Smart hydrogel microspheres using Calixcrown molecules as cross-linking units for selective uptake and thermo-triggered release of cesium - 5134

The separation of the radioactive cesium is of great concern for the reprocessing of spent fuels and environmental remediation after nuclear accidents like Fukushima event. In this study, a new class of smart hydrogel microspheres containing calixcrown host molecules with affinity to Cs(I) was developed. The calixcrown molecules were supplemented with bifunctional arms of carbon-carbon double bonds, and were employed as cross-linking units of the thermo-responsive poly(N-isopropyl acrylamide) (PNIPAM) network. Due to the formation of host-guest complexes, the functionalized microspheres showed selective adsorption of Cs(I) over the analogous alkali metal ions such as K(I) and Na(I). The selectivity factors SF[Cs/K] and SF[Cs/Na] were found to be 20.0 and 34.0, respectively. The adsorption behavior of the microspheres showed a temperature-dependent feature, owing to the thermo-sensitive conformation change of the 3D hydrogel network which manipulated the calixcrown-Cs(I) complexation. This provided a feasible mechanism for the controllable release of the absorbed Cs(I) by tuning the surrounding temperature. Furthermore, reversible uptake-release cycles were achieved without compromising the adsorption ability of the microspheres. This kind of calixcrown functionalized hydrogel microspheres is of potential for the treatment of Cs(I)-containing radioactive wastes. (authors)