Plant-mediated synthesis and uv-activated adsorption behavior of ZnO nanoparticles produced from Azadirachta indica extract

Abstract

This study demonstrates a sustainable and eco-friendly synthesis of zinc oxide nanoparticles (ZnO-NPs) using aqueous leaf extract of Azadirachta indica (neem) as a natural reducing, capping, and stabilizing agent. The ZnO-NPs were characterized using SEM, XRD, TEM, FTIR, and UV–Visible spectroscopy to determine their morphology, crystallinity, particle size, functional groups, and optical properties. SEM revealed particle sizes of 30–50 nm, while XRD indicated an average crystallite size of 19.8 nm. TEM micrographs showed particle sizes ranging from 2.72 to 15.30 nm, and FTIR confirmed Zn–O bond formation with a strong peak at 875 cm⁻¹. The adsorption performance of the synthesized ZnO-NPs was evaluated for the removal of Cu²⁺, Cr³⁺, Cd²⁺, Pb²⁺, and Ni²⁺ ions from aqueous solutions through batch adsorption experiments conducted under UV light and dark conditions. Under UV irradiation, maximum removal efficiencies reached 91% for Cu²⁺, 72% for Ni²⁺, 99% for Pb²⁺, 86% for Cd²⁺, and 69% for Cr³⁺. Without UV exposure, Cr³⁺ and Pb²⁺ adsorption increased, while Cd²⁺ and Cu²⁺ slightly decreased, and Ni²⁺ remained unchanged. Adsorption data fitted best to the Freundlich isotherm model, indicating multilayer adsorption on heterogeneous surfaces, while kinetic studies followed a pseudo-second-order model with a correlation coefficient (R²) of 0.9915. Overall, the green synthesis of ZnO-NPs using Azadirachta indica provides a cost-effective and environmentally benign approach for efficient removal of toxic heavy metals from aqueous systems.