Unraveling the Presence and Positions of Nitrogen Defects in Defective g‐C₃N₄ for Improved Organic Photocatalytic Degradation: Insights from Experiments and Theoretical Calculations

Abstract In this work, nitrogen‐defective g‐C₃N₄ with different nitrogen defect densities is synthesized for ciprofloxacin photocatalytic degradation. Compared with pristine g‐C₃N₄, g‐C₃N₄ etched with NaBH₄ for 1 h exhibits an approximately ten‐fold increase in the rate constant of ciprofloxacin (CIP) degradation. The combined experimental analysis and theoretical calculations reveal that nitrogen defects can be incorporated into g‐C₃N₄ in all nitrogen sites and that C─N═C is the most susceptible site. By incorporating nitrogen defects to induce defect states between the conduction band (CB) and valence band (VB), the electronic and band structures are tuned. The induced defect states can be downshifted to approach the valance band, reaching increased nitrogen defect density within optimum ranges to accommodate excited electrons to narrow the bandgap, extend the light absorption capability, and enhance the charge carrier separation and transfer efficiency. The g‐C₃N₄ etched by NaBH₄ for 2 h with over‐introduced nitrogen defects exhibits a declined performance due to a deteriorated structure, and the over‐downshifted defect states turn out to be a new recombination center for charge carriers.