Green fabrication of MgO nanoparticles using combined Psidium guajava and Eucalyptus leaf extracts: Synthesis, characterization and photocatalytic applications

The present study aimed to synthesize MgO nanoparticles using aqueous extracts of Psidium guajava and Eucalyptus leaves and evaluates their photocatalytic performance toward the degradation of organic dyes. The synthesized nanoparticles were characterized using FESEM with EDX, FTIR, HRTEM, PL, UV-Vis, XRD and XPS. XRD analysis confirmed the formation of highly crystalline MgO nanoparticles with an average crystallite size of approximately 9 nm. The UV-Vis spectrum exhibited an absorption peak at 272 nm and the estimated band gap energy was 2.76 eV, indicating excellent structural and optical properties suitable for photocatalytic applications. The photocatalytic activity of the synthesized MgO nanoparticles was evaluated for the degradation of Methylene Blue (MB) and Congo Red (CR) dyes under UV irradiation, achieving maximum degradation efficiencies of 90.00% and 95.41%, respectively. The optimum photocatalytic conditions were obtained at a catalyst dosage of 20 mg and an initial dye concentration of 10 ppm for both dyes, while the highest degradation efficiencies were observed at pH 9 for MB and pH 3 for CR. The degradation kinetics followed a pseudo first order model, with R 2 values of 0.97553 for MB and 0.86635 for CR, indicating better kinetic conformity for MB compared to CR. Radical scavenger experiments revealed that isopropyl alcohol caused the greatest inhibition in degradation efficiency, confirming hydroxyl radicals (•OH) as the dominant reactive species responsible for the photocatalytic degradation process. Overall, the study highlights the potential of green-synthesized MgO nanoparticles as an efficient and environmentally sustainable material for wastewater dye remediation.