Nanostructural organization and anion effects in the optical Kerr effect spectra of binary ionic liquid mixtures

This article reports a study of the effect of anions on the optical Kerr effect (OKE) spectra of binary ionic liquid mixtures with one mixture comprising the 3-methyl-1-pentylimidazolium ([C 5mim] (+)) cation and the anions PF 6 (-) and CF 3CO 2 (-) (TFA (-)), and another mixture comprising the [C 5mim] (+) cation and the anions Br (-) and bis(trifluomethanesulfonyl)imide (NTf 2 (-)). The spectra were obtained by the use of optical heterodyne-detected Raman-induced Kerr Effect Spectroscopy at 295 K. The OKE spectra of the mixtures are compared with the calculated mole-fraction weighted sum of the normalized OKE spectra of the neat liquids. The OKE spectra are nearly additive for [C 5mim]Br/[C 5mim][NTf 2] mixtures, but nonadditive for [C 5mim][PF 6]/[C 5mim][TFA] mixtures. In the case of the equimolar [C 5mim][PF 6]/[C 5mim][TFA] mixture, the nonadditivity is such that the experimental OKE spectrum is narrower than the calculated OKE spectrum. The additivity or nonadditivity of OKE spectra for IL mixtures can be explained by assuming ionic liquids are nanostructurally organized into nonpolar regions and ionic networks. The ionic networks in mixtures will be characterized by "random co-networks" for anions that are nearly the same in size (PF 6 (-) and TFA (-)) and by "block co-networks" for anions that differ greatly in size (Br (-) and NTf 2 (-)).     

An electrochemical study of the oxidation of hydrogen at platinum electrodes in several room temperature ionic liquids

The electrochemical oxidation of dissolved hydrogen gas has been studied in a range of room-temperature ionic liquids (RTILs), namely [C(2)mim][NTf(2)], [C(4)mim][NTf(2)], [N(6,2,2,2)][NTf(2)], [P(14,6,6,6)][NTf(2)], [C(4)mpyrr][NTf(2)], [C(4)mim][BF(4)], [C(4)mim][PF(6)], [C(4)mim][OTf], and [C(6)mim]Cl on a platinum microdisk electrode of diameter 10 microm. In all cases, except [C(6)mim]Cl, a broad quasi-electrochemically reversible oxidation peak between 0.3 to 1.3 V vs Ag was seen prior to electrode activation ([C(6)mim]Cl showed an almost irreversible wave). When the electrode was pre-anodized ("activated") at 2.0 V vs Ag for 1 min, the peak separations became smaller, and the peak shape became more electrochemically reversible. It is thought that the electrogenerated protons chemically combine with the anions (A-) of the RTIL. The appearance and position of the reverse (reduction) peak on the voltammograms is thought to depend on three factors: (1) the stability of the protonated anion, HA, (2) the position of equilibrium of the protonation reaction HA<==> H+ + A- , and (3) any follow-up chemistry, e.g., dissociation or reaction of the protonated anion, HA. This is discussed for the five different anions studied. The reduction of HNTf(2) was also studied in two [NTf(2)]- -based RTILs and was compared to the oxidation waves from hydrogen. The results have implications for the defining of pKa in RTIL media, for the development of suitable reference electrodes for use in RTILs, and in the possible amperometric sensing of H2 gas.     

Raman and ab initio studies of simple and binary 1-alkyl-3-methylimidazolium ionic liquids

Raman spectra of the ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]), 1-hexyl-3-methylimidazolium chloride ([C6mim]Cl), and 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]), and binary mixtures thereof, have been assigned using ab initio MP2 calculations. The previously reported anti and gauche forms of the [C4mim]+ cation have been observed, and this study reveals this to be a general feature of the long-chain 1-alkyl derivatives. Analysis of mixtures of [C6mim]Cl and [C6mim][PF6] has provided information on the nature of the hydrogen bonding between the imidazolium headgroup and the anions, and the invariance of the essentially 50:50 mixture of the predominant conformers informs on the nature of glass formation in these systems.     

