Journal of Ionic Liquids最新文献

The dynamics in mixtures of ionic liquid and monoatomic cations has been studied at different time scales ranging from the nanosecond up to the second. The mixtures were composed of cholinium bis(trifluoromethanesulfonyl)imide ([Chol][TFSI]) and LiTFSI, with LiTFSI mole fraction,

Deep eutectic solvents (DESs) are green anhydrous solvents that have recently been proposed in sustainable non-aqueous metal electrodeposition processes. The use of DESs over aqueous solutions allows metal electrodeposition without significant side reactions, such as the evolution of hydrogen gas, which is responsible for embrittlement phenomena. In the current work, the electrolytic deposition of Fe-Mn alloys, which present good application in temporary biomedical devices, using DESs was assessed. Three DESs were studied: (a) choline chloride and ethylene glycol (ChCl/EG), (b) choline chloride and glycerol (ChCl/Gly), and (c) choline chloride and urea (ChCl/Urea). The physicochemical properties (viscosity and conductivity) of the three DESs of interest, with and without the presence of dissolved Fe and Mn salts, were thoroughly studied. Cyclic voltammetry analyses showed that the reduction potential of both metals was within the potential window for the three DESs studied, which allowed the successful electrodeposition of Fe-Mn alloys. The deposit obtained from the ChCl/Urea DES presented the highest amount of Mn (49.71 at%). The latter, as well as the fact that the ChCl/Urea based electrolyte showed good stability at T = 80 °C after four electrodeposition cycles, are promising indicators of the potential success of the use of non-aqueous electrodeposition of Fe-Mn alloys using DESs.

Ionic liquid crystals have received increasing interest due to their positional and/or orientational order as well as the freedom in molecular motions that arise from the formation of mesophases between solid and liquid. While phase changes of non-fluorinated ionic liquids have been widely reported, there have been few reports on the temperature-dependent phase behavior of fluorinated ionic liquids. Here, we present a series of fluorinated ionic liquids with methylimidazolium cations bearing 1H, 1H, 2H, 2H-perfluoroalkyl chains (butyl, hexyl, and octyl) and halide counterions, and demonstrate their thermotropic mesomorphism. These cations were synthesized under solvent-free conditions, and anion exchange was used to vary the halide counterion. The thermal behavior of the compounds was studied using thermogravimetric analysis and differential scanning calorimetry, revealing both liquid crystalline phases and solid-solid phase transitions. We discovered that the mesomorphic properties of the ionic liquids depend strongly on the length of the perfluoroalkyl pendants. Specifically, ionic liquids with a fluorinated butyl chain showed no mesophase behavior while those with hexyl and octyl fluorinated chains displayed liquid crystalline phases at temperatures above 100 °C. The mesophases were further characterized by polarized optical microscopy and powder X-ray diffraction, highlighting the impact of the fluorinated alkyl chain length.

The decomposition of the ionic liquid hydroxylammonium nitrate (HAN) produces gas phase products which have utility in spacecraft propulsion systems. Among the various gas phase species generated from HAN decomposition is the nitroxyl (HNO) radical, a highly reactive molecule with implications in both chemical and electric propulsion applications. The work described here used a laser-induced fluorescence platform to directly detect the relative density of the HNO radical formed by passing HAN vapor through heated porous disks of varying composition. The use of heated porous 316-stainless steel and aluminum disks showed significant HNO density production and is attributed to a surface hydrogen abstraction mechanism. There was also evidence of surface modification to the metal disks which resulted in a shift in the HNO density temperature profiles. The results reported demonstrate that use of a heated porous material can easily generate a molecular vapor at moderate temperatures for combustion and electric propulsion applications.

