No description available.

The formation of thick, robust, mesoporous titania films is of particular interest and the focus of this thesis has been the study and comparison of the surfactant templated formation of such materials by three methods. film structure has been studied using TEM and small angle X-ray and neutron scattering while formation was studied using Brewster angle microscopy and X-ray and neutron reflectometry. Repetitive dip-coating was used to produce films for development into dye sensitized solar cells allowing development of cells of reasonable efficiency when four depositions were used. This research showed that repetitive deposition does not necessarily lead to a linear increase in film thickness, as subsequent depositions may be thinner making the future application of this method for solar cells problematic. In contrast to dip-coating, a fluorinated surfactant was used in a largely alcohol solvent to produce mesostructured films at the air-solution interface. Film formation occurred by a surface driven mechanism via addition of individual precursors and micelles producing a lamellar structure in-situ. After removal from the interface a cubic phase developed after drying of the film. Although films are not stable to calcination the calcined material remains porous. The surfactant templated formation of ZnO films at the air-solution interface was also studied. The di-block copolymer PEPEG2250 was also used to template titania films at the air-solution interface from alcoholic solvent. Film formation occurred via a bulk driven mechanism. Although these films were found to be disordered at the interface and not stable to calcinations they were unusually robust and self supporting after removal from the interface. Studies of subphase development allowed the first time-resolved observation of surfactant templated titania particle formation.

The main objective of this work was to study the applicability of Nano porous/Nanocrystalline TiO2 films for serving the growing demand for fast accurate and low cost air quality analysis techniques. The sensitivity of response to variations in microstructure pointed the way to obtain controlled, reproducible and regular microstructures with critical dimensions proportionate with the Debye- length of the oxide. This work aimed to study the sensor properties of thin films of Nanocrystalline Titania and Titania nanotubes at room temperature. Nano porous/Nanocrystalline TiO2 films were fabricated through evaporation driven convection/sol-gel method by controlling the process conditions. We also fabricated ordered TiO2 nanotube arrays by carefully controlling the anodization conditions. TiO2 nanotube arrays were fabricated through potentiostatic anodization of a Ti metal sheet in various electrolyte mediums. The electrolyte mediums consisted of mixtures of acids ranging from HF, HCl, HNO3, H2SO4, H3PO4 and CH3COOH and polar organic solvents like C2H6OS(DMSO) and C2H4(OH)2(Ethylene Glycol) . Well ordered films consisting of TiO2 nanotube arrays (25 μm to 250 μm in length) were obtained. Contacts were deposited on to the annealed samples. Capacitive gas sensors were fabricated and their response to ammonia gas was evaluated.

The photocatalytic conversion of carbon dioxide (CO2) to methanol was investigated. The procedure for the carbon dioxide conversion was carried out using a small scale filter type photocatalytic reactor. In conducting the experiments, carbon dioxide mixed with water vapor was discharged into the photocatalytic reactor in the presence of a catalyst and light irradiation from a UV lamp for conversion to methanol. The catalyst that were used for the experiments were titanium dioxide (titania) and copper-loaded titania which were impregnated on a ceramic filter that was initially treated with gamma-alumina which was a good catalyst support for the catalyst. SEM, XRD and particle size analysis was performed as a means of characterization of the catalyst. The effect of the flow rate of carbon dioxide on the conversion process using a UV lamp with a wavelength of 254 nm was studied.