室温离子液体对氨基苯磺酸的萃取性能

系统研究了[C₄mim][PF₆], [C₆mim][PF₆], [C₆mim][BF₄]和[C₈mim][BF₄]室温离子液体对间氨基苯磺酸、对氨基苯磺酸稀水溶液的萃取平衡. 实验结果表明: 萃取温度和相体积比的变化对分配比影响不大; 水相pH值对萃取平衡有较大的影响, 氨基苯磺酸在离子液体/水体系中的分配比在pH＝4.2时达到最大值; 水相中CaCl₂或Na₂SO₄的存在能较大幅度地提高氨基苯磺酸的分配比; 离子液体的阴离子的性质对分配比有显著的影响, 阴离子为[BF₄]^－的离子液体对氨基苯磺酸的萃取能力大于阴离子为[PF₆]^－的离子液体; 咪唑环上烷基链的长度也对萃取效果有一定的影响. 在所研究的离子液体中, [C₆mim][BF₄]和[C₈mim][BF₄]对氨基苯磺酸有较好的萃取性能, 且萃取相中的氨基苯磺酸可回收利用, 离子液体也可循环使用.     

Why are viscosities lower for ionic liquids with -CH2Si(CH3)3 vs -CH2C(CH3)3 substitutions on the imidazolium cations?

We have prepared novel room temperature ionic liquids (RTILs) with trimethylsilylmethyl (TMSiM)-substituted imidazolium cations and compared the properties of these liquids with those for which the TMSiM group is replaced by the analogous neopentyl group. The ionic liquids are prepared with both tetrafluoroborate (BF(4)(-)) and bis(trifluoromethylsulfonyl)imide (NTf(2)(-)) anions paired with the imidazolium cations. At 22 degrees C, the TMSiM-substituted imidazolium ILs have shear viscosities that are reduced by a factor of 1.6 and 7.4 relative to the alkylimidazolium ILs for the NTf(2)(-) and BF(4)(-) anions, respectively. To understand the effect of silicon substitution on the viscosity, the charge densities have been calculated by using density functional theory electronic structure calculations. The ultrafast intermolecular, vibrational, and orientational dynamics of these RTILs have been measured by using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The intermolecular dynamical spectrum provides an estimate of the strength of interactions between the ions in the RTILs, and provides a qualitative explanation for the observed reduction in viscosity for the silicon-substituted RTILs.     

Separation of benzene and hexane by solvent extraction with 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide ionic liquids: effect of the alkyl-substituent length

The influence of the alkyl-substituent chain in 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide ionic liquids ([C(n)mim][NTf(2)], where n is the length of a linear alkyl chain) as solvents for the separation of benzene and hexane by liquid extraction was investigated. The liquid-liquid equilibrium (LLE) at 25 degrees C for the ternary systems ([C(n)mim][NTf(2)] + hexane + benzene), with n taking the values 4, 8, 10, and 12, were determined. These data were analyzed and compared to those previously reported for the system ([C(2)mim][NTf(2)] + hexane + benzene). The results show that short alkyl chains on the imidazolium cation of the ionic liquid lead to a better extractive separation of benzene and hexane, and reveal the influence of the relative degree of ordering in the ionic liquids on the extraction parameters.     

Preparation and characterization of new room temperature ionic liquids

A new series [C(n)O(m )mim][X] of imidazolium cation-based room temperature ionic liquids (RTILs), with ether and alcohol functional groups on the alkyl side-chain has been prepared. Some physical properties of these RTILs were measured, namely solubility in common solvents, viscosity and density. The solubility of LiCl, HgCl(2) and LaCl(3) in room temperature ionic liquids was also determined. The features of the solid-liquid phase transition were analysed, namely the glass transition temperature and the heat capacity jump associated with the transition from the non-equilibrium glass to the metastable supercooled liquid. These properties were compared with those reported for the 1-n-alkyl-3-methylimidazolium [C(n )mim][X] series. While the density and solid-liquid phase transition properties are similar for both series, the new RTILs present a considerably lower viscosity and an increased ability to dissolve HgCl(2) and LaCl(3) (up to 16 times higher).     

