Photocatalytic selective oxidation of biomass-derived 5-hydroxymethylfurfural to 2,5-diformylfuran under ambient conditions over CdIn2S4/g-C3N4 heterojunctions

Abstract

Selective photocatalytic oxidation rather than mineralisation is essential for the catalytic valorisation of biomass, which requires precise control of the generation of reactive oxygen species via the rational construction of heterogeneous junctions. In this paper, CdIn₂S₄/g-C₃N₄ (CIS/CNNS) heterojunctions were constructed by a microwave-assisted method and used for selective photocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF), a key intermediate for fine chemical synthesis and an important furan-based polymer monomer. According to the electron transfer mechanism of the heterojunctions, the effective separation of charges and holes led to a significant enhancement of the utilization efficiency of photogenerated electrons (PGEs). Specifically, the valence band (VB) potential of the constructed heterojunctions did not reach the oxidation potential of ˙OH/OH⁻, which avoided the massive generation of strongly oxidizing active species ˙OH and thus increased the reaction selectivity. Under visible light irradiation, 65.2% HMF conversion and 91.5% DFF selectivity could be achieved over CIS/CNNS, with a product yield 3.26 times higher than monomeric CdlIn₂S₄ and 4.2 times higher than monomeric CNNS. The radical quenching experiments verified that ˙O₂⁻ was the predominant active species in the reaction process, and the ˙O₂⁻ signal of the composite was significantly enhanced in the ESR characterization, achieving highly selective conversion of HMF to DFF.