Ionic Liquid Systems Research Articles

Interfacial properties of aqueous ionic liquids on graphene surface in supercapacitors

It is expected to improve the energy density of supercapacitors by applying ionic liquids (ILs) with wide voltage window as electrolyte and graphene high specific surface area as the electrode. Due to the hygroscopic nature of ILs, some water presenting in ILs electrolyte is found to be easy stacked near the positive electrode and effect the supercapacitors’ performance. In this work, acetonitrile (ACN) was taken to add into the ILs electrolyte to solve this problem, and the interfacial properties of aqueous ACN-ILs on charged graphene surface in supercapacitors was investigated from microscopic perspective. The effect of ACN content and charge density was also discussed. The results show that the addition of ACN not only increases the wettability of aqueous ILs on graphene surfaces, but also significantly inhibits the aggregation of water molecules on the positive electrode surface and reduces the aggregation degree of anions and cations in the electrolyte solution, particularly within hydrophilic ILs systems. In addition, cyclic voltammetry experiments confirmed that the electrochemical window of aqueous ILs was improved with addition of ACN. This study provides a significant foundation for further promoting the application of ILs as electrolyte in supercapatiors.

Enhanced operating voltage and desalination performance using ionic liquids as electrolyte for flow electrode capacitive deionisation

Flow-electrode capacitive deionisation (FCDI) technology is a promising approach for desalinating brackish water. Selecting the electrolyte with a high voltage window is essential for improving the FCDI performance. In this study, ionic liquids were used for the first time as a new electrolyte for FCDI systems. The water-desalting efficiency was selected as the evaluation index, and single-factor experiments were conducted on the activated carbon content of electrode slurry, brine flow rate, initial brine concentration, and electrolyte volume ratio, respectively. Box-Behnken design response surface experiments were used and models were constructed to analyse the desalting results of the single factor influence and interaction effects for the aqueous and ionic liquid systems respectively, to determine further the key influencing factors and optimal conditions for the brine desalination in the FCDI system. The results showed that the brine flow rate was the most significant factor affecting the desalination efficiency of the aqueous and ionic liquid FCDI systems (p < 0.0001). The optimal process conditions for the ionic liquid system fitted by the model were as follows: 6.6 wt% activated carbon content in the electrode slurry, a brine flow rate of 45 mL/min, an initial brine concentration of 1 g/L, and an electrolyte ratio of N, N-Dimethylformamide/1-ethyl-3-methylimidazolium tetrafluoroborate = 3. The desalination effect of FCDI under the above optimal process conditions was up to 99.739% at a voltage of 3.5 V, and the water-desalting efficiency was still maintained at over 95% after 20 cycles. Compared with the aqueous electrolyte, using ionic liquid electrolytes significantly improves the desalination rate and cycling stability, and this study provides new ideas and methods for developing and applying high-performance electrolytes in FCDI systems.

Understanding the Mid-Infrared Spectra of Protic Ionic Liquids by Density Functional Theory.

Protic ionic liquids (PILs) are promising candidates as electrolytes for proton exchange polymer membrane fuel cells. In order to optimize their properties, a detailed understanding of the molecular interactions within the bulk and at the electrode-electrolyte interface is needed, which can be obtained by infrared spectra. A prerequisite for extracting information on the molecular structure and inter- or intramolecular interactions from an experimental spectrum is a reasonable interpretation of the observed spectral features. Here, we employed density functional theory to understand the vibration modes of PILs composed of ammonium cations and different counteranions. Different from the previous calculation methods performed on small cluster model systems consisting of isolated species, a periodically repeated system of four ion pairs was used in order to approximate the bulk liquid environment. The computed frequencies and IR intensity match well with the corresponding experimental spectra, allowing for its proper interpretation, especially the characteristic features of the interionic interaction. The presented approach enables accurate computation of a variety of ionic liquid systems in a highly efficient way.

