TiC>2, photocatalysis

Fig. 3 Energy levels in TiC>2 photocatalysis (given in terms of reduction potentials at pH 0) (A) shows the reduction of acceptor A, (B) the direct oxidation of donor D, and (C) the oxidation of D mediated by a sensitizer S...

Shepard et al. [167] also reported the use of TiC>2 photocatalysis for the degradation of three microcystin variants, -LR, -YR and -YA. Each of these toxins rapidly decomposed on photo catalysis and a half fife of less than 5 min was reported for each microcystin. The effect of pH was found to strongly influence the destruction of a series of microcystins including LR, RR, LW and... 

Conversely, Rincon et al. [192] looked at the residual effect of TiC>2 photocatalysis of E. coli K12 in deionised water, and showed that even up to 60 h after photocatalytic treatment, there was no bacterial re-growth. Although they did point out that this was dependent on the light intensity used. Huang... 

In this paper, we report a study of the photocatalytic oxidation in the neat-liquid phase and at room temperature of various model hydrocarbons containing one or two C6 rings (cyclohexane, methyl- and dimethyl-cyclohexane, cyclohexene, decalin and tetralin) over TiC>2 to further investigate the possibilities of heterogeneous photocatalysis in the field of fine chemicals. Bibliographic investigations gave no references on the photocatalytic oxidation of the various hydrocarbons cited above, except for cyclohexane (refs 6 - 8) with which wa have initiated the study of liquid cycloalkanes (ref. 9). 

Kinetic studies of photoreactions on semiconductor nanoparticles are important for both science and practice. Of scientific interest are the so-called quantum size effects, which are most pronounced on these particles shifting the edge of adsorption band, participation of hot electrons in the reactions and recombination, dependence of the quantum yield of luminescence and reactions on the excitation wavelength, etc. In one way or another all these phenomena affect the features of photocatalytic reactions. At present photocatalysis on semiconductors is widely used for practical purposes, mainly for the removal of organic contamination from water and air. The most efficient commercial semiconductor photocatalysts (mainly the TiC>2 photocatalysts) have primary particles of size 10-20 nm, i.e., they consist of nanoparticles. Results of studying the photoprocesses on semiconductor particles (even of different nature) are used to explain the regularities of photocatalytic processes. This indicates the practical significance of these processes. 

In this work the authors summarize their own studies of photoprocesses on CdS colloids with particles of various size. In these studies, attention was given precisely to photocatalytic reactions on CdS, the photocatalytic reactions on TiC>2 were considered concurrently with the reported ones. In most cases photocatalytic reactions on semiconductors are the redox reactions. So of special interest was to study the regularities of reactions of interfacial transfer of photoexcited electron by the pulse photolysis and luminescence quenching methods. Many interesting phenomena were found while studying the model photocatalytic reactions by the method of stationary photolysis, i.e., under the conditions of real photocatalysis. 

Martyanov, Igor N. is a Ph.D. researcher and recently worked in the laboratory of photocatalysis on semiconductors at the Boreskov Institute of Catalysis, SB RAS, Novosibirsk, Russia. The title of his PhD Thesis (1998) was Kinetics of photocatalytic redox reactions of organic molecules in semiconductor suspensions (CdS and TiC>2) . Areas of his interests kinetics of photocatalytic reactions in liquid phase at deep conversion the influence of the surfactants. 

Bulk semiconductor photocatalysts (Section 4), such as TiC>2 and Ti02-containing materials (Sections 2.1 and 4), have continued to gain attention, because of their application to the electrochemical photolysis of water (Fujishima and Honda, 1972) and also because of their importance in photocatalysis (Anpo, 2005). 

The presence of oestrogenic compounds in potable water supplies has also raised concerns in recent years. The destruction of 17-/i-oeslradiaol on immobilised TiC>2 films has been achieved with 98% decomposition observed in 3.5 h photocatalysis [169]. 

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