New decomposition method of organic environmental pollutants during photocatalytic reactions : Photocatalyst and Multi-photoexcitation

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One-electron oxidation reaction mechanisms of aromatic sulfides in a colloidal TiO_2 aqueous solution. Laser flash photolysis technique has been employed to clarify the oxidation reaction processes of 4-methylthiophenylmethanol and 2-phenythioethanol in the colloidal TiO_2 aqueous solution. The significant variations in the spectral shape and formation rates of the radical cation clearly suggest two oxidation processes with the valence band and/or trapped holes and the free OH radicals. Effects of the adsorption and the electronic interaction between aromatic compounds and the TiO_2 surface on the efficiency of the one-electron oxidation reaction. The TiO_2 photocatalytic one-electron oxidation mechanism of aromatic compounds adsorbed on the surface of a TiO_2 powder slurried in acetonitrile has been investigated by time-resolved diffuse reflectance spectroscopy. The efficiency of the one-electron oxidation of substrates adsorbed on the TiO_2 surface, which was determined from the relationship between the amount of adsorbates and the concentration of the generated radical cations, significantly depended on the electronic coupling elements, but not on the oxidation potential of substrates determined in homogeneous solution. Cascade hole transfer giving free radical cations. The formation of the 1,1-dianisylethylene (DAE) dimer radical cation during TiO_2 photocatalytic reactions was successfully investigated by the transient absorption measurement with time-resolved diffuse reflectance spectroscopy. The reaction was explained in terms of the cascade hole transfer processes from the photo-generated holes in the TiO_2 particles to free DAE in the bulk solution mediated by the radical cation of p-phenylbenzoic acid adsorbed on the TiO_2 surface.