Schottky Barrier-Mediated Charge Separation in an MXene/ZnIn2S4 Heterojunction for Enhanced Photocatalytic HMF-to-DFF Conversion

2,5-Diformylfuran (DFF) is an important biomass-derived platform chemical, widely recognized as a key intermediate building block in the synthesis of biodegradable polymers and pharmaceutical compounds. The mild and sustainable nature of photocatalysis has attracted considerable attention for such valorization processes, highlighting the need for in-depth exploration of heterostructure-based photocatalysts to enhance catalytic performance. In this study, we report the fabrication and photocatalytic application of a Nb2CTx MXene/ZnIn2S4 (ZIS) Schottky heterojunction with intimate interfacial contact. This heterostructure significantly enhances the separation efficiency of photogenerated charge carriers while prolonging their lifetime. The observed enhancement is attributed to the synergistic interaction between the n-type ZIS semiconductor and the two-dimensional metallic conductor MXene, which induces favorable band bending in ZIS and facilitates the formation of a Schottky barrier at the MXene–ZIS interface. This barrier effectively inhibits electron backflow, thereby promoting charge carrier separation and enhancing interfacial charge dynamics. Compared to pristine ZIS, the Nb2CTx/ZIS heterojunction catalyst achieves a significantly higher DFF yield under ambient temperature and pressure, without the need for additional oxidants. This finding not only demonstrates a highly efficient route for DFF production under mild conditions but also offers a new design strategy for MXene-based Schottky heterojunctions in biomass valorization via photocatalysis.