Cation-based Ionic Liquids Research Articles

Voronoi Polyhedra as a Tool for the Characterization of Inhomogeneous Distribution in 1-Butyl-3-methylimidazolium Cation-Based Ionic Liquids.

The inhomogeneity distribution in four imidazolium-based ionic liquids (ILs) containing the 1-butyl-3-methylimidazolium (C4mim) cation, coupled with tetrafluoroborate (BF4), hexafluorophosphate (PF6), bis(trifluoromethanesulfonyl)amide (TFSA), and trifluoromethanesulfonate (TfO) anions, was characterized using Voronoi polyhedra. For this purpose, molecular dynamic simulations have been performed on the isothermal-isobaric (NpT) ensemble. We checked the ability of the potential models to reproduce the experimental density, heat of vaporization, and transport properties (diffusion and viscosity) of these ionic liquids. The inhomogeneity distribution of ions around the ring, methyl, and butyl chain terminal hydrogen atoms of the C4mim cation was investigated by means of Voronoi polyhedra analysis. For this purpose, the position of the C4mim cation was described successively by the ring, methyl, and butyl chain terminal hydrogen atoms, while that of the anions was described by their F or O atom. We calculated the Voronoi polyhedra distributions of the volume, the density, and the asphericity parameters as well as that of the radius of the spherical intermolecular voids. We carried out the analysis in two steps. In the first step, both ions were taken into account. The calculated distributions gave information on the neighboring ions around a reference one. In the second step, to distinguish between like and oppositely charged ions and then to get information on the inhomogeneity distribution of the like ions, we repeated the same calculations on the same sample configurations and removed one of the ions and considered only the other one. Detailed analysis of these distributions has revealed that the ring hydrogen atoms are mainly solvated by the anions, while the methyl and butyl terminal H atoms are surrounded by like atoms. The extent of this inhomogeneity was assessed by calculating the cluster size distribution that shows that the dimers are the most abundant ones.

Furfural and levoglucosenone production from the pyrolysis of ionic liquid pre-treated sugarcane straw

The current work focuses on the comparison of renewable choline cation-based ionic liquids (ILs) with imidazolium cation-based ILs for their delignification performance. Choline cation-based ILs removed a higher percentage of lignin (78.1–83.7% vs. 51.4–64.5%) and hemicellulose (64.7–72.8% vs. 7.1–29.9%) from sugarcane straw pre-treatment compared to imidazolium cation-based ILs. This was mainly attributed to the presence of fewer alkyl group and extra –OH group in choline cation. In general, ILs pre-treatment significantly increased the volatile matter and reduced fixed carbon in regenerated cellulose-rich material. Higher content of cellulose and higher crystallinity in the case of choline-based ILs enhanced the production of furfural and levoglucosenone from the pyrolysis of regenerated cellulose rich material. On the contrary, the presence of higher content of amorphous cellulose from imidazolium-based ILs, particularly 1-ethyl-3-methylimidazolium acetate produced γ-butyrolactone. Therefore, ILs pre-treatment can be favourable for the selective production of platform chemicals via pyrolysis route.

Low-Frequency Spectra of 1-Methyl-3-octylimidazolium Tetrafluoroborate Mixtures with Methanol, Acetonitrile, and Dimethyl Sulfoxide: A Combined Study of Femtosecond Raman-Induced Kerr Effect Spectroscopy and Molecular Dynamics Simulations.

In this study, we examined the low-frequency spectra of 1-methyl-3-octylimidazolium tetrafluoroborate ([MOIm][BF4]) mixtures with methanol (MeOH), acetonitrile (MeCN), and dimethyl sulfoxide (DMSO), which were obtained by femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES) and molecular dynamics (MD) simulations. In addition, we estimated the liquid properties of the mixtures, such as density ρ, surface tension γ, viscosity η, and electrical conductivity σ. The line shapes of the low-frequency Kerr spectra of the three [MOIm][BF4] mixture systems strongly depend on the mole fraction of the molecular liquid, XML. The spectral intensity increases with increasing XML of the [MOIm][BF4]/MeCN system but decreases for the [MOIm][BF4]/MeOH and [MOIm][BF4]/DMSO systems. These behaviors of the spectral intensities reasonably agree with the vibrational density-of-states spectra when the polarizability anisotropies of MeOH, MeCN, DMSO, and ion species are considered. The characteristic frequencies (first moments, M1) of the low-frequency spectra of the three mixture systems are almost insensitive at XML = 0-0.6. However, the frequencies vary mildly at XML = 0.6-0.9 and dramatically at XML = 0.9-1. The XML-dependent M1 in the Kerr spectra are well reproduced by the MD simulations. Plots of M1 versus bulk parameter, (γ/ρ)1/2, for the three mixture systems show that the mixtures at XML = 0-0.6 behave like aromatic cation-based ionic liquids (ILs), those at XML = 0.9-1 are molecular liquids (MLs), and those at XML = 0.6-0.9 are transitioning between aromatic cation-based ILs and MLs. MD simulations show that the solvent molecules localized at the interface between the ionic and the alkyl group regions without forming large solvent networks at XML = 0-0.6. However, solvent networks or regions develop largely at XML = 0.6-0.9 and the constituent ions of the IL disperse in the MLs at XML = 0.9-1. The MD simulations corroborate the results obtained by fs-RIKES.

