Thèses sur le sujet « Titanium-doping »

Local defect structures are significant to determine material properties since defects introduced into host materials would affect the local/average crystal environments and thus lead to a change of macroscopic physicochemical performances. The intentional design of specific local defects not only depends on the selected synthesis method and preparation process but also relies on the selected dopant or co-dopant ions. A deep understanding of the intrinsic relationships between local defect structures, chemical synthesis and associated properties is thought as one major framework of material genome plan. It also pushes the design, development and application of novel multifunctional materials. Based on local defect structural design coupled with new synthesis strategies, indium and niobium co-doped anatase titanium oxide nanocrystals are synthesized. It is experimentally demonstrated that the dual mechanisms of nucleation and diffusion doping are responsible for the synergistic incorporation of indium difficult-dopants and niobium easy-dopants, and theoretically evidenced that the local defect structures created by indium, niobium co-dopants, reduced titanium and oxygen vacancies are composed of defect clusters and defect pairs. These introduced local defect structures act as nucleation centres of baddeleyite- and lead oxide-like metastable polymorphic phases and induce an abnormal trans-regime structural transition of co-doped anatase titanium oxide nanocrystals under high pressure. Furthermore, these small co-doped nanocrystals can be used as raw materials to manufacture titania-based ceramic capacitors designed in terms of electron-pinned defect dipole mechanism. The sintering temperature is thus lowered to 1200 °C, which conquers the technological bottleneck using this material. To develop the third generation of high-efficient visible light catalysts, nitrogen and niobium co-doped anatase titania nanocrystals are synthesized. Experimental and theoretical investigations demonstrate that the formation of highly concentrated defect-pairs is key to significantly enhance visible light catalytic efficiency. In further combination of local defect structural design and the exploration of new synthesis strategies, anatase nanocrystals containing nitrogen and reduced titanium ions are synthesized. The formation of local defect clusters is demonstrated to play an important role on the obvious enhancement of Rhodamine B degradation efficiency under only visible light illumination. It is thus unveiled that a fundamental understanding of the functions of local defect structures and a well-controlled synthetic strategy are critical to develop highly efficient visible light catalysts with unprecedented photocatalytic performances. Through these systematic investigations, it is concluded that local defect structures generated by introduced co-dopants are complicated in strong-correlated titania systems and differ from case to case. A major difficulty to efficiently introduce difficult-dopant ions such as nitrogen and indium at high concentrations is solved. Two high-efficient visible light catalysts are achieved for environmental remediation by using the clean and renewable solar energy; and one raw material for manufacturing new ceramic capacitors and new metastable polymorphic phases is provided. The discussion on the doping mechanisms, the defect formation and their associated impacts on material performances will not only benefit the future development of physical chemistry, material science and defect chemistry, but also opens a new route to design novel multifunctional materials based on local defect structure design.

The main objective and the major value of this work is to provide a combined setup of theoretical and experimental techniques to simulate and measure a number of properties altered and/or induced by defects in three representative and technologically relevant oxides: zinc oxide (ZnO), zirconium dioxide (ZrO2) and magnesium oxide (MgO). Zinc oxide and zirconium dioxide are wide-gap semiconductors with a vast set of technological applications generally related to the inclusion of defects and impurities and spanning from optoelectronics to spintronics devices and photocatalysis. They are the subjects of Part II and Part III, respectively. A detailed description of their structure and chemical-physical properties is provided in the respective background sections. Part II deals with the main subject of this work: bulk and surface zinc oxide properties. After synthesis, ZnO commonly presents n-type conductivity and in Chapter 3 some of the most common donor defects (specifically: hydrogen interstitial and substitutional to oxygen, zinc interstitial and oxygen vacancy) have been investigated in terms of thermodynamic and optical transition energy levels. The good agreement with existing experimental data provides a powerful validation of the computational method presented in Sec. 2.1.5.1. In Chapter 4 copper doping of ZnO has been analyzed under different perspectives, spanning from the presence of donor and acceptor states, to magnetic interactions, to cluster tendency and to the interaction with oxygen vacancies. In particular, in conjunction with HREELS experiments, for the first time the inclusion of copper donor impurities in bulk ZnO has been observed which, on the basis of our calculations, we have assigned to interstitial copper species. In Chapter 5, the most promising shallow acceptor candidate for p-type doping of ZnO, i.e. nitrogen substitutional to oxygen, is investigated. First, nitrogen has been observed in polycrystalline sample and characterized in terms of hyperfine and quadrupolar coupling constants through a combined EPR and theoretical study. Secondly, the nitrogen doping process has been analysed upon the sputtering with ammonia of the mixed-terminated ZnO (10 0) surface through TDS experiments. The effectiveness of the doping process and the fundamental role of post-treatment oxidation were proved. The defective states within the optical gap have been estimated using HREELS measurements with a 66 eV electron primary energy. The computation of the transition energy levels have then demonstrated that nitrogen acts as a deep acceptor species in ZnO, disappointing the hopes to achieve p-type conductivity through nitrogen-doping. In order to get more insight in the nitrogen doping mechanism, the reactivity of ZnO single crystal and powders towards ammonia has been addressed by a combined theoretical and HREEL and UHV-FTIR study, in Chapter 6. Different coverages have been considered and, while at low concentration only molecularly adsorbed species have been observed, at a full monolayer coverage the repulsive steric interactions between adsorbates have been shown to induce the formation of an ordered adlayer with (2 x 1) periodicity, presenting alternating molecular NH3 and singly deprotonated NH2 moieties adsorbed on cationic sites. Part III is focused on ZrO2, specifically the tetragonal polymorph which is commonly stabilized by impurities. In particular, here the interest is related to the titanium doping of the material, which was experimentally found to induce a large red shift of the optical absorption edge. In Chapter 7 we proposed a rationalization of this experimental observation based on the computation of the optical transition levels of Ti species. The possible interaction with oxygen vacancies has also been considered. In Part IV the nitrogen doping of MgO, recently proposed as potential route to achieve room temperature ferromagnetism has been investigated. This work was divided in two parts. In Chapter 8 the electronic structure and the spin properties of nitrogen impurities have been theoretically studied, considering also possible charge transfers with magnesium or oxygen vacancies. Finally, in Chapter 9 we show how a trapped N2‒ radical anion in the polycrystalline material has been identified and characterized through a combined EPR and DFT study.

Consumers across the world use lithium-ion batteries in some fashion in their everyday life. The growing demand for energy has led to batteries dying quicker than consumers want. Thus, there are calls for researchers to develop batteries that are longer lasting. However, the initial increase in battery life over the years has been from better engineering and not necessarily from making a better material for a battery. This thesis focuses on the understanding of the chemistry of the materials of a battery. Throughout the chapters, the research delves into the how and why materials with extra nickel degrade quickly. Then, it investigates a method of making these nickelrich materials last longer and how the chemistry within these materials are affected by the addition of a different metal. Overall, the findings indicate that the addition of titanium creates a more stable material because it mitigates the release of oxygen and prevents irreversible changes within the structure of the material. It determines that the chemistry behind the failings of nickel-rich lithium-ion batteries and a potential method for allowing the batteries to last longer. It also provides insight and guidance for potential future research of stabilization of lithium-ion materials.
Master of Science
Consumers across the world use lithium-ion batteries in some fashion in their everyday life. The growing demand for energy has led to batteries dying quicker than consumers want. Thus, there are calls for researchers to develop batteries that are longer lasting. However, the initial increase in battery life over the years has been from better engineering and not necessarily from making a better material for a battery. This thesis focuses on the understanding of the chemistry of the materials of a battery. Throughout the chapters, the research delves into the how and why materials with extra nickel degrade quickly. Then, it investigates a method of making these nickel-rich materials last longer and how the chemistry within these materials are affected by the addition of a different metal. Overall, the findings indicate that the addition of titanium creates a more stable material because it mitigates the release of oxygen and prevents irreversible changes within the structure of the material. It determines that the chemistry behind the failings of nickel-rich lithium-ion batteries and a potential method for allowing the batteries to last longer. It also provides insight and guidance for potential future research of stabilization of lithium-ion materials.

A titanium dioxide powder co-doped with boron and zirconium was prepared by mechanical ball milling. Photocatalytic performance of the powder was evaluated by degradation of methylene blue (MB) solution under UV illumination. XRD patterns were refined by Rietveld analysis method to obtain accurate lattice parameters and position of the atoms in the crystal structure of TiO2. XRD analysis indicated that the B and/or Zr doped TiO2 powders composed of anatase and did not exhibit any additional phase. Rietveld analysis suggested that dopant B and Zr elements were successfully weaved into crystal structure and distorted the lattice of TiO2. The highest distortion was obtained by co-doping. SEM investigations confirmed that mechanical ball milling technique led to a decrease in particle size of TiO2 powder. XPS analysis revealed that dopant B and Zr atoms did not appear in any form of compound including Ti and O elements. Results of photocatalytic activity test suggested that boron and zirconium co-doped TiO2 particles exhibited a better visible light response and photocatalytic activity than that of mono element doped TiO2 (i.e. B-TiO2 and Zr-TiO2) and undoped TiO2 particles. A 20% improvement in photocatalytic activity of reference TiO2 powder (powder ball milled without dopant addition) was achieved by B and Zr co-doping. The enhanced photocatalytic activity is attributed to synergistic effects of B-Zr co-doping the lattice of TiO2 as well as particle size reduction.