Thermochemistry of imidazolium-based ionic liquids: experiment and first-principles calculations

In this work the molar enthalpy of formation of the ionic liquid 1-ethyl-3-methylimidazolium dicyanoamide in the gaseous phase [C(2)MIM][N(CN)(2)] was measured by means of combustion calorimetry and enthalpy of vaporization using transpiration. Available, but scarce, primary experimental results on enthalpies of formation of imidazolium based ionic liquids with the cation [C(n)MIM] (where n = 2 and 4) and anions [N(CN)(2)], [NO(3)] and [NTf(2)] were collected and checked for consistency using a group additivity procedure. First-principles calculations of the enthalpies of formation in the gaseous phase for the ionic liquids with the common cation [C(n)MIM] (where n = 2 and 4) and with the anions [N(CN)(2)], [NO(3)], [NTf(2)], [Cl], [BF(4)] and [PF(6)] have been performed using the G3MP2 theory. It has been established that the gaseous phase enthalpies of formation of these ionic liquids obey the group additivity rules.     

Nicotine: on the potential role of ionic liquids for its processing and purification

Marked solubility differences of nicotine in the ionic liquids [C(2)mim][NTf(2)], [C(2)mim][EtOSO(3)], and [C(n)mim]Cl, 6 相似文献   

Lower critical solution temperature behavior of linear polymers in ionic liquids and the corresponding volume phase transition of polymer gels

Poly(benzyl methacrylate) (PBzMA) and its copolymers exhibit lower critical solution temperature (LCST)-type phase separation in common hydrophobic ionic liquids (ILs) such as 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfone)imide ([C(2)mim][NTf2]). The turbidity measurements for PBzMA/IL mixed systems reveal that the LCST-type phase separation temperatures change significantly with the changes in the chemical structures of polymers and ILs. Moreover, cross-linked PBzMA gels show reversible and discontinuous volume phase transition in [C(2)mim][NTf2] with the changes in temperature.     

咪唑基离子液体的物理化学性质估算及预测(英文)

根据经验和半经验方程及空隙模型理论,可以估算及预测离子液体在298.15K的物理化学性质.本文讨论了离子液体的分子体积,密度,标准熵,晶格能,表面张力,等张比容,摩尔蒸发焓,空隙体积,空隙率和热膨胀系数.通过实验测得的三种离子液体1-乙基-3-甲基咪唑硫酸乙酯([C2mim][EtSO4)]),1-丁基-3-甲基咪唑硫酸辛酯([C4mim][OcSO4])和1-乙基-3-甲基咪唑双三氟甲磺酰亚胺盐([C2mim][NTf2])的密度和表面张力估算了它们的其它物理化学性质.由这三种离子液体的分子体积及等张比容预测了同系列中其它离子液体[Cnmim][EtSO4],[Cnmim][OcSO4]和[Cnmim][NTf2](n=1-6)的分子体积及等张比容,由此计算出它们的密度及表面张力.进而预测了它们的物理化学性质.将预测的离子液体[C4mim][NTf2]和[C2mim][OcSO4]的密度值与文献报导的实验值进行比较,其偏差在实验误差范围内.最后,将由Kabo经验方程计算的七个离子液体[C2mim][EtSO4]、[C4mim][OcSO4]、[C2mim][NTf2]、[C4mim][NTf2]、丁基三甲基铵双三氟甲磺酰亚胺盐([N4111][NTf2])、甲基三辛基铵双三氟甲磺酰亚胺盐([N8881][NTf2])和1-辛基-3-甲基吡啶四氟硼酸盐([m3opy][BF4])的摩尔蒸发焓与由Verevkin简单规则预测的摩尔蒸发焓进行比较,发现两者符合很好.因此,在缺乏密度和表面张力实验数据的情况下,可以用Verevkin简单规则来预测离子液体的摩尔蒸发焓.     

