Solar-Driven Selective Photocatalytic Self-Hydrogen Transfer Cleavage of Lignin Models by a ZnIn₂S₄/TiO₂ Heterojunction with Efficient Internal Electric Field

Photocatalysis under mild conditions has been demonstrated as an effective way of depolymerizing lignin to produce aromatic monomers. However, challenges still persist in light absorption, charge separation, and charge utilization. The efficiency and selectivity of lignin cleavage still require further improvement. In response to these challenges, a type-II heterojunction ZnIn2S4 nanoflowers/TiO2 nanosheets (ZT) was used to selectively break the Cβ–O bond of β-O-4 linkage under solar illumination. The best conversion rate is 98%, with almost no intermediate product formed, and the yields of main products are 85 and 67%, respectively. According to the material characterization results, the establishment of heterojunction enhances the catalyst light absorption range and forms a powerful internal electric field and efficient type-II electron transfer pathway. Therefore, ZT heterojunction enhances charge separation efficiency, playing a crucial role in breaking the Cβ–O bond. This study offers a promising strategy for the future development of photocatalytic lignin value-added conversion.