Neste trabalho foram preparados materiais híbridos do tipo silicatos organicamente modificados (ormosils) contendo fosfotungstato, [PW12O40]-3 e dopados com nanopartículas de TiO2. O objetivo é obter uma ação sinérgica destes dois fotocatalisadores na prevenção de formação de biofilmes e/ou sua fotodegradação. O fotocatalisador principal no sistema é o fosfotungstato, sendo o co-adjuvante o TiO2. Sendo assim, procurou-se manter a concentração deste no menor nível possível. Os materiais foram caracterizados por espectroscopias vibracionais, espectroscopia de fotoelétrons de raios X (XPS), Fluorescência de Raios X, Microscopia de força atômica e Microscopia eletrônica de varredura (MEV). Os filmes não mostraram eficácia na fotodegradação de biomoléculas como fosfolipídios encontrados na membrana celular. Os ensaios de inibição de crescimento de biofilmes de Escherichia coli sobre os ormosils mostraram que a maior inibição de bactérias é do filme contendo maior teor de nanopartículas de titânia portanto, são bons candidatos para filmes e revestimentos bactericidas/bacteriostáticos a serem usados em máscaras respiratórias, revestimentos de superfícies em salas de cirurgia e em filtros de ar em sistemas fechados (sistemas de ar condicionado e ventilação em geral). / This thesis deals with hybrid materials named organically modified silicates (Ormosils) with phosphotungstate, [PW12O40]-3 , and doped with TiO2 nanoparticles. The aim was to achieve a synergic action between both photocatalysts resulting on a more efficient coating for inhibition of the biofilm growing and/or its photodegradation. The photocatalyst in main system is the phosphotungstate, being the co-adjuvant the TiO2. Therefore, we tried to maintain the concentration of this at the lowest level possible The materials were characterized by vibrational spectroscopies, X-Ray Photoelectron Spectroscopy, X- ray Fluorescence Spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy. The films were unable to photodegradate biomolecules films such as phospholipids as well as they display interesting inhibition capacity against formation of biofilm of E.Coli bacteria. The tests of inhibition of growth of Escherichia coli biofilms on the ormosils showed that a greater inhibition of bacterias exists in the film containing higher content of nanoparticles of titania. Therefore, they are good candidates for bactericidal films and coatings to be used in respirators, surface coatings in surgery rooms and air filters in closed systems (systems of air conditioning and ventilation in general).

Neste trabalho foram preparados materiais híbridos do tipo silicatos organicamente modificados (ormosils) contendo fosfotungstato, [PW12O40]-3 e dopados com nanopartículas de TiO2. O objetivo é obter uma ação sinérgica destes dois fotocatalisadores na prevenção de formação de biofilmes e/ou sua fotodegradação. O fotocatalisador principal no sistema é o fosfotungstato, sendo o co-adjuvante o TiO2. Sendo assim, procurou-se manter a concentração deste no menor nível possível. Os materiais foram caracterizados por espectroscopias vibracionais, espectroscopia de fotoelétrons de raios X (XPS), Fluorescência de Raios X, Microscopia de força atômica e Microscopia eletrônica de varredura (MEV). Os filmes não mostraram eficácia na fotodegradação de biomoléculas como fosfolipídios encontrados na membrana celular. Os ensaios de inibição de crescimento de biofilmes de Escherichia coli sobre os ormosils mostraram que a maior inibição de bactérias é do filme contendo maior teor de nanopartículas de titânia portanto, são bons candidatos para filmes e revestimentos bactericidas/bacteriostáticos a serem usados em máscaras respiratórias, revestimentos de superfícies em salas de cirurgia e em filtros de ar em sistemas fechados (sistemas de ar condicionado e ventilação em geral). / This thesis deals with hybrid materials named organically modified silicates (Ormosils) with phosphotungstate, [PW12O40]-3 , and doped with TiO2 nanoparticles. The aim was to achieve a synergic action between both photocatalysts resulting on a more efficient coating for inhibition of the biofilm growing and/or its photodegradation. The photocatalyst in main system is the phosphotungstate, being the co-adjuvant the TiO2. Therefore, we tried to maintain the concentration of this at the lowest level possible The materials were characterized by vibrational spectroscopies, X-Ray Photoelectron Spectroscopy, X- ray Fluorescence Spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy. The films were unable to photodegradate biomolecules films such as phospholipids as well as they display interesting inhibition capacity against formation of biofilm of E.Coli bacteria. The tests of inhibition of growth of Escherichia coli biofilms on the ormosils showed that a greater inhibition of bacterias exists in the film containing higher content of nanoparticles of titania. Therefore, they are good candidates for bactericidal films and coatings to be used in respirators, surface coatings in surgery rooms and air filters in closed systems (systems of air conditioning and ventilation in general).

