Dissertations / Theses on the topic 'Photoelectrocatalysi'

Générer des carburants solaires, comme l’hydrogène via la photoélectrolyse de l’eau, est une stratégie à explorer pour notre futur énergétique. Pour éviter l’emploi du platine en tant que catalyseur de production d’hydrogène, des métaux abondants peuvent être utilisés. Au laboratoire, le complexe diimine-dioxime de cobalt, catalyseur moléculaire de réduction des protons, a pu être immobilisé pour créer une cathode produisant de manière stable de l’hydrogène en milieu aqueux. Dans ces travaux, nous avons étudié l’introduction du catalyseur dans des dispositifs photoélectrocatalytiques. Différentes conditions opératoires dans l’eau, solvant de choix, ont été examinées. Le complexe se dégrade s’il est en solution mais son activité est maintenue, même en présence d’oxygène, s’il est supporté sur électrode. Cette électrode a ainsi pu être intégrée en cellule tandem. De nouveaux dérivés du complexe ont aussi été développés pour l’attachement sur oxydes transparents conducteurs. Un dérivé a été co-immobilisé avec des photosensibilisateurs sur une surface de NiO, oxyde de type p. Les photocathodes co-greffées obtenues ont été caractérisées par un ensemble de techniques analytiques et ont démontré la production d’hydrogène en conditions photoélectrocatalytiques. Des entités colorant-catalyseur pouvant s’ancrer sur surface ont également été synthétisées et ouvrent de nouvelles voies pour élaborer des photocathodes moléculaires
Solar fuels generated from the light-induced splitting of water into H2 and O2 is an appealing strategy for securing future energy. The use of platinum for catalyzing hydrogen evolution may be bypassed with earth-abundant catalysts. In a previous study, our lab realized the immobilization of a proton reduction catalyst, the cobalt diimine-dioxime molecular complex, within a cathode material steadily evolving H2 from fully aqueous media. In this work, we report on the implementation of this catalyst into light-driven devices. Operating conditions in the solvent of interest, water, were screened. The molecular catalyst degrades when free in solution, but retains activity when supported on an electrode, even in the presence of O2, and could thus be integrated into a tandem cell. Further on, new derivatives of the catalyst were developed for the attachment onto transparent conducting oxides. Co-grafted photocathodes were constructed by anchoring a functionalized catalyst along with photosensitizers onto p-type NiO. These architectures were checked by a whole set of analytical techniques and light-driven catalytic hydrogen evolution was achieved by photocathodes assessed under device-related photoelectrochemical conditions. Immobilizable dye-catalyst dyads were also successfully synthetized as alternative derivatives and open up new possibilities to develop molecular photocathodes

La photoelectrocatalyse de l'eau par rayonnement solaire est une solution communément proposée pour la production propre d'hydrogène. En termes de rendement solaire-à-hydrogène, un tandem dual photosystème est accepté comme la configuration plus efficace concernant les cellules photoelectrocatalytique pour la dissociation de l'eau. Ce travail s'intéresse au trioxyde de tungstène (WO3) et au bismuth vanadate (BiVO4) sous la forme de photoanodes type n en couches minces pour la complétion d'oxydation de l'eau dans la demi-réaction pour la dissociation complète de l'eau dans une cellule tandem dual photosystème photoelectrocatalytique. Ces couches minces sont fabriquées par des méthodes robustes, économiques, et extensibles de sol-gel dip coating, et caractérisées par différentes techniques pour vérifier leurs caractéristiques physiques et leur performance photoelectrochimique. WO3 et BiVO4 sont optimises par nanostructuration, modification des couches interfaciales, et addition des co-catalyseurs de surface pour améliorer les performances et la stabilité, respectivement dans des conditions acides et neutres. Ces matériaux sont couples avec une photocathode de type p en oxyde de cuivre (II) pour compléter la réaction de dissociation de l'eau. La cellule photoelectrocatalytique ainsi construite est inspirée par la littérature concernant les systèmes innovateurs de tandem dual photosystèmes. Ce travail aboutit à l'une des seules cellules de dissociation de l'eau par photoelectrocatalyse à base des oxydes de métaux, fabriquée via des techniques faciles et économiques. L'efficacité de la production solaire-à-hydrogène est de 0.01%, et applied-bias-to-photon efficacité de 0.06%
Solar water splitting by photoelectrocatalysis is a proposed long term solution for the production of renewable hydrogen. A wired dual photosystem photoelectrocatalytic cell is thermodynamically considered to possess the highest attainable solar-to-hydrogen efficiency. To realize a photoelectrocatalytic water splitting cell for practical application, facile fabrication methods and abundant low cost materials are essential. This research investigates tungsten trioxide (WO3) and bismuth vanadate (BiVO4) as thin film n-photoanodes to complete the oxygen evolution half reaction for water splitting application in a tandem dual photosystem photoeletrocatalyic water splitting cell. These thin films are fabricated by low cost, robust, scalable, sol-gel dip coating methods and characterized by several techniques to verify the physical characteristics and photochemical performance. WO3 and BiVO4 are optimized by nanostructuration, interfacial surface modification, and addition of surface co-catalysts to increase performance and stability in acidic and neutral conditions, respectively. These materials are coupled with a copper (II) oxide p-photocathode to drive the hydrogen evolution reaction in a photoelectrocatalyic cell to complete the water splitting reaction. The photoelectrocatalytic cell constructed is inspired by previous literature reports encompassing an innovative tandem dual photosystem approach. As a result, this research reports one of the only entirely metal oxide based photoelectrocatalytic water splitting cells, fabricated by inexpensive, unexcessive techniques, resulting in a solar-to-hydrogen efficiency of 0.01% and an applied bias to photon efficiency of 0.06%

Solar energy conversion and storage into hydrogen is a valuable approach to capture the energy that is freely available from sunlight and to turn it into a clean fuel. Photoelectrochemical (PEC) water splitting through the dual-absorber tandem cell technology has emerged as a promising strategy to this aim. The work conducted in the frame of this PhD thesis aimed at playing a part in the development and optimization of efficient oxide-based semiconductor photoanodes for water oxidation, which is the kinetic bottleneck of the overall PEC water splitting process. Photoanodes based on films of absorbing materials were successfully synthesized with a high optical transparency as important requirement for maximizing the solar energy conversion efficiency of the final tandem cell device. Subsequently, their intrinsic properties as single photoabsorber photoanodes were largely improved, on the basis of the results obtained through comprehensive PEC studies in parallel with thorough structural, morphological, and spectroscopic investigations. The attention was focused on three different classes of promising ternary metal oxides, able to absorb a large portion of the solar spectrum, namely i) BiVO4 (bandgap Eg = 2.4 eV), known for its excellent solar light to hydrogen conversion efficiency, ii) the copper tungstate-based materials CuWO4 (Eg = 2.3 eV) and CuW(1-x)Mo(x)O4 (Eg = 2.0 eV), ideal to be employed as visible-light active alternative to WO3, and iii) ZnFe2O4 (Eg = 2.0 eV) belonging to the spinel ferrites class, possessing excellent photothermal and chemical stability. Specifically, BiVO4 was studied either as a visible light sensitizer towards TiO2 or as a single photoanode material to focus on the identification and improvement of its intrinsically poor electron transport and interfacial transfer properties. In the first case, the TiO2/BiVO4 heterojunction system was proved to be effective in producing highly reductive electrons, suitable for overall water splitting, through TiO2 sensitization towards visible light. This, together with the counterintuitive mechanism at the basis of the observed impressive functionality, was effectively disclosed through combined PEC and photocatalytic reduction test studies. The multifaceted role of Mo6+ doping onto both the bulk and surface properties of BiVO4 films was also revealed through an in-depth PEC and impedance spectroscopy study. By improving either the bulk conductivity or the interfacial charge transfer of optimized Mo6+ doped BiVO4 photoanodes a conspicuous enhancement was attained of their photoactivity towards water oxidation with respect to the pure material. The presence of intra-gap states in CuWO4, acting as electron traps and thus being responsible for a severe internal charge recombination, was verified by means of the first ultrafast transient absorption study performed with this material, in combination with both an electrochemical and a photochromic characterization. This issue, which strongly limits the PEC performance of CuWO4 photoanodes, was addressed by adopting a 50% Mo for W substitution resulting in CuW0.5Mo0.5O4 photoanodes, exhibiting not only a greatly extended visible light-induced photoactivity compared to the pure material, as a result of enhanced absorption, but also a considerably improved charge separation. All these factors contributed to the much better PEC performance attained with respect to CuWO4 electrodes. This study was finalized by the identification of a suitable hole scavenger species for copper tungstate-based materials, able to ensure enhanced photocurrent generation compared to pure water oxidation while minimizing dark currents. Finally, in the frame of my seven months stage in Prof. Sivula’s group at the EPFL in Lausanne, a thorough study was performed on the impact that several parameters, such as the annealing temperature, the film thickness and the creation of oxygen vacancies through a reductive treatment in hydrogen atmosphere, have on the PEC performance of ZnFe2O4 photoanodes. The verified synergism between the higher crystallinity of the films subjected to a high-temperature annealing treatment and the hydrogenation efficiency, which proved effective in optimizing charge separation in the thicker photoactive layers, allowed one to maximize the performance of ZnFe2O4 electrodes for water oxidation. This study also shed light onto the strict correlation occurring between structural parameters, i.e. the film crystallinity and the spinel inversion degree, and the resulting PEC performance, which proved to be in turn controlled by the film morphology.

Thesis advisor: Udayan Mohanty
Among the existing strategies to direct solar energy harvesting and storage, solar fuel production by photoelectrocatalysis promises a comparatively simple, low-cost route. The science behind this process is straightforward: stable semiconductors absorb sunlight and use the energy to excite charges, which then drive redox reactions at the surface. Careful studies of the photoelectrode surface provide important considerations in building a high-performance photoelectrode. Specifically, I focused on controlling the surface band alignment of Cu2O photocathode|water for hydrogen evolution reaction. A ZnS buried heterojunction is formed to improve the photovoltage. Then I focused on understanding the influence of chemical species on surface kinetics and energetics for water oxidation reaction. Two hematite photoanodes with preferably exposed {001} and {012} facets were examined. Further, I systematically studied three different types of surfaces, bare hematite, hematite with a heterogenized Ir water oxidation catalyst (WOC), and a heterogeneous IrOx WOC. While both WOCs improve the performance of hematite by a large margin, their working mechanisms are found to be fundamentally different. I also focused on utilizing surface photoexcited species to control product selectivity. Selective CO production by photoelectrochemical methane oxidation is successfully demonstrated. Detailed experimental investigations revealed that a synergistic effect by adjacent Ti3+ sites is the key to CO formation
Thesis (PhD) — Boston College, 2018
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

The thesis project is focused on the synthesis and characterization of nanostructured bismuth ferrite, BiFeO3 (BFO), thin films with enhanced photoelectrocatalytic properties. Photoelectrocatalytic materials are semiconductors that are able to catalyze water splitting processes or other reactions under sunlight irradiation. They can, through the absorption of photons, create electron/hole pairs which can be exploited to carry out electrochemical reactions. BFO is a very promising perovskite-type material with an optical band gap that fits well with the sunlight irradiation in the visible region. Since most of the conventional photocatalyst like TiO2 is limited by a wide band gap and a UV light absorption, the BFO material is an interesting visible light driven photoactive material for solar energy conversion. The main disadvantages of such material are poor efficiency and high variability in the photoelectrocatalytic performance. BFO’s performance depends on structure, defects, phase, electronic properties, which are directly connected with the synthetic methodology. In this thesis a sol-gel synthesis has been optimized in order to prepare highly reproducible thin films, that could be directly applied to a device, with modified structure and improved photoelectrocatalytic performance. Moreover, in order to achieve sensitization in the Near Infrared Region where pure BFO is not active, a composite nanomaterial has been developed. Previously prepared nanoparticles with peculiar optical properties have been dispersed in a BFO matrix and the optical and structural characterization have been carried out to correlate the enhancement of photoelectrocatalytic properties with the modification caused by the nanoparticles doping.

This work systematically investigate the nanoparticulate TiO2 photocatalysis and photoelectrocatalysis based methods for decomposition, detoxification and disinfection of a series of biological contaminants ranged from small biological compounds such as amino acids and nucleotide bases, to large biological compounds including protein, lipid and DNA, to living microorganisms such as bacteria and virus. The small biological compounds (e.g., amino acids and nucleotide bases) are the basic building blocks of the large biological compounds (e.g., proteins and DNA), and the large biological compounds are the building blocks of the living microorganisms (e.g., bacteria and viruses). Due to the complicity involved, in order to understand the full spectrum of the decomposition, detoxification and disinfection mechanisms of living microorganisms, a bottom-up strategy was employed in this study. The photocatalytic and photoelectrocatalytic degradation of small biological compounds were firstly investigated to gain the necessary information for a better understanding of degradation mechanisms of large biological compounds. The photocatalytic and photoelectrocatalytic degradation of large biological compounds were then investigated to gain the necessary information for a better understanding of decomposition/disinfection mechanisms of living microorganisms. This was followed by the investigation of photocatalytic and photoelectrocatalytic decomposition/detoxification/disinfection of living microorganisms. Chapter 1 of the thesis provides comprehensive literature reviews of the present status of research developments relevant to this work and the justification for the research topic. Nanoparticulate TiO2 photoanode is a key element of the proposed research. Chapter 2 describes the fabrication and characterisation of the nanoparticulate TiO2 photoanode. The nanoparticulate TiO2 photoanode was successfully fabricated using a sol-gel method. The photoelectrocatalytic properties of the resultant TiO2 photoanodes were systematically evaluated using water, as well as organic model compounds in both bulk and thin-layer photoelectrochemical cells. The results indicated that the resultant photoanodes possess high photocatalytic activity. The measured net charge under the exhaustive conditions in a thin-layer photoelectrochemical cell is essentially the same as the theoretically required charge, demonstrating a superior oxidation power and 100% electron collection efficiency. Photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of small biological compounds such as amino acids and nucleotide bases were carried out in Chapters 3 and 4. These small biological compounds were found to be photocatalytically and photoelectrocatalytically degradable. The degradation efficiency of PEC method was found to be higher than that of PC method for all compounds investigated. The organic nitrogens in the original compounds can be oxidised to either NH3/NH4 + or NO3- or both, depending the chemical structures of the original compounds and the degradation methods used. Both experimental results and the theoretically calculated frontier electron densities values of (2FEDHOMO)2 and (FEDHOMO)2+(FEDLUMO)2 demonstrated that the reaction mechanisms/pathways of PEC processes differed remarkably from that of PC processes. As a part of the proposed “bottom-up” strategy, PC and PEC degradation of large biological compounds such as bovine serum albumin (BSA), lecithin and bacteria genomic DNA were performed in Chapter 5. A new method for estimating the theoretical charge required to mineralise these large biological compounds with unknown chemical formula was firstly developed and experimentally validated. The degradation efficiency of PEC method was found to be higher than that of PC method for all large biological compounds investigated. In Chapter 6, a bactericidal technique (PEC-Br) utilising in situ photoelectrocatalytically generated photohole (h+), Br2•- and active oxygen species (AOS) for instant inactivation and rapid decomposition of Gram-negative bacteria such as E. coli was proposed and experimentally validated. The method is capable of inactivating 99.90% and 100% of 9×106 CFU/mL E. coli within 0.40 s and 1.57 s, respectively. To achieve the same inactivation effect, the PEC-Br method is 358 and 199 times faster than that of the PEC method, and 2250 and 764 times faster than that of the PC method. The Chapter 7 demonstrated the bactericidal technique developed in Chapter 6 can also be applied as a virucidal technique for rapid inactivation of viruses such as replication-deficient recombinant adenovirus (RDRADS). The PEC-Br method is capable of deactivating 99.77% and 100% of RDRADS within 14.32 s and 31.65 s, respectively. The final chapter of the thesis (Chapter 8) summarises the outcomes of this study and future work.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
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Los materiales llamados semiconductores (muchos de ellos óxidos metálicos) son capaces de generar portadores de carga (huecos y electrones) cuando se iluminan con luz suficientemente energética. Estos portadores son capaces de sostener reacciones redox. Los electrones de la banda de conducción (BC) y los huecos de la banda de valencia (BV) pueden reducir y oxidar, respectivamente, especies que estén en contacto directo con el semiconductor. Además, los electrones y huecos fotogenerados pueden eliminarse en el proceso que se conoce como recombinación. El grado en que se producen estas reacciones redox depende de la eficiencia en la separación de las cargas fotogeneradas. Una separación de los portadores efectiva da lugar a aplicaciones. En esta tesis se abordan detalladamente los procesos de foto(electro)cromismo y foto(electro)catálisis. La separación de los portadores de carga en un material puede verse favorecida por: - La creación de heterouniones entre dos semiconductores (óxidos) distintos. - El diseño adecuado de la nanoestructura de los óxidos: estructuras ordenadas y/o estructuras con mucha superficie interfacial. - La modificación de la superficie o del seno de los óxidos semiconductores (dopado). En las aplicaciones prácticas se pretende que haya una transferencia de carga capaz de impulsar el proceso de interés. Por lo tanto, el control de los procesos de transferencia de carga del semiconductor a través de sus interfases es fundamental en el diseño de materiales para una determinada aplicación. Teniendo todo esto en cuenta, los objetivos establecidos para esta tesis han sido: I. Preparar estructuras ordenadas de nanobarras de α-Fe2O3 (hematita) sobre vidrio conductor e investigar sus propiedades catalíticas para fotooxidar agua. Optimizar el proceso de fotooxidación del agua sobre electrodos de hematita aplicando un pretratamiento electroquímico. Estudiar el efecto del pretratamiento sobre la composición, morfología y estructura electrónica de la hematita. II. Modificar los electrodos de hematita con Ti de dos maneras distintas, una que afecte principalmente a todo el material y otra que afecte a la superficie de la hematita, con el fin de mejorar sus propiedades catalíticas para fotooxidar agua. Aplicar y estudiar el pretratamiento reductivo para los electrodos de hematita tras ser modificados con Ti. III. Modificar la superficie de las nanobarras de hematita con trimetilaluminio (TMA) mediante depósito de capa atómica (Atomic layer deposition - ALD) desde fase gas o por adsorción en fase líquida, con el fin de mejorar sus propiedades fotoelectroquímicas para oxidar agua. Investigar los cambios en las propiedades electrónicas y electroquímicas de los electrodos de hematita tras ser modificados. IV. Preparar electrodos nanoporosos de Ni(OH)2 sobre vidrio conductor (SnO2:F - FTO) e investigar sus propiedades catalíticas para oxidar agua en medio alcalino en función de la cantidad depositada y de la morfología del hidróxido. V. Preparar electrodos nanoporosos basados en capas mixtas TiO2/Ni(OH)2 sobre vidrio conductor e investigar la separación de carga en los mismos con el fin de estudiar su posible utilización en dispositivos fotoelectrocrómicos. Estudiar las cinéticas de los procesos de la coloración y decoloración a través de medidas (foto)(espectro)electroquímicas. Las siguientes cinco conclusiones generales resumen los resultados más importantes en relación con los cinco objetivos previamente mencionados. I. En este estudio se ha conseguido sintetizar barras de hematita nanoestructuradas y con orientación (110) depositadas sobre vidrio conductor a través de un método de baño químico. Estas capas se han utilizado para estudiar el proceso de fotoxidación del agua. Para mejorar las propiedades fotocatalíticas de estas capas se ha empleado un pretratamiento electroquímico simple y altamente controlable que consiste en la aplicación de potenciales negativos por un tiempo muy corto (en el rango de segundos). Este pretratamiento da lugar a una mejora de la fotocorriente de hasta ocho veces asociada a la oxidación del agua, junto con un desplazamiento negativo de 20 mV del potencial de inicio de la fotocorriente. Este pretratamiento también induce cambios en la morfología de los electrodos, capacidad electrocatalítica y en su estructura electrónica. Por lo tanto, el dopado electroquímico no puede considerarse simplemente como un dopado tipo-n capaz de aumentar la fotoactividad de las capas debido a una mejora en el transporte de electrones. En realidad, los resultados obtenidos muestran claramente que se producen cambios mucho más profundos en la estructura electrónica y la composición de las capas que mejoran significativamente las propiedades tanto electro- como foto-electrocatalíticas. De hecho, ambas propiedades siguen una tendencia general similar con el potencial del pretratamiento empleado. Dentro de un marco más general, el pretratamiento reductivo puede ser utilizado también para la mejora de estructuras de hematita previamente modificadas o dopadas. Desde una perspectiva práctica, el dopaje electroquímico tiene la limitación de no ser permanente, lo que significa que debe aplicarse periódicamente. Esto no es un inconveniente serio en un dispositivo práctico, siempre y cuando la mejora inducida por el pretratamiento compense claramente esta limitación. II. Se han diseñado dos estrategias de modificación de hematita económicas utilizando una disolución con un mismo precursor de Ti. En un procedimiento el Ti se introduce en la estructura de hematita, mientras que en la otra, se forma una capa de TiO2 ultra-delgada que cubre por completo la superficie de hematita. Ambas modificaciones inducen un aumento significativo en la fotocorriente para la oxidación de agua (4 - 6 veces). La razón principal de la mejora en las capas modificadas con Ti es la disminución significativa del proceso de recombinación. El freno de la recombinación en las muestras modificadas con una sobre-capa de TiO2 se atribuye principalmente al bloqueo de estados superficiales, mientras que en el caso de las muestras modificadas con Ti intercalado en la estructura se relaciona principalmente con el aumento del área interfacial junto con un aumento de la conductividad electrónica. III. Se han preparado electrodos basados en nanobarras de hematita modificadas con TMA empleando una estrategia simple de impregnación a partir de una disolución de hexano. Los resultados se han comparado con los obtenidos modificando los electrodos de hematita con TMA por ALD. Los electrodos modificados muestran una importante mejora, aumentando tres veces la fotocorriente de oxidación de agua. Por un lado, el TMA bloquea los estados superficiales de hematita y por otro, induce un enriquecimiento electrónico. Tal conclusión fue confirmada cualitativamente en el caso de muestras modificadas con TMA utilizando la técnica de ALD. A pesar de que la modificación en fase líquida ha dado una foto-actividad menor en términos de la magnitud de la fotocorriente que la de ALD, representa una alternativa mucho más económica. Además, el método de impregnación a partir de una disolución es industrialmente escalable. Dentro de un marco más general, la modificación con TMA es potencialmente aplicable a otros semiconductores tipo n. Por lo tanto, podría constituir una estrategia relevante para mejorar la eficiencia de la fotooxidación de agua utilizando otros materiales tales como TiO2, BiVO4, WO3, entre otros. IV. Este estudio muestra que, a través de un procedimiento simple y potencialmente escalable como el baño químico, se pueden producir capas nanoestructuradas ultra-finas de Ni(OH)2 sobre FTO. Estas películas se caracterizan por una gran actividad electrocatalítica. Son capaces de oxidar el agua desarrollando corrientes iguales o superiores a las de películas mucho más gruesas. Esto último está relacionado con el hecho de que la reacción de generación de oxígeno depende de la formación de níquel (IV) que puede verse limitada por la baja conductividad eléctrica de Ni(OH)2. Por tanto, el proceso se favorece en capas finas donde la distancia al substrato conductor es menor. Esta noción es muy importante de cara a su aplicación. No solo se minimiza la cantidad de Ni(OH)2 necesaria sino se producen también ánodos altamente eficientes transparentes y prácticamente incoloros. V. Este trabajo ha mostrado que una capa nanoporosa mixta y delgada de TiO2/Ni(OH)2 depositada sobre vidrio conductor y sometida a un potencial catódico constante puede colorearse al ser iluminada con luz ultravioleta, mientras que se decolora completamente cuando se interrumpe la iluminación. Este fenómeno se ha denominado “fotoelectrocromismo reversible potenciostatico”. El valor del potencial empleado permite seleccionar tanto el contraste en la coloración como la cinética de la decoloración. Este fenómeno es posible debido a la existencia de un área interfacial extendida de contacto TiO2/Ni(OH)2 debido a la estructura nanoporosa que permite un contacto íntimo entre ambos componentes. Desde un punto de vista práctico, estos resultados podrían facilitar el desarrollo de ventanas inteligentes con una nueva funcionalidad porque, además del convencional efecto electrocrómico, trabajarían en un segundo modo, en el que, la coloración respondería a la intensidad de la luz incidente (a un potencial constante).

