Isolated Iodine Single Atoms Regulating the in-Plane Electronic Structure of G-C3N4 for Enhanced CO2 Photoreduction.

Carbon nitride (CN) is a promising metal-free photocatalyst for carbon dioxide (CO2) reduction, yet it remains challenging due to its instability under irradiation in vapor environments and low electron-hole separation efficiency. Here, we demonstrate that the decoration of iodine (I) single atoms on ultrathin CN (IUCN) benefit the formation of C═O during vapor-engaged photocatalytic processes, reduces the adsorption capacity of OH species, and strengthens the tri-coordinated bridging nitrogen atoms (C─N═C) linkages, preventing the self-decomposition of IUCN. The formed C─I covalent bond at the IUCN surface provides a direct channel for photogenerated hole transfer, improving the separation of the in-plane electron-hole pairs. Furthermore, orbital hybridization between the N-2p orbitals of IUCN and the C-2p orbitals of CO2 lowers the energy of antibonding orbitals in CO2, enhancing its activation and subsequent transformation. The optimal IUCN photocatalyst achieved CO and CH4 yields of 181.09 and 16.27 µmol g-1 h-1 under simulated solar light irradiation, respectively. The CO and CH4 yields are 90.29 and 17.92 µmol g-1 h-1 under visible light irradiation, respectively. This study expands the synthetic approaches for nonmetal single-atom catalysts and offers insights into the relationship between the configuration of single atoms and the reaction pathways.