Photocatalytic membranes have been designed using two types of fine-scale alumina fibres, namely Nano Alumina Fibre (NAF) from Metallurg Engineering, Estonia and commercially available Saffil® Alumina Fibre (SAF) produced by Saffil Limited, UK. NAF fibres have an average diameter of about 15 nm and SAF about 4 μm. Membranes were produced in various ways. The fibre network architecture within the membranes, along with their porosity, specific surface area and mechanical properties, have been examined. These NAF-SAF membranes were impregnated with titania-based sol-gel coatings, to produce photocatalytic membranes. Their mechanical properties, specific surface area and flow properties were assessed and photocatalytic potential was measured by studying rates of degradation of aqueous dye solution. Membranes with photo-active top layers were designed by sedimentation of a fibrous layer of NAF-SAF, containing titania nanoparticles on a pre-sedimented support layer. Two types of photocatalyst were used, one a commercially available anatase nanopowder and the other silver-coated anatase. The latter was produced via modification of the first. Optimisation of the nanoparticle loadings was performed via assessing their photocatalytic efficiency. Specific permeability values were obtained experimentally and by prediction from the pore architecture. A novel form of photo-active membrane was designed by direct casting of milled SAF and titania-based sol-gel into circular moulds. Effects of fibre milling time and fibre to sol-gel ratio on their performance were studied, besides mechanical properties, porosity and specific surface area. Their flow properties and photocatalytic efficiency were also examined. Due to the availability of these fibres, especially the high production rates (kg/h range) and low cost of NAF, these membranes offer potential for large scale application.

The hydrophobicity of a titania surface was increased by adsorption of octadecyltrihydrosilane (OTHS). The modified titania surface was characterised using a number of techniques: tapping mode AFM, streaming potential, X-Ray photoelectron spectroscopy and contact angle measurements. With a partial surface coverage of OTHS, a bell-shaped dependence of contact angle with respect to pH was observed, with the maximum advancing contact angle occurring at the point of zero charge of the titanium dioxide substrate. The contact angle change was also influenced by the surface coverage and salt concentration. At extreme pH values there was no further decrease in the contact angle, i.e. saturation occurred. A thermodynamic model was used to describe the influence of surface charge on the contact angle. The results were interpreted as a reduction in the solid-liquid interfacial free energy. The model described the results well until the point where saturation occurred.

TiO2. Structural and electronic properties of TiO2 polymorphs denser than rutile, i.e. £\-PbO2-, baddeleyite, fluorite, and cotunnite-type were calculated by a first-principle pseudo-potential method based on density functional theory with local density approximation. Using experimental and theoretical lattice parameters of ambient TiO2, i.e. anatase and rutile as standard, the fluorite-type TiO2 has the narrowest band gap among the post-rutile phases. This character is important for the potential applications as visible-light-responsive photocatalyst. In additional to the bulk properties of dense TiO2 polymorphs the surface energies of

This study combined photocatalytic technology with activated carbon adsorption to decompose gaseous pollutants. Gaseous pollutants were initially adsorbed and concentrated by activated carbon and could be further decomposed more effectively by photocatalytic technology. This study coated TiO2 on the activated carbon fiber (ACF) by a sol-gel process for conducting the adsorption and decomposition of acetone in a batch reactor. Operating parameters investigated in this study included the initial concentration of acetone (13.6 £gM and 27.2 £gM), reaction temperature (50¢J~70¢J), oxygen concentration (0.5%~20%), and water vapor (0 £gM~244.9 £gM). The incident UV light of 365 nm was irradiated by a 15-watt low-pressure mercury lamp placing above the photocatalytic batch reactor. The ACF coated with TiO2 was placed in the center of the reactor. Acetone was injected into the reactor to conduct photocatalytic tests. Reactants and products were analyzed quantitatively by a gas chromatography with electron capture detector (GC/ECD) and a flame ionization detector followed by a methaneizer (GC/FID-Methaneizer). Results from the photocatalysis tests indicated that, among the commercial TiO2 (Degussa P-25), NO3-/TiO2 and SO42-/TiO2, SO42-/TiO2 had the best photoactivity reduced acetone concentration and reaction time substantially. The end products was mainly CO2 and CO, which resulted in the mineralization ratio above 95%. Results from the operating parameter tests revealed that the increase of the initial acetone concentration enhanced the amount of acetone adsorbed on the ACF, which however did not increase the reaction rate of acetone. Although the increase of reaction temperature could reduce the amount of acetone adsorbed on the ACF, decomposition rate of acetone could be promoted, so as the yield rate and mineralization ratio of products (CO2 and CO). Increasing oxygen concentration did not influence the decomposition significantly except for oxygen concentration lower than 1%. The increase of water vapor would slightly decrease the amount of acetone adsorbed on the ACF, which did not decrease the decomposition of acetone anyway. This study revealed that the decomposition of acetone on TiO2/ACF can enhance the mass transfer of acetone substantially.