Synergistic engineering of oxygen-doped porous carbon nitride for visible-light-driven photocatalytic lignin valorization via selective Cα–Cβ bond cleavage

Photocatalytic depolymerization of lignin represents a sustainable route to value-added aromatic compounds; however, the selective cleavage of inherently stable C–C bonds remains a central challenge. Herein, we report the concerted engineering of electronic and textural properties in g-C 3 N 4 to achieve efficient photocatalytic cleavage of lignin C α –C β bonds. An oxygen-doped porous g-C 3 N 4 (O-PCN) catalyst was synthesized via one-step thermal co-condensation of nitric acid-treated melamine with ammonium chloride. Oxygen doping modulates the electronic band structure, enhancing the oxidative power of photogenerated holes. Concurrently, the gas templating effect from ammonium chloride decomposition creates a mesoporous architecture with a high specific surface area (131 m 2 g −1 ), which facilitates oxygen adsorption and provides abundant accessible active sites. This synergistic optimization leads to exceptional performance in the photocatalytic cleavage of the lignin model compound 2-phenoxy-1-phenylethanol. Under 405 nm light irradiation, the O-PCN catalyst achieves 96.9% substrate conversion with 92.9% benzaldehyde yield, significantly surpassing pristine g-C 3 N 4 (48.7%), oxygen-doped bulk (62.1%), and porous (71.0%) analogs. Mechanistic investigations reveal that photogenerated holes and 1 O 2 are the primary active species driving the selective bond cleavage. More encouragingly, for the depolymerization of organosolv lignin that possesses natural lignin structures, a 4 wt% yield of high-value vanillin could be obtained. This work demonstrates a dual-strategy design for simultaneously tailoring the photophysical and surface properties of photocatalysts, offering a promising avenue for solar-driven biomass valorization.