L’objet de cette thèse est le développement et l’étude de la photoréactivité de TiO2, absorbant dans le visible et ayant des propriétés autonettoyantes et de dépollution de l’eau et de l‘air. Dans ce contexte, des films d’épaisseur controlée et mésostructurés de TiO2 non dopés et dopés par différents métaux (platine, vanadium et tungstène) , ont été synthétisés par voie sol-gel combinée au procédé d'auto-assemblage induit par évaporation. Les propriétés structurales et optiques ainsi que la composition chimique de la surface des films ont été caractérisées par de nombreuses techniques de caractérisation telles que DRX, GISAXS, TEM, MEB ellipsoporosimétrie, DRUV et XPS. Une étude complète des propriétés photocatalytiques des films à base de TiO2 aux interfaces solide-solide, solide-liquide et solide-gaz a été réalisée en utilisant respectivement les tests avec de l’acide stéarique, du bleu de méthylène et de l’acétone. Durant cette étude, nous avons montré qu’un contrôle adapté de l’épaisseur des films, de la nature et de la quantité du dopant peut améliorer l’activité photocatalytique jusqu’à un facteur de 16 par rapport à des films non dopés. Des tests préliminaires de piégeage chimiques des radicaux OH• par l’acide téréphtalique sous irradiation UV ont montré qu’il existait une bonne corrélation entre la photoréactivité et la génération des radicaux OH•
The aim of this thesis is the development and study of photocatalytic properties of visible light photoactive mesoporous TiO2-based films to act as self-cleaning, and purification systems applied to air and water. Pure and doped mesoporous titania films with different metals as Pt, V and W were prepared by sol-gel method combined with evaporation induced self-assembly process at different thicknesses. Structural, optical properties and chemical composition of these films were characterized by XRD, GISAXS, TEM, SEM, ellipsoporosimetry , DRUV and XPS. In order to better characterize and compare the efficiency of these films at solid-solid, liquid-solid and air-solid interfaces, several tests were used: mineralization of stearic acid, photobleaching of methylene blue and photooxidation of acetone. In this study, it is shown how a suitable control of the film thickness, the nature and amount of the dopant can improve the photocatalytic activity up to a factor of 16 relative to un-doped films. Preliminary results on the OH• radicals production using terephtalic acid as a chemical probe showed good correlation between photoreactivity and generation of these radicals

Transparent conductive oxides (TCOs) are key functional materials in existing and future electro-optical devices in the fields of energy efficiency, energy generation and information technology. The main application of TCOs is as thin films transparent electrodes where a combination of maximum electrical conductivity and transmittance in the visible to nearinfrared spectral range is required. However, due to the interdependence of the optical properties and the free electron density and mobility, respectively, these requirements cannot be achieved simultaneously in degenerately doped wide band-gap oxide semiconductors. Therefore, a detailed understanding of the mechanisms governing the generation of free charge carriers by extrinsic doping and the charge transport in these materials is essential for further development of high performance TCOs and corresponding deposition methods. The present work is aimed at a comprehensive investigation of the electrical, optical and structural properties as well as the elemental composition of (Al,Ga) doped ZnO and Nb doped TiO2 thin films prepared by pulsed DC reactive magnetron sputtering. The evolution of the film properties is studied in dependence of various deposition parameters through a combination of characterization techniques including Hall-effect, spectroscopic ellipsometry, spectral photometry, X-ray diffraction, X-ray near edge absorption, Rutherford backscattering spectrometry and particle induced X-ray emission. This approach resulted in the development of an alternative process control method based on the material specific current-voltage pressure characteristics of the reactive magnetron discharge which allows to precisely control the oxygen deficiency of the sputter deposited films. Based on the experimental data, models have been established that describe the room temperature charge transport properties and the dielectric function of the obtained ZnO and TiO2 based transparent conductors. On the one hand, these findings allow the prediction of material specific electron mobility limits by identifying the dominating charge carrier scattering mechanisms. On the other hand, new insight is gained into the origin of the observed transition from highly conductive to electrically insulating ZnO layers upon the incorporation of increasing concentrations of Al at elevated growth temperatures. Moreover, the Al and Ga dopant activation in ZnO have been quantified systematically for a wide range of Al concentrations and deposition conditions. A direct comparison of the Ga and Al doping efficiency demonstrates that Ga is a more efficient electron donor in ZnO. Further, it has been shown that high free electron mobilities in polycrystalline and epitaxial Nb:TiO2 layers can be achieved by reactive magnetron sputtering of TiNb alloy targets. The suppression of rutile phase formation and the control of the Nb dopant activation by fine tuning the oxygen deficiency have been identified as crucial for the growth of high quality TiO2 based TCO layers.

Le couplage direct de la séparation et de la photo-catalyse en utilisant des membranes à base de dioxyde de titane, est une approche intéressante habituellement appliquée dans les dispositifs de traitement de l'eau, et récemment envisagée pour d’autres applications, telle que la production d’hydrogène par photo-électrolyse de l’eau. En effet, le dioxyde de titane (TiO2) est bien connu pour ses propriétés photo-catalytiques. En outre, s’il est immobilisé sur support membranaire plutôt qu’utilisé en suspension, son intégration en procédé de séparation est facilitée, sans compter les gains apportés au procédé en termes de compacité, d’intégrité et de capacité séparative. Pour une telle application, des cellules originales sous forme de multicouches sont requises. Certains systèmes sont décrits dans la littérature mais aucun d’entre eux n’est réellement intégré (c’est-à-dire basé sur une géométrie de type multicouche micro-architecturée), ni formé de couches minces obtenus par procédés plasma. Or les procédés plasma sont généralement compétitifs pour l’obtention de systèmes multicouches de hautes intégrité et compacité. Dans le cadre de récents travaux menés à l’IEM, différents types de couches minces ont été préparés par PECVD (Plasma Enhanced Chemical Vapor Deposition), à savoir des films de TiO2 connus pour leurs propriétés photo-catalytiques et des membranes phosphoniques de conduction protonique avérée. En outre, des films minces de platine efficaces pour la réduction catalytique des protons en hydrogène peuvent être également déposés par un autre procédé plasma, la pulvérisation cathodique. Au cours de ce travail de thèse, des films de TiO2 obtenus par PECVD Basse Fréquence sont optimisés en termes d’activité photo-catalytique et de propriétés séparatives; cette optimisation, qui concerne le dopage à l’azote du TiO2 (permettant le déplacement de la bande interdite de la région UV vers la région visible), est le premier objectif de ce projet de thèse. Les films minces sont caractérisés du point de vue de leurs propriétés structurales et fonctionnelles. Le second objectif de la thèse est de montrer l’intérêt de ces films de TiO2 dans la production/séparation d’hydrogène par voie solaire. Dans ce but, la photo-activité des films dans le noir, sous UV et sous visible est étudiée dans une cellule mono-compartiment où les deux électrodes baignent dans un électrolyte liquide. Des études électrochimiques plus poussées en présence d’une membrane électrolyte commerciale et d’une cathode de platine (dont les caractérisations en propre sont portées en annexes de ce travail), sont aussi abordées. Le dernier objectif de cette thèse est le transfert de la technologie des procédés plasma de l’Institut Européen des Membranes de l’Université de Montpellier vers le Laboratoire Chimie-Physique des Matériaux de l’Université Libanaise. Les détails de l’installation du réacteur au Liban font l’objet du dernier chapitre de la thèse ainsi que les résultats des premiers tests de dépôt sur la base de conditions opératoires précédemment optimisées à l’Institut Européen des Membranes
Direct coupling of separation and photo-catalysis using membranes based on titanium dioxide, is an interesting approach usually applied in water treatment devices, and recently considered for other applications, such as hydrogen production by water photo-electrolysis. Indeed, titanium dioxide (TiO2) is well-known for its photo-catalytic properties. In addition, if it is immobilized on membrane supports rather than used in suspensions, its integration in the separation process is facilitated and some advantages of the process in terms of compactness, integrity and separation capacity are provided. For such an application, original multilayered cells are required. Some systems are described in the literature but none of them is truly integrated (that is to say based on a micro-architecture geometry of multi-layer type) or formed of thin layers obtained by plasma processes. Now plasma processes are generally competitive for obtaining multilayered systems with high integrity and compactness. As part of recent works at IEM, various types of thin films were prepared by PECVD (Plasma Enhanced Chemical Vapor Deposition) to include TiO2 films known for their photo-catalytic properties and phosphonic acid membranes with average protons conductivity. In addition, effective platinum thin films for the protons catalytic reduction into hydrogen could also be deposited by another plasma process, sputtering. In this work, TiO2 films obtained by Low Frequency PECVD are optimized in terms of photo-catalytic activity and separation properties; this optimization, regarding the nitrogen doping of TiO2 (for the band gap shifting from the UV region to the visible region), is the first objective of this thesis project. The thin films structural and functional properties are characterized.The second aim of this thesis is to demonstrate the competitiveness of these films for the Hydrogen production/separation by solar energy. To this end, the layers photo-response has been tested in the dark, under UV and under visible light in a mono-compartment cell where both electrodes are immersed in a liquid electrolyte. Further studies integrating the TiO2 layers in contact with a commercial electrolyte membrane and a platinum counter-electrode (whose characterizations are presented in annexes), are also performed. The last aim of this work is the Plasma technology transfer from the European Membrane Institute of University of Montpellier to the Laboratory of Physical Chemistry of Materials of Lebanese University. The installation and configuration details are presented in the last chapter as well as the results of the first depositions based on operating conditions already optimized at European Membrane Institute

