Comprehensive Study on the Impact of the Cation Alkyl Side Chain Length on the Solubility of Water in Ionic Liquids

Condensable Gases Capture with Ionic Liquids

Condensable gases are the sum of condensable and volatile steam or organic compounds, including water vapor, which are discharged into the atmosphere in gaseous form at atmospheric pressure and room temperature. Condensable toxic and harmful gases emitted from petrochemical, chemical, packaging and printing, industrial coatings, and mineral mining activities seriously pollute the atmospheric environment and endanger human health. Meanwhile, these gases are necessary chemical raw materials; therefore, developing green and efficient capture technology is significant for efficiently utilizing condensed gas resources. To overcome the problems of pollution and corrosion existing in traditional organic solvent and alkali absorption methods, ionic liquids (ILs), known as "liquid molecular sieves", have received unprecedented attention thanks to their excellent separation and regeneration performance and have gradually become green solvents used by scholars to replace traditional absorbents. This work reviews the research progress of ILs in separating condensate gas. As the basis of chemical engineering, this review first provides a detailed discussion of the origin of predictive molecular thermodynamics and its broad application in theory and industry. Afterward, this review focuses on the latest research results of ILs in the capture of several important typical condensable gases, including water vapor, aromatic VOCs (i.e., BTEX), chlorinated VOC, fluorinated refrigerant gas, low-carbon alcohols, ketones, ethers, ester vapors, etc. Using pure IL, mixed ILs, and IL + organic solvent mixtures as absorbents also briefly expanded the related reports of porous materials loaded with an IL as adsorbents. Finally, future development and research directions in this exciting field are remarked.

Effect of cation alkyl chain length on 3-sulfopropylmethacrylate-based draw solutes having lower critical solution temperature

We investigated the effect of change in alkyl chain length of cation in tributylalkylphosphonium 3-sulfopropyl methacrylate ([P444#][C3S], # = 4, 6, and 8) ionic liquids (ILs) on their osmolality and recovery properties as the draw solute in the forward osmosis (FO) process. The ILs aqueous solutions exhibited a characteristic of the lower critical solution temperature (LCST)-type phase separation, which allowed for the easy recovery of the draw solute or clean water from the diluted draw solution. The LCSTs of 31, 26, 22, and 18 °C were obtained from 2.5, 5.0, 7.5, and 10.0 wt% aqueous solutions of [P4446][C3S]. When deionized water, 2000 ppm NaCl solution, and 10.0 wt% orange juice aqueous solution were used as feed solution, the water fluxes of the aqueous [P4446][C3S] solutions were approximately 4.49, 3.87, and 1.55 LMH, respectively, in the active layer facing the draw solution mode at 7.5 wt% of draw solution. This study demonstrates the applicability of a thermoresponsive ionic structure material as a draw solute for the FO process.

Investigation of Sulfonium-Iodide-Based Ionic Liquids to Inhibit Corrosion of API 5L X52 Steel in Different Flow Regimes in Acid Medium

The present work deals with the corrosion inhibition mechanism of API 5L X52 steel in 1 M H₂SO₄ employing the ionic liquid (IL) decyl(dimethyl)sulfonium iodide [DDMS⁺I^-]. Such a mechanism was elicited by the polarization resistance (R _p), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) techniques, both in stationary and dynamic states. The electrochemical results indicated that the corrosion inhibition was controlled by a charge transfer process and that the IL behaved as a mixed-type corrosion inhibitor (CI) with anodic preference. The experimental results revealed maximal inhibition efficiency (IE) rates up to 93% at 150 ppm in the stationary state, whereas in turbulent flow, the IE fell to 65% due to the formation of microvortexes that promoted higher desorption of IL molecules from the surface. The Gibbs free energy of adsorption (ΔG°_ads) value of -34.89 kJ mol^-1, obtained through the Langmuir isotherm, indicated the formation of an IL monolayer on the metal surface by combining physisorption and chemisorption. The surface analysis techniques confirmed the presence of Fe _x O _y , FeOOH, and IL on the surface and showed that corrosion damage diminished in the presence of IL. Furthermore, the quantum chemistry calculations (DFT) indicated that the iodide anion hosted most of the highest occupied molecular orbital (HOMO), which eased its adsorption on the anodic sites, preventing the deposition of sulfate ions on the electrode surface.

