Visible light photocatalytic synthesis of H₂O₂ on synergistic phosphorus-doped and defect engineered graphite C₃N₄

H₂O₂ is a green oxidant, which is widely used in chemical production, environmental remediation, sustainable energy conversion and the medical industry. The traditional anthraquinone method for producing H₂O₂ is facing issues, such as potential safety hazards and environmental pollution. Therefore, green and sustainable production of H₂O₂ is desirably investigated. Solar-driven photocatalytic synthesis of H₂O₂ is a promising method, which requires no additional energy input and will not produce new pollution. g-C₃N₄ is a kind of nonmetallic photocatalyst, which has the advantages of low cost, environmental friendliness and high stability. However, g-C₃N₄ still faces the problems of a narrow visible light response range, low photo-generated electron/hole separation efficiency and short carrier lifetime. The polymer properties of g-C₃N₄ are conducive to introducing foreign atoms into the main body of the tri-s-triazine structure. The electronic structure and optical properties of g-C₃N₄ can be adjusted by doping, which can significantly improve the photocatalytic performance of g-C₃N₄. In this work, phosphorus doped g-C₃N₄ (P/g-C₃N₄) is prepared by a simple chemical vapor deposition method. The doping process also introduced defects in the bulk phase of g-C₃N₄, which overcomes drawbacks such as weak visible light capturing ability, low charge separation and transfer efficiency, and a slow mass transfer rate. In addition, the optimized conduction band position further enhances the reduction ability of photo-generated electrons, making its photocatalytic performance magnify by one order of magnitude compared to that of pure g-C₃N₄. Driven by visible light, P/g-C₃N₄ produces H₂O₂ through the photocatalytic oxygen reduction reaction (ORR) in 2 h, reaching a high concentration of 1460.22 μM, and it also maintains good catalytic repeatability in three-cycle catalytic experiments.