Removal of heavy metal ions using a novel cross-linked polyzwitterionic phosphonate

A novel cross-linked polyzwitterionic acid (CPZA) was synthesized via cyclocopolymerization of diallylaminomethylphosphonic acid and 1,1,4,4-tetraallylpiperazinium dichloride (10 mol%), a cross-linker, in the presence of tert-butylhydroperoxide in aqueous solution at 85 °C. CPZA, upon treatment with NaOH, was converted into a cross-linked anionic polyelectrolyte (CAPE). The experimental data for the adsorption of Pb ²⁺ and Cu ²⁺ on CAPE fitted Lagergren second-order kinetic model and Langmuir as well as Freundlich isotherm models. The adsorption capacity of Pb ²⁺ was higher than that of Cu ²⁺ while the rate of adsorption was found to be higher for Cu ²⁺. The adsorption process was spontaneous and endothermic in nature with negative and positive values for ΔG and ΔH, respectively. The low activation energies of 12.8 and 17.9 kJ/mol for Cu ²⁺ and Pb ²⁺, respectively, indicated the adsorption as a favorable process. The excellent adsorption and very good desorption efficiencies implied the efficacy of the resin in removing as well as recovering the metal ions from aqueous solution. An efficient synthetic access to the resin would enable its use in the treatment of contaminated waste water.