Effect of charge balance vacancies on the ultraviolet photocatalytic activity of Fe³⁺-doped anatase

The presence of Fe³⁺ dopant ions rastically decreases the activity of TiO₂ powders in the photocatalytic decolorization of methyl orange. A comparison of the photocatalytic activities of the 0.6 at% Fe³⁺: TiO₂ and 0.6 at% Cr³⁺: TiO₂ samples before and after their hydrogen annealing shows that this negative effect is mainly due to the formation of charge balance oxygen vacancies VO, and it does almost not depend on the physicochemical properties of M³⁺ dopants. The ⁵⁷Fe Mössbauer spectrum of 2 at% Fe³⁺: TiO₂ indicates that nearly every other Fe³⁺ ion introduced into TiO₂ possesses a vacancy VO in its nearest surrounding.