Improvement on the Radiation Stability of Multi-scale Supramolecular Assembly in Ionic Liquid-Based Extraction

Abstract

The multi-scale supramolecular assembly (MSSA)based extraction strategy with hydroxyl-functionalized ionic liquid (IL) is promising in the separation of metal ions from radioactive environments for which a comprehensive understanding toward the radiation stability of the MSSA system is necessary. Herein, we report on the analyses of the radiation stability of MSSA in extraction, especially the adopted ILs 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (IL-1) and 1-(2-hydroxyethyl)-2,3dimethylimidazolium bis(trifluoromethylsulfonyl) imide (IL-2), by UV−vis, 1 H NMR, and ESI-HRMS. It was found that the macroscopic assembly (MA) sphere could not be formed after γ irradiation on the extraction system with IL-1. On the contrary, the trisubstituted IL-2 instead of the disubstituted IL-1 remarkably improved the radiation stability of the MSSA system to guarantee the formation of the MA sphere. The high extraction efficiency could be kept, and the mechanism of such an improvement was revealed.

Spontaneous Multi-scale Supramolecular Assembly Driven by Noncovalent Interactions Coupled with the Continuous Marangoni Effect

“…It is well-known that supramolecular chemistry aims at developing complex chemical systems through noncovalent intermolecular forces, and self-organization drives toward the systems of increasing complexity, toward more and more complex forms of matter. − So far, a large number of supramolecular materials have been developed. − However, most supramolecular systems investigated at the present time occupy generally the space between the molecular and the nano- to meso-scale worlds . In our previous work, the spontaneous supramolecular process covering molecular, mesoscopic, and macroscopic levels was realized in the ionic liquid (IL)-based extraction system, which was denominated as the multi-scale supramolecular assembly (MSSA). − When mixing the IL 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethyl-sulfonyl) imide (C 2 OHmimNTf 2 ) bearing octyl(phenyl)- N , N -diisobutylcarbamoylmethylphosphine oxide (CMPO) and an aqueous solution of metal ions in the presence of HNO 3 , visible spherical assemblies were first formed at the IL–water interface, and then, they further assembled into a single macroscopic assembly (MA) sphere in the glassy state. , The clear picture of a four-step assembly mechanism of the spontaneous MSSA process was depicted . The structures at four levels, i.e., the complex ions, elementary building blocks (EBBs), [EBB] n clusters, and the single MA sphere were formed step by step.…”

“…Differently, the MSSA-based extraction process could be adjusted simultaneously by factors at micro-, meso-, and macro-scales, and a new concept, i.e., multi-scale selectivity (MSS) was therefore suggested . The effective acid and radiation resistance as well as the high selectivity led us to believe that the MSSA-based extraction strategy has great potential for the separation of metal ions in either nonradioactive or radioactive environments, especially in spent nuclear fuel reprocessing …”

“…16 The effective acid and radiation resistance as well as the high selectivity led us to believe that the MSSA-based extraction strategy has great potential for the separation of metal ions in either nonradioactive or radioactive environments, especially in spent nuclear fuel reprocessing. 17 The Marangoni effect is referred to as the phenomenon that a temperature or concentration gradient causes an interfacial tension gradient, which naturally makes the liquid flow from the low to high surface tension region. 20,21 Specifically, the fourth step of the MSSA process aforesaid is the macroscopic supramolecular assembly at the interface, and the spontaneous and continuous Marangoni effect was inferred to be the driving force.…”