Use of 1-alkyl-3-methylimidazolium hexafluorophosphate room temperature ionic liquids as chelate extraction solvent with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione

Possible use of room temperature ionic liquids (RTILs) as chelate extraction solvent was evaluated by using 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF₆]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF₆]). These RTILs showed high extraction performance for divalent metal cations with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (Htta). The extracted metals were back-extracted into 1 mol dm⁻³ nitric acid quantitatively. Furthermore, the extracted species were estimated as neutral hydrated complexes M(tta)₂(H₂O)_n (n= 1 or 2) for M = Ni, Cu and Pb and anionic complexes M(tta)₃⁻ for M = Mn, Co, Zn and Cd.     

Sensitive determination of cadmium in water samples by room temperature ionic liquid-based preconcentration and electrothermal atomic absorption spectrometry

A sensitive preconcentration methodology for Cd determination at trace levels in water samples was developed in this work. 1-Butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]) room temperature ionic liquid (RTIL) was successfully used for Cd preconcentration, as cadmium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complex [Cd-5-Br-PADAP]. Subsequently, Cd was back-extracted from the RTIL phase with 500 μL of 0.5 mol L⁻¹ nitric acid and determined by electrothermal atomic absorption spectrometry (ETAAS). A preconcentration factor of 40 was achieved with 20 mL of sample. The limit of detection (LOD) obtained under optimum conditions was 3 ng L⁻¹ and the relative standard deviation (R.S.D.) for 10 replicates at 1 μg L⁻¹ Cd²⁺ concentration level was 3.5%, calculated at peak heights. The calibration graph was linear from concentration levels near the detection limits up to at least 5 μg L⁻¹. A correlation coefficient of 0.9997 was achieved. Validation of the methodology was performed by standard addition method and analysis of certified reference material (CRM). The method was successfully applied to the determination of Cd in river and tap water samples.     

Density and viscosity of three (2,2,2-trifluoroethanol + 1-butyl-3-methylimidazolium) ionic liquid binary systems

Densities and viscosities were determined for binary mixtures of 2,2,2-trifluoroethanol (TFE) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) or 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([bmim][NTf₂]) over the entire range of composition. The experimental measurements were carried out at temperatures ranging from 278.15 K to 333.15 K, at atmospheric pressure. The densities and viscosities of the pure ionic liquids and their mixtures with TFE were described successfully by an empirical third-order polynomial and by the Vogel–Fulcher–Tammann equation, respectively. In addition, excess molar volumes and viscosity deviations were determined from densities and viscosities of mixtures, respectively, and fitted by using the Redlich–Kister equation.     

High-pressure phase behavior of CO2 + 1-butyl-3-methylimidazolium chloride system

The phase behavior of carbon dioxide (CO₂) and the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) was measured and correlated at high pressures up to ∼40 MPa and at temperatures between 353.15 K and 373.15 K. The solubility data of CO₂ in [bmim][Cl] were obtained by observing the bubble point pressure at specific temperatures. A variable-volume view cell, which is a high-pressure equilibrium apparatus, was used to measure the CO₂ + [bmim][Cl] system solubility under varying pressure and temperature conditions. In addition, liquid–liquid–vapor (LLV) three-phase behavior was investigated using the equilibrium cell to be able to determine the classification of phase-behavior type by Scott and Van Konynenburg. Based on the LLV phase behavior, this system most likely has type III phase-behavior which is common for IL + CO₂ systems. The resulting data showed that CO₂ dissolved well in the IL at low CO₂ concentrations, but that the pressure derivative of CO₂ solubility dramatically decreased as the mole fraction of CO₂ was increased. The experimental data were well fitted by the Peng–Robinson equation of state with a quadratic mixing rule and cubic parameters estimated by the Joback method.     

Partial molar volumes of selected gases in some ionic liquids

The partial molar volume of a gas that is dissolved at high dilution in a solvent is required to express the influence of pressure on Henry's constant as well as to describe the volume change (expansion) of the liquid caused by the dissolved gas. The correlations of recently published experimental results for the solubility of some selected gases (CO₂, Xe, CH₄, CF₄, H₂, CO, O₂) in three imidazolium-based ionic liquids (1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), 1-n-butyl-3-methylimidazolium methyl sulfate ([bmim][CH₃SO₄]), and 1-n-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([hmim][Tf₂N])) determined by the synthetic method were re-evaluated by also considering the experimentally determined volumetric properties. The new evaluation does not change the published results for Henry's constants, but additionally yields reliable information on the partial molar volume of those gases in the mentioned ionic liquids at temperatures from about 293 to 413 K.     

