Highly Selective Photocatalytic Conversion of 5-Hydroxymethylfurfural to 2,5-Diformylfuran by ZnS Nanocrystals.

The photocatalytic oxidation of 5-hydroxymethylfurfural (5-HMF) to 2,5-diformylfuran (DFF) is very attractive for its economic and environmental values. How to improve the selectivity to DFF and suppress the deep oxidation to by-products (e.g., 5-formyl-2-furancarboxylic acid, 2,5-furandicarboxylic acid, and maleic acid) is challenging. Here, the utilization of ZnS nanocrystals (7-8 nm) is proposed with different crystalline structures for the photocatalytic oxidation of 5-HMF to DFF. By using the cubic ZnS nanocrystals, the selectivity and yield of DFF can both reach 99%. The underlying mechanism for the high performance of cubic ZnS nanocrystals is studied by combination of photoelectric properties, quenching experiments, in situ electron spin resonance measurements, and theoretical calculations. It is found that the cubic ZnS nanocrystals have medium ability for both adsorbing and activating O₂, thus suppressing the deep oxidation of 5-HMF to by-products and improving the DFF selectivity.