Radiation Induced Redox Reactions and Fragmentation of Constituent Ions in Ionic Liquids. 1. Anions

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

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)-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide (IL-2), by UV-vis, 1H 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.

Predicting Degradation Mechanisms in Lithium Bistriflimide "Water-In-Salt" Electrolytes For Aqueous Batteries

Aqueous solutions are crucial to most domains in biology and chemistry, including in energy fields such as catalysis and batteries. Water-in-salt electrolytes (WISEs), which extend the stability of aqueous electrolytes in rechargeable batteries, are one example. While the hype for WISEs is huge, commercial WISE-based rechargeable batteries are still far from reality, and there remain several fundamental knowledge gaps such as those related to their long-term reactivity and stability. Here, we propose a comprehensive approach to accelerating the study of WISE reactivity by using radiolysis to exacerbate the degradation mechanisms of concentrated LiTFSI-based aqueous solutions. We find that the nature of the degradation species depends strongly on the molality of the electrolye, with degradation routes driven by the water or the anion at low or high molalities, respectively. The main aging products are consistent with those observed by electrochemical cycling, yet radiolysis also reveals minor degradation species, providing a unique glimpse of the long-term (un)stability of these electrolytes.

Thermoelectric Performance of Polypropylene/Carbon Nanotube/Ionic Liquid Composites and Its Dependence on Electron Beam Irradiation

The thermoelectric behavior of polypropylene (PP) based nanocomposites containing single walled carbon nanotubes (SWCNTs) and five kinds of ionic liquids (Ils) dependent on composite composition and electron beam irradiation (EB) was studied. Therefore, several samples were melt-mixed in a micro compounder, while five Ils with sufficiently different anions and/or cations were incorporated into the PP/SWCNT composites followed by an EB treatment for selected composites. Extensive investigations were carried out considering the electrical, thermal, mechanical, rheological, morphological and, most significantly, thermoelectric properties. It was found that it is possible to prepare n-type melt-mixed polymer composites from p-type commercial SWCNTs with relatively high Seebeck coefficients when adding four of the selected Ils. The highest Seebeck coefficients achieved in this study were +49.3 µV/K (PP/2 wt.% SWCNT) for p-type composites and −27.6 µV/K (PP/2 wt.% SWCNT/4 wt.% IL type AMIM Cl) for n-type composites. Generally, the type of IL is decisive whether p- or n-type thermoelectric behavior is achieved. After IL addition higher volume conductivity could be reached. Electron beam treatment of PP/SWCNT leads to increased values of the Seebeck coefficient, whereas the EB treated sample with IL (AMIM Cl) shows a less negative Seebeck coefficient value.

Photodetachment and Electron Dynamics in 1-Butyl-1-methyl-pyrrolidinium Dicyanamide

The ultrafast transient absorption spectrum of 1-butyl-1-methyl-pyrrolidinium dicyanamide, [Pyr_1,4⁺][DCA^-], was measured in the visible and near-infrared (IR) spectral regions. Excitation of the liquid at 4.6 eV created initially delocalized and highly reactive electrons that either geminately recombined (69%) or localized onto a cavity with a time constant of ∼300 fs. Electron localization was reflected in the evolution of the TA spectrum and the time-dependent loss of reactivity with a dichloromethane quencher. The delocalized initial state and spectrum of the free electrons were consistent with computational predictions by Xu and Margulis [ J. Phys. Chem. B, 2015, 119, 532-542] on excess electrons in [Pyr_1,4⁺][DCA^-]. The computational study considered two possible localization mechanisms for excess electrons, localization on ions, and localization on cavities. In the case of photogenerated electron-hole pairs, the results presented here demonstrate localization to cavities as the dominant channel. Following localization onto a cavity, the free electrons underwent solvation and loss of reactivity with the quencher with rates that slowed in time. The dynamics were similar to an analogous prior study on the related liquid [Pyr_1,x⁺][NTf₂^-]. One significant difference was the larger yield of free electrons from photoexcitation of [Pyr_1,4⁺][DCA^-]. This was found to primarily reflect more efficient localization onto cavities rather than a slower geminate recombination rate.

γ-Radiolysis of Room-Temperature Ionic Liquids: An EPR Spin-Trapping Study

The radiolytic stability of a series of room-temperature ionic liquids (ILs) composed of bis(trifluoromethylsulfonyl)imide anion (Tf₂N^-) and triethylammonium, 1-butyl-1-methylpyrrolidinium, trihexyl(tetradecyl)phosphonium, 1-hexyl-3-methylpyridinium, and 1-hexyl-3-methylimidazolium (hmim) cations was studied using spin-trap electron paramagnetic resonance (EPR) spectroscopy with a spin-trap α-(4-pyridyl N-oxide)-N-tert-butylnitrone (POBN). The trapped radical yields were measured as a function of POBN concentration and as a function of radiation dose by double integration of the broad unresolved lines. Well-resolved motionally narrowed EPR spectra for the trapped radicals were obtained by dilution of the ILs with CH₂Cl₂ after irradiation. The trapped radicals were identified as mainly carbon-centered alkyl and ^•CF₃, and their ratio varies greatly across the series of ILs. Expected nitrogen-centered radicals derived from Tf₂N^- were not observed. The hmim liquid proved most interesting because a large part of the trapped radical yield (entirely carbon-centered) grew in over several hours after irradiation. We also discovered a complicated narrow-line stable radical signal in this neat IL with no spin trap added, which grows in over several hours after irradiation and decays over several weeks.

