Non-fluorinated Ionic Liquids Research Articles

Advanced Uranium Removal with Pure, Nonfluorinated Ionic Liquids: Fine-Tuning Hydrophilic and Hydrophobic Properties for Enhanced Selectivity.

Ionic liquids (ILs) have significant potential for eco-friendly extraction of uranium from aqueous solutions, which is critical for nuclear technology, fuel cycle management, and environmental protection. This study examines the impact of the adjustable hydrophobic/hydrophilic properties of ILs on the removal of uranium(VI) (UO22+) from aqueous solutions utilizing both a novel hydrophilic IL (1-butoxyethyl-1-methylmorpholinium butoxyethylphosphite - Mor1-2O4-BOEP) and 1-heptyl-1-methylmorpholinium heptylphosphite (Mor1-7-HP) as an example of a hydrophobic IL with a similar structure. The transfer mechanism of uranyl ions from water to organic or solid phases closely depends on the physicochemical properties of ILs, especially their hydrophobicity. The hydrophobic Mor1-7-HP extracts uranyl via neutral complex formation as UO2(NO3)2-(Mor1-7-HP)2. Conversely, hydrophilic Mor1-2O4-BOEP induced selective precipitation as UO2(NO3)-(BOEP), transferring uranyl to the solid phase. Optimization of the working parameters, in terms of acidity of the aqueous solution and amount of ILs used, allowed the extraction of over 98% of U(VI). The stoichiometry of the organic complex and the precipitate was determined using physicochemical techniques. These tunable H-phosphonate-based ILs have advantages over traditional solvent extraction and conventional ILs, allowing easier handling, improved selectivity, and lower environmental impact. This work advances uranium separation techniques with applications in hydrometallurgy, particularly in the treatment of wastewater and radioactive waste for sustainable uranium recovery.

Mesomorphism of imidazolium-based fluorinated ionic liquids

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.

Effect of structural variation in biomass-derived nonfluorinated ionic liquids electrolytes on the performance of supercapacitors

There is a growing interest in sustainable and high performance supercapacitors (SCs) operating at elevated temperatures as they are highly demanded in heat-durable electronics. Here, we present a biomass-derived nonfluorinated ionic liquid (IL) [P4444][HFuA] and its structural analogue [P4444][TpA] as electrolytes for supercapacitors comprising multiwall carbon nanotubes and activated charcoal (MWCNTs/AC) mixed carbon composite electrodes. A detailed investigation of the effect of scan rate, temperature, potential window and orientation of ions on the electrodes surfaces is performed. The supercapacitors exhibited relatively lower specific capacitance for both [P4444][HFuA] and [P4444][TpA] ILs at room temperature. However, the specific capacitance has significantly increased with an increase in temperature and potential window. The equivalent serie resistances of the SCs is deceased with increasing temperatures, which is a result of improved ionic conductivities of the IL electrolytes. In CV cycling at 60 °C, the capacitor with [P4444][HFuA] IL-based electrolyte retained about 90% of its initial capacitance, while the capacitor with [P4444][TpA] IL-based electrolyte retained about 83% of its initial capacitance. Atomistic computations revealed that the aromatic [FuA]− and [TpA]− anions displayed perpendicular distribution that can effectively neutralize charges on the carbon surfaces. However, the [HFuA]− anion exhibited somewhat tilted configurations on the carbon electrode surfaces, contributing to their outstanding capacitive performance in electrochemical devices.

