Photoinduced electron transfer at solid surfaces: the TiO2–SiO2 system

Abstract

Small particles of TiO₂ have been synthesized on porous silica. XRD and spectral measurements place the sizes of the particles at about 50 Å. With these small particles the band gap of the semiconductor material is markedly blue shifted with respect to bulk TiO₂. This enables the direct excitation of co-adsorbed arenes on the TiO₂–SiO₂ material. Direct excitation of TiO₂ leads to Ti³⁺, by photoinduced extraction from the SiO₂. Direct excitation of pyrene on the material leads to a shortened fluorescence lifetime and lower quantum yield. Meanwhile, the yield of pyrene cation radical increases compared to that on pure SiO₂. The production of Ti³⁺ on the pyrene samples, by direct excitation of the TiO₂, leads to a shortened pyrene fluorescence lifetime and decreased quantum yield, the quantum yield decreasing to zero at high enough Ti³⁺. Removal of Ti³⁺ by O₂ causes the original properties of the pyrene fluorescence to return.