Origin of Photocatalytic Deactivation of TiO₂ Film Coated on Ceramic Substrate

The deactivation origin of the TiO2 film coated on an Al2O3-based ceramic substrate was revealed via investigating the physicochemical behaviors of the mixtures of TiO2 with different oxides of various species found in the film such as Al, Si, and Ca. The production of these species mainly present as individual oxides at the boundaries among the TiO2 particles in the film originated from their thermal diffusion from substrate during the formation of TiO2 film at calcination temperature. It was demonstrated that Al present as Al2O3 with TiO2 caused a remarkable reduction in the production of hydroxyl radicals over the UV-irradiated TiO2, whereas the presence of SiO2 or CaO, especially SiO2, together with TiO2 gave a rise in the formation of hydroxyl radicals. The investigation also showed that a part of Al3+ substitutes for Ti4+ in the TiO2, resulting in the formation of oxygen vacancies in the lattice for the charge balance. The oxygen vacancies present in the TiO2 lattice acting as effective combination ...