Heterogeneous electrocatalysis is the usage of solid materials to decrease the amount of energy needed to produce chemicals using electricity. It is of core importance for modern life, as it enables production of chemicals, such as chlorine gas and sodium chlorate, needed for e.g. materials and pharmaceuticals production. Furthermore, as the need to make a transition to usage of renewable energy sources is growing, the importance for electrocatalysis used for electrolytic production of clean fuels, such as hydrogen, is rising. In this thesis, work aimed at understanding and improving electrocatalysts used for these purposes is presented. A main part of the work has been focused on the selectivity between chlorine gas, or sodium chlorate formation, and parasitic oxygen evolution. An activation of anode surface Ti cations by nearby Ru cations is suggested as a reason for the high chlorine selectivity of the “dimensionally stable anode” (DSA), the standard anode used in industrial chlorine and sodium chlorate production. Furthermore, theoretical methods have been used to screen for dopants that can be used to improve the activity and selectivity of DSA, and several promising candidates have been found. Moreover, the connection between the rate of chlorate formation and the rate of parasitic oxygen evolution, as well as the possible catalytic effects of electrolyte contaminants on parasitic oxygen evolution in the chlorate process, have been studied experimentally. Additionally, the properties of a Co-doped DSA have been studied, and it is found that the doping makes the electrode more active for hydrogen evolution. Finally, the hydrogen evolution reaction on both RuO2 and the noble-metal-free electrocatalyst material MoS2 has been studied using a combination of experimental and theoretically calculated X-ray photoelectron chemical shifts. In this way, insight into structural changes accompanying hydrogen evolution on these materials is obtained.
Heterogen elektrokatalys innebär användningen av fasta material för att minska energimängden som krävs för produktion av kemikalier med hjälp av elektricitet. Heterogen elektrokatalys har en central roll i det moderna samhället, eftersom det möjliggör produktionen av kemikalier såsom klorgas och natriumklorat, som i sin tur används för produktion av t ex konstruktionsmaterial och läkemedel. Vikten av användning av elektrokatalys för produktion av förnybara bränslen, såsom vätgas, växer dessutom i takt med att en övergång till användning av förnybar energi blir allt nödvändigare. I denna avhandling presenteras arbete som utförts för att förstå och förbättra sådana elektrokatalysatorer. En stor del av arbetet har varit fokuserat på selektiviteten mellan klorgas och biprodukten syrgas i klor-alkali och kloratprocesserna. Inom ramen för detta arbete har teoretisk modellering av det dominerande anodmaterialet i dessa industriella processer, den så kallade “dimensionsstabila anoden” (DSA), använts för att föreslå en fundamental anledning till att detta material är speciellt klorselektivt. Vi föreslår att klorselektiviteten kan förklaras av en laddningsöverföring från ruteniumkatjoner i materialet till titankatjonerna i anodytan, vilket aktiverar titankatjonerna. Baserat på en bred studie av ett stort antal andra dopämnen föreslår vi dessutom vilka dopämnen som är bäst lämpade för produktion av aktiva och klorselektiva anoder. Med hjälp av experimentella studier föreslår vi dessutom en koppling mellan kloratbildning och oönskad syrgasbildning i kloratprocessen, och vidare har en bred studie av tänkbara elektrolytföroreningar utförts för att öka förståelsen för syrgasbildningen i denna process. Två studier relaterade till elektrokemisk vätgasproduktion har också gjorts. En experimentell studie av Co-dopad DSA har utförts, och detta elektrodmaterial visade sig vara mer aktivt för vätgasutveckling än en standard-DSA. Vidare har en kombination av experimentell och teoretisk röntgenfotoelektronspektroskopi använts för att öka förståelsen för strukturella förändringar som sker i RuO2 och i det ädelmetallfria elektrodmaterialet MoS2 under vätgasutveckling.

QC 20151119

Ce travail de thèse consiste à synthétiser des nanoparticules de dioxyde de titane pour la décontamination d’agents chimiques par photocatalyse. L’objectif principal est d’optimiser le photocatalyseur pour la dégradation du sulfure de diéthyle (DES), simulant de l’ypérite. L’oxydation du DES produit des sulfates qui empoisonne le TiO2. Le but est donc de limiter cette désactivation ainsi que le rejet de molécules toxiques. Une solution est d’augmenter la surface spécifique par deux méthodes : le dopage du TiO2 au tantale ou à l’étain et l’ajout d’un porogène lors de la synthèse par voie sol-gel. Les catalyseurs optimisés présentent des taux de conversion élevés pour l’élimination du DES en phase gazeuse sous flux continu grâce à leur surface spécifique importante et leurs propriétés d’adsorption. Les matériaux les plus performants sont ensuite immobilisés sur des mousses tridimensionnelles de β-SiC. Ces média photocatalytiques se désactivent mois rapidement que les matériaux pulvérulents. Une régénération par une solution de soude permet de retrouver leur activité initiale. Ce qui permet une utilisation industrielle possible des catalyseurs. Cette thèse ouvre la voie à la réalisation d’un prototype de décontamination de l’air pour l’élimination d’agents chimiques de guerre
This work consists in the synthesis of titanium dioxide nanoparticles for the decontamination of chemical warfare agents by photocatalysis. The main goal is to optimize the photocatalyst to eliminate diethylsulfide (DES), simulating yperite. The oxidation of DES generates sulfates that lead to the poisoning of TiO2. Thus, the aim is to limit this deactivation and to avoid a release of harmful products. A solution is to increase the specific suface area by two methods: doping TiO2 with tantalum or tin and adding a porogen during the sol-gel synthesis. These optimized catalysts exhibit high conversion rates for DES elimination in the gas phase under a continuous flow thanks to their high specific surface area and their adsorption properties. The best catalysts are immobilized on tridimensional β-SiC foams. These photocatalytic foams deactivates slower than the TiO2 powders. A regeneration by an NaOH solution can restore their initial activity. It allows a possible industrial application for these catalysts. This thesis opens the way to realize a decontamination prototype for air to eliminate chemical warfare agents

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
The optimization of the synthetic route of titanium dioxide nanoparticles doped with nitrogen was carried out in order to obtain photocatalysts with improved photocatalytic activity. Thereby, from the synthesized photocatalysts was possible to reach about 100% discoloration and 64% mineralization of Ponceau 4R (P4R) dye. Both doped (with largest and smallest photocatalyitc activity) and undoped catalysts were analyzed by X-ray diffraction showing the predominance of the crystalline anatase phase. Besides, using the Rietveld method, the results showed 17.3% of brookite phase in the undoped oxides. By further analysis of diffuse reflectance spectroscopy was observed that doped catalysts presented slight shift on absorption band to the visible region, highlighting the best photocatalyitc activity of the oxide with a band gap of 3,29 eV. This oxide (K1) exhibited specific area of 63.03 g/m2 while the oxide with lower photocatalytic activity (K2) exhibited a specific area of 12.82 g/m2. The Raman spectroscopy analysis showed that doped samples are more ordered than no doped, and vibrational modes related to nitrogen was not observed. Infrared spectra showed that calcination of the doped oxides leads to considerable loss in nitrogen content, and this is corroborated by the XPS measurements. Photocatalytic assays were carried out on laboratory scale using K1 catalyst in order to optimize the mineralization of P4R. Thus, the substrate concentration, catalyst concentration and pH of reaction medium were evaluated and the best result was 85% mineralization using 15 mg/L of P4R, 100 mg/L of catalyst and pH 6.4. Additional photocatalytic tests were conducted under solar radiation showing that doping increases photocatalytic activity under UV-A and visible irradiation, since 600 kJ of accumulated UV-A radiation (referring to 9 minutes of reaction time in bench scale) proved to be enough to reach 100% mineralization of dye using doped catalyst against 77% mineralization using undoped catalyst.
Com a finalidade de obter um fotocatalisador com atividade fotocatalítica melhorada otimizou-se a rota de síntese para a obtenção de nanopartículas de dióxido de titânio dopado com nitrogênio. A partir deste procedimento foi possível obter um fotocatalisador capaz de descolorir em 100% o corante Ponceau 4R (P4R), e mineralizar 64% sua carga orgânica. Os catalisadores que apresentaram a maior e menor atividade fotocatalítica, e o óxido não dopado foram analisados por difração de raios-X, que mostrou a predominância da fase cristalina anatase nos óxidos dopados. Além disso, no óxido não dopado, além da fase anatase constatou-se, usando o método de Rietveld, a presença de 17,3 % da fase broquita. Por espectroscopia de reflectância difusa observou-se, para os óxidos dopados, um pequeno deslocamento da absorção de luz para a região do visível, com destaque para o óxido com a maior atividade fotocatalítica, que apresentou um band gap de 3,29 eV. Este óxido, (K1), apresentou área específica de 63,03 g/m2, enquanto que para o de menor atividade fotocatalítica, (K2), foi de 12,82 g/m2. Por espectroscopia Raman verificou-se que as amostras dopadas são mais ordenadas que a amostra não dopada. Por outro lado, não foram observados modos vibracionais relacionados ao nitrogênio. Os espectros de infravermelho mostraram que a calcinação dos óxidos dopados causa uma perda considerável no conteúdo de nitrogênio, o que é confirmado por medidas de XPS. Para o catalisador K1 foram realizados experimentos em escala de laboratório com o intuito de otimizar as condições reacionais para a mineralização do P4R. Foram avaliados o efeito da concentração do substrato, concentração do catalisador e pH do meio reacional, onde os melhores resultados (85% de mineralização) foram obtidos utilizando-se 15 mg/L do P4R, 100 mg/L do catalisador, em pH 6.4. Os testes fotocatalíticos feitos sob irradiação solar evidenciaram que a dopagem amplia a atividade fotocatalítica sob irradiação no UVA e visível, já que com 600 kJ m-2 (equivalente a 9 minutos de reação nos experimentos em escala de bancada) de radiação UV-A acumulada, 100% do corante foi mineralizado com o catalisador dopado, e apenas 77% com o seu similar não dopado.
Doutor em Química

