Selective Photocatalytic Cleavage of Cα–Cβ Bond in Natural Lignin and Its Models Enabled by Z-Scheme Bi QDs/g-C3N4 van der Waals Heterojunction

Abstract

Photocatalytic valorization of lignin into value-added aromatic chemicals constitutes a sustainable strategy for utilizing renewable biomass resources. However, the efficiency of this process is hampered by the requirement of harsh conditions and the inherent complexity of lignin depolymerization. To address these challenges, a novel, cost-effective, and efficient strategy is reported for selectively cleaving the lignin Cα–Cβ bonds over Z-scheme mixed-dimensional bismuth quantum dots/ultrathin g-C3N4 nanosheet (Bi QDs/g-C3N4) van der Waals (vdW) heterojunction under ambient conditions and visible-light illumination. The design of the vdW heterojunction between Bi QDs and the g-C3N4 nanosheet not only improves the interface separation and transmission of photoexcited carriers but also broadens the visible-light absorption range, collectively culminating in observed superior catalytic performance. 15Bi QDs/g-C3N4 achieved complete conversion of lignin β–O–4 models, with a Cα–Cβ bond breakage selectivity as high as 97.7%. Additionally, the universality of this system was further confirmed through the efficient valorization of native lignin. Combined experimental and theoretical calculations demonstrate that the interfacial transfer of photogenerated charge carriers in this system follows a Z-scheme pathway. Mechanistic experiments indicated that the photoexcited holes and ·O2– were the main active species, synergistically driving the efficient breakage of lignin Cα–Cβ bonds. This work provides a profound insight into building an advanced photocatalytic system for valorizing lignin into valuable chemicals.