Room Temperature Ionic Liquid Solvents Research Articles

Effects of operating temperature on Li-O2 battery with ionic liquid-based binary electrolyte

Awaiting a breakthrough, the Li-oxygen battery (LOB) is considered a promising candidate to meet the high energy demands in the future. Among various critical challenges which hamper its development, the mystery of the electrolyte with optimal properties remains unsolved to this day. In this study, we comprehensively investigated the effects of operating temperature (20C, 40 °C and 60 °C) on the electrochemical performance of LOBs incorporated with room temperature ionic liquid (RTIL) and organic solvent binary electrolyte. We designed and investigated 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2C1im][Tf2N]) RTIL and dimethyl sulfoxide (DMSO) organic solvent at various volume ratios ((4:1), (1:1), (1:4)). Among the binary electrolytes, ([C2C1im][Tf2N]/DMSO (1:4)) delivered the highest discharge capacities of 3.70 Ah g− 1 (20 °C), 4.0 Ah g− 1 (40 °C) and 3.65 Ah g− 1 (60 °C) as compared with pure [C2C1im][Tf2N] and DMSO. Cycling stability tests showed superior stability of the binary electrolyte ([C2C1im][Tf2N]/DMSO (1:4)) irrespective of the operating temperature. From viscosity and ionic conductivity measurements (at 20–60 °C), [C2C1im][Tf2N]/DMSO (1:4) exhibited the highest ionic conductivity and the lowest viscosity compared with other binary electrolytes (even with pure electrolytes) at any given temperature. Cyclic voltammetry (CV) tests revealed the highest reaction rates for [C2C1im][Tf2N]/DMSO (1:4) binary electrolytes than pure electrolytes. The superior performance of [C2C1im][Tf2N]/DMSO (1:4) binary electrolyte was ascribed to enhanced stability against reactive intermediate species during oxygen reduction reaction (ORR), increased ionic conductivity, low viscosity (comparable with organic electrolytes), improved oxygen solubility, and relatively low evaporation rates.

Voltammetry and Spectroelectrochemistry of TCNQ in Acetonitrile/RTIL Mixtures.

Understanding the solvation and ion-pairing interactions of anionic substrates in room-temperature ionic liquids (RTIL) is key for the electrochemical applications of these new classes of solvents. In this work, cyclic voltammetry and visible and infrared spectroelectrochemistry of tetracyanoquinodimethane (TCNQ) was examined in molecular (acetonitrile) and RTIL solvents, as well as mixtures of these solvents. The overall results were consistent with the formation of RTIL/acetonitrile nanodomains. The voltammetry indicated that the first electrogenerated product, TCNQ−, was not incorporated into the RTIL nanodomain, while the second electrogenerated product, TCNQ2−, was strongly attracted to the RTIL nanodomain. The visible spectroelectrochemistry was also consistent with these observations. Infrared spectroelectrochemistry showed no discrete ion pairing between the cation and TCNQ− in either the acetonitrile or RTIL solutions. Discrete ion pairing was, however, observed in the acetonitrile domain between the tetrabutylammonium ion and TCNQ2−. On the other hand, no discrete ion pairing was observed in BMImPF6 or BMImBF4 solutions with TCNQ2−. In BMImNTf2, however, discrete ion pairs were formed with BMIm+ and TCNQ2−. Density function theory (DFT) calculations showed that the cations paired above and below the aromatic ring. The results of this work support the understanding of the redox chemistry in RTIL solutions.

Formation of 3-Dimensional Gold, Copper and Palladium Microelectrode Arrays for Enhanced Electrochemical Sensing Applications.

Microelectrodes offer higher current density and lower ohmic drop due to increased radial diffusion. They are beneficial for electroanalytical applications, particularly for the detection of analytes at trace concentrations. Microelectrodes can be fabricated as arrays to improve the current response, but are presently only commercially available with gold or platinum electrode surfaces, thus limiting the sensing of analytes that are more electroactive on other surfaces. In this work, gold (Au), copper (Cu), and palladium (Pd) are electrodeposited at two different potentials into the recessed holes of commercial microelectrode arrays to produce 3-dimensional (3D) spiky, dendritic or coral-like structures. The rough fractal structures that are produced afford enhanced electroactive surface area and increased radial diffusion due to the 3D nature, which drastically improves the sensitivity. 2,4,6-trinitrotoluene (TNT), carbon dioxide gas (CO2), and hydrogen gas (H2) were chosen as model analytes in room temperature ionic liquid solvents, to demonstrate improvements in the sensitivity of the modified microelectrode arrays, and, in some cases (e.g., for CO2 and H2), enhancements in the electrocatalytic ability. With the deposition of different materials, we have demonstrated enhanced sensitivity and electrocatalytic behaviour towards the chosen analytes.

