New Chelating Ion-Exchange Resin Synthesized via the Cyclopolymerization Protocol and Its Uptake Performance for Metal Ion Removal

Azoisobutyronitrile-initiated cycloterpolymerization of [(diallylamino)propyl]phosphonic acid hydrochloride (90 mol %), cross-linker 1,1,4,4-tetraallylpiperazinium dichloride (10 mol %), and SO₂ (100 mol %) afforded a new pH-responsive cross-linked polyzwitterionic acid which, upon alkaline treatment, was transformed to a cross-linked dianionic polyelectrolyte (CDAPE). Chelating ion-exchange resin CDAPE was tested for the uptake of Pb²⁺ and Cu²⁺ ions; the adsorption process followed pseudo-second-order kinetics with respective E_a values of 13.4 and 13.8 kJ mol^-1. The adsorption data fitted well to the Langmuir, Freundlich, and Temkin as well as Dubinin-Radushkevich isotherm models. The maximum uptakes of Pb²⁺ and Cu²⁺ were determined to be 3.83 and 10.1 mmol g^-1, respectively. The scanning electron microscopy images and energy-dispersive X-ray spectroscopy analysis confirmed that the CDAPE adsorbed the metal ions on the surface as well as throughout the polymer. The negative ΔG° and positive ΔH° ensured the adsorption process as favorable and endothermic in nature. The excellent adsorption and desorption efficiencies demonstrated by the resin would enable its use for the removal of toxic metal ions from wastewater. A comparison of CDAPE with several other adsorbents in recent works ascertains the excellent efficiency of the current resin for the removal of toxic metal ions.