Ternary (liquid + liquid) equilibria of the azeotrope (ethyl acetate + 2-propanol) with different ionic liquids at T = 298.15 K

Experimental (liquid + liquid) equilibria involving ionic liquids {1,3-dimethylimidazolium methyl sulfate (MMIM MeSO₄)}, {2-propanol + ethyl acetate + 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF₆)} and {2-propanol + ethyl acetate + 1-hexyl-3-methylimidazolium hexafluorophosphate (HMIM PF₆)} were carried out to separate the azeotropic mixture ethyl acetate and 2-propanol. Selectivity and distribution ratio values, derived from the tie-lines data, were presented in order to analyze the best separation solvent in a liquid extraction process. Experimental (liquid + liquid) equilibria data were compared with the correlated values obtained by means of the NRTL, Othmer-Tobias and Hand equations. These equations were verified to accurately correlate the experimental data.     

Liquid structures of 1-butyl-3-methylimidazolium tetrafluoroborate and carbon dioxide mixtures by X-ray diffraction measurements

X-ray diffraction measurements for the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF₄], mixed with CO₂ were carried out at high pressures using our developed polymer cell. The intermolecular distribution functions obtained for [BMIM][BF₄]–CO₂ mixtures showed that CO₂ molecules are preferentially solvated to the [BF₄]⁻ anion. The similar preferential solvation was previously observed in analogous 1-btuyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF₆], with a different anion, which is in harmony with the present results in [BMIM][BF₄]–CO₂.     

Densities and viscosities for ionic liquids mixtures containing [eOHmim][BF4], [bmim][BF4] and [bpy][BF4]

Densities and viscosities of binary ionic liquids mixtures, 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([eOHmim][BF₄]) + 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]), 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([eOHmim][BF₄]) + N-butylpyridinium tetrafluoroborate ([bpy][BF₄]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) + N-butylpyridinium tetrafluoroborate ([bpy][BF₄]) were measured over the entire mole fraction from T = (298.15 to 343.15) K. The excess molar volumes were calculated and correlated by Redlich–Kiser polynomial expansions. The viscosities for pure ionic liquids were analyzed by means of the Vogel–Tammann–Fulcher equation and ideal mixing rules were applied for the ILs mixtures.     

Ionic liquids extraction of Para Red and Sudan dyes from chilli powder, chilli oil and food additive combined with high performance liquid chromatography

A simple analytical method, based on the coupling of ionic liquid-based extraction with high performance liquid chromatography (HPLC), is developed for the determination of Sudan dyes (I, II, III and IV) and Para Red in chilli powder, chilli oil and food additive samples. Two ionic liquids (ILs), 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim][PF₆]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([C₈mim][PF₆]), were compared as extraction solvents; experiments indicated that the latter possesses higher recoveries for each analyte. Parameters related to extraction of Sudan dyes and Para Red were also optimized. Under the optimal conditions, good reproducibility of extraction performance was obtained, with the relative standard deviation (RSD) values ranging from 2.0% to 3.5%. The detection limits of Sudan dyes and Para Red (LOD, S/N = 3) were in the range of 7.0-8.2 μg kg⁻¹ for chilli powder and 11.2-13.2 μg L⁻¹ for chilli oil and food additive. The recoveries were in the range of 76.8-109.5% for chilli powder samples and 70.7-107.8% for chilli oil and food additive samples.     

