g-C3N4/Bi2MoO6 heterojunctions for enhanced visible light photocatalytic oxidation of biomass-derived 5-hydroxymethylfurfural to 2,5-diformylfuran under ambient conditions

Abstract

Sustainable green energy has emerged as critically important topics, with catalytic valorization and utilization of biomass receiving considerable attentions in recent years. This study investigates the photocatalytic selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) using sonochemically synthesized g-C3N4/Bi2MoO6 heterostructured catalyst. A series of composites with varying mass ratios were fabricated, with the 1:1 (w/w) g-C3N4/Bi2MoO6 demonstrating the optimal catalytic performance. Systematic investigations were conducted to elucidate the effects of reaction conditions including irradiation wavelength, solvent polarity, reaction atmosphere, and substrate concentration on photocatalytic efficiency. The system achieved exceptional DFF selectivity of 90.8% with 92.2% HMF conversion under very mild conditions (air atmosphere and 10 W blue LED, 455 nm) with the generation of H2O2 as co-product, demonstrated the extremely high catalytic activity of the catalyst. The catalyst exhibited remarkable stability, as confirmed by recycling tests and post-reaction X-ray diffraction (XRD) characterization. Mechanistic studies through radical quenching experiments and electron paramagnetic resonance (EPR) spectroscopy identified superoxide radicals (·O2−) and photogenerated holes (h+) as the dominant reactive species, propose a dual-pathway oxidation mechanism. In this study, the S-scheme heterojunction charge transfer mechanism was comprehensively validated through systematic characterization and theoretical calculations, highlighting the pivotal role of S-scheme heterojunctions in selective oxidation reactions.