This study explores the impact of carboxylate ionic liquids (ILs) on the phase transition properties of methylcellulose (MC) in the diluted and semi-diluted regime. Conductivity measurements were used to examine the aggregation of ILs 1-decyl-3-methylimidazolium butanoate ([C₁₀MIM][BUT]), 1-decyl-3-methylimidazolium crotonate ([C₁₀MIM][CRO]), and 1-decyl-3-methylimidazolium pentanoate ([C₁₀MIM][PEN]) in the presence and absence of MC. The interaction between ILs and MC was confirmed using ¹H NMR spectroscopy. The effect of ILs on the phase transition of MC was investigated through UV–vis spectroscopy and oscillatory rheometry. Results indicated that the carboxylate ILs studied tend to interact with MC, reducing polymer-polymer interactions and the apparent viscosity of MC solutions. Furthermore, carboxylate ILs were observed to modulate the sol-gel transition temperature of MC to higher temperatures, while weakening the resulting gel compared to pure MC gels.

Ionic liquids posses efficiency as solvents, co-solvents or agents for applications involving biomolecules. Due to the increasing interest in systems containing proteins and ionic liquids, we hereby present results from molecular dynamics simulations on solutions containing the polypeptide melittin in pure water, in the neat ionic liquid 1-butyl-3-methyl-imidazolium acetate ([BMI][OAc]) and in the equimolar [BMI][OAc]/H₂O mixture. When compared to the solutions containing the ionic liquid, melittin displays higher mobility and flexibility, lower stability and poorer secondary structure preservation in water. The intramolecular hydrogen bonds in melittin do not play a major role in the structural preservation, but intermolecular hydrogen bonds between melittin and the solvent are important. The micro-solvation of melittin demonstrates that anions and water molecules are in closer contact to melittin, whereas the cations maintain larger distances to the polypeptide. The presence of [BMI][OAc] reduces fluctuation in melittin's structure. Only small differences have been found in the structural arrangement of melittin in the neat ionic liquid and the ionic liquid/water mixture.

The ionic liquid hydroxylammonium nitrate (HAN) is a promising propellant for various types of spacecraft propulsion systems. With respect to combustion and plasma-based electric propulsion, the thermal decomposition of HAN into gas phase species provides a convenient feed gas supply. While the decomposition of HAN in the liquid phase has been extensively studied, little is known about the decomposition chemistry of HAN vapor interacting with heated surfaces. The ability to decompose HAN vapor on a reactive surface could provide a means to control the feed gas composition and enhance the performance of spacecraft propulsion systems.

In this initial qualitative study, HAN was vaporized and thermally decomposed using porous 316-stainless-steel and quartz disks under vacuum conditions. Decomposition products with low vapor pressures would condense on an in-line quartz tube which was subsequently collected and analyzed with Raman spectroscopy, NMR spectroscopy, and FT-IR spectroscopy. At temperatures above 440 K the 316-stainless-steel system produced significant quantities of ammonia which reacted with vaporized nitric acid to form ammonium nitrate. Temperatures below 440 K yielded partial HAN decomposition which resulted in a binary mixture of HAN and ammonium nitrate. The degree to which HAN was consumed was determined by analysis of the 1008 cm⁻¹N-OH asymmetric Raman band of HAN and the 1049 cm⁻¹ symmetric stretching Raman band of the nitrate ion, NO₃⁻. The quartz system yielded significantly different results with no ammonium nitrate detected at temperatures above 440 K. Reformed HAN was the primary product detected at lower temperatures. The difference in reported measurements and visual observations highlights the distinct differences in HAN vapor decomposition chemistry from the two materials examined.

