Abstract
The photo-activity of TiO2(anatase P. 25) samples with a “fully hydroxylated surface” was studied in the presence of oxygen. Photo-adsorption of oxygen was observed in the early stages of u.v. illumination reducing the pressure to < 0.1 N m–2. After this fast adsorption, slow photo-desorption of oxygen was detected continuing for several hours. Thermal removal of water and hydroxyl groups reduced photo-adsorption and the process became diffusion controlled. Rehydration restored fast photo-adsorption and first order kinetics. Photo-desorption of water accompanied photo-adsorption of oxygen on these “fully hydrated surfaces”. A mechanism involving the formation of OH· radicals and their reaction to give H2O2, which decomposes leading to oxygen photo-desorption, is proposed to explain these facts.
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