ZnO-NiO nanocomposites as highly recyclable adsorbent for effective removal of Pb(II) and Cd(II) from aqueous solution

In continuation to our recent study on the synthesis and characterization of ZnO-NiO nanocomposites (ZNO), in the present study the nanocomposites has been evaluated for the removal of Pb(II) and Cd(II) from the aqueous solution. The conditions for the sorption have been optimized and kinetic and thermodynamic studies were performed to understand the adsorption behavior of the nanocomposites. Though the Pb(II) and Cd(II) sorption by the nanocomposites takes place in wide pH range, pH 7 was found most favorable and at this pH the adsorption equilibrium data were modeled using the Langmuir and Freundlich isotherms. The data fitted more satisfactorily to Langmuir isotherm indicating unilayer adsorption. Based on Langmuir model, Q_max was calculated to be 1519.7 mgg^-1. The adsorption showed pseudo second order kinetics indicating chemisorptions. The nanocomposites were successfully recycled for three consecutive adsorption-desorption cycles with only a marginal loss in its efficiency indicating its high reusability.