Ionic Liquids Assisted Topical Drug Delivery for Permeation Enhancement: Formulation Strategies, Biomedical Applications, and Toxicological Perspective

Topical drug delivery provides several benefits over other conventional routes by providing localizing therapeutic effects and also avoids the gastrointestinal tract circumventing the first-pass metabolism and enzymatic drug degradation. Being painless, the topical route also prevents the difficulties linked with the parenteral route. However, there are limitations to the current topical systems which necessitate the need for further research to find functional excipients to overcome these limitations. This review deals in depth with the ionic liquids concerning their physicochemical properties and applicability as well as their role in the arena of topical drug delivery in permeation enhancement, bioavailability enhancement of the drugs by solvation, and drug moiety modification. The review gives a detailed insight into the recent literature on ionic liquid-based topical formulations like ionic liquid-based emulsions, active pharmaceutical ingredient-ionic liquids, ionic liquid-based bacterial cellulose membranes, topical small interfering RNA (siRNA) delivery, and ionogels as a possible solutions for overcoming the challenges associated with the topical route. This review also takes into account the toxicological aspects and biomedical applications of ionic liquids.

Imidazolium-type ionic liquid-based carbon quantum dot doped gels for information encryption

Here, a strategy for the preparation of adjustable imidazolium-type ionic liquid (IL)-based carbon quantum dots (CQDs) was reported. The effect of chemical structure, including carbon chain length of the N-substitution and the type of anion, on the amphiphilicity of CQDs was systematically investigated. It was found that the hydrophobicity of CQDs can be increased with the increase of carbon chain length for substitution at the N3 position. Moreover, the amphiphilicity of CQDs was also switched by changing the hydrophilic anions to hydrophobic anions. Due to adjustable amphiphilicity, the hydrophilic and hydrophobic CQDs were used for the preparation of fluorescent hydrogels and organogels, respectively. The fluorescent CQD-doped gels showed light- and force-dual stimuli responsiveness, which provides more secure information encryption than traditional single encryption inks.

A comprehensive study on the impact of chemical structures of ionic liquids on the solubility of ethane

The solubility of ethane is not only governed by the electrostatic–misfit of the solute toward ionic liquids, but also the existence of a preferential site for ethane to interact with the ionic liquid's non-polar moiety.

Expanding the Electrochemical Window: New Tunable Aryl Alkyl Ionic Liquids (TAAILs) with Dicyanamide Anions

A set of new tunable aryl alkyl ionic liquids (TAAILs) based on the 1-aryl-3-alkyl imidazolium motif has been synthesized, in which the following variables were systematically changed: alkyl chain length, aryl substitution (group and position), and counter ion. TAAILs with dicyanamide (DCA) and bis(trifluoromethylsulfonyl)imide (N(SO₂ CF₃ )₂ , NTf₂ ) anions showed remarkable differences of their physical properties: NTf₂ ionic liquids were found to have high decomposition temperatures and viscosities well below those of the DCA TAAILs. In contrast, the dicyanamide anion increased the electrochemical stability leading to TAAILs with an extremely wide electrochemical window of up to 7.17 V. Additionally, both classes of TAAILs extract transition metals from aqueous solutions: TAAILs with the DCA anion extract both platinum and copper while TAAILs with the NTf₂ anion are selective towards platinum. This demonstrates that minor changes of the molecular structure lead to TAAILs with drastically changed physicochemical properties.

Understanding the adsorption of ionic liquids onto zeolite ZSM-5 from aqueous solution: experimental and computational modelling

Ionic liquids are considered as emergent pollutants as these compounds possess high persistence in aqueous solution and toxicity toward aquatic organisms. In this work, the adsorption equilibrium of 27 ionic liquids, with different cation head groups, alkyl chain lengths, and anions, onto ZSM-5 was measured experimentally at several compositions and at temperature 298.15 K and 0.1 MPa. The extensive number of ionic liquids studied allows a comprehensive study on the impact of adsorbate chemical structures toward their adsorption process. The gathered experimental results show that the anions have a dominant effect, when compared to the cation head group and the alkyl chain length, in ruling the adsorption of ionic liquids from aqueous solution onto ZSM-5. The adsorption isotherms reveal that the adsorption process is a combination between Langmuir and Freundlich behaviors, with the latter leading the general process. Moreover, computational modelling using COSMO-RS demonstrates the existence of several molecular forces that rule the adsorption process, reinforcing the idea that the ionic liquid anion rules the adsorption. The results collected in the present work provide new understanding on the molecular mechanism for the development of efficient adsorbents for removal and recovery of ionic liquids from aqueous solution.

