Role of surface functionalization of ZnO nanoparticles as sorbents for heavy metal ions

Abstract

ABSTRACT The surface functionalization of ZnO nanoparticles (ZnO NPs) was carried out by a simple one pot co-precipitation method followed by a facile ligand introduction onto the surface. This technique allows for tailoring of the surface chemistry to impart the specificity and affinity toward the target analytes (heavy metal ions like Pb and Hg) depending on the ligand incorporated on the surface resulting in highly selective sorbents. The functionalized ZnO NPs were characterized using different techniques. Elemental, IR, and thermal analysis studies confirm the presence of functional groups. X-ray diffraction (XRD) shows functionalization does not result in change of ZnO NPs but reduces their crystallinity. The average crystallite size of the nanoparticles is not affected by functionalization indicating that the process is restricted to the surface only. Surface area measurements reveal that functionalization results in mesoporous structures as can be deduced from the average pore diameter. Functionalization resulted in enhanced uptake of Pb and Hg, and the kinetics were very fast. Different models were used to understand the sorption behavior. The Langmuir uptake capacity values for lead and mercury using the thiol-functionalized ZnO NPs were found to be 78 and 145 mg/g, respectively. The role of interfering ions on the sorption was evaluated to get an idea of the selective nature of the sorbent.