On-line ionic liquid-based preconcentration system coupled to flame atomic absorption spectrometry for trace cadmium determination in plastic food packaging materials

A novel on-line preconcentration method based on liquid-liquid (L-L) extraction with room temperature ionic liquids (RTILs) coupled to flame atomic absorption spectrometry (FAAS) was developed for cadmium determination in plastic food packaging materials. The methodology is based on the complexation of Cd with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) reagent after sample digestion followed by extraction of the complex with the RTIL 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim][PF₆]). The mixture was loaded into a flow injection analysis (FIA) manifold and the RTIL rich-phase was retained in a microcolumn filled with silica gel. The RTIL rich-phase was then eluted directly into FAAS. A enhancement factor of 35 was achieved with 20 mL of sample. The limit of detection (LOD), obtained as IUPAC recommendation, was 6 ng g⁻¹ and the relative standard deviation (R.S.D.) for 10 replicates at 10 μg L⁻¹ Cd concentration level was 3.9%, calculated at the peak heights. The calibration graph was linear and a correlation coefficient of 0.9998 was achieved. The accuracy of the method was evaluated by both a recovery study and comparison of results with direct determination by electrothermal atomic absorption spectrometry (ETAAS). The method was successfully applied for Cd determination in plastic food packaging materials and Cd concentrations found were in the range of 0.04-10.4 μg g⁻¹.     

离子液体型表面活性剂研究

以1-甲基咪唑为原料, 制备了6个常规离子液体: 1-正丁基-3-甲基咪唑四氟硼酸盐及六氟磷酸盐(简称[bmim][BF₄]及[bmim][PF₆])、1-正己基-3-甲基咪唑四氟硼酸盐及六氟磷酸盐(简称[hmim][BF₄]及[hmim][PF₆])、1-正十六烷基-3-甲基咪唑四氟硼酸盐及六氟磷酸盐(简称[C₁₆mim][BF₄]及[C₁₆mim][PF₆])和4个功能化离子液体: 1-(2-羟乙基)-3-甲基咪唑四氟硼酸盐及六氟磷酸盐(简称[2-hemim][BF₄]及[2-hemim][PF₆])、1-乙氧羰基甲基-3-甲基咪唑四氟硼酸盐及六氟磷酸盐(简称[eocmmim][BF₄]及[eocmmim][PF₆]). 研究了这两类离子液体的一些物理性能, 旨在挖掘离子液体在香料香精化妆品工业中的应用价值. 分别检测了它们与一般溶剂的互溶性, 并测定了它们的表面张力和发泡性能, 实验结果表明, 仅[C₁₆mim][BF₄]和[C₁₆mim][PF₆]具有发泡性能, 发泡力分别为68和120 mm.     

Solubility of H2S in 1-(2-hydroxyethyl)-3-methylimidazolium ionic liquids with different anions

The solubility of hydrogen sulfide in a series of 1-(2-hydroxyethyl)-3-methylimidazolium ([HOemim]⁺)-based ionic liquids (ILs) containing different anions, viz. hexafluorophosphate ([PF₆]⁻), trifluoromethanesulfonate ([OTf]⁻), and bis-(trifluoromethyl)sulfonylimide ([Tf₂N]⁻) at temperatures ranging from 303.15 to 353.15 K and pressures of up to about 1.8 MPa was measured by a volumetric based static apparatus. The solubility data were correlated using two models: (1) the Krichevsky–Kasarnovsky equation and (2) the extended Henry's law combined with the Pitzer's virial expansion for the excess Gibbs energy. Henry's law constants (at zero pressure) in mole-fraction and molality scales were obtained at different temperatures by means of these two models. Using the solubility data, the partial molar thermodynamic functions of solution, i.e. Gibbs energy, enthalpy, and entropy were calculated. Comparison showed that the solubility of H₂S is greater than that of CO₂ in the corresponding ILs studied in this work and that the solubility of both gases increases as the number of trifluoromethyl (–CF₃) groups in the anion increases, i.e. the solubility behavior of both gases follows the order [HOemim][Tf₂N] ≥ [HOemim][OTf] > [HOemim][PF₆] > [HOemim][BF₄].     

