Photochemical oxidation of water with thin AgCl layers

Thin silver chloride layers on SnO2-coated glass plates evolve oxygen in the presence of a small excess of Ag+ ions in aqueous solution, with a maximum evolution rate at pH 4-5. The system shows self-sensitization of photochemical O-2 evolution, which means that new photoactive colour centres are formed on near-UV illumination (340-390 nm) composed of reduced silver species. A non-linear dependence of the O-2 evolution rate on the light intensity at low intensities changes into a linear dependence in the medium range (above about 300 mu W cm(-2)). The quantum yield per redox equivalent for O-2 evolution in the linear range is approximately 0.8 on illumination with UV light and the same on illumination with blue light (420-480 nm). It is approximately 0.5 in the green range (500-540 nm). A mechanism for O-2 evolution is discussed.