Mechanistic insights into the formation of N-vacancies at sp2-hybridized sites in non-metal doped g-C3N4 for solar-to-H2 conversion and environmental remediation reactions

Abstract

Designing and constructing an efficient photocatalyst based on graphitic carbon nitride (g-C₃N₄) nanosheets is vital for solar-to-fuel and pollutant degradation reactions. Particularly, defect engineering can effectively modify the electronic band structures, serve as active sites and promote charge separation, leading to enhanced photocatalytic activity. Herein, we report dual non-metal doped g-C₃N₄ (C- and O-doped g-C₃N₄) with N-vacancies for photoredox reactions. Benefitting from dual doping, N-defects and a porous nature, the optimized g-C₃N₄ photocatalyst displays extended visible-light harvesting, a higher specific surface area, and efficient photoinduced charge separation. Consequently, the as-designed g-C₃N₄ exhibits a higher visible-light-driven photocatalytic H₂ evolution activity of approximately 1850 µmol g⁻¹ h⁻¹, along with stable performance over 24 hours. In addition, the defect-engineered g-C₃N₄ photocatalyst delivers a high tetracycline degradation efficiency of 82%. The enhanced activity can be attributed to the synergistic effects of midgap states induced by doping and N-defects, along with improved charge-carrier separation. Furthermore, the physical mechanism governing carrier dynamics is systematically investigated. Our work offers useful guidance for the design of two-dimensional (2D) porous nanosheets for photocatalytic systems and optoelectronic device applications.