| Abstract
| - Surface platinized TiO2 (Pt/TiO2) has been frequently studied, but its photocatalytic reactivities reported inthe literature are not consistent in some cases. To understand the discrepancies, the effects of Pt speciationon TiO2 on the photocatalytic degradation (PCD) of a few chlorinated organic compounds (trichloroethylene(TCE), perchloroethylene (PCE), dichloroacetate, etc.) were investigated with several Pt/TiO2 samples thatwere prepared differently. The oxidation state of Pt deposits was analyzed by X-ray photoelectron spectroscopyand was found to be the most important factor in determining the initial PCD rates of chlorinated organiccompounds. TiO2 with oxidized Pt species (Ptox/TiO2) was less reactive than TiO2 with metallic Pt (Pt0/TiO2)for all substrates tested. In particular, Ptox/TiO2 strongly inhibited the PCD of TCE and PCE whereas it wasmore reactive than pure TiO2 for the PCD of other compounds. The photocurrents obtained with the Ptox/TiO2 electrode were lower than those with the Pt0/TiO2 electrode, which was ascribed to the role of Ptoxspecies as a recombination center. It is proposed that TCE adsorbed on Ptox chemically mediates the chargerecombination through the redox cycle of TCE. The Pt effects in photocatalysis are highly substrate-specificand depend on the Pt−substrate interaction as well as the properties of Pt deposits.
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