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Anodic aluminum oxide (AAO) nanopores are excellent templates to fabricate different nanostructures. However, the pores are limited to a hexagonal arrangement with a domain size of a few micrometers.  In this dissertation, focused ion beam (FIB) is used to create pre-patterned concaves to guide the anodization. Due to the advantage of FIB lithography, highly ordered AAO arrays with different arrangements, alternating diameters, and periodic pore densities are successfully achieved. Anodization window to fabricate ordered AAO is enlarged due to the FIB pre-pattern guidance. AAO has also been successfully used as a template to nanoimprint prepolymer to synthesize vertically aligned and high aspect ratio h-PDMS nanorod arrays with Moiré pattern arrangements. The formation mechanism of anodic TiO2 nanotubes is proposed in this dissertation. Moreover, FIB pre-pattern guided anodization is introduced to synthesize highly ordered TiO₂ nanotubes with different morphologies. The effects of inter-tube distance and arrangement to the structure of TiO₂ nanotubes are investigated. TiO2 nanotubes with branched and bamboo-type structures are achieved by adjusting anodization voltage. The influence of patterned concave depth and surface curvature on the growth of TiO₂ nanotubes and AAO are studied. The efficiency of TiO₂ nanotubes in supercapacitors and photoelectrochemical water splitting are optimized by enlarging surface area and increasing electrical conductivity. Focused ion beam can not only create concave arrays to guide the electrochemical anodization, but also be used for nanoscale sculpting and 3D analysis. When the TiO₂ nanotube surface is bombarded by FIB, there is a mass transfers due to ion-induced viscous flow and sputter milling, thus the TiO₂ nanotubes are selectively closed and opened. By combining FIB cutting and SEM imaging to create a series of 2D cross section SEM images, 3D reconstruction can be obtained by stacking SEM images together. This 3D reconstruction offers an opportunity to directly and quantitatively observe the pore evolution to understand the sintering process. / Ph. D.

Tesis por compendio / 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]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/107952 / Compendio

Cette étude avait pour objectif de développer un nouveau support photocatalytique pour des applications potentielles dans le domaine du traitement des eaux. Le choix s'est porté sur les nanotubes d'oxyde de titane (TiO2) et l'étude a plus particulièrement porté sur l'optimisation de leurs propriétés photocatalytiques vis-à-vis de la l'oxydation de solution aqueuse de composés azotés. Les nanotubes de TiO2 ont été préparés par anodisation électrochimique en faisant varier le potentiel appliqué, la durée d'anodisation, le pH et la viscosité du milieu électrolytique (milieu aqueux ou milieu glycérol), ainsi que la nature du substrat sur lequel étaient déposés ces nanotubes. Une fois anodisés, ces nanotubes amorphes et se présentant sous forme sous-stœchiométrique (O/Ti <2) ont été recuits à différentes températures afin d'obtenir des phases de TiO2 variées (anatase, anatase/rutile). Au cours de ces différentes étapes, les différents nanotubes obtenus ont été caractérisés morphologiquement et structurellement par analyses par diffraction des rayons X (DRX) et par microscopie électronique à balayage (MEB).L'activité photocatalytique de ces différents matériaux a été déterminée à partir des rendements de photodégradation d'un composé modèle, la 4-nitroaniline. Là aussi, différents facteurs ont été étudiés, à savoir le pH du milieu réactionnel, le type de lampe UV et les durées d'irradiation.Les résultats montrent que les performances photocatalytiques des nanotubes de TiO2 les meilleures sont obtenues lorsqu'ils sont déposés sur substrat de Ti massif, anodisés en solution aqueuse à 20 V et pendant 20 minutes, et recuits à 450 °C (structure anatase). / This study aimed to design a new photocatalytic support for potential uses in the field of water treatment. Titanium dioxide (TiO2) nanotubes were chosen and studied as a function of their photocatalytic properties towards nitrogenous compounds.TiO2 nanotubes were prepared by electrochemical anodization by varying the applied potential, anodization duration, pH and viscosity of the electrolytic medium (aqueous or glycerol medium), and by the nature of substrates where these nanotubes were deposited (titanium foil (Ti) or deposited on silicon (Ti / Si)). Once anodized, these amorphous and under-stoechiometric (O/Ti <2) were calcined at various temperatures in order to obtain different TiO2 phases (anatase or anatase/rutile). During these different steps, the whole nanotubes obtained were morphologically and structurally characterized par X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic activity of the different materials was determined from the photodegradation yields of a model compound, namely 4-nitroaniline. Here again, different factors were studied, such as pH of reaction medium, kind of UV lamps and irradiation durations. The results show that the best photocatalytic performances of TiO2 nanotubes were obtained when deposited on Ti foils, anodized in aqueous medium at 20 V and for 20 minutes, and calcined at 450 °C (anatase phase).