Green chemical engineering in China

In China, the rapid development greatly promotes the national economic power and living standard but also inevitably brings a series of environmental problems. In order to resolve these problems fundamentally, Chinese scientists have been undertaking research in the area of green chemical engineering (GCE) for many years and achieved great progresses. In this paper, we reviewed the research progresses related to GCE in China and screened four typical topics related to the Chinese resources characteristics and environmental requirements, i.e. ionic liquids and their applications, biomass utilization and bio-based materials/products, green solvent-mediated extraction technologies, and cold plasmas for coal conversion. Afterwards, the perspectives and development tendencies of GCE were proposed, and the challenges which will be faced while developing available industrial technologies in China were mentioned.

X-ray-Induced Fragmentation of Imidazolium-Based Ionic Liquids Studied by Soft X-ray Absorption Spectroscopy

We investigated the X-ray absorption spectroscopy (XAS) fingerprint of EMImTFSI ionic liquid (IL) and its fragmentation products created by X-ray irradiation. To accomplish this, we used an open geometry where an IL droplet is directly exposed in the vacuum chamber and an enclosed geometry where the IL is confined in a cell covered by an X-ray transparent membrane. In the open geometry, the XAS signature was stable and consistent with experimental and theoretical spectra reported in the literature. In contrast, when the IL is enclosed, its XAS evolves continuously under X-ray illumination due to the accumulation of volatile fragmentation products inside the closed cell, while they evaporate in the open geometry. The changes in the XAS from the core levels of relevant elements (C, N, S, F) together with density functional theory calculations allowed us to identify the chemical nature of the fragment products and the chemical bonds most vulnerable to rupture under soft X-ray irradiation.

Evidence for Indirect Action of Ionizing Radiation in 18-Crown-6 Complexes with Halogenous Salts of Strontium: Simulation of Radiation-Induced Transformations in Ionic Liquid/Crown Ether Compositions

Ionic liquid/crown ether compositions are an attractive alternative to traditional extractants in the processes for spent nuclear fuel and liquid radioactive wastes reprocessing. These compositions are exposed to ionizing radiation, and their radiation stability, especially in the presence of metal salts, is a crucial issue. In the present study, the macrocyclic 18C6·Sr(BF₄)₂ and 18C6·Sr(PF₆)₂ complexes simulating the components of metal loaded ionic liquid/crown ether extractants were synthesized and their structures were characterized by FTIR spectroscopy and single-crystal X-ray diffraction analysis. Inclusion of Sr²⁺ cation into the 18C6 cavity resulted in more symmetric D_3d conformations of the macrocycle. The structural transformations of the crown ether were accompanied by an elongation of polyether C-O bonds that could increase the possibility of radiolytic cleavage of the macrocycle. However, EPR study of the synthesized compounds subjected to X-ray irradiation revealed predominant formation of macrocyclic -CH₂-ĊH-O- radicals. This result demonstrated an evidence for indirect action of ionizing radiation on individual components of the complexes and was reasonably described by a positive "hole" transfer from primary macrocyclic radical cation to fluorous anion at the primary stages of radiolysis and a subsequent interaction of fluorine atom with 18C6 macrocycle in secondary radical reactions. The observed effects may be partially responsible for enhanced sensitivity of the ionic liquid/crown ether extractants to ionizing radiation due to chemical blocking of the crown ether with radiolytic HF, radiation-chemical degradation of the 18C6, and precipitation of a low-soluble SrF₂.

Radiolysis of alkyl substituted tridentate 2,6-bis(1,2,4-triazine-3-yl)pyridines: an experimental study with DFT validation

The radiolysis products of alkyl substituted tridentate 2,6-bis(1,2,4-triazine-3-yl)pyridines (BTPs) were studied by an experimental study with DFT validation.

Thermal, electrochemical and radiolytic stabilities of ionic liquids

Ionic liquids show instability when exposed to high temperature, to high voltage as electrolytes, or under irradiation.

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

Experimental study with DFT validation on the effect of radiation on 1-carboxymethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([HOOCCH₂MIM][NTf₂]) as a solvent and extractant in rapid homogeneous extraction of UO₂²⁺ was performed for the first time. The radiolytic products of the anions and cations of [HOOCCH₂MIM][NTf₂] were identified by ¹⁹F NMR and high-resolution ESI-MS, respectively, and they were attributed to a decrease in UO₂²⁺ partitioning. Experimental study with DFT validation for complexing reactions between [HOOCCH₂MIM][NTf₂] and radiolytic products proved that F^- competition was one of the main reasons for the decrease in UO₂²⁺ partitioning. However, UO₂²⁺ partitioning in irradiated [HOOCCH₂MIM][NTf₂] can largely be recovered after thorough water washing because of the removal of radiolytic products of [NTf₂]^-.

