A New Resin Containing Aminopropylphosphonate Chelating Ligand for High-Performance Mitigation of Heavy Metal Ions

Cyclopolymerization, initiated by t-butylhydroperoxide, of an aqueous solution of N-(3-phosphonopropyl)diallylammonium hydrochloride and cross-linker tetraallylpiperazinium dichloride in 9:1 mol ratio, led to a pH-responsive cross-linked resin (80% yield). The resin showed exceptional efficiency for entrapping toxic metal ions from aqueous systems. Using Langmuir adsorption isotherm, the respective maximum uptake (Q_m) of Pb²⁺ and Cu²⁺ ions was determined to be 7.18 and 6.76 mmol g⁻¹. The very impressive performance accorded the resin a prestigious place among many sorbents in recent works. The adsorption data fitted second-order kinetics with respective E_a of 35.5 and 31.1 kJ mol⁻¹ for Pb²⁺and Cu²⁺ ions. While the initial rapid adsorption of metal ions was due to film diffusion, the slower adsorption followed intraparticle diffusion. SEM and EDX analyses confirmed the metal ions’ adsorption onto sorbent. The negative ΔG° and positive ΔH° values demonstrated the endothermic adsorption as a favorable process. The sorbent is recyclable as evinced by the excellent adsorption/desorption process.