Iodine-Deficient BiOI Nanosheets with Lowered Valence Band Maximum To Enable Visible Light Photocatalytic Activity

Bismuth oxyhalides with layered structures have emerged as an important class of photocatalysts but usually suffer from low activity largely due to their unfavorable band structures. Although point defects as typical electronic structure modifiers have been actively used to modify electronic structures of photocatalysts for high photocatalytic activity, the underlying role of halogen vacancies in improving activity of bismuth oxyhalides has been overlooked. In this study, we demonstrate the substantial role of iodine vacancies in enabling photocatalytic activity of BiOI as a model oxyhalide photocatalyst. It is found that iodine vacancies cause a 0.23 eV downward shift of the valence band maximum of BiOI but not much change in the bandgap. Such band structure modification leads to the formation of photogenerated holes with a stronger oxidative ability, which is favorable for photocatalysis with the holes induced half reaction as a rate-determining step. The results obtained might provide an important implication in designing highly efficient oxyhalide-based photocatalysts by controlling halogen vacancies.