Anion Of Ionic Liquid Research Articles

Ionic liquid (IL) cation and anion structural effects on the extraction of metal ions into N-alkylpyridinium-based ILs by a macrocyclic polyether

ABSTRACT Previous studies of the effect of IL cation/anion hydrophobicity and the nature of the aqueous phase anion on the partitioning of alkali and alkaline earth cations between an acidic aqueous phase and 1,3-dialkylimidazolium-based or quaternary ammonium-based ILs in the presence of a crown ether have revealed significant similarities between the behavior of the two IL families. To further explore the generality of these observations and their potential application in the rational design of ILs for use as replacements for the molecular diluents typically employed as extraction solvents, the extraction of several metal ions (Na+, Sr2+ and Ba2+) from nitric and hydrochloric acid solutions by dicyclohexano-18-crown-6 (DCH18C6) into a series of N-alkylpyridinium-based ILs (Cn-pyr+ ILs) has been studied. Although much of the extraction behavior observed in these systems is consistent with that seen for the 1,3-dialkylimidazolium and quaternary ammonium-based ILs, certain observations, in particular the effect of IL cation hydrophobicity on divalent metal ion extraction from HNO3 by N-alkylpyridinium-ILs bearing long (dodecyl- and tetradecyl-) alkyl chains, cannot be fully explained by the established three-path model for metal ion partitioning. Instead a complete description of metal ion extraction in these systems requires consideration of the aggregation of the IL cation in the aqueous phase. The effects of this aggregation on the efficiency and selectivity of metal ion extraction into Cn-pyr+ ILs by the crown ether are systematically explored.

A systematic approach of using green solvent for the extraction of Pb (II) from aqueous solution

In this article, the extraction behavior of halogen-free ionic liquid, 1-butyl-3-methylimidazolium octyl sulfate, was investigated in the separation of lead from the aqueous solution. Experimental parameters include time, impact of pH, feed concentration, amount of ionic liquid, ionic strength, and temperature were optimized for the evaluation of the lead extraction. From the optimum conditions, it was emanated that the maximum extraction efficiency of lead was 97% with the feed concentration of 10 ppm in an equilibrium time of 60 min at the pH of 5 and 2 g of the ionic liquid, respectively. Furthermore, the extraction results revealed that the higher efficiency was achieved without the addition of salt and that the extraction process was spontaneous and endothermic in nature. The metal complexation was formed by the exchange of ionic liquid anion to the aqueous phase, and thereby, the extraction mechanism was proposed. The ionic liquid in the organic phase was stripped using sodium sulfate as a stripping agent. FTIR analysis confirmed the recoverable ionic liquid and effectively reused it five times in the course of extraction. From the analysis, it was authenticated that the ionic liquid, 1-butyl-3-methylimidazolium octyl sulfate, was an effective extractant for the elimination of lead (II) and could be employed for the tertiary treatment of industrial wastes.

Enhancing Artemisinin Solubility in Aqueous Solutions: Searching for Hydrotropes based on Ionic Liquids

Artemisinin is a sesquiterpenoid lactone peroxide, known for its potent antimalarial activity that can be extracted from Artemisia annua L. This compound is only sparingly soluble in water, making its extraction using environmental-friendly and non-toxic aqueous solvents difficult. In the attempt to overcome this limitation, hydrotropes, which are a class of compounds that can assist in increasing the solubility of hydrophobic solutes in water, were investigated in this work. In particular, the hydrotropic capability of ionic liquids (ILs) on the aqueous solubility of artemisinin was studied. The effects of IL concentration and anion nature of 1-butyl-3-methylimidazolium-based ILs on the solubility of artemisinin at 303.2 K in water were evaluated. It is here shown the excellent capacity of ILs containing thiocyanate or dicyanamide anions to enhance the solubility of artemisinin in aqueous media, with a magnitude comparable to that obtained with the best organic solvents. Furthermore, solvatochromic parameters of the ILs aqueous solutions were also measured and combined with COSMO-RS and the cooperative hydrotropy model to establish relations between the artemisinin solubility enhancement and the solvent characteristics. The solubility enhancement of artemisinin is favored by the apolarity of the medium and the lower hydrogen-bond acceptor character of the hydrotrope.

