Can OH Radicals Diffuse from the UV-Irradiated Photocatalytic TiO2 Surfaces? Laser-Induced-Fluorescence Study

Diffusion of OH radicals from UV-irradiated TiO 2 surface to the gas phase was successfully detected using a laser-induced-fluorescence technique for various types of TiO 2 powders. The diffusion time of OH radicals was found to vary with the types of TiO 2 powders and to be affected by the heat treatments of these powders, depending on the treatment temperatures. The diffusion mechanism was discussed based on the characteristic OH-LIF intensities for individual TiO 2 powders and the observations of OD-LIF after the exposure of D 2 O vapors over the TiO 2 powders. The quantum yield of OH radicals diffused from the TiO 2 surface was estimated to be about 5 × 10 -5 by comparing the OH-LIF intensities produced by the 266-nm photolysis of HNO 3.