<p>The present research utilizes a sol–gel auto-combustion method to produce NiFe₂O₄/g-C₃N₄ heterojunction and utilized XRD, FT-IR, SEM, EDX, HRTEM, XPS, and UV–Vis DRS analytical techniques to evaluate physical, chemical, and optical properties. Compared to other routes like one-pot hydrothermal synthesis or sol–gel for P-doped variants, this method effectively produces the desired heterojunction, contributing to enhanced photocatalytic degradation of methylene blue dye. The XRD study reveals that the produced NiFe₂O₄/g-C₃N₄ heterojunction exhibits two-phase mixing, while pure g-C₃N₄ and NiFe₂O₄ exhibit hexagonal and cubic phases, respectively. Pure g-C₃N₄ and NiFe₂O₄, and g-NiFe₂O₄/g-C₃N₄ have energy band gaps of 2.60, 1.54, and 2.49&#xa0;eV, respectively. The prepared heterojunctions were used as photocatalysts to degrade the methylene blue (MB) dye. The prepared NiFe₂O₄/g-C₃N₄ heterojunction showed higher photocatalytic degradation efficacy than pristine g-C₃N₄ and NiFe₂O₄ due to greater visible light absorbance and strong heterojunction formation. The 10% NiFe₂O₄/g-C₃N₄ heterojunction showed 97.82% (0.0255&#xa0;min⁻¹) degradation efficiency towards MB in 100&#xa0;min, and it was 4.88 times higher than pristine g-C₃N₄ (0.0052&#xa0;min⁻¹) and 7.25 times higher than pure NiFe₂O₄ (0.0035&#xa0;min⁻¹) nanoparticles. The radical trapping experiment confirms that the superoxide (O₂^•−) and hydroxyl (^•OH) radicals are the key species in the MB degradation. Therefore, the Z-scheme NiFe₂O₄/g-C₃N₄ heterojunction acts as a potential photocatalyst and can be used practically for wastewater treatment.</p> Graphical Abstract <p></p>