Iodine adlayer mediated gold electrooxidation in bis(trifluoromethylsulfonyl)amide-based ionic liquids

Conventional complexing ligands for the wet etching of gold are hazardous, making large-scale utilization problematic. In particular, the environmental risks caused by these materials must be minimized. To address this problem, an electrochemical etching method for gold using bis(trifluoromethylsulfonyl)amide ([Tf2N]–)-based ionic liquids (ILs) has been developed. Here, only one layer of conventional complexing ligand, that is, iodine on gold, is required to achieve the continuous dissolution of gold under a positive electrode potential. In addition, the etching behavior involves sacrificial anode electrolysis (SAE) to generate gold nanoparticles (AuNPs). It was found that the electrochemical oxidation of gold is strongly dependent upon the type of halide ion, and the iodine-modified gold electrode produced a large oxidation peak in [Tf2N]–-based ILs. The voltammetric profiles of iodine-modified gold electrodes reveal that the electronic charge consumed during the electrochemical oxidation is affected by the IL cation and the crystallographic orientation of gold, increasing as ammonium < imidazolium < pyrrolidinium and Au(111) < Au(100) < Au(110), respectively. Of the IL anions evaluated in this study, the apparent oxidation peak was only observed for iodine-modified gold electrode in [Tf2N]–-based ILs, suggesting that [Tf2N]– anions promote gold complexation and act as ligands. Further, microscopic and spectroscopic measurements provide evidence of gold dissolution after electrochemical oxidation and the formation of gold complexes, followed by the generation of AuNPs. The results reveal a mechanism for the iodine-catalyzed electrochemical oxidation of gold in [Tf2N]–-based ILs. The electrolysis of gold in the ILs reported here opens avenues for acquiring novel aurate salts with IL anions and AuNPs.

All printed soft actuators based on ionic liquid/polymer hybrid materials

Soft actuators are increasingly being required for a variety of application ranging from robotics to biomedicine. This work reports on the development of printable materials for soft actuator applications based on ionic liquids (ILs) and a fluorinated polymer, poly(vinylidene fluoride) (PVDF). ILs sharing the same cation 1‑butyl‑3-methylimidazolium, [Bmim]+ and different anions (tricyanomethanide, [C(CN3)]−, dicyanamide, [N(CN2)]− and thiocyanate, [SCN]−) were incorporated into the PVDF polymer matrix at 40% wt. and processed by direct writing printing technique.Rheological measurements of the IL/PVDF solutions allowed to stablish a correlation between shear stress and viscosity, being observed a shear thinning behavior. Independently of the IL anion, the inclusion ILs leads to variations in the sample morphology related to the formation of significantly smaller spherulites than in PVDF with well-defined borders and an increase of the electroactive β phase content and crystallinity degree of the polymer. The incorporation of the ILs into the PVDF matrix induces a mechanical plasticizing effect. A maximum ionic conductivity of 5.2 × 10−5 S/cm has been achieved for the [Bmim][N(CN2)]/PVDF composite. The potential of the developed printable materials as soft actuators has been experimentally demonstrated and theoretically evaluated, the highest displacement of 1.0 mm at an applied voltage of 4 Vpp being obtained for [Bmim][SCN]/PVDF. Finally, the implementation of an all printed micro gripper shows the potential of the materials for applications.

Selective adsorption of acidic gases from ternary mixture by acetate- and sulfonate-based ionic liquids at molecular level.

