Insights into enhancing photocatalytic reduction of CO₂: Substitutional defect strategy of modified g-C₃N₄ by experimental and theoretical calculation approaches

The defects in g-C₃N₄ by material substitution have been proven to enhance photocatalytic reaction. Even so, accurate position substitution of carbon doping for defects in g-C₃N₄ structure remains a significant challenge. Herein, we investigate the effects of C/doping on the optical and electronic structure of g-C₃N₄ by combining experiments and density functional theory (DFT). The results reveal that substitution of C atom with N site by 12.7% defect concentration confer efficient separation of electron-hole pairs and photocatalytic activity in comparison with the pristine g-C₃N₄. The defect constructed at C_N1 site position exhibits expanded light absorption edge of g-C₃N₄, and indicates a small bandgap while maintaining a negative value of CB potential for CO₂ reduction to methanol. During performance testing, the highest methanol yield of 651.7 µmol g_cat⁻¹ h⁻¹ and AQY = 0.019 with ca. 40% improvement are reported over 0.2C/g-C₃N₄ compared to pristine g-C₃N₄. First principle calculations attest the defect position of g-C₃N₄ structure, introduced by carbon dopant, is beneficial as a tuneable energy band gap that increases light harvesting. This work highlights defect engineering of g-C₃N₄ structure by carbon doping is a promising way to enhance the performance of photocatalytic carbon dioxide reduction to methanol.