Synthesis and Characterisation of Novel Zinc Oxide Nanoparticles from Moringa oleifera Leaf Extract for Photocatalytic Dye Degradation

Green synthesis of metal oxide nanoparticles using plant extracts offers an environmentally benign alternative to conventional chemical methods, and the photocatalytic activity of the resulting nanoparticles for organic dye degradation addresses a critical water treatment need in Nigeria. This study synthesised zinc oxide nanoparticles using aqueous extract of Moringa oleifera leaves obtained from Katsina State and characterised the structural, optical, and photocatalytic properties of the product. Synthesis was optimised by varying extract concentration, zinc salt precursor concentration, temperature, and pH. The nanoparticles were characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, and BET surface area analysis. Photocatalytic performance was evaluated by assessing methylene blue and Congo red dye degradation under visible and ultraviolet light irradiation. X-ray diffraction confirmed the wurtzite crystal structure with an average crystallite size of 18.4 nm, indicating successful nanoparticle formation. The band gap energy was 3.12 eV, slightly red-shifted from bulk zinc oxide, consistent with quantum confinement and organic capping effects. Under ultraviolet irradiation, 97.8 percent of methylene blue was degraded within 90 minutes. The degradation kinetics followed a pseudo-first-order Langmuir-Hinshelwood model. The superior photocatalytic activity was attributed to the high surface area of 84 m2/g and the role of residual phytochemicals from the extract acting as sensitisers. This work fills a gap in green nanoparticle photocatalysis research and demonstrates a locally sourced, scalable approach to water treatment applicable in Nigerian textile effluent management.

Keywords: zinc oxide nanoparticles, green synthesis, Moringa oleifera, photocatalysis, dye degradation