Cascade Electric Field in ZnIn2S4/CuCo2O4 Photocatalyst for the Selective Oxidation of Biomass-Derived 5-Hydroxymethylfurfural in Aqueous Solutions

The photocatalytic conversion of biomass feedstock represents a promising and environmentally friendly strategy for achieving selective transformation and value addition. The slow charge dynamics and sluggish hole transfer in the oxidation reactions severely limit the photocatalytic activity. Here, the heterojunction is fabricated by synthesizing ultra thin ZnIn2S4 nanoflower with spinel CuCo2O4. The internal and interfacial electric fields are successfully constructed, which shows superior 5-hydroxymethylfurfural (HMF) valorization. HMF undergoes severe mineralization when ZnIn2S4 is used as the catalyst, resulting in 0.9% 2,5-diformylfuran (DFF) yield in water, while the ZnIn2S4/CuCo2O4 heterojunction catalyst exhibits 77% DFF selectivity with 88.6% HMF conversion, The cascaded bulk and internal electric fields greatly reduce the oxidation potential of holes and enhance the charge separation efficiency, thus give a remarkable 70-fold increase in DFF yield. This work overcomes the limitations of ZnIn2S4 application for HMF and similar alcohol oxidation reactions that typically require organic solvents, achieving a high DFF evolution rate of 724.9 µmol·g−1·h−1 in water within the first hour of the reaction, surpassing most reports of photocatalytic HMF selective oxidation.