Removal of Cu(II) from aqueous solutions by zinc oxide-montmorillonite composite

Background: Cu(II) is considered to be a heavy metal ion that is quite hazardous to water. Aims: Zinc oxide-montmorillonite composite (ZnO-Mt) for the removal of Cu(II) from aqueous solutions. Materials & Methods: ZnO-Mt was prepared through ion exchange followed by heat treatment to form a highly effective adsorbent. Results: The structure and morphology of the composite were investigated by X-ray diffraction, scanning electron microscope, and fourier transform infrared spectroscopy and it was found that Zinc oxide was successfully coated on montmorillonite. The composite has a superior removal effect on Cu(II) in an aqueous solution with an adsorption capacity of 192.89 mg-g(-1). The adsorption kinetic model and the adsorption isotherm model are described by the pseudosecond-order kinetic equation and the Langmuir equation, respectively. The activation energy (Ea) was 84.18 kJ-mol-1, indicating that the adsorption was dominated by chemisorption. In addition, ZnO-Mt can be applied in a wide pH range (3 similar to 8) and exhibits satisfactory selectivity for the adsorption of Cu(II) in the presence of coexisting cations. The removal efficiency of ZnO-Mt for Cu(II) remains at 72% of the fresh adsorbent after five cycles. Discussion: A combination of experiment, characterization, and density functional theory analysis showed that the mechanism of Cu(II) removal was mainly surface complexation, ion exchange, and electrostatic attraction. Conclusion: Therefore, the ZnO-Mt composite is a promising and efficient adsorbent for the removal of Cu(II) from aqueous solutions.