Master’s thesis deals with synthesis of anatase and its anion doping by carbo-nitridation. Prepared samples were used for testing of the photocatalytic activity. Low-temperature anatase was synthesized at 80 °C for 6 hours and carbo-nitridatation was carried out in ammonia/tetrachloromethane atmosphere at 500 °C for 3 hours. The influence of silver content on low-temperature crystallization of anatase was studied by reaction of titanium tetraisopropoxide with water. Silver nanoparticles were prepared by reduction of silver nitrate by D-glukose and sodium citrate. One of the results is the draft for one-pot synthesis of anatase by titanium tetraisopropoxide with complexing agent (sodium citrate, ammonium citrate, citric acid). The study of photocatalysis water splitting was carried out in the presence of 20 % vol. of methanol. Anatase prepared with citric acid has the highest photocatalytic activity (Pt 0,5 %) in UV/VIS spectral region. The activity achieved 38,6 % effectiveness of TiO2 standard (Degussa P25). Doping by nitrogen didn’t lead to increase of photocatalytic activity.

Thesis (Ph.D.)--University of Delaware, 2008.
Principal faculty advisors: Chin-Pao Huang, Dept. of Civil and Environmental Engineering, and S. Ismat Shah, Dept. of Materials Science Includes bibliographical references.

The techniques mostly used to decontaminate air as well as water pollutants have drawbacks in terms of higher costs, require secondary treatment, and some methods are very slow. So, emphasis has been given to water though the use of photocatalysts, which break organic pollutants to water and carbon dioxide and leave no trace of by-products at the end. Photocatalytic remediation aligns with the waste and wastewater industries’ zero waste schemes with lower cost, eco-friendly and sustainable treatment technology. The commonly used photocatalysts such as titanium oxide (TiO2), zinc oxide (ZnO), tungsten oxide (WO3) have band gap of nearly 3.2 eV. The lower energy band-gap of a semiconductor makes it a better photocatalyst. The major drawbacks of photocatalysts are its inefficiency to work under visible light and high photocorrosion which limits its uses. These limitations can be mitigated through dopants and the formation of varying morphologies like nanowires, nanoparticles, nanotubes etc. Several organic pollutants are insoluble in water, which inhibits the pollutant (insoluble) to come in contact with photocatalytic material thus hindering remediation characteristic of a photocatalyst. Binder material used to immobilize the photocatalytic material tends to decompose due to oxidative and reduction reactions around the photocatalyst which causes the loss of photocatalytic material. This investigation displays the advantage of organic remediation in visible radiation using graphene (G) doped TiO2 nanoparticles and nanowires. The nanostructured G-TiO2 nanoparticles and G-TiO2 nanowires were synthesized using sol-gel and hydrothermal methods. The nanostructured materials were characterized using scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR) and particle analyser procedures. The remediation of organic compounds (methyl orange) in water was achieved under visible radiation using graphene doped nanostructured photocatalytic materials. The sol-gel synthesized G-TiO2 nanoparticles has shown complete remediation of methyl orange (MO) in less than four hours, thus displaying enhanced photocatalytic activity achieved through graphene doping on TiO2 nanostructures The dopant and structure introduced in zinc oxide (ZnO) nanomaterials bring foundation for enhanced photocatalytic activity due to lowering of the band gap, and decreasing of photocorrosion through delaying of electron-hole recombination. The challenge to synthesize both nanowire and nanoparticle structures of ZnO doped with graphene (G) are carried out by simple and cost effective hydrothermal as well as super saturation precipitation techniques, respectively. Various nanostructures of ZnO have been synthesized using precipitation and hydrothermal methods are ZnO nanoparticles, G doped ZnO nanoparticles, ZnO nanowires, G doped ZnO nanowires, TiO2 seeded ZnO nanowires and G doped TiO2 seeded ZnO nanowires The synthesized ZnO based nanostructures were characterized using SEM, TEM, XRD, UV-vis, FTIR and particle analyser methods respectively. The standard organic pollutant methyl orange (MO) dye was employed in the water to understand the effective remediation using ZnO nanostructured materials under visible light radiation. The G-ZnO NW structure has shown effective remediation of MO in water in three hours compared to other synthesized nanostructured ZnO materials. The petroleum compounds were photocatalytically remediated from water using G- TiO2 nanoparticles material in visible light radiation. The G-TiO2 nanoparticle was synthesized using sol-gel technique and used on various petroleum-based chemicals (toluene, naphthalene and diesel) were remediated, and samples were analysed using optical and gas chromatography (GC) techniques. The importance of pollutant to come in contact with photocatalyst have been demonstrated by employing surfactant along with G-TiO2 nanoparticles to remediate naphthalene. Earlier studies in this investigation have shown that graphene (G) doping in both titanium oxide (TiO2) and zinc oxide (ZnO), has brought about a reduction in photocorrosion, and an increase in the photocatalytic efficiency for remediation of organics under visible light (λ > 400nm). However, the graphene doped photocatalysts have proven to be hard to coat on a surface, due to the strong hydrophobic nature of graphene. So, attempts have been made to use polyaniline (PANI), a conducting polymer, as a binder material by insitu polymerization of aniline over G-TiO2 nanoparticles (G-TiO2 NP) and G-ZnO nanowires (G-ZnO NW) & characterized using SEM, XRD, UV-vis and FTIR techniques. The photocatalytic, as well as photoelectrochemical catalytic performance of PANI:G-TiO2 NP and PANI:G-ZnO NW, were investigated. The standard MO in water was used for both PANI:G-TiO2 NP and PANI:G-ZnO NW electrodes on conducting substrates. 1:1 PANI:G-TiO2 NP shows an increase of 31% in the remediation of MO in water at potential of +1000 mV, and with the ease in coating PANI:G-TiO2 NP and PANI:G-ZnO NW on various substrates, on top of the visible light remediation allows for the use of these materials and process to be used for practical applications of remediation of organics from water.