Solvent extraction of U(VI) by trioctylphosphine oxide using a room-temperature ionic liquid

The unique physical and chemical properties of room-temperature ionic liquids(RTILs) have recently received increasing attention as solvent alternatives for possible application in the field of nuclear industry, particularly in liquid-liquid separations of radioactive nuclides. We investigated solvent extraction of U(VI) from aqueous solutions into a commonly used ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide([C4mim][NTf2]) using trioctylphosphine oxide(TOPO) as an extractant. The effects of contact time, TOPO concentration, acidity, and nitrate ions on the U(VI) extraction are discussed in detail. The extraction mechanism was proposed based on slope analysis and UV-Vis measurement. The results clearly show that TOPO/[C4mim][NTf2] provides a highly efficient extraction of U(VI) from aqueous solution under near-neutral conditions. When the TOPO concentration was 10 mmol/L, the extraction of 1 mmol/L U(VI) was almost complete( 97%). Both the extraction efficiency and distribution coefficient were much larger than in conventional organic solvents such as dichloromethane. Slope analysis confirmed that three TOPO molecules in [C4mim][NTf2] bound with one U(VI) ion and one nitrate ion was also involved in the complexation and formed the final extracted species of [UO2(NO3)(TOPO)3]+. Such a complex suggests that extraction occurs by a cation-exchange mode, which was subsequently evidenced by the fact that the concentration of C4mim+ in the aqueous phase increased linearly with the extraction percent of U(VI) recorded by UV-Vis measurement.     

Ionic liquids as a convenient new medium for the catalytic asymmetric dihydroxylation of olefins using a recoverable and reusable osmium/ligand

The use of room-temperature ionic liquids (RTILs) in the Sharpless catalytic asymmetric dihydroxylation (AD) as a cosolvent or replacement of the tert-butanol was studied in detail by screening 11 different RTILs. The AD reaction is faster in 1-n-butyl-3-methylimidazolium hexafluorophosphate [C(4)mim][PF(6)] as a cosolvent than in the conventional system of tert-butanol/H(2)O. For the range of six substrates tested, comparable or even higher yields and enantiomeric excess (ee) were found using [C(4)mim][PF(6)] or 1-n-octyl-3-methylimidazolium hexafluorophosphate [C(8)mim][PF(6)] compared to the conventional solvent system. Due to high affinity of the catalytic osmium/quiral ligand system to the ionic liquid, the use of ionic liquid/water (biphasic) or ionic liquid/water/tert-butanol (monophasic) solvent systems provides a recoverable, reusable, robust, efficient, and simple system for the AD reaction. Using 1-hexene and [C(4)mim][PF(6)] as RTIL it was possible to reuse the catalytic system for 9 cycles with only a 5% of yield reduction from the first cycle, allowing an overall yield of 87%, TON = 1566, and with similar ee. Additionally, for each cycle, after extraction of the reaction mixture with diethyl ether, the osmium content in the organic phase (containing the AD product) and in the aqueous phase was in the range of the detection limit (相似文献   

Water-clustering in hygroscopic ionic liquids-an implicit solvent analysis

Most ionic liquids are known to be hygroscopic to varying degrees, and that can be detrimental or useful depending upon the application in question. Water can accumulate slowly over hours or days to saturation levels corresponding to the humidity level. When designing or deploying a new ionic liquid it is important to be able to estimate its maximum moisture absorbing ability at the temperature and pressure of its operation. With this goal in mind we have carried out computational studies on three ionic liquid systems based on [BF(4)](-), [PF(6)](-), and [Tf(2)N](-) anions and 1-alkyl-3-methyl-imidazolium ([C(n)mim](+)) cations within an implicit solvent formalism. For highly hygroscopic systems like [C(n)mim][BF(4)] we find that non-iterative calculations with single water molecules can lead to significant underestimation of the maximum moisture content, while iterative calculations can result in miscibility behavior qualitatively different from experimental observations. On the other hand, the inclusion of small hydrogen-bonded water-clusters up to an appropriately chosen size is shown to yield better quantitative agreements with experimentally observed water uptake. Additionally, such calculations appear consistent with a number of thermodynamically interesting phase behaviors, including limited-solubility to full-miscibility transitions as a function of temperature and as a function of the alkyl chain length of the imidazolium cation. For hydrophobic systems like [C(n)mim][PF(6)] and [C(n)mim][Tf(2)N] the computed solubility (for each n) is found to have a smooth convergence behavior as a function of the largest cluster-size considered with the results for the larger clusters being close to that obtained by iterative calculations with single water molecules.     