Extraction of Metal Ions from Aqueous Solutions Using Imidazolium Based Ionic Liquids

This article represents a step towards how to choose an ionic liquid as the solvent to improve metal ion (Ag⁺ and Pb²⁺) extraction. The liquid-liquid solvent extraction is proposed with the following imidazolium ionic liquids (ILs): 1-ethyl-3-ethylimidazolium, or 1-butyl-3-ethylimidazolium, or 1-hexyl-3-ethylimidazolium bis{(trifluoromethyl)sylfonyl}imide [EEIM][NTf₂], or [BEIM][NTf₂], or [HEIM][NTf₂], or 1-butyl-3-ethylimidazolium hexafluorophosphate [BEIM][PF₆], or 1-hexyl-3-ethylimidazolium hexafluorophosphate [HEIM][PF₆] and the popular 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF₆] for comparison. The effect of anion type (NTf₂⁻ versus PF₆⁻) and the effect of structural components of an ionic liquid including alkyl chain length at the cation and the ethyl substituent instead methyl at the cation, on the extraction and re-extraction processes by using dithizone as a metal chelator, were studied at 296 K. Dithizone was employed to form neutral metal-dithizone complexes with heavy metal ions to extract them from aqueous solution into the ILs. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users. Presented at the 236th ACS National Meeting, August 17–21, Philadelphia, USA.     

Micropolarity and aggregation behavior in ionic liquid + organic solvent solutions

UV–vis spectroscopy and conductivity measurement techniques were used to study the physicochemical and structural properties of the binary or ternary mixtures of 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) + organic solvent and 1-n-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) + organic solvent systems. The solvents involved were acetonitrile, water, ethanol, ethyl acetate, and tetrahydrofuran. It was indicated that the micropolarity and the aggregation behavior of the mixtures depend strongly on the dielectric constants of the solvents and the composition of the mixtures.     

Homogeneous ionic liquid microextraction of the active constituents from fruits of Schisandra chinensis and Schisandra sphenanthera

Homogeneous ionic liquid microextraction (HILME) was developed for the extraction of schizandrin, schisantherin A and deoxyschizandrin from Schisandra chinensis and Schisandra sphenanthera. 1-Butyl-3-methylimidazolium tetrafluoroborate ([C₄MIM][BF₄]) aqueous solution was used as extraction solvent, and ammonium hexafluorophosphate ([NH₄][PF₆]) was used as ion-pairing agent. 1-Butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]), which is barely soluble in water, was formed in situ, and was used as sample solution. High-performance liquid chromatography (HPLC) was employed for separation and determination of the analytes. The calibration curve showed good linear relationship (r > 0.9998). The recoveries were between 69.71% and 88.33% with RSDs lower than 4.86%. External standard method was adopted in the proposed method, and internal standard method was applied for the evaluation of the proposed method. The two methods were compared and the results indicated that the proposed method was acceptable and simple. The HILME is free of volatile organic solvents, and represents lower expenditures of sample, extraction time and solvent, compared with ultrasonic and Soxhlet extraction. There was no obvious difference in the extraction yields of active constitutions obtained by the three extraction methods.     

Highly selective ionic liquid-based microextraction method for sensitive trace cobalt determination in environmental and biological samples

A simple and rapid dispersive liquid-liquid microextraction procedure based on an ionic liquid (IL-DLLME) was developed for selective determination of cobalt (Co) with electrothermal atomic absorption spectrometry (ETAAS) detection. Cobalt was initially complexed with 1-nitroso-2-naphtol (1N2N) reagent at pH 4.0. The IL-DLLME procedure was then performed by using a few microliters of the room temperature ionic liquid (RTIL) 1-hexyl-3-methylimidazolium hexafluorophosphate [C₆mim][PF₆] as extractant while methanol was the dispersant solvent. After microextraction procedure, the Co-enriched RTIL phase was solubilized in methanol and directly injected into the graphite furnace. The effect of several variables on Co-1N2N complex formation, extraction with the dispersed RTIL phase, and analyte detection with ETAAS, was carefully studied in this work. An enrichment factor of 120 was obtained with only 6 mL of sample solution and under optimal experimental conditions. The resultant limit of detection (LOD) was 3.8 ng L⁻¹, while the relative standard deviation (RSD) was 3.4% (at 1 μg L⁻¹ Co level and n = 10), calculated from the peak height of absorbance signals. The accuracy of the proposed methodology was tested by analysis of a certified reference material. The method was successfully applied for the determination of Co in environmental and biological samples.     

