Abstract: Combining solar-driven H₂ evolution with the selective conversion of the biomass platform compound 5-hydroxymethylfurfural (HMF) into high-value-added chemicals is promising. However, the development of this approach is impeded by slow electron-hole separation and uncontrollable HMF conversion. In this study, we present a novel S-scheme sp²-carbon COF (TFPD)/CdS heterojunction bifunctional photocatalyst for the highly selective oxidation of HMF or C-C coupling, integrated with H₂ production. The TFPD/CdS heterojunction forms an intrinsic electric field that facilitates efficient charge separation and migration during the photocatalytic process. Additionally, theoretical calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reveal that the adsorption and desorption of (CHOH)C₄H₂(CHO)· radical on the catalyst surface are critical for the selective conversion of HMF. Consequently, depending on the reaction atmosphere, this photocatalyst selectively oxidizes HMF to 2,5-diformylfuran (DFF) with over 90 % selectivity, or to 2,5-furandicarboxylic acid (FDCA) with approximately 80 % selectivity. Notably, by controlling the solvent to promote the desorption of the (CHOH)C₄H₂(CHO)· radical, this system also produces HMF dimers with about 89 % selectivity, alongside simultaneous H₂ generation. This work pioneers the photocatalytic oxidation of HMF to C-C coupling products, providing insights into guiding radical reaction pathways for the selective photocatalytic conversion of HMF.

Key words: Covalent organic frameworks, Hydrogen evolution, Selective oxidation, 5-hydroxymethylfurfural, S-scheme heterojunction