Facilitating extensive CC bond cleavage in lignin models through customized CeO2/C3N4 S-scheme heterojunction

Abstract

Photocatalytic depolymerization of lignin offers a sustainable approach to producing high-value-added aromatic compounds. Recently, carbon nitride has demonstrated notable selectivity for the CC bonds in lignin model compounds. However, limitations of pure carbon nitride include the low mobility of photogenerated electrons and the difficulty in precisely controlling the cleavage pathways and products of CC bonds. In this study, we constructed an S-Scheme heterojunction by in situ loading of Ce ions onto C₃N₄ to form a CeO₂/C₃N₄ composite. This heterojunction achieves efficient lignin depolymerization under blue LED irradiation in an oxygen-rich environment. Comparative analysis indicated that the yield of primary products, benzaldehyde and phenyl formate, increased by 7.8-fold and 7.75-fold, respectively, compared with pure CeO₂, and by 1.4 and 1.8 times relative to unmodified C₃N₄. After optimizing the reaction conditions, dealkalized lignin is applied to the system and successfully depolymerized. Comprehensive characterization and theoretical simulations verify the heterojunction's ability to enhance carrier separation and redox activity, with CeO₂ serving as an active dehydrogenation site that significantly boosts the depolymerization efficiency of lignin model compounds. This photocatalytic strategy presents a valuable step forward in lignin valorization and supports the sustainable utilization of biomass resources.