Photocatalytic selective oxidation of biomass-derived 5-hydroxymethylfurfural to 2,5-diformylfuran on metal-free g-C3N4 under visible light irradiation

Metal-free graphitic carbon nitride (g-C 3 N 4 ) catalyst was synthesized by a simple calcination of melamine. The characterization results indicate that the water treatment during preparation process is in favor of the formation of pore structure, enhancing light-harvest ability and suppressing the recombination of the photoexcited electron-hole pair. The as-prepared g-C 3 N 4 catalyst was applied in the photocatalytic selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF). The effects of incident wavelength, solvent, reaction time and scavenger on the photocatalytic performance were investigated. The results indicate that O 2 − plays a key role as dominant active species in photocatalytic oxidation of 5-HMF. Compared with visible light, the UV light illumination is easier to cause the overoxidation of target product and thus leads to a lower DFF selectivity. Under the irradiation of light with wavelength >400   nm, the highest DFF selectivity of 85.6% can be achieved with HMF conversion of 31.2% in the presence of O 2 .