S-Scheme Heterojunction Cs3Bi2Br9/Bi2WO6 for Efficient Photocatalytic Cleavage of C-C Bonds in β-1 Lignin Models

Abstract

The selective cleavage of C-C bonds is a significant process for depolymerizing lignin to obtain high-value aromatic chemicals. However, achieving this under mild reaction conditions remains a formidable challenge under mild reaction conditions due to the relatively high bond dissociation energy. Herein, a lead-free Cs3Bi2Br9/Bi2WO6 (CBB/BWO) photocatalyst was successfully constructed via electrostatic self-assembly. Compared to pure CBB and BWO, the resulting CBB/BWO exhibited a well-designed S-scheme heterojunction structure with enhanced light absorption and separation of electrons and holes due to the internal electric field between CBB and BWO. The CBB/BWO photocatalyst demonstrated excellent catalytic performance in the selective Cα-Cβ bond cleavage of β-1 lignin models with reaction rates 6.8 times and 3.8 times higher than those of the single-component catalysts CBB and BWO, respectively. Various Cα-Cβ model compounds were depolymerized into the corresponding aromatic aldehydes and aromatic acid products with yields ranging from 76% to 88%. Mechanistic studies revealed that the formation of a six-membered ring transition state by Cβ radical intermediate and superoxide anion radical played a crucial role in Cα-Cβ bond cleavage.