The photocatalytic properties of titanium dioxide have been widely studied since the discovery in 1972 of water photolysis by TiO2 electrodes. Rutile and anatase are the most studied of the different TiO2 polymorphs due to their chemo-physical properties. When irradiated with ultraviolet light, TiO2 is able to absorb photons, creating on the surface an electron and a positive “hole”. This electron-hole pair then reacts with water and oxygen, generating chemical radicals. These are very unstable and reactive species which can neutralise pollutants. In the introduction pollutants and their influence in the air quality are described as well as the state of art of TiO2, photochemistry; semiconductor doping, chemo-physical principles, and TiO2 coatings. Various protocols to test photoactivity of both powders and coatings are discussed studying both gas phase and liquid phase reactions looking at UV and visible light irradiation. The sol-gel synthesis of pure and tungsten- and cobalt-doped TiO2, as well as graphene/TiO2 hybrids, was explored modifying the conditions and parameters to optimise the photocatalytic activation of TiO2 in the visible light range. A comprehensive study of manufactured and commercially available TiO2 powders and coatings was performed to identify the differences between photocatalytic properties, using electron microscopy, Raman and UV-vis diffusive spectroscopy and X-ray diffraction. An important question that was answered in this thesis is whether the physical properties of nanoparticles or their electronic properties are critical for their photocatalytic behaviour. Results for doped powders of different particle size and surface area showed how the positioning of their electronic band gap with the wavelength of the visible light source was fundamental for an effective photocatalytic process for the application wantedIn the application of TiO2 for the built environment, lime and MDF were considered as substrates for coatings. Lime-based coatings were prepared mixing commercial K7000 TiO2 with the plaster and photoactivity of the coatings was evaluated looking at formaldehyde degradation. MDF based coating were produced using both produced sol-gel pure, doped TiO2 and tested by observing degradation of Ink Intelligent inks under both UV and visible light confirming the photoactivity. Throughout this work sol-gel was employed for the production of pure and doped TiO2 nanoparticles with the anatase crystalline phase. Photocatalytic tests on the synthesised particles under UV light shows comparable performances with commercial particles. Synthesised particles and coatings shows promising performances, higher than commercially available particles when irradiated with visible light confirming a possible application in indoor environment.

Surface Organometallic Chemistry leads to the combination of the high activity and specificity of homogeneous catalysts with the recoverability and practicality of heterogeneous catalysts. Most metal complexes used in this chemistry are grafted on metal oxide supports such as amorphous silica (SiO2) and γ-alumina (Al2O3). In this thesis, we sought to enable the use of titania (TiO2) as a new support for single-site well-defined grafting of metal complexes. This was achieved by synthesizing a special type of anatase-TiO2, bearing a high density of identical hydroxyl groups, through hydrothermal synthesis then post-treatment under high vacuum followed by oxygen flow, and characterized by several analytical techniques including X-ray diffraction, transmission electron microscopy, infrared spectroscopy and nuclear magnetic resonance. Finally, as a proof of concept, the grafting of vanadium oxychloride (VOCl3) was successfully attempted.

No description available.

