Photocatalytic Performance of the Synergetic Coupling of NiO-MgO Nanostructures on a g-C3N4 Composite Towards Methylene Blue Under Visible-Light Irradiation

In this study, a ternary Ni/Mg/g-C3N4 composite was synthesized via a controlled precipitation–calcination route and evaluated for its visible-light-assisted degradation of methylene blue (MB). The structural, morphological, and optical characteristics of the composites were systematically investigated using XRD, FT-IR, FESEM, BET, and UV–Vis analyses. The results confirmed the successful construction of Ni/Mg/g-C3N4 heterojunctions with strong interfacial coupling and enhanced surface porosity. Among all samples, the Ni/Mg/CN20 composite exhibited the highest activity, achieving 66% MB degradation within 180 min under visible light. This superior performance was attributed to synergistic effects arising from efficient interfacial charge transfer, broadened light absorption, and abundant active sites. The composite also displayed excellent thermal stability. This work demonstrates that the rational control of g-C3N4 loading plays a decisive role in tuning the physicochemical and catalytic properties of Ni/Mg/g-C3N4 composites. The findings provide new insights into the design of cost-effective, thermally stable, and high-performance photocatalysts for visible-light-driven wastewater treatment.