Engineering Sm single atoms in g-C₃N₄ nanosheets with interlayer asymmetric coordination environment for enhanced photocatalytic CO₂ reduction

Single-atom engineered photocatalysts are promising for the development of efficient photocatalytic CO₂ reduction systems but remain challenging. Herein, Sm single atoms anchored graphitic carbon nitride (CN) was synthesized via an in-situ pyrolysis strategy (xSm-CN). During the synthesis, an asymmetric coordination structure of Sm-N₈ between the layers was generated. This configuration can facilitate electron transfer through the delocalized π-conjugated network of CN, resulting in the formation of an electron-rich Sm-N region, as proved via DFT calculations and experimental studies. The charge-density difference after CO₂ adsorption indicates that the electron-rich catalytic environment triggered around the Sm single atoms is favorable for the further progression of CO₂ reduction. Meanwhile, this unique structure lowers the energy barrier for the formation of the key COOH* intermediate. Benefiting from these features, the optimized 2Sm-CN exhibits a CO generation rate of 44.27 μmol g^-1h⁻¹ and high CO selectivity of 96.8 % when irradiated without sacrificial agents. The generation rate is a 4.7-fold increase compared to the original CN and exceeded most reported CN-based photocatalysts to date. This study emphasizes the critical role of Sm single atoms in the local coordination environment and provides insights into understanding the structure–activity relationship at the atomic level.