Effects of soil components and solution inorganic cations on interactions of imidazolium-based ionic liquid with soils

Effects of alkyl chain length of ionic liquid (IL), soil components and solution inorganic cations on a selected IL (1-methyl-3-octylimidazolium chloride, [OMIM]Cl) interaction with Chinese soils were investigated using batch sorption experiments. The results indicated that sorption energy was mainly controlled by chain length of [OMIM]Cl and contents of soil organic matter (SOM). [OMIM]Cl sorption on soils was mainly controlled by cation exchange process. Contributions of SOM and clay minerals (CMs) to [OMIM]Cl sorption were 7.3%-53.8% and 46.2%-92.7%, respectively. SOM possessed higher energy cation-exchange binding sites than CMs. To predict the sorption of [OMIM]Cl on soils, a model for the relationship between sorption coefficient (K_d) and cation exchange capacity (CEC) from soil components (SOM and CMs, i.e., CEC_SOM and CEC_CMs) as well as solution concentration (C_e) was established: LogK_d = Log(1.67*CEC_SOM + 3.22*CEC_CMs) - 0.58LogC_e. This model could provide a good prediction for sorption coefficients and the prediction errors were within 0.48 log unit. Competitive effects caused by inorganic cations followed the order of Ca²⁺ = Mg²⁺ > K⁺ > Na⁺. Concentrations and valence of coexisting ions both affect their competitive capability on [OMIM]Cl sorption. The finding of this study provided valuable information for evaluating the fate of [OMIM]Cl in soils.

Comparison of Electronic and Physicochemical Properties between Imidazolium-Based and Pyridinium-Based Ionic Liquids

To compare 1-butyl-3-methylimidazolium ([BMIM]⁺)- and 1-butyl-3-methylpyridinium ([BMPy]⁺)-based ionic liquids (ILs) and investigate the influence of intramolecular and intermolecular interactions on physicochemical properties, a systematic study was performed on the electronic structures and physicochemical properties of [BMIM]⁺ tetrafluoroborate ([BMIM][BF₄]), [BMIM]⁺ hexafluorophosphate ([BMIM][PF₆]), [BMIM]⁺ hydrogen sulfate ([BMIM][HSO₄]), [BMIM]⁺ methylsulfate ([BMIM][MSO₄]), [BMIM]⁺ ethylsulfate ([BMIM][ESO₄]), [BMPy]⁺ tetrafluoroborate ([BMPy][BF₄]), [BMPy]⁺ hexafluorophosphate ([BMPy][PF₆]), [BMPy]⁺ hydrogen sulfate ([BMPy][HSO₄]), [BMPy]⁺ methylsulfate ([BMPy][MSO₄]), and [BMPy]⁺ ethylsulfate ([BMPy][ESO₄]) using density functional theory and molecular dynamics simulation. The results reveal that aggregation behavior exists in [HSO₄]^-- and [ESO₄]^--based ILs, and the differences between their densities and self-diffusion coefficients are smaller when there is an aggregation effect in ILs. A dimer is formed by two strong hydrogen bonds between two [HSO₄]^- anions in [HSO₄]-based ILs, and the existence of hydrogen bonds in ILs increases density and decreases the self-diffusion coefficient. The intermolecular interaction strength of [BMIM]⁺-based ILs is stronger than that of [BMPy]⁺-based ILs.

