Structural investigation of the efficient capture of Cs+ and Sr2+ by a microporous Cd-Sn-Se ion exchanger constructed from mono-lacunary supertetrahedral clusterst

Visualization of the ion exchange mechanism for Cs-137 and Sr-90 decontamination is important for safe radioactive liquid waste reprocessing and emergency response improvement in the event of a nuclear accident. Here, the remediation of Cs+ and Sr2+ was achieved through ion exchange using a cadmium selenidostannate, [CH3NH3](3)[NH4](3)Cd4Sn3Se13 center dot 3H(2)O (CdSnSe-1), with rapid exchange kinetics, high beta/gamma radiation resistances, broad pH durability and facile elution. The framework constructed from monolacunary supertetrahedral clusters features a great negative charge density of 3.27 x 10(-3) that accounts for the superhigh exchange capacities of 371.4 (Cs+) and 128.4 mg g(-1) (Sr2+). Single-crystal structural analysis on the exchanger during the pristine-ion exchange-elution cycle supplies instructive information to elucidate the uptake and recycle mechanism for Cs+ and Sr2+. The broken symmetry of the cluster caused by a vacant site, combined with the co-templating effects of mixed methylammonium/ ammonium, contributes to the formation of voids I and II that show adsorption activity for both Cs+ and K+ ions. In comparison, the divalent Sr2+ ions with higher hydration degree exchange with (alkyl) ammonium cations in a 1: 2 molar ratio, resulting in its location at a new void (III) closer to the framework and thus a higher binding strength. The energy variation during the adsorption process based on a DFT calculation illustrates the high efficiency of CdSnSe-1 for capture of both Cs+ and Sr2+. This visualized ion exchange underlines the robustness and flexibility of CdSnSe-1 as a Cs+ and Sr2+ trapper, and reveals the deeper structure function relationship from a new surface interaction viewpoint.

Automated summary

Visualization of the ion exchange mechanism for Cs-137 and Sr-90 decontamination was achieved in this study. The results provide important insights for safe radioactive liquid waste reprocessing and emergency response improvement in the event of a nuclear accident.