Heavy Metal Adsorption Capacity and Biological Potential of Green Synthesized Zinc Oxide Nanoparticles Using Gomphrena globosa Leaves

The aim of this study is to synthesize zinc oxide nanoparticles (ZnO NPs) using G. globosa aqueous leaf extract. The preliminary screening of the phytochemicals was performed with the G. globosa aqueous leaf extract. The physical and chemical characteristics of G. globosa-mediated ZnO NPs were evaluated using UV-Vis spectroscopy, Fourier-transform infra-red spectroscopy (FTIR), X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), nanoanalysis and thermogravimetry. The antibacterial activity of G. globosa-mediated ZnO NPs was assessed against Gram-negative bacteria. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) analyses were performed to evaluate the antibacterial efficacy of the G. globosa-mediated ZnO NPs. The heavy metal adsorption capacity of the synthesized ZnO NPs was evaluated using atomic adsorption spectroscopy (AAS). The UV-Vis spectrum of G. globosa-mediated ZnO NPs proved the excitonic absorption of the synthesized ZnO NPs. FTIR analysis determined the presence of metal oxide functional groups in the G. globosa-mediated ZnO NPs. The average size of 60 nm and the spherical shape of G. globosa-mediated ZnO NPs were confirmed by HRTEM and SEM analyses. The synthesized ZnO NPs had prominent antibacterial activity against Klebsiella pneumoniae and Escherichia coli. G. globosa-mediated ZnO NPs acted as an important adsorbent of heavy metals such as cadmium and lead. Adsorption kinetic studies (pseudo-first-order and pseudo-second-order kinetics) and isotherm analyses (Langmuir and Freundlich models) were performed. The kinetic studies and isotherm models revealed that the synthesized ZnO NPs showed higher adsorption efficiency for cadmium.