Engineering charge transfer in a two-dimensional S-scheme heterojunction photocatalyst via built-in electric field for selective biomass valorization

Photocatalytic selective oxidation of 5-hydroxymethylfurfural (HMF) into value-added chemicals offers a promising green route to bridge biomass resources with diverse industries owing to its low-cost valorization and environmental sustainability. Nevertheless, efficiently upgrading HMF into target products remains a big challenge. Herein, a microflower-like hybrid S-scheme heterojunction photocatalyst was developed via the in situ growth of layered ZnIn2S4 on NH2-MIL-125 (Ti) metal-organic framework nanosheets (denoted as ZIS/NMTs) for HMF oxidation. The thin nanosheet structure of ZIS/NMTs provided abundant heterojunction interfaces and numerous exposed active sites for charge migration and molecule adsorption. Meanwhile, systematic spectroscopic analysis and theoretical calculations comprehensively demonstrated the formation of an interface internal electric field in the ZIS/NMT S-scheme heterojunction, accelerating interfacial charge separation of photo-induced carriers. The optimal ZIS/NMT-10 photocatalyst exhibited impressive visible-light photocatalytic activity with nearly complete HMF conversion and 92.5% 5-formyl-2-furancarboxylic acid (FFCA) selectivity, which could be attributed to the synergistic effect of its two components. This study presents new insights into designing efficient heterojunction photocatalysts for converting HMF into target products and can be extended to other biomass valorization.