Radiation Effect of Carboxyl-Functionalized Task-Specific Ionic Liquids on UO₂²⁺ Removal: Experimental Study with DFT Validation

Abstract

Experimental study with DFT validation on the effect of radiation on 1-carboxymethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([HOOCCHMIM][NTf]) as a solvent and extractant in rapid homogeneous extraction of UO was performed for the first time. The radiolytic products of the anions and cations of [HOOCCHMIM][NTf] were identified by F NMR and high-resolution ESI-MS, respectively, and they were attributed to a decrease in UO partitioning. Experimental study with DFT validation for complexing reactions between [HOOCCHMIM][NTf] and radiolytic products proved that F competition was one of the main reasons for the decrease in UO partitioning. However, UO partitioning in irradiated [HOOCCHMIM][NTf] can largely be recovered after thorough water washing because of the removal of radiolytic products of [NTf].

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

“…It was found that the imide anions are relatively stable due to N–N σ 2 σ* 1 bond formation involving the parent anion, − although a small amount of free radical CF 3 · and TfN· – is produced after radiation. In contrast, the cation 1,3-dialkyl imidazolium is not as so stable as the imide anions, and its radiation stability has been widely studied. − The γ radiolysis of imidazolium ILs most likely leads to the formation of 2-imidazolyl radicals, which either are protonated or react with the parent cation forming C(2)–C(2) σσ*-bound dimer radicals. The elimination of substituted alkyl groups at the N­(1,3) sites was also observed for radiation effects. − In addition, Adhikari et al , demonstrated that the introduction of a hydroxyl group into the alkyl side chain of the imidazolium moiety can result in a significant change in the physicochemical properties of ILs and promote various degradation channels.…”

“…In contrast, the cation 1,3-dialkyl imidazolium is not as so stable as the imide anions, and its radiation stability has been widely studied. − The γ radiolysis of imidazolium ILs most likely leads to the formation of 2-imidazolyl radicals, which either are protonated or react with the parent cation forming C(2)–C(2) σσ*-bound dimer radicals. The elimination of substituted alkyl groups at the N­(1,3) sites was also observed for radiation effects. − In addition, Adhikari et al , demonstrated that the introduction of a hydroxyl group into the alkyl side chain of the imidazolium moiety can result in a significant change in the physicochemical properties of ILs and promote various degradation channels. The radiation stability of 1-(2-hydroxyethyl)-3-methylimidazolium was suggested to be lower than that of 1-ethyl-3-methylimidazolium. , However, the specific reactions and products of hydroxyl-functionalized imidazolium induced by radiation are still unclear.…”