Surface and interface engineering of two-dimensional bismuth-based photocatalysts for ambient molecule activation

Two-dimensional (2D) nanomaterials with a high surface-to-volume ratio and unique electronic structure have now become one of the hottest topics in photocatalytic research. In parallel with the discovery of emerging photocatalytic materials, strenuous efforts are devoted to maneuvering these surface-related parameters in a predictable manner or to endowing materials with an engineered surface/interface to meet the requirements of photocatalytic reactions. This review endeavors to reveal the inherent functionality of the surface and interface in photocatalysis, with 2D Bi-based photocatalysts as the platform. Herein, we start with various parameters at the surface/interface molecular level, such as defects, surface terminations, facets, pore structures, band bending etc., to gain insight into the structural sensitivity of the surface/interface to the reactivity and selectivity of photocatalytic reactions. As a bridging section, advanced characterization techniques that can visualize the fine structure of the surface/interface at the atomic level are discussed. Special attention is placed on engineering protocols to design and tune 2D Bi-based photocatalysts to ameliorate the performance: surface engineering via heteroatom doping, defect tailoring, and surface state/facet/lateral size and thickness regulation, together with an equal focus on interface engineering including the basal interface and lateral interface. Moreover, the advancements of diversiform photocatalytic applications of 2D Bi-based photocatalysts in ambient molecule activation, including but not limited to CO₂ reduction, O₂ activation, H₂O dissociation, N₂ fixation and activation of other molecules, are discussed, with an emphasis on the surface/interface–activity relationship. Finally, the challenges and opportunities in this emerging field are featured based on its current development. The critical thinking on surface/interface chemistry facilitates consolidating and advancing the fundamental theory of heterogeneous photocatalysis and also broadening insights into the rational design of high-performance photocatalysts.