Transient IR absorption study of charge carriers photogenerated in sulfur-doped TiO₂

Sulfur-doped TiO₂ was prepared by two methods; one was simple oxidation annealing of TiS₂, the other was mixing of titanium isopropoxide and thiourea. These two sulfur-doped TiO₂ 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.