Au cours de cette étude, nous avons synthétisé par chimie douce en solution aqueuse des particules de TiO2 sous forme anatase, brookite et rutile. Chaque polymorphe a été obtenu pur, avec des nanoparticules de taille et de morphologie contrôlées. Ces particules ont ensuite été calcinées à des températures comprises entre 500 et 750°C afin d'étudier le phénomène de frittage. Nous avons observé que la morphologie initiale des particules a un impact sur celle des particules frittées. Nous avons également montré que les mécanismes et les cinétiques de transition de phase anatase → rutile et brookite → rutile étaient fortement impactés par le changement morphologique des nanoparticules initiales ainsi que par la nature de l'atmosphère gazeuse et par la présence d'impuretés en surface des particules. Cette dernière propriété a été utilisée dans un second temps pour stabiliser thermiquement les particules d'anatase et de brookite par des dopages au lanthane, ce qui a permis de gagner au moins 100°C sur la température de transition et d'obtenir ainsi des surfaces spécifiques conséquentes, même à 500°C. Ces études se sont appuyées sur de nombreuses techniques de caractérisations comme l'analyse thermogravimétrique, la spectroscopie UV, les microscopies électroniques à balayage et en transmission. La diffraction des Rayons X a été abondamment utilisée afin de caractériser les tailles, les morphologies et l'évolution des différentes phases avec la température / During this study, we have synthesized TiO2 nanoparticles by soft routes in aqueous media. Anatase, brookite and rutile have been obtained in pure phases, with well-defined size and morphology. Thermal treatments were conducted at temperatures ranging from 500 to 750°C to study particles sintering. We have observed the influence of initial morphology on particles sintering. We also have shown that the anatase → rutile and brookite → rutile phase transition and kinetic were modified by initial morpholgy of particules, but also by annealing gas atmosphere and by the presence of impurities on the particles. This last result was used in a second point to thermically stabilized anatase and brookite nanoparticles by lanthanum doping. Particles have been characterized by numerous techniques, such as high resolution transmission electron microscopy, thermogravimetric analyses and differential scanning calorimetry. X-ray diffraction was widely used to characterize sizes, morphologies and phase transition during sintering

Apesar de a fotocatálise heterogênea ser reconhecida como uma abordagem promissora e sustentável para promover processos de remediação ambiental, aplicações práticas de processos fotocatalíticos ainda são muito limitadas devido à baixa eficiência dos fotocatalisadores existentes. Neste contexto, a pesquisa na interface Química/Ciência dos Materiais é de grande relevância para o desenvolvimento de rotas sintéticas que permitam a obtenção e o controle das propriedades de novos fotocatalisadores multi-componentes visando desempenho fotocatalítico aprimorado. Os trabalhos descritos nesta tese abordam rotas sintéticas desenvolvidas ou aprimoradas para preparação de partículas e aerogéis nanoestruturados baseados na incorporação do fotocatalisador de alta atividade TiO2 em escala nanométrica junto à estruturas de sílica, que atuam como suporte estrutural de alta estabilidade térmica. Adicionalmente, os materiais sintetizados foram modificados com o hexacianometalato Fe4[Fe(CN)6]3, o Azul da Prússia (PB) como tentativa para aumento do desempenho fotocatalítico em reações de redução. A caracterização detalhada dos materiais foi realizada por amplo conjunto de técnicas visando correlacionar atividade fotocatalítica com propriedades físicas e estruturais. Na primeira etapa do trabalho partículas core-shell SiO2@TiO2 foram preparadas pela adsorção e hidrólise controlada do precursor Isopropóxido de Titânio na superfície de partículas submicrométricas de sílica. Variando a composição do solvente (razão isopropanol/etanol) foi possível controlar a cinética de deposição do TiO2, levando à controle sobre composição e morfologia das partículas SiO2@TiO2 sintetizadas. Este material apresentou eficiência de fotodegradação do corante Cristal Violeta superior a do TiO2 não-suportado, assim como elevada estabilidade térmica devido à formação de ligações interfaciais Si-O-Ti. Em uma segunda etapa, novas rotas de preparação de aerogéis de sílica-titânia foram desenvolvidas empregando TiCl4 como precursor alternativo aos alcóxidos de titânio e processamento dos materiais por secagem em CO2 supercrítico. Explorou-se a reação de termo-hidrólise do TiCl4 para promover a deposição termo-induzida de titania em géis monolíticos de sílica, bem como o método de gelificação assistida por epóxido para formação de rede tridimensional porosa de titânia ao redor de partículas de aerogel de sílica, levando à preparação de aerogéis core-shell SiO2@TiO2 e aerogéis nanocompósitos SiO2/TiO2, respectivamente. A