Highly efficient extraction of actinides with pillar[5]arene-derived diglycolamides in ionic liquids via a unique mechanism involving competitive host-guest interactions.

Actinide partitioning is considered as one of the most challenging issues in nuclear waste remediation. Herein, we unravel a novel extraction mode pertinent to the competitive host-guest interactions for highly efficient actinide extraction. The host-guest recognition event involves binding of a room temperature ionic liquid (RTIL), 1-n-octyl-3 methylimidazolium bis(trifluoromethane)sulfonamide (CmimNTf), as both the guest and the solvent by the hosts pillar[5]arene-based diglycolamides (P5DGAs) and the subsequent displacement of the guest by a metal ion. This two-step process suggests a unique competitive ion-mediated displacement mechanism for the metal ion partitioning in the extraction process. The supramolecular extraction system is evaluated for its extraction abilities towards actinide ions such as UO, PuO, Pu, Am, and fission product elements such as Eu, Sr, Cs. The results demonstrate the exceedingly high distribution ratios and favorable separation of Am and Pu in nitric acid media. All the three P5DGAs form 1 : 1 complexes with Am. Time resolved laser fluorescence spectroscopic (TRLFS) studies reveal a strong complexation involving no inner-sphere water molecules in the Eu-P5DGA complexes when CmimNTf is used as the diluent. With high efficiency in the extraction of actinides and a quantitative back extraction outcome, the RTIL-based solvent systems containing pillar[5]arene-DGA ligands developed in this work hold potential as promising candidates for nuclear waste remediation in a more sustainable fashion.