Novel cross-linked polymers having pH-responsive amino acid residues for the removal of Cu2+ from aqueous solution at low concentrations

Two novel cross-linked anionic polyelectrolytes (CAPE) I and II containing pH-responsive amino acid residues have been synthesized via cycloco- and ter-polymerization of a monomer having diallylammonioethanoate motif (90 mol%) and a cross-linker 1,1,4,4-tetraallylpiperazinium dichloride (10 mol%) in the absence and presence of SO2 (100 mol%), respectively. The experimental data for the adsorption of Cu2+ on the CAPES fitted Lagergren second-order kinetic model thereby indicating the chemical nature of the adsorption process. The fitness order of Freundlich > Langmuir > Temkin for the isotherm models for CAPE I showed the favorability of adsorption on a heterogeneous surface, whereas for CAPE II the fitness order of Langmuir > Freundlich > Temkin certified the favorability toward monolayer adsorption. The adsorption process was spontaneous and endothermic in nature with negative and positive values for Delta G and Delta H, respectively. For the sorbents CAPE land CAPE II, the efficiency of Cu2+ removal at an initial metal concentration of 200 ppb was found to be 77.5 and 99.4%, respectively. Desorption efficiencies were found to be 88 and 93% for CAPE 1 and CAPE II, respectively. Treatment of real wastewater samples spiked with Cu2+ ions showed the excellent ability of the resins to adsorb metal ions. (C) 2013 Elsevier B.V. All rights reserved.