Various Ti-oxide based photocatalysts such as the highly dispersed Ti-oxide species within zeolite frameworks, TiO 2 nano-particles hybridized with hydrophobic zeolite adsorbents as well as visible light responsive TiO 2 thin films have been successfully prepared. Characterization studies at the molecular level, such as X-ray absorption fine structure (XAFS) and photoluminescence (PL), revealed that the highly dispersed Ti-oxide species within the nano-spaces of zeolites possess a tetrahedral coordination and that they demonstrate unique and high performance for the photocatalytic decomposition of NOx and the photocatalytic reduction of CO 2 with H 2 O. A high photocatalytic reactivity for the TiO 2 semiconducting photocatalysts could be achieved by blending them with hydrophobic siliceous zeolites which was equal to the performance of TiO 2 deposited with expensive Pt particles. The role of the siliceous zeolites can be described as a so-called ''catch and release effect of organic compounds'', i.e., (i) the condensation of the reactants within the hydrophobic cavities of zeolites and; (ii) the efficient diffusion of the reactant onto the TiO 2 photocatalytic sites. Furthermore, a novel photocatalytic system which can convert abundant solar energy into renewable H 2 energy by the decomposition of H 2 O into H 2 and O 2 can also be achieved by using visible light responsive TiO 2 thin film photocatalysts prepared by a RF-magnetron sputtering deposition method. The conversion efficiency of solar energy into H 2 energy may be estimated at ca. 0.1% from the initial rate of H 2 evolution.

Abstract-TiO 2 photocatalysts were prepared by a multi-gelation method and the effect of the changes in the pH during the pH swing times, i.e., by a controlled pH swing, on the morphology of the TiO 2 particles was investigated. The photocatalytic properties of the TiO 2 catalysts prepared by controlled pH swing were compared with TiO 2 particles prepared without adjusting the pH during the swing times. The photocatalytic degradation reaction of these TiO 2 catalysts was investigated by comparing their effectiveness in 2-propanol oxidation. The experimental results showed that the TiO 2 photocatalysts prepared without adjusting the pH performed better in controlling the important parameters of the catalysts such as particle size, surface area, anatase/rutile phase ratio and pore size, as well as pore volume than the TiO 2 photocatalysts prepared by a controlled pH swing method.