Unveiling the pathway of water activation and proton transfer in photocatalytic lignin biomass hydrogenolysis over Mo vacancy and Mo–S bond engineered Bi2Mo1–xO6/ZnIn2S4 S-scheme heterojunction

Utilizing water as a green and abundant proton source for the photocatalytic hydrogenolysis of lignin under mild conditions represents a promising approach for biomass conversion. However, the microscopic mechanism of water activation and subsequent proton transfer remains unclear, hindering the rational design of efficient catalytic system. Herein, Mo vacancy-engineered S-scheme Bi 2 Mo 1– x O 6 /ZnIn 2 S 4 heterojunction was constructed via a facile in-situ solvothermal process. Combining density functional theory calculations, in-situ electron paramagnetic resonance and X-ray photoelectron spectroscopy analyses reveal that the presented Mo vacancies play a dual role; they not only induce the formation of interfacial Mo–S bonds, creating atomic-level charge-transfer channels, but also drive hole localization, promoting water dissociation and generating protons for the selective hydrogenolysis of lignin C β −O bonds. Crucially, isotope labeling experiments directly confirm that the protons generated from water dissociation serve as the direct hydrogen source for the lignin hydrogenolysis reaction. Under visible light exposure ( λ > 420 nm) and an air atmosphere, the developed catalyst achieves over 90% photoconversion of 2-phenoxy-1-phenylethanol (PP-ol) lignin with a quantum yield of 5.71%, outperforming the most reported photocatalysts. Through synergistic engineering of Mo vacancies and interfacial bonds in S-scheme heterojunctions, this study provides key insights into the water-driven proton transfer mechanism in photocatalytic hydrogenolysis of lignin, highlighting an efficient biomass photoconversion strategy.