Chemical oxygen demand (COD) is an important water quality parameter for estimating organic pollution. Conventional COD method has several drawbacks including lengthy assay time, complex procedure and requiring the use of highly toxic and expensive chemicals. Considerable efforts have been devoted to improve conventional COD methods. In this regard, the PeCODTM method has been the most noticeable technique. This method utilizes the superior oxidation power of UV illuminated nanostructured titanium dioxide (TiO2) to achieve organic degradation while simultaneously enabling quantification of the COD value by directly measuring the photocatalytic oxidation current/charge that originated from photocatalytic degradation of organics. The method is an absolute method that requires no calibration. It is an environmentally friendly method that requires/generates no toxic reagent. It is a simple and rapid method for sensitive and accurate COD determination. However, PeCODTM method needs to be improved in few aspects for more broad applications, especially for the field-based applications. These include the portability and high degradation efficiency for those oraganic compounds with difficulty to be oxidized. This study is therefore focused on improving the portability and applicability of PeCODTM method.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

With industrialization rapidly progressing in recent decades, great amounts of refractory organic pollutants are found in water bodies, which severely jeopardizes ecosystem health. Monitoring the organic compounds in water bodies and removing organic pollutants from wastewater is essential for ameliorating threats to aquatic life and human health. Photocatalytic (PC) and photoelectrocatalytic (PEC) degradation and detection of organic pollutants in wastewater are promising strategies for fulfilling these goals sustainably, since PC and PEC technologies can take advantage of solar energy, which is one of the most abundant energy sources on earth. Titanium dioxide (TiO2) is a commonly used photocatalyst due to its appropriate band position, high chemical stability, low cost, and nontoxicity. However, pristine TiO2 photocatalysts can only be stimulated by UV irradiation because the band gap of pristine TiO2 is higher than 3.0 eV, which seriously impedes its development with low-cost and environmentally friendly solar energy. There are several efficient strategies to overcome these disadvantages of pristine TiO2, such as morphology modification, bandgap engineering, and applying co-catalysts with the host photocatalysts. Herein, this thesis aims to utilize different strategies to enhance the photocatalytic performance of TiO2-based photocatalysts under visible light irradiation and apply those modified photocatalysts to degradation and detection of organics in wastewater. In the first study, a photoelectrochemical Chemical Oxygen Demand (COD) sensor based on a linear photocurrent-concentration analytical principle was designed for the on-site determination of COD. A high-performance anatase-branch@hydrogenated rutile-nanorod TiO2 (AB@H-RTNR) photoelectrode was fabricated. The as-prepared photoanodes successfully achieved sensitive determination of COD with a detection limit of 0.2 ppm (S/N = 3), an RSD% of 1.5 %, a wide linear detection range of 1.25−576 ppm, and an average recovery rate fluctuating between 100% ± 4% for artificial wastewater sample analyses. The satisfying results of this work suggest that AB@H-RTNR can serve as a promising photocatalyst for fast and accurate detection of organic compounds in water bodies. In addition to detecting COD in water bodies, the degradation of refractory organic compounds in water is also crucial for healthy ecosystems. Highly efficient, low-cost, and portable wastewater treatment and purification solutions are urgently needed for aqueous pollution removal. Herein, in the second study, we coupled a TiO2-based PC system with a persulphate (PS) oxidation system into a portable advanced oxidation device for rapid and deep degradation of organic contaminants in wastewater. Using hydrogenation, we fabricated hydrogenated anatase branched-rutile TiO2 nanorod (H-AB@RTNR) photocatalysts that enable PC degradation to occur under visible light to improve the utilization of solar energy. A degradation rate of 100% and a reaction rate constant of 0.0221 min−1 for degrading 1 L Rhodamine B (20 mg L-1) was achieved in 120 min in a specially designed thin-layer cell under visible light irradiation. These encouraging results suggest that the H-AB@RTNR photocatalysts/PS synergistic degradation system could be an alternative approach for the efficient degradation of organic pollutants in wastewater. Motivated by the result of the PC/PS synergistic degradation system, we further employed a PC/chlorination system for synergistic degradation of antibiotics. In the third study, we demonstrated the use of visible light (>420 nm) to produce •HO and •ClO through the assistance of photocatalysts (TiO2/WO3 nanofibers) and free chlorine (HOCl/ClO−). The introduction of visible-light-driven photocatalysts can significantly boost the yield of active radicals, which favors the degradation of antibiotics in water bodies. The synergistic PC/chlorination degradation system obtained a pseudo-first-order degradation rate constant of a model antibiotic, tetracycline hydrochloride, of 21.438 min-1, which is 3.66 and 86.57 times higher than that in the pure TiO2/WO3 photocatalysis and traditional chlorination processes, respectively. The stability test exhibits that the performance decline is negligible after multiple use cycles. The results of this study suggest that PC/chlorine degradation is a feasible, lowcost, and environmental-friendly strategy for antibiotics removal under visible irradiation. Another approach to improve the degradation efficiency of TiO2-based photocatalysts is using co-catalysts to assist the host photocatalysts. In the fourth study, we fabricated noble-metal free co-catalysts, i.e., N-doped carbon wrapped FeNi nanoparticles (FeNi@NGC), via a pyrolysis method. Hydrogenated TiO2 (H-TiO2) was synthesized as the host photocatalysts and coupled with as-prepared FeNi@NGC to obtain superior PC activity in the degradation of tetracycline hydrochloride (TC-HCl), a model antibiotic. The FeNi@NGC/H-TiO2 system achieved a degradation rate of 100% within 120 min on degrading 100 mL 20 mg L-1 TC-HCl under visible light irradiation (λ>420 nm). The degradation rate constant of the FeNi@NGC/H-TiO2 system reached 23.18 min-1, which was 33.99, 26.98, and 2.23 times compared to that of TiO2, FeNi@NGC/TiO2, and H-TiO2 system. The favorable performance of the FeNi@NGC/H-TiO2 system can be ascribed to two reasons: the secondary electron transfer in the FeNi intermetallic compounds that facilitates the photo-induced charge separation in photocatalysts; and the enhanced visible light absorption ability resulted from the N-doped graphitized carbon shell. Moreover, the oxygen vacancies brought by the hydrogenation process also improves the visible light absorbance of the photocatalysts, which favors the degradation performance. This study suggests that coupling FeNi@NGC cocatalyst with H-TiO2 is a promising strategy for improving the photocatalytic degradation performance on antibiotics. In summary, the strategies presented in this thesis show that the morphology and electronic properties of TiO2 can be manipulated to resolve the problems of poor visible light absorption and the large recombination rate of photogenerated charge carriers. Moreover, the degradation performances of organic compounds show that applying a synergistic system with TiO2-based materials is promising in the removal of refractory organics in the wastewater. The strategies utilized in the thesis (i.e., morphology manipulation, bandgap engineering, and applying co-catalysts) can be utilized in other members of the semiconductors family (such as SnO2, BiVO4, SrTiO3) for developing more sustainable and low-cost approaches and techniques to improve human and aquatic ecosystem health.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text

In this thesis, titanium dioxide (TiO2)-based thin film photocatalysts of different morphologies were synthesized and studied for their photoelectrocatalytic and photocatalytic properties. The superhydrophilicity of selected TiO2 films were also assessed. The work started with the synthesis of nanocrystalline TiO2 thin films with minimal porosity. A photoelectrocatalytic study was performed to evaluate the films?? photocurrent response in the presence of various organic compounds. At low concentrations, the amount of photocurrent generated was found to be influenced by the molecular structure of the organic compounds. As the concentration increased, the photocurrent response became dependent on the level of interaction of the organic compounds and their partially degraded intermediates with the TiO2 surface. Highly dispersed platinum (Pt) were added onto TiO2 films by a photo-deposition method, and their photocatalytic and photoelectrocatalytic activities were assessed using a novel thin-layer photo(electrochemical)-catalytic system. The system allowed the photocurrent data that originated from the photoelectrocatalysis process to be collected in the reaction cell, and the amount of organic compound being oxidized to be quantified. The Pt deposits were found to enhance photocatalysis by increasing the photogenerated charge-carriers separation, but conversely they retarded the photoelectrocatalysis process. The next part of the work covered the development of mesoporous TiO2 films via the evaporative-induced self-assembly procedure. The structural characteristics of the films were altered by controlling the relative humidity and temperature during the coating and thermal treatment processes. The effect of key structural parameters, such as film porosity, surface area and crystallinity, on the photoelectrocatalytic activity was investigated. These parameters were found to affect the photoelectrocatalysis because the performance of a catalyst in the photoelectrocatalysis application relies strongly on attributes such as the photocatalyst particles?? interconnectivity and the contact to the conducting substrate. The last part of this thesis demonstrated the effort undertaken to improve the UV-induced superhydrophilic effect of a TiO2 film. A multilayer structure of TiO2 nanoparticles was assembled to create a novel TiO2 film that required no UV-activation to induce a uniform water sheeting across its surface. The novel TiO2 thin film exhibited stable superhydrophilic wetting and anti-fogging behaviors after repetitive cycles of heat and wetting treatment, and this performance was affected by the porosity and surface hydroxyl (-OH) contents.

Baseado na técnica de Microextração Liquido-Líquido Dispersiva (DLLME) desenvolveu-se uma metodologia de extração para analisar, por Cromatografia Líquida de Alta Eficiência com detector ultravioleta (HPLC-UV), a presença do propilparabeno (PrP) e do butilparabeno (BuP) nas águas da Bacia do Rio Pardo. O método proposto apresentou um limite de detecção e de quantificação de 62,60 e 187,60 µg/L para o Prp e de 58,40 e 175,20 µg/L para o BuP. Análise das amostras coletadas (18 amostras) apresentou um teor de 2,2 a 6,8 µg/L para o PrP e de 1,9 a 4,9 µg/L para o Bup. Além de analisar a presença dos parabenos nas águas do Rio Pardo, estudou-se também a degradação do PrP, do BuP e da mistura PrP mais BuP ( PrP + BuP) pelas técnicas de fotólise e fotoeletrocatálise em solução de água deionizada e em água de rio (Rio Pardo) em diferentes concentrações (5, 10, 20 e 30 mg/L) e pH (4, 7 e 10). A remoção dos parabenos em ambas as técnicas foi superior a 99%. Na fotólise, o tempo de degradação da menor para a maior concentração variou de 25 a 85 minutos enquanto na fotoeletrocatálise ele foi de 12 a 55 minutos, sendo as melhores condições em água deionizada e em meio ácido e neutro (pH 4 e 7). Análise do Carbono Orgânico Total (TOC) das soluções fotolisadas em água deionizada e em diferentes pH\'s (4, 7 e 10) revelou, para o PrP, uma remoção de 16,3 a 25,25 %. Para o BuP, na mesma sequência de pH, a remoção foi de 15 a 23,55%. Na fotoeletrocatálise a remoção de TOC para o PrP nos pH 4, 7 e 10 variou de 33,3 a 36,5 % enquanto para o BuP ela foi de 35,2 a 38,3 %. Teste de citotoxicidade mostrou que o PrP, o BuP e a mistura PrP-BuP são atóxico para as células de fibroblastos Balb/c 3T3 clone A31 antes e após as degradações, todavia são estrogênicos para as células de adenocarcinoma mamário MCF-7. Para o PrP, após ambos os processos de degradação, a estrogenicidde foi completamente abolida, enquanto que para o BuP e para mistura (PrP+BuP) ela foi reduzida, porém não totalmente eliminada.
Based on the dispersive Liquid-Liquid Microextraction technique (DLLME) developed an extraction methodology to analyze by High Performance Liquid Chromatography with Ultraviolet detection (HPLC-UV), the presence of propylparaben (PrP) and butylparaben (BuP) in the waters of the Pardo River Basin. The proposed method has a limit of detection and quantification of 62,60 and 187,60 µg /L of PrP and 58.40 and 175.20 µg /L for BuP. Analysis of the samples (18 samples) showed a content of 2.2 to 6.8 µg / L for the PrP and 1.9 to 4.9 µg / L for the Bup. In addition to analyzing the presence of parabens in the waters of the Pardo River, studied also the degradation of PrP, BuP and mixture PrP more BuP (PrP + BuP) for photolysis and photoelectrocatalysis techniques in deionized water solution and river water (Pardo River) at different concentrations (5, 10, 20 and 30 mg / L) and pH (4, 7 and 10). Removal of parabens in both techniques was greater than 98%. The degradation time in the photolysis ranged from 25 to 85 minutes while in photoelectrocatalysis was of 12 to 55 minutes, being the best conditions in deionized water and in acidic and neutral medium (pH 4 and 7). Analysis of Total Organic Carbon (TOC) of the solution photolysed in deionized water at different pHs (4, 7 and 10) showed to PrP, a removal of 16.3 25.25%. For BuP in the same sequence pH, the removal was 15 to 23.55%. In photoelectrocatalysis TOC removal for PrP in pH 4, 7 and 10 ranged from 33.3 to 36.5% whereas for BuP it was 35.2 to 38.3%.Cytotoxicity test showed that PrP, BUP and PrP-BuP mixture is nontoxic to the cells fibroblasts Balb / c 3T3 clone A31 before and after degradation, however are estrogenic for breast adenocarcinoma cells MCF-7. For the PrP, after photolysis and photoelectrocatalysis, it was completely abolished whereas for BuP and mixture (PrP + BuP), it was reduced but not completely eliminated.

