Engineered Mn4+-OV-Co2+ sites in Mn-Co spinel for enhanced photocatalytic oxidation of HMF to high-value chemicals

5-Hydroxymethylfurfural (HMF) serves as a key platform molecule for producing high-value chemicals via green and efficient photocatalytic oxidation. Transition metal oxides, particularly spinel substances, are promising heterogeneous catalysts due to their ability to promote interfacial electron transfer. However, the impact of interfacial electron transfer in HMF photocatalytic oxidation on spinel catalysts remains largely unexplored. In this study, we engineered Mn 4+ -O V -Co 2+ active sites in cobalt-based spinel by in-situ (MCO 4-δ -1) and post-doping (MCO 4-δ -2) strategies to investigate their impact on photocatalytic HMF oxidation. The microstructure morphology, chemical valence states, and band structure of prepared catalysts were systematically characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra (DRS) techniques. The results revealed that the post-doping catalyst (MCO 4-δ -2) exhibited a higher density of surface oxygen vacancy (Ov), significantly enhancing charge transfer and HMF photocatalytic conversion activity. Specifically, MCO 4-δ -2 achieved an outstanding HMF oxidation product yield of 356.55 μmol g −1 under visible light over 4 h. Furthermore, density functional theory (DFT) calculations provided mechanistic insights, revealing that the oxygen in the aldehyde group of HMF preferentially occupies surface Ov sites at Mn 4+ -Ov-Co 2+ interfaces, thereby facilitating selective HMF oxidation pathways. This study not only expand the application scope of cobalt-based spinel photocatalysts in biomass valorization but also provides an insight on the effects of doping-induced interfacial electronic effects in photocatalytic oxidation reactions.