Physical properties and antioxidant activity of ZnO nanoparticles synthesized by Moringa oleifera leaf extract at different pH values

Abstract

We have demonstrated green synthesis of ZnO nanoparticles using Moringa oleifera leaves (Mor-ZnO NPs) extractby co-precipitation method under 450oC for 2 hours with different pH-5, pH-7, and pH-8. The physical properties (i.e. structural, morphology, and absorbance) have been analyzed using X-ray diffraction (XRD) measurement, scanning electronmicroscopy (SEM), and ultraviolet-visible (UV-Vis) spectrophotometer. Furthermore, to investigate the functional group andantioxidant activity we performed Fourier transform infra-red (FTIR) analysis and 2,2-diphenyl-1-picrylhydrazyl (DPPH)assay. Structurally, all samples possess polycrystalline hexagonal wurtzite structure. Morphologically, the pH values affectthe morphology of Mor-ZnO NPs. Optically, the Mor-ZnO NPs with pH-8 have strong absorption in the range of shortultraviolet (200-280 nm). We predict that the basic pH value on green synthesize of Mor-ZnO NPs tune the near band edgeabsorption (NBA), which relates to the recombination of the free excitons. Whereas, based on the FTIR spectra analysis, theZn-O stretching can be identified at 442.67 cm-1, 458.67 cm-1, and 442.67 cm-1 for Mor-ZnO NPs with the pH-5, pH-7, andpH-8, respectively. According to DPPH assay, the Mor-ZnO NPs with pH-8 at 200 mg/ml has higher inhibition rate (67.7%). Hence, we believed that the Mor-ZnO NPs are potential antioxidants.