This thesis work is focused on the synthesis of TiO2 based hetero-nanostructured mixed metal oxides for their used as photo-anodes in different photo-electrochemical applications. Compared to single-phase photocatalysts, hetero-nanostructured mixed metal oxides can increase the efficiency of charges separation and lifetime, enhance the interfacial charge transfer to adsorbed substrate as well as improve the light-response range to the visible region.
This thesis work is focused on the synthesis of TiO2 based hetero-nanostructured mixed metal oxides for their used as photo-anodes in different photo-electrochemical applications. Compared to single-phase photocatalysts, hetero-nanostructured mixed metal oxides can increase the efficiency of charges separation and lifetime, enhance the interfacial charge transfer to adsorbed substrate as well as improve the light-response range to the visible region.

Orientador: Maria Valnice Boldrin Zanoni
Banca: Paulo Roberto Bueno
Banca: Arthur de Jesus Motheo
Banca: Romeu Cardozo Rocha Filho
Bana: Rodnei Bertazolli
Resumo: O comportamento eletroquímico de três corantes dispersos, Vermelho Disperso 1, Laranja Disperso 1 e Vermelho Disperso 13 foi investigado em N,N-dimetilformamida usando tetrafluorborato de tetrabutilamônio como eletrólito de suporte. O grupo nitro dos corantes é reduzido em potenciais de -0,85 V, -0,79 V e -0,69 V, respectivamente, para os corantes Vermelho Disperso 1, Laranja Disperso 1 e Vermelho Disperso 13. A oxidação do grupo amino, também presente nos corantes investigados, ocorre, respectivamente, em potencial de 0,95 V, 0,90 V e 1,0 V e promove a clivagem do grupo azo. Devido à toxicidade e mutagenicidade destes corantes, analisada pelos testes de citotoxicidade em células humanas embrionárias HEK293 e de Ames, respectivamente, investigou-se no presente trabalho novos métodos de degradação dos mesmos em meio aquoso usando o agente dispersante comercial "Emulsogen" por meio de tratamento com cloro ativo (cloração convencional) e fotoeletroquimicamente pela geração de radicais cloro "in situ" sobre eletrodos nanoparticulados de Ti/TiO2, preparados pelo método sol-gel, em NaCl 0,1 mol L-1. A oxidação fotoeletrocatalítica, sobre eletrodos nanoparticulados de Ti/TiO2 em NaCl, mostrou-se mais eficiente quando comparada à cloração convencional, tanto na descoloração que promoveu 100% de remoção de cor, quanto na mineralização dos mesmos (até 60% de remoção de COT). A mutagenicidade dos corantes estudados foi drasticamente reduzida após tratamento fotoeletroquímico. No entanto, a cloração convencional não foi eficiente para total remoção da atividade mutagênica dos corantes, observando-se, ainda, um aumento para o corante Vermelho Disperso 13. A degradação também foi investigada sobre eletrodos de nanotubos de Ti/TiO2, preparados pelo método de anodização eletroquímica... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The electrochemical behavior of three disperse dyes, Disperse Red 1, Disperse Orange 1 and Disperse Red 13, was investigated using N,N-dimethylformamide using in tetrabutylammonium tetrafluoroborate as supporting electrolyte. The nitro group of the dyes is reduced in potential of -0.85 V, 0.79 V and -0.69 V, respectively, for Disperse Red 1, Disperse Orange 1 and Disperse Red 13. The oxidation of amine group, also presents in the dyes molecules, occurs, respectively, at 0.95 V, 0.90 V and 1.0 V and promotes cleavage of azo group. Because of these dyes toxicity and mutagenicity, analyzed by citotoxicity in embryonic human cells HEK293 and mutagenicity detected by Ames test, respectively, new methods of degradation of these dyes in aqueous medium using the commercial dispersant agent "Emulsogen" was investigated by active chlorine treatment (conventional chlorination) and photoelectrochemically by "in situ" chlorine radicals generation using Ti/TiO2 nanoparticulates electrodes, prepared by solgel method, in 0.1 mol L-1 NaCl. The photoelectrocatalytic oxidation, using Ti/TiO2 nanoparticulates electrodes in NaCl presented higher efficiency when compared to conventional chlorination, leading to 100% of color removal and also 60% of mineralization of dyes measured as TOC removal. The mutagenicity of all investigated dyes was dramatically reduced after photoelectrochemical treatment. However, the conventional chlorination was not efficient for mutagenic activity removal of dyes and promoted an increase for Disperse Red 13. The degradation was also investigated using Ti/TiO2 nanotubes electrodes, prepared by electrochemical anodization in fluoride medium and characterized by SEM and photocurrent curves. These electrodes presented 100% of discoloration of all investigated dyes and total organic carbon removal around 70% after 3 hours of photoelectrocatalytic degradation... (Complete abstract click electronic access below)
Doutor

In this work, electrophotocatalytic disinfection on selected microorganisms was verified. The electrophotocatalytic system allows the application of electrical bias to the photoanode coated with a titanium dioxide layer. The disinfecting effect was observed on E.coli and C.glabrata in aqueous solution. The effect of radiation intensity on electrophotocatalysis and selected optimal conditions for further experiments was observed in the E. coli organism. Photocatalytic disinfection was carried out under suitable conditions on C.glabrata yeast and the effect of sodium sulfate electrolyte on electrophotocatalytic disinfection was observed in this case.

The dioxygen reduction reaction (ORR) is a key process for renewable energy technologies such as batteries and fuel cells. Reliance on dioxygen as the terminal oxidant in fuel cell technologies requires the development of electrocatalysts that proceed at low overpotentials with fast rates, while maintaining adequate selectivity for H₂O production over thousands of hours of operation. While many advances have been made, the discovery of efficient and inexpensive ORR electrocatalytic materials remains a holy-grail of energy science. The study of soluble, molecular electrocatalysts allow for more detailed structure : activity analyses to be made than for electrocatalytic materials, providing an atomic level understanding of catalytic barriers and opportunities for improvement.

Chapters 1-5 of this thesis develop a rational approach for analyzing, comparing, and improving homogeneous and molecular ORR electrocatalysts in non-aqueous solvents, and use this approach to study the reduction of dioxygen to water using iron porphyrin electrocatalysts. Quantification of the equilibrium potential for O₂/H₂O under the conditions of study allowed, for the first time, accurate estimations of the reaction overpotential in non-aqueous solvents. Knowledge of the reaction overpotential proved critical for comparing electrocatalysts under the somewhat diverse conditions encountered for homogeneous catalysts with varying solubilities in organic solvents.

A detailed kinetic and mechanistic study was then conducted on iron tetraphenyl porphyrin, Fe(TPP), which revealed that the turnover limiting step is protonation of the iron(III) superoxo adduct, formed via pre-equilibrium dioxygen binding to Fe^II(TPP). The protonation step was found to have a large kinetic barrier, suggesting that targeting proton delivery to the active site may improve the ORR activity of iron porphyrin electrocatalysts.

Studies of eleven substituted iron porphyrin ORR electrocatalysts all showed high selectivity for the 4H⁺/4e ^- reduction to water. The turnover frequencies (TOFs) were found to correlate with the reduction potential required to initiate electrocatalysis, in two log(TOF):overpotential linear free energy relationships (LFERs). The iron porphyrin electrocatalysts with well-positioned proton donors above the active site fell upon the same LFER as those without such proton relays, suggesting that the second coordination sphere does not directly participate in the rate-limiting proton transfer. These results contradict the general sense that well-positioned proton relays should decrease kinetic barriers. However, some iron porphyrin catalysts in the series can break the LFER, leading to more efficient catalysis. Computational studies suggest that, rather than directly participating in an intramolecular proton transfer, the second coordination sphere of some iron porphyrins can hydrogen bond with the O₂ adduct to influence the thermochemistry for proton transfer. Importantly, the presence of these LFERs was shown to stem from the electrocatalyst E_1/2 influencing the thermodynamics for O₂ binding and proton transfer. Analogies are drawn between these linear free energy relationships and the scaling relationship analyses used for electrocatalytic materials for the ORR.

Using the mechanism, rate law, and thermochemistry, the log(TOF) : overpotential correlations were then derived for ORR catalyzed by iron porphyrins. Given that the TOF is a function of the catalytic rate law (TOF = k _cat[O₂][HA]) and the overpotential is a function of the reaction conditions, the predicted correlation between log(TOF) and effective overpotential is independently. derived for changes in the reaction conditions or for changes to the catalyst E_1/2. For each parameter varied, a unique correlation coefficient was identified and shown to agree with experimental data. The very shallow dependence between log(TOF) and the pK _a of the acid used was used to enable Fe(TPP) catalyzed ORR to break the prior LFERs by 10⁴ s^-1 in TOF. These scaling relations highlight how decoupling the ET, PT and substrate binding events can lead to diverse scaling relationships, providing opportunities for improving the activity of a catalytic system by targeting the medium, as opposed to the catalyst.

In chapter 6, an exploratory research project on driving the ORR using sunlight to produce hydrogen peroxide (H₂O₂) is discussed. H₂O₂ is a commodity chemical with diverse applications in water purification, as an oxidant, and as a liquid fuel. Preparation of nickel(II) oxide photocathodes sensitized with simple dyes revealed that these photocathodes are surprisingly active for H₂O₂ production, proceeding to produce H₂O₂ with unity faradaic efficiency at low overpotentials (<20 mV). The reaction is found to proceed via outer sphere electron transfer from reduced dyes to O₂, forming superoxide, which disproportionates in solution, forming H₂O₂. Remarkably, these unoptimized systems are among the most active photocathodes for H ₂O₂ production. These results are promising for developing the delocalized production of H₂O₂ using dye-sensitized photoelectrosynthesis cells.

Neste projeto investigou-se o uso de três técnicas: (i) eletrólise, (ii) fotoeletrocatálise e (iii) fotólise, na degradação do hormônio estradiol, comumente encontrado nos esgotos domésticos, e que geram sérias preocupações com a ação nefasta que podem provocar na vida selvagem e humana. Os ensaios eletroquímicos foram realizados sobre eletrodos de platina e carbono vítreo. A técnica de fotoeletrocatálise foi aplicada empregando-se placas de titânio recobertas com nanocamadas de TiO2. Como fonte de radiação ultravioleta utilizou-se uma lâmpada de vapor de mercúrio de 125 W tanto na fotoeletrocatálise como na fotólise. Através dos estudos da oxidação do estradiol por voltametria cíclica, sobre os eletrodos acima mencionados, foi possível definir o seu potencial de oxidação em soluções de KCl e tampão fosfato (pH 7), sobre platina e carbono vítreo. Estes parâmetros serviram de base para a realização das eletrólises sob condições controladas. A fotoeletrocatálise do estradiol foi realizada sobre Ti/TiO2 preparado por técnica sol-gel e se mostrou muito mais efetiva que a eletrólise eletrolítica. Finalmente, a fotólise também foi testada empregando-se apenas a lâmpada de vapor de mercúrio. Neste último caso a degradação do estradiol foi ligeiramente inferior que aquela observada por fotoeletrocatálise. Identificou-se que em soluções de KCl há a formação de hipoclorito, o que auxilia o processo oxidativo do estradiol. Espectroscopia de UV-vís e cromatografia líquida (HPLC) foram empregadas para acompanhar os processos de degradação. Apesar de ter sido observado o surgimento de bandas e picos cromatográficos devidos aos produtos formados, não foi possível identifica-los.
In this project the use of three techniques was investigated: (i) electrolysis, (ii) photoelectrocatalysis and (iii) photolysis, in the degradation of the hormone estradiol, commonly found in the domestic sewers. This hormone can generate serious concerns with a disastrous action that can provoke in the wild and human life. The electrochemistry studies were accomplished on platinum and glassy carbon electrodes. The photoelectrocatalysis technique was applied using titanium plate covered with nanolayers of TiO2. As a source of ultra-violet radiation was used a lamp bulb of mercury vapor of 125 W for the photoelectrocatalysis as also in the photolysis. Through the studies of the oxidation of the estradiol by cyclic voltammetry, on the electrodes above mentioned, it was possible to define the oxidation potential of the organic specie in both solutions, KCl and phosphate buffers (pH 7), for platinum and glassy carbon. These parameters served as base for the realization of the electrolysis under controlled conditions. The photoelectrocatalysis of the estradiol was accomplished on Ti/TiO2 prepared by sol-gel technique and it was shown much more effective than the electrolyitc electrolysis. Finally, the photolysis was also tested being just used the mercury vapor lamp. In this last case the degradation of the estradiol was lightly inferior to that observed by photoelectrocatalysis It was identified that in solutions of KCl there is the hypochlorite formation, what aids the oxidation of the estradiol. Spectroscopy of UV-vis and high performance liquid chromatography (HPLC) were used to accompany the degradation processes. In spite of the appearance of bands and chromatographyc peaks owed to the formed products having been observed, however, it were not possible identify them.

Cette thèse concerne l’étude de la réaction photoélectrochimique de réduction du CO2 (PEC CO2RR) sur le semi-conducteur de type p CuCo2O4 en abordant le rôle cocatalytique des RTIL à base d'imidazolium par microscopie photoélectrochimique à balayage (SPECM). Le CuCo2O4 a été étudié dans différents électrolytes supports, notamment une solution aqueuse, une solution de mélange binaire (25 vol.% [C2mim][BF4]/H2O et 25 vol.% [C4mim][BF4]/H2O) et des liquides ioniques pur pour explorer par SPECM le rôle des RTIL dans les performances des PEC. Un courant de photoréduction significativement amélioré sous l'éclairage UV-vis et visible est obtenu dans une solution à 25 vol.% [C2mim][BF4]/H2O. Seul le CO généré par la PEC CO2RR a été détecté sur une fibre optique à double sonde - ultra-microélectrode (OF-UME) développée au laboratoire et sur une électrolyse en volume sous illumination. La formation de CO à des potentiels plus positifs que la valeur thermodynamique est rapportée ici et il est clairement indiqué que la réduction directe du CO2 à la surface de l'électrode n'est pas le mécanisme. Un schéma de réaction possible pour la PEC CO2RR par l'intermédiaire de [C2mim]+ est proposé. Ainsi, nos résultats ont démontré pour la première fois le rôle cocatalytique de [C2mim]+ pour le PEC CO2RR. En outre, la CO2RR électrochimique a également été étudiée sur divers catalyseurs de métaux de transition, d'azote et de carbone (M–N–Cs). 25%Fe25%Co–N–C a montré la meilleure performance parmi les M–N–Cs étudiés. La présence de sites Co a fourni un effet synergique pour la génération de microcubes distribués riches en Fe, qui agissent comme des sites actifs dans la CO2RR électrochimique
This thesis studies photoelectrochemical CO2 reduction reaction (PEC CO2RR) on p-type semiconductor CuCo2O4 addressing the cocatalytic role of imidazolium based RTILs by scanning photoelectrochemical microscopy (SPECM). CuCo2O4 was studied in different solvent supporting electrolyte systems including: aqueous solution (0.1 M KHCO3 and 0.1 M Na2SO4), binary mixture solution (25 vol.% [C2mim][BF4]/H2O and 25 vol.% [C4mim][BF4]/H2O) and pure RTILs ([C2mim][BF4], [C4mim][BF4]) to explore by SPECM the role of RTILs in CuCo2O4 semiconductor PEC performance. Significantly enhanced photoreduction current under both UV-vis and visible light illumination is reported in 25 vol.% [C2mim][BF4]/H2O solution. Only CO generated from PEC CO2RR was detected using an in-situ detection method based on a home-made dual tip optical fiber-ultramicroelectrode (OF-UME) and from bulk electrolysis under illumination. The formation of CO at potentials more positive than the thermodynamic value clearly points out that direct CO2 reduction on the electrode surface is not the mechanism. A possible reaction scheme for the PEC CO2RR mediated by [C2mim]+ is proposed. Thus, our results have demonstrated for the first time the cocatalytic role of [C2mim]+ for the PEC CO2RR. In addition, electrochemical CO2RR has also been studied on various synthesized transition metal–nitrogen–carbon catalysts (M–N–Cs) by rotating disk electrode. 25%Fe25%Co–N–C exhibited the best performance among the studied M–N–Cs in this thesis. The presence of Co sites in that catalyst provided synergic effect for the generation of distributed Fe-rich microcubes, which act as active sites in electrochemical CO2RR

This thesis aims to study the modifications induced by vanadium in titanium dioxide, an oxide semiconductor used for photoelectrocatalytic applications, such as water-splitting for hydrogen production and air and water remediation. The modification of this material is necessary to improve its conversion efficiency of light into chemical energy. In fact, its main limitation is the poor visible light absorption due to its wide energy gap (3.2 eV). In this work, V was introduced during the preparation of the sample, either in form of thin films or nanoparticles, using radio-frequency magnetron sputtering and inert gas phase condensation technique, respectively. A structural characterization by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy showed that V does not induce critical changes in TiO2 matrix; X-ray near edge absorption spectroscopy was used to determine the local environment of V and Ti, revealing that V is substitutional. Femtosecond transient absorbance spectroscopy was adopted to provide the basis for the interpretation of the photoelctrocatalytic behavior of V-modified and unmodified TiO2, used as photoanodes in a photoelectrochemical cell. FTAS revealed that vanadium accelerates electron-hole recombination upon UV irradiation, explaining the lower conversion efficiency in the UV spectral range with respect to unmodified TiO2. In the visible range, for modified samples, FTAS revealed the presence of a transient signal due to free electrons and trapped holes after pumping at 530 nm. These results were supported by the new photoelectrocatalytic activity in the visible range, attributed to a V-induced introduction of intragap levels at ≈ 2.2 eV below the conduction band. Similar results were obtained for thin films and nanoparticle based samples. IPCE spectra showed that incorporation of vanadium in TiO2 extends water splitting in the visible range up to ≈ 530 nm, a significant improvement compared to unmodified TiO2 that is active only in the UV range.