Heavy oil SARA components interaction with p,o,m-xylene solvents/ionic liquids-molecular dynamics simulation and experiment

Oily sludge is generally produced in the process of oil extraction, refining, storage and transportation and disposal of oily wastewater. Is mixed with crude oil, all kinds of refined oil and residual oil and other heavy oil sludge. The main components of heavy oil are saturated fraction, aromatic fraction, colloid and asphaltene which are difficult to treat in oily sludge. In the treatment of oil-containing sludge is usually used solvent extraction method, but due to the high price of extractant, low recycling rate process is a relatively long, complex process, with high treatment costs. Therefore, it is important to find an efficient and cheap extraction solvent. And ionic liquids as inexpensive, environmentally friendly, strengthen the oil-solid separation effect of green solvents, in the auxiliary oil sludge separation on the research has attracted wide attention. In this paper, through molecular dynamics simulation, the diffusion behavior of the four components of heavy oil under different solvents was simulated by using Material Studio software, and the mean square displacement (MSD) was used to describe the diffusion characteristics of the four components of heavy oil under different solvent systems, and the interactions of the four components of heavy oil under different solvents were analyzed in a microscopic point of view. The results showed that the diffusion coefficients of the four components of heavy oil were large and the diffusion rate was fast in the xylene system, while the diffusion coefficients of the four components of heavy oil were small and the diffusion rate was slow in the ionic liquid system.

Optimizing protic ionic liquid electrolyte for pre-intercalated Ti3C2Tx MXene supercapacitor electrodes

Electrical double-layer capacitors (EDLCs) are of increasing importance in energy storage from renewable sources. The properties of the electrode and electrolyte materials influence the energy and power densities of EDLCs. We examined the specific capacitance and ion dynamics of a protic ionic liquid confined in pre-intercalated Ti3C2Tx MXene. Our electrochemical measurements demonstrated that the creation of a protic ionic liquid, 1-butyl-3-H-imidazolium bis(trifluoromethanesulfonyl)imide (BuIMH-NTf2), using a mixture of ionic liquid, 1-butyl imidazole (BuIM), and salt, bis(trifluoromethanesulfonyl)imide (HNTf2), in a ratio of 0.8:0.2 led to the optimal capacitance. Remarkably, quasi-elastic neutron scattering measurements revealed increased particle mobility at this composition, attributed to the more efficient accumulation of BuIMH+ on the electrode surface. This deposit of additional ions results in fewer BuIM molecules away from the surface, enhancing their mobility due to reduced crowding. This composition-dependent electrochemical behavior will guide the formulation of more efficient protic ionic liquid systems, enabling faster ion transport in energy storage devices.

Phase behavior of aqueous two-phase systems formed with cholinium-based magnetic ionic liquids: Experimental insights and theoretical correlations

In this work, three cholinium-based MILs were synthesized, characterized and successfully applied to construct the magnetically responsive aqueous two-phase system (ATPs). This ATPs combined the advantages of ILs and magnetic responsiveness, and showed great potential in the field of extraction and separation. Phase behavior for the magnetic ionic liquid aqueous two-phase systems (MIL-ATPSs) containing [N 1 1n 2OH] [TEMPO-OSO3] + salts + water was investigated experimentally at different temperatures. Merchuk equation was adopted to fit the experimental binodal data with satisfactory correlation performances. The effects of the structure of MILs, temperature and types of salts on the phase behavior were evaluated. Investigation on the phase separation mechanism showed that the phase formation was affected by the structure and viscosity of MILs. The salting-out effect is recognized as the major force for phase separation, which is closely related to the Gibbs free energy of hydration (ΔhydG) and entropy of hydration (ΔhydS) of salts. In addition, a larger biphasic area was obtained by increasing the temperature, indicating the phase separation process was endothermic and entropically driven. The binodal curve at different temperature confirms that this MIL-ATPs has low critical solution temperature (LCST) phase transition behavior. All these experimentally measured data and the theoretical correlations can provide meaningful and valuable information that may promote further research and application.