Nonpolar solvation dynamics for a nonpolar solute in room temperature ionic liquid: a nonequilibrium molecular dynamics simulation study

Nonpolar solvation dynamics of a nonpolar diatomic solute in a room temperature ionic liquid (RTIL) has been followed via nonequilibrium molecular dynamics (MD) simulation. Frank-Condon type excitation of the solute, previously in equilibrium in RTIL solvent, has been modelled by abruptly changing the Lennard-Jones (LJ) diameter of the solute atoms and thereby disrupting the equilibrium situation. The rearrangement of the RTIL solvent molecules, which has been seen to be mostly contributed by the solute’s first solvation shell, around the excited solute results overall spectral narrowing and biphasic decay of the solvation energy; a dominant and very rapid process having sub-100 fs relaxation time, followed by a slower one relaxing at a timescale of $$\sim $$ 5 ps. A mode-coupling theory based calculation is also used to obtain the nonpolar solvation relaxation function for a model nonpolar solute dissolved in model RTIL solvent. The theoretical relaxation decay is not in very good agreement with the simulated nonequilibrium solvation response function; the theory predicts the short time relaxation component slower and the longtime component faster than those of the simulated nonequilibrium relaxation. We have also checked the validity of the linear response theory (LRT) for nonpolar solvation in RTIL by looking at the equilibrium solvation energy correlation in the RTIL solvent in presence of the ground state (GS) and the excited state (ES) solute. Apparent breakdown of the LRT in the present case elucidates the probable disagreement between the theoretical and simulated nonequilibrium nonpolar solvation response functions. SYNOPSIS Nonpolar solvation dynamics of a nondipolar solute probe in an imidazolium ionic liquid has been studied using classical molecular dynamics simulation method. The equilibrium and non-equilibrium simulated solvation response functions have been compared with experimentally measured (using 3PEPS) and theoretically predicted (using mode coupling based theory) solvation response function. The study reveals that the experimental solvation timescales can originate from the purely nonpolar interaction between excited solute and ionic liquid solvent molecules.

Effect of microheterogeneity in room temperature ionic liquids on energy and electron transfer processes

Triplet − triplet energy transfer (TET) and electron transfer (ET) processes involving a few long-lived (lifetime of about a few microsecond) triplet states as energy donors and radical anions as electron donors, respectively, have been investigated here in a series of 1-alkyl-3-methyl-imidazolium cation based ionic liquids, SDS micelle as well as in a few conventional solvents. Long lifetimes of the transient donors ensure occurrence of these processes in the ‘stationary quenching regime’ even in highly viscous RTIL solvents. Results of our molecular dynamic simulations reveal that self-organization of the RTIL solvent molecules, which creates nonionic and ionic pockets in RTIL, becomes more significant as the alkyl chain length increases. In the cases, where both the reactants are neutral molecules, which prefer to stay inside the nonionic or nonpolar pockets, the diffusive motion of the reactants experiences much smaller microscopic viscosity as compared to the bulk or macroscopic viscosity of the solution. However, if one of two reactants is ionic and the other is nonionic, they reside at ionic and nonionic pockets of the RTIL solution, respectively, and the motion of the reactants occur through different regions of the RTIL solution. Therefore, the reactants experience the macroscopic viscosity of the solution and the reaction rates show a linear relationship with inverse of viscosity of the solution (Smoluchowski equation). Present study clearly establishes the inherent microscopic heterogeneities in room temperature ionic liquids (RTILs), which have been the subject of intense discussion in recent times.

Screen-Printed Graphite Electrodes as Low-Cost Devices for Oxygen Gas Detection in Room-Temperature Ionic Liquids.