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Os estudos de degradação do corante VAT idantreno verde oliva foram realizados empregando-se solução 5x10-5 mol L-1 do corante em meio de NaCl 0,1 mol L-1 , pH=2,0 por meio do processo fotoeletrocatalítico sobre eletrodos de filmes finos de Ti/TiO2. Após 210 min de tratamento foi obtido 100% de descoloração e 86 % de mineralização. A aplicação do método fotocatalítico nas mesmas condições experimentais leva a apenas 60% de remoção do corante, indicando que o método fotoeletrocatalítico apresenta maior eficiência que a técnica de fotocatálise. A degradação do corante ácido vermelho 8 foi investigada através de processo fotoquímico empregando irradiação UV com lâmpada germicida de 4 W e lâmpada de mercúrio de 80 W. Foi observado significativa remoção da cor, porém análises de carbono orgânico total mostraram que o processo não apresenta nenhuma mineralização da matéria orgânica. Utilizando-se lâmpada de 80 W a degradação do corante ocorre segundo reação de pseudo primeira ordem com constante de velocidade de 0,0122 min-1 . A degradação do corante vermelho 8 é mais eficiente pelo processo fotocatalítico. A oxidação fotocatalítica de solução 5x10-5 mol L-1 do corante em meio de Na2SO4 0,1 mol L-1 , pH=6,0, sobre vidro/TiO2 promoveu 100 % de remoção da cor e aproximadamente 43 % de mineralização do corante. A eficiência fotocatalítica de filmes de TiO2 suportados em substrato de vidro obtidos pelo método dip-coating foi investigada testando-se a degradação do corante ácido vermelho em filmes obtidos variando-se os parâmetros: número de etapas de recobrimento, velocidade de deposição e temperatura de calcinação. O filme que mostrou maior eficiência fotocatalítica na degradação do corante ácido vermelho 8, foi construído com 1 depósito de TiO2, velocidade de recobrimento de 50 mm/min e temperatura...
Studies of degradation of the dye VAT Indanthrene olive green were performed using solution was 5x10-5 mol L-1 dye in NaCl 0.1 mol L-1 , pH = 2.0 through the process photoelectrocatalytic thin-film electrodes Ti/TiO2. After 210min of treatment was obtained 100% discoloration and 86% of mineralization. The application of the photocatalytic the same experimental condition leads to 60% removal of dye, indicating that the method photoelectrocatalytic is more efficient than the technique of photocatalysis. The degradation of acid red dye 8 was investigated by photochemical process using irradiation with UV germicidal lamp 4W and mercury lamp of 80W. Have been observed significant removal of color, but the analysis of carbon organic total no shows mineralization of organic matter. Using 80W lamp degradation of the dye is second reaction under pseudo first order rate constant of 0.0122 min-1 . The degradation of the red dye 8 is more efficient for the photocatalytic process. The photocatalytic oxidation of solution 5x10-5 mol L-1 dye in the midst of Na2SO4 0.1 mol L-1 , pH= 6.0 on glass/TiO2 promoted 100% removal of color and approximately 43% mineralization of the dye. The efficiency of photocatalytic TiO2 films supported on glass substrate obtained by dip-coating method was investigated by testing the degradation of acid red dye in films obtained by varying the parameters: number of steps of coating, deposition rate and temperature calcination. The film showed better photocatalytic degradation of dye Acid Red 8, was built with 1 deposit TiO2, coating speed of 50 mm/min and calcination temperature of 350°C film. Under these conditions the degradation of the dye second reaction is pseudo first-order rate constant of degradation of k = 0.121 min-1 . Therefore, it is concluded that the technique of photolysis and photocatalysis can be an excellent alternative to decolorize... (Complete abstract click electronic access below)

Este trabalho visa o estudo de processos de degradação fotocatalítica e fotoeletrocatalítica de corantes sobre dióxido de titânio. O enfoque está voltado ao uso de técnicas espectroscópicas, com especial destaque para o desenvolvimento de metodologias de espectroscopia vibracional Raman intensificada. Nesse sentido, tem-se em vista a investigação dos mecanismos envolvidos nos processos de fotodegradação e fotoeletrodegradação de corantes, através da identificação de intermediários e produtos de processos de degradação por técnicas de espectroscopia eletrônica e Raman. Os estudos de fotocatálise são também expandidos para ambientes eletroquímicos. Nos chamados processos fotoeletrocatalíticos, a combinação de processos eletroquímicos e fotoquímicos mostra-se bastante promissora para a degradação de poluentes orgânicos. O primeiro desafio no desenvolvimento desse trabalho foi construir o fotorreator adequado que permitisse a obtenção de amostras para serem analisadas por espectroscopia Raman, e apresentasse boa eficiência nos processos de fotocatálise e também fotoeletrocatálise. Encontrado o fotorreator adequado, investigamos o comportamento cinético dos processos foto(eletro)degradação de corantes, buscando verificar a dependência com o potencial eletroquímico aplicado, o efeito do eletrólito suporte, e a identificação de intermediários formados durante o processo de degradação. Analisamos também aspectos relacionados aos mecanismos de adsorção de corantes sobre a superfície do dióxido de titânio. Tais aspectos podem ser de significativa relevância no desenvolvimento de técnicas eficazes para o tratamento de poluentes orgânicos. Nossos estudos estiveram principalmente centrados em dois corantes: o azocorante verde de Janus e o corante antraquinônico alizarina vermelha S. Os resultados obtidos nos estudos da cinética dos processos fotoeletrocatalíticos sugerem que o efeito do potencial aplicado depende de maneira significativa da natureza química do corante. Observou-se uma tendência dos processos fotoeletrocatalíticos serem mais eficientes na remoção da coloração da solução corante do verde de Janus quando comparados aos fotocatalíticos. Tal tendência não foi observada para o corante alizarina vermelha S. Essa diferença de comportamento pôde ser relacionada à natureza das interações específicas de entre cada corante e a superfície do catalisador. Nossos estudos a respeito dos mecanismos envolvidos nos processos de degradação do verde de Janus revelaram que as primeiras etapas dos processos de fotodegradação e fotoeletrodegradação seguem mecanismos diferentes. Os resultados obtidos mostram que a degradação do verde de Janus em suspensão de TiO2 envolve entre suas etapas modificações na ligação azo desse corante (N=N), resultando na formação de um composto intermediário derivado da fenossafranina. No processo fotoeletrocatalítico, por outro lado, observa-se um mecanismo diferenciado o qual não envolve em suas etapas iniciais a quebra da ligação azo do corante
This work focuses on the study of photocatalytic and photoelectrocatalytic degradation processes of dyes over titanium dioxide. The main approach is based on the use of spectroscopic techniques, with special emphasis to methodologies based on surface-enhanced Raman spectroscopy. Within this context, the mechanisms involved in the photodegradation and photoelectrodegradation of dyes are investigated by the identification of degradation intermediates through vibrational and electronic spectroscopies. In the so-called photoelectrocatalytic processes, the combination of electrochemical and photochemical processes is an interesting and promising approach for the degradation of a wide variety of organic pollutants. The first step in the development of the present work was to build a photo reactor that allowed the analysis of samples through Raman spectroscopy and presented a good efficiency for both photocatalytic and photoelectrocatalytic processes. We then investigated the kinetic behavior of the photo(electro)degradation of dyes in order to verify the dependence upon the electrochemical applied potential, the effect of the supporting electrolyte, and the identification of intermediate products formed during the degradation process. We also analyzed aspects related to the adsorption mechanisms of the dyes on the titanium dioxide surface. Such aspects can be relevant to the understanding and to the development of efficient techniques for the remediation of organic pollutants. Our studies focused mainly on two dyes: the azo dye Janus green and the anthraquinonic dye alizarin red S. The results obtained in the kinetic study of the photoelectrocatalytic processes suggest that the effect of the applied electrochemical potential strongly depends on the chemical nature of the investigated dye. We have observed that the decolorization of Janus green is favored for photoelectrocatalytic process as compared to the photocatalytic degradation. Such behavior was not observed for the anthraquinonic dye alizarin red S. This difference was related to the nature of the specific interactions between each dye and the catalyst surface. Our studies regarding the mechanisms of degradation revealed that the first steps of the photocatalytic and photoelectrocatalytic processes of Janus green followed different routes. The obtained results indicate that the degradation of Janus green in aqueous TiO2 suspension involves changes in the azo bond (N=N), resulting in the formation of an intermediate compound a derived from the phenosafranine structure, whereas for the photoelectrocatalytic process there are evidences of a different mechanism that does not involve the cleavage of the azo bond.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O comportamento eletroquímico de três corantes dispersos, Vermelho Disperso 1, Laranja Disperso 1 e Vermelho Disperso 13 foi investigado em N,N-dimetilformamida usando tetrafluorborato de tetrabutilamônio como eletrólito de suporte. O grupo nitro dos corantes é reduzido em potenciais de -0,85 V, -0,79 V e -0,69 V, respectivamente, para os corantes Vermelho Disperso 1, Laranja Disperso 1 e Vermelho Disperso 13. A oxidação do grupo amino, também presente nos corantes investigados, ocorre, respectivamente, em potencial de 0,95 V, 0,90 V e 1,0 V e promove a clivagem do grupo azo. Devido à toxicidade e mutagenicidade destes corantes, analisada pelos testes de citotoxicidade em células humanas embrionárias HEK293 e de Ames, respectivamente, investigou-se no presente trabalho novos métodos de degradação dos mesmos em meio aquoso usando o agente dispersante comercial “Emulsogen” por meio de tratamento com cloro ativo (cloração convencional) e fotoeletroquimicamente pela geração de radicais cloro “in situ” sobre eletrodos nanoparticulados de Ti/TiO2, preparados pelo método sol-gel, em NaCl 0,1 mol L-1. A oxidação fotoeletrocatalítica, sobre eletrodos nanoparticulados de Ti/TiO2 em NaCl, mostrou-se mais eficiente quando comparada à cloração convencional, tanto na descoloração que promoveu 100% de remoção de cor, quanto na mineralização dos mesmos (até 60% de remoção de COT). A mutagenicidade dos corantes estudados foi drasticamente reduzida após tratamento fotoeletroquímico. No entanto, a cloração convencional não foi eficiente para total remoção da atividade mutagênica dos corantes, observando-se, ainda, um aumento para o corante Vermelho Disperso 13. A degradação também foi investigada sobre eletrodos de nanotubos de Ti/TiO2, preparados pelo método de anodização eletroquímica...
The electrochemical behavior of three disperse dyes, Disperse Red 1, Disperse Orange 1 and Disperse Red 13, was investigated using N,N-dimethylformamide using in tetrabutylammonium tetrafluoroborate as supporting electrolyte. The nitro group of the dyes is reduced in potential of –0.85 V, 0.79 V and –0.69 V, respectively, for Disperse Red 1, Disperse Orange 1 and Disperse Red 13. The oxidation of amine group, also presents in the dyes molecules, occurs, respectively, at 0.95 V, 0.90 V and 1.0 V and promotes cleavage of azo group. Because of these dyes toxicity and mutagenicity, analyzed by citotoxicity in embryonic human cells HEK293 and mutagenicity detected by Ames test, respectively, new methods of degradation of these dyes in aqueous medium using the commercial dispersant agent “Emulsogen” was investigated by active chlorine treatment (conventional chlorination) and photoelectrochemically by “in situ” chlorine radicals generation using Ti/TiO2 nanoparticulates electrodes, prepared by solgel method, in 0.1 mol L-1 NaCl. The photoelectrocatalytic oxidation, using Ti/TiO2 nanoparticulates electrodes in NaCl presented higher efficiency when compared to conventional chlorination, leading to 100% of color removal and also 60% of mineralization of dyes measured as TOC removal. The mutagenicity of all investigated dyes was dramatically reduced after photoelectrochemical treatment. However, the conventional chlorination was not efficient for mutagenic activity removal of dyes and promoted an increase for Disperse Red 13. The degradation was also investigated using Ti/TiO2 nanotubes electrodes, prepared by electrochemical anodization in fluoride medium and characterized by SEM and photocurrent curves. These electrodes presented 100% of discoloration of all investigated dyes and total organic carbon removal around 70% after 3 hours of photoelectrocatalytic degradation... (Complete abstract click electronic access below)

The last century has seen a skyrocketing role of energy resources. The industrial world was overwhelmed by this dramatic change, making the exploitation of renewable energy resources one of the greatest challenges of 21st century. In this context, hydrogen arises as the most promising candidate to substitute crude oil and an increased interest on this topic has been observed over the last years. In particular, last years saw an increasing interest on this topic. In particular, researchers focused on sustainable methods for hydrogen production: currently, the scientific frontier is represented by photoelectrocatalytic water splitting, the most promising method for hydrogen production through water splitting. In this work, useful results for technological advance in the field of photoelectrocatalytic water splitting are introduced. More specifically, a new, easily realised probe for investigation of catalyst is described: in particular, attention is focused on pH detection over microstructured photoelectrocatalysts during water splitting process. The study, design, fabrication and characterisation of this integrated scanning ion conductance microscope - electrochemical (SICM-EC) probe, with new electrodic material and insulating coating, are presented. Approach to hydrogen sensing through electrochemical measurements using the integrated device as sensing electrode are shown. Influence of different pH on open circuit potential of the sensing probe is described and exploited for investigation on water splitting process over macro and micro electrodes. Microelectrodes covered with Co-Pi photoelectrocatalyst, known for coupling many elements of natural photosynthesis with a self-repairing behaviour, were fabricated. They were used to perform water splitting and data from experimental tests are shown. Finally, a new microfluidic device was designed to combine advantages of photoelectrocatalysis with the positive features of microfluidic systems. Moreover, fluid dynamics in this proposed device is investigated through simulations. Further perspectives include simultaneous pH sensing and topographical imaging of photoelectrocatalysts and deep studies on their behaviour inside a microfluidic system.
Nel secolo scorso si è visto un incremento drammatico dell'importanza delle risorse energetiche. Il mondo industriale è stato segnato da questo cambiamento profondo, rendendo lo sfruttamento delle fonti energetiche rinnovabili una delle più grandi sfide del XXI secolo. In questo contesto, l'idrogeno si pone come il candidato più promettente per la sostituzione del petrolio greggio e negli ultimi anni si è visto un interesse crescente su questo argomento. In particolare, i ricercatori si sono concentrati su metodi sostenibili per la produzione di idrogeno: attualmente la frontiera scientifica è rappresentata dalla scissione dell'acqua mediante fotoelettrocatalisi, il metodo più promettente per la produzione di idrogeno mediante la scissione dell'acqua. In questo lavoro vengono introdotti risultati utili per l'avanzamento tecnologico nel campo della scissione fotoelettrocatalitica dell'acqua. Più specificatamente, viene descritta una nuova sonda per lo studio del catalizzatore, facilmente realizzata: in particolare, l'attenzione viene posta sul rilevamento del pH durante il processo di scissione dell'acqua al di sopra di fotoelettrocatalizzatori microstrutturati. Viene presentato lo studio, la progettazione, la fabbricazione e la caratterizzazione di questo dispositivo integrato microscopio a scansione di conduttanza ionica - elettrochimico (SICM-EC), preparato con materiale elettrodico e rivestimento isolante nuovi. Viene mostrato l'approccio al rilevamento di idrogeno attraverso misure elettrochimiche usando il dispositivo integrato come elettrodo di rilevamento. Viene descritta l'influenza che valori diversi di pH hanno sul potenziale di circuito aperto della sonda, sfruttata per l'analisi del processo di scissione dell'acqua su macro e microelettrodi. Sono stati fabbricati microelettrodi ricoperti da fotoelettrocatalizzatore Co-Pi, noto per combinare molti elementi della fotosintesi naturale con un comportamento auto-riparante. Questi microelettrodi sono stati usati per effettuare la scissione dell'acqua e vengono mostrati dati provenienti da prove sperimentali. Infine, è stato progettato un nuovo dispositivo microfluidico per combinare i vantaggi della fotoelettrocatalisi con le caratteristiche positive dei sistemi microfluidici. Inoltre, attraverso simulazioni è studiata la fluidodinamica che avviene in questo dispositivo proposto. Ulteriori prospettive includono il rilevamento simultaneo di pH e l'imaging topografico dei fotoelettrocatalizzatori, con studi approfonditi sul loro comportamento all'interno di un sistema microfluidico.

