Cobalt-doped ZnIn₂S₄for highly efficient photocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran

The photocatalytic transformation of 5-hydroxymethylfurfural (HMF) into high-value chemicals has been widely studied; however, selectively converting HMF to the valuable chemical 2,5-diformylfuran (DFF) remains challenging. In this work, we explored the doping of transition metal Co into ZnIn₂S₄ and systematically investigated the photocatalytic conversion of HMF to DFF. Doping transition metal Co into ZnIn₂S₄ significantly enhances its catalytic activity for converting HMF to DFF, achieving a yield of 88%, and the selectivity approaches 90%, which is significantly higher than that of pure ZnIn₂S₄, thus improving HMF utilization. Electron spin resonance (ESR) experiments show that doping Co promotes the formation of singlet oxygen (¹O₂) and superoxide radicals (·O₂⁻). Density functional theory (DFT) calculations suggest that introducing Co reduced the surface binding energy between DFF and the catalyst, and accelerated the desorption of DFF from the Co/ZIS surface, improving active site utilization and enhancing HMF-to-DFF conversion activity. Also, in situ FTIR and DFT studied the surface O₂ adsorption behavior. This work presents an effective strategy for constructing a novel, low-cost photocatalytic system, providing new insights into HMF transformation into high-value chemicals.