Screen-printed graphite electrodes (SPGEs) have been used for the first time as platforms to detect oxygen gas in room-temperature ionic liquids (RTILs). Up until now, carbon-based SPEs have shown inferior behaviour compared to platinum and gold SPEs for gas sensing with RTIL solvents. The electrochemical reduction of oxygen (O2) in a range of RTILs has therefore been explored on home-made SPGEs, and is compared to the behaviour on commercially-available carbon SPEs (C-SPEs). Six common RTILs are initially employed for O2 detection using cyclic voltammetry (CV), and two RTILs ([C2mim][NTf2] and [C4mim][PF6]) chosen for further detailed analytical studies. Long-term chronoamperometry (LTCA) was also performed to test the ability of the sensor surface for real-time gas monitoring. Both CV and LTCA gave linear calibration graphs—for CV in the 10–100% vol. range, and for LTCA in the 0.1–20% vol. range—on the SPGE. The responses on the SPGE were far superior to the commercial C-SPEs; more instability in the electrochemical responses were observed on the C-SPEs, together with some breaking-up or dissolution of the electrode surface materials. This study highlights that not all screen-printed ink formulations are compatible with RTIL solvents for longer-term electrochemical experiments, and that the choice of RTIL is also important. Overall, the low-cost SPGEs appear to be promising platforms for the detection of O2, particularly in [C4mim][PF6].

Fatty acid methyl ester heterogeneous self‐metathesis in hydrophobic green solvent: Mass transfer limitations, catalyst recyclability, and stability

AbstractThe role of room‐temperature ionic liquids (RTILs), [bmim][PF6] and [bmim][Tf2N], as reaction media regarding the catalytic activity and stability of methyltrioxorhenium (MTO) supported on ZnCl2‐modified mesoporous Al2O3 has been studied for self‐metathesis of a functionalized olefin, methyl oleate. The humidity influence on the catalytic activity was probed. The catalyst recycling ability and the kinetics of the metathesis reaction using these RTILs were also investigated. It was found that the MTO‐based catalyst was efficient in viscous hydrophobic RTIL solvents. However, their high viscosity was found to increase the mass transfer limitations thus somewhat impacting the reaction kinetics. Nevertheless, better catalyst stability was reached allowing its possible recycling when used in RTIL media.

Comparison of Voltammetric Techniques for the Electroanalysis of Dissolved Solids and Gases in Water, Acetonitrile and Room Temperature Ionic Liquids (RTILs): Unusual Behaviour for Gases

Square wave voltammetry (SWV) and differential pulse voltammetry (DPV) are commonly used in electroanalysis, typically in aqueous solvents, as they are usually an order of magnitude more sensitive than linear sweep voltammetry (LSV)/cyclic voltammetry (CV), (e.g. detection limits as low as nanomolar are possible using SWV). These more sensitive techniques are often applied in the development of electrochemical sensors and biosensors over the last ten years due to the negligible capacitive current compared to faradaic current (in protic solvents).1,2 Over the last two decades there has been great attention focused on the improvement of electrochemical gas sensors to monitor toxic gases using amperometric gas sensors (AGSs), which typically employ water/sulphuric acid electrolytes as solvents. Room temperature ionic liquids (RTILs) have been attracting great attention3 as replacement electrolytes in AGSs due to their unique physical properties such as low volatility and negligible vapor pressure, wide electrochemical windows, high ionic conductivity, high chemical and thermal stability and their ability to dissolve a wide range of gases. To the best of our knowledge, there are limited studies on the sensitivity of SWV, DPV and LSV for the sensing of gaseous analytes in RTIL solvents. In this presentation, a comparison of three different electrochemical techniques (SWV, DPV and LSV) will be employed for two gases (ammonia and oxygen) in RTILs. As a control, oxygen gas will also be studied in acetonitrile and water solvents, and dissolved solid analytes are also studied (K3Fe(CN)6in water, ferrocene in acetonitrile and ferrocene in RTILs). For all dissolved solid analytes, SWV gave the highest current response compared to DPV and LSV, respectively. For dissolved gases, the behavior was different. For oxygen, LSV gave larger currents (although relatively comparable) to SWV, with DPV giving the lowest currents. For ammonia, LSV was far superior to both SWV and DPV and was consistent throughout eight different RTIL solvents. This suggests that the generally accepted methods for low concentration analyte detection may not apply for dissolved gases.

