Carbon Doping Tailors Terminal Groups in g-C ₃ N ₄ for Product-Tunable Photocatalytic 5-Hydroxymethylfurfural Valorization via Enhanced Aqueous Mass Transfer

Photocatalytic biomass conversion in water is an ideal method for producing high-value-added chemicals. Nonetheless, as a pivotal bioplatform molecule, the aqueous photocatalytic oxidation of HMF often faces challenges. This research introduces a carbon-integrated graphitic carbon nitride (g-C3N4) capable of directly converting HMF into diverse products in aqueous solution. The incorporated carbon substitutes the positions of the central nitrogen atom within the triazine framework, generating a shallow acceptor level that facilitates charge separation and prolongs carrier lifetimes. More importantly, carbon doping increases the amino-N content in the framework, not only providing active sites for oxidation but also enabling efficient mass transfer and activation of C–H and O–H bonds in hydroxymethyl via intermolecular hydrogen bonding, thereby mitigating HMF mineralization by suppressing its solvation while preserving its selective oxidation pathway. As a result, the modified catalyst not only achieves controllable products, including DFF, FFCA, FDCA, etc., but also increases the product yield from nearly 0 to over 40%. This study emphasizes the crucial role of constructing anchoring sites on the catalyst surface to weaken the solvation of HMF, thereby enhancing its mass transfer and adsorption, which significantly promote HMF conversion.