estrutura mesoporosa robusta dos aerogéis e a capacidade da sílica de inibir a transformação de fase anatase-rutilo se refletiram em um aumento de atividade fotocatalítica com o aumento da temperatura de calcinação, sendo que os aerogéis de sílica-titânia tratados a 1000ºC apresentaram eficiência fotocatalítica superiores a dos aerogéis de titânia pura e do fotocatalisador comercial P25. Na parte final do trabalho, as partículas e aerogéis de SiO2/TiO2 e TiO2 foram modificados adicionalmente com o PB e com PB/MoS2 por métodos de fotodeposição. Demonstrou-se que o PB pode atuar como co-catalisador na reação de redução fotocatalítica de espécie altamente tóxicas de Cr(VI) em compostos não tóxicos de Cr(III), aumentando substancialmente a eficiência dos materiais baseados em TiO2 sobre radiação UV. Finalmente, a modificação concomitante dos fotocatalisadores com PB e o semicondutor MoS2 levam a aumento sinérgico de atividade redução fotocatalítica de Cr(VI) também sob luz visível. Os materiais desenvolvidos neste trabalho apresentam interessante potencial para aplicações em processos de remediação ambiental e desenvolvimento de revestimentos cerâmicos auto-limpantes. / Despite its potential as a promising and sustainable approach for environmental remediation, heterogeneous photocatalysis still has limited practical applicability due to the low efficiency of the existing photocatalysts. In this context, research on the Chemistry/Materials Science interface is of utmost importance for the development of synthetic routes that allow preparation of novel multi-component photocatalysts with controlled properties and enhanced photocatalytic performance. The studies reported in this thesis describe newly developed or improved synthetic routes for the preparation of nanostructured photocatalysts in the form of particles and aerogels through incorporation of highly photoactive TiO2 nanoparticles in silica materials as thermally stable structural supports. Additionally, the prepared silica-titania photocatalysts were further modified with Prussian Blue (PB), hexacyanometallate Fe4[Fe(CN)6]3, in order to enhance the efficiency of photocatalytic reduction reactions. In order to correlate the observed photocatalytic performance with the physical/structural properties of the photocatalysts, the prepared photocatalysts were characterized using an array of complimentary techniques. In the first part of the study, core-shell SiO2@TiO2 particles were prepared by the adsorption and controlled hydrolysis of titanium isopropoxide precursor on the surface of submicron silica particles. The rate of titania deposition and the resultant particle morphology as well as TiO2 loading could be effectively controlled by changing solvent composition (isopropanol/ethanol ratio). The prepared SiO2@TiO2 core-shell particles showed superior performance for crystal violet dye photodegradation as compared to unsupported TiO2, in addition to their improved thermal stability due to the formation of Si-O-Ti interfacial bonds. In the second part of thesis, new synthetic routes were developed for the preparation of high surface area silica-titania aerogels employing TiCl4 as an alternative titania precursor. We explored the thermohydrolysis of TiCl4 to promote thermo-induced deposition of titania on silica monolithic gels and epoxide-assisted gelation method for formation of titania gel network around silica aerogel particles, thus yielding SiO2@TiO2 core-shell and SiO2/TiO2 composite aerogels, respectively. The prepared silica-titania aerogels displayed remarkable physical properties, including high surface area, large pore volume and outstanding thermal stability of the supported anatase nanoparticles. The robust thermally stable mesoporous structure of the prepared aerogels, coupled with the ability of silica to inhibit anatase-to-rutile transformation, led to the enhancement of photocatalytic activity with an increase in annealing temperature to as high as 1000 ºC. In fact, the photocatalytic activity of silica-titania aerogels annealed at 1000 ºC outperforms that of both pristine titania aerogels and Degussa P25 commercial photocatalyst. In the final part of the study, the prepared TiO2-based particles and aerogels were further modified with PB and PB/MoS2 by photodeposition method. We could demonstrate that PB can act as an efficient co-catalyst for the photocatalytic reduction of highly toxic Cr(VI) species to the non-toxic Cr(III), thus largely improving the photocatalytic performance of TiO2-based photocatalysts under UV illumination. Finally, simultaneous modification of the titania-based photocatalysts with both PB and the visible-light active semiconductor MoS2 lead to a synergistic enhancement of photocatalytic reduction of Cr(VI) under visible-light as well. The photocatalytic materials developed in this study may find useful application in many areas such as environmental remediation, wastewater purification and the development of self-cleaning ceramic coatings.