Submitted by Bruna Rodrigues (bruna92rodrigues@yahoo.com.br) on 2016-09-27T11:47:25Z No. of bitstreams: 1 DissMD.pdf: 3874080 bytes, checksum: f245af64331a5190649cede80208ac01 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-04T18:10:35Z (GMT) No. of bitstreams: 1 DissMD.pdf: 3874080 bytes, checksum: f245af64331a5190649cede80208ac01 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-04T18:10:41Z (GMT) No. of bitstreams: 1 DissMD.pdf: 3874080 bytes, checksum: f245af64331a5190649cede80208ac01 (MD5) / Made available in DSpace on 2016-10-04T18:10:51Z (GMT). No. of bitstreams: 1 DissMD.pdf: 3874080 bytes, checksum: f245af64331a5190649cede80208ac01 (MD5) Previous issue date: 2015-03-30 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / This dissertation studies the application of rutile substrate as an alternative support for anatase films, specifically, on the growth and properties of anatase films. The films were utilized as catalysts for the photodegradation of water contaminants (Atrazine and Rhodamine B). Ti4+ precursor resin was prepared by the polymeric precursor method and deposited by spin coating onto polycrystalline rutile and rutile coated glass substrates. The films were calcined at different temperatures (350 °C to 500 °C) to form anatase TiO2 films. The influence of temperature on the properties of the films has been reported in this study. A comparative study of the films was also done using X-ray diffraction technique (XRD), grazing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). XRD and GIXRD results confirmed the formation of anatase on the (101) plane depending on the calcination temperature. Bandgap modification of the films with respect to calcination temperature was measured by UV visible diffuse reflectance spectroscopy. The bandgaps were in the range of 2.74 to 2.85 eV. Photocatalytic activity of the films supported on rutile substrate was studied for the degradation of Atrazine (ATZ) and Rhodamine B (Rhod-B) under UV light. Further, the stability of the films was evaluated on four consecutive cycles where the films maintained their photocatalytic properties in all cases. The kinetics of Rhod-B and ATZ degradation followed a pseudo first order and first order exponential decay respectively. The films calcined at 450 °C and 500 °C showed superior photocatalytic activity for Rhod-B degradation than the films calcined at 350 °C and 400 °C. This is attributed to the adequate crystallinity of anatase. For ATZ degradation, the films were also efficient but no specific trend was observed. The results can contribute towards the development of TiO2 films on rutile phase substrates. / Esta dissertação estuda a aplicação de substratos de rutilo como suportes alternativos para filmes de anatase, especificamente, sobre o crescimento e propriedades de filmes de anatase sobre rutilo. Os filmes foram utilizados como catalisadores para a fotodegradação de contaminantes de água (Atrazina e Rodamina B). A resina de Ti4+ foi preparada pelo método de precursores poliméricos e depositada por spin coating sobre rutilo policristalino e em substratos de vidro revestido de rutilo. As amostras foram calcinadas a diferentes temperaturas (350 a 500 °C) para formar filmes de anatase TiO2. Um estudo comparativo dos filmes foi feito usando a técnica de difração de raios X (DRX), difração de raios X com ângulo rasante (DRXR), microscopia de força atômica (AFM) e microscopia eletrônica de varredura (MEV). Os resultados de DRX e DRXR confirmaram a formação de anatase nos filmes ao longo do plano (101) dependendo da temperatura de calcinação. Modificações do bandgap dos filmes de acordo com a temperatura de calcinação foram medidas por reflectância difusa de UV-visível onde os bandgaps variou de 2,74 para 2,85 eV. Atividade fotocatalítica dos filmes imobilizados sobre substrato de rutilo foi estudada para a degradação de Atrazina (ATZ) e Rodamina B (Rhod-B) sob luz UV. Além disso, a estabilidade dos filmes foi avaliada em quatro ciclos consecutivos onde os filmes mantiveram suas propriedades fotocatalíticas em todos os ciclos. As cinéticas de degradação de Rhod-B e de ATZ seguiram um ajuste de pseudo-primeira ordem e decaimento exponencial de primeira ordem, respectivamente. Os filmes que foram calcinados a 450 °C e 500 °C mostraram atividade fotocatalítica superior para a degradação de Rhod-B aos filmes calcinados a 350 °C e 400 °C. Isto foi atribuído à cristalinidade adequada da fase anatase. Para ATZ, os filmes foram eficientes mas nenhuma tendência especifica foi observada. Os resultados podem contribuir para o desenvolvimento de filmes de TiO2 imobilizados sobre substratos de rutilo.

abstract: The mitigation and conversion of carbon dioxide (CO2) to more useful carbon chemicals is a research topic that is at the forefront of current engineering and sustainability applications. Direct photocatalytic reduction of CO2 with water (H2O) vapor to C1-C4 hydrocarbons has significant potential in setting substantial groundwork for meeting the increasing energy demands with minimal environmental impact. Previous studies indicate that titanium dioxide (TiO2) containing materials serve as the best photocatalyst for CO2 and H2O conversion to higher-value products. An understanding of the CO2-H2O reaction mechanism over TiO2 materials allows one to increase the yield of certain products such as carbon monoxide (CO) and methane (CH4). The basis of the work discussed in this thesis, investigates the interaction of small molecules (CO, CH4,H2O) over the least studied TiO2 polymorph - brookite. Using the Gaussian03 computational chemistry software package, density functional theory (DFT) calculations were performed to investigate the adsorption behavior of CO, H2O, and CH4 gases on perfect and oxygen-deficient brookite TiO2 (210) and anatase TiO2 (101) surfaces. The most geometrically and energetically favorable configurations of these molecules on the TiO2 surfaces were computed using the B3LYP/6-31+G(2df,p) functional/basis set. Calculations from this theoretical study indicate all three molecules adsorb more favorably onto the brookite TiO2 (210) surface. Diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) was used to investigate the adsorption and desorption behavior of H2O and CH4 on Evonik P25 TiO2. Results from the experimental studies and theoretical work will serve as a significant basis for reaction prediction on brookite TiO2 surfaces. / Dissertation/Thesis / M.S. Chemical Engineering 2012