Oil-miscible, halogen-free, and surface-active lauryl sulphate-derived ionic liquids for enhancement of tribological properties

Halogen-free ionic liquids, comprising low-cost surface-active precursors, having good miscibility with synthetic and mineral lube base oils, and enhance the lubrication properties by reducing the friction and wear, are gaining increasing attention for tribological applications. The present work addresses lauryl sulphate-derived tetraalkylammonium/phosphonium ionic liquids. Total four ionic liquids comprising tetrabutyl- and tetraoctyl-based quaternary structure are synthesized and then demonstrated them as additives to mineral and synthetic lube base oil for enhancement of lubrication properties. The tetraalkylphosphonium cation-based ionic liquids exhibited higher thermal stability, whereas the tetraalkylammonium cations-based analogue showed superior viscosity. These ionic liquids as an additive to PEG 200 and SN 150 lube base oils increased the viscosity index. The 1.5 w/v% of lauryl sulphate anion-based ionic liquids as an optimized dose to PEG 200 oil significantly improved the tribological properties by decreasing the friction (28%) and wear volume (91%). The enhancement of tribological properties by these ionic liquids is attributed to the formation of tribochemical thin film on the contact interfaces as deduced from their spectroscopic measurements. Furthermore, the tribo results revealed that the alkyl chains in cationic moieties and the viscosity of ionic liquids govern the frictional characteristics.

Stability of Boronium Cation-Based Ionic Liquid Electrolytes on the Li Metal Anode Surface

Augmented cycling performance in lithium metal batteries is often attributed to the formation of a stable solid electrolyte interphase (SEI) layer that forms on the Li surface. Boronium cation-base...

Predicting Melting Points of Biofriendly Choline-Based Ionic Liquids with Molecular Dynamics

In this work, we introduce a simulation-based method for predicting the melting point of ionic liquids without prior knowledge of their crystal structure. We run molecular dynamics simulations of biofriendly, choline cation-based ionic liquids and apply the method to predict their melting point. The root-mean-square error of the predicted values is below 24 K. We advocate that such precision is sufficient for designing ionic liquids with relatively low melting points. The workflow for simulations is available for everyone and can be adopted for any species from the wide chemical space of ionic liquids.

Recovery and Elimination of Phenolic Pollutants from Water Using [NTf2] and [Nf2]-Based Ionic Liquids

At present, pollution is one of the most important problems worldwide. Industrial growth makes it necessary to develop techniques to remove pollutant substances from water, since water is an important natural source for life. One of these techniques is liquid–liquid extraction, which is used to remove phenolic compounds from wastewaters. Volatile organic compounds are used as common extraction solvents in liquid–liquid extractions; nevertheless, some of their properties, such as toxicity and volatility, make it necessary to replace them with other less toxic solvents. In this work, the capability of four ionic liquids, based on bis(trifluoromethylsulfonyl)imide [NTf2] and bis(fluorosulfonyl)imide [Nf2] anions and different cations to remove phenolic compounds from water was studied. The phenolic compounds used in this study were phenol, o-cresol, and 2-chlorophenol, and the effects of the extraction solvent and phenol structures were analyzed. For that, a liquid–liquid extraction was carried out, and the extraction yield was determined. In general, high extraction efficiencies were obtained for all studied systems, obtaining the highest extraction efficiencies using the pyrrolidinium cation-based ionic liquids.

