Small-molecule surface-modified bismuth-based semiconductors as a new class of visible-light-driven photocatalytic materials: Structure-dependent photocatalytic properties and photosensitization mechanism

Visible light photocatalysis driven via ligand-to-metal charge transfer (LMCT) can provide a new opportunity for solar energy utilization, yet investigations on non-TiO 2 catalysts are rather limited and the mechanism of LMCT remains unclear. This study focused on the controllable synthesis, applications, and LMCT photosensitization mechanism of bismuth-based materials. BiOIO3, with tunable surface-exposed Bi(III), was first synthesized by a facile hydrothermal route and then applied to visible light photocatalytic decomposition of six dihydroxybenzoic acids (DHBAs) to optimize the conditions of surface complexation and photosensitization. After that, nine additional DHBA analogues and seven bismuth-based semiconductors with different crystal and band structures were used as alternative ligands and modified materials, respectively, to verify and support the hypothesis. It was found that organics with an ortho-dihydroxyphenyl substructure could chelate well with Bi(III) to form colored metal-organic complexes and caused the formation of surface oxygen vacancies (OVs) in the semiconductors, which resulted in the structural dependence and selective photocatalytic properties over the catalysts. In addition, the obtained materials could be used as either normal visible-light-driven photoelectric conversion materials or photocatalysts for environmental contaminants removal through producing highly reactive center dot OH, center dot O-2(-), and O-1(2) oxygen species. Theoretical calculations were performed to analyze the coordination, light absorption, molecular orbitals, and band structures of the complexes. With reference to the principles of semiconductor heterojunction, a novel visible-light-sensitization mechanism for small-molecule surface-modified bismuth-based semiconductors was proposed. The results develop the LMCT mechanism and significantly extend the applications of semiconductor photocatalytic materials.