Sustainable Neodymium Recovery Using an Electrochemical Approach

Neodymium is a technologically important metal in green energy due to its properties which are critical in wind turbines as permanent magnets and in rechargeable batteries for electric vehicles. However, its production and supply are concentrated in China and this, together with its high demand, has led to categorise it as a critical metal. Therefore, instead of relying exclusively on mining, neodymium recovery from end of life products is one of the most interesting ways to tackle the availability.Our research has been focused on electrolyte synthesis to attain Nd in the metallic and more expensive form via electrodeposition as an environmentally friendly approach.Electrochemical deposition of neodymium has also been attempted in several ionic liquids, but only been partially successful in phosphonium -based ILs, therefore that family of ionic liquids have been at the core of our research. The long alkyl chain trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide, [P66614][TFSI], have been selected due to its hydrophobic properties and electrochemical stability. The effect of concentration and water has been explored in our research concluding that, in fact, water promoted the Nd electrodeposition. A three-fold increase in current densities was observed in comparison with the analogous mixture with less water, which leads to more abundant deposits.[1] , [2] An in-depth study of the Nd3+ solvation in the bulk electrolyte indicated the presence of both bis(trifluoromethylsulfonyl)imide (TFSI) and water in the solvation sphere, as well as insight into the different mode of coordination of TFSI with Nd3+ (i.e. cis/ trans and mono/bidentate).More recently, we have reported a cleaner approach to recover Nd using a pyrrolidinium non-fluorinated ionic liquid (IL) (N-butyl-N-methylpyrrolidinium dicyanamide ([C4mpyr][DCA])) in the presence of neodymium nitrate. The main advantages of these electrolyte mixtures, is the elimination of higher risk of persistence, ecotoxicity when fluorine is decomposed. Additionally, relatively low manufacturing cost as opposed to fluorinated systems as contain only carbon and nitrogen. Our results presented eight times higher current density (-38 mA cm-2) at a lower temperature (halved to 50 °C) and less controlled environment (0.15 – 4.6 wt% H2O) compared to the literature.[3] This is translated into a more cost-effective recovery process. [1] Laura Sánchez-Cupido, Jennifer M. Pringle, Amal L. Siriwardana, Ainhoa Unzurrunzaga, Matthias Hilder, Maria Forsyth, Cristina Pozo-Gonzalo, “Water Facilitated Electrodeposition of Neodymium in a Phosphonium-based Ionic Liquid”, The Journal of Physical Chemistry Letters, 2019, 10, 2, 289-294 [2] Laura Sanchez Cupido, Jennifer M. Pringle, Amal Siriwardana, Matthias Hilder, Maria Forsyth, Cristina Pozo-Gonzalo,” Correlating electrochemical behaviour and speciation in neodymium ionic liquid electrolyte mixtures in the presence of water”, ACS Sustainable Chemistry & Engineering, 2020, 8, 14047-14057 [3] Kalani Periyapperuma, Jennifer M. Pringle, Laura Sanchez-Cupido, Maria Forsyth, and Cristina Pozo-Gonzalo,“Fluorine-Free Ionic Liquid Electrolytes for Sustainable Neodymium Recovery Using an Electrochemical Approach, Green chemistry”, 2021, DOI: 10.1039/D1GC00361E

Surface Tension and Viscosity of Binary Mixtures of the Fluorinated and Non-fluorinated Ionic Liquids [PFBMIm][PF6] and [C4C1Im][PF6] by the Pendant Drop Method and Surface Light Scattering

Mixtures of fluorinated and non-fluorinated ionic liquids (ILs) show a distinct structural organization in the bulk and at the surface. To understand how such microscopic effects influence the macroscopic bulk and surface properties of IL mixtures, knowledge of corresponding thermophysical properties including viscosity and surface tension is required yet lacking. With the intention of investigating surface enrichment effects of the fluorinated IL [PFBMIm][PF6] (3-methyl-1-(3,3,4,4,4-pentafluorobutyl)imidazolium hexafluorophosphate) in mixtures with the structurally similar, non-fluorinated IL [C4C1Im][PF6] (1-butyl-3-methylimidazolium hexafluorophosphate) observed with angle-resolved X-ray photoelectron spectroscopy (ARXPS), the pendant drop method and surface light scattering (SLS) were applied in the present study to determine surface tension and dynamic viscosity between (293 and 368) K. By adding small amounts of [PFBMIm][PF6] up to 9 mol %, a distinct increase in the viscosity and decrease in the surface tension of the mixtures relative to the properties of pure [C4C1Im][PF6] was found. This behavior reflects the nanosegregated structure in the bulk and at the surface of the binary IL mixtures. Using the results about the pronounced surface enrichment of the fluorinated chain of [PFBMIm][PF6] quantified by ARXPS, a linear mixing rule for the surface tension of the IL mixtures based on the surface tensions of the pure ILs and the surface concentration of their most surface-active groups is suggested.