Novel ionic liquid systems based on three-nitro phenoxide: Spectroscopic and electronic characterization using theoretical and experimental study

After extensive computations, novel trinitro compounds, triethyl ammonium 2,4,6-trinitro phenoxide (TEA-TNP) and tetramethyl guanidinium 2,4,6-trinitro phenoxide (TMG-TNP), are designed, synthesized, and identified. The Geometrical parameters, electronic properties, and spectroscopic analysis have been investigated by comparison of theoretical and experimental methods. Spectrum features that include IR and Raman have been calculated, and 1H and 13C NMR spectra are compared to experimental data. Electronic analysis has been investigated through NLO, FMO, UV-Vis, NBO, and MEP calculations. B3LYP/6-311++G(d,p) is highly successful and dependable for predicting ionic liquid stability, electrical characteristics, and spectroscopy. Both TEA-TNP and TMG-TNP are introduced as suitable candidates for NLO material. TMG-TNP with greater nucleophilicity (N) is a noncorrosive lubricant additive that reduces friction and wear for tribological performance.

A novel trialkyl phosphate – Ionic liquid mixture for an efficient separation of Lithium ion from its acidic feed solution

Separation of Lithium ion (Li+) using conventional non-crown type ligands through solvent extraction process is a challenging task and can only be feasible by tuning the organic phase with an additional polar environment. In this context, we have projected an extracting system containing a traditional trialkyl phosphate (T(alk)P): Tri-iso-amyl phosphate (TiAP) containing a minimal amount of ionic liquid (IL): [C4mpip][NTf2] (1-butyl-1-methylpiperidinium bis(trifluoromethanesulfonyl)imide) for the efficient extraction and separation of Li+ from its hydrochloric acid feed. The extraction performances pertaining various experimental parameters were realized to explore the solvent potentiality of TiAP/[C4mpip][NTf2] towards Li+ coordination. Involvement of two ligand molecules in extraction in presence of 10 % (v/v) IL diluent offers fast extraction kinetics and turns the extraction mechanism into a cation exchange pathway, which was further examined by using different classes of ILs in conjunction with TiAP for Li+ uptake. The selectivity of Li+ over other alkali (or alkaline earth) metal ions was investigated to highlight the affinity of the proposed IL system towards Li+. Extraction scenario in TiAP phase was compared with that in TBP phase containing same IL to bring out the efficacy of the proposed IL system. The stripping performance of Li+ from the loaded organic phase was studied using an acid solution to establish the sustainability of the proposed extraction process.

The Degradation of the 2-Hydroxyethylhydrazinium Nitrate Ionic Liquid System.

The mechanism by which the 2-hydroxyethylhydrazinium nitrate (HEHN) ionic liquid (IL) dissociates via the formation and loss of nitric acid is investigated utilizing the effective fragment potential (EFP) method and various ab initio methods. Additionally, the interactions that dictate the stability of the HEHN IL and contribute to the formation of nitric acid are further assessed using the quasi-atomic orbital (QUAO) bonding analysis. From this work, it is suggested that the formation of nitric acid is dictated by the presence of hydrogen-bonding interactions which appear to become increasingly ionic in nature as the system approaches the bulk, limiting the formation of nitric acid.

Binary imidazolium based aqueous ionic liquid droplet on a rough surface: a molecular dynamics study

