Nb 2 O 5 /g‐C 3 N 4 Heterojunction Facilitates 2,5‐Diformylfuran Production via Photocatalytic Oxidation of 5‐Hydroxymethylfurfural under Direct Sunlight Irradiation

Herein, we report the enriched synthesis of 2,5‐diformylfuran (DFF) from 5‐hydroxymethylfurfural (HMF) over a Nb 2 O 5 /g‐C 3 N 4 heterojunction under direct sunlight irradiation. The analytical characterization established the improved quality of the heterojunction compared to the original characteristics of the single photocatalysts, especially the surface properties and alignment of band edge positions, towards the control of recombination of the charge carriers for its application in the photocatalytic oxidation of HMF. Acetonitrile possessing a moderate polarity provided significant assistance in the higher HMF conversion (72 %), resulting in a 61 % wt. DFF yield and 84 % selectivity under modest reaction conditions. The result is comparatively 1.5 to 3.3 times higher than the single photocatalysts (g‐C 3 N 4 and Nb 2 O 5 ) under similar conditions, indicating the potential of the heterostructure (type‐II heterojunction) in DFF synthesis through the synergistic action of Nb 2 O 5 and g‐C 3 N 4 by controlling the e − –h + pair recombination. Moreover, the heterojunction enabled selective conversion without the supply of O 2 gas or oxidizing agent. The photogenerated holes (h + ) played a key role in the augmented HMF conversion (based on radical trap studies), which obeyed first‐order kinetics.