Electrodeposition of silver from the ionic liquid Butylpyridinium dicyanamide

The electrodeposition of silver was performed on a platinum electrode from a non-fluorinated ionic liquid (IL), butylpyridinium dicyanamide (Pyri4-DCA). The as-studied IL is characterized by a high ionic conductivity (11.03 mS.cm−1) and a low dynamic viscosity (24.4 mPa.s), which are appropriate for the electrodeposition process. The cyclic voltammetry (CV) curves recorded in Ag-DCA/Pyri4-DCA solutions showed the presence of reduction and oxidation peaks, respectively associated with the deposition and stripping of silver from the Pt surface. The diffusion coefficient of Ag(I) calculated from CV curves varied from 5.3 10−7 to 1.1 10−7 when Ag+ concentration was changed from 1 to 10 mM. The silver was electrodeposited on the Pt surface at different constant potentials. The nuclei size and population density of silver were monitored by varying the electrolyte concentration, the applied potential and the deposition time. From the analysis of the experimental transient curves, it was shown that the electrochemical deposition process of silver follows a 3D nucleation with diffusion-controlled growth. The nuclei population densities and diffusion coefficients were also determined for various chronoamperometric parameters by using the fitting model of Scharifker and Hills for 3D nucleation and growth.

Enhanced absorption separation of hydrofluorocarbon/hydrofluoroolefin refrigerant blends using ionic liquids

The separation of hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs) from novel refrigerant blends will become essential to boost the recycling of these compounds and drastically reduce the emission of HFCs, which are powerful greenhouse gases. In this work, the use of ionic liquids (ILs) as solvent media is explored to perform the selective separation of HFC/HFO refrigerant mixtures composed of the HFCs R32 (difluoromethane) and R134a (1,1,1,2-tetrafluoroethane) and the HFO R1234yf (2,3,3,3-tetrafluoropropene). The low-viscosity IL 1-ethyl-3-methylimidazolium thiocyanate, [C2mim][SCN], is selected as separation agent to prove that small and non-fluorinated ILs, with lower hydrogen bonding capability than other ILs, can provide enhanced solubility selectivity and mass transport properties for the selective separation of HFC/HFO refrigerant blends. The phase behavior of IL-refrigerant systems is determined at temperatures between 283.15 and 313.15 K and pressures up to 0.7 MPa. Results are parametrized according to the NRTL activity model and the separation selectivity is assessed in terms of Henry’s law constants, solvation enthalpies and entropies, infinite dilution coefficients, Gibbs free energy of mixing, and ideal and noncompetitive selectivity. Results show superior HFC/HFO solubility selectivity in [C2mim][SCN] compared to other ILs due to unfavorable entropic effects that difficult the solvation of large molecules such as R1234yf.

Separation of Rare Earths from the Transition Metals Using a Novel Ionic-Liquid-Based Aqueous Two-Phase System: Toward Green and Efficient Recycling of Rare Earths from the NdFeB Magnets

An ionic-liquid-based aqueous two-phase system (iL-ATPS) consisting of an ionic liquid, tributylmethylammonium nitrate (N4441NO3), and NaNO3 aqueous solutions was developed for the extraction and separation of rare-earth ions, for example Nd(III), from transition-metal ions. The excellent selectivity of a green nonfluorinated ionic liquid and the low-viscosity feature of an aqueous two-phase system were combined in our suggested iL-ATPS. The results indicated that efficient separation of Nd(III) from transition-metal ions, Fe(III), Ni(II), and Co(II), could be obtained in our suggested iL-ATPS. Furthermore, different parameters of the separation process, including the concentrations of HNO3 and NaNO3 and the added amount of N4441NO3, were optimized. Notably, the extraction kinetics of Nd(III) could be improved significantly in the present iL-ATPS compared with the conventional organic-solvent-based ionic-liquid extraction systems. The similar environment across the liquid–liquid interface was revealed by ...