Efficient use of renewable energies is one of the most difficult technological challenges facing humanity. Among all renewable energy sources, the sunlight is considered as the most abundant and accessible one. To convert it into usable and controllable form, the modern technology relies on generation of electron-hole pairs in semiconductors upon light absorption. The obtained separated charge carriers possess extra energy brought by the converted sunlight which can be further utilized in various ways. Currently, the most common approach consists in its direct transformation into electricity in p-n junctions. Alternatively, the electrons and holes can be used to perform chemical reactions. The electrons can be transferred to reduce various organic compounds or inorganic species, while simultaneously the holes can play the role of oxidizer by subtracting the electrons from the other substances. Through these reactions it would be possible to accumulate the solar energy in chemical species allowing thus to alleviate the intermittence of the sunlight. Unfortunately, the existing materials do not easily cross the laboratory level to realize this approach on industrial scale. That is why the development of new semiconductor photocatalysts, which harvest and convert efficiently the visible part of solar spectrum, is of paramount importance. For many years the most often studied photocatalytic materials have been ZnO and TiO2. However, it has been recently shown that composites based on ZnO and TiO2 possess even more promising properties than many other semiconductors in various photocatalytic applications. Despite many works reporting high photoactivity of these composites in different applications, the detailed information about the structure–properties correlation is lacking. In order to fill this gap we decided to focus our attention to study the influence of microstructure of ZnO/TiO2 composites on their properties in photocatalytic degradation of organic pollutants, and in application in half-reaction of ‘solar fuel’ generation, namely photoassisted water electro-oxidation. To realize such study the composites should satisfy the requirements of a high surface area and good electric conductivity. We chose therefore the design based on ZnO nanorods supported on ITO (Indium Tin Oxide)-coated glass electrode. The ZnO nanorods (NRs) were then covered with a layer of TiO2 under different deposition conditions. The composition and microstructure of the obtained ZnO(core)/TiO2(shell) composites were modified in the aim to elucidate how these parameters influence their photocatalytic activity. Consequently, the efforts were made to impart visible light activity to the elaborated ZnO/TiO2 composites by modifying titanium dioxide layers with nitrogen and decoration with Au nanoparticles. The thesis consists of three parts: Bibliography, Experimental and Results and Discussion. First part of the present PhD thesis, Bibliography, is dedicated to the analysis of literature concerning fundamental properties of semiconductor materials, solid/electrolyte interface as well as principles of photocatalysis and photoelectrochemical water oxidation. Also, the photocatalytic properties of ZnO and TiO2, and those of their composites are reviewed in this section. Furthermore, methods for improvement visible-light absorption are also described, i.e. N-doping and surface plasmonic effects due to the noble metal nanoparticles (Au NPs) deposited on semiconductors. The second part, Experimental, covers the preparation procedures and characterization techniques used in the work. First, the details are given for electrochemical seeding of ITO support, hydrothermal growth of ZnO nanorods, sol-gel deposition of TiO2 (and N-doped TiO2), and photodeposition of Au NPs. Second, the characterization techniques used in realization of this project are described: SEM (Scanning Electron Microscopy), HAADF-STEM and HR-TEM (High Angle Annular Dark Field Scanning Electron Transmission Microscopy and High Resolution Transmission Electron Microscopy), XRD (X-ray Diffraction Analysis), XPS (X-ray Photoelectron Spectroscopy), EDS ‘or EDX’ (Energy Dispersive Spectroscopy) analyses connected with electron microscopy techniques, UV-vis Spectroscopy and DRS (Diffuse Reflectance UV-vis Spectroscopy, TGA-DSC (Thermogravimetry Differential Scanning Calorimetry Analysis), TOC (Total Organic Carbon) analysis, RT-PL (Room Temperature Photoluminescence Spectroscopy), electrochemical techniques including: LSV (Linear Sweep Voltammetry), CV (Cyclic Voltammetry), chronoamperometry, chronopotentiometry, as well as the set-ups elaborated by the author for the purpose of photocatalytic and photoelectrochemical measurements. The main results of the PhD thesis are presented in the third part, Results and Discussion, consisting of four chapters. In the first chapter (Chapter 4.1), the results of the studies on electrochemical seeding of ITO-electrode in Zn(CH3COO)2 solution are presented. The length and width of ZnO nanorods grown by hydrothermal method from Zn(NO3)2 aqueous solution on Zn/ZnO-seeded ITO substrate were shown to depend strongly on initial Zn2+ concentration and the synthesis duration. The arrays of well-separated ZnO ‘obelisk-like’ nanorods of width varied from 100 nm at tips to ~ 300 nm at bottom and average length of 1.9 µm were prepared under optimized conditions, and used as starting point for further fabrication of (core)ZnO/TiO2(shell) composites. In the second chapter (Chapter 4.2), a simple and low-cost sol-gel method was developed in order to form TiO2 thin layers on ZnO nanorods by hydrolysis of titanium(IV) butoxide. The results of studies lead to elaboration of two most distinctive variants of sol-gel procedure that allow to deposit TiO2 layers of controlled thicknesses and different morphology (rugged or compact). The rugged TiO2 layers were obtained after 6 hours of one step sol-gel synthesis followed by calcination of the sample at 450 oC, ensuring formation of anatase-TiO2, whereas the uniform coating of 25 nm – 40 nm thickness was obtained via three successive 30 min-synthesis with the intermediate calcination of the sample after each deposition cycle. The composite containing the rugged TiO2 layer was shown to possess significantly higher activity in model pollutant (methylene blue, MB) degradation and in photoassisted H2O electro-oxidation under 400 nm monochromatic light irradiation. This improved photoactivity was correlated with the composite microstructure and attributed to a higher porosity and better accessibility of ZnO/TiO2 interface region through the rugged TiO2 layer by the reagents. The TiO2 (shell) layers of similar morphology were also prepared by atomic layer (ALD) and chemical vapor deposition (CVD) techniques and it was shown that the composites fabricated by us with the use of simple sol-gel procedure yield comparable (or even higher) photoactivity. Finally, it was confirmed by total organic carbon (TOC) analysis that the ZnO/TiO2 composites elaborated in this work are also active in decomposition of the pollutants in a dumb hill leachate solution (waste water) under 400 nm monochromatic irradiation. In Chapter 4.3 it is shown that the ZnO/TiO2 interface plays a key role in enhancement of photodecomposition of MB under 400 nm illumination. The increase of photocatalytic activity was attributed to the shift of absorption edge of ZnO/TiO2 towards visible light in comparison to that of the ZnO(core)-etched TiO2. Further enhancement of photocatalytic activity of ZnO/TiO2 was achieved through its additional calcination at 450 °C for 3 h. This simple treatment brings 40% increase in the rate of MB decomposition and a two-fold rise of the photocurrent in H2O oxidation. Measurements of open circuit potential (VOC) showed that the improved properties of additionally calcined ZnO/TiO2 composites stem from the decrease of electron-hole recombination rate. STEM (Scanning Transmission Electron Microscopy) studies showed that the additional calcination resulted in formation of voids at the ZnO/TiO2 interface. EDX (Energy Dispersive X-ray) analysis and XPS (X-ray Photoelectron Spectroscopy) results proved that formation of voids is accompanied by the outward diffusion of Zn ions into TiO2 layer and allowed to conclude about the existence of the Kirkendall effect at ZnO/TiO2 interface. Occurrence of this effect observed for the first time at unusually moderate temperature (450 °C) was shown and attributed to a highly defective nature of the surface layer of the ZnO nanorods. In the last chapter (Chapter 4.4), the composites consisting of ITO-supported ZnO nanorods covered with nitrogen-doped titanium dioxide, TiO2(N), shell were decorated with gold nanoparticles (Au NPs) in order to improve their photocatalytic activity under visible light. The photocatalytic properties of ZnO/TiO2/Au and ZnO/TiO2(N)/Au ternary composites were studied under illumination with Xe lamp equipped with a 400 nm cut-off filter. It was found that low Au NPs loading (0.37% at.) resulted in 60% enhancement of photocatalytic decolorization of MB under visible light with respect to the Au-free sample owing to plasmonic effects. Also, a simultaneous N-doping and Au NPs-decoration allows to multiply by three the photocurrent in photoelectrochemical water oxidation at the potential of 0.8 V vs. Ag/AgCl. It was also demonstrated that the Au-decorated composites possess a strong electrocatalytic activity in reduction O2 to active oxygen species (via formation of O2⦁– radicals) under a small negative bias (–0.25 V vs. Ag/AgCl) in dark. Illumination of the polarized sample with visible light was shown to enhance this process resulting in rapid decomposition a model pollutant (MB) even in the presence of Na2SO4. This approach allows to completely overcome a problem of inhibition of the photocatalytic process by dissolved inorganic salts on non-polarized catalysts, thus meeting the aim of promising material for photoelectrocatalytic remediation of waste water, often containing a significant amount of inorganic ions.

Cette thèse concerne la réalisation des films minces d’oxydes et l’étude de leurs propriétés physiques pour les cellules photovoltaïques (PV) et les modules thermoélectriques. Dans une première partie, les propriétés de l’oxyde de titane TiOx (1,45
This thesis concerns the realization of oxide thin films and the study of their properties for photovoltaic or thermoelectric devices. In the first part, the TiOx properties are studied for use as an optically active transparent conductive oxide to put in front of the PV cells or, as optical coupling layer to interpose between the metal reflector and the absorbent layer of a PV cell. The layers are deposited by pulsed laser deposition (PLD). This method allows to get stoichiometric or oxygen deficient layers by controlling the oxygen partial pressure during the growth. The layers are doped with Nb to enhance electrical conductivity and/or with Nd for the conversion of Ultra-Violet photons to Near Infra-Red photons. Insulating and transparent layers, luminescent layers or conducting and absorbent layers are obtained. The TiO₁,₄₅₋₁,₆₀ films show polaronic or bipolaronic conductivity and exhibited the jump of electrical conductivity with jump height and temperature depending on the nature of the dopants. A second part of the manuscript concerns thermoelectricity in which the properties of cobalt calcium oxide are modulated for an efficient conversion of low temperature gradients centered at 300-365K. The control of the oxygen concentration of films allows to obtain the polymorphic phases CaxCoO₂,Ca₃Co₄O₉ and Ca₃Co₄O₆,₄₋₆,₈ having metallic or semiconducting behavior depending on the deposition temperature. The Ca₃Co₄O₆,₄₋₆,₈ films show high Seebeck coefficients (S) ≥ 1 000 μV/K and low electrical resistivity (3.8 to 6 mΩ.cm). Such interesting values have to be confirmed by additional experiments in order to be used as thermoelectric films

碩士
逢甲大學
材料科學所
94
In the present study, titanium dioxide powders concluding sub-micron (denoted as M-TiO2), nanometer-sized (N-TiO2, STO1, and P-25), and nanotube (NT-TiO2), were modified by adsorbing nickel ions with impregnation process. Post heat treating at 500 oC for 4 hours under reductive hydrogen atmosphere was performed. Characteristics of the titanium dioxide powders before and after surface modification were investigated. The EDS results showed that only limited amount of nickel was adsorbed on the TiO2 surface. X-ray diffraction results showed that the relative rutile phase within the N-TiO2 and P-25 powders increased after heat treatment, while no distinguishable differences can be observed for M-TiO2 powders. Synchrotron X-ray absorption spectra revealed that nickel ions adsorbed on N-TiO2 and NT-TiO2 powders were reduced to nickel metal after heat treatment. While the reduction of nickel ion was not successfully in the other powders. Strong-metal support interaction phenomenon was not observed for all the powders examined in the present study. P25-TiO2 powders after Ni modification exhibited the best photocatalytic properties where methylene blue can be decomposed completely after 3 hours under UV radiation.

