Photoionization of titanium dioxide particles incorporated into silica gels of different pore sizes

Abstract

Titanium dioxide particles, with three different average size ranges, prepared by three different methods, were incorporated into silica gel pores by impregnation. The TiO₂ incorporated into silica gel pores was photoionized by 240–400 nm irradiation at 77 K by a one-photon process to form trapped hole centres on oxygen and trapped electron centres on titanium which are detected by EPR at 77 K. The smallest size range of TiO₂ particles can be incorporated into silica gels with 2.5–15 nm pores. However, the largest size range of TiO₂ particles can only be incorporated into silica gels with 6–15 nm pores and not into silica gels with 2.5–4 nm pores. The photoyield and stability of the photoinduced hole and electron centres depend on the silica gel pore sizes and surface area, as well as on the TiO₂ loading. In large-pore silica gels, photoinduced charge separation reaches a plateau at shorter irradiation times and the trapped hole and electron centres are more stable to decay.