Ionic liquids (ILs) have garnered immense attention due to their tunable physicochemical properties. In this study, we delve into the wetting behaviour and interfacial properties of aqueous binary IL mixtures containing [EMIM] [BF4] and [HMIM] [BF4] on both smooth and rough graphite surfaces. Employing classical molecular dynamics simulations, we systematically explored the effects of IL concentration and surface morphology on wetting phenomena. To ensure the equilibrium of the systems, we began by calculating the interaction energies between the components. Subsequently, contact angles were computed, shedding light on the wetting characteristics of the aqueous binary IL mixtures. We meticulously examined the density profiles of the IL systems from the substrate to unravel the dominance of one IL over the other, exploiting the hydrophilic nature of [EMIM] [BF4] and the hydrophobic nature of [HMIM] [BF4]. A comprehensive analysis of hydrogen bond distribution allowed us to discern the intricate nature of these aqueous binary IL droplets. We probed the changes in intermolecular forces within the aqueous IL solution by investigating surface tensions. The tunability of these ILs emerges as a significant aspect of our study, paving the way for their tailored application in engineering and scientific domains. Schematic diagram showing the density distribution of hydrophilic and hydrophobic ILs ([EMIM] [BF4] and [HMIM] [BF4]) in water and also the hydrogen bond (HB) distribution of anion ([BF4]−) water inside the droplet on a pillared surface with a surface fraction ( f ) of 0.4 and pillar height of H = 4 .

Regenerated nanofibrous cellulose electrospun from ionic liquid: Tuning properties toward tissue engineering.

Regenerated fibrous cellulose possesses a unique set of properties, including biocompatibility, biodegradability, and high surface area potential, but its applications in the biomedical sector have not been sufficiently explored. In this study, nanofibrous cellulose matrices were fabricated via a wet-electrospinning process using a binary system of the solvent ionic liquid (IL) 1-butyl-3-methylimidazolium acetate (BMIMAc) and co-solvent dimethyl sulfoxide (DMSO). The morphology of the matrices was controlled by varying the ratio of BMIMAc versus DMSO in the solvent system. The most effective ratio of 1:1 produced smooth fibers with diameters ranging from 200 to 400 nm. The nanofibrous cellulose matrix showed no cytotoxicity when tested on mouse fibroblast L929 cells whose viability remained above 95%. Human triple-negative breast cancer MDA-MB-231 cells also exhibited high viability even after 7 days of seeding and were able to penetrate deeper layers of the matrix, indicating high biocompatibility. These properties of nanofibrous cellulose demonstrate its potential for tissue engineering and cell culture applications.

High Strength and Tough Ionogels with Bicontinuous Phase Network Structure Induced by Electrostatic Adsorption Triggered Microphase Separation

AbstractA simple one‐step approach is presented to fabricate high strength and tough ionogels by copolymerizing zwitterionic monomers and monomers rich in functional groups capable of forming hydrogen bonds within an ionic liquid. The electrostatic adsorption of ionic liquid by the polyzwitterionic segment induces the formation of a bicontinuous phase network structure consisting of a polymer‐rich phase and a solvent‐rich phase. Within this structure, a polymer‐rich phase with hydrogen bonds dissipates energy and enhances the toughness of the ionogel, while an elastic solvent‐rich phase facilitates significant strain. The prepared ionogels exhibit high fracture strength (8.89 MPa), toughness (41.12 MJ m−3), and Young's modulus (58.9 MPa). The critical point for triggering the formation of a bicontinuous phase network can be precisely controlled by the maximum adsorption capacity of the zwitterionic monomers for the ionic liquid. Ionogels at the critical point of bicontinuous phase network formation demonstrate excellent fatigue resistance, with residual strain of only ≈25% under 50% to 250% strain conditions, recovering to their original state within 5 s. Due to the widespread presence of electrostatic interactions, this strategy for constructing a bicontinuous phase network structure exhibits excellent adaptability across different ionic liquid systems.

Scaling Laws in Polysaccharide Rheology: Comparative Analysis of Water and Ionic Liquid Systems.

