Engineering Electronic Properties of g‐C ₃ N ₄ via Cyano‐Defects and (S, Na, B) Co‐Doping for Enhanced Photocatalytic CO ₂ Reduction

ABSTRACT The photocatalytic efficiency of graphitic carbon nitride (g‐C ₃ N ₄ ) is constrained by its inherent limitations of inefficient charge carrier transfer and a scarcity of active surface sites. To surmount these challenges, we herein report a rational design of g‐C ₃ N ₄ nanosheets featuring synchronous cyano‐defects and (S, Na, B) co‐doping (CNS‐NaB). This synergistic modification enhances charge separation and provides abundant catalytic centers. Through comprehensive structural characterizations and density functional theory (DFT) calculations, we elucidate the distinct roles of each dopant in generating a synergistic effect. Specifically, Na─N coordination facilitates interlayer charges transfer, B─N bond optimizes the electronic properties, and S─C bond serves as active sites. Meanwhile, the cyano‐defects work as electron acceptors and charge‐transfer mediators. These synergy interactions spatially separate the LUMO and HOMO in CNS‐NaB, inhibit the charge recombination, and reduce the exciton binding energy to 51.50 meV. As a result, CNS‐NaB exhibits a CO ₂ ‐to‐CO conversion rate of 779.2 µmol h ⁻¹ g ⁻¹ , and enhanced H ₂ evolution rate of 3637.9 µmol h ⁻¹ g ⁻¹ , with an apparent quantum yield of 15.6% at 432 nm. This study proves that element co‐doping coupled with structural defect offers a good strategy to optimize the electronic properties, and the photocatalytic activity of g‐C ₃ N ₄ for solar‐to‐chemical conversion.