Influence of gamma irradiation on hydrophobic room-temperature ionic liquids [BuMeIm]PF6 and [BuMeIm](CF3SO2)2N

Abstract

Stability of neat hydrophobic Room-Temperature Ionic Liquids (RTIL) [BuMeIm]X, where [BuMeIm]+ is 1-butyl-3-methylimidazolium and X- is PF6-, and (CF3SO2)2N-, was studied under gamma radiolysis (137Cs) in an argon atmosphere and in air. It was found that the density, surface tension, and refraction index of RTILs are unchanged even by an absorbed dose of approximately 600 kGy. Studied RTILs exhibit considerable darkening when subjected to gamma irradiation. The light absorbance of ionic liquids increases linearly with the irradiation dose. Water has no influence on radiolytic darkening. A comparative study of [BuMeIm]X and [Bu4N][Tf2N] leads to the conclusion that the formation of colored products is related to gamma radiolysis of the [BuMeIm]+ cation. The radiolytic darkening kinetics of RTILs is influenced by the anions as follows: Cl- < (CF3SO2)2N- < PF6-. Electrospray ionization mass spectrometry and NMR analysis reveal the presence of nonvolatile radiolysis products at concentrations below 1 mol% for an absorbed dose exceeding 1200 kGy. Initial step of BuMeIm+ cation radiolysis is the loss of the Bu* group, the H* atom from the 2 position on the imidazolium ring, and the H* atom from the butyl chain. Radiolysis of ionic liquid anions yields F* and CF3* from PF6- and [Tf2N]-, respectively. Recombinations of these primary products of radiolysis lead to various polymeric and acidic species.

Reactivity Towards Europium(III) of the Radiolysis Products of the Ionic Liquid 1‐Methyl‐3‐butyl‐1H‐imidazolium Bis[(trifluoromethyl)sulfonyl]amide (C4‐mimTf2N) and Effect of Water: A TRLFS (Time‐Resolved Laser‐Induced Fluorescence Spectroscopy) Preliminary Study

“…Either g, a, or b irradiations have been conducted, up to very high doses, in the range of 2 MGy at maximum. All these studies agree that ILs are very stable under irradiation, their physical and chemical properties being only slightly affected by irradiation, except for the conductivity and color [5]. Actually, a significant darkening of the ILs under investigation has been reported, which is attributed to the appearance of stable radiolytic products in very low yields but presenting a very high molar absorption [4] [5].…”

Effects of gamma radiation on electrochemical properties of ionic liquids

“…A few ILs were previously subjected to variable intensities of gamma irradiation [16]. One IL was subjected to alpha, beta, and gamma irradiation (alpha dose= 1 kGy, beta and gamma dose= 400 kGy) [17].…”

Influence of FeCl3 on radiation stability of ionic liquid BmimCl

“…Higher dose ensures sufficient source of solvated electron to reduce Fe(III). The value obtained in this study was higher than the radiolytic disappearance yield of the cations of the ionic liquid BmimNTf 2 (0.28±0.02 μmol/J) measured by ESI-MS [23].…”