Nanocomposite ion gels based on silica nanoparticles and an ionic liquid: ionic transport, viscoelastic properties, and microstructure

The dispersion of silica nanoparticles made an ionic liquid, 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)amide ([C(2)mim][NTf(2)]), gelled even by the addition of 2-3 wt %, due to the formation of interconnected particulate silica networks in [C(2)mim][NTf(2)]. The ionic transport and viscoelastic properties of these nanocomposite ion gels were investigated in relation to the microstructure. Despite their solid-like behavior, the nanocomposite ion gels exhibited a high ionic conductivity of approximately 10(-2) S cm(-1) at 30 degrees C, which is comparable to that of neat [C(2)mim][NTf(2)]. Intriguing viscoelastic responses, such as shear-thinning and shear-induced sol-gel transitions, were found in all of the nanocomposite ion gels. By adjusting the silica concentration, the elastic modulus ( G') could be precisely controlled in a range of more than 3 orders of magnitude and reached approximately 10(6) Pa without a considerable decrease in the ionic conductivity; the characteristic viscoelastic response was also maintained. For the aggregation mechanism in [C 2 mim][NTf(2)], the reaction-limited cluster aggregation (RLCA) model was proposed by rheology and light scattering measurements.     

Decoupling charge transport from the structural dynamics in room temperature ionic liquids

Light scattering and dielectric spectroscopy measurements were performed on the room temperature ionic liquid (RTIL) [C4mim][NTf2] in a broad temperature and frequency range. Ionic conductivity was used to estimate self-diffusion of ions, while light scattering was used to study structural relaxation. We demonstrate that the ionic diffusion decouples from the structural relaxation process as the temperature of the sample decreases toward T(g). The strength of the decoupling appears to be significantly lower than that expected for a supercooled liquid of similar fragility. The structural relaxation process in the RTIL follows well the high-temperature mode coupling theory (MCT) scenario. Using the MCT analysis we estimated the dynamic crossover temperature in [C4mim][NTf2] to be T(c) ~ 225 ± 5 K. However, our analysis reveals no sign of the dynamic crossover in the ionic diffusion process.     

Study on the Conductivities of Pure and Aqueous Bromide-Based Ionic Liquids at Different Temperatures

Electrical conductivities were measured for the pure ionic liquids [C₆mim][Br] (1-hexyl-3-methylimidazolium bromide) and [C₈mim][Br] (1-octyl-3-methylimidazolium bromide) at 0.1 MPa from 293.15 to 333.15 K. Conductivity measurements were also made for the binary water + [C₆mim][Br] and water + [C₈mim][Br] systems and their ternary water + [C₆mim][Br] + [C₈mim][Br] system at 0.1 MPa and 293.15, 298.15, and 303.15 K. The conductivity data of the pure ionic liquids were correlated by the VFT (Vogel-Tamman-Fulcher) equation, and the fitting parameters and mean absolute deviations were determined. New explanations are presented for the molality-dependent behavior of the conductivity of the binary water + [C₆mim][Br] and water + [C₈mim][Br] systems. The generalized Young’s rule and the semi-ideal solution theory for conductivity were used to predict the conductivities of the ternary water + [C₆mim][Br] + [C₈mim][Br] system from the conductivities of its corresponding binary water + [C₆mim][Br] and water + [C₈mim][Br] subsystems. The predictions are in good agreement with the measured values.     