This study investigates the rheological behavior of two plant-based polysaccharides, with different degrees of hydrophilicity, agar (highly hydrophilic) and guar gum (hydrophilic), in water and 1-ethyl-3-methylimidazolium acetate (EMImAc). The rheological response of these polymers is highly dependent on the solvent's ability to disrupt intermolecular associations. In water, agar forms hydrogels, while guar gum behaves as a viscoelastic liquid with slow modes. The plateau modulus (GN0) scales with polymer concentration (c) as GN0 ∼ c3, consistent with other natural polymers. In EMImAc, both polysaccharides form viscoelastic liquids, exhibiting GN0 ∼ c2.3, as expected for semiflexible polymer solutions. However, the terminal relaxation time, τD, and the specific viscosity, ηsp, scale as τD ∼ c5.3 and ηsp ∼ c7.6, indicative of intermolecular chain-chain associations. Despite the solvent or polysaccharide, the fractional viscosity overshoot and the shear strain at the maximum stress show a terminal Weissenberg number dependence similar to other synthetic polymers.

Cyphos Nitrate Selectively Separates Y(III) from Sr(II) Present in Acidic Feed Solution: An Efficient Ionic Liquid based Extraction Process

AbstractMutual separation of Y(III) and Sr(II) from their waste solution has been an emerging research domain due to their various industrial applications. In this investigation, we emphasize the feasibility of selective separation of Y(III) from Sr(II) present in nitric acid medium using undiluted cyphos nitrate ionic liquid (IL): trihexyl(tetradecyl)phosphonium nitrate ([P66614][NO3]) as the ligating phase. The set experimental parameters were the feed phase acidity, initial nitrate ion concentration, initial feed metal ion concentration, equilibration time and temperature to unveil the efficacy of the proposed system. Efficient extraction of Y(III) selectively in presence of Sr(II) using only a salting agent in aqueous phase without additional extractant in IL phase was highlighted. A remarkable separation factor (SF) obtained for Y(III) over Sr(II) explored the efficacy of the proposed IL system. Y(III) loading in IL phase both in unirradiated and irradiated conditions was compared to evaluate the coordination behavior of irradiated moieties. In addition, a most important advantage of the proposed system is that it employs Milli‐Q water for the back extraction (stripping) of the loaded Y(III) from IL phase and does not demand any complexing agent (water soluble). This undoubtedly corroborates the economic and environmental benefits of the proposed IL system.

A mixed solvent system of amino crown ether and ionic liquids for a high-efficient extraction of cesium

Efficient extraction of Cs+ from aqueous solution was investigated by liquid–liquid extraction based on ionic liquids (ILs). In this study, Di(aminobenzo)-18-crown-6 (DAB18C6) was used as the extractant and three ILs (1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]), and 1-butyl-3-methylimidazolium bis-trifluoromethyl sulfonamide ([C4mim][NTf2])) were employed as co-extractants in the construction of a liquid–liquid extraction system for efficient and selective extraction of Cs+ from aqueous solutions. It was demonstrated that the DAB18C6-[C4mim][NTf2] mixed solvent system at 0.12 mol/L DAB18C6, a mass ratio of ILs/CHCl3 of 1:4 and a volumetric ratio of O/A of 1:1 exhibited a high % extraction of Cs+ up to 99.94 %, with a higher selectivity for Cs+ relative to coexisting ions such as K+ (βCs/K = 1216.7) and Rb+ (βCs/Rb = 139.03). The high selectivity of the extraction system for Cs+ was attributed to the lower hydration binding energy of Cs+ (−366.51 kJ/mol) and the stronger interaction between DAB18C6 and Cs+, g(r) = 12.7. Further, the hydrogen bonding interaction between the amino crown ether and ionic liquid increases the viscosity and surface tension of the extraction system, thus enhancing the stability of the system. Noteworthy, the most stable structure formed by DAB18C6-Cs+-[NTF2]− is attributed to cation exchange. In summary, this study demonstrates the great potential for efficient separation and extraction of cesium from aqueous solutions.

