Benzene-modified carbon nitride with enhanced π–π adsorption for efficient lignin C–C bond photocleavage

Photocatalytic cleavage of lignin C–C bonds using graphitic carbon nitride (g-C 3 N 4 ) offers a sustainable route to aromatic monomers; however, its practical efficiency is critically constrained by the generation yield of superoxide radicals. Herein, we address this constraint through a simple yet effective design: replacing the edge amino groups of g-C 3 N 4 with benzene rings to construct a benzene–g-C 3 N 4 copolymer. DFT calculations suggest that the introduced benzene ring contributes an empty low-lying orbital that may serve as a temporary electron trap. This effect, together with in-situ XPS evidence for photo-induced charge redistribution, is consistent with the formation of an S-scheme charge transfer pathway and the observed suppression of picosecond-scale electron–hole recombination. The benzene ring is proposed to function as a π–π adsorption anchor, selectively binding the lignin C β carbocation in close proximity to the C–N = C sites where superoxide radicals are generated. This directed adsorption overcomes the mass-transfer limitation of superoxide radical typically encountered under chemisorption conditions, thereby enabling spontaneous and diffusion-free oxidation of the C β site. This benzene–g-C 3 N 4 copolymer exhibits a 134% higher reaction efficiency than g-C 3 N 4 in C–C bond photocleavage, while also demonstrating excellent cleavage performance on industrial lignin. Collectively, this work offers an effective approach to overcoming kinetic limitations in photocatalysis.