Two phosphonium cation-based ionic liquids as lubricant additive to a polyalphaolefin base oil

This paper studies the tribological performance of two phosphonium cation-based ionic liquids: trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphinate ([P6,6,6,14][(iC8)2PO2]) and trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate ([P6,6,6,14][BEHP]), as lubricant additive at 1 wt% to a polyalphaolefin. A comparison of their tribological behavior was made to that of one type of zinc dialkyldithiophosphate (ZDDP). Stribeck curve tests were made in a Mini Traction Machine (MTM) tribometer at entrainment speeds ranging from 2000 to 10 mm/s, 30 N-load, slide-to-roll ratio (SRR) of 50%, and temperatures of 40, 60, 80 and 100 °C. Tribofilm formation tests were also conducted in the MTM at 100 °C, load of 50 N, entrainment speed of 150 mm/s, SRR of 50%, and duration of 60 min. Additionally, reciprocating 60-min wear tests at 60 N-load, frequency of 15 Hz, stroke length of 4 mm and at room temperature were performed with IL-containing mixtures at 0.5 and 1 wt%. Coefficient of friction was recorded during the tests, and wear on the discs surface was measured using confocal microscopy. SEM-EDS and XPS were also used for studying the lubricant-surface interactions after these tests. Lubricants including [P6,6,6,14][(iC8)2PO2] exhibited better tribological performance than [P6,6,6,14][BEHP] ones and close to the ZDDP results. SEM images of worn surfaces exhibited evidence of plastic deformation and adhesive wear and EDS analysis showed that only active elements (P, S, Zn) were detected for mixtures containing ZDDP. XPS analysis indicated a different lubrication mechanism of the blends with ionic liquids compared with the ZDDP ones.

Photo-excitation dynamics of N, N-dimethyl-p-nitroaniline in ionic liquids: Effect of cation alkyl-chain length

Transient absorption spectroscopy has been applied to study the photo-excitation dynamics of N, N-dimethyl-p-nitroaniline in twelve imidazolium/phosphonium cation-based ionic liquids (ILs) with alkyl chains of different lengths. The transient absorption spectra showed an initial bleach signal around the absorption center (400 nm) and a stimulated emission band around 500 nm. The bleach signal was recovered mostly within a few picoseconds, and a hot band absorption appeared around 450 nm. The time profiles of the band integrals for the bleach and absorption spectral regions were simulated by a sum of four exponential decays. The internal conversion rate corresponding to the back electron transfer (b-ET) rate from the charge-separated excited state, was determined by the time profile of the band integral of the bleach region. The vibrational energy relaxation (VER) rate in the ground state was determined from the time profile of the hot band absorption decay band integral. The b-ET rate decreased with increasing number of alkyl carbons in the cation (#C). The solvent dependence was discussed in terms of the free energy change at the Marcus inverted region, which was indicated by the blue-shift of the ground state absorption band. The change of the free energy is ascribed to the change of the charge concentration of ILs. The VER rate decreased slightly with increasing #C. The reason was discussed in terms of the interaction of DMpNA with the polar region of ILs. The intersystem crossing yield also increased with increasing #C, reflecting an increase in the non-polar region of the ILs.

Environmental properties of phosphonium, imidazolium and ammonium cation-based ionic liquids as potential lubricant additives

This research compares the environmental properties (bacterial toxicity and biodegradability) of 12 ionic liquids -ILs- (7 phosphonium, 2 imidazolium and 3 ammonium cation-based ones), potentially applicable as lubricant additive, with two types of the traditional lubricant additive ZDDP. Aquatic toxicity was determined by means of Vibrio fischeri and Escherichia coli bacteria, while biodegradability was evaluated through biological oxygen demand (BOD5) and chemical oxygen demand (COD) measurements. Regarding toxicity results, [P4442][DEP] was the least toxic IL (acute 3 according to GHS) for both bacteria, whereas ZDDP fell into the acute 1 category (very toxic). All samples tested turned out to be poorly biodegradable, showing BOD5/COD values below 0.1. Two ILs showed better combined tribological and environmental properties than ZDDP.

Measurement and correlation of CO2 solubility in 1-butyl-3-methylimidazolium ([BMIM]) cation-based ionic liquids: [BMIM][Ac], [BMIM][Cl], [BMIM][MeSO4

The solubility of CO2 in three different 1-butyl-3-methylimidazolium ([BMIM]) cation-based ionic liquids: 1-butyl-3-methylimidazolium acetate ([BMIM][Ac]), 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), and 1-butyl-3-methylimidazolium methyl sulfate ([BMIM][MeSO4]) was investigated. The CO2 solubility was determined by the measurement of the bubble-point or cloud-point pressure of the CO2 + IL mixtures. The temperature and pressure ranges were 303.15–403.15 K and 0.39–34.55 MPa, respectively.The results of this study show that the CO2 solubility in ILs were strongly affected by the different type of anions and also increased with pressure, and decreased with temperature. The sequence of magnitude of the CO2 solubility was [BMIM][Ac] >> [BMIM][MeSO4] > [BMIM][Cl]. For correlating the experimental data, we used the PR-EoS with one fluid mixing rule and the modified Lydersen-Joback-Reid method. The average absolute deviations of pressure (AAD-P) were 0.0335 for CO2 + [BMIM][Ac], 0.0128 for CO2 + [BMIM][Cl], and 0.0213 for CO2 + [BMIM][MeSO4] systems.

