Ion-recognizable hydrogels for efficient removal of cesium ions from aqueous environment

Abstract

At present, selective and efficient removal of cesium ions (Cs⁺) from nuclear waste is of significant importance but still challenging. In this study, an easy-to-get and low-cost hydrogel adsorbent has been developed for effective adsorption and removal of Cs⁺ from aqueous environment. The novel Cs⁺-recognizable poly(acrylic acid-co-benzo-18-crown-6-acrylamide) (poly(AAc-co-B18C6Am)) hydrogel is specifically designed with a synergistic effect, in which the AAc units are designed to attract Cs⁺ via electrostatic attraction and the B18C6Am units are designed to capture the attracted Cs⁺ by forming stable 2:1 "sandwich" complexes. The poly(AAc-co-B18C6Am) hydrogels are simply synthesized by thermally initiated free-radical copolymerization and display excellent Cs⁺ adsorption from commonly coexisting metal ions. Important parameters affecting the adsorption are investigated comprehensively, and the adsorption kinetics and adsorption isotherms are also discussed systematically. The poly(AAc-co-B18C6Am) hydrogels exhibit rapid Cs⁺ adsorption within 30min and the adsorption process is governed by the pseudo-second order model. Adsorption isotherm results demonstrate that the equilibrium data are well fitted by the Langmuir isotherm model, indicating that the Cs⁺ adsorption is probably a monolayer adsorption process. Such Cs⁺-recognizable hydrogel materials based on the host-guest complexation are promising as efficient and feasible candidates for adsorption and removal of radioactive Cs⁺ from nuclear contaminants.

Keywords: Adsorption; Cesium ions; Cross-linked hydrogels; Crown ethers; Host-guest systems.