La chimie organométallique de surface (COMS) est une technique utilisée pour concevoir des catalyseurs structurellement bien définis. Elle a été employée ici pour établir les fondements de la COMS sur des supports photoactifs. L’oxyde de titane, TiO2 à savoir l’anatase a été utilisé comme support photo-catalytique en raison de sa haute stabilité, photo-activité and non toxicité. La nature chimique et la densité des sites réactifs de surface ont été établies. Un complexe de Ta bien connu de la littérature a été utilisé pour mener les premières études d’interaction entre la surface et le complexe organométallique. Les résultats ont permis d’observer le greffage organométallique couplé à des mécanismes transfert de charge métal sur métal, en route vers des photo-catalyseurs bien définis / Surface organometallic chemistry (SOMC) is used to design well-defined catalysts. It has been employed here to lay the foundation of SOMC on photocatalytic support, a previously little if any explored area. TiO2 anatase was used as the photocatalytic support due to its high stability, photoactivity and nontoxicity. The chemical nature and the surface density of the reactive moieties found on anatase support has been determined. A Ta complex, well-known in literature, was used to conduct the first principal studies regarding the interaction between the surface and the organometallic complex. The results provide solid insights into organometallic grafting and metal to metal charge transfer mechanisms for developing well-defined photocatalysts by SOMC

We use different methods to deposit Ti thin film on the ITO glass substrate. Under the circumstances of using fixed concentration of electrolyte, changing anodic time, and applying voltage, we are able to use anodic method to make ordered nano TiO2 thin film,of which the smallest pore size is 18nm and the thickness is 4500

La presente tesis doctoral está centrada en la investigación de los parámetros estructurales que determinan las propiedades catalíticas en la síntesis de Fischer-Tropsch (SFT) de catalizadores de cobalto soportados en TiO2. Por un lado, el estudio de la influencia del polimorfo de óxido de titanio (rutilo vs. anatasa) utilizado como soporte en catalizadores de Co promovidos con Ru ha permitido obtener correlaciones entre la estructura cristalina del soporte, la extensión del efecto SMSI (interacción fuerte metal-soporte) y los resultados catalíticos. Por otro lado, mediante la modificación de las propiedades texturales del soporte TiO2-anatasa con el objetivo de obtener catalizadores con baja, media y alta área superficial se ha podido avanzar en el conocimiento del efecto SMSI y su correlación con las propiedades texturales del soporte. Además, las consecuencias del aumento en área superficial del soporte en la actividad y selectividad de catalizadores CoRu/TiO2 para la SFT se han podido explicar en base a las relaciones establecidas entre estructura y efecto SMSI. Adicionalmente, el uso de técnicas de luz sincrotrón junto con caracterización espectroscópica in situ realizada a presiones superiores a la atmosférica, ha permitido explicar el papel de la adición y concentración de Ru como promotor en catalizadores CoRu/TiO2. Finalmente, se han estudiado tratamientos de reducción-oxidación-reducción (ROR) en catalizadores CoRu/TiO2 con el objetivo de mejorar su actividad catalítica. Como conclusión general, los conocimientos derivados de los resultados obtenidos en esta tesis doctoral pueden aportar estrategias adecuadas para el diseño de catalizadores de FT mejorados basados en Co empleando TiO2 como soporte. / The present doctoral thesis focused on the investigation of the structural parameters that can determine the ultimate catalytic properties for Fischer-Tropsch synthesis (FTS) of TiO2-supported cobalt catalysts. On the one hand, the study of the influence of the titania polymorph (rutile vs. anatase) as support for Ru-promoted Co and Ru nanoparticles (NPs) has allowed to identify some correlations between the TiO2 crystalline phase, the SMSI (strong metal-support interaction) effect, and the catalytic performance for FTS of the catalysts. On the other hand, by preparing CoRu catalysts supported on TiO2-anatase with low, medium, and high surface area, further insights into the SMSI effect and its dependence on the textural properties of the TiO2-anatase support have been gained. Besides, the consequences of increasing the surface area of the support on the activity and selectivity of the catalysts for FTS have been explained based on the established structure-SMSI relationships. Moreover, a detailed study involving the use of in situ synchrotron-based spectroscopic characterizations at pressures higher than the ambient pressure usually applied in most previous works, has been carried out aiming at explaining the role of Ru addition and concentration as promoter in Co/TiO2 catalysts. Finally, reduction-oxidation-reduction (ROR) treatments have been applied on CoRu/TiO2 catalysts to revert the SMSI effect as a feasible strategy to enhance their catalytic activity. Overall, the results reported in this thesis provide grounds for designing TiO2-supported Co catalysts with improved activity and selectivity for FTS. / La present tesi doctoral està centrada en la investigació dels paràmetres estructurals que poden tenir influència en les propietats catalítiques dels catalitzadors que s'han aplicat a la reacció de síntesi de Fischer-Tropsch (SFT). S'ha estudiat la influència del polimorf de titani (rutil o anatasa) utilitzat com a suport de nanopartícules (NPs) de Co i Ru, observant correlacions entre l'estructura cristal·lina del suport, l'efecte SMSI (forta interacció metall-suport) i els resultats catalítics. D'altra banda, es va fer un estudi modificant les propietats texturals de la anatasa amb l'objectiu d'obtenir catalitzadors amb diferent àrea superficial, i s'ha pogut establir un coneixement més profund de l'efecte SMSI i la seua correlació amb les propietats texturals del suport. A més, la influència de l'augment de l'àrea superficial del suport per a la reacció de SFT, en termes d'activitat i selectivitat, han sigut explicats d'acord a les relacions establides entre l'estructura i l'efecte SMSI. Addicionalment, fent ús de tècniques de llum sincrotró juntament amb caracterització in situ realitzada a altes pressions, ha sigut possible explicar el paper de l'addició i concentració de Ru com a promotor en catalitzadors CoRu/TiO2. Finalment, s'han estudiat els tractaments de reducció-oxidació-reducció (ROR) en catalitzadors CoRu/TiO2 amb l'objectiu de millorar la seua activitat catalítica. En resum, els coneixements derivats dels resultats obtinguts en esta tesi doctoral permeten establir estratègies per al disseny de catalitzadors millorats per a la síntesi de FT basats en cobalt utilitzant TiO2 com a suport. / Bertella, F. (2018). Structural, promotion and metal-support interaction effects in Co/TiO2 catalysts for Fischer-Tropsch synthesis [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/107952 / TESIS

