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

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.