N-defects and P-doping synergistically promote carbon nitride photocatalytic activation of peroxomonosulfate: Triggering the selective generation of 1O2 to degrade 4-Chlorophenol

Metal-based catalyst could be used for efficient peroxymonosulfate (PMS) activation, but inevitably suffered from metal ion leaching. Metal-free graphitic carbon nitride (g-C₃N₄) materials that can activate PMS are more conducive for practical water treatment. In this study, g-C₃N₄ with both N-defects and P-doping (CN-NP) was synthesized, which mainly produce singlet oxygen (¹O₂), and 97 % of 4-CP (4-Chlorophenol) was removed by CN-NP/PMS/Vis reaction system within 60 min. The active species was identified by quenching experiments and electron spin resonance (ESR) tests, and the origin of mainly active species was further verified by the concentration change of PMS during the reaction. It was verified by experiments and theoretical calculations that the introduction of N-defects led to the separation of photoinduced electron-hole pairs and improved photocatalytic activity. Notably, density functional theory (DFT) revealed that both N-defects and P-doping are electron-deficient sites, and P-doping acts as the main PMS adsorption site to promote the loss of electrons from PMS to generate ¹O₂. In addition, the catalysts developed in this research were anticipated to be applied in real wastewater treatment, contributing to further comprehend the mechanisms of element doping and defect modification in g-C₃N₄ activating PMS, and providing new insights for the design of PMS-activating catalysts.