TiO(2) crystal facet-dependent antimony adsorption and photocatalytic oxidation

Anatase TiO₂ crystal facets are garnering increasing attention due to their unique surface property. However, no specific linear relationship had been derived between the facet exposed on TiO₂ and the surface adsorption capacity as well as photocatalytic performance. This study systematically explored the facet effects on antimony (Sb) adsorption and photocatalytic oxidation using high-index {201} and low-index {101}, {001}, and {100} TiO₂. The results suggest that high-index {201} TiO₂ exhibits the best Sb(III) adsorption and photocatalytic activity compared to the low-index TiO₂. Both the Sb(III) adsorption density and the amount of OH and O₂^- generated in solution were correlated to the magnitude of surface energy on TiO₂ facets. Photocatalytically generated OH and O₂^- were responsible for Sb(III) photooxidation as evidenced by radical-trapping experiments. The great contribution of OH was observed only on {201}, not on low-index TiO₂. This phenomenon was found to be attributable to the high surface energy on {201}, which enables the generation of a large amount of photogeneration OH to compensate for the fast rate of OH dissipation. Therefore, the predominant participation of OH in Sb(III) photooxidation was only possible on high-index {201} TiO₂, which resulted in an enhanced photocatalytic rate. On the other hand, O₂^- dominated the Sb(III) photocatalytic oxidation on low-index TiO₂. The intrinsic facet-dependent adsorption and photocatalytic mechanism obtained from this study would be useful for developing TiO₂-based environmental technologies.