Enhancing photocatalytic performance for H2O2 production by constructing triazine-heptazine-based carbon nitride and coupling lignin CC bond cleavage

Photocatalytic H₂O₂ production and lignin CC bond cleavage have a positive effect on promoting green and sustainable development. At present, the photocatalytic efficiency of these two reactions can yet be greatly enhanced. Herein, a series of carbon nitride-based photocatalysts with triazine and heptazine units were synthesized. The ratio of triazine and heptazine units was successfully adjusted by changing the ratio of raw materials (urea and melem). When the mass ratio of urea to melem was 1:1, the synthesized photocatalyst 1 U/M-CN had the best photocatalytic performance for H₂O₂ production. The amount of H₂O₂ production was increased by 14 times via the addition of 1,2-diphenylethanol (Dpol, β-1 lignin model) to induce the oxidative half-reaction. Under optimal conditions, the concentration of H₂O₂ production and the cleavage efficiency of lignin CC bonds in Dpol reached 1126.1 μmol/g and 91.2 %, respectively. Mechanistic studies show that the electron transfer pathway in 1 U/M-CN follows the S-Scheme mechanism. The photocatalytic production of H₂O₂ conforms to the indirect reaction pathway, and the photocatalytic lignin CC bond cleavage follows the C_β radical mechanism. This work provides a new idea for simultaneous photocatalytic H₂O₂ production and lignin CC bond cleavage by constructing triazine-heptazine-based carbon nitride photocatalysts.