Selective and efficient cleavage of Cα–Cβ bonds in lignin models and native lignin using an S-scheme CeO2/g-C3N4 heterojunction photocatalyst†

Abstract

The selective photocatalytic breaking of C_α–C_β bonds holds significant promise in converting lignin biomass into value-added aromatic chemicals. However, achieving high efficiency under environmentally benign conditions remains challenging owing to the high bond-dissociation energy involved and the harsh depolymerization requirements. Herein, an S-scheme CeO₂/g-C₃N₄ heterojunction photocatalyst was successfully constructed for the efficient cleavage of the crucial C_α–C_β bond in natural lignin and its β-O-4 model compounds under visible light irradiation and ambient conditions. The fabrication of the S-scheme heterojunction between CeO₂ nanoparticles and g-C₃N₄ nanosheets not only broadened the optical absorption range but also promoted the redox capacities and charge transport efficiency of the two semi-components, collectively contributing to the observed superior photocatalytic performance. Remarkably, the photocatalytic system achieved nearly quantitative conversion (100%) of 2-phenoxy-1-phenylethanol (PP-ol) with C_α–C_β bond cleavage selectivity of 96.7%. Meanwhile, the versatility of this photocatalyst was further demonstrated through the efficient conversion of various β-O-4 models and natural lignin. Mechanistic studies confirmed that photogenerated holes and superoxide radicals played pivotal roles in the photocatalytic C_α–C_β bond cleavage process. This work presents a perspective for efficiently valorizing lignin into valuable aromatic compounds using green energy.