Surface Density of Cobalt Single Atoms Manipulating Hydroxyl Radical Generation Via Dual Pathways: Electrons Supply and Active sites

Abstract Photocatalytic generation of ^•OH from O₃ is an intriguing avenue for aqueous organics degradation due to the high utilization of photogenerated electrons, but ambiguous information about charge transfer and surface‐active sites hinders the optimization of photocatalysts. In this work, a series of cobalt single‐atom catalysts (SACs) anchored on graphitic carbon nitride to improve ^•OH generation from O₃ via electron reduction and catalytic activation dual pathway is synthesized. Various characterization and density functional theory calculations reveal that cobalt single atoms can introduce trap states for holes, which improve the light‐harvesting ability and accelerate the transfer of electrons and holes. Meanwhile, Co single atoms can also act as active sites to accelerate ozone decomposition and produce ^•OH directly. Particularly, the influence of different surface densities of Co single atoms on photogenerated electron supply and surface reaction is disclosed. A higher density of Co provided more active sites for O₃ catalytic activation, but the narrowed distance between oxidation and reduction centers reduces the supply of available electrons by worsening the charge recombination. This work offers an atomic‐level correlation of the isolated metal density and photocatalytic properties, and can scientifically guide the design of high‐performance photocatalysts for organic synthesis and water purification.