This paper attempts to elucidate the competitive adsorption mechanism of thin films of ionic liquids (ILs) on the surface of porous materials for acidic gases at a molecular level in order to design a proper material for the diminishment of gas emissions. Thin film 1-butyl-3-methylimidazalium ([BMIM]+) cation-based IL systems composed of four different anions such as [CH3CO2]- and [CF3CO2]- (acetate-based), and [CH3SO3]- and [CF3SO3]- (sulfonate-based) are created in contact with the gas phase containing ternary H2S/CO2/CH4:1/25/74 mixture. To define gas adsorption performance at gas-liquid interface and bulk liquid phase, classical molecular dynamics simulations are carried out. Adsorption of acidic gases is governed by the formation of an adsorbed gas layer on the surface of the ionic liquid based on thermodynamics aspects, and then the partial dissolution of gases in the bulk liquid phase is accompanied by the transport of gases. These behaviors are followed by several analysis methods in simulation approaches such as radial distribution function (RDF) of gases around specific atoms of ILs, lateral displacement of gas molecules, radial distance between gas and ILs, interaction energy between gases and ILs, and average number of hydrogen bonding between ions with and without adsorbed gases. Acetate-based ILs performed twice as good in CO2 adsorption capacity than sulfonate-based ILs. However, the one having -CF3 group in acetate-based ILs has short CO2 retention time and high CH4 adsorption capacity, diminishing the H2S+CO2/CH4 adsorption selectivity. High CO2 adsorption performance of acetate-based ILs is related to their strong anion-cation interaction and less hydrogen-bonding ability between cation tail and anion, which is the source for free space between anion and cation. Those with high adsorption capacities and long retention times are those that can ensure that CO2 molecules are coordinated in these free volumes between cation tails and anions. Therefore, here, the effect of different parameters on the CO2 and H2S adsorption over CH4 is revealed via atomistic design, and the importance of selection of suitable anions in IL for identifying potential nanocomposite adsorbent materials for acidic gas removal is highlighted.

Design of carboxylate-based ionic liquids (ILs) containing OH and CF3 groups; influence of intramolecular hydrogen bonds and inductive effect on the binding energy between the cation and anion of ILs, a DFT study

Ionic liquids, which are widely known as room temperature molten salts, have been the subject of much scientific debate for more than a decade.

Experimental and DFT calculation study of interaction between silver nanoparticle and 1-butyl-3-methyl imidazolium tetrafluoroborate ionic liquid

The mechanism of stabilization of silver nanoparticles (Ag NPs) by 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid (IL) is elucidated from experimental spectroscopic investigations and density functional theory (DFT) calculations. FTIR spectrum of the synthesized IL stabilized silver nanoparticles reveals small red shift in B–F stretching frequency while C–H stretching remains unshifted. There is no shift in NMR peaks of IL before and after the synthesis of IL stabilized Ag NPs. This suggests that Ag NPs are surrounded by anions of ILs. The optimized structure obtained from density functional theory (DFT) calculations also shows the anionic part of the IL surrounding the Ag nanocluster. This is supported by the IR frequency data calculated using DFT. The calculated binding energy and interaction energy obtained between cluster and IL is considerably attractive. Density of State (DOS) calculation shows that the HOMO-LUMO gap of the Ag cluster-IL composite is significantly lesser than that of the IL alone.

The keto-enol tautomerization of ethyl acetoacetate in choline ionic liquids: the role of cation and anion in switching the tautomeric equilibrium.

In this work, density functional theory (DFT) calculations were carried out to study the role of the explicit treatment of four different choline-based ionic liquids (CS, CP, NS, and NP) by utilizing two different cations and anions in the tautomeric equilibrium of ethyl acetoacetate (EAA). The involvement of the acidic N-H proton from the cationic part of NS and NP ionic liquid offers the possibility to have two more additional transition states for the tautomeric equilibrium of EAA. The computed results demonstrated that a high activation free energy barrier (ΔG = 49.4 kcal mol-1) is associated with the direct enol to keto (E → K) interconversion via a 4-membered ring transition state. Upon explicit involvement of the cationic part of ionic liquids in the tautomeric equilibrium via a 6-membered ring transition state (CAT), ΔG is substantially reduced to 21.88 kcal mol-1. Further, ΔG is drastically reduced to 10.57 kcal mol-1 upon the involvement of the anionic part of the ionic liquid explicitly via an 8-membered ring transition state (AAT). The W-shaped TS in the CAT pathway causes steric hindrance and increases the energy penalty, while the sickle-shaped TS in AAT facilitates easy proton transfer without the influence of the steric factor. In addition, the RDG scatter graphs predict large negative values of ρ*, which indicate that the hydrogen bonding network in AAT is stronger, enhancing the delocalization of the electron density. The QTAIM analysis substantiated the role of intermolecular hydrogen bonding interactions between the ionic liquid and EAA and within the anion-cation pair in stabilizing the keto group of EAA. Besides, the involvement of the acidic N-H proton in the transition state is the key factor in influencing the energetics of the keto-enol tautomerization reaction. The present study illustrates molecular-level insights into the role of individual ions of ionic liquids and also provides adequate ideas for designing novel ionic liquid-based catalysts for industrially relevant chemical reactions.

