Effects of Sn4+ dopant ions located either in the bulk or at crystallite surfaces on the ultraviolet photocatalytic activity of anatase

Isovalent Sn4+ dopant cations do not have a significant effect on the ultraviolet photocatalytic activity of anatase (TiO2) regardless of their location in the bulk or at the surfaces of crystallites. This is due to the formation of no charge balance oxygen vacancies VO acting as (e–,h⁺) recombination centers towards photogenerated electrons and holes upon doping with Sn4+. Nevertheless, the analysis of a sample containing surfacelocated heterovalent Sb3+ ions (isoelectronic with Sn²⁺) revealed a significant weakening of the negative effect of VO, which can be accounted for by the presence of a stereochemically active lone pair E of 5s electrons in the nearest vicinity of VO.