Yatskiv V. TiO2 porosity and phase composition effects on kinetics and mechanism of photocatalytic transformation of alcohols and ketones.

Template sol-gel synthesis has been used for the preparation of powders and films of porous titanium (IV) dioxide. Structural, sorption (crystallinity, specific surface area, pores and crystallite's sizes, maximum sorption volume of the pores etc.) and optical characteris-tics of the samples have been comprehensively studied. Origin of a change of structural-sorption characteristics at ageing, calcinations and hydrothermal treatment of the samples has been elucidated. The effects of modifications additives (transition metals ions), their nature and content on structural-sorption parameters of porous TiO2 have been examined. It has been found that synthesized materials based on porous titania act as efficient photocatalysts for the reductive decomposition of alcohol-water mixtures with the evolu-tion of molecular hydrogen. Kinetics of this process has been examined in details. It was shown for the first time that peculiarities of the photocatalytic evolution of dihydrogen systems studied consist in theaccumulation of long-lived "free" electrons and Ti(III) ions in irradiated samples as well as slow electron transport to outer surface of TiO2 grains. These features determine the dependence of the quantum yield of the photoprocess both on the light intensity and the duration of the storage of irradiated samples in the dark. A possible mechanism of the photoreaction has been proposed. It has been established that porous TiO2 can efficiently catalyze gas-phase oxidation of methanol, ethanol, 1-propanol, 2-propanol and acetone by oxygen. Kinetics of these processes has been studied. A correlation between structural-sorption characteristics of the samples based on porous titania and their photocatalytic activity in gas-phase reactions has been found. It has been shown that a factor governing the rate of heterogeneous gas-phase oxidation is sorption capacity of the photocatalyst determining the possibility of preliminary sorptive concentration of substrates on the surface of TiO2 where subsequent photooxidation takes place.