Herein, we report the enriched synthesis of 2,5‐diformylfuran (DFF) from 5‐hydroxymethylfurfural (HMF) over a Nb2O5/g‐C3N4 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‐C3N4 and Nb2O5) under similar conditions, indicating the potential of the heterostructure (type‐II heterojunction) in DFF synthesis through the synergistic action of Nb2O5 and g‐C3N4 by controlling the e−–h+ pair recombination. Moreover, the heterojunction enabled selective conversion without the supply of O2 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. [ABSTRACT FROM AUTHOR]