Orientador: Maria Valnice Boldrin
Banca: Hideko Yamanaka
Banca: Mercedes de Moraes
Banca: Jeosadaque José de Sene
Banca: Denise Alves Fungaro
Resumo: Os estudos de degradação do corante VAT idantreno verde oliva foram realizados empregando-se solução 5x10-5 mol L-1 do corante em meio de NaCl 0,1 mol L-1 , pH=2,0 por meio do processo fotoeletrocatalítico sobre eletrodos de filmes finos de Ti/TiO2. Após 210 min de tratamento foi obtido 100% de descoloração e 86 % de mineralização. A aplicação do método fotocatalítico nas mesmas condições experimentais leva a apenas 60% de remoção do corante, indicando que o método fotoeletrocatalítico apresenta maior eficiência que a técnica de fotocatálise. A degradação do corante ácido vermelho 8 foi investigada através de processo fotoquímico empregando irradiação UV com lâmpada germicida de 4 W e lâmpada de mercúrio de 80 W. Foi observado significativa remoção da cor, porém análises de carbono orgânico total mostraram que o processo não apresenta nenhuma mineralização da matéria orgânica. Utilizando-se lâmpada de 80 W a degradação do corante ocorre segundo reação de pseudo primeira ordem com constante de velocidade de 0,0122 min-1 . A degradação do corante vermelho 8 é mais eficiente pelo processo fotocatalítico. A oxidação fotocatalítica de solução 5x10-5 mol L-1 do corante em meio de Na2SO4 0,1 mol L-1 , pH=6,0, sobre vidro/TiO2 promoveu 100 % de remoção da cor e aproximadamente 43 % de mineralização do corante. A eficiência fotocatalítica de filmes de TiO2 suportados em substrato de vidro obtidos pelo método dip-coating foi investigada testando-se a degradação do corante ácido vermelho em filmes obtidos variando-se os parâmetros: número de etapas de recobrimento, velocidade de deposição e temperatura de calcinação. O filme que mostrou maior eficiência fotocatalítica na degradação do corante ácido vermelho 8, foi construído com 1 depósito de TiO2, velocidade de recobrimento de 50 mm/min e temperatura... (resumo completo, clicar acesso eletrônico abaixo)
Abstract: Studies of degradation of the dye VAT Indanthrene olive green were performed using solution was 5x10-5 mol L-1 dye in NaCl 0.1 mol L-1 , pH = 2.0 through the process photoelectrocatalytic thin-film electrodes Ti/TiO2. After 210min of treatment was obtained 100% discoloration and 86% of mineralization. The application of the photocatalytic the same experimental condition leads to 60% removal of dye, indicating that the method photoelectrocatalytic is more efficient than the technique of photocatalysis. The degradation of acid red dye 8 was investigated by photochemical process using irradiation with UV germicidal lamp 4W and mercury lamp of 80W. Have been observed significant removal of color, but the analysis of carbon organic total no shows mineralization of organic matter. Using 80W lamp degradation of the dye is second reaction under pseudo first order rate constant of 0.0122 min-1 . The degradation of the red dye 8 is more efficient for the photocatalytic process. The photocatalytic oxidation of solution 5x10-5 mol L-1 dye in the midst of Na2SO4 0.1 mol L-1 , pH= 6.0 on glass/TiO2 promoted 100% removal of color and approximately 43% mineralization of the dye. The efficiency of photocatalytic TiO2 films supported on glass substrate obtained by dip-coating method was investigated by testing the degradation of acid red dye in films obtained by varying the parameters: number of steps of coating, deposition rate and temperature calcination. The film showed better photocatalytic degradation of dye Acid Red 8, was built with 1 deposit TiO2, coating speed of 50 mm/min and calcination temperature of 350°C film. Under these conditions the degradation of the dye second reaction is pseudo first-order rate constant of degradation of k = 0.121 min-1 . Therefore, it is concluded that the technique of photolysis and photocatalysis can be an excellent alternative to decolorize... (Complete abstract click electronic access below)
Doutor

Le développement de traitements photo(électro)catalytiques pour l’élimination de polluants organiques requiert la préparation de nano-TiO2 immobilisé sur des supports pour simplifier leur séparation du liquide traité. Deux procédés ont été développés dans le cadre de cette thèse. Le premier consiste à préparer des mousses en TiO2/SiC puis à les intégrer dans un réacteur annulaire entouré de lampes UV-C. Plusieurs paramètres ont été étudiés : le nombre de lampes, la température, la concentration en polluant (paraquat, herbicide) et la stabilité mécanique des mousses. Ensuite, les sous-produits de dégradation ont été identifiés. L’autre procédé développé vise à améliorer la séparation des paires électrons-trous en appliquant une différence de potentiel. Le photocatalyseur doit alors être immobilisé sur une surface conductrice. Dans cette optique, la synthèse par anodisation électrochimique de nanotubes de TiO2/Ti en milieu fluoré est une technique très prometteuse. Plusieurs paramètres ont été étudiés afin de réaliser des électrodes de grande surface et favoriser le passage de l’échelle laboratoire à l’échelle pilote. Les propriétés photoélectrochimiques des nanotubes ont ensuite été optimisées notamment via la détermination de leur longueur optimale. Par la suite, la dégradation photoélectrocatalytique du paraquat a mis en évidence qu’une faible différence de potentiel (0,5 à 1 volt) suffit pour maximiser la séparation des paires électron-trou. La conductivité de l’électrolyte doit également être suffisamment élevée pour maximiser les performances du procédé photoélectrocatalytique
The development of photo(electro)catalytic methods for the removal of organic pollutants requires the elaboration of supported TiO2 nanomaterials in order to simplify the recovery of the photocatalyst from treated effluents. Two different approaches were developed during this PhD thesis. The first approach consists in producing a thin film of TiO2 onto alveolar SiC foams. The TiO2/SiC assembly was then integrated into a tubular reactor surrounded by UV-C lamps. Many parameters were studied: number of lamps, the temperature, pollutant’s concentration (paraquat, weed killer) and the mechanical stability of TiO2/SiC foams. Then, paraquat’s by-products of degradation were identified. Another approach was then developed in order to improve the electron-hole pair of the photocatalytic process by applying a small electrical bias. For this purpose, the photocatalyst must be coated on a conductive surface. In this field, TiO2 nanotubes grown on titanium substrate by electrochemical synthesis in a fluoride media are very promising. Many parameters were studied in order to produce large electrodes and favor the upscaling. Photoelectrochemical properties of TiO2 nanotubes were studied and optimized especially concerning nanotube’s length. Besides, photoelectrocatalytic degradation of paraquat evidences that a small applied bias (0,5 to 1 volt) is enough to ensure optimal electron-hole separation. It was also demonstrated that the effluent conductivity also has a large influence on the photoelectrochemical performances

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CNPq
No presente trabalho foi investigado o desempenho de nanotubos de TiO2 sensibilizados com quantum dots de CdS na geração de hidrogênio por meio da reação de dissociação da água por meio da fotocatálise e fotoeletrocatálise. Os nanotubos de TiO2 foram obtidos pelo método de anodização (30 V, 1 hora) de chapas de Ti, em etilenoglicol e água contendo íons fluoreto. As amostras anodizadas foram submetidas a tratamento térmico 400°C durante 3 horas. Posteriormente as amostras foram sensibilizadas com quantum dots de CdS via síntese hidrotérmica in situ usando o ácido 3-mercaptopropiônico como agente estabilizante. A eficiência fotocatalítica dos materiais na produção de hidrogênio foi investigada por meio da reação de dissociação da água utilizando como fonte de irradiação um simulador solar. A quantificação do hidrogênio gerado foi determinada por meio de cromatógrafia gasosa. Por outro lado, para estimar a eficiência de geração de hidrogênio via fotoeletrocatálise, as amostras foram avaliadas como fotoânodos e medidas da fotocorrente gerada pela irradiação em uma célula fotoeletroquímica (PEC) de três eletrodos foram realizadas. A sensibilização dos nanotubos de TiO2 com os quantum dots de CdS a partir da síntese hidrotérmica in situ, permitiu uma boa impregnação e distribuição uniforme dos quantum dots ao redor da superfície dos nanotubos, de acordo com as análises de EDS e XPS. O perfil de profundidade de XPS mostrou que a concentração de CdS permaneceu praticamente inalterada (homogênea) ao longo da matriz nanotubular. A presença de ânions sulfato evidenciou a oxidação do material preferentemente na superfície. Os nanotubos conferem uma proteção ao CdS frente à oxidação e protegem também os quantum dots quanto à fotocorrosão na solução de sacrifício S2-/SO32- utilizada. Este comportamento define uma boa estabilidade na fotocorrente gerada como mostrado em experimentos de longa duração (20 horas) sob irradiação. Os resultados experimentais mostraram três comportamentos diferentes para a geração de H2 quando o tempo de síntese dos QDs de CdS aumenta. Foram observados, efeitos similares, antagônicos e sinérgicos frente à atividade fotocatalítica em relação aos nanotubos de TiO2. O efeito antagônico parece estar relacionado com a presença de duas populações de tamanhos de QDs de CdS, onde a população com um band gap menor atua como uma armadilha para os elétrons fotogerados pela população com um band gap maior, diminuindo a atividade fotocatalítica do TiO2 na região ultravioleta. A transferência de elétrons a partir dos QDs de CdS para o TiO2 foi comprovada pelos resultados de UPS combinados com as medidas do band gap óptico. A maior absorção no visível após a sensibilização com o CdS combinada com a transferência de elétrons possibilita um incremento na taxa de geração de hidrogênio por meio da fotocatálise a partir de luz visível de quase zero para os nanotubos de TiO2 até cerca de 0,3 μmol cm-2 h-1 após sensibilização com os QDs de CdS. No caso da fotoeletrocatálise em uma PEC, a taxa de geração de H2 a partir de luz visível estimada pela fotocorrente gerada após a sensibilização (1,79 μmol cm-2 h-1) chega a ser até 12 vezes maior que para os nanotubos de TiO2 sem sensibilizar (0,15 μmol cm-2 h-1).
In the present work, we investigated the performance of TiO2 nanotubes sensitized with CdS quantum dots on the photocatalytic and photoelectrocatalytic H2 production reaction. TiO2 nanotubes were obtained by anodization of Ti foil, followed by annealing to crystallize the nanotubes into anatase phase. Afterwards, the samples were sensitized with CdS quantum dots via an in situ hydrothermal route using 3-mercaptopropionic acid as the capping agent. This sensitization technique permits high loading and uniform distribution of CdS quantum dots onto TiO2 nanotubes. The XPS depth profile showed that CdS concentration remains almost unchanged (homogenous), while the concentration relative to the sulfate anion decreases by more than 80 % with respect to the initial value after ~200 nm in depth. The presence of sulfate anions is due to the oxidation of sulfide and occurs in greater proportion in the material surface. This protection for air oxidation inside the nanotubular matrix also protected the CdS from photocorrosion in sacrificial solution leading to good stability properties proved by a long duration photocurrent measurements. The effect of the sizes of CdS quantum dots attached to TiO2 nanotubes on the hydrogen production via photocatalysis was investigated. The experimental results showed three different behaviors when the CdS size is increased in the sensitized samples, e.g., similar, deactivation and activation effects on the hydrogen production with regard to TiO2 nanotubes. The deactivation effect was related with two populations of sizes of CdS, where the population with a shorter band gap acts as a trap for the electrons photogenerated by the population with a larger band gap. Electron transfer from CdS quantum dots to TiO2 semiconductor nanotubes was proven by the results of UPS combined with optical band gap measurements. This property facilitates an improvement of the visible-light photocatalytic hydrogen evolution rate from zero, for TiO2 nanotubes, to approximately 0.3 μmolcm-2h-1 for TiO2 nanotubes sensitized with CdS quantum dots. The hydrogen generation rate estimated from photocurrents measurements via photoelectrocatalysis in PEC systems was also investigated. The hydrogen generation rate after sensitization was improved from 0,15 μmol cm-2 h-1 to 1,79 μmol cm-2 h-1, near to 12 times better performance under visible-light irradiation.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
A produção de etanol e açúcar a partir de cana-de-açúcar é um atividade de grande importância no Brasil, mas também fonte de grande preocupação ambiental devido ao grande acúmulo de biomassa na forma de bagaço e vinhaça gerados como rejeitos. A biomassa lignocelulósica é constituída de celulose, com estrutura formada de unidades de glicose polimerizadas, deste modo estudos voltados para a conversão de glicose em compostos químicos com maior valor agregado seria relevante para buscar novas formas de aproveitamento destes rejeitos. O objetivo do presente trabalho é investigar a aplicabilidade da técnica de fotoeletrocatálise para promover a oxidação de glicose em meio aquoso utilizando nanotubos de dióxido de titânio (NT-Ti/TiO2) como fotoanodos com vistas a obtenção de compostos com maior valor agregado. Os eletrodos de nanotubos de dióxido de titânio (NT-Ti/TiO2) foram preparados por oxidação eletroquímica de Ti em solução 1,0 mol L-1 de NaH2PO4 + 0,3% (m/m) HF como eletrólito de suporte sob potencial de 20V por 2 h e calcinado a 450 °C. Um método analitico baseado em cromatografia de troca iônica com detecção amperométrica foi desenvolvido para análise de glicose, acido glicônico, acido glicárico, arabitol e arabinose e curvas analíticas foram construídas em concentrações de 1,00 a 20,0x10-6 mol L-1, r = 0,9995, e o método alcançou limites de detecção e determinação ao redor de LD = 0,03x10-6 mol L-1 e LQ = 0,08x10-6 mol L-1 para a determinação de glicose. O método foi utilizado para monitoramento dos produtos gerados durante oxidação fotoeletrocatalítica de 10,0 mmol L-1 de glicose sob potencial de +1,5 V vs Ag/AgCl e irradiação UV/Vis que alcançou 72% de conversão após 180 min de tratamento. Medidas de remoção de carbono orgânico total mostraram que 28% da glicose foi convertida a CO2 e o restante foi transformado em outro produtos, tais como Arabinose, arabinitol, 4-cetoglicose, glucohexodialdose, glucona-δ-lactona, 6-desoxiglucose e o ácido glicônico, cuja maioria foi confirmada por espectrometria de massas. Os resultados demonstram que a técnica de fotoeletrocatálise pode ser uma alternativa simples, econômica e promissora para promover a conversão da glicose em alguns produtos de interesse econômico.
The production of sugar and ethanol from sugarcane is an activity very important in Brazil, but it is also a source of great environmental concern due to the large accumulation of biomass in form of bagasse and vinasse generated as waste of this process. The lignocellulosic biomass is made up of cellulose, wich structure is made of polymerized glucose units. Thereby studies focused on the conversion of glucose into added value chemical compounds would be relevant to seek new ways to use these waste. This work describes the construction electrodes of titanium dioxide nanotubes (NT-Ti / TiO2) and its application in photoeletrocatalytic oxidation of glucose in aqueous media aimed at converting glucose into compounds with higher added value. The electrodes were prepared by electrochemical oxidation of Ti in solution of 1.0 mol L-1 NaH2PO4 + 0.3% (m/m) HF as supporting electrolyte under a potential of 20V for 2 h and calcined at 450 ° C. An analytical method based on ion exchange chromatography with amperometric detection was developed for glucose, gluconic acid, glucarico acid, arabitol and Arabinose analysis and analytical curves were constructed at concentrations of 1.00 to 20,0x10-5 mol L-1, r = 0.9995, and the method achieved detection limits and determination around 0,03x10-6 mol L-1 and 0,08x10-6 mol L-1 for glucose determination, respectively. The method was used for monitoring the generated products due the oxidation photoeletrocatalytic 10.0 mmol L-1 glucose solution under potential of +1.5 V vs Ag / AgCl and irradiating UV / Vis that achieved 72% conversion after 180 min of treatment. Measurements of total organic carbon removal showed that 28% of the glucose was converted to CO2 and the rest was transformed into other products, such as arabinose, arabinitol, 4- ketoglicose, glucohexodialdose, Glucone-δ-lactone, 6-deoxyglucose and acid gluconic, most of which was confirmed by mass spectrometry. The results demonstrate that photoelectrocatalysis technique may be a simple, economical and attractive alternative to promote glucose conversion into some products of economic interest.

Dans une société qui peine à renoncer à l'utilisation des énergies fossiles, la production d'hydrogène à partir d'eau par photocatalyse solaire est une alternative que les chimistes se doivent d'explorer. La mise en place de cette solution est conditionnée à la résolution de deux problèmes majeurs : augmenter l'efficacité de la conversion solaire par le développement de nouveaux semi-conducteurs, et améliorer la réactivité en surface par le développement de co-catalyseurs efficaces. Dans un premier temps, nous avons contribué à l'étude d'une nouvelle famille de semi-conducteurs par des calculs ab initio DFT. Différentes propriétés clés ont été calculées et comparées aux valeurs expérimentales. Nous avons montré que pour une même famille de matériaux, l'absorption peut être contrôlée par modification de la composition.Ensuite, nous nous sommes focalisés sur la réaction d'oxydation de l'eau (OER). Pour cette réaction les catalyseurs de type oxyhydroxydes et leurs dérivés sont très prometteurs car à la fois efficaces et contenant des éléments abondants sur Terre, mais la compréhension de son mécanisme reste limitée. Sur le composé modèle CoOOH, nous en avons réalisé une analyse approfondie par une étude exhaustive des intermédiaires ainsi que par modélisation explicite du potentiel électrochimique. Nos études ont montré la nécessite de prendre en compte plusieurs sites réactionnels dans la détermination des mécanismes d'oxydation de l'eau sur la surface de ces catalyseurs. Enfin, une étude préliminaire de l'utilisation de la biomasse a été menée, dans le but de combiner valorisation de la biomasse et production d'hydrogène. Le cas de l'oxydation du glycérol est envisagé
In a society struggling to waive the use of fossil fuels, hydrogen production from water by solar photocatalysis is a alternative chemists have to consider. Setting up of this solutions asks to tackle two major issues : increase solar energy conversion by developing new semiconductors, and enhance the surface reactivity by developing efficient cocatalysts.First, DFT \emph{ab initio} calculations were carried out on a new family of semiconductor materials. Different key properties were computed and compared to experimental values. We showed that for a same material family, absorption can be controlled by changing the composition.Then, we focused on Oxygen Evolution Reaction (OER). For this reaction oxyhydroxides catalysts and their derivatives seem promising as both efficient and containing earth-abundant elements, but the understanding of its mechanism still remains unclear. On CoOOH model compound, we realised an extended analysis by a comprehensive study of intermediates and by explicit modelling of electrochemical potential. Our studies showed that taking into account several reactive sites is necessary to determine the OER mechanism on these catalysts' surface.Last, a preliminary study of biomass use was carried, in order to combine its valorization along with hydrogen production. The case of glycerol photoreforming is considered

