Microwave-Assisted Green Precipitation Synthesis of NiO-ZnO-MgO Nanocomposite for Removal of Methylene Blue From Wastewater

A NiO-ZnO-MgO ternary heterojunction nanocomposite was synthesized in this work using a microwave-assisted green precipitation approach to improve the photocatalytic removal of methylene blue (MB) dye driven by visible light. Structural analysis via SEM explored round-shaped particles with an average dimension of 14 nm, whereas FTIR established the existence of Zn-O (512 cm⁻¹), Ni-O (564 cm⁻¹), and Mg-O (1399 cm⁻¹) vibrational modes. BET surface analysis demonstrated a high specific surface area of 77.26 m²/g, a pore radius of 15.98 Å, and a pore volume of 0.037 cc/g. Under optimized conditions (pH 9.2, 40°C, visible light intensity of 100 W), the nanocomposite achieved a MB dye degradation efficiency of 90.9% within 120 min, which is superior to many conventional photocatalysts such as TiO₂ (15%–30%), ZnO (70%–85%), and binary ZnO-NiO composites (~80%–85%) under similar light exposure conditions. The quantum yield (QY) and space–time yield (STY) were estimated as 7.49 × 10⁻⁷ molecules/photon and 6.57 × 10⁻⁸ molecules/photon·mg, respectively. Degradation performance was further enhanced by the creation of defect states and reactive oxygen species (ROS), especially superoxide radicals (•O₂⁻). The NiO-ZnO-MgO nanocomposite's promise as an economical and ecologically friendly photocatalyst for wastewater treatment is shown by these results.