Solar-driven catalytic oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-diformylfuran (DFF) coupled with H2 evolution has been considered a promising approach. The exploration of an active and stable photocatalyst still remains challenging work. Herein, we found that the flexible ultrathin graphitic carbon nitride (UCNT) could be an ideal candidate. The UCNT exhibits photocatalytic performance in selective oxidation of HMF into DFF coupled with H2 evolution with activities of 95.0 and 92.0 μmol g–1 h–1 under visible light irradiation. Importantly, the UCNT also demonstrates high DFF selectivity (95%) and good cycling stability. The activity may be ascribed to the strong specific interaction between HMF and UCNT. Solid-state nuclear magnetic resonance (NMR) and density functional theory (DFT) results reveal that the twisted structure of HMF molecules could form a strong interaction between HMF and UCNT, reducing the dehydrogenation energy barrier for HMF oxidation. In addition, mechanistic studies reveal that •C6H4O3 is the key radical intermediate during the HMF oxidation process by a in situ electron spin resonance (ESR) trapping test. Our work clarifies the interaction of complex biomass molecules on the flexible catalyst surface and provides views on the further development of heterogeneous catalytic biomass conversion.

In order to obtain reliable kinetic parameters, it is required to measure the reaction kinetics of important heterogeneous reactions at ambient relative humidity (RH). In this study, the uptake coefficients and HONO yields for the heterogeneous reaction of NO 2 on kaolin and hematite were measured at RH from 7% to 74% and at ambient pressure in the dark using a coated-wall flow tube reactor. The initial true uptake coefficient (g t,ini ) of NO 2 at RH 7% was measured to be (1.44 AE 0.10) Â 10 À7 and (1.58 AE 0.13) Â 10 À6 on kaolin and hematite, respectively, while it decreased notably on both minerals, accompanied by an increase of HONO yields, as RH increased. The average g t,ini at 32-74% RH was (4.42 AE 1.17) Â 10 À8 and (2.83 AE 0.84) Â 10 À7 on kaolin and hematite, respectively. The corresponding mean HONO yield was (36.0 AE 16.1)% and (75.9 AE 3.32)%, respectively.

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