Nanostructural organization in carbon disulfide∕ionic liquid mixtures: molecular dynamics simulations and optical Kerr effect spectroscopy

In this paper, the nanostructural organization and subpicosecond intermolecular dynamics in the mixtures of CS(2) and the room temperature ionic liquid (IL) 1-pentyl-3-methylimidazolium bis{(trifluoromethane)sulfonyl}amide ([C(5)mim][NTf(2)]) were studied as a function of concentration using molecular dynamics (MD) simulations and optical heterodyne-detected Raman-induced Kerr effect spectroscopy. At low CS(2) concentrations (<10 mol.% CS(2)/IL), the MD simulations indicate that the CS(2) molecules are localized in the nonpolar domains. In contrast, at higher concentrations (≥10 mol.% CS(2)/IL), the MD simulations show aggregation of the CS(2) molecules. The optical Kerr effect (OKE) spectra of the mixtures are interpreted in terms of an additivity model with the components arising from the subpicosecond dynamics of CS(2) and the IL. Comparison of the CS(2)-component with the OKE spectra of CS(2) in alkane solvents is consistent with CS(2) mainly being localized in the nonpolar domains, even at high CS(2) concentrations, and the local CS(2) concentration being higher than the bulk CS(2) concentration.     

Colloidal stability of bare and polymer-grafted silica nanoparticles in ionic liquids

The colloidal stability of bare and poly(methyl methacrylate) (PMMA)-grafted silica nanoparticles was studied in 1-alkyl-3-methylimidazolium ([C(n)mim])-based ionic liquids (ILs) with different anionic structures. The theoretical estimation of the colloidal interaction between monodispersed bare silica particles by using the Derjaguin-Landau-Verwey-Overbeek theory indicates that bare silica particles cannot be stabilized and they rapidly form aggregates in all the ILs used in this study. The instability of bare silica particles was experimentally confirmed by dynamic light scattering measurement and in situ transmission electron microscopy observations by utilizing the negligible vapor pressure of ILs. This evidence suggests that electrostatic stabilization is inefficient in ILs because of the high ionic atmosphere and the resulting surface-charge screening. The PMMA-grafted silica particles exhibited long-term colloidal stability in [C(4)mim][PF(6)] and [C(n)mim][NTf(2)], which are compatible with the grafted PMMA. On the other hand, the PMMA-grafted particles could not be stabilized in [C 4mim][BF 4] due to the poor solubility of the grafted PMMA in the IL. Effective steric stabilization is important for obtaining stable colloidal particles in ILs.     

Extraction separation of rare-earth ions via competitive ligand complexations between aqueous and ionic-liquid phases

The extraction separation of rare earth elements is one of the most challenging separation processes in hydrometallurgy and advanced nuclear fuel cycles. The TALSPEAK process (trivalent actinide lanthanide separations by phosphorus-reagent extraction from aqueous komplexes) is a prime example of these separation processes. The objective of this paper is to explore the use of ionic liquids (ILs) for the TALSPEAK-like process, to further enhance its extraction efficiencies for lanthanides, and to investigate the potential of using this modified TALSPEAK process for separation of lanthanides among themselves. Eight imidazolium ILs ([C(n)mim][NTf(2)] and [C(n)mim][BETI], n = 4,6,8,10) and one pyrrolidinium IL ([C(4)mPy][NTf(2)]) were investigated as diluents using di(2-ethylhexyl)phosphoric acid (HDEHP) as an extractant for the separation of lanthanide ions from aqueous solutions of 50 mM glycolic acid or citric acid and 5 mM diethylenetriamine pentaacetic acid (DTPA). The extraction efficiencies were studied in comparison with diisopropylbenzene (DIPB), an organic solvent used as a diluent for the conventional TALSPEAK extraction system. Excellent extraction efficiencies and selectivities were found for a number of lanthanide ions using HDEHP as an extractant in these ILs. The effects of different alkyl chain lengths in the cations of ILs and of different anions on extraction efficiencies and selectivities of lanthanide ions are also presented in this paper.