Enhanced separation performance of aqueous biphasic systems formed by carbohydrates and tetraalkylphosphonium- or tetraalkylammonium-based ionic liquids

Aiming at establishing more effective and sustainable separation processes, herein we propose the use of carbohydrates combined with tetralkylphosphonium- and tetralkylammonium-based ionic liquids (ILs) to form aqueous biphasic systems (ABS). The formation of ABS composed of non-aromatic and non-fluorinated ILs with carbohydrates is here shown for the first time. These novel systems are competive extraction platforms when compared against more conventional ABS formed by ILs and salts or fluorinated ILs and carbohydrates. Finally, it is shown that these systems can be efficiently recovered and reused.

Highly efficient extraction and selective separation of uranium (VI) from transition metals using new class of undiluted ionic liquids based on H-phosphonate anions

In this paper, we report the development of an environmental friendly process to decontaminate uranium-containing ores and nuclear wastes by using non-fluorinated ionic liquids (ILs). The main advantages of this extraction process are the absence of any organic diluent and extra extraction agents added to the organic phase. Moreover, the process is cost-effective and maybe applied as a sustainable hydrometallurgical method to recover uranium. The distribution ratio (DU) and the extraction efficiency (%E) of uranium(VI) (UO22+) were found to be dependent on the acidity of the aqueous phase, the extraction time, the alkyl chain length in the ILs, the concentration of the aqueous feed and molar quantity of ILs. The DU value is higher than 600 and the %E is equal to 98.6% when [HNO3]=7M. The extraction reactions follows a neutral partition or ionic exchange mechanism depending on nitric acid concentration. The nature of bonding in the extracted complexes was investigated by spectroscopic techniques. The potential use of Mor1-8-OP for the separation of UO22+ from a mixture containing transition metal ions Mn+ was also examined. The UO22+ ions were separated and extracted efficiently. These ILs are promising candidates for the recovery and separation of uranium.

Proton conducting ionic liquid electrolytes for liquid and solid-state electrochemical pseudocapacitors

Proton conducting polymer electrolytes employed in many electrochemical pseudocapacitors are typically based on aqueous systems, which limit the operating potential and temperature range of these energy storage devices. In this study, we developed non-aqueous polymer electrolytes based on protic ionic liquids (PIL). We relied on cationic substitution to obtain proton conducting yet environmentally benign non-fluorinated ionic liquids. By developing binary systems of PILs with different cations, eutectic compositions of PILs with drastically lowered melting points were demonstrated. Through thermal analyses of these binary systems, phase diagrams were constructed which allowed us to obtain eutectic binary PIL mixtures exhibiting a liquidus range from −70°C to 150°C. These eutectic PIL mixtures were incorporated into polymer systems to develop non-aqueous thin film proton-conducting polymer electrolytes for solid pseudocapacitors. The proton conductivity of the eutectic ionic liquids was observed in the polymer electrolyte systems and promoted pseudocapacitive behavior in solid and liquid capacitor cells.

Highly efficient and eco-friendly extraction of neodymium using, undiluted and non-fluorinated ionic liquids. Direct electrochemical metal separation

Abstract A new approach for highly efficient extraction and recovery of neodymium from acidic medium by new undiluted ionic liquids (ILs) as extractants. The distribution ratio DNd and the extraction efficiency %E was measured as a function of nitric acid concentration, extraction time, nature of the IL, concentration of the aqueous feed and molar quantity of complexing agent. DNd is higher than 105 and %E is close to 100% when the HNO3 concentration is greater than 6 M. The extraction process follows solvation mechanism, suggesting the involvement of three molecules in the extraction of one (Nd3+)-nitrate complex. The nature of bonding in the extracted complexes was investigated by various spectroscopic techniques. The recovery process, of metal was performed by direct electrodeposition from the IL phase. The electrodeposition of metal was realized by potentiostatic electrolysis at −2 V. The current efficiency evaluated from the mass change of the anode was more than 83%. The particles were obtained as small crystallite rods with various size approximately 3–70 μm and diameters range of 0.5–30 μm. The liquid-liquid extraction and the direct electrodeposition of neodymium by these H-phosphonate based ILs, are new efficient and eco-friendly process.