α-Al2O3 is an important refractory material which has numerous technical applications: as an in situ growing self-healing oxide scale, as a massive material and as reinforcement fibres in composites. For modelling diffusion controlled processes (creep, sintering, alpha-alumina scale growth on aluminium bearing Fe or Ni base alloys) it is necessary to study self-diffusion of the constituent elements.

Leung Cheuk-wan.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2006.
Includes bibliographical references.
Abstracts in English and Chinese.
Abstract --- p.i
Abstract (Chinese) --- p.ii
Acknowledgement --- p.iii
Table of Contents --- p.v
Lists of Tables --- p.ix
Lists of Figures --- p.x
Chapter Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- TiO2 Photocatalysis --- p.1
Chapter 1.1.1 --- Mechanisms of TiO2 Photocatalysis --- p.1
Chapter 1.2 --- Visible Light Photocatalyst --- p.4
Chapter 1.2.1 --- Preparation of Visible Light Ti02 Photocatalysts --- p.5
Chapter 1.2.1.1 --- Dye Sensitization --- p.5
Chapter 1.2.1.2 --- Metal Doping --- p.6
Chapter 1.2.1.3 --- Coupling of Semiconductors --- p.6
Chapter 1.2.1.4 --- Nonmetal Doping --- p.7
Chapter 1.3 --- Enhanced TiO2 Photocatalytic Activity under UV Light --- p.8
Chapter 1.3.1 --- Preparation of TiO2 Photocatalyst with Enhanced Activity in UV Light --- p.8
Chapter 1.3.1.1 --- Loading of Metal --- p.8
Chapter 1.3.1.2 --- Impurity Co-doping --- p.9
Chapter 1.3.1.3 --- Morphological Control --- p.10
Chapter 1.3.1.4 --- Increasing Surface Area --- p.10
Chapter 1.4 --- Summary --- p.11
Chapter 1.6 --- Aim of This Research and its Significance --- p.12
Chapter 1.7 --- References --- p.13
Chapter Chapter 2 --- Preparation of N-doped TiO2 with Enhanced Surface Area: A Detailed Characterization and Mechanism --- p.19
Chapter 2.1 --- Introduction --- p.19
Chapter 2.2 --- Experimental --- p.21
Chapter 2.2.1 --- Materials and Catalyst Preparation --- p.21
Chapter 2.2.2 --- Characterization --- p.21
Chapter 2.2.3 --- Photocatalytic Activity --- p.23
Chapter 2.3 --- Results and Discussion --- p.24
Chapter 2.3.1 --- XRD Analysis --- p.24
Chapter 2.3.2 --- UV-Vis Absorption Spectroscopy and Bandgap Energies --- p.27
Chapter 2.3.3 --- N2 Sorption Analysis --- p.29
Chapter 2.3.4 --- SEM Analysis --- p.33
Chapter 2.3.5 --- TEM Analysis --- p.35
Chapter 2.3.6 --- FT-IR Spectroscopy --- p.36
Chapter 2.3.7 --- Raman Spectroscopy --- p.39
Chapter 2.3.8 --- XPS Studies --- p.44
Chapter 2.3.9 --- PL Measurements --- p.49
Chapter 2.3.10 --- Photocatalytic Activity Measurements --- p.50
Chapter 2.3.11 --- Advantages of Using Urea as a N-doping Source --- p.54
Chapter 2.3.12 --- Mechanisms for N-doping --- p.56
Chapter 2.4 --- Conclusions --- p.58
Chapter 2.5 --- References --- p.59
Chapter Chapter 3 --- Preparation of Nanoporous Interstitial B-doped TiCO2 with Enhanced Photocatalytic Activity --- p.63
Chapter 3.1 --- Introduction --- p.63
Chapter 3.2 --- Experimental --- p.65
Chapter 3.2.1 --- Materials and Catalyst Preparation --- p.65
Chapter 3.2.2 --- Characterization --- p.66
Chapter 3.2.3 --- Photocatalytic Activity --- p.67
Chapter 3.3 --- Results and Discussion --- p.68
Chapter 3.3.1 --- XRD Analysis --- p.68
Chapter 3.3.2 --- UV-Vis Absorption Spectroscopy and Bandgap Energies --- p.71
Chapter 3.3.3 --- N2 Sorption Analysis --- p.73
Chapter 3.3.4 --- SEM and TEM --- p.76
Chapter 3.3.5 --- FT-IR Spectroscopy --- p.80
Chapter 3.3.6 --- Raman Spectroscopy --- p.82
Chapter 3.3.7 --- PL Measurements --- p.84
Chapter 3.3.8 --- XPS Studies --- p.85
Chapter 3.3.9 --- Photocatalytic Activity Measurements --- p.89
Chapter 3.3.10 --- State and Form of Boron in TiO2 Lattice and its Effects --- p.91
Chapter 3.4 --- Conclusions --- p.93
Chapter 3.5 --- References --- p.94
Chapter Chapter 4 --- Conclusions --- p.97

碩士
長庚大學
電子工程學系
102
The purpose of this research is to realize a novel method of potassium ion sensing membrane fabrication which is compatible with CMOS technology. Ion sensitivity platform is selected as Electrolyte Insulator Silicon (EIS) of Ion Sensitivity Field Effect Transistor (ISFET). In this research, Titanium Nitride, popularly applied to Semiconductor process, is used as the basic sensing membrane of EIS. In this research, adjusting different N2 ratio and different power of Si target in sputtering, sensitivity of sensing membrane could be improved. Besides, the surface roughness, sensitivity and linearity could be also modified by rapid thermal anneal process. The advantages of inorganic adjustment are stableness and consistency, contributing mass production and quality control. The Titanium Nitride shows that, pH sensitivity is 61.3mV/pH and linearity is 99% when the N2 ratio is 20%. Doping silicon dioxide with RF power at 150W, potassium ion sensitivity is 21.7mV/pK and linearity is 99.05%, selective coefficients KK,H is 3.87.

碩士
中原大學
生物環境工程研究所
104
In this study, the waste fluorescence powder used acid leaching to rare earth metal leach out and doped with titanium dioxide (TiO2). This reduced the TiO2 energy gap, making the light source can be changed to visible light from ultraviolet light, which can effectively reduce energy problem. Membrane treatment procedure for the widespread use of the current technology. Literature indicated by photocatalyst coating material was applied on the membrane hydrophilic, it could effectively improve performance and reduced the impact of fouling materials. In this study, the modified PVDF membrane by low temperature plasma and preparation of lanthanum-doped titanium dioxide coated on it. The modified membrane surface properties and photocatalytic reaction which reduced the fouling material and eliminate it. The results showed that in acid leaching, use 5M nitric acid and solid-liquid ratio is 1: 5；1M HNO3 → 5M HNO3 → 5M HCl combination leaching 6 hours can obtained better lanthanum content. Photocatalytic reaction results showed that the amount of additive with 1wt% lanthanum had best additive amount of experiments. It showed lanthanum-doped titanium dioxide the amount exceeds 3wt%, the photocatalytic degradation efficiency tends to be slow. Experimental test different light sources the display blue light was best, and tested for their photocatalyst repeatability results show times can be repeated up to 11 times. One wt% La-TiO2 coated on the membrane, its photocatalytic degradation efficiency of the dye decreased, but still has the ability of photocatalytic. La-TiO2/PVDF membrane is hydrophilic but it lead to increased pressure through the mold.

碩士
明志科技大學
材料工程研究所
99
In this study, calculations of titanium dioxide doped with different elements of the electronic structure changes and formation energy with concentration from first principles. Density functional theory (DFT) in describing the band structure is quite successful for many systems, but no longer applicable for strongly correlated, in order to correct the description of localized electron orbitals, we use DFT + U (Hubbard U correction) method for computing the model structure. From the simulation show that N impurities introduce some energy levels above the top of the O 2p valence band.Density of states analysis, the major component of the conduction band of anatase TiO 2 is the Ti 3d states, while that of the valence band is the O 2p states. Such as titanium dioxide in the presence of oxygen vacancies, Titanium atoms near the oxygen vacancies into the trivalent positive, Ti3+ produced in the band gap and bottom of conduction band, And adding nitrogen-doped is filled N 2p orbital, Such as nitrogen substitutet with oxygen vacancies and found that the receptor produced by nitrogen substitute to fill the order by electroni. Double doping due to different doping distance electronic structure, such as the closest bonds, P orbitals of nitrogen atoms and the existence of electronic vacancies more than a single doping, it can be found in the density map, due to band to band, there are two different quantum state distribution. Far bond, the nitrogen and iron can be seen as a single doping.