Measurement and Correlation of CO2 Solubility in 1-Ethyl-3-methylimidazolium ([EMIM]) Cation-Based Ionic Liquids: [EMIM][Ac], [EMIM][Cl], and [EMIM][MeSO4

The solubility of carbon dioxide (CO2) was investigated using three different 1-ethyl-3-methylimidazolium ([EMIM]) cation-based ionic liquids: 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]), 1-ethyl-3-methylimidazolium chloride ([EMIM][Cl]), and 1-ethyl-3-methylimidazolium methyl sulfate ([EMIM][MeSO4]). The CO2 solubility data for the three ionic liquids were produced by measuring the bubble-point and cloud-point pressures of the CO2 + ionic liquid mixtures. The temperature range was from 303.15 to 403.15 K, and the pressure range was from 0.45 to 48.6 MPa. The experimental data provided results showing that the solubility of CO2 in ionic liquids increased with pressure, decreased with temperature, and was also affected by the different anions used in the experiment. The solubility is determined by CO2 mole fraction in ionic liquids, and the order of magnitude of the CO2 solubility was found to be [EMIM][Ac] > [EMIM][MeSO4] > [EMIM][Cl]. For the correlation and calculation of the experimental data, we ...

Study of the antimicrobial activity of cyclic cation-based ionic liquids via experimental and group contribution QSAR model

Over the past decades, Ionic liquids (ILs) have gained considerable attention from the scientific community in reason of their versatility and performance in many fields. However, they nowadays remain mainly for laboratory scale use. The main barrier hampering their use in a larger scale is their questionable ecological toxicity. This study investigated the effect of hydrophobic and hydrophilic cyclic cation-based ILs against four pathogenic bacteria that infect humans. For that, cations, either of aromatic character (imidazolium or pyridinium) or of non-aromatic nature, (pyrrolidinium or piperidinium), were selected with different alkyl chain lengths and combined with both hydrophilic and hydrophobic anionic moieties. The results clearly demonstrated that introducing of hydrophobic anion namely bis((trifluoromethyl)sulfonyl)amide, [NTF2] and the elongation of the cations substitutions dramatically affect ILs toxicity behaviour. The established toxicity data [50% effective concentration (EC50)] along with similar endpoint collected from previous work against Aeromonas hydrophila were combined to developed quantitative structure-activity relationship (QSAR) model for toxicity prediction. The model was developed and validated in the light of Organization for Economic Co-operation and Development (OECD) guidelines strategy, producing good correlation coefficient R2 of 0.904 and small mean square error (MSE) of 0.095. The reliability of the QSAR model was further determined using k-fold cross validation.

Lubricity Improvement of Imidazolium Cation-based Ionic Liquids Treated with Carbon Dioxide

Lubricity Improvement of Imidazolium Cation-based Ionic Liquids Treated with Carbon Dioxide

Lubrication performance of an ammonium cation-based ionic liquid used as an additive in a polar oil

Abstract This paper studies the tribological behavior of the ionic liquid methyltrioctylammonium bis(trifluoromethylsulfonyl)imide ([N 1888 ][NTf 2 ]) as additive at different concentrations (1.25, 2.50, 3.75 and 5.00 wt%) in a polar base oil (diester). A tribometer using a ball-on-disk reciprocating configuration under fully flooded lubrication was used at a frequency of 15 Hz, at three different loads (40, 80 and 120 N), stroke length of 4 mm, and duration of 45 min. Worn surface on the disk was studied by confocal microscopy, SEM and XPS. Main results showed similar coefficient of friction for all lubricant samples; but different wear results were found at different loads, probably related with the chemical states found for fluorine on the worn surface and the temperature-dependent adsorption-desorption processes.

Microheterogeneity in imidazolium and piperidinium cation-based ionic liquids: 1D and 2D NMR studies.

Existence of microheterogeneity of imidazolium and piperidinium cation-based ionic liquids (ILs) containing PF6 and NTf2 anions has been investigated by 1D and 2D NMR spectroscopy. 2D NMR (especially NOESY and HOESY) has been employed for studying the interactions present between cation and anion as well as the intermolecular interaction among cations. HOESY spectrum shows that fluorine of anion ( PF6- and NTf2-) significantly interacts with proton of the cations. Combined results of HOESY and NOESY for imidazolium IL indicate that the PF6- and imidazolium cation are distributed in organized manner, resulting a heterogeneous environment in liquid state. We have also observed existence of heterogeneous environment for piperidinium cation-based ILs which is different from imidazolium ILs. It appears that existence of microheterogeneity in IL is ubiquitous and therefore open up the ILs field to revisit. Copyright © 2017 John Wiley & Sons, Ltd.