Solvent extraction of lithium from aqueous solution using non-fluorinated functionalized ionic liquids as extraction agents

Two non-fluorinated ionic liquids (ILs), namely tetrabutylammonium bis(2-ethylhexyl)-phosphate, [N4444][DEHP], and tetraoctylammonium bis(2-ethylhexyl)-phosphate, [N8888][DEHP], were synthesized and fully characterized by 1H and 13C NMR spectroscopy. These functionalized ILs were subsequently evaluated in terms of their ability to extract lithium ions from aqueous solution. The extraction efficiencies of these functionalized ILs for lithium ions were measured as a function of various extraction parameters, including aqueous acidity, temperature and extractant concentration. The extracted species were determined using a slope analysis method, which indicated that the ILs formed a 1:1 (metal:ligand) complex. Fourier transform infrared spectroscopy studies were conducted to better understand the nature of the extracted species. We also investigated the stripping of the lithium ions from the organic phase and the re-use of the ionic liquid in a subsequent extraction step.

Influence of Nanosegregation on the Surface Tension of Fluorinated Ionic Liquids

We have investigated, both theoretically and experimentally, the balance between the presence of alkyl and perfluoroalkyl side chains on the surface organization and surface tension of fluorinated ionic liquids (FILs). A series of ionic liquids (ILs) composed of 1-alkyl-3-methylimidazolium cations ([CnC1im] with n = 2, 4, 6, 8, 10, or 12) combined with the perfluorobutanesulfonate anion was used. The surface tensions of the investigated liquid salts are considerably lower than those reported for non-fluorinated ionic liquids. The most surprising and striking feature is the identification, for the first time, of a minimum at n = 8 in the surface tension versus the length of the IL cation alkyl side chain. Supported by molecular dynamics (MD) simulations, it was found that this trend is a result of the competition between the two nonpolar domains (perfluorinated and aliphatic) pointing toward the gas-liquid interface, a phenomenon which occurs in ILs with perfluorinated anions. Furthermore, these ILs present the lowest surface entropy reported to date.

Solvent Extraction of Neodymium(III) by Functionalized Ionic Liquid Trioctylmethylammonium Dioctyl Diglycolamate in Fluorine-free Ionic Liquid Diluent

The extraction behavior of neodymium and other rare earths from nitric acid media by the functionalized ionic liquid trioctylmethylammonium dioctyl diglycolamate, [A336][DGA], was investigated. The nonfluorinated ionic liquid trioctylmethylammonium nitrate, [A336][NO3], was used as diluent. The extraction behavior of neodymium(III) in this ionic liquid solution was carried out as a function of various parameters such as the pH, concentration of the extractant, type of acidic media, temperature, concentration of salting-out agent, and concentration of the aqueous feed. The extraction behavior of [A336][DGA] in [A336][NO3] was compared with that of [A336][DGA] in the chloride-containing ionic liquid diluent [A336][Cl] (Aliquat 336). The distribution ratios obtained in [A336][DGA] were compared with those observed in molecular extractant N,N-dioctyl diglycol amic acid (HDGA), from which the anion of the ionic liquid extractant was prepared. The distribution ratio for extraction of neodymium(III) by [A336][DGA] in [A336][NO3] was higher than that for extraction by HDGA in [A336][NO3], at pH values >2. The effects of thermodynamic parameters, the stripping of neodymium(III) from the ionic liquid, and the reusability of the functionalized ionic liquid were studied in detail. The general applicability of the extraction system was illustrated by the extraction of lanthanide(III) ions other than neodymium(III).