Thesis (Ph. D. (Physics)) -- University of Limpopo, 2016.
Single and double doped nanometric powders of Single and double doped nanometric powders of titanium dioxide (TiO2) were synthesised by the sol-gel process using titanium isopropoxide (TTIP) as the precursor. For comparison, an undoped sample was also prepared. The metal dopants, Ag and Cu, were used at doping levels of 5% molar weight. The samples were dried at 100°C in air and post annealing was done at 300°C, 600°C, 900°C and 1100°C. Structural characterisation of the samples was carried out by X-ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Energy dispersive X-ray Spectrometry (EDS) techniques. Most samples annealed at the 300°C temperature (and lower) revealed the predominantly-anatase phase, while those annealed at 900°C and above were rutile-only. The double-doped powder that was annealed at 300°C was found to be constituted by anatase and brookite phases (with the dopants incorporated into the TiO2 matrix), and the one annealed at 600°C was a mixture of brookite and rutile. The results suggest that multiple doping of titania may favour a two-phase structure at lower temperatures than singly-doped powders. The co-existence of brookite with anatase is believed to be responsible for the enhancement of anatase to rutile transformation in the double-doped sample. UV-visible (UV-vis) and Photoluminescence (PL) measurements were also carried out to study the optical properties of the TiO2 nanoparticles. This revealed the active PL band at around 440 nm. By narrowing the band gap, the double-doped powders that exhibited the brookite phase, again showed improved visible light photo absorption over the other samples, with a significant shift of the absorption edge to shorter wavelengths. Further, PL spectra revealed a change in PL intensity with phase change, as well as the presence of exciton energy levels at the base of the conduction band. The changes in the electrical conductivities of representative anatase and rutile TiO2 nanopowders upon exposure to water-vapour, ammonia (NH3) and hydrogen (H2) were also investigated. Sensing measurements for water-vapour was done at room temperature for various humidity levels ranging from 5.4% RH to 88.4% RH. The detection of NH3 and H2 gases were carried out at temperatures extending from room temperature to 350°C and over concentration ranges of 25 sccm to 500 sccm and 15 v sccm to 200 sccm respectively. The gas-sensing results show that the sol-gel fabricated TiO2 nanoparticles (particularly in anatase form), has excellent fast and stable dynamic responses to humidity, NH3 and H2. They feature good sensitivities, even at a low operating temperatures. However, acceptor behaviour, for which there was a conductivity switch from n-type to p-type, was recorded for the Ag-doped rutile powders at operating temperatures of 300ºC and 350ºC. Overall, the double-doped sample annealed at 300ºC was deemed the most promising candidate for gassensing. (TiO2) were synthesised by the sol-gel process using titanium isopropoxide (TTIP) as the precursor. For comparison, an undoped sample was also prepared. The metal dopants, Ag and Cu, were used at doping levels of 5% molar weight. The samples were dried at 100°C in air and post annealing was done at 300°C, 600°C, 900°C and 1100°C. Structural characterisation of the samples was carried out by X-ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Energy dispersive X-ray Spectrometry (EDS) techniques. Most samples annealed at the 300°C temperature (and lower) revealed the predominantly-anatase phase, while those annealed at 900°C and above were rutile-only. The double-doped powder that was annealed at 300°C was found to be constituted by anatase and brookite phases (with the dopants incorporated into the TiO2 matrix), and the one annealed at 600°C was a mixture of brookite and rutile. The results suggest that multiple doping of titania may favour a two-phase structure at lower temperatures than singly-doped powders. The co-existence of brookite with anatase is believed to be responsible for the enhancement of anatase to rutile transformation in the double-doped sample. UV-visible (UV-vis) and Photoluminescence (PL) measurements were also carried out to study the optical properties of the TiO2 nanoparticles. This revealed the active PL band at around 440 nm. By narrowing the band gap, the double-doped powders that exhibited the brookite phase, again showed improved visible light photo absorption over the other samples, with a significant shift of the absorption edge to shorter wavelengths. Further, PL spectra revealed a change in PL intensity with phase change, as well as the presence of exciton energy levels at the base of the conduction band. The changes in the electrical conductivities of representative anatase and rutile TiO2 nanopowders upon exposure to water-vapour, ammonia (NH3) and hydrogen (H2) were also investigated. Sensing measurements for water-vapour was done at room temperature for various humidity levels ranging from 5.4% RH to 88.4% RH. The detection of NH3 and H2 gases were carried out at temperatures extending from room temperature to 350°C and over concentration ranges of 25 sccm to 500 sccm and 15 v sccm to 200 sccm respectively. The gas-sensing results show that the sol-gel fabricated TiO2 nanoparticles (particularly in anatase form), has excellent fast and stable dynamic responses to humidity, NH3 and H2. They feature good sensitivities, even at a low operating temperatures. However, acceptor behaviour, for which there was a conductivity switch from n-type to p-type, was recorded for the Ag-doped rutile powders at operating temperatures of 300ºC and 350ºC. Overall, the double-doped sample annealed at 300ºC was deemed the most promising candidate for gassensing.

碩士
國立高雄海洋科技大學
微電子工程研究所
102
The TiO2:N2 relative humidity sensing devices were accomplished in accordance with semiconductor structures. The optimum growth parameter of TiO2:N2 sensing film was decided to fabricate the well-defined relative humidity sensor. In this study, the optimum growth temperature of TiO2:N2 sensing film is at 27oC with well properties in the surface morphology, crystallization, and electronic transportation. By the Hall effect measurement, the TiO2:N2 sensing film is revealed the n-type in carrier type. The carrier concentration and mobility of TiO2:N2 sensing films are 3.4×1018 cm3 and 3.4 cm2/Vs respectively. The resistivity and conductivity of TiO2:N2 sensing films are also 1.8Ω-cm and 2.9/Ω-cm respectively. The TiO2:N2 relative humidity sensing devices were fabricated by using photo lithography and lift-off techniques. The adsorption time and desorption time of TiO2:N2 relative humidity sensing devices are respectively 30 seconds from 30% RH up to 90% RH and 65 seconds from 90% RH down to the 30% RH. The sensitivities of TiO2:N2 relative humidity sensing devices in hysteresis and I-V characteristics are respectively 0.12 and 10.41.

碩士
國立清華大學
材料科學工程學系
94
Vanadium oxides compound (V2O3, V2O5, and VO2, etc.) is a well known thermal-sensitive material, undergoing a phase transition from a low temperature, semiconducting state to a high temperature, metallic state. This change is accompanied by an abrupt resistivity modification near room temperature, made vanadium oxide a candidate material for bolometric sensors application. In this application, the bolometer sensitivity is directly related to the temperature coefficient of resistance (TCR), defined as the slope of log resistivity. To produce a highly sensitive uncooled microbolometer, the development of a thermometric material with a high temperature coefficient of resistance is essential. In this worker, Vanadium oxide thin film was fabricated by metal organic chemical vapor deposition (MOCVD) from pure vanadium tri-isopropoxide oxide precursor. Furthermore, we used Titanium as a dopant during the MOCVD process. Using MOCVD method, offers advantages of both high deposition rate, low fabricated temperature, and particular the ability easily to tailor the chemical composition, The correlations between the crystal structures and the growth recipes were investigated by the x-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and x-ray photoelectron spectroscopy (XPS). Also, the electrical characteristics of vanadium oxide thin films resulted from the crystal structures and phase changes were measured by four-point probe equipment. Compared with pure vanadium oxide thin films, titanium-doped vanadium oxide thin films obviously showed a higher temperature coefficient of resistance, lower resistivty and negligible electrical hysteresis. It can be concluded that the developed vanadium-titanium oxide is an excellent electrochromic material for the fabrication of high performance uncooled mircobolometer.