Aspersão térmica é um processo de produção de revestimentos metálicos, poliméricos, cerâmicos ou compósitos sobre superfícies previamente preparadas que objetiva na maioria das vezes a prevenção contra o desgaste e/ou corrosão e também a recuperação dimensional de superfícies desgastadas. Ligas de Ni-Al são extensivamente empregadas na aspersão térmica para reconstrução dimensional e como camada de ligação como materiais que não se ligam adequadamente à superfície a ser revestida. A baixa dureza e resistência ao desgaste (principalmente em aplicações de reconstrução dimensional) desta liga poderiam ser contornadas pela adição de partículas ou compostos de altas durezas na matéria prima em pó antes da aspersão. Neste trabalho avaliou-se a influência da adição de NbC e do composto cerâmico Al2O3+TiO2 no desempenho ao desgaste de revestimentos de Ni-Al, bem como verificou-se as alterações microestruturais, químicas, e mecânicas decorrentes. Para tanto se adicionou 25%p de NbC ou 25%p do composto Al2O3+TiO2 à liga base de Ni-Al, formando-se dois materiais compósitos: Ni-Al + NbC e Ni-Al + (Al2O3+TiO2). Utilizou-se microscópio eletrônico de varredura com EDS para caracterizar as matérias primas e os revestimentos produzidos, assim como determinar o mecanismo de desgaste nos ensaios de micro-abrasão tipo \"esfera-livre\" e \"esfera-fixa\". Mediram-se as durezas superficiais e as microdurezas das fases por meio dos ensaios Rockwell Superficial e microdureza Vickers. Avaliou-se a resistência ao desgaste por meio de ensaios de micro-abrasão nas modalidades \"esfera-livre\" e \"esfera-fixa\". As adições dos materiais citados na liga a base de níquel alteraram características microestruturais importantes, como aumento do percentual de óxidos, bem como a composição química e distribuição dos elementos nas camadas formadas; ocorreram também aumentos significativos das durezas e nas resistências ao desgaste dos revestimentos. / Thermo Spray is a metallic, polymeric, ceramic and composite coating process applied over a previously prepared surface usually seeking to improve wear and/or corrosion resistance. It is also used to repair worn surfaces restoring the original dimensions. Ni-Al alloys are used as a primer coating to promote the adhesion between surface and incompatible coatings and also extensively in the reconstruction of worn surfaces. The low hardness and wear resistance (when used in reconstruction applications) of this alloy could be improved by the addition of hard particles/composites to the powdered raw material prior to the spray operation. In this work the influence of NbC and Al2O3+TiO2 additions to Ni-Al alloys were evaluated concerning wear performance and the resulting changes in microstructure, chemical and mechanical behavior. The experimental procedure included the preparation of samples of the Ni-Al base alloy with additions of 25wt% of NbC or 25wt% of Al2O3+TiO2, what resulted in two different sprayed composite materials: Ni-Al + NbC e Ni-Al + (Al2O3+TiO2). SEM with EDS microprobe was used to characterize the raw materials, the sprayed coating samples and the type of wear mechanism occurring in the wear tests of the type \"free sphere\" and \"fixed sphere\" micro abrasion that were used to evaluate the wear resistance of the samples. Surface hardness and micro hardness of the different phases in the coatings were evaluated using Rockwell and Vickers micro hardness testing machines respectively. The addition of the hard phases promoted important changes in the Ni-Al base alloy, decreasing the porosity level and increasing the percentage of oxides. Hardness were significantly increased as well as the wear resistance of the coatings.

