Green synthesis of ZnO nanoparticles using leaf extract of Diospyros Mespiliftmis and its application

Abstract

Zinc oxide nanoparticles (ZnO NPs) were successfully synthesized via a sustainable green route using Diospyros mespiliformis leaf extract as both reducing and capping agent. The formation of ZnO NPs was confirmed by UV–Visible spectroscopy, which exhibited a characteristic excitonic absorption peak at 340 nm, indicating a pronounced blue shift relative to bulk ZnO and an estimated optical bandgap of 3.65 eV. X-ray diffraction (XRD) analysis revealed a highly crystalline, multiphase structure dominated by Zincite (83%), with minor contributions from Gahnite (13%) and Cristobalite (3.8%). The calculated crystallite sizes ranged from 8.6 to 13.7 nm, consistent with nanoscale dimensions and quantum confinement effects. Scanning electron microscopy (SEM) images showed a porous and granular morphology, indicative of a high surface area, while energy-dispersive X-ray (EDX) analysis confirmed the presence of Zn (40.59 wt%) along with a significant sodium content (57.28 wt%) and trace bio-minerals (Ca, K, Si, and Ti) originating from the plant extract. Fourier transform infrared (FTIR) spectroscopy identified key functional groups, particularly hydroxyl (3301 cm⁻¹) and carbonyl groups, which play crucial roles in nanoparticle stabilization and metal ion binding. The adsorption performance of the synthesized ZnO NPs was evaluated for the removal of Pb²⁺ ions from aqueous solutions. Batch adsorption studies demonstrated that removal efficiency is strongly influenced by initial metal ion concentration and solution pH. A maximum removal efficiency of 78.39% was achieved at an initial Pb²⁺ concentration of 0.574 mg/L, while optimal performance was observed under alkaline conditions, reaching 83.8% removal at pH 10.3. The enhanced adsorption capacity is attributed to the high surface-to-volume ratio, porous morphology, surface functionalization, and defect-rich crystalline structure of the nanoparticles. Overall, the results highlight the potential of these green-synthesized ZnO nanoparticles as efficient, eco-friendly, and scalable nano-adsorbents for heavy metal remediation in contaminated water systems.

 Keywords: Diospyros Mespiliftmis, UV – Visible spectroscopy, Scanning electron microscope, XRD, FTIR