The present project has made a comprehensive assessment of the effect of Nb doping on various charge-transfer related properties of TiO2. Of particular focus, the electrical properties of Nb-doped TiO2 (0.65 at %) have been investigated using the simultaneous measurement of electrical conductivity and thermoelectric power. This investigation was undertaken at elevated temperatures (1073 K -- 1298 K) in equilibrium with a gas phase of controlled oxygen activity (10-10 Pa < p(O2) < 75 kPa). In addition, the effect of segregation on the surface versus bulk composition of Nb-doped TiO2 was also investigated at a function of temperature and oxygen activity. Specifically, the following determinations were undertaken: The effect of oxygen activity, p(O2) and temperature on both electrical conductivity and thermoelectric power The effect of Nb on the defect disorder and related electrical properties of TiO2 The determination of equilibration kinetics and the associated chemical diffusion data for Nb-doped TiO2 The determination of Nb bulk diffusion in TiO2 The effect of p(O2), temperature and dopant content on Nb segregation and the related surface composition of Nb-doped TiO2 The obtained electrical properties enable the determination of a defect disorder model for Nb-doped TiO2, which may be considered within the following p(O2) regimes: Strongly Reduced Regime. In this regime, the predominant ionic defect was anticipated to be oxygen vacancies compensated electronically by electrons. While the transition to this regime (from higher p(O2)) was clearly observed, the predominant defect disorder existing beyond this transition was not confirmed due to an inability to obtain sufficiently low oxygen activity. Metallic-type conductivity behaviour was observed within this transition region. Reduced Regime I. In this regime, the predominate defect disorder defined by the electronic compensation of incorporated Nb ions by electrons was clearly observed. Reduced Regime II. In this regime, the predominate defect disorder defined by the ionic compensation of incorporated Nb ions by quadruply-charged titanium vacancies, was clearly observed. The present project included the determination of diffusion data which included: Temperature dependence of 93Nb tracer diffusion in single crystal TiO2 over the temperature range 1073 K -- 1573 K Chemical diffusion coefficient over the temperature range 1073 K -- 1298 K and oxygen activity range, 10-10 Pa < p(O2) < 75 kPa These pioneering studies are significant as they enable the prediction of the processing conditions required to reliably 1) incorporate Nb into the TiO2 lattice, and 2) achieve equilibrium with the gas phase. Finally, the present project included investigations on the effect of Nb segregation on the surface composition of Nb-doped TiO2, with the following outcomes: Due to segregation, the surface can be significantly enriched in Nb compared to the bulk The extent of enrichment increases as the bulk Nb content or the oxygen activity is decreased Following enrichment, the surface Nb concentration could be sufficiently high to assume a unique surface phase The outcomes of the present project are significant as they can enable the processing of TiO2 with enhanced charge transport and controlled surface properties.

碩士
國立東華大學
材料科學與工程學系
106
In this study, by using hydrothermal method to synthesis titanium dioxide aggregation. The particle size was about 300 nanometer to 1 micrometer to achieve high scattering effect, and the morphology was similar with hydrangea. By mixing hydrangea TiO2 and P25-TiO2, makes more fitting with scattering electrode and the working electrode, so that efficiency can be improved. 　　Graphene Oxide can reduce the recombination of electrons in the electrolyte, we used freeze-drying method to get porous graphene oxide, and added to electrolyte, so that pores make the electrolyte more filling, increasing current transfer as well, enhancing the efficiency to dye-sensitized solar cells.

Transparent conductive oxides (TCOs) are key functional materials in existing and future electro-optical devices in the fields of energy efficiency, energy generation and information technology. The main application of TCOs is as thin films transparent electrodes where a combination of maximum electrical conductivity and transmittance in the visible to nearinfrared spectral range is required. However, due to the interdependence of the optical properties and the free electron density and mobility, respectively, these requirements cannot be achieved simultaneously in degenerately doped wide band-gap oxide semiconductors. Therefore, a detailed understanding of the mechanisms governing the generation of free charge carriers by extrinsic doping and the charge transport in these materials is essential for further development of high performance TCOs and corresponding deposition methods. The present work is aimed at a comprehensive investigation of the electrical, optical and structural properties as well as the elemental composition of (Al,Ga) doped ZnO and Nb doped TiO2 thin films prepared by pulsed DC reactive magnetron sputtering. The evolution of the film properties is studied in dependence of various deposition parameters through a combination of characterization techniques including Hall-effect, spectroscopic ellipsometry, spectral photometry, X-ray diffraction, X-ray near edge absorption, Rutherford backscattering spectrometry and particle induced X-ray emission. This approach resulted in the development of an alternative process control method based on the material specific current-voltage pressure characteristics of the reactive magnetron discharge which allows to precisely control the oxygen deficiency of the sputter deposited films. Based on the experimental data, models have been established that describe the room temperature charge transport properties and the dielectric function of the obtained ZnO and TiO2 based transparent conductors. On the one hand, these findings allow the prediction of material specific electron mobility limits by identifying the dominating charge carrier scattering mechanisms. On the other hand, new insight is gained into the origin of the observed transition from highly conductive to electrically insulating ZnO layers upon the incorporation of increasing concentrations of Al at elevated growth temperatures. Moreover, the Al and Ga dopant activation in ZnO have been quantified systematically for a wide range of Al concentrations and deposition conditions. A direct comparison of the Ga and Al doping efficiency demonstrates that Ga is a more efficient electron donor in ZnO. Further, it has been shown that high free electron mobilities in polycrystalline and epitaxial Nb:TiO2 layers can be achieved by reactive magnetron sputtering of TiNb alloy targets. The suppression of rutile phase formation and the control of the Nb dopant activation by fine tuning the oxygen deficiency have been identified as crucial for the growth of high quality TiO2 based TCO layers.

The aim of this diploma thesis is deposition of TiO2 thin films onto different types and sizes of substrates, and some of these layers dope by iron or silver. During the work was range of TiO2 layers created using a method of physical vapor deposition namely magnetron sputtering. For these processes was chosen the Dreva ARC 400 Hard Material Coating Plant device. The main aim of these depositions was to attempt to create TiO2 thin films on a substrates of larger surface than its in average laboratory processes usual. For this purpose were TiO2 layers deposited onto square glass plates of side length 10 cm. For comparsion and analysis were also as a substrates used microscope slides and fragments of silicon wafers. These substrates were used for testing of photocatalytic activity and on surface morphology (SEM). The theoretical part of this thesis aims to a methods of deposition TiO2 layers and their characteristics. In the experimental part is the used coating equipment and parameters of each deposition process described. Further the characteristics and results of individual experiments are described.

MSc (Physics)
Department of Physics
Titanium dioxide (TiO2) is considered to be an ideal semiconductor for photocatalysis because of its high stability, low cost and safety towards both humans and the environment. Doping TiO2 with different elements has attracted much attention as the most important way of enhancing the visible light absorption, in order to improve the efficiency of the dye sensitized solar cells (DSSCs). In this study, first principle density functional theory was used to investigate electronic and optical properties of bulk anatase TiO2, undoped, and ruthenium (Ru) and strontium (Sr) doped anatase TiO2 (1 0 0) surface. Two different doping approaches i.e., substitutional and adsorption mechanisms were considered in this study. The results showed that absorption band edges of Ru and Sr-doped anatase TiO2 (1 0 0) surface shift to the long wavelength region compared to the bulk anatase TiO2 and undoped anatase TiO2 (1 0 0) surface. Also, the results revealed that the band gap values and the carrier mobility in the valence band, conduction band and impurity energy levels have a synergetic influence on the visible-light absorption and photocatalytic activity of the doped anatase TiO2 (1 0 0) surface. Furthermore, according to the calculated results, we propose the optical transition mechanisms of Ru and Sr-doped anatase TiO2 (1 0 0) surface. Thus, we conclude that the visible light response of TiO2 can be modulated by doping with both Ru and Sr. However, Sr-doped system shows higher photocatalytic activity than the Ru-doped system. The study has successfully probed the interesting optical response mechanism of TiO2 (1 0 0) surface.
NRF

Dissertação de mestrado em Ciências e Tecnologias do Ambiente (área de especialização em Energia)
Processos de oxidação avançados (POA’s) têm demostrado ser um método efetivo para o tratamento de efluentes da indústria têxtil. Os POA’s oxidam as moléculas orgânicas, como corantes, utilizando radicais hidroxilo (OH•) gerados em reações de fotocatálise. O dióxido de titânio (TiO2) é o catalisador mais associado com este processo, mas apresenta a desvantagem de apenas ser ativado com radiação ultravioleta (UV). Para obter um catalisador funcional na zona do espectro visível utilizou-se antes o titanato de cobalto (CoTiO3) dopado com zinco e/ou flúor. Neste trabalho foram preparadas de perosvkites mistas com propriedades catalíticas de (ZnxCo1-x)TiO3, dopadas com flúor. As partículas foram caracterizadas por DRX e espectrometria UV/Vis. Os testes para avaliar a capacidade fotocatalítica: ensaios de fotodegradação de moléculas orgânicas usando o azul de metileno como modelo e medição da capacidade de geração de radicais hidroxilo através da fluorescência do ácido 2-hidroxitereftálico. Os catalisadores que apresentaram maiores taxas de catálise foram aqueles com maior conteúdo de cobalto e os dopados com flúor.
Advanced oxidation processes (AOPs) have proven to be an effective method for the treatment of effluents from the textile industry. POA's oxidize organic molecules, such as dyes, using hydroxyl radicals (OH •) generated in photocatalysis reactions. Titanium dioxide (TiO2) is the catalyst most associated with this process, but it has the disadvantage of only being activated with ultraviolet (UV) radiation. To obtain a functional catalyst in the visible spectrum, TiO2 was doped with the cobalt, zinc and fluorine ions. In this work were prepared perovskites (ZnxCo1-x) TiO3, doped with fluorine with catalytic properties. The particles were characterized by XRD and UV / Vis spectrometry. Tests were carried out to evaluate photocatalytic capacity in two ways: photodegradation tests of organic molecules using methylene blue as a model and fluorometry for hydroxyl radical generation capacity. Higher rates of catalysis presented in those with higher content of cobalt and doped with fluoride.