A aplicação do processo de fotoeletrocatálise à eliminação de interferentes orgânicos em baixa concentração na eletroanálise de metais foi abordada tomando o quelato Cu(II)-EDTA como sistema modelo e o restabelecimento da onda voltamétrica do cobre como indicador de efetividade. Desenvolveram-se células eletroquímicas de camada delgada (espessura de 600 micrômetros) nas quais alguns microlitros de amostra são tratados sobre um eletrodo modificado com TiO2 (tipo P25, rico em anatase), cuja superfície é irradiada através de uma janela por um LED (370 nm). Foram construídos e avaliados os seguintes eletrodos: pasta de carbono, TiO2 e óleo parafínico (CPE-TiO2), compósitos de grafite, TiO2 e adesivo epóxi ou de silicone e ouro com oclusão de TiO2 por eletrodeposição. Estudo do efeito de parâmetros como potencial aplicado ao eletrodo, composição do eletrólito e concentração de EDTA sobre a fotocorrente permitiu selecionar condições de trabalho e estabelecer algumas correlações. Por exemplo, observou-se linearidade entre a fotocorrente e a concentração de EDTA até 1,0 mmol/L, aparente limite superior do controle difusional do processo para potência radiante aplicada, acima do qual, a cinética de oxidação passa a sobrepujar o transporte no controle da velocidade de reação. O restabelecimento pleno da onda de Cu(II) 1,0 mmol.L-1 foi observado após a irradiação por 10 min quando a concentração de EDTA não excedia 0,94 mmol.L-1. Descobriu-se um procedimento mais rápido que consiste na aplicação do tratamento fotoeletrocatalítico simultâneo ao registro de voltamogramas cíclicos repetitivos (eletrodo de Au-TiO2, 0,3 a 0,7 V vs. Ag/AgCl, 100 mV.s-1). Após o sexto ciclo, a altura do pico de redissolução anódica do Cu (reduzido durante a varredura no sentido negativo) estabiliza, permitindo a quantificação sem etapa prévia de abertura.
The photoelectrocatalysis process was investigated for the elimination of organic compounds interference on the electroanalysis of trace metals. Cu(II)-EDTA chelate was chosen as model system and the recovery of copper voltammetric peak, as effectiveness indicator. Thin layer cells (thickness of 600 micrometers) were designed for the treatment of some microliters of sample by irradiation (370 nm LED) of an electrode modified with TiO2 (P25, anatase rich). The following modified electrodes were prepared and evaluated: carbon paste with TiO2 and paraffin oil (CPE-TiO2), composites of graphite, TiO2 and epoxy or silicone binders and TiO2 occluded in electrodeposited gold on a gold substrate. The effect of parameters like potential bias, electrolyte composition and EDTA concentration on the photocurrent was evaluated to setup working conditions. Some correlations were observed, e.g., a linear dependence between photocurrent and EDTA concentration up to 1.0 mmol/L. For the irradiance applied, this concentration is possibly the upper limit of operation diffusion transport control, above which, the kinetics of the oxidation at the TiO2 modified electrode becomes the controlling process. For EDTA concentrations not exceeding 0.94 mmol.L-1, full recovery of 1.0 mmol.L-1 Cu(II) voltammetric peaks was observed after 10 min of irradiation. A faster procedure was discovered and consists in recording repetitive cyclic voltammograms (Au-TiO2 electrode, 0,3 to 0,7 V vs. Ag/AgCl scans, 100 mV.s-1) simultaneously with continuous irradiation. After the sixth cycle, the copper anodic stripping peak height stabilizes allowing quantification without previous sample pre-treatment step.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Among the variety of semiconductor materials investigated to apply in electrochemical cells bismuth vanadate (BiVO4) is one of the candidate which would be used as photoanode. Thus, this study aimed to synthesize thin films of BiVO4 and their modification with a thin layer of iron (III) oxyhydroxide (FeOOH) by photodeposition and study their photoelectrocatalytic properties. The optimization of BiVO4 synthesis condition was assessed by a factorial design 23 and an analysis of univariate type. The parameters studied were annealing temperature (500 and 600 °C), calcinations time (30, 60, 150 and 270 min.), solvent type employed for dissolving the BiVO4 precursor reagents (poly ethylene glycol 300-PEG 300, PEG 400, ethylene glycol-EG, mixture 1:1 by volume of PEG 300 and EG), deposition method of BiVO4 films (dropping and spin coating) and method of drying layers (heating at 500 °C, heat gun and no drying). From the optimized condition BiVO4 film was prepared by dissolving bismuth (III) nitrate and ammonium metavanadate in a mixture of 1:1 by volume of EG and PEG 300, it was deposited onto glass containing FTO by spin coating and then calcinated directly at 500 °C for 60 min. The photodeposition was carried out in the mixture FeSO4 and sodium citrate medium both 1 mmol L-1 and pH 4.7 by applying the open circuit potential for 5 min. and under light incidence. and then polarizing at 1.2 V for 1 min. BiVO4 and BiVO4/FeOOH films were characterized by XRD, SEM, EDS, UV-vis, voltammetry (cyclic and linear) and electrochemical impedance spectroscopy. The results reveled that photocurrent values increased 2.5 times at 0.71 V and the on set potential shifted to less positive value in the presence of FeOOH, also there was a considerable reduction of the charge transfer resistance in the interface photoanode/solution. The bare BiVO4 films were photostable during the illumination time studied which was 4 h. However, the modified films did not show the same behavior, the photocurrent value decreased 29% after 4 h illuminated. The results in the sulphite presence showed that photocurrent value for bare BiVO4 and BiVO4/FeOOH were less than the maximum photocurrent value which would achieve for this materias.
Dentre os diversos materiais semicondutores estudados para aplicação em células fotoeletroquímicas encontra-se o vanadato de bismuto (BiVO4), o qual pode ser utilizado como fotoanodo. Deste modo, o presente trabalho teve como objetivo principal a síntese de filmes finos de BiVO4 e sua modificação com uma fina camada de oxihidróxido de ferro (III) (FeOOH) por fotodeposição e avaliação das propriedades fotoeletrocatalíticas destes materiais. A otimização das condições de síntese do BiVO4 foi avaliada por um planejamento fatorial 23 e por uma análise do tipo univariada. Os parâmetros estudados foram temperatura de calcinação (500 e 600 °C), tempo de calcinação (30, 60, 150 e 270 min.), tipo de solvente empregado para dissolução dos reagentes precursores do BiVO4 (polietileno glicol 300-PEG 300, PEG 400, etileno glicol-EG, mistura 1:1 em volume de PEG 300 e EG), método de deposição dos filmes de BiVO4 (dropping e spin coating) e método de secagem das camadas dos filmes (aquecimento a 500 °C, soprador térmico e sem secar). Nas condições otimizadas o filme de BiVO4 foi preparado pela dissolução de nitrato de bismuto (III) e metavanadato de amônio em uma mistura de 1:1 em volume de EG e PEG 300, depositado sobre vidro contendo FTO por spin coating e depois calcinado diretamente a 500 ºC por 60 min. A fotodeposição foi realizada em meio da mistura FeSO4 e citrato de sódio ambos a 1 mmol L-1 e pH 4,7, aplicando-se o potencial de circuito aberto por 5 min. e com incidência de luz, seguida de polarização em 1,2 V por 1 min. Os filmes de BiVO4 e BiVO4/FeOOH foram caracterizados por DRX, MEV, EDX, UV-vis, voltametria (cíclica e linear) e espectroscopia de impedância eletroquímica. Os resultados mostram que na presença do FeOOH houve aumento de 2,5 vezes nos valores de densidade fotocorrente em 0,71 V e o potencial de on set deslocou-se para valores menos positivos, bem como uma redução considerável na resistência de transferência de carga na interface fotoanodo/solução. Os filmes de BiVO4 puro apresentaram-se fotoestáveis durante o tempo de iluminação estudado, 4 h. No entanto, os filmes modificados não apresentaram o mesmo comportamento, houve um decréscimo de 29% no valor de densidade de fotocorrente após 4 h de iluminação. O estudo na presença do sulfito mostrou que os valores de fotocorrentes para o BiVO4 puro e o BiVO4/FeOOH estão abaixo do valor máximo que se poderia obter para estes materiais.

Os azo corantes Disperse Red 1, Disperse Orange 1 e Disperse Red 13 são amplamente utilizados para o tingimento de fibras e são mutagênicos para o ensaio de Salmonella/microssoma e para o ensaio de micronúcleos. O aumento da complexidade e dificuldades para o tratamento de efluentes têxteis tem levado à busca constante de novas metodologias para o tratamento destes rejeitos. A cloração é um método amplamente empregado para a desinfecção de águas e efluentes, mas também para remover ou reduzir a cor do efluente a fim de atender o padrão de emissão da legislação brasileira. Porém, muitos trabalhos mostram que este tratamento muitas vezes não é capaz de remover a mutagenicidade dos corantes e em alguns casos pode até aumentar a toxicidade da amostra. Já a fotoeletrocatálise, aparentemente, é eficiente tanto na degradação desses compostos em amostras aquosas como na redução da atividade mutagênica, como demonstraram alguns ensaios preliminares. Este trabalho tem como objetivo a avaliação da eficiência do tratamento por fotoeletrocatálise na remoção da mutagenicidade dos azo corantes Disperse Red 1, Disperse Orange 1 e Disperse Red 13 presentes em amostras aquosas em comparação à cloração química convencional utilizando o teste de micronúcleos (MNs) em células HepG2. Os resultados demonstraram que a freqüência de MNs induzidos pelas diferentes concentrações testadas das soluções dos corantes estudados não foram significativamente diferentes do controle negativo. Nossos dados também revelaram que os índices de proliferação do bloqueio da citocinese (IPBC) em cultura de células HepG2 tratadas com os três corantes após a cloração e fotoeletrocatálise também não apresentaram diferenças estatísticas em relação aos seus respectivos controles negativos. A análise comparativa dos azo corantes Disperse Red 1, Disperse Orange 1 e Disperse Red 13 clorados e fotoeletrocatalisados com os corantes originais estudados pelo nosso grupo (CHEQUER, 2008; CHEQUER et al., 2009) mostrou uma diminuição no número de MNs indicando que após os tratamentos houve a remoção da mutagenicidade a partir da concentração de 1,0 µg/mL para os três corantes estudados. Portanto, podemos concluir que a cloração química convencional e a fotoeletrocatálise, nas condições testadas, são eficientes na remoção da mutagenicidade dos azo corantes Disperse Red 1, Disperse Orange 1 e Disperse Red 13 em relação à indução de micronúcleos.
The azo dyes Disperse Red 1, Disperse Orange 1 and Disperse Red 13 are widely used in dyeing processes and are mutagenic for Salmonella/microsome and micronucleus assays. The increasing of the complexity and difficulties for treatments of textile effluents has led to a constant search for new methodologies for the treatment of these wastewaters. Chlorination is a method extensively used for water and wastewaters disinfection and to remove or reduce the color of effluents in order to respect the standard of discharges issued by the Brazilian legislation. However, a lot of studies have shown that this treatment is not often able to remove the mutagenicity of the dyes, and in some cases it may even increase the toxicity of the sample. On the other hand, photoelectrocatalysis is apparently efficient both in the degradation of these compounds in aqueous samples and in reduction of the mutagenic activity, as demonstrated by some preliminary assays. This study aims to evaluate the efficiency of the photoelectrocatalysis treatment in the removal of the mutagenicity of the azo dyes Disperse Red 1, Disperse Orange 1 and Disperse Red 13 present in aqueous sample in comparison to conventional chemical chlorination using the micronucleus test (MNs) in HepG2 cells. The results showed that the frequency of MNs induced by different tested concentrations of the solutions of the studied dyes were not significantly different from the negative control. Our data also revealed that the cytokinesis-block proliferation index (CPBI) in cultures of HepG2 cells treated with the three dyes after chlorination and photoelectrocatalysis also showed no statistical differences related to the their respective negative controls. The comparative analysis of azo dyes chlorinated and photoelectrocatalysed Disperse Red 1, Disperse Orange 1 and Disperse Red 13 with the original dyes studied by our group (CHEQUER, 2008; CHEQUER et al., 2009) showed a decrease in the number of MNs indicating that after the treatments occurred the removal of the mutagenicity potencial at concentration of 1,0 µg/mL for the three dyes studied. Therefore, we conclude that conventional chemical chlorination and photoelectrocatalysis, under the conditions tested, are effective in removing of the mutagenicity of the azo dyes Disperse Red 1, Disperse Orange 1 and Disperse Red 13 related to induction of micronucleus.

This diploma thesis deals with the coating and printing of thin layers based on nanoparticles of titanium dioxide and organosilica binder on various substrates. The influence of the ratio of the both components on the activity of the prepared immobilized layers was studied. Five compositions with different ratios of TiO2 and binder were prepared. The work focuses mainly on the study of photocatalytic and photoelectrocatalytic properties of prepared layers. It was also important to characterize the mechanical properties of the layer such as hardness or adhesion. Both photocatalytic and photoelectrocatalytic activity were determined by monitoring the degradation of the model pollutants in aqueous solutions. The dye Acid Orange 7 and UV filter 2-hydroxy-4-methoxybenzophenone were used in conjunction with UV/VIS spectroscopy or high performance liquid chromatography techniques. Both photocatalytic and photoelectrocatalytic activity were expressed using kinetic characteristics.

Tesis por compendio
[ES] La presente Tesis Doctoral se centra en el desarrollo de nanoestructuras de óxido de zinc (ZnO) mediante anodizado electroquímico en diferentes condiciones para su aplicación en el área energética, en particular, en la producción de hidrógeno mediante la rotura fotelectrocatalítica de la molécula de agua. El hidrógeno es un vector energético que se plantea como solución al problema asociado a la intermitencia diurna y estacional de la energía solar y a la variabilidad en la demanda de energía. Por otra parte, el ZnO es un material semiconductor prometedor como fotocatalizador para la producción de hidrógeno debido a sus características y propiedades. En este contexto, el ZnO es un material muy abundante, y por extensión, relativamente barato, no es tóxico y presenta una energía de banda prohibida de 3,37 eV, lo que le permite la absorción de fotones en la región UV del espectro solar. Asimismo, las posiciones de sus bandas de energía son apropiadas para llevar a cabo la fotoelectrólisis del agua. En la presente Tesis Doctoral la síntesis de nanoestructuras de ZnO se llevó a cabo mediante anodizado electroquímico, puesto que este método presenta múltiples ventajas frente a otros métodos de síntesis habituales. En general, el anodizado electroquímico constituye un método rápido, sencillo y eficaz de síntesis de nanoestructuras de ZnO mediante el que es posible diseñar las características superficiales de las nanoestructuras (tamaño y morfología) a través del control de sus parámetros. Como resultado de una revisión bibliográfica en profundidad, se analizó la influencia de los parámetros del anodizado en las características superficiales de las nanoestructuras. Además, se investigaron aquellos parámetros cuya influencia todavía no había sido analizada. Por una parte, se estudió la influencia de emplear diferentes condiciones hidrodinámicas de flujo (dadas por la variación de la velocidad de rotación del electrodo). Por otra parte, se estudió la influencia conjunta de modificar el electrolito con la adición de un disolvente orgánico (etanol o glicerol en distintas proporciones) y variar la velocidad de rotación del electrodo. Las muestras de ZnO sintetizadas se sometieron a una caracterización morfológica, estructural, electroquímica y fotoelectroquímica y se estudiaron sus propiedades para ser empleadas como fotocatalizadores en la producción de hidrógeno. De acuerdo con los resultados, las diferentes condiciones de anodizado dieron lugar a diversas nanoestructuras de ZnO con diferentes características superficiales y fotoelectrocatalíticas. Así, se obtuvieron nanoestructuras de elevada área superficial con morfologías de nanocables de distintos tamaños, nanotubos, nanoesferas y nanoesponjas. Asimismo, tras el calentamiento térmico las muestras presentaron una estructura cristalina hexagonal wurtzita con elevada cristalinidad y la presencia de defectos estructurales. Igualmente, las nanoestructuras sintetizadas presentaron una elevada fotoactividad, dada por los valores elevados de densidad de fotocorriente, presentando propiedades apropiadas para su utilización en la producción de hidrógeno. La muestra que presentó el valor de densidad de fotocorriente más elevado (0,34 mA/cm2) fue la muestra de nanocables de ZnO anodizada a 0 rpm en un electrolito con un contenido en etanol del 10 % en volumen. En la aplicación de dicha muestra en la producción de hidrógeno se obtuvo un volumen teórico de hidrógeno de 1,55 litros por hora de sol y metro cuadrado de ZnO.
[CA] La present Tesi Doctoral se centra en el desenvolupament de nanoestructures d'òxid de zinc (ZnO) mitjançant anoditzat electroquímic en diferents condicions per a l'aplicació en l'àrea energètica, en particular, en la producció d'hidrogen mitjançant el trencament fotelectrocatalític de la molècula d'aigua. L'hidrogen és un vector energètic que es planteja com a solució al problema associat a la intermitència diürna i estacional de l'energia solar i a la variabilitat en la demanda d'energia. D'altra banda, el ZnO és un material semiconductor prometedor com a fotocatalitzador per a la producció d'hidrogen degut a les seues característiques i propietats. En aquest context, el ZnO és un material molt abundant, i per extensió, relativament barat, no és tòxic i presenta una energia de banda prohibida de 3,37 eV, la qual cosa li permet l'absorció de fotons a la regió UV de l'espectre solar. Així mateix, les posicions de les seues bandes d'energia són apropiades per a dur a terme la fotoelectròlisi de l'aigua. En la present Tesi Doctoral la síntesi de nanoestructures de ZnO es va dur a terme mitjançant anoditzat electroquímic, ja que aquest mètode presenta múltiples avantatges enfront d'altres mètodes de síntesi habituals. En general, l'anoditzat electroquímic constitueix un mètode ràpid, senzill i eficaç de síntesi de nanoestructures de ZnO mitjançant el qual és possible dissenyar les característiques superficials de les nanoestructures (grandària i morfologia) a través del control dels seus paràmetres. Com a resultat d'una revisió bibliogràfica en profunditat, es va analitzar la influència dels paràmetres de l'anoditzat en les característiques superficials de les nanoestructures. A més, es van investigar aquells paràmetres la influència dels quals encara no havia sigut analitzada. D'una banda, es va estudiar la influència d'emprar diferents condicions hidrodinàmiques de flux (donades per la variació de la velocitat de rotació de l'elèctrode). D'altra banda, es va estudiar la influència conjunta de modificar l'electròlit amb l'addició d'un dissolvent orgànic (etanol o glicerol en diferents proporcions) i variar la velocitat de rotació de l'elèctrode. Les mostres de ZnO sintetitzades es van sotmetre a una caracterització morfològica, estructural, electroquímica i fotoelectroquímica i es van estudiar les seues propietats per a ser emprades com fotocatalitzadors en la producció d'hidrogen. D'acord amb els resultats, les diferents condicions d'anoditzat van donar lloc a diverses nanoestructures de ZnO amb diferents característiques superficials i fotoelectrocatalítiques. Així, es van obtindre nanoestructures d'elevada àrea superficial amb morfologies de nanocables de diferents grandàries, nanotubs, nanoesferes i nanoesponges. Així mateix, després del calfament tèrmic les mostres van presentar una estructura cristal·lina hexagonal wurtzita amb elevada cristallinitat i la presència de defectes estructurals. Igualment, les nanoestructures sintetitzades van presentar una elevada fotoactivitat, donada pels valors elevats de densitat de fotocorrent, presentant propietats apropiades per a la seua utilització en la producció d'hidrogen. La mostra que va presentar el valor de densitat de fotocorrent més elevat (0,34 mA/cm²) va ser la mostra de nanocables de ZnO anoditzada a 0 rpm en un electròlit amb un contingut en etanol del 10% en volum. En l'aplicació d'aquesta mostra en la producció d'hidrogen es va obtindre un volum teòric d'hidrogen de 1,55 litres per hora de sol i metre quadrat de ZnO.
[EN] This Doctoral Thesis focuses on the development of zinc oxide (ZnO) nanostructures by electrochemical anodization under different conditions for its application in the energy area, in particular, in the production of hydrogen through photoelectrochemical water splitting. Hydrogen is an energy vector that is proposed as a solution to the problem associated with the diurnal and seasonal intermittency of solar energy and the variability in the energy demand. On the other hand, ZnO is a promising semiconductor material as a photocatalyst for hydrogen production due to its characteristics and properties. In this context, ZnO is a very abundant material, and by extension, relatively cheap, it is non-toxic and has a band-gap energy of 3.37 eV, which allows it to absorb photons in the UV region of the solar spectrum. Besides, the positions of ZnO energy bands are appropriate to carry out photoelectrochemical water splitting. In the present Doctoral Thesis, the synthesis of ZnO nanostructures was carried out by electrochemical anodization, since this method has multiple advantages compared to other common synthesis methods. In general, electrochemical anodization constitutes a fast, simple, and effective method of synthesis of ZnO nanostructures by means of which it is possible to design the surface characteristics of the nanostructures (size and morphology) by controlling anodization parameters. As a result of an in-depth bibliographic review, the influence of anodization parameters on the surface characteristics of nanostructures was analyzed. In addition, those parameters whose influence had not yet been analyzed were investigated. On the one hand, the influence of using different controlled hydrodynamic conditions (given by the variation of the rotation speed of the electrode) was studied. On the other hand, the influence of both modifying the electrolyte with the addition of an organic solvent (ethanol or glycerol in different proportions) and varying the electrode rotation speed was studied. The synthesized ZnO samples were subjected to a morphological, structural, electrochemical and photoelectrochemical characterization and their properties were studied to be used as photocatalysts in hydrogen production. According to the results, the different anodization conditions gave rise to various ZnO nanostructures with different surface and photoelectrocatalytic characteristics. Thus, high surface area nanostructures were obtained with morphologies of nanowires of different sizes, nanotubes, nanospheres and nanosponges. Likewise, after thermal annealing the samples presented a wurtzite hexagonal crystalline structure with high crystallinity and the presence of structural defects. Likewise, the synthesized nanostructures presented high photoactivity, given by the high values of photocurrent density, presenting appropriate properties for their use in the production of hydrogen. The sample that presented the highest photocurrent density value (0.34 mA / cm2) was the ZnO nanowires anodized at 0 rpm in an electrolyte with an ethanol content of 10 % by volume. In the application of this sample in the hydrogen production, a theoretical volume of hydrogen of 1.55 liters per hour of sun and square meter of ZnO was obtained.
Authors would like to express their gratitude for the financial support to the Generalitat Valenciana and to the European Social Fund within the subvention to improve formation and employability of technical and management staff of I+D (GJIDI/2018/A/067) and for its financial support through the project: IDIFEDER/018/044. Authors also thank for the financial support to the Ministerio de Economía y Competitividad (Project Code: CTQ2016-79203-R) and to the Ministerio de Ciencia e Innovación-Agencia Estatal de Investigación (Project Code: PID2019-105844RB-I00) for its help in the Laser Raman Microscope acquisition (UPOV08-3E- 012) and for the co-finance by the European Social Fund.
Batista Grau, P. (2021). Desarrollo de nanoestructuras de ZnO mediante anodizado electroquímico en diferentes condiciones para su aplicación en el área energética [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172606
TESIS
Compendio