Actinide ion extraction using room temperature ionic liquids: opportunities and challenges for nuclear fuel cycle applications

Studies on the extraction of actinide ions from radioactive wastes have great relevance in nuclear fuel cycle activities, mainly in the back end processes focused on reprocessing and waste management.

Toward a Greenish Nuclear Fuel Cycle: Ionic Liquids as Solvents for Spent Nuclear Fuel Reprocessing and Other Decontamination Processes for Contaminated Metal Waste

The final disposition of spent nuclear fuel (SNF) is an area that requires innovative solutions. The use of ionic liquids (ILs) has been examined as one means to remediate SNF in a variety of different chemical environments and with different chemical starting materials. The effectiveness of various ILs for SNF reprocessing, as well as the reaction chemistry that occurs in them, is discussed.

Porous nanostructures of SnSe: role of ionic liquid, tuning of nanomorphology and mechanistic studies

Porous SnSe nanoparticles have been synthesized in imidazolium based RTILviaelectron beam irradiation. RTIL provides a stabilizing environment as well as anin situsource of reducing radicals for the reduction of precursors.

The AHA Moment: Assessment of the Redox Stability of Ionic Liquids Based on Aromatic Heterocyclic Anions (AHAs) for Nuclear Separations and Electric Energy Storage

Because of their extended conjugated bond network, aromatic compounds generally have higher redox stability than less saturated compounds. We conjectured that ionic liquids (ILs) consisting of aromatic heterocyclic anions (AHAs) may exhibit improved radiation and electrochemical stability. Such properties are important in applications of these ILs as diluents in radionuclide separations and electrolytes in the electric energy storage devices. In this study, we systematically examine the redox chemistry of the AHAs. Three classes of these anions have been studied: (i) simple 5-atom ring AHAs, such as the pyrazolide and triazolides, (ii) AHAs containing an adjacent benzene ring, and (iii) AHAs containing electron-withdrawing groups that were introduced to reduce their basicity and interaction with metal ions. It is shown that fragmentation in the reduced and oxidized states of these AHAs does not generally occur, and the two main products, respectively, are the H atom adduct and the imidyl radical. The latter species occurs either as an N σ-radical or as an N π-radical, depending on the length of the N-N bond, and the state that is stabilized in the solid matrix is frequently different from that having the lowest energy in the gas phase. In some instances, the formation of the sandwich π-stack dimer radical anions has been observed. For trifluoromethylated anions, H adduct formation did not occur; instead, there was facile loss of fluoride from their fluorinated groups. The latter can be problematic in nuclear separations, but beneficial in batteries. Overall, our study suggests that AHA-based ILs are viable candidates for use as radiation-exposed diluents and electrolytes.

Polymerization of room-temperature ionic liquid monomers by electron beam irradiation with the aim of fabricating three-dimensional micropolymer/nanopolymer structures

A novel method for fabricating microsized and nanosized polymer structures from a room-temperature ionic liquid (RTIL) on a Si substrate was developed by the patterned irradiation of an electron beam (EB). An extremely low vapor pressure of the RTIL, 1-allyl-3-ethylimidazolium bis((trifluoromethane)sulfonyl)amide, allows it to be introduced into the high-vacuum chamber of an electron beam apparatus to conduct a radiation-induced polymerization in the nanoregion. We prepared various three-dimensional (3D) micro/nanopolymer structures having high aspect ratios of up to 5 with a resolution of sub-100 nm. In addition, the effects of the irradiation dose and beam current on the physicochemical properties of the deposited polymers were investigated by recording the FT-IR spectra and Young's modulus. Interestingly, the overall shapes of the obtained structures were different from those prepared in our recent study using a focused ion beam (FIB) even if the samples were irradiated in a similar manner. This may be due to the different transmission between the two types of beams as discussed on the basis of the theoretical calculations of the quantum beam trajectories. Perceptions obtained in this study provide facile preparation procedures for the micro/nanostructures.

Tetraarylphosphonium polyelectrolyte chromophores: synthesis, stability, photophysics, film morphology and critical surface energy

Chromophore-modified polymers with tetraarylphosphonium units in the main chain have been prepared by a Ni-catalysed P–C bond-forming reaction.

Free electrons and ionic liquids: study of excited states by means of electron-energy loss spectroscopy and the density functional theory multireference configuration interaction method

Collisions of slow electrons with ionic liquids and DFT/MRCI calculations reveal triplet states and interesting physics at low energies.

α-Radiolysis of ionic liquid irradiated with helium ion beam and the influence of radiolytic products on Dy3+extraction

Helium ion beam produced by a heavy ion linear accelerator was used to simulate α-rays for studying the radiation effect on 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid.

Towards understanding the color change of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide during gamma irradiation: an experimental and theoretical study

The radiation-induced color change of [BMIm][NTf₂] originates from the formation of double bonds in cations and various associated species containing [BMIm-H₂][NTf₂].