Microwave-assisted synthesis of glutathione-coated hollow zinc oxide for the removal of heavy metal ions from aqueous systems

Abstract

Glutathione has tremendous binding potential with metal ions present in water. However, the solubility of glutathione in water limits its productivity in the removal of these toxic ions from aqueous systems. The removability of heavy ions with glutathione and the associated adsorption capability are enhanced; for this purpose, glutathione is coated over hollow zinc oxide particles. Glutathione-coated hollow zinc oxide (Glu@h-ZnO) was successfully synthesized under microwave (MW) conditions using polystyrene (PS) as the template. The as-synthesized material was characterized by Fourier transform infrared (FTIR) spectroscopy, and the results were supported by X-ray diffraction crystallography (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), dynamic light scattering (DLS), Brunauer–Emmett–Teller (BET) studies and zeta potential (ζ) analysis. The sorption performance of Glu@h-ZnO towards the uptake of Hg²⁺, Cd²⁺ and Pb²⁺ ions from an aqueous medium under non-competitive batch conditions was investigated and the material was found to have the maximum affinity for Hg²⁺ ions with a maximum adsorption (q_m) capacity of 233 mg g⁻¹. The adsorption kinetics for Hg²⁺ ions and the effects of pH and ζ on the adsorption properties were also studied in detail. Finally, the experimental data were correlated with theoretical data obtained from density functional theory (DFT) studies and good agreement between the two was obtained.