatalysts were prepared by the sol-gel method. Copper loadings from, 1.0 to 5.0 wt % were used. The materials were annealed at different temperatures (from 400 to 600 °C) to study the formation of brookite and copper ionic species. The photocatalysts were characterized by X-ray diffraction, UV–vis, Raman and XPS spectroscopies, H2-temperature programmed reduction (TPR), N2 physisorption, and SEM–EDS to quantify the actual copper loadings and characterize morphology. The photocatalysts were evaluated during the hydrogen photocatalytic production using an ethanolic solution (50% v/v) under UV and visible radiation. The best hydrogen production was performed by Ti-Cu 1.0 with an overall hydrogen production that was five times higher than that obtained with photolysis. This sample had an optimal thermal treatment at 500 °C, and at this temperature, the Cu2O and brookite/anatase ratio boosted the photocatalytic production of hydrogen. In addition, a deactivation test was carried out for the most active sample (TiO2-Cu 1.0), showing unchanged H2 production for three cycles with negligible Cu lixiviation. The activity of hydrogen-through-copper production reported in this research work is comparable with the one featured by noble metals and that reported in the literature for doped TiO2 materials."
"Nickel-doped-TiO2 catalysts were prepared by the sol–gel method and surface modified with gold nanoparticles (AuNPs) by the urea-deposition-precipitation technique. The as-synthesized catalysts were characterized by X-ray diffraction, Raman and XPS spectroscopies, N2 physisorption, STEM-HAADF microscopy and TPR hydrogen consumption. The Au/TiO2-Ni catalysts were evaluated catalytically performing CO oxidation reactions. The catalyst with nickel content of 1 wt. % (Au/TiO2-Ni 1) showed the highest CO conversion with respect to the high-nickel-content or bare/commercial TiO2 at 0 °C. In situ DRIFTS showed a strong participation of both nickel due to the presence of surface-nickel-metallic nanoparticles formed during the CO adsorption process at reaction temperatures above 200 °C, and surface-bridged-nickel-CO species. A minor deactivation rate was observed for the Au/TiO2-Ni 1 catalyst in comparison with the Au/TiO2 one. The oxygen vacancies that were created on the sol–gel-doped TiO2 improved the catalytic behavior during the performance of CO oxidation reactions, and inhibited the AuNP sintering."
"Heterostructures based on ZnO-TiO2/delaminated montmorillonite coated with Ag have been prepared by sol–gel and photoreduction procedures, varying the Ag and ZnO contents. They have been thoroughly characterized by XRD, WDXRF, UV–Vis, and XPS spectroscopies, and N2 adsorption, SEM, and TEM. In all cases, the montmorillonite was effectively delaminated with the formation of TiO2 anatase particles anchored on the clay layer’s surface, yielding porous materials with high surface areas. The structural and textural properties of the heterostructures synthesized were unaffected by the ZnO incorporated. The photoreduction led to solids with Ag nanoparticles decorating the surface. These materials were tested as photocatalysts for the degradation of several emerging contaminants with different nitrogen-bearing chemical structures under solar light. The catalysts yielded high rates of disappearance of the starting pollutants and showed quite stable performance upon successive applications."
"The photocatalytic degradation/adsorption process of the β-blocker atenolol (ATL) under UV irradiation is described using two types of silver decorated catalysts: silver/titania and silver/titanates. The silver ions were reduced on the surface of TiO2-P25-Degussa using gallic acid. Silver/titanates were prepared by a microwave-assisted hydrothermal method using the silver/titania as the starting material to obtain the hydrogen titanate (H2Ti3O7) structure with tubular morphology. These materials were characterized by X-ray diffraction, UV-Vis spectroscopy, N2 physisorption, temperature programmed reduction, TEM, and FTIR spectroscopy. During the photocatalytic process, the ATL molecules were completely converted to amino-diol byproducts. It is the first time that these materials have been applied during the photocatalytic process in the degradation of pharmaceuticals products. The success of the silver nanoparticles (2 nm) consists of the homogeneous distribution over the surface of titanate nanotubes inhibiting the hole/electron recombination promoting the oxidation process. The Ag@H2Ti3O7 with a concentration of silver as 1.0% shows the highest adsorption/degradation of ATL than the Ag@TiO2 and the P25-Degussa. The great performance in the reuse test consists in the strong attachment of the silver nanoparticles on the titanium surface that inhibits the silver lixiviation during the photocatalytic tests."