Transport of imidazolium-based ionic liquids with different anion/cation species in sand/soil columns

Ionic liquids (ILs) have been widely used as environmentally friendly solvents to replace volatile organic solvents in the chemistry industries. They have a high water solubility and potential risk to organisms in the soil-water environment. At present, most studies focused on the batch sorption of ILs in soil and neglected the investigation of IL transports in soil, which results in a lack of understanding of the structure-dependent mobility of ILs in the environment. Laboratory-scale sand/soil column experiments were performed to study the transport of imidazolium-based ILs, such as [C₄mim][OTF], [C₄mim][TOS], [C₄mim][MeSO₃], [C₄mim][BF₄], [C₂mim][BF₄], and [C₆mim][BF₄] including different counteranions and alkyl chain lengths of IL cations. Batch experiments were also carried out to compare the difference of sorption distribution coefficient (K_d) between the batch and column experiments. A one-dimensional convective-dispersive model using CXTFIT code was created based on the measured breakthrough curves (BTCs) to estimate the column transport parameters. For the anion, [BF₄^-], the K_d of ILs in both batch and column experiments increased with increasing alkyl chain lengths of the IL cation. In batch tests, counteranions showed no influence on the K_d of [C₄mim][OTF], [C₄mim][TOS], [C₄mim][MeSO₃], [C₄mim][BF₄], [C₂mim][BF₄], and [C₆mim][BF₄]. However, in column tests, the BTCs of 1-butyl-3-methylimidazolium-based ILs were anion dependent as evidenced by the change of retardation factor (R) for different counteranions. Furthermore, the effects of transport distance (11cm, 15cm, 19cm, and 24cm) on the mobility of ILs were estimated. The longer distances signified an increase in the contact time and more binding sites for ILs and therefore, the smoother shapes of BTCs in column experiments.

Thermodynamic Properties of Selected Homologous Series of Ionic Liquids Calculated Using Molecular Dynamics

This work presents a molecular dynamics simulation study concerning the thermodynamic data of ionic liquids (ILs) including phase change enthalpies, liquid phase densities, radial and spatial distribution functions, and diffusive properties. Three homologous series of ILs were selected for this study, namely, 1-alkyl-3-methylimidazolium tetrafluoroborates, hexafluorophosphates, and 1,1,2,2-tetrafluoroethanesulfonates, so that properties of 36 ILs are calculated in total. The trends of calculated properties are compared to available experimental data and thoroughly discussed in context of the homologous series. The calculated trends of the vaporization enthalpies within the series are supported by analyzing the structural properties of the ILs. An excellent agreement of calculated structural properties (liquid phase density) with the experimental counterparts is reached. The calculated enthalpic properties are overestimated considerably; thus, further development of the force fields for ILs is required.

Mutual solubility of water and hydrophobic ionic liquids in the presence of hydrochloric acid

Possible mechanism for ionic liquid dissolution in HCl solution.

Hydrogen-bond acidity of ionic liquids: an extended scale

One of the main drawbacks comprising an appropriate selection of ionic liquids (ILs) for a target application is related to the lack of an extended and well-established polarity scale for these neoteric fluids. Albeit considerable progress has been made on identifying chemical structures and factors that influence the polarity of ILs, there still exists a high inconsistency in the experimental values reported by different authors. Furthermore, due to the extremely large number of possible ILs that can be synthesized, the experimental characterization of their polarity is a major limitation when envisaging the choice of an IL with a desired polarity. Therefore, it is of crucial relevance to develop correlation schemes and a priori predictive methods able to forecast the polarity of new (or not yet synthesized) fluids. In this context, and aiming at broadening the experimental polarity scale available for ILs, the solvatochromic Kamlet-Taft parameters of a broad range of bis(trifluoromethylsulfonyl)imide-([NTf2](-))-based fluids were determined. The impact of the IL cation structure on the hydrogen-bond donating ability of the fluid was comprehensively addressed. Based on the large amount of novel experimental values obtained, we then evaluated COSMO-RS, COnductor-like Screening MOdel for Real Solvents, as an alternative tool to estimate the hydrogen-bond acidity of ILs. A three-parameter model based on the cation-anion interaction energies was found to adequately describe the experimental hydrogen-bond acidity or hydrogen-bond donating ability of ILs. The proposed three-parameter model is also shown to present a predictive capacity and to provide novel molecular-level insights into the chemical structure characteristics that influence the acidity of a given IL. It is shown that although the equimolar cation-anion hydrogen-bonding energies (EHB) play the major role, the electrostatic-misfit interactions (EMF) and van der Waals forces (EvdW) also contribute, admittedly in a lower extent, towards the hydrogen-bond acidity of ILs. The new extended scale provided for the hydrogen-bond acidity of ILs is of high value for the design of new ILs for task-specific applications.