Influence of Oxygen-Containing functional groups in sulfonated biochar on 5-Hydroxymethylfurfural synthesis in aqueous Solvents: Mechanistic insights and theoretical analysis

This study presents a novel method for synthesizing biochar catalysts with multiple oxygen-containing functional groups, enabling the high-yield production of the biomass-derived platform compound 5-hydroxymethylfurfural (HMF) under mild conditions. Using an aqueous–methyl isobutyl ketone (MIBK) biphasic system, fructose conversion at 100°C for 4 h achieved an HMF yield of 92%. Furthermore, the roles of various functional groups on sulfonated biochar in substrate conversion were elucidated through molecular binding energy calculations, intermolecular weak interaction analysis, and frontier orbital theory. Detailed density functional theory (DFT) calculations further explored the catalytic mechanism, reaction energy barriers, and solvent effects in aqueous-phase fructose-to-HMF conversion. The results revealed that, compared to sulfate and sulfonic groups, hydroxyl and carboxyl groups on sulfonated biochar exhibited higher binding energies with fructose but lower energy gaps, facilitating electron exchange with reaction substrates and promoting nucleophilic side reactions. This study provides a solid theoretical foundation and valuable insights for the efficient and green synthesis of HMF using biochar catalysts in aqueous solvents.