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.

An analysis of decomposition of methylene blue (MB) in an aerated aqueous solution by its action spectrum has shown that sulfur-doped titania (S-TiO 2 ) has activity under visible-light irradiation and that the decomposition mechanism depends on the excitation wavelength. This suggests that photosensitive materials are not suitable as probe chemicals for photocatalytic activity tests, especially those for evaluation of activity under visible light.It is confirmed using acetic acid instead of MB that S-TiO 2 , but not ordinary non-doped titania, leads to the photocatalytic reaction under visible radiation below 600 nm, which corresponds to its absorption spectrum. *Corresponding

Carbonate (CO32−) species-doped titanium dioxide (TiO2) photocatalysts were prepared. By doping carbonate species into a TiO2 lattice, the absorption edge of TiO2 was largely shifted from 400 to 700 nm. Furthermore, methylene blue was photocatalytically decomposed at high efficiency on carbonate species-doped TiO2 photocatalysts under visible light at a wavelength longer than 550 nm.

Sulfur-doped TiO 2 was prepared by two methods; one was simple oxidation annealing of TiS 2 , the other was mixing of titanium isopropoxide and thiourea. These two sulfur-doped TiO 2 preparations showed fairly different photocatalytic activity under visible light. The dynamics of photogenerated charge carriers were studied by the transient absorption measurement in the region of mid-IR. In both samples, excitation by 532 nm pulse led to photocarrier generation to the same extent. Nevertheless, the reactivity of the photocarriers was totally different. Photogenerated electrons and holes transferred to reactant gas in the latter sample, whereas they did not in the former sample. We attributed the different carrier behavior to the difference in the distribution of S atoms or particle size. These observations can explain the difference in capability of photocatalysis under visible light.