Removal of heavy metals from aqueous solution by poly(ethyleneimine)-functionalized silica: studies on equilibrium isotherm, kinetics, and thermodynamics of interactions

In this study, the equilibrium isotherms, kinetics, and thermodynamics of Cu(II), Ni(II), Cd(II), and Pb(II) ions adsorption onto on the surface of poly(ethyleneimine)-functionalized silica from aqueous solution were investigated. The effects of various parameters on the adsorption process, such as contact time, solution pH, initial concentrations of metal ions, and temperature, were studied to optimize the conditions for maximum adsorption. Constant adsorption capacities were seen in the range of pH 4–8. An equilibrium state was reached within 30 min. The experimental values of maximum adsorption capacities for Cu(II), Ni(II), Cd(II), and Pb(II) ions onto poly(ethyleneimine)-functionalized silica gel were 32.7, 28.5, 40.3, and 54.3 mg g−1, respectively. The batch adsorption kinetics was studied for pseudo-first-order model, pseudo-second-order model, Elovich model, and intra-particle diffusion model, and it was found that the pseudo-second-order model was observed to be the best. Freundlich and Langmuir adsorption isotherm models were used to fit the equilibrium data, and it was found that the Langmuir adsorption model provided a good fit. Various thermodynamic parameters such as ΔG°, ΔH°, and ΔS° indicated that the adsorption process was a spontaneous and endothermic process.