Anti-electrostatic hydrogen bonding between anions of ionic liquids: a density functional theory study.

Hydrogen bonds (HBs) play a crucial role in the physicochemical properties of ionic liquids (ILs). To date, HBs between cations and anions (Ca-An) or between cations (Ca-Ca) in ILs have been reported extensively. Here, we provided DFT evidence for the existence of HBs between anions (An-An) in the IL 1-(2-hydroxyethyl)-3-methylimidazolium 4-(2-hydroxyethyl)imidazolide [HEMIm][HEIm]. The thermodynamic stabilities of anionic, cationic, and H2O dimers together with ionic pairs were studied using potential energy scans. The results show that the cation-anion pair is the most stable one, while the HB in the anionic dimer possesses similar thermodynamic stability to the water dimer. The further geometric, spectral and electronic structure analyses demonstrate that the inter-anionic HB meets the general theoretical criteria of traditional HBs. The strength order of four HBs in complexes is cation-anion pair > H2O dimer ≈ cationic dimer > anionic dimer. The energy decomposition analysis indicates that induction and dispersion interactions are the crucial factors to overcome strong Coulomb repulsions, forming inter-anionic HBs. Finally, the presence of inter-anionic HBs in the ionic cluster has been confirmed by a global minimum search for a system containing two ionic pairs. Even though hydroxyl-functionalized cations are more likely to form HBs with anions, there are still inter-anionic HBs between hydroxyl groups in the low-lying structures. Our studies broaden the understanding of HBs in ionic liquids and support the recently proposed concept of anti-electrostatic HBs.

Understanding liquid-liquid equilibria in binary mixtures of hydrocarbons with a thermally robust perarylphosphonium-based ionic liquid.

Binary mixtures of hydrocarbons and a thermally robust ionic liquid (IL) incorporating a perarylphosphonium-based cation are investigated experimentally and computationally. Experimentally, it is seen that excess toluene added to the IL forms two distinct liquid phases, an “ion-rich” phase of fixed composition and a phase that is nearly pure toluene. Conversely, n-heptane is observed to be essentially immiscible in the neat IL. Molecular dynamics simulations capture both of these behaviours. Furthermore, the simulated composition of the toluene-rich IL phase is within 10% of the experimentally determined composition. Additional simulations are performed on the binary mixtures of the IL and ten other small hydrocarbons having mixed aromatic/aliphatic character. It is found that hydrocarbons with a predominant aliphatic character are largely immiscible with the IL, while those with a predominant aromatic character readily mix with the IL. A detailed analysis of the structure and energetic changes that occur on mixing reveals the nature of the ion-rich phase. The simulations show a bicontinuous phase with hydrocarbon uptake akin to absorption and swelling by a porous absorbent. Aromatic hydrocarbons are driven into the neat IL via dispersion forces with the IL cations and, to a lesser extent, the IL anions. The ion–ion network expands to accommodate the hydrocarbons, yet maintains a core connective structure. At a certain loading, this network becomes stretched to its limit. The energetic penalty associated with breaking the core connective network outweighs the gain from new hydrocarbon–IL interactions, leaving additional hydrocarbons in the neat phase. The spatially alternating charge of the expanded IL network is shown to interact favourably with the stacked aromatic subphase, something not possible for aliphatic hydrocarbons.

Insights into the translational and rotational dynamics of cations and anions in protic ionic liquids by means of NMR fast-field-cycling relaxometry.