Molecular simulations of understanding the Zn2+ ion structure, dynamics and thermodynamic properties in water in ionic liquids

We utilize all-atom molecular dynamics simulations to explore the intermolecular structure, dynamics and thermodynamic properties of Zn2+ ions in water-in-ionic liquid. Two ionic liquid systems featuring the same cation 1-ethyl-3-methyl-imidazolium [EMIM]+ and distinct anions tetrafluoroborate [BF4]− and hexafluorophosphate [PF6]− are considered. We consider the water (H2O) mole fractions (x) varying from 0.33 to 0.71. We observe a significant interactions of Zn2+ ions with water in the case of [BF4]− when compared to [PF6]−. On the other hand Zn2+ ions mobility rises more in [EMIM]+[BF4]− as compared to [EMIM]+[PF6]− with x. Higher self-diffusion (D) of Zn2+ ions is seen in the case of [EMIM]+[BF4]−. The ionic conductivity (σ) of [EMIM]+[BF4]− is greater compared to [EMIM]+[PF6]− with the rise in x. Overall, this article furnishes in-depth molecular-level insights into the behaviour of Zn2+ ions in the presence of water mixed ionic liquid electrolytes.

Direct lithium extraction from Canadian oil and gas produced water using functional ionic liquids – A preliminary study

In this study, a functional ionic liquid system was successfully applied to extract lithium from the Canadian oil and gas produced water samples without further dilution at ambient conditions. The effects of interference cations, dissolved organics and other factors on the extraction were studied in detail. Chemical precipitation method was applied to reduce the concentrations of divalent ions before the ionic liquid extraction. The extraction efficiency is about 70% on average and can be as high as 90%. It appears that this extraction method can be directly applied to the oilfield brine samples with both high Na/Li and Mg/Li ratios. In addition, it seems that the dissolved organics in the produced water did not impact the extraction efficiency. Efforts shall be made in the future to reduce the cost by replacing the diluent with another type of solvent and further improving the recycle and reuse of the IL systems. In summary, the technology can achieve satisfactory lithium extraction from the Canadian oil and gas produced water.

Modulation of Triton X-100 Aqueous Micelle Interface by Ionic Liquid: A Molecular Level Interaction Studied by Time-resolved Fluorescence Spectroscopy

Background: Self-assembly structure is an important area of research for understanding biological systems, owing to its resemblance to the membrane structure of the phospholipid bilayer. In a self-assembly medium, chemical reactions and chemical or physical processes are dramatically different than the bulk phase. Understanding this process in synthesizing self-assembly structures may allow us to explore various biological processes occurring in cell membranes. Objective: The study aimed to understand water dynamics in the TX-100 micellar interface via steady state and a time-resolved fluorescence spectroscopy study. The objective was also to determine the two different ionic liquids (ILs), namely 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim][BF4]) and 1-decyl-3-methyl imidazolium tetrafluoroborate ([dmim][BF4]), inducing surfactant aggregation changes at the molecular level. Also, the focus was on determining the hydration and its dynamics at the palisade layer of TX-100 micelle in the presence of two different ionic liquids. Methods: Steady state and time-resolved fluorescence spectroscopy have been used to study TX-100 micellar systems. Employing time-resolved spectroscopy, two chemical dynamic processes, solvation dynamics and rotational relaxation dynamics, have been studied to investigate structural changes in TX100 by adding ILs. Solvation dynamics was studied by measuring the time-dependent Stokes shift of the fluorescent probe. From the Stokes shift, time-resolved emission spectra were constructed to quantify the solvation dynamics. Also, using the polarization properties of light, time-resolved anisotropy was constructed to explore the rotation relaxation of the probe molecule. Results: The absorption and emission spectra of C-153 in TX-100 were red-shifted in the presence of both the ILs. Also, the C-153 experienced faster solvation dynamics and rotational relaxation with the addition of both ILs. In our previous study, we observed a significantly increased rate of solvation dynamics with the addition of [bmim][BF4] (J. Phys. Chem. B, 115, 6957-6963) [38]. However, with the addition of the same amount of [dmim][BF4], the IL rate of solvation enhancement was more pronounced than with [bmim][BF4]. The faster solvation and rotational relaxation have been found to be associated with the penetration of more free water at the TX100 micellar stern layer, leading to increased fluidity of the micellar interface. Conclusion: Upon incorporating ILs in TX100 micelle, substantially faster solvation dynamics of water as well as rotational relaxation dynamics of C-153 have been observed. By decreasing surfactant aggregations, [bmim][BF4] ILs facilitated more water molecules approaching the TX-100 micellar phase. On the other hand, [dmim][BF4] ILs comprising mixed micelles induced even more free water molecules at the palisade layer, yielding faster solvation dynamics in comparison to pure TX-100 micelle or TX100 micelle + [bmim][BF4] ILs systems. Time-resolved anisotropy study has also supported the finding and strengthened the solvation dynamics observation.