Is There Room for Ionic Liquids in the Development of Mg Batteries?

Magnesium anode batteries: Batteries with pure Mg metal anodes have been noted as being potential post Li-ion technologies for the following reasons: -Mg holds almost 6 times the specific energy of LiC6 -Mg is cheaper than Li -Mg is a safer material than Li Despite the clear motivation for assembling Mg batteries, their shortfall to date has been in large part due to the fact that conventional Mg electrolytes are simply not compatible with reversible Mg electrodeposition and dissolution. Electrolytes providing a reversible Mg2+/Mg0 couple: Families of Mg electrolytes known to give reversible deposition and dissolution of Mg include RMgX, Mg(BR4)2, Rm,,(RO)mMgX2-m + AX3-nR’n (A=Al,B; X=F,Cl,Br; R=alkyl or aryl group). Unfortunately, these materials have not found commercial success primarily due to issues with one or more of the following: low anodic stability, low conductivity, low cycling efficiency, corrosiveness, difficulty with production on a large scale, high nucleophilicity, and or lack of compatible cathode materials. The reader is referred to the literature to understand specific drawbacks for each species.1,2 The Case for Room Temperature Ionic Liquids (RTILs): In recent years, ionic liquids have generated a lot of excitement in several branches of science, one of them being energy storage. To date, use of ionic liquid media for Mg electrochemistry has been met with very limited success. There have been claims of reversible Mg deposition and dissolution using conventional Mg salts in RTILs but not without considerable subsequent criticism.3,4It may be that RTILs simply cannot provide an appropriate environment, however, we feel as though they may be overlooked and are more compatible than previously suggested. The obvious benefits from using RTILs in batteries are the following general physical properties: Non-volatileHigh Thermal stability and liquid rangeIntrinsically conductiveWide electrochemical windows The first two characteristics allow us to create extremely dry and inert environments by performing electrochemistry under vacuum as well as high temperatures. In such conditions (0.4mTorr, 100°C) we show moderate stripping behavior, not observed under normal inert gas atmospheres (fig 1 black curve). Furthermore, we believe there are interesting lessons to be learned from work being done with Li and Zn batteries using RTIL solvents. Specifically, double layer structures and solvation environments behave much differently in RTILs than in conventional solvents and have been shown to drastically alter the electrochemical response. For instance, the voltammograms in figure 1 with Zn and Mg salts show unusual cathodic current dips possibly due to a compact ion double layer changing as the potential is swept. See Figure 1:Comparison of Mg, Zn, & Li-TFSI electrolyte solutions in BMPTFSI (~0.1M). We will here present the challenges faced with using Mg electrolytes in RTILs and the possible strategies for using them to create an environment capable of providing facile, reversible Mg/Mg2+electrochemistry. Acknowledgment We acknowledge support from the Army Research Office grant number W911NF-11-1-0432.

Development of lithium-sulfur batteries using room temperature ionic liquid-based quasi-solid-state electrolytes

Quasi-solid-state electrolytes (QSEs), consisting of pseudo-ternary system, i.e., room temperature ionic liquid (RTIL)-lithium bis(trifluoromethanesulfonyl)amide (Li-TFSA)-fumed silica nano particles, were prepared for use as electrolytes in bulk-type all-solid-state cell configuration lithium-sulfur rechargeable batteries. Regardless of the high concentration of RTIL-Li-salt mixtures with fumed silica nano particles, i.e., 80-90% volume ratio, the composites were white powders. Further blending with 5wt% polytetrafluoroethylene (PTFE) powder caused the composite powders to become transparent sheets of 30-200μm in thickness. The electrolyte sheets exhibited liquid-like high apparent conductivities regardless of their solid-like appearance. Sulfur utilization ratios were enhanced using conductive additives with high specific surface areas. Cells with notable performance were successfully assembled after the optimization of the RTIL solvent composition, electrolyte thickness, and conductive additive species. The initial discharge capacity was 1100mAh g−1 at 0.05 C. After 45 discharge-charge cycles, the discharge capacity was still 690mAhg−1. This performance is comparable to lithium-sulfur cells that use the RTIL-Li-salt liquid electrolytes.