Enrichment and sensitive determination of dichlorodiphenyltrichloroethane and its metabolites with temperature controlled ionic liquid dispersive liquid phase microextraction prior to high performance liquid phase chromatography

Dichlorodiphenyltrichloroethane (DDT) and its main metabolites are important environmental pollutants and have been in the focusing center. It is of great value to develop simple, rapid, sensitive and easy to operate method for monitoring them. Present work established a novel temperature controlled ionic liquid dispersive liquid phase microextraction method in combination with high performance liquid chromatography for the enrichment and determination of DDT and its metabolites. Proposed method used only ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) for the enrichment and overcame the demerits of conventional single drop liquid phase microextraction and dispersive liquid-liquid microextraction. Temperature has two functions here, one is to promote the dispersing of ionic liquid into the solution and forming infinitesimal micro-drop and increasing the chance of the analytes extracted into ionic liquid phase, and the other one is to perform phase-separation. A series of factors that would affect the extraction performance was systematically investigated and optimized. The experimental results indicated that the detection limits obtained for p,p′-DDD, p,p′-DDT, o,p′-DDT and p,p′-DDE were 0.24, 0.24, 0.45, 0.24 ng mL⁻¹, respectively. The linear ranges for them were from 1.0 to 100 ng mL⁻¹, and the precisions were between 3.8% and 6.7% (n = 6). The proposed method was validated with four real-world samples and excellent results were achieved.     

Volumetric and compressibility behaviour of ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate and tetrabutylammonium hexafluorophosphate in organic solvents at T = 298.15 K

Density and speed of sound measurements have been made on the systems containing the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) and some organic solvents having a wide range of dielectric constants. Similar studies have been carried out for tetrabutylammonium hexafluorophosphate ([TBA][PF₆]), which has common anion ([PF₆]⁻) with the studied ionic liquid. For the systems investigated, the apparent molar volumes and apparent molar isentropic compressibilities were determined and fitted to the Redlich–Mayer and the Pitzer equations from which the corresponding limiting values were obtained. These limiting values were used to obtain some information about ion–solvent interactions. Furthermore, using the ionic limiting apparent volume values for [TBA]⁺ from the literature and limiting apparent molar volume for the ionic liquid and [TBA][PF₆] obtained in this work, the ionic limiting apparent molar volume values for the cation [BMIM]⁺ in different organic solvents were also estimated.     

Preparation of Hierarchical Porous Activated Carbon from Banana Leaves for High-performance Supercapacitor: Effect of Type of Electrolytes on Performance

We demonstrate a facile efficient way to fabricate activated carbon nanosheets (ACNSs) consisting of hierarchical porous carbon materials. Simply heating banana leaves with K₂CO₃ produce ACNSs having a unique combination of macro-, meso- and micropores with a high specific surface area of ∼1459 m² g⁻¹. The effects of different electrolytes on the electrochemical supercapacitor performance and stability of the ACNSs are tested using a two-electrode system. The specific capacitance (C_sp) values are 55, 114, and 190 F g⁻¹ in aqueous 0.5 M sodium sulfate, organic 1 M tetraethylammonium tetrafluoroborate in acetonitrile, and pure ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) electrolytes, respectively. The ACNSs also shows the largest potential window of 3.0 V, the highest specific energy (59 Wh kg⁻¹) and specific power (750 W kg⁻¹) in [BMIM][PF₆]. A mini-prototype device is prepared to demonstrate the practicality of the ACNSs.     

Isobaric vapor–liquid equilibria for ethanol–water system containing different ionic liquids at atmospheric pressure

Isobaric vapor–liquid equilibrium (VLE) data for ethanol–water systems containing ionic liquids (ILs) 1-methyl-3-methylimidazolium dimethylphosphate ([MMIM][DMP]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), 1-butyl-3-methylimidazolium bromide ([BMIM][Br]), 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) at atmospheric pressure (101.32 kPa) were measured with a circulation still. The results showed that the VLE of ethanol–water systems in the presence of different ILs was obviously different from that of the IL-free system. All ILs studied showed a salting-out effect, which gave rise to a change of the relative volatility of ethanol, and even to an elimination of the azeotropic point. It was found that the salting-out effect followed the order of [BMIM][Cl] > [BMIM][Br] > [BMIM][PF₆] and [MMIM][DMP] > [EMIM][DEP], which was ascribed to the preferential solvation ability of the ions resulting from the dissociation of the IL.