Tecnologias efetivas para o tratamento de águas e efluentes representam um dos grandes desafios da nossa sociedade; dentre as opções, a fotoeletrocatálise pode ser considerada como uma técnica alternativa e de interesse. Nesse contexto, o presente trabalho teve como objetivo desenvolver eletrodos de TiO2 modificados visando o tratamento fotoeletrocatalítico de interferentes endócrinos. Realizou-se inicialmente a síntese de nanotubos de TiO2 (TiO2-NT) sobre substrato de Ti metálico via anodização eletroquímica em eletrólito NaH2PO4/HF. Para minimizar as limitações inerentes ao TiO2 realizou-se a eletrodeposição de WO3 sobre os nanotubos de TiO2 (Ti/TiO2-NT/WO3) e diretamente sobre o substrato de Ti metálico. Este último revelou a formação de uma camada fina de TiO2 sobre a superfície, posterior ao tratamento térmico, formando um compósito (Ti/TiO2/WO3). A análise de difração de raios-X confirmou a formação da fase monoclínica de WO3 para ambas as sínteses e a fase anatase para os eletrodos de Ti/TiO2-NT/WO3. Para as duas sínteses, as medidas de energia dispersiva de raios-X revelaram uma quantidade crescente de W na composição dos eletrodos com o aumento do tempo de eletrodeposição. Teores elevados de W (acima de 1,2 %) apresentaram uma diminuição expressiva nos valores de fotocorrente. No entanto, baixos teores de W (entre 0,4 e 1,2 %) indicaram um aumento de 20 % nos valores de fotocorrente para os eletrodos de Ti/TiO2-NT/WO3 (20 mA cm-2) e Ti/TiO2/WO3 (17 mA cm-2) comparados aos não modificados, no potencial de +2,0 V. As análises de reflectância difusa mostraram uma baixa energia de bandgap (≈ 2,90 eV, eletrodos de Ti/TiO2-NT/WO3) e um aumento na absorção da irradiação UV-Vis. Posteriormente, os eletrodos modificados foram aplicados na oxidação fotoeletrocatalítica (FE) dos compostos bisfenol-A (BPA) e propilparabeno (PPB), sob irradiação UV-Vis. O método FE apresentou um excelente desempenho em condições ácidas, aplicando-se potencial de +1,50 V e +0,50 V para os eletrodos Ti/TiO2-NT/WO3 e Ti/TiO2/WO3, respectivamente. A mineralização dos compostos BPA e PPB foi superior a 80 % tanto para o Ti/TiO2-NT/WO3 como para o Ti/TiO2/WO3. Quanto à taxa de remoção, o BPA e PPB foram completamente removidos após 45 e 60 min, respectivamente, para os eletrodos de Ti/TiO2/WO3 e após 30 minutos para os eletrodos de Ti/TiO2-NT/WO3. Adicionalmente, os eletrodos apresentaram um baixo consumo energético e boa estabilidade química. Comparada à técnica de fotocatálise (FC), a FE revelou uma eficiência de mineralização 2 vezes superior para o Ti/TiO2-NT/WO3 e mais de 20 % superior para o Ti/TiO2/WO3. Logo, as modificações dos eletrodos de TiO2 com WO3 constituíram importantes contribuições para o desempenho dos materiais, sendo um passo importante para a aplicação em tratamentos alternativos de descontaminação de águas residuárias. Ainda foi de interesse neste trabalho propor um método para a inserção de nanotubos (TiNT) e nanofolhas (TiNS) de titanatos no interior de nanotubos de TiO2 via eletroforese. O estudo possibilitou o desenvolvimento de um método simples e eficiente para a modificação de nanoestruturas complexas. A movimentação do contra eletrodo sobre a superfície do eletrodo de trabalho, adaptado com uma escova nas laterais, reduziu a espessura da camada de TiNS/TiNT. O potencial aplicado (20 V) e a estimulação mecânica da superfície foram importantes para a incorporação das nanoestruturas dentro dos poros de TiO2-NTs. Como resultado, os eletrodos apresentaram um aumento da hidrofobicidade e uma melhora na capacidade de oxidação direta comparado ao eletrodo não modificado.
Effective technologies for the water and wastewater treatment represent a challenges for our society; among the options, the photoelectrocatalysis can be considered a promising and interesting alternative. In this context, the objective of this study was to develop modified TiO2 electrodes for the photoelectrocatalytic treatment of endocrine disruptors. The synthesis of TiO2 nanotubes (TiO2-NT) on metallic Ti substrate was carried out via electrochemical anodization in NaH2PO4 /HF electrolyte. In order to minimize the limitations inherent of TiO2, the electrodeposition of WO3 was performed on the TiO2 nanotubes (Ti/TiO2-NT/WO3) and also in the metallic Ti substrate. The deposition on the Ti metallic produced a thin layer of TiO2 on the surface, subsequent to the heat treatment, generating a composite (Ti/TiO2/WO3). The X-ray diffraction analysis (XRD) confirmed the monoclinic phase of WO3 for both the syntheses and the anatase phase of TiO2 for the Ti/TiO2-NT/WO3 electrodes. For the two syntheses, the X-ray dispersive energy (EDX) analisys indicated an increasing amount of tungsten (W) in the composition of the electrodes with increasing of electrodeposition time. High W content (above 1.2%) showed a significant decrease in the photocurrent values. However, low content of W (between 0.4 and 1.2 %) indicated an increase of 20 % in the photocurrent values for the electrodes Ti/TiO2-NT/WO3 (20 mA cm-2) and Ti/TiO2/WO3 (17 mA cm-2) compared to the unmodified ones, at the potential of +2.0 V. Difuse reflectance analysis indicated low bandgap energy (≈ 2.90 eV, Ti/TiO2-NT/WO3 electrodes) and an increase in the UV-Vis irradiation absorption. The best electrodes modified with WO3 to the both syntheses were applied in the photoelectrocatalytic oxidation (PEC) of bisphenol-A (BPA) and propylparaben (PPB) compounds, under UV-Vis irradiation. The PEC method presented an excellent performance in acidic conditions, applying a bias potential of +1.50 V and +0.50 V for Ti/TiO2-NT/WO3 and Ti/TiO2/WO3 electrodes, respectively. The mineralization of BPA and PPB compounds was greater than 80% for both Ti/TiO2-NT/WO3 and Ti/TiO2/WO3. In relation to the removal rate, BPA and PPB were completely removed after 45 and 60 min, respectively, for Ti/TiO2/WO3 electrodes and after 30 minutes for Ti/TiO2-NT/WO3 electrodes. Additionally, the electrodes presented a low energy consumption and good chemical stability. Compared to the photocatalysis (PC), the PEC was 2 times higher to the mineralization efficiency for Ti/TiO2-NT/WO3 and almost 20% higher for Ti/TiO2/WO3. Thus, the modifications of the TiO2 electrodes with WO3 represent an important contribution to the performance of materials and, therefore, a positive step for the application in alternative treatments of decontamination of wastewater. It was also of interest in this work to propose a new method for the insertion of nanotubes (TiNT) and nanosheets (TiNS) of titanates inside of TiO2 nanotubes via electrophoretic deposition. In this study was developed a simple and efficient method for the modification of complex nanostructures. The movement of the counter electrode on the surface of the working electrode, adapted with a brush on the edges, reduced the thickness of the TiNS/TiNT layer. The potential applied (20 V) and the mechanical stimulation in the surface were important for the incorporation of TiNS/TiNT into the pores of TiO2-NTs. As a result, the electrodes increased the hydrophobicity and an improvement to the direct oxidation capacity compared to the unmodified electrode.

Ce travail de thèse traite de la production d’hydrogène par le procédé de photoélectrocatalyse en utilisant une photoanode à base de nanotubes de TiO2 verticalement alignés. L’utilisation du TiO2 étant limité pour des applications solaires en raison de son large gap, il est nécessaire de le modifier. Deux approches sont proposées pour modifier les nanotubes de TiO2 et leur permettre d’absorber la lumière visible. La première est une modification chimique du TiO2 par co-dopage cationique-anionique (Ta-N) ou (Nb-N). Les cations sont insérés durant la croissance des nanotubes grâce à une approche inédite, et l’azote est inséré durant le traitement thermique. Ceci a pour effet la formation d’orbitales hybrides qui entraîne une réduction du gap et une activité sous lumière visible, tout en permettant une stabilité de la structure. La seconde approche consiste à déposer des nanoparticules d’Ag sur la surface des nanotubes de TiO2. Grâce au contrôle de la morphologie des nanoparticules d’Ag, leur résonnance plasmonique permet de stimuler l’absorption du TiO2 et ainsi d’augmenter son rendement à la fois sous lumière UV et sous lumière visible
This work is about the production of hydrogen by photoelectrocatalysis using a vertically aligned TiO2 nanotubes based photoanode. Utilization of TiO2 for solar applications is limited due to its large band gap, it has to be modified. Two approaches are proposed for the modification of the TiO2 nanotubes to make them absorb visible light. The first one is the chemical modification of the TiO2 by (Ta-N) or (Nb-N) cationic-anionic co-doping. Cations are inserted during the growth of the nanotubes by a novel approach, and nitrogen is inserted during heat treatment. This leads to the formation of hybrid orbitals resulting in a band gap reduction and of activity under visible light. The second approach consists of the deposition of Ag nanoparticles on the surface of the TiO2 nanotubes. Thanks to the control of the morphology of the Ag nanoparticles, their plasmonic resonance can enhance the absorption of TiO2 and thus increase its activity both under UV and visible light

Os azo corantes atualmente são considerados um assunto preocupante no que se refere à saúde pública e ambiental, pois quando lançados nos efluentes industriais contaminam o meio ambiente. Infelizmente, o método convencional de tratamento de efluentes têxteis, bem como de águas brutas que os recebem não são capazes de remover de maneira eficaz os corantes bem como sua toxicidade. Dentro deste contexto, este trabalho teve como objetivo avaliar a eficiência do tratamento de amostras aquosas por fotoeletrocatálise em comparação com a cloração convencional como método alternativo de degradação de azo corantes, usando os corantes Disperse Orange 1, Disperse Red 1 e Disperse Red 13 como modelo. Adicionalmente, foi avaliada a citotoxicidade dos corantes originais em condrócitos bovinos e células HepG2 em cultura em monocamadas e 3D. Para tanto, soluções desses corantes originais, clorados e fotoeletrocatalisados foram avaliadas utilizando ensaios de genotoxicidade/mutagenicidade, citotoxicidade e ecotoxicidade. Todos os corantes originais e clorados foram genotóxicos para as células HepG2 no ensaio cometa. Para o ensaio com Salmonella, a cloração reduziu a mutagenicidade dos corantes para a linhagem YG1041 e aumentou o efeito para a linhagem TA98, exceto o Disperse Red 13 que teve a mutagenicidade reduzida para as duas linhagens após cloração. A fotoeletrocatálise removeu tanto a genotoxicidade quanto a mutagenicidade. Somente o Disperse Orange 1 induziu apoptose pelo ensaio com anexina V, mas essa citotoxicidade foi removida após os tratamentos. Os corantes Disperse Red 1 e Disperse Red 13 foram tóxicos para D. similis enquanto somente o Disperse Red 1 foi tóxico para V. fischeri, sendo que os tratamentos por cloração e fotoeletrocatálise diminuíram a toxicidade apresentada. Os corantes Disperse Orange 1 e Disperse Red 13 passaram a ser tóxicos para V. fischeri após cloração, sendo que a fotoeletrocatálise do Disperse Red 13 também gerou produtos tóxicos para esse organismo. Assim, embora seja um método de tratamento promissor, atenção deve ser dada na avaliação e aplicação da fotoeletrocatálise como um método alternativo à cloração. Os corantes originais Disperse Orange 1 e Disperse Red 13 diminuíram a atividade mitocondrial dos condrócitos, sendo que o Disperse Red 13 também diminuiu a produção de lactato. Todos os corantes reduziram a atividade mitocondrial das células HepG2 em monocamadas, ao passo que o Disperse Orange 1 deixou de exercer esse efeito no cultivo em 3D. Somente o Disperse Red 13 diminuiu a atividade de desidrogenases das células HepG2 e tal efeito foi observado tanto no cultivo em monocamadas quanto em 3D.
The azo dyes are currently considered as a concern regarding the environmental and public health, since when released in industrial effluents they pollute the environment. Unfortunately, the conventional method of treatment of textile effluents is not able to effectively remove both dyes and their toxicity. Within this context, this study aimed to evaluate the effectiveness of the treatment of aqueous samples by photoelectrocatalysis compared to conventional chlorination as an alternative method of degradation of azo dyes, using the dyes Disperse Orange 1, Disperse Red 1 and Disperse Red 13 as a model. Additionally, we evaluated the cytotoxicity of the original dyes using HepG2 cells and chondrocytes cultured in monolayer and in 3D. To this end, solutions of these original dyes, chlorinated and photoelectrocatalysed were evaluated using tests of genotoxicity / mutagenicity, cytotoxicity and ecotoxicity. All the dyes, original and chlorinated, were genotoxic to HepG2 cells in the comet assay. For the test with Salmonella, chlorination reduced the mutagenicity of the dyes for the YG1041 strain and increased the effect for the TA98 strain, except Disperse Red 13, which had the mutagenic effect reduced for both strains after chlorination. The photoelectrocatalysis removed both genotoxicity and mutagenicity. Only Disperse Orange 1 induced apoptosis by annexin V assay, but this cytotoxicity was removed after treatment. The dye Disperse Red 1 and Disperse Red 13 were toxic to D. similis while only the Disperse Red 1 was toxic to V. fischeri, and the treatment by chlorination and photoelectrocatalysis decreased the toxicity showed. The dyes Disperse Orange 1 and Disperse Red 13 began toxic to V. fischeri after chlorination, and the photoelectrocatalysis of the Disperse Red 13 generated toxic products for this organism. So, while it is a promising treatment method, attention should be given in the evaluation and application of photoelectrocatalysis as an alternative to chlorination. The dyes Disperse Orange 1 and Disperse Red 13 decreased the mitochondrial activity of chondrocytes, and the dye Disperse Red 13 also decreased the production of lactate. All the dyes reduced the mitochondrial activity of the HepG2 cells cultured in monolayer, while the Disperse Orange 1 did no show this effect in 3D. Only Disperse Red 13 decreased the activity of dehydrogenases of HepG2 cells and this effect was observed both in monolayer and in 3D.

