Chitosan/attapulgite/poly(acrylic acid) hydrogel prepared by glow-discharge electrolysis plasma as a reusable adsorbent for selective removal of Pb2+ ions

A chitosan/attapulgite/poly(acrylic acid) (CS/ATP/PAA) hydrogel was prepared by glow-discharge electrolysis plasma (GDEP) technique, in which N,N'-methylene-bis-acrylamide was acted as a crossing-linker, and then it was used as an adsorbent for the removal of Pb2+ ions from aqueous solutions. A possible polymerization mechanism is proposed. The structure, morphology and adsorption mechanism of CS/ATP/PAA hydrogel were characterized by FTIR, XRD, SEM and XPS techniques. The influences of pH, contact time and initial concentration on the Pb2+ adsorption were systematically examined. The selective adsorption of CS/ATP/PAA hydrogel for Pb2+ ions with the coexistence of Cd2+, Co2+ and Ni2+ ions was investigated, as well. In addition, regeneration of hydrogel was also discussed in detail. The results indicated that the optimal adsorption pH was 4.8, and the time of adsorption equilibrium was 60 min. The adsorption behaviors fitted well to the pseudo-second-order kinetic model and Langmuir isotherm. The maximum adsorption capacity of CS/ATP/PAA hydrogel for Pb2+ ions based on Langmuir isotherm was 531.9 mg g–1. The CS/ATP/PAA adsorbent exhibited promising selectivity for Pb2+ ions with the coexistence of Cd2+, Co2+ and Ni2+ ions, and excellent reusability using EDTA-4Na solution as desorption solution. The adsorption process of Pb2+ ions on CS/ATP/PAA hydrogel was presented by the coordination between N or O atoms and Pb2+ ion, and the ion-exchange between Na+ and Pb2+ ions.