Understanding the translational and rotational dynamics of cations and anions in hydrogen bonded protic ionic liquids (PIls) is still a challenge. In this study, we determine self-diffusion coefficients and rotational correlation times of both ions in triethylammonium based PILs by means of NMR Fast-Field-Cycling (FFC) relaxometry. Global fits of 1H and 19F nuclear magnetic relaxation dispersion (NMRD) curves allowed proper separation into intra and inter molecular relaxation rates for both NMR sensitive nuclei and thus a reliable description of translational and rotational motion for both ions individually. The diffusion coefficients of the cations are in the order of 6 × 10-11 m2 s-1 at room temperature and about 50 per cent larger than those of the anions. The diffusion coefficients of cations and anions in both PILs were compared with those we derived from applying an universal dispersion power law and those known from pulsed field gradient (PFG) NMR studies. Considering the Nernst-Einstein equation, molar conductivities were calculated from cationic and anionic diffusion coefficients and related to directly measured molar conductivities, allowing the determination of the degree of dissociation. The rotational correlation times τR ranging from 50 ps up to 2 ns as a function of temperature were compared with those obtained from high-field NMR quadrupolar relaxation time measurements addressing explicitly the rotation of the NH vector and giving insights into the acidic proton mobility. The Stokes-Einstein and Stokes-Einstein-Debye relations were applied to relate the diffusion coefficients and rotational correlation times to the macroscopic bulk viscosity. The results were also discussed with respect to the archetypical PIL ethylammonium nitrate.

Influence of adsorption of ionic liquid constituents on the stability of layered double hydroxide colloids.

The influence of ionic liquid (IL) anions and cations on the charging and aggregation properties of layered double hydroxide (LDH) nanoparticles was systematically studied. Surface charge characteristics were explored using zeta potential measurements, while aggregation processes were followed in dynamic light scattering experiments in aqueous IL solutions. The results revealed that the aggregation rates of LDHs were sensitive to the composition of ILs leading to IL-dependent critical coagulation concentration (CCC) values being obtained. The origin of the interparticle forces was found to be electrostatic, in line with the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, as the experimental aggregation kinetics were in good agreement with the predicted data. The ion specific adsorption of IL anions led to different surface charge densities for LDHs, which decreased in the order Cl- > Br- > DCA- > SCN- > NO3- for counterions and BMIM+ > BMPYR+ > BMPY+ > BMPIP+ in the case of coions resulting in weaker electrical double layer repulsion in these sequences. Since van der Waals forces are always present and their strength does not depend significantly on the ionic strength, the CCC values decreased in the above order. The present results shed light on the importance of the interfacial arrangement of the IL constituent ions on the colloidal stability of particle dispersions and provide important information on the design of stable or unstable particle-ionic liquid systems.

The combined action of cations and anions of ionic liquids modulates the formation and stability of G-quadruplex DNA.

G-Quadruplex (Gq) formation and stabilization by any molecule is an essential requirement for its application in therapy, especially in oncology. Metal cations have shown higher propensity of the formation of the Gq structure and its stabilization. In this study, the role of both cations and anions of ionic liquids (ILs) on the Gq formation of human telomere (hTeloG) and its stability was investigated using spectroscopic and molecular dynamics simulation techniques. Irrespective of the nature of anions of ILs, tetramethylguanidinium (TMG) cations associated with different anions can form an antiparallel Gq structure in hTeloG. However, the propensity of the formation of an antiparallel Gq structure and its stability depend on the chain length of anions of ILs. Gq is significantly less stable in ILs having longer hydrocarbon chain anions compared to the short chain anions suggesting that the hydrophobicity of the anion plays a critical role in the stability and formation of the Gq structure by ILs. The data indicate that longer hydrocarbon chain anions of ILs preferably interact in the loop region of Gq through hydrophobic interaction which enhances the overall binding of the cation of ILs with Gq causing a decrease in the stacking energy between the G-quartets as well as Hoogsteen hydrogen bonds between the guanine bases leading to the destabilization of the antiparallel Gq structure.