Non-hydroxyl radical dominated catalytic oxidation of lignin-derived vanillyl alcohol by H2O2 upon ionic liquids for vanillin production

Oxidative conversion of lignin-derived vanillyl alcohol (VA) into value-added vanillin (VN) represents an important move towards sustainable valorization of lignin resource. However, the oxidation upon hydrogen peroxide often suffers from side reactions like over-oxidation, limiting the reaction efficiency. The key step to enhance VN yield from VA oxidized by H2O2 lies in the generation of selectively active oxidizing species as an alternative to hydroxyl radicals. To this end, we demonstrate a homogeneous oxidation of VA for VN acquisition using H2O2 in ionic liquid (IL) triethylammonium acetate [Et3NH][CH3COO] catalyzed by cobalt (II). The generation of hydroxyl radical was proved to be inhibited by [Et3NH][CH3COO], and the oxidative high valent metal–oxygen complexes Co(IV) = O with higher selectivity might be involved to promote the conversion efficiency upon the coordination of IL anion with cobalt ion. Compared to the oxidation proceed in non-IL system, the IL system contributed to higher reaction efficiency. 11.85 % VN yield was achieved for 81.65 % conversion rate of VA at 60 ℃ for 2 h in atmosphere with the addition of 0.04 mmol of Co2+ in [Et3NH][CH3COO].

On the Moisture Absorption Capability of Ionic Liquids.

Due to their many attractive physicochemical properties, ionic liquids (ILs) have received extensive attention with numerous applications proposed in various fields of science and technology. Despite this, the molecular origins of many of their properties, such as the moisture absorption capability, are still not well understood. For insight into this, we systematically synthesized 24 types of ILs by the combination of the dimethyl phosphate anion with various types of alkyl group-substituted cyclic cations─imidazolium, pyrazolium, 1,2,3-triazolium, and 1,2,4-triazolium cations─and performed a detailed analysis of the dehumidification properties of these ILs and their aqueous solutions. It was found that these IL systems have a high dehumidification capability (DC). Among the monocationic ILs, the best performance was obtained with 1-cyclohexylmethyl-4-methyl-1,2,4-triazolium dimethyl phosphate, whose DC (per mol) value is 14 times higher than that of popular solid desiccants like CaCl2 and silica gel. Dicationic ILs, such as 1,1'-(propane-1,3-diyl)bis(4-methyl-1,2,4-triazolium) bis(dimethyl phosphate), showed an even better moisture absorption, with a DC (per mol) value about 20 times higher than that of CaCl2. Small- and wide-angle X-ray scattering measurements of eight types of 1,2,4-triazolium dimethyl phosphate ILs were performed and revealed that the majority of these ILs form nanostructures. Such nanostructures, which vary with the identity of the IL and the water content, fall into three main categories: bicontinuous microemulsions, hexagonal cylinders, and micelle-like structures. Water in the solutions exists primarily in polar regions in the nanostructures; these spaces function as water pockets at relatively low water concentrations. Since the structure and stability of the aggregated forms of the ILs are mainly governed by the interactions of nonpolar groups, the alkyl side chains of the cations play an important role in the DC and temperature-dependent equilibrium water vapor pressure of the IL solutions. Our experimental findings and molecular dynamics simulation results shed light on the moisture absorption mechanism of the IL aqueous solutions from a molecular perspective.