Sodium Chloride-Assisted Polymerization of Carbon Nitride for Efficient Photocatalytic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

The photocatalytic oxidation of 5-hydroxymethylfurfural (5-HMF) to 2,5-furandicarboxylic acid (FDCA) represents a sustainable strategy for the conversion of biomass-based platform compounds into high-value chemicals. In this work, a supramolecular self-assembly strategy is employed to synthesize tubular carbon nitride (T-MCN), and sodium ion-doped carbon nitride (Na-T-MCN) is obtained via sodium chloride-assisted thermal polymerization. The optimized catalyst demonstrates superior activity in the oxidation of 5-HMF, achieving a high yield of FDCA (90%) within 8 h. The exceptional photocatalytic performance of Na-T-MCN is attributed to the incorporation of Na⁺ ions and cyanamide groups, which facilitate the separation of photogenerated charges and holes. To elucidate the underlying mechanism, intermediate trapping experiments and electron paramagnetic resonance (EPR) spectroscopy are employed to investigate the dynamics of photoinduced charge separation, electron transfer, and the reaction pathway of photocatalytic oxidation of 5-HMF. The findings reveal that the key active species in the oxidation reaction are the ^•O₂^– and h⁺ species. This study provides a viable and efficient strategy for converting biomass platform compounds into high-value-added products.