Photocatalytic oxidation reactivity of holes in the sulfur- and carbon-doped TiO2 powders studied by time-resolved diffuse reflectance spectroscopy

The photocatalytic oxidation reactivities of the photogenerated holes (h(+)) during ultraviolet or visible laser flash photolysis of pure anatase and sulfur- and carbon-doped TiO2 powders were investigated using time-resolved diffuse reflectance (TDR) spectroscopy. The one-electron oxidation processes of substrates such as methanol and 4-(methylthio)phenyl methanol (MTPM) by h(+) at the TiO2 surface were examined. The TDR spectra and time traces observed for charge carriers and the MTPM radical cation (MTPM.+) revealed that the oxidation reactions of substrates by h(+) generated during the 355-nm laser photolysis of TiO2 powders increased in the order of pure TiO2 > S-doped TiO2 > C-doped TiO2. On the other hand, no one-electron oxidation reactions of the substrates were observed during the 430-nm laser photolysis of the S- and C-doped TiO2 powders, although the charge carriers were sufficiently generated upon excitation. The effects of the trapping and detrapping processes of h(+) at the doping sites on the oxidation reactions during the laser flash photolyses of the TiO2 powders are discussed.