Made available in DSpace on 2017-07-21T20:42:40Z (GMT). No. of bitstreams: 1 Renata Martins Silva.pdf: 2842741 bytes, checksum: 00c605c84616c33c3c08c2e35031efa1 (MD5) Previous issue date: 2013-02-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Was synthesized particulate material based on containing a small amount of bismuth compounds and molybdenum with satisfactory reproducibility. The material was produced starting from a composition of 99% (mol %) of rutile TiO2 and 1% of MoO3, which were previously mixed and calcined at 1200ºC. The composition studied consisted of 99.8% of the above mixture and 0.2% of bismuth subnitrate hexahydrate, Bi5O(OH)9 NO3)4.6H2O. This powder mixture [(99.8% of TiO2+MoO3 and 0.2% of Bi5O(OH)9 (NO3)4.6H2O)] was homogenized and calcined in tubular furnace at 1200ºC using four different heating rates: 1, 30, 40 e 60 °C/min. The ascalcined powder was characterized by X-ray diffraction (XRD) for identification of the phases resulting, scanning electron microscopy (SEM) to evaluate the microstructure and degree of gglomeration of powders and particle size was estimated by laser scattering technique. The color properties were expressed as CIEL*a*b* coordinates. X-ray patterns indicated the presence of TiO2, Bi2O3, γ-Bi2MoO6, Bi2Ti2O7, Bi2Ti4O11 depending on the heating rate. The yellow color was attributed to the presence of α-Bi2O3, Bi2MoO6 e Bi2Ti2O7. The different heating rates showed no relevant influence on the powder morphology, but the particle size of the powder was suitable for using the material as an inorganic pigment. / Foi sintetizado um material particulado a base de TiO2, contendo uma pequena quantidade de compostos de bismuto e de molibdênio apresentando boa reprodutibilidade. O material foi produzido a partir de uma composição de 99% (mol%) de rutilo TiO2 e 1% de MoO3, previamente misturados e calcinado a 1200 °C. A composição estudada consistia de 99,8% da mistura acima e 0,2% de subnitrato de bismuto hexahidratado, Bi5O(OH)9 (NO3)4.6H2O. Esta mistura em pó [(99,8% de TiO2 + MoO3 e 0,2% de Bi5O(OH)9 (NO3) 4.6H2O)], foi homogeneizada e calcinada em forno tubular a 1200 ºC, utilizando-se quatro taxas de aquecimento diferentes: 1, 30, 40 e 60 °C /min. O pó calcinado foi caracterizado por difração de raios X (DRX) para identificação das fases resultantes, por microscopia eletrônica de varredura (MEV) para avaliação da microestrutura e grau de aglomeração dos pós, o tamanho de partículas foi estimado por espectroscopia de fotocorrelação (PCS) e as propriedades colorimétricas através das coordenadas CIEL*a*b* . O DRX indicou a presença das fases TiO2, α-Bi2O3, γ-Bi2MoO6, Bi2Ti2O7, Bi2Ti4O11 sendo estas dependentes das taxas de aquecimento utilizadas. A cor amarela foi atribuída à presença de α-Bi2O3, -Bi2MoO6 e Bi2Ti2O7. As taxas de aquecimento diferentes não apresentaram nenhuma influência relevante sobre a morfologia do pó, porém o tamanho de partícula do pó mostrou-se adequado para a utilização do material, como um pigmento inorgânico.