Electrochemical liquid-liquid interface between oil and ionic liquid for reductive deposition of metal nanostructures

Abstract An electrochemical system at the ionic liquid (IL) | oil (O) interface has been constructed and utilized as electrochemical reaction field for reductive deposition of metal nanostructures. The interface between 1-(3-hydroxypropyl)-3-methylimidazolium chloride (C3OHmimCl), a hydrophilic IL, and 1,6-dichlorohexane (containing an organic electrolyte) exhibits a polarized potential window of 150 mV, which is limited by the ion transfer (IT) of the IL cation and anion at the positive and negative edges, respectively. The polarizable IL | O interface has allowed to record voltammograms for the electron transfer (ET) and IT processes across the IL | O interface that are involved in the reductive deposition of gold at the IL | O interface. The ET between AuCl4− in the IL phase and decamethylferrocene in the O phase proceeds without applying external voltage by coupling with the IT of AuCl4−, spontaneously forming Au nanostructures at the IL | O interface.

A novel strategy to reduce the viscosity of cellulose-ionic liquid solution assisted by transition metal ions

The high viscosity of ionic liquids, even at relatively high temperatures, can greatly affect the production of cellulose fibers through the wet-spinning process. The high viscosity mainly by due to the hydrogen bond interaction between the cations and anions of ionic liquids. It is possible to reduce the viscosity by modulating the hydrogen bond interaction. In the present work, copper chloride (CuCl2) was dissolved in 1-butyl-3-methylimidazolium chloride ([Bmim]Cl)-cellulose solution, followed by the formation of a complex with the chloride anions by converting it to [CuCl4]2− anion. Through this strategy, the extrusion velocity of the solution improved, and the produced fibers obtained smoother surfaces and shrunken diameters.

Exploring the interaction of amino acid-based ionic liquids in water and organic solvents: Insight from MD simulations and QM calculations

Molecular dynamic (MD) simulations and quantum mechanics calculations were performed on 1-ethyl-3-methylimidazolium ([C2mim])-based ionic liquids having the amino acid anion. The corresponding mixtures with water, methanol, and chloroform were conducted to investigate the effect of interactions between the cation and anions of the amino acid ionic liquids (AAILs). The MD simulation results indicate that the interaction of the AAILs is affected by the mole ratio of chloroform, methanol, and water. The AAILs are accumulated with increasing the mole ratio of chloroform to 0.9. These results show that the strength of the interaction in AAILs increases in the presence of chloroform, which is gradually affected by the mole ratios higher than 0.5 in methanol and water. Therefore, the polarity and mole ratio of the solvent plays a major role in ion aggregation and cross complex formation of the AAILs. Density Functional Theory (DFT) calculations were performed to investigate the interaction of AAILs at M06-2X/6–311++G(d,p) level of theory. The obtained results indicate that the highest interaction energy between the cation and anion of the ILs belongs to the gas phase. Also, it is demonstrated that the interaction energy in methanol and water is lower than chloroform, which confirms that the structure of the AAILs is affected in the presence of the polar solvent. The natural bond orbital (NBO) and non-covalent interaction (NCI) analyses confirm that the H-bond formation is an important interaction between the ion pairs of the AAILs. Finally, MD simulations and DFT calculations are in good agreement with the experimental results.

