Strategy for improving photocatalytic ozonation activity of g-C3N4 by halogen doping for water purification

Feasibility of improving photocatalytic ozonation (PCO) activity of g-C3N4 (CN) by doping halogen (F, Cl, Br and I) was evaluated from the aspect of O3/O2 mass transfer and photogenerated electron (e-) and hole (h+) recombination. All halogen-CN had better activity (F-CN>I-CN>Cl-CN>Br-CN) for degrading ATZ than that of CN. Experimental and theoretical simulations results showed that doping halogen made the electron unevenly distributed and formed hydrophobic sites on CN, narrowed Eg of CN and enlarged e- migration space. The above properties were favorable for enhancing mass transfer of O3/O2 and suppressed e--h+ recombination. Besides, they either upshifted CB (C-I) or downshifted VB (C-F, C-Cl) to enhance the oxidation function of •OH or h+. One-electron reduction (high e- utilization) of O3 was weakened and three-electron reduction (low e- utilization) of O2 was enhanced with decrease of halogen electronegativity. This work provided insights into catalyst design for PCO process.