Effect of Cation on Proton Conductivity of a Non-fluorinated Ionic Liquid

1-Ethyl-3-methyl imidazolium hydrogensulfate (EMIHSO4), a non-fluorinated IL, was studied both as liquid and polymer electrolytes for electrochemical capacitors [1]. While EMIHSO4exhibited a reasonable ionic conductivity, improvement in proton conductivity is possible by altering the structure of the cation, which warrants further investigation. The objectives of this study are twofold: to investigate the effect of cationic functional groups on the properties of the IL; and to select and characterize the IL system with optimum proton conductivity. The electrolytes were prepared using ILs with different cations, namely 1-ethyl-3-methyl imidazolium hydrogensulfate (EMIHSO4), 1-methylimidazolium hydrogensulfate (MIHSO4), and imidazolium hydrogensulfate (ImHSO4) in methanol solutions. For comparison, a solution of EMIHSO4 with propylene carbonate (PC), an aprotic solvent, was prepared with the same concentration as those in methanol-based electrolytes. To demonstrate the proton conductivity of the electrolytes, standard two-electrode cells were assembled utilizing pseudocapacitive electrodes such as RuO2and nanocarbon/polyoxometalate (POMs) composites [2].The cell performance were characterized using cyclic voltammtery (CV) and ac impedance spectroscopy. RuO2 exhibits pseudocapacitance via a coupled proton–electron transfer in a protic electrolyte. Figure 1 shows the CV profiles of the RuO2-based cells in all electrolytes. The ImHSO4 and MIHSO4-based cells demonstrated similar CVs and the highest capacitance performance. Their higher capacitance compared to EMIHSO4-based cell indicates the higher proton conductivity of ImHSO4 and MIHSO4, which can contribute to the electrochemical reactions of RuO2 electrodes. Due to the role of solvent on proton dissociation, the cell performance was superior using EMIHSO4/MeOH electrolytes than that for EMIHSO4/PC. The proton conductivity of PILs was further examined on a carbon/POM electrode and compared to the bare carbon electrodes. POMs involve fast and reversible multielectron transfer reactions in proton containing electrolytes. For a better comparison, the respective carbon/POM cells were also tested in 0.5M H2SO4. The electrochemical performance of the carbon/POM-based cells in the PIL electrolytes followed a similar trend as those for RuO2-based electrolytes. Figure 2 (a) shows the CV profiles of the carbon/POM-based cells and the bare carbon in ImHSO4/MeOH electrolyte. The increased capacitance of the carbon/POM cell over that for the bare carbon implies the proton conducting characteristic of ImHSO4 electrolyte which participates in the redox reaction of the POM. Figure 2 (b) presents the capacitance ratio of the carbon/POM cells in the respective PILs to H2SO4 electrolyte. ImHSO4-based cells showed the highest capacitance ratio followed by MIHSO4 and EMIHSO4in both MeOH and PC solutions. Imidazoles consist of two nitrogen sites, and their protonated and unprotonated nitrogen functions may act as proton donor and acceptor in proton transfer reactions. As the nitrogen sites decrease in MI and EMI cations, the contribution from proton conduction becomes smaller. More details on optimizing the proton conductivity of these PILs for room temperature applications, especially polymer electrolytes will be presented.

Liquid–liquid extraction of europium(iii) and other trivalent rare-earth ions using a non-fluorinated functionalized ionic liquid

A new non-fluorinated malonamide-based ionic liquid extractant was synthesized and investigated for the extraction behavior of europium(III) and other trivalent rare-earth ions from nitric acid medium. The extractant was the functionalized ionic liquid trihexyl(tetradecyl)phosphonium N,N,N',N'-tetra(2-ethylhexyl)malonate, [P66614][MA], and it was used in combination with the non-fluorinated ionic liquid trihexyl(tetradecyl)phosphonium nitrate, [P66614][NO3], as diluents. The extraction behavior of europium in this ionic liquid solution was studied as a function of various parameters such as the pH, concentration of the extractant, the type of acidic medium, temperature, concentration of the salting-out agent and the metal concentration of the aqueous feed. The extraction behavior of [P66614][MA] in [P66614][NO3] was compared with that of [P66614][MA] in the chloride-containing ionic liquid diluent trihexyl(tetradecyl)phosphonium chloride, [P66614][Cl] (Cyphos IL 101). The nitrate system was found to be superior. Marked differences in extraction behavior were observed between [P66614][MA] and the molecular malonamide extractant N,N,N',N'-tetra(2-ethylhexyl)malonamide (TEHMA), i.e. the compound from which the anion of the ionic liquid extractant was prepared. The extraction behavior of other rare earths (La, Ce, Nd, Sm, Ho, Yb) and some transition metals (Ni, Co, Zn) was investigated using this functionalized ionic liquid. A good separation of the rare earths from the transition metals could be achieved. For the rare earths, the extraction efficiency increases over the lanthanide series. The effects of thermodynamic parameters, the stripping of europium(iii) from the ionic liquid and the reusability of the functionalized ionic liquid were studied in detail.

