<p>The potential uses of heterogeneous photocatalysts in photocatalytic water splitting for H₂ production and the breakdown of organic pollutants in wastewater have attracted a lot of attention. In this work, we present the wet impregnation construction of a g-C₃N₄/Fe₂O₃ heterostructure. The successful heterostructure formation was confirmed by XRD analysis and TEM, indicating rhombohedral phases of Fe₂O₃ interfaced with g-C₃N₄. The shifting of Fe 2p and O 1s core levels to lower binding energies in comparison with pristine Fe₂O₃ also confirmed the heterostructure formation. UV–visible absorption spectra showed improved light absorption for g-C₃N₄/Fe₂O₃ relative to pure Fe₂O₃. Photocatalytic studies showed that under natural sunlight, g-C₃N₄/Fe₂O₃ achieved ~ 85% removal of 20 ppm 4-nitrophenol (4-NP) at a rate of 1.5 × 10^–3 min⁻¹, while Fe₂O₃ achieved ~ 40% removal at 4.4 × 10⁻³ min⁻¹. Under artificial light illumination, the heterostructure degraded ~ 80% of 4-NP, compared to ~ 25% degradation by Fe₂O_3. Kinetic studies revealed that the photodegradation of 4-NP under natural sunlight by these photocatalysts followed the Langmuir–Hinshelwood model. Reactive oxygen species (ROS) scavenging experiments validated that superoxide anion radicals (O₂^−•) were the predominant species responsible for 4-NP degradation, with a minor contribution from hydroxyl radicals (^•OH). In addition, the g-C₃N₄/Fe₂O₃ heterostructure displayed higher photocatalytic hydrogen evolution (~ 60 mmol g⁻¹), which surpassed both individual g-C₃N₄ and Fe₂O₃. These results demonstrate the effective dual utility of g-C₃N₄/Fe₂O₃ for both wastewater treatment and green hydrogen production.</p>