Terephthalic acid (H₂TPA) solubility in several ionic liquids (ILs) at multiple concentrations is higher than for any other known solvents at lower temperatures and pressures which suggests low energy purification of H₂TPA from its major impurity, 4-carboxybenzaldehyde (4-CBA) might be possible. To understand the mechanism several strategies were explored to purify H₂TPA by taking advantage of this high solubilizing power of ILs for H₂TPA in the crystallization of unique salts and cocrystals. Using either zwitterionic carboxylate IL-precursors or direct salt formation with carboxylate ILs or amines, a series of salts of mono, dibasic and two ionic cocrystals were obtained including monobasic, [C₁C₁im][HTPA], [N₄₄₄₁][HTPA], [C₄C₁im][HTPA]•0.5H₂TPA (a cocrystal), and [C₁Him][HTPA] ([C₁C₁im]⁺ = 1,3-dimethylimidazolium, [N₄₄₄₁]⁺ = tribuytlmethylammonium, [C₁Him]⁺ = 1-methyl-3-H-imidazolium), dibasic [C₁C₁im]₂[TPA], [C₄C₁im]₂[TPA], [N₄₄₄₄]₂[TPA], [C₁Him]₂[TPA], [H₂N₂₂]₂[TPA], [H₃N₆]₂[TPA], and [HN(CH₂CH₂OH)₃]₂[TPA] ([C₄C₁im]⁺ = 1-butyl-3-methylimidazolium, [N₄₄₄₄]⁺ = tetrabuylammonium, [H₃N₆]⁺ = hexylammonium, [HN(CH₂CH₂OH)₃]⁺ = triethanolammonium, [H₂N₂₂]⁺= diethylammonium), and a second cocrystal [C₂C₁im]Cl•0.5H₂TPA. The formation of these salts suggest a viable method to purify H₂TPA because of preferred salt formation at low energy conditions. One elegant route using 1-ethyl-3-methylimidazolium chloride ([C₂C₁im]Cl) could be especially promising because the cocrystal [C₂C₁im]Cl•0.5H₂TPA was readily isolated and is easily dissociated when exposed to ambient conditions into crystalline H₂TPA and a liquid of hydrated [C₂C₁im]Cl.

Interaction of ionic liquids with iron porphyrin (FeP) arises in a number of application of ionic liquids such as dye-sensitized solar cells, batteries, and conversion of CO₂ to value-added products, etc. Furthermore, ionic liquid-FeP interactions are thought to be responsible for ionic liquid biodegradation and catalytic breakdown of ionic liquids. Despite the importance of ionic liquid-FeP interactions, there is a lack of information on what conformations ionic liquids adopt when presented to FeP and how thermodynamics of subsequent electron transfer reaction is affected. To begin to answer these questions, electronic structure calculations are performed to assess how the binding propensity of the homologous series of 1-n-alkyl-3-methylimidazolium [C_nmim]Cl (n = 2, 4, 6, 8, 10) to FeP is affected as the alkyl chain length and the initial conformation of the cation presented to FeP are varied. The conceptual density functional theory framework is then invoked to compute the electrophilicity index of the ionic liquid-FeP complex to glean insight into the ability of the complex to acquire an electron. Calculations suggest two equally likely conformations of ionic liquids with similar Gibbs free energy change; however, the enthalpic and entropic contributions differ based on the conformation adopted by ionic liquids which in turn affects the propensity of the subsequent electron transfer process. The importance of results is discussed in terms of experimentally observed alkyl chain length-dependent biodegradability of ionic liquids.

Due to the sudden rise in demand, a shortfall in the supply of critical metals or high technology metals, especially gallium (Ga), germanium (Ge) and indium (In) is experienced throughout the globe. The different primary and secondary resources are being utilized to recover and recycle these metals through the widely accepted technique, solvent extraction (SX). The extraction of metals may be potentially achieved by compounds of negligible volatility, phosphonium ionic liquids (Phos ILs). Ionic liquids (ILs) are potential and useful compounds to separate and recover Ga, Ge and In from synthetic solutions and waste materials due to their tunable nature to achieve higher selectivity, superior physicochemical properties and diverse structural properties. Ion exchange mechanism was mainly found applicable for the extractive separation of such metals through Phos ILs. Based on the efficiency, extraction mechanism and diverse operating conditions of Phos ILs, the present review provides a comprehensive description of separation as well as recovery of Ga, Ge and In from the synthetic solutions as well as waste materials.