Ionization of ionic liquids under laser desorption/ionization

Despite various studies of ILs as MALDI matrices, however, so far no relationship has been foundbetween the composition of ILs and their ability to serve as «good» matrices. For a preliminary experiment,in order to evaluate the characteristics of ILs before being used as a matrix in MALDI-MS, it is necessary tostudy the mass spectral behavior for the matrices themselves under LDI conditions. Therefore, the purpose of this work was to analyse ion liquids based on the cation imidazolium in combination with different types ofanions by the LDI method. Ionic liquids were synthesized in the Laboratory of catalytic processes for thesynthesis of organoelement compounds of G.K. Boreskov Institute of catalysis SB RAS (Novosibirsk). Itshould be noted that this ionic liquid was first synthesized in this Laboratory. Analyses were performed usinga Bruker UltraFlex II time of-flight mass spectrometer. Eleven ion liquids based on substituted cation imidazolium in combination with different types of anions were analysed by method laser desorption/ionization in the paper. In all mass spectra of ionic liquids obtained in the positive ion mode, cation produced a major peak and its fragmented ions. Homologous series characterized by the loss of the methyl group have been recorded. According to the more stable carbon-carbon or nitrogen bond in the heterocyclic system than in the carbon-carbon bond in the aliphatic, ion peaks are observed in the mass spectra, characteristic of the loss of methyl fragments from the aliphatic chain. In the LDI spectra obtained in the negative ion mode, the signals of the anions of ionic liquids and their fragments were observed. The combined use of the spectra obtained in positive and negative mode makes it possible to increase the reliability of identification. This makes it possible to use the revealed patterns of fragmentation for the structural analysis of ionic liquids. The analyzed ILs can be used as MALDI matrices, because they do not form dimers, assassinates, are characterized by the absence of adducts with metal ions, which is important for their further use as matrices. BMIMC6F5BF3 was first described by the LDI-MS method. It was shown that the observed fragmentation of the molecular ion of this IL is typical for most ILs with similar cations.

CO2 electroreduction on Cu Electrodes in Ionic Liquid-Containing Electrolytes

The CO2 level is increasing continuously in the atmosphere and causing environmental problems. Among the several methods which have been studied to mitigate the CO2 amount in the atmosphere, CO2 electroreduction (CO2ER) has attracted much attention. However, CO2 electroreduction is not efficient due to poor selectivity, high overpotential requirement and the presence of the parasitic hydrogen evolution reaction (HER). As a method to address these challenges, using ionic liquids (ILs) has been recently proposed due to their unique properties such as high CO2 absorption capacity. ILs can enhance CO2ER by making a complex with CO2 and stabilizing the intermediates on the surface. The properties of ILs are affected by several factors such as the nature of anion, cation, and functional groups. In this study, we have investigated the effect of anion in diluted IL/water mixtures on the product selectivity and activity of the copper catalysts.CO2ER was performed on electropolished Cu foils in electrolytes containing 0.1 M KHCO3 and 10 mM of an IL. A range of ILs with same cation (1-butyl-3-methylimidazolium ([BMIM]+)) and different anions (bis(trifluoromethylsulfonyl)imide ([NTF2]-), triflate ([OTF]-), dicyanamide ([DCA]-), acetate ([Ac]-), and chloride ([Cl]-)) were used. These ILs were chosen to cover different size, hydrophilicity and CO2 absorption ability. The catalytic activity was significantly impacted by adding ILs to the electrolyte. The cyclic voltammograms (CVs) in CO2-saturated electrolytes showed that by adding ILs (except for [BMIM][DCA]) to the buffer electrolyte, the onset potential shifted toward positive potentialswhich indicates the enhanced activity in the presence of ILs. Moreover, electrochemical impedance spectroscopy (EIS) showed that all ILs (except for [BMIM][DCA]) had alower charge transfer resistance compared to IL-free electrolyte at -0.92 V. Results also showed that ILs significantly affected the product selectivity. Faradaic efficiency (FE%) toward formate for all ILs increased (except for [BMIM][DCA]) compared to IL-free electrolyte. [BMIM][NTF2] showed the maximum FE% for formate (39%) at -0.92 V. This observation can be attributed to its high CO2 absorption capacity and high hydrophobicity which could attract more CO2 molecules to the surface. The results showed that adding ILs decreased the FE% toward the C2 products compared to IL-free electrolyte likely due to the presence of adsorbed [BMIM]+ cations on the surface which prevent CO2 molecules approach to each other and do dimerization. [BMIM][Ac] had the maximum FE% for CO (a 211% increase in FECO% compared to IL-free electrolyte at -1.02V) and C2 products (a 27% increase in FEC2% compared to IL-free electrolyte at -1.12V) compared to other ILs studied. It has been reported that [BMIM][Ac] can chemically react with CO2, where other ILs in this study were expected to have physical interaction with CO2. A completely different behavior was observed for [BMIM][DCA] in our study. [BMIM][DCA] had a very high activity and low charge transfer resistance in both N2- and CO2-saturate electrolytes. However, this activity was due to the enhanced HER not CO2ER. [BMIM][DCA] had the highest FE% for hydrogen and the lowest FEs for hydrocarbons.This is likely attributed to the high hydrophilicity and low CO2 absorption capacity of [BMIM][DCA] which can cause more water molecules to be attracted to the surface and enhance HER. X-ray photoelectron spectroscopy (XPS) for the Cu electrodes after CO2ER showed that ILs had a strong interaction with the electrode surface. This study showed how anions of imidazolium-based ILs affect the selectivity and activity in CO2 electroreduction.