Synthesis and Characterization of Ionic Polymer Networks in a Room-Temperature Ionic Liquid

Ionic liquid gels (ILGs) for potential use in ion transport and separation applications were generated via a free radical copolymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and N,N'-methylene(bis)acrylamide (MBA) using 1-ethyl-3-methylimidazolium ethylsulfate (IL) as a room temperature ionic liquid solvent medium. The AMPS and MBA monomer solubility window in the IL in the temperature range of 25 to 65 °C was determined. In situ ATR-FTIR showed near complete conversion of monomers to a cross-linked polymer network. ILGs with glass transition temperatures (T(g)s) near -50 °C were generated with T(g) decreasing with increasing IL content. The elastic moduli in compression (200 to 6600 kPa) decreased with increasing IL content and increasing AMPS content while the conductivities (0.35 to 2.14 mS cm⁻¹) increased with increasing IL content and decreasing MBA content. The polymer-IL interaction parameter (χ) (0.48 to 0.55) was determined via a modified version of the Bray and Merrill equation.

Oxygen reduction voltammetry on platinum macrodisk and screen-printed electrodes in ionic liquids: Reaction of the electrogenerated superoxide species with compounds used in the paste of Pt screen-printed electrodes?

Screen-printed electrodes (SPEs) are widely investigated as simple, three-electrode planar surfaces for electrochemical sensing applications, and may be ideal for gas sensing purposes when combined with non-volatile room temperature ionic liquids (RTILs). In this report the suitability of SPEs with RTIL solvents has been investigated for oxygen detection. Oxygen reduction has been studied on commercially available platinum SPEs in eight RTILs. Cyclic voltammetric wave shapes were found to be significantly different on Pt SPE surfaces compared to conventional solid Pt macroelectrodes, suggesting a possible reaction of the electrogenerated superoxide with the compounds that make up the ink/paste of the SPE surface. The only RTIL that did not show such drastically different voltammetry was one that contained a pyrrolidinium cation, suggesting a more chemically stable solvent environment compared to the other imidazolium and phosphonium cations studied. The analytical utility was then studied on four SPE surfaces (carbon, gold, platinum and silver) in two RTILs (one with a pyrrolidinium and one with an imidazolium cation) and linear responses were observed between current and % concentration in the range 10–100% O2. This suggests that SPEs may indeed be suitable for oxygen sensing in some RTILs, but significantly more pre-treatment of the surface is required to obtain reliable results. However, the reaction of superoxide with the SPE ink, together with a noticeable deterioration of the signal over time, suggests that this type of sensing platform may only be suitable for “single-use” oxygen sensing applications.

Electron Injection Efficiency in Ru-Dye Sensitized TiO2 in the Presence of Room Temperature Ionic Liquid Solvents Probed by Femtosecond Transient Absorption Spectroscopy: Effect of Varying Anions

We investigated the electron injection efficiency of a Ru-complex dye (N719) sensitized TiO2 system using femtosecond transient absorption in the presence of two different room temperature ionic liquids (ILs) varying their anionic counterparts (tetracyanoborate [TCB]− and dicyanoamide [DCA]−), keeping the cationic counterpart (ethylmethylimidazolium [EMIm]+) invariant. We also investigated the effect of varying IL environments on the metal–ligand charge transfer band of the adsorbed N719 on TiO2 film using steady state absorption spectroscopy and the effect on cyano stretching frequency of ILs in the presence of TiO2 films using attenuated total reflectance-IR method. The downshift of conduction band (CB) edge energy of TiO2 nanoparticles in presence of [EMIm][TCB] IL environment has recently been reported (J. Phys. Chem. C2011, 115, 816–822). Based on CB edge energy modulation and transient absorption spectroscopic data, we found that the electron injection efficiency is higher in the N719/TiO2 system in the presence of [EMIm][TCB] IL environment than in the presence of [EMIm][DCA] IL environment by ∼20%.

The feasibility of a pyrrolidinium-based ionic liquid solvent for non-graphitic carbon electrodes

The feasibility of a pyrrolidinium-based room-temperature ionic liquid (RTIL) as the solvent for lithium-ion batteries is tested by analyzing its intercalation behavior and thermal stability. The RTIL-cations are intercalated into a graphitic carbon and a part of them are irreversibly trapped inside the graphene layers. These trapped cations block Li + intercalation to give only a marginal capacity. In contrast, such a cation insertion/trapping is absent in two non-graphitic carbons; hard carbon and soft carbon. A stable cycle performance with a Li + insertion capacity of about 200 mAh g − 1 is attained. The absence of RTIL-cation insertion is evidenced by the cyclic voltammograms and Raman spectra. A calorimetric study reveals that this RTIL has a higher thermal stability and less reactivity with lithiated carbons as compared with the carbonate-based solvent. The use of this RTIL solvent for the non-graphitic carbons seems to be feasible.

