Hydroxymethylfurfural adsorption modulating charge separation characteristics of carbon-rich carbon nitrides for simultaneous photocatalytic hydrogen evolution and 2,5-diformylfuran production

Carbon-rich melon-based carbon nitrides (CNs), in which the sp2 N atoms and the terminal C-NH2 within the heptazine rings are partially replaced by the graphitic carbon atoms and C-H terminals, respectively, are synthesized through the condensation of 2,4,6-triaminopyrimidine-added supramolecular complexes comprising melamine and cyanuric acid. Optical characterizations reveal that increasing the C/N ratio in CNs improves their light-harvesting and charge-separation capabilities. Nevertheless, the photocatalytic activities of carbon nitrides reach an optimal level at an appropriate C/N ratio for simultaneous H-2 evolution and 2,5-diformylfuran (DFF) production from 5-(hydroxymethyl) furfural (HMF) aqueous solution. Hydrogen evolution from water and DFF production by selective HMF oxidation are driven by photogenerated electrons and holes, respectively. Density functional theory calculations suggest that the adsorption of HMF on carbon-CN dramatically influences the molecular orbital contributions to the lowest singlet excited state, altering its charge separation character and, consequently, the photocatalytic activity. The improvement of charge separation in the optimized CN by HMF adsorption is further confirmed by experimental measurements. (c) 2024 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.