Green synthesis of nanostructured zinc oxide by Ocimum tenuiflorum extract: characterization, adsorption modeling, cytotoxic screening, and metal ions adsorption applications

Abstract Nano-ZnO was synthesized by the reduction of Zn (CH 3 COO) 2 .2H 2 O salt using the extract of Ocimum tenuiflorum leaves. The generated ZnO NPs were characterized by FT-IR, XRD, SEM, and EDX techniques. FT-IR results approved the characteristic peaks, the formation of ZnO bonds, and the morphology changes after the adsorption of Cd 2+ and Pb 2+ from solutions. The outlined data of the XRD pointed to the formation of a hexagonal wurtzite structure. SEM images showed the spherical nature of the synthesized particles with an average diameter of 19 nm. Moreover, the best conditions for the adsorption of Cd 2+ and Pb 2+ by ZnO NPs were evaluated and fitted to isotherm and kinetic models. Short contact time of ~ 20 min and a small sorbent dosage of 40 mg were sufficient conditions for attaining maximum Pb 2+ adsorption capacity. Based on the modeling parameters, the adsorption follows pseudo-second-order kinetics where ZnO and metal ions are involved in the rate-determining step. Two important applications were thoroughly studied. The nanoparticles significantly removed Pb 2+ and Cd 2+ contaminants from real environmental water samples collected from different locations in Egypt. Additionally, the cytotoxic activity results provided perfect evidence for the higher efficacy of the synthesized ZnO NPs as an anticancer agent against Panc-1, PC-3, and CACO-2 cell lines with IC 50 of 1.70, 3.67, and 5.70 μgml −1 , respectively, compared to cisplatin (IC 50 = 3.57, 5.09, and 7.75 μgml −1 ). Furthermore, a low cytotoxic effect was observed on the normal human lung cell line (MRC-5, IC 50 = 22.40 μgml −1 ). The data can be used as a preliminary study for anticancer drug design after further clinical investigations. Graphical Abstract