Preparation of synthetic wood composites using ionic liquids

Synthetic wood composite films containing cellulose, hemicelluloses, and lignin, the three major components of natural wood, were prepared in a room temperature ionic liquid solvent, 1-ethyl-3-methylimidazolium acetate, [EMIM][Ac]. Various synthetic wood composites were obtained by dissolution of individual wood components together with additives, including polyethylene glycol (PEG), chitosan, and multi-wall carbon nanotubes (MWNTs) in [EMIM][Ac]. The addition of water affords a gel that was dried in either a low humidity environment or under vacuum. Synthetic wood films showed smoother surface textures, higher water resistance, and higher tensile strengths than cellulose films formed by the same methods. Tailor-made synthetic wood composites were also prepared having a variety of desirable properties, including antimicrobial activities, controlled hydro-phobicity/philicity, high relative dielectric constant, and a high degree of cohesiveness.

(Invited) Amperometric Gas Detection Using Room Temperature Ionic Liquid Solvents

The electrochemistry of various gases, including oxygen, carbon dioxide, hydrogen, ammonia, hydrogen sulfi de, sulfur dioxide and nitrogen dioxide, in room temperature ionic liquids (RTILs) is reviewed. The application of RTILs to gas sensor design and development is highlighted.

Room-Temperature Ionic Liquids and Composite Materials: Platform Technologies for CO2 Capture

Clean energy production has become one of the most prominent global issues of the early 21st century, prompting social, economic, and scientific debates regarding energy usage, energy sources, and sustainable energy strategies. The reduction of greenhouse gas emissions, specifically carbon dioxide (CO(2)), figures prominently in the discussions on the future of global energy policy. Billions of tons of annual CO(2) emissions are the direct result of fossil fuel combustion to generate electricity. Producing clean energy from abundant sources such as coal will require a massive infrastructure and highly efficient capture technologies to curb CO(2) emissions. Current technologies for CO(2) removal from other gases, such as those used in natural gas sweetening, are also capable of capturing CO(2) from power plant emissions. Aqueous amine processes are found in the vast majority of natural gas sweetening operations in the United States. However, conventional aqueous amine processes are highly energy intensive; their implementation for postcombustion CO(2) capture from power plant emissions would drastically cut plant output and efficiency. Membranes, another technology used in natural gas sweetening, have been proposed as an alternative mechanism for CO(2) capture from flue gas. Although membranes offer a potentially less energy-intensive approach, their development and industrial implementation lags far behind that of amine processes. Thus, to minimize the impact of postcombustion CO(2) capture on the economics of energy production, advances are needed in both of these areas. In this Account, we review our recent research devoted to absorptive processes and membranes. Specifically, we have explored the use of room-temperature ionic liquids (RTILs) in absorptive and membrane technologies for CO(2) capture. RTILs present a highly versatile and tunable platform for the development of new processes and materials aimed at the capture of CO(2) from power plant flue gas and in natural gas sweetening. The desirable properties of RTIL solvents, such as negligible vapor pressures, thermal stability, and a large liquid range, make them interesting candidates as new materials in well-known CO(2) capture processes. Here, we focus on the use of RTILs (1) as absorbents, including in combination with amines, and (2) in the design of polymer membranes. RTIL amine solvents have many potential advantages over aqueous amines, and the versatile chemistry of imidazolium-based RTILs also allows for the generation of new types of CO(2)-selective polymer membranes. RTIL and RTIL-based composites can compete with, or improve upon, current technologies. Moreover, owing to our experience in this area, we are developing new imidazolium-based polymer architectures and thermotropic and lyotropic liquid crystals as highly tailorable materials based on and capable of interacting with RTILs.