The thesis deals with photocatalysis of organic pollutants on UV-activated anatase particles, on UV-activated anatase particles with hydrogen peroxide and hydrogen peroxide itself. The measurement is carried out on a pilot plant UV photoreactor. The aim of the thesis is to determine the effectiveness of azo dyes and antibiotics degradation. The level of azo dyes and antibiotics degradation is measured by UV-VIS spectrometry.

A specific allotrope of titanium dioxide (anatase) was synthesized with a highly anisotropic morphology ({001}-anatase) dominated by the {001} facet (81%). its surface chemistry after dehydroxylation was studied by 1H NMR and FT-IR. Influence of surface fluorides on surface chemistry was also studied by 1H NMR, FT-IR and DFT. Full attribution of the IR and NMR spectra of anatase with dominant {001} facets could be provided based on experimental data and further confirmed by DFT. Our results showed that chemisorbed H2O are still present on anatase after dehydroxylation at 350°C, and that the type of surface hydroxyls present on the {001} facet is dependent on the presence of fluorides. They also provided general insight on the nature of surface species on both fluorinated and fluorine-free anatase. The use of vanadium oxychloride (VOCl3) allowed determining the accessibility of the various OH groups spectroscopically observed. A platinum complex, (CH3)2Pt(COD), is then grafted via surface organometallic chemistry (SOMC) on morphology-controlled Anatase TiO2 to generate single, isolated Pt atoms on TiO2 nano-platelets. The resulting material is characterized by FT-IR, High resolution scanning transmission electron microscopy (HRSTEM), NMR, and XAS, and then used to perform photocatalytic water splitting. The photocatalyst with SOMC-grafted Pt shows superior performance in photocatalytic hydrogen evolution and strongly suppresses backwards reaction of H2 and O2 forming H2O under dark conditions, compared to photocatalyst prepared by standard wet impregnation at the same Pt loading. However, single Pt atoms on this surface also rapidly coalesce into nanoparticles under photocatalytic conditions. It was also found that adsorbtion of carbon monoxide gas at room temperature also triggers the aggregation of Pt single atoms into nanoparticles. A detailed mechanism is investigated for the mobility of Pt in the formation of its carbonyls using density functional theory (DFT) calculations.