碩士
國立成功大學
化學工程學系
88
Titanium dioxide is widely applied in photocatalysis to carry out the redox reaction. Recently, the usage of photoenergy is a significant subject of study in photocatalytic reaction. The usage of photoenergy of tungsten oxide is larger than titanium dioxide due to its smaller energy band-gap. However, the recombination of electron hole pair owing to inadequate reduction potential of conduction band of tungsten oxide results in bad phototcatalysis performance. In this study, using bias potential to improve tungsten oxide photocatalytic capability is investigated. Meanwhile, the influence of the electrode preparation condition and photoelectrocatalytic reaction factors is discussed. The photocatalyst electrode was prepared by deposited the semiconductor on conductive substrate with reactive sputtering. XRD, SEM, Potentiostat/Galvanostat, UV/VIS sepectrophotometer, and profilometer were used to analyze the characteristics of photoelectrode. An Arc lamp for simulating ultraviolet of sunlight used to induce photoelectrocatalytic decolorization of methyl orange. Mehtyl orange is an azo compound in dye wastewater. The prepared TiOx/Ti and WOy/Ti electrode show the excellent crystal structure without calcination. The TiOx film prepared by reactive sputtering is very uniform and it presents a slight blue shift. The blue shift effect means the photocatalyst is needed UV light with larger energy to excite electron hole pair. The best photocurrent of the TiOx/Ti electrode was obtained at the deposited condition with 300 W sputtering power and 3.2´10-2 mbar total sputtering pressure containing 25 % oxygen partial pressure. The results indicate that WOy/Ti film electrode also has excellent photoactivity by applying a bias potential and irradiation simultaneously. Decolorization of methyl orange proceeded through oxidation reaction promoted by the hydroxyl radical (OH·) that was generated from the reaction of holes and hydroxyl groups or water adsorbed on the surface of WO3. Decolorization of methyl orange proceeded through reduction reaction promoted by the electron is not observed. The photoactivity of WOy/Ti film electrode decreases quickly in the alkaline solution due to the WO3 was dissolved. The pH value of the aqueous solution, concentration of methyl orange, and bias potential are the major factors affecting the photoelectrocatalytic decolorization of methyl orange but the effect of power of UV light is minor. The photocurrent efficiency is evaluated by the ratio of concentration change of methyl orange and photocurrent. The photocurrent efficiency is about 1.2% and 12% in alkaline and acidic solution, respectively. The low photocurrent efficiency results from deactivation of hydroxyl radical. Increasing bias potential results in higher reaction rate and lower photocurrent efficiency. Based on the experiment results, the mechanism of photoelectrocatalytic reaction is proposed and a semitheoretical kinetic rate equation is obtained. Theoretical analysis ones correlate well with experimental results. The rate determined step is methyl orange reacted with hydroxyl radical. Langmuir- Hinshlewood adsorption of methyl orange is suitable to this system. The semitheoretical kinetic rate equation is represented as following （I-1） where Ri is decolorization rate of methyl orange (mM/min). P, E, and [MO] represent power of UV light, applied bias potential, and concentration of methyl orange, respectively. a and b are the reaction order of power of UV light and applied bias potential, respectively. The value of rate constants including Kp, K’, and K6 calculated from experimental data are

碩士
國立臺灣科技大學
化學工程系
96
Zinc oxide nanorods (ZNR) on substrate were prepared in this study by chemical bath deposition method. In order to obtain ZNR of high aspect ratio and high photocatalytic activity of ZNR, we added polyethylenimine (PEI) and Ag were added. PEI was used to hinder the lateral growth of the nanorods. All the catalysts prepared in this study were characterized by XRD, SEM, UV-vis, and AA. The photocatalytic activity of ZNR arrays was measured by photobleaching of 10 mg/L methylene blue, in a photo-reactor equipped with a light of 128 W and λmax=300 nm. The efficiency of photoconversion of ZNR was evaluated by 100 W Xe arc lamp illuminating the work-electrode in 1 M KOH solution. As the synthesis time increased from 5 to 20 hours, the results showed that, the length of the ZNR increased from 3.3μm to 12.4μm , the diameter increased from 100 nm to 400 nm, the average aspect ratio was about 34. Adding PEI to the synthesis solution would increase the aspect ratio to 60. For ZNR of 10μm length, the photobleaching activity of ZNR prepared with the addition of PEI is higher than that of zinc oxide nanoparticles film (ZNP). The most active photocatalytic catalyst was prepared by adding PEI in the synthesis solution and with the incorporation of Ag. The same catalyst also had the highest efficiency of photoconversion and incident monochromatic photo-to-current conversion in water splitting reaction.

The global energy demand increases with the development of civilisation. Widely used energy sources are mostly based on fossil fuels (e.g. coal, oil, natural gas), and technologies used for production of energy strongly affect the degradation of the environment. Increasing environmental pollution and temperature rise due to greenhouse gas emissions may lead to an ecological disaster. Therefore, research aimed at, on the one hand, the development of an efficient energy production process but not related to CO2 emissions and, on the other hand, the reduction of environmental pollution has been of great interest in recent years. One of the most widely reported topics is the use of solar energy, the resources of which significantly exceed the global energy consumption and at the same time it is widely available in large parts of the world. In addition to energy production, its efficient storage is crucial. In this respect, hydrogen can play an important role, as it is considered to be the main vector for future energy storage and processing. Chemical energy stored in the form of H2 can be converted into electricity through appropriately designed fuel cells that produce water as the only by-product. Therefore, the production of H2 in the photoelectrochemical water splitting process seems to be a good solution. Furthermore, photocatalysis can be successfully used to remove harmful gases and greenhouse gases such as CO2 or NOx. Over the past decades, photocatalytic processes have been widely used to treat water from organic pollutants. Important advantages of this process are: i) the possibility of complete decomposition of pollutants and ii) the relatively low temperature required for this process. This dissertation presents experimental results, together with their detailed analysis, concerning both above mentioned processes, photoelectrochemical water splitting and decomposition of organic pollutants in water. Both the simple method of preparation of photoanodes based on earth-abundant elements, as well as actions taken to increase their efficiency are presented. This work also deals with the problem of explaining the mechanism of photoelectrocatalytic processes taking place at the boundary formed between photoabsorbers, i.e. the semiconductor light-absorbing material, and catalysts at the moment when the created system contains both elements. In the first part of the thesis the influence of the photoabsorber/electrocatalyst interface on the photoelectrochemical decomposition of organic pollutants was evaluated. In this part, photo- anodes made of TiO2 and modified with plasmonic nanostructures of Au or Ag were used. For both types of the electrodes studied it was shown that the modification initially enhanced the photoelectrocatalytic activity towards acetic acid and 2-propanol decomposition (used as model organic pollutant) using radiation in the visible light range. However, repeated measurements of the incident photon-to-current conversion efficiency (IPCE) for the generated photocurrent showed a rapid decrease in the spectral range, where an increase in intensity was originally observed as a result of the presence of plasmonic nanostructures. This has been shown to be caused by irreversible surface oxidation of plasmonic nanostructures, which strongly suggests that deactivation of photocatalysts is of general importance and should always be considered in the context of designing new efficient photoelectrocatalytic and photocatalytic systems. Then, as part of this work, an efficient oxygen evolution reaction catalyst consisting of three metal oxides was developed together with an activation method that improves its photoelectrochemical activity. It has also been shown that the successful combination of this electrocatalyst with the TiO2 photoanode cannot be easily transferred to other photoanodes. The application of this strategy revealed that even the combination of the same photoabsorber and catalyst but only using a different photoanode architecture may lead to completely different results. A thorough examination of a carefully chosen set of oxygen evolution catalysts in combination with the same photoabsorber (Mo-doped BiVO4) showed that the initial theory of the special behaviour of certain materials as catalysts is quite general and can be applied to a wide range of catalysts. In a further step, selected oxygen evolution catalysts were combined with another photoabsorber (WO3) in two of the previously tested configurations. This work has shown that the conscious design of the interface between the photoabsorber and the catalyst drastically changes the performance of the resulting hybrid system. The results obtained once again have shown that the nature of the catalyst is not a dominant factor in improving the performance of the photoanode, but the interface formed between the photoabsorber and the catalyst should always be taken into consideration as well. Finally, the influence of the combination of the photoabsorber with the catalyst on the stability of the photoanode was evaluated. Experiments on photocorrosion of the photoanode material were carried out. It was shown that the addition of a catalyst can also be used to protect the photoanode against photocorrosion as well as to modify the dissolution profile of its components. The methods and results described in this work allowed to deepen the knowledge of environmentally friendly photoelectrocatalysis and to produce materials with increased activity, which can be used in light-assisted water electrolysis or decomposition of organic pollutants. The obtained results clearly indicate the important role of the interface formed between photoabsorbers and electrocatalysts in photoelectrochemical processes and provided valuable information on this phenomenon. The knowledge gained in this work on the nature of the interface formed between a photoabsorber and a catalyst can be potentially used in other important photoelectrochemical processes, such as light-assisted CO2 electroreduction.
Światowe zapotrzebowanie na energię wzrasta wraz z rozwojem cywilizacji. Powszechnie wykorzystywane źródła energii są w większości oparte na paliwach kopalnych (węgiel, ropa naftowa, gaz ziemny), a technologie służące produkcji energii silnie wpływają na degradację środowiska naturalnego. Wzrastające zanieczyszczenie środowiska oraz wzrost temperatury spowodowany emisją gazów cieplarnianych może doprowadzić do katastrofy ekologicznej. W związku z tym, badania mające na celu, z jednej strony opracowanie wydajnego procesu wytwarzania energii, ale nie związanego z emisją CO2, a z drugiej ograniczenie zanieczyszczenia środowiska cieszą się w ostatnich latach dużym zainteresowaniem. Jednym z szeroko badanych zagadnień jest wykorzystanie energii światła słonecznego, której zasoby znacznie przewyższają globalne zużycie energii i jednocześnie jest ona powszechnie dostępna w dużej części naszego globu. Oprócz wytwarzania energii kluczowe jest jej efektywne magazynowanie. W tym zakresie ważną rolę może odegrać wodór, który jest uważany za substancję podstawową dla przyszłego magazynowania i przetwarzania energii. Energia chemiczna przechowywana w postaci H2 może być przetwarzana w energię elektryczną poprzez odpowiednio zaprojektowane ogniwa paliwowe wytwarzające wodę jako jedyny produkt uboczny. Dlatego też produkcja H2 w procesie fotoelektrochemicznego rozkładu wody (ang. photoelectrochemical water splitting, PEC water splitting) wydaje się być dobrym rozwiązaniem. Ponadto, fotokataliza może być z powodzeniem wykorzystana do usuwania szkodliwych gazów i gazów cieplarnianych, takich jak CO2 czy NOx. W ciągu ostatnich dziesięcioleci procesy fotokatalityczne były szeroko stosowane do oczyszczania wód z zanieczyszczeń organicznych. Istotnymi zaletami tego procesu są: i) możliwość całkowitego rozkładu zanieczyszczeń i ii) stosunkowo niska temperatura wymagana dla tego procesu. W niniejszej rozprawie doktorskiej przedstawiono wyniki eksperymentów, wraz z ich szczegółową analizą, dotyczące obu wspomnianych wyżej procesów, fotoelektrochemicznego rozkładu wody oraz oczyszczania wód z zanieczyszczeń organicznych. Przedstawione zostały, zarówno prosta metoda syntezy fotoanod opartych na pierwiastkach powszechnie występujących na ziemi, jak i działania podjęte w celu zwiększenia ich wydajności. Praca ta dotyczy również problemu wyjaśnienia mechanizmu procesów fotoelektrokatalitycznych zachodzących na granicy formującej się między fotoabsorberami (półprzewodnikowy materiał absorbujący światło) a katalizatorami w momencie tworzenia układów zawierających oba elementy. W pierwszej części pracy oceniono wpływ granicy fotoabsorber-elektrokatalizator na fotoelektrochemiczny rozkład zanieczyszczeń organicznych. W tej części pracy wykorzystywane były fotoanody z TiO2 modyfikowane plasmonicznymi nanostrukturamii Au lub Ag. W przypadku obu typów badanych elektrod wykazano, że modyfikacja początkowo wzmocniła aktywność fotoelektrokatalityczną w kierunku rozkładu kwasu octowego i 2- propanolu (stosowanych jako modelowe zanieczyszczenie organiczne) z wykorzystaniem promieniowania w zakresie światła widzialnego. Wielokrotnie powtarzane pomiary generowanego fotoprądu w zależności od energii światła padającego na elektrodę (ang. incident photon-to-current conversion efficiency, IPCE) wykazały jednak szybki spadek wartości IPCE w zakresie spektralnym, w którym pierwotnie obserwowano wzrost intensywności w wyniku obecności nanostruktur plazmonicznych. Przyczyną tego stanu rzeczy było nieodwracalne utlenianie powierzchniowe nanostruktur plazmonowych, co silnie wskazuje, że dezaktywacja fotokatalizatorów ma znaczenie ogólne i powinna być zawsze brana pod uwagę w kontekście projektowania nowych, wydajnych układów fotoelektrokatalitycznych oraz fotokatalitycznych. Następnie, w ramach niniejszej pracy, opracowano wydajny katalizator wydzielania tlenu (ang. oxygen evolution reaction catalyst, OER catalyst) składający się z trzech tlenków metali wraz z metodą aktywacji, która poprawia jego aktywność fotoelektrochemiczną. Wykazano również, że udane połączenie tego elektrokatalizatora z fotoanodą TiO2 nie może być łatwo przeniesione do innych fotoanod. Zastosowanie tej strategii ujawniło, że nawet zastosowanie tego samego fotoabsorbera i tego samego katalizatora oraz modyfikacja jedynie architektury fotoanody prowadzi do kompletnie różnych wyników. Dokładne zbadanie starannie dobranego zestawu katalizatorów wydzielania tlenu w połączeniu z tym samym fotoabsorberem (Mo:BiVO4) wykazało, że wstępna teoria o szczególnym zachowaniu niektórych materiałów jako katalizatorów jest dość ogólną cechą i może być stosowana do szerokiej gamy katalizatorów. W kolejnym etapie wybrane katalizatory wydzielania tlenu zostały połączone z innym fotoabsorberem (WO3) w dwóch wcześniej przebadanych konfiguracjach. Praca ta pokazała, że świadome projektowanie granicy pomiędzy fotoabsorberem a katalizatorem, drastycznie zmienia wydajność otrzymanego układu hybrydowego. Uzyskane wyniki po raz kolejny pokazały, że charakter katalizatora nie jest czynnikiem dominującym dla poprawy działania fotoanody, natomiast zawsze należy wziąć pod uwagę również granicę utworzoną pomiędzy fotoabsorberem a katalizatorem. Na końcu oceniono wpływ połączenia fotoabsorbera z katalizatorem na stabilność fotoanody. Przeprowadzone zostały eksperymenty fotokorozji materiału fotoanody. Wykazano, że dodatek katalizatora może być stosowany również w celu ochrony fotoanody przed fotokorozją, a także w celu modyfikacji profilu rozpuszczania jej składników. Opisane w niniejszej pracy metody i wyniki pozwoliły na pogłębienie wiedzy na temat przyjaznej dla środowiska fotoelektrokatalizy oraz na wytworzenie materiałów o zwiększonej aktywności, które mogą być wykorzystywane w procesie wspomaganej światłem elektrolizy wody lub rozkładu zanieczyszczeń organicznych. Uzyskane wyniki wyraźnie wskazują na ważną rolę granicy utworzonej pomiędzy fotoabsorberami a elektrokatalizatorami w procesach fotoelektrochemicznych i dostarczyły cennych informacji na temat tego zjawiska. Jestem przekonana, że uzyskana w ramach niniejszej pracy wiedza na temat charakteru granicy powstającej pomiędzy fotoabsorberem a katalizatorem może być z powodzeniem wykorzystana w innych ważnych procesach fotoelektrochemicznych, takich jak np. wspomagana światłem elektroredukcja CO2.

碩士
國立高雄第一科技大學
環境與安全衛生工程研究所
103
This study aimed to develop bias-assisted photocatalytic degradation processes, or named as photoelectrocatalytic (PEC) processes, to remove a typical azo dye- methyl orange by using TiO2/ITO composite thin films as photocatalysts. The catalysts were prepared by magnetron sputtering techniques though which thin films of TiO2 was immobilized on commercial ITO glass plates. In the study, photoelectrocatalytic of methyl orange under various intensity of external biases and concentrations of electrolytes were investigated. In addition, the characteristic testing results for the tested thin-film catalysts including cyclic voltammetry (CV), UV-Visible, SEM, XRD tests were collected for investigating the affecting factors and reaction mechanism for the degradation of methyl orange. Some important results were achieved in the study including: higher degradation rates for methyl orange were achieved in PEC reaction processes than in simple photocatalytic (PC) reaction processes. In comparison of simple PC reactions, the degradation rate of methyl orange was enhanced up to 14.9~29.4 folds by the PEC processes. The degradation rates also can be enhanced by being provided with proper-concentration of Na2SO4. It was observed more than 2 times increase in the reaction rate while concentration of Na2SO4 was enhanced from 0.01 M to 0.05 M. The main reason for achieving higher reaction rates by PEC processes than pure PC processes was due the reduce in the recombination rate of electro-hole pairs while external biases provided. It is expected that more electro-holes can be involved in the reaction as their recombination rates can be retarded.

碩士
國立高雄第一科技大學
環境與安全衛生工程研究所
103
The study applied TiO2-based photocatalytic thin-film probes as photocatalysts to decompose a volatile organic compound- benzene under various external biases. There were two series of photocatalysts, Ti30 and TNCu5, prepared with sputtering processes in this study to investigate the effects of operating parameters (electric circuit spacing, applied biases, light sources, moisture content, and reaction temperature) on the photoelectrocatalytic degradation rate of benzene.All the experiments were conducted in a bench-scale photoelectrocatalytic reactor.The experimental results indicate photoelectrocatalysisof benzene basically following the first-order reaction kinetic. Based on the observed degradation rate of benzene, both Ti30-250 and TNCu5-250 were two photocatalysts with the highest reaction rate for benzene because both of them had lower electric resistance. It is expected that the recombination rates of electro-hole pairs can be more retarded by them. For the effects of external biases on the benzene degradation rate, the degradation rateincreased with increasing biases initially but further declined with applied biases for higher biases.For the effects of different light sources on benzene decomposition rate, the experimental results indicated TNCu-250 (LED)> Ti30-250 (UV) and TNCu-750 (LED)> Ti30-750 (UV). The experimental results successfully demonstrated the achieved TNCu5 series photocatalysts can work under illumination of LED blue light. In addition, for the effects of humidity and reaction temperature on the benzene degradation rate, there was a peak reaction rate observed, showing typical reaction patterns of heterogeneous reactions. Finally, in terms of degradation rate of benzene, the highest reaction rates were observed when the reaction temperature was 75℃,the water vapor concentration was 165 �嵱, and applied bias was 1.0 V for Ti30 sampleas irradiated by UV light (kTi30-250= 0. 4.82hr-1) andwhen the reactiontemperature was 75℃, in adry condition, and applied bias was 0.8 V for TNCu5sampleas irradiated byLED blue light (kTNCu5-250= 2.214 hr-1.