Interpretation of CO2 Solubility and Selectivity in Nitrile-Functionalized Room-Temperature Ionic Liquids Using a Group Contribution Approach

In this work, tuning the solubility parameter of room-temperature ionic liquids (RTILs) with appended functional groups was explored using a combination of experiment and theory. By predictably altering the solubility parameters of several RTIL solvents, their gas solubility and separation performance were tailored. This concept was demonstrated by synthesizing and characterizing imidazolium-based RTILs that incorporate nitrile and alkyne functional substituents. The ideal solubility and selectivity values of CO2, N2, and CH4 at near ambient temperature and pressure were measured for these RTILs. These functionalized RTIL solvents exhibited lower CO2, N2, and CH4 solubility values but improved CO2/N2 and CO2/CH4 solubility selectivity when compared to analogous nonfunctionalized, n-alkyl-substituted RTILs. A group contribution method was used to predict the solubility parameters of the functionalized RTILs, and these values were used with regular solution theory to predict the solubility and selectivity of the three gases. These predicted gas solubility values were found to be in good agreement with those measured experimentally. Furthermore, the predictions from the group contribution method indicated that inclusion of the nitrile and alkyne functional groups increased the solubility parameter relative to the analogous, n-alkyl-substituted RTILs. These initial results show that the group contribution method offers a valuable guide for systematically designing functionalized RTILs with specific gas solubility and selectivity performance.

Measuring the solubility of benzoic acid in room temperature ionic liquids using chronoamperometric techniques

AbstractThe electrochemical reduction of benzoic acid (BZA) has been studied at platinum micro‐electrodes (10 and 2 µm diameters) in acetonitrile (MeCN) and six room temperature ionic liquids (RTILs): [C2mim][NTf2], [C4mim][NTf2], [C4mpyrr][NTf2], [C4mim][BF4], [C4mim][NO3] and [C4mim][PF6] (where [Cnmim]+ = 1‐alkyl‐3‐methylimidazolium, [NTf2]− = bis(trifluoromethylsulphonyl)imide, [C4mpyrr]+ = N‐butyl‐N‐methylpyrrolidinium, [BF4]− = tetrafluoroborate, [NO3]− = nitrate and [PF6]− = hexafluorophosphate). Based on the theoretical fitting to experimental chronoamperometric transients in [C4mpyrr][NTf2] and MeCN at several concentrations and on different size electrodes, it is suggested that a fast chemical step preceeds the electron transfer step in a CE mechanism (given below) in both RTILs and MeCN, leading to the appearance of a simple one‐electron transfer mechanism. The six RTIL solvents and MeCN were saturated with BZA, and potential‐step chronoamperometry revealed diffusion coefficients of 170, 4.6, 3.2, 2.7, 1.8, 0.26 and 0.96 × 10−11 m2 s−1 and solubilities of 850, 75, 78, 74, 220, 2850 and 48 mM in MeCN and the six ionic liquids, respectively, at 298 K. The high solubility of BZA in [C4mim][NO3] may suggest a strong interaction of the dissolved proton with the nitrate anion. Although there are relatively few literature reports of solubilities of organic solutes in RTILs at present, these results suggest the need for further studies on the solubilities of organic species (particularly acids) in RTILs, because of the contrasting interaction of dissolved species with the RTIL ions. Chronoamperometry is suggested as a convenient methodology for this purpose. Copyright © 2008 John Wiley & Sons, Ltd.

Cloud point phenomena for POE-type nonionic surfactants in a model room temperature ionic liquid

The cloud point phenomenon has been investigated for the solutions of polyoxyethylene (POE)-type nonionic surfactants (C 12E 5, C 12E 6, C 12E 7, C 10E 6, and C 14E 6) in 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF 4), a typical room temperature ionic liquid (RTIL). The cloud point, T c , increases with the elongation of the POE chain, while decreases with the increase in the hydrocarbon chain length. This demonstrates that the solvophilicity/solvophobicity of the surfactants in RTIL comes from POE chain/hydrocarbon chain. When compared with an aqueous system, the chain length dependence of T c is larger for the RTIL system regarding both POE and hydrocarbon chains; in particular, hydrocarbon chain length affects T c much more strongly in the RTIL system than in equivalent aqueous systems. In a similar fashion to the much-studied aqueous systems, the micellar growth is also observed in this RTIL solvent as the temperature approaches T c . The cloud point curves have been analyzed using a Flory–Huggins-type model based on phase separation in polymer solutions.