Study on photocatalytic depolymerization of lignin C_β—O bonds by 3-MPA modified CdS-ZnIn₂S₄ semiconductor composite catalyst

As the most abundant aromatic resource in nature, lignin has great potential in the production of bio-based fuels and chemicals. Photocatalysis, with its advantages of mild reaction conditions, low energy consumption, and high selectivity, is widely applied in the field of biomass conversion. In this study, a lavender-like 6.5-ZIS (3-MPA_95%) composite photocatalyst was prepared using the hydrothermal method, aiming to effectively depolymerize the lignin model compound 2-phenoxy-1-phenylethanol (PP-ol) under ambient temperature and pressure. The results demonstrated that the composite catalyst 6.5-ZIS (3-MPA_95%) exhibits a significantly larger specific surface area, a wider light absorption range, and higher carrier transport efficiency. Under optimal reaction conditions, the depolymerization rate of PP-ol reached up to 98.74%, and the yields of phenol, benzaldehyde, and acetophenone were 71.85%, 5.31%, and 70.65%, respectively; it also exhibited good recyclability. Mechanistic studies from the perspective of free radicals confirmed that the composite catalyst 6.5-ZIS (3-MPA_95%) generates photogenerated electrons and holes during the depolymerization process. Through the synergistic action of ·OH, ·O₂⁻, and Cα·, the C_β—O bond is cleaved to produce phenol and acetophenone. This study is expected to provide solid theoretical support and practical applications for the photocatalytic cleavage of the C_β—O bond in model compounds.