The antagonistic role of chaotropic hexafluorophosphate anions and imidazolium cations composing ionic liquids applied as phase additives in the separation of tri-cyclic antidepressants

The main advantage of alkylimidazolium cation-based ionic liquids (ILs) as phase additives in RP-HPLC is believed to be the suppression of deleterious residual free silanols in chemically modified silica stationary phases. However, up to now, the influence of ILs was usually evaluated having in mind a particular IL salt as one compound, not as a specific mixture of cations and anions. This in fact led to some misinterpretation of observed results, very often related to the suppression effect, while in fact caused by the nature of IL anions, which contribute to the elevated chaotropicity of the separation phases.In the present study, we have attempted to consider the effect gained due to the presence of both ionic liquid entities in the mobile phase used for the separation of basic compounds. Tri-cyclic antidepressants (TCAs) were taken as representative analytes. The effect of ILs on the chromatographic separation of TCAs was investigated in comparison to common mobile phase additives and by the presentation of retention factors, tailing factors and theoretical plates. In addition, an overloading study was performed for the IL-based phases for the first time. In general, it was found that the effect of chaotropic hexafluorophosphate anions in ILs is much stronger and opposite to that caused by imidazolium cations. The overloading study gives interesting information on how imidazolium cations affect the separation of cationic analytes. Finally, the usefulness of imidazolium-based ILs as mobile phase modifiers in the RP-HPLC separation of basic compounds was discussed.

High efficiency dye-sensitized solar cells with tetra alkyl ammonium cation-based ionic liquid functionalized graphene oxide as a novel additive in nanocomposite electrolyte

For the first time, we report on the preparation of highly effective electrolyte additive by combining graphene oxide (GO) covalently functionalized with ammonium-based ionic liquid in dye-sensitized solar cell (DSSC). GO was modified in two-step, first, with 1–6, hexamethylenediamine then, the products were reacting with alkyl-halide. The effects of GO- hexamethylene tributyl-ammonium iodide and GO-hexamethylene trimethyl-ammonium iodide as additives on the photovoltaic performance of DSSCs were studied to find the ideal characteristics for minimize the aggregation in ionic liquids based electrolytes. The investigation showed the addition of IL-functionalized GO forms a molecular bridge for electrons transfer in the ionic liquid based electrolyte that has a significant increase in photovoltaic density (Jsc) from 7.141 to 16.847 mA cm−2 more than twice. Under an optimized additive/electrolyte ratio of 4 wt%, the conversion efficiency of DSSCs was remarkably enhanced to 8.33% from initial 3.96% that of referenced ionic liquids-based device. Furthermore, based on these nanocomposite electrolytes, the resulting DSSCs exhibited better electron diffusion coefficient of I− and I3− and ionic conductivity which improves Jsc. It is anticipated that this work may provide an effectual way to develop nanocomposite consisting of graphene derivatives as a great potential for practical application.

Two phosphonium cation-based ionic liquids used as lubricant additive. Part II: Tribofilm analysis and friction torque loss in cylindrical roller thrust bearings at constant temperature

Two phosphonium cation-based ionic liquids (ILs): [P66614][(iC8)2PO2] (IL1) and [P66614][BEHP] (IL2) were used as an additive to a mineral oil at 0.5 and 1.0wt%. All IL-containing mixtures and the base oil were tested using a cylindrical roller thrust bearings test configuration. Friction and torque tests were performed and different analytical techniques were used for wear evaluation. The results showed that: IL-containing mixtures decreased friction in comparison with the neat base oil; IL2 performed better than IL1 as antifriction and antiwear additive; and chemical reaction of the ILs with the surface was found related to the tribological behaviour.

Theoretical Exploration of the Role of CO2 in an Imidazolium Cation-Based Ionic Liquid

Optimized structures of imidazolium cation-based ionic liquids (ILs) and CO2 were obtained using the Gaussian 09 software package and density functional theory (B3LYP/6-31+G(d,p)) with dispersion correction. The interaction energy between cation and anion for imidazolium cation-based ILs, as well as that between ILs and CO2 , were estimated to investigate specific interactions. The presence of CO2 highly impacts the formation of the optimized geometry of imidazolium-based IL. The wavenumber of the C2-H stretching frequency in the imidazolium cation was calculated. The shift of the C2-H stretching wavenumber verified the strong interaction of CO2 with imidazolium and halogen based ILs.