Novel thermo-responsive hydrogel microspheres with calixcrown host molecules as cross-links for highly specific binding and controllable release of cesium

摘要

In this study, a new bifunctional calixcrown host molecule with superb complexation of cesium (Cs) (distribution ratio D > 45) was synthesized, which was first employed as cross-linker for building a novel class of thermo-responsive poly(N-isopropylacrylamide) microspheres. AFM cross-section analysis revealed a negative shift of lower critical solution temperature (LCST) of the hydrogel microspheres, owing to the calixcrown moieties at the cross-links affecting the balance of hydrogen bonding and hydrophobic association in the 3D polymer network. Due to the host-guest ion recognition, the hydrogel microspheres showed the highest selectivity factors (SFs) so far of Cs over the competing alkali cations (SFCs/K = 20.0, SFCs/Na = 34.0). Moreover, since the thermo-triggered conformation change of polymer network interacting with the calixcrown-Cs complexation, the hydrogel microspheres exhibited a temperature-sensitive ion-binding behavior, which provided a feasible mechanism for controllable release of the bound Cs by tuning the surrounding temperature. Reversible Cs uptake-release cycles were achieved without compromising their complexation property. From a practical perspective, the calixcrown integrated hydrogel microspheres were proven to be able to effectively remove the trace Cs in real seawater (removal rate similar to 93.5%).