(Invited) Soft Materials Containing Ionic Liquid As Solvent

Ionic liquids (ILs) are now being recognized as the third group of solvents, following water and organic solvents. They are easily available and possess unique properties such as nonvolatility, high thermal stability, and designability, which make it possible to use them on demand and under harsh conditions. Our study had been focused on understanding of the unique properties of ILs and on their utilization as neoteric solvents for innovative polymeric materials and devices1,2 that can help realize a sustainable society. ILs exhibit unique solubility toward polymers;1 this opens up a new field of intelligent materials chemistry. By utilizing the unique solubility, we have proposed soft materials containing ionic liquids, which we named “ion gels”.1,2 Ion gels are a novel platform for many applications such as electrolyte membranes for batteries3 and fuel cells,4 actuators,5 gas-separation membranes,6 and electric double layer transistors.7 Especially, due to the recent surge in flexible and wearable devices, highly durable ion gels have attracted much attention. In this lecture, I will address the recent advances in the development of ion gels that have healing functions against mechanical damages. As stimuli-responsive healing strategy, light- and thermally-induced healing of ion gels are discussed mainly based on block copolymer self-assenbly changes in ILs.8-10 Then, self-healable ion gels based on supramolecular11 and dynamic bond12 chemistry are addressed. By judicious designing of polymer nanostructures in ILs and interactions between polymer chains and IL cations and anions, tough, highly stretchable, and self-healable ion gels are recently demonstrated. References T. Ueki, T. M. Watanabe, Macromolecules, 41, 3739 (2008).Y. Kitazawa, K. Ueno, M. Watanabe, Chem. Record, 18, 391 (2018).Y. Kitazawa, K. Iwata, R. Kido, S. Imaizumi, S. Tsuzuki, W. Shinoda, K. Ueno, T. Mandai, H. Kokubo, K. Dokko, M. Watanabe, Chem. Mater., 30, 252 (2018).S.-Y. Lee, A. Ogawa, M. Kanno, H. Nakamoto, T. Yasuda, M. Watanabe, J. Am. Chem. Soc. 132, 9764 (2010).S. Imaizumi, H. Kokubo, M. Watanabe, Macromolecules, 45, 401 (2012).A. Ito, T. Yasuda, T. Yoshioka, A. Yoshida, X. Li, K. Hashimoto, K. Nagai, M. Shibayama, M. Watanabe, Macromolecules, 51, 7112 (2018).M. Matsumoto, S. Shimizu, R. Sotoike, M. Watanabe, Y. Iwasa, T. Aida, J. Am. Chem. Soc., 139, 16072 (2017).R. Tamate, K. Hashimoto, T. Ueki, M. Watanabe, Phys. Chem. Chem. Phys., 20, 25123 (2018).T. Ueki, R. Usui, Y. Kitazawa, T. Lodge, M. Watanabe, Macromolecules, 48, 5928 (2015).C. Wang, K. Hashimoto, R. Tamate, H. Kokubo, M. Watanabe, Angew. Chem. Int. Ed., 57, 227 (2018).A. Saruwatari, R. Tamate, H. Kokubo, M. Watanabe, Chem. Commun., 54, 13371 (2018).R. Tamate, K. Hashimoto, T. Horii, X. Li, M. Shibayama, M. Watanabe, Adv. Mater., 30, 1802792 (2018).