Lithium electrochemistry and cycling behaviour of ionic liquids using cyano based anions

Lithium based battery technologies are increasingly being considered for large-scale energy storage applications such as grid storage associated with wind and solar power installations. Safety and cost are very significant factors in these large scale devices. Ionic liquid (IL) electrolytes that are inherently non-volatile and non-flammable offer a safer alternative to mainstream lithium battery electrolytes, which are typically based on volatile and flammable organic carbonates. Hence, in recent years there have been many investigations of ionic liquid electrolytes in lithium batteries with some highly promising results to date, however in most cases cost of the anion remains a significant impediment to widespread application. Amongst the various possible combinations the dicyanamide (DCA) anion based ionic liquids offer exceptionally low viscosities and high conductivities – highly desirable characteristics for Li electrolyte solvents. DCA ILs can be manufactured relatively inexpensively because DCA is already a commodity anion, containing only carbon and nitrogen, which is produced in large amounts for the pharmaceutical industry. In this study we use the non-fluorinated ionic liquid N-methyl-N-butylpyrrolidinium dicyanamide to form non-volatile lithium battery electrolytes. We demonstrate good capacity retention for lithium metal and LiFePO4 in such electrolytes and discharge capacities above 130 mAh.g−1 at 50 °C. We show that it is important to control moisture contents in this electrolyte system in order to reduce capacity fade and rationalise this observation using cyclic voltammetry and lithium symmetrical cell cycling. Having approximately 200 ppm of moisture content produces the optimum cycling ability. We also describe plastic crystal solid state electrolytes based on the DCA anion in the lithium metal–LiFePO4 battery configuration and demonstrate over 150 mAh.g−1 discharge capacity without any significant capacity fading at 80 °C.

Solubility of carbon dioxide in the low-viscosity ionic liquid 1-hexyl-3-methylimidazolium tetracyanoborate

The solubility of carbon dioxide (CO2) in a new low-viscosity and non-fluorinated ionic liquid, 1-hexyl-3-methylimidazolium tetracyanoborate ([hmim][TCB]), has been studied experimentally using a synthetic method. Bubble point pressures (up to 12.34MPa) of the system CO2+[hmim][TCB] are reported for CO2 concentrations ranging from 10.09 to 70.16mol% and within a temperature range of 283.56–364.04K. The experimental values of the density, the viscosity and the surface tension of [hmim][TCB] are also reported. The results obtained are compared to available CO2 solubility data and physicochemical properties of other 1-hexyl-3-methylimidazolium based ionic liquids in order to study the effect of the type of anion. It is found that [hmim][TCB] shows higher CO2 absorptive capacity (higher solubility) as well as faster CO2 mass transfer kinetics (lower viscosity), which makes this ionic liquid an attractive solvent for gas separation processes.

Improving Carbon Dioxide Solubility in Ionic Liquids

Previously we showed that CO2 could be used to extract organic molecules from ionic liquids without contamination of the ionic liquid. Consequently a number of other groups demonstrated that ionic liquid/CO2 biphasic systems could be used for homogeneously catalyzed reactions. Large differences in the solubility of various gases in ionic liquids present the possibility of using them for gas separations. More recently we and others have shown that the presence of CO2 increases the solubility of other gases that are poorly soluble in the ionic liquid phase. Therefore, a knowledge and understanding of the phase behavior of these ionic liquid/CO2 systems is important. With the aim of finding ionic liquids that improve CO2 solubility and gaining more information to help us understand how to design CO2-philic ionic liquids, we present the low- and high-pressure measurements of CO2 solubility in a range of ionic liquids possessing structures likely to increase the solubility of CO2. We examined the CO2 solubility in a number of ionic liquids with systematic increases in fluorination. We also studied nonfluorinated ionic liquids that have structural features known to improve CO2 solubility in other compounds such as polymers, for example, carbonyl groups and long alkyl chains with branching or ether linkages. Results show that ionic liquids containing increased fluoroalkyl chains on either the cation or anion do improve CO2 solubility when compared to less fluorinated ionic liquids previously studied. It was also found that it was possible to obtain similar, high levels of CO2 solubility in nonfluorous ionic liquids. In agreement with our previous results, we found that the anion frequently plays a key role in determining CO2 solubility in ionic liquids.