Self-doped Ti@TiO2 visible light photocatalyst: Influence of synthetic parameters on the H2 production activity

Self-doped TiO₂ shows visible light photocatalytic activity, while pristine TiO₂ is only UV responsive. Ti³⁺ has been demonstrated to be responsible for this improvement. We systematically studied various experimental parameters, such as the amount of reducing agent imidazole, types of imidazoles and Ti sources, and determined effects of these parameters on the combustion process and final materials. The phase composition, Ti³⁺ concentration, light absorption, surface area, and crystallinity of the product are significantly affected by the amount of imidazoles. Through comparing different imidazoles, we found that only flammable/combustible imidazoles are able to convert Ti⁴⁺ into Ti³⁺. This result is very helpful in understanding the mechanism and reactions in combustion process. Titanium precursors also have a great influence in production of Ti³⁺ doped TiO₂ materials. Titanium alkoxides allow the successful synthesis of blue partially reduced TiO₂, while TiCl₄ only lead to white pristine TiO₂.