Sulfur Vacancy-Driven Water Activation for Proton-Enhanced Photocatalytic Lignin Hydrogenolysis

Photocatalytic lignin valorization has garnered significant interest because of its mild reaction conditions and high selectivity. However, the unclear relationships among photocatalysts, reaction solvents, and catalytic activities have hindered further exploration. Herein, we report the innovative synthesis of sulfur vacancy-rich MoS2@ZnIn2S4 heterostructures through one-pot sulfidation of Mo-based metal–organic frameworks (MOFs) for efficient photocatalytic lignin depolymerization. The Mo-MOF-derived MoS2 provides a large surface area and high porosity, enhancing mass transfer, whereas the sulfur vacancies on ZnIn2S4 promote effective charge carrier separation. Notably, the presence of water in the reaction solvent enables the sulfur vacancies to efficiently adsorb and activate water molecules, facilitating proton generation from water dissociation for selective lignin Cβ–O bond hydrogenolysis. The bond cleavage efficiency exhibits a volcano-type trend with increasing water content, achieving optimal performance with 100% conversion of the lignin model compound 2-phenoxy-1-phenylethanol, yielding 78% phenol and 89% acetophenone. This performance significantly surpasses those of MoS2, ZnIn2S4, and the sulfur vacancy-poor MoS2@ZnIn2S4. This work provides critical insights into the solvent-dependent reactivity of catalysts in lignin depolymerization and underscores the potential of defect engineering in photocatalytic biomass valorization.