Selective and efficient cleavage of Cα-Cβ bond in lignin models and native lignin through S-scheme CeO2/g-C3N4 heterojunction photocatalyst

Abstract

The selective photocatalytic breaking of C_α-C_β bonds holds significant promise for converting lignin biomass into value-added aromatic chemicals. However, achieving high efficiency under environmentally benign conditions remains challenging due to the high bond-dissociation energy involved and the harsh depolymerization requirements. Herein, a 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 at ambient condition. The fabrication of S-scheme heterojunction between CeO₂ nanoparticle and g-C₃N₄ nanosheet not only broadens the optical absorption range, but also promotes the redox capacities and charge transport efficiency in two semi-components, collectively contributing to 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 hole and superoxide radical played pivotal roles in the photocatalytic Cα-Cβ bond cleavage process. This work presented a perspective for efficiently valorizing lignin into valuable aromatic compounds by green energy.