Electron rich P doped g-C₃N₄ for photodegradation of 2,4-dichlorophenoxyacetic acid under visible light by improving oxygen adsorption: Performance and catalytic mechanism

In the paper, the phosphorus-doped g-C₃N₄ (PCN) photocatalyst was synthesized by thermal polycondensation, and its photocatalytic performance and mechanism for 2,4-dichlorophenoxyacetic acid (2,4-D) degradation were investigated. Element composition and bonding analysis identified that P atoms replaced some carbon atoms in g-C₃N₄. Optical property and photoelectrochemistry analysis showed that P doping weakened the bandgap of g-C₃N₄ and enhanced the rate of photogenerated charge migration. The density of states calculated by density functional theory (DFT) indicated that the above results were due to the formation of impurity levels by P doping. The PCN with the best performance possessed 5 times the photodegradation rate for 2,4-D compared with pure g-C₃N₄. ·O₂^– and h⁺ played important roles during the photodegradation of 2,4-D. The difference charge densities and O₂ adsorption model showed that P doping changed the catalytic reaction site and promoted O₂ adsorption, thus generating more ·O₂^–.