Bismuth-rich bismuth oxyhalides: a new opportunity to trigger high-efficiency photocatalysis

As the continuation and advances in traditional BiOX (X = Cl, Br, I), bismuth-rich bismuth oxyhalides (BiaObXc) show distinct differences in the surface local atomic structure, electronic structure, optical properties, and electrical conductivity relative to BiOX. These features endow bismuth-rich BiaObXc with more tunable properties to achieve excellent photocatalytic performance. Here, the state-of-the-art progress in bismuth-rich bismuth oxyhalides is reviewed to clarify the key structure-activity relationship for enhanced photocatalytic performance. Various methods for the controllable synthesis and formation mechanism of bismuth-rich BiaObXc are presented. Different strategies to tailor the photocatalytic behaviors are summarized, namely thickness tuning, morphological control, heteroatom doping, surface defect engineering, single atom engineering, surface modification, preparation of a solid solution and engineering of semiconductor heterojunctions. Moreover, the recent advances in BiaObXc for diversified photocatalytic applications, such as H-2 generation, O-2 production, CO2 reduction, N-2 reduction, organic synthesis and pollutant removal, are summarized. Finally, the existing challenges and perspectives are also presented to bring about new opportunities for future research.