Ces travaux de thèse ont pour but d’analyser les outils de photolithographies permettant d’inscrire des réseaux des diffractions et d’identifier ceux qui sont suffisamment flexibles pour être adapté à des substrats non conventionnels tel que des cylindres ou des tubes. Les outils de photolithographies développés ont aussi été ajustés afin d’inscrire directement un réseau de diffraction dans une couche fonctionnelle de TiO2, apporté par la voie sol-gel. Cette thèse est une étude prospective car la périodicité ou le motif des structures diffractantes inscrites n’ont pas été définis pour une application spécifique. Deux outils de photolithographies ont été adaptés avec succès aux substrats cylindriques. Ils seront présentés ici et s’accompagneront d’une perspective en vue d’une application particulière. Enfin, le dernier chapitre se distincte des précédents car il ne porte pas sur le développement d’un outil de photolithographie mais sur la transformation chimique du TiO2 (diélectrique) en TiN (métal), il reste néanmoins dans la continuité de ses travaux de thèse car cette transformation est adaptée à tous types de substrats / The aim of this thesis is to analyze the photolithography tools used to print diffraction gratings and to identify those that are sufficiently flexible to be adapted to unconventional substrates such as cylinders or tubes. The photolithography tools developed have also been adjusted in order to write directly a diffraction grating in a functional layer of TiO2, supplied by the sol-gel pathway. This thesis is a prospective study because the periodicity or the pattern of the registered diffracting structures has not been defined for a specific application. Two photolithography tools have been successfully adapted to cylindrical substrates. They will be presented here and will be accompanied with a perspective for a specific application. Finally, the last chapter is distinct from the previous ones because it does not concern the development of a photolithography tool but on the chemical transformation of TiO2 (dielectric) into TiN (metal), it nevertheless remains in the continuity of its thesis because this transformation is adapted to all types of substrates

Ce travail de thèse porte sur l’effet de la fluoration sur la réactivité du dioxyde de titane. Dans ce travail, trois familles de TiO2, dont l’anatase pure, le rutile pure et le TiO2 de la phase mixte anatase/rutile ont été fluorées par la méthode dite du choc thermique à différentes températures, de 400 – 950°C. Les influences de la fluoration sur les propriétés et la composition élémentaire de leur surface ont été étudiées par spectroscopie photoélectronique à rayonnements X (XPS). L’évolution de la structure cristalline, la morphologie et les propriétés optiques de ces catalyseurs en fonction de la fluoration a été également étudiée en détail par diffraction des rayons X, nanosonde Auger et spectroscopie de réflectance diffuse UV - Visible. Leur activité photocatalytique a été évaluée par la dégradation du bleu de méthylène en solution. Jusqu’à 500°C, la fluoration est uniquement surfacique et ne modifie ni la structure ni la morphologie des particules TiO2. Cependant la fluoration augmente la teneur en groupement OH de surface, ce qui contribue à l’augmentation de l’activité photocatalytique. Par contre, au-delà de 500°C, la méthode de fluoration forme une phase parasite anisotrope, K2Ti6O13 qui réduit les performances photocatalytiques. La réactivité de surface des catalyseurs fluorés a été également évaluée par l’adsorption de sondes gazeuses acide SO2 et basique NH3, couplée à l’analyse XPS. Les résultats montrent que tous les catalyseurs possèdent des surfaces amphotères dont l’acidité et la basicité sont significativement influencées par la fluoration. / The thesis aimed to investigate the influences of fluorination on the reactivity of titanium dioxide. In this work, three crystallographic families of TiO2: pure anatase, pure rutile and TiO2 P25 (mixed phase anatase/rutile), were fluorinated by thermal shock method at different temperatures, from 400 to 950°C. The influence of fluorination on the properties and elementary composition of their surface was studied by X ray photoelectron spectroscopy (XPS). The evolution of crystal structure, morphology and optic properties of these catalysts versus the fluorination was also studied in detail by X ray diffraction, Auger nanoprobe and diffuse reflectance UV – Visible spectroscopy. Their photocatalytic activity was evaluated by the degradation of methylene blue in solution. According to the results, the fluorination below 600°C only occurs on the surface and does not modify the structure and the particle size of TiO2. However, the fluorination enhances the surface hydroxyl groups, which are assigned to the improvement of photocatalytic activity. For the fluorination over 600°C, the parasite anisotropic K2Ti6O13 phase is formed, resulting in the reduction of photocatalytic performances.The surface reactivity of our catalysts was also evaluated by the adsorption of probe molecules acid SO2 and basic NH3, coupled with XPS analysis. The results show that the surface of all catalysts is amphoteric with the acidity and basicity significantly affected by fluorination.