Imidazolium-based Ionic Liquids Research Articles

Curing kinetics effect on thermo-mechanical properties of an epoxy resin cured by imidazolium-based ionic liquid

Curing kinetics effect on thermo-mechanical properties of an epoxy resin cured by imidazolium-based ionic liquid

Imidazolium-based ionic liquids as proton reservoir for stable polyaniline cathode in zinc-iodine batteries

Aqueous zinc (Zn)-iodine (I2) batteries (ZIBs) are promising large-scale energy storage systems with high safety and low cost. However, the practical application of ZIBs is hindered by the dissolution of I3- ions, which leads to the shuttle effect and the loss of active iodine. Herein, we adopt an electrolyte modification strategy using two imidazolium-based ionic liquids (1-butyl-3-methylimidazolium iodide ([BMIM]I) and 1-ethyl-3-methylimidazolium iodide ([EMIM]I)) as electrolyte additives to restrain the dissolution of I3- ions and enhance the performance of ZIBs. To be specific, the imidazole rings in [BMIM]+ and [EMIM]+ can be used as the proton sources, promoting the conversion of imine to protonated amines –NH+= in the polyaniline and subsequent adsorption of I3- ions. Therefore, the dissolution of I3- ions and shuttle effect are prevented, facilitating the reaction kinetics of cathode. As a proof of concept, the ZIB using [BMIM]I and [EMIM]I as electrolyte additives demonstrates remarkable cycling performance (72.2 % capacity retention after 1000 cycles) at a high current density of 20 mA cm−2

Novel application of citric acid based natural deep eutectic solvent in drilling fluids for shale swelling prevention

Swelling of shale in clastic reservoirs poses a significant challenge, causing instability in wellbores. Utilizing water-based drilling mud with shale inhibitors is preferable for environmental reasons over oil-based mud. Ionic liquids (ILs) have garnered interest as shale inhibitors due to their customizable properties and strong electrostatic features. However, widely used imidazolium-based ILs in drilling fluids are found to be toxic, non-biodegradable, and expensive. Deep Eutectic Solvents (DES), considered a more economical and less toxic alternative to ILs, still fall short in terms of environmental sustainability. The latest advancement in this field introduces Natural Deep Eutectic Solvents (NADES), renowned for their genuine eco-friendliness. This study explores NADES formulated with citric acid (as a Hydrogen Bond Acceptor) and glycerine (as a Hydrogen Bond Donor) as additives in drilling fluids. The NADES based drilling mud was prepared according to API 13B-1 standards and their efficacy was compared with KCl, imidazolium based ionic liquid, and Choline Chloride: Urea-DES based mud. A thorough physicochemical characterization of the in-house prepared NADES is detailed. The research evaluates rheological, filtration and shale inhibition properties of the mud, demonstrating that NADES enhanced the yield point to plastic viscosity ratio (YP/PV), reduced mudcake thickness by 26%, and decreased filtrate volume by 30.1% at a 3% concentration. Notably, NADES achieved an impressive 49.14% inhibition of swelling and improved shale recovery by 86.36%. These outcomes are attributed to NADES’ ability to modify surface activity, zeta potential, and clay layer spacing which are discussed to understand the underlying mechanism. This sustainable drilling fluid promises to reshape the drilling industry by offering a non-toxic, cost-effective, and highly efficient alternative to conventional shale inhibitors, paving the way for environmentally conscious drilling practices.

Secondary electron emission measurements from imidazolium-based ionic liquids

Abstract The electron-induced secondary electron emission (SEE) yields of imidazolium-based ionic liquids are presented for primary electron beam energies between 30 and 1000 eV. These results are important for understanding plasma synthesis of nanoparticles in plasma discharges with an ionic liquid electrode. Due to their low vapor pressure and high conductivity, ionic liquids can produce metal nanoparticles in low-pressure plasmas through reduction of dissolved metal salts. In this work, the low vapor pressure of ionic liquids is exploited to directly measure SEE yields by bombarding the liquid with electrons and measuring the resulting currents. The ionic liquids studied are [BMIM][Ac], [EMIM][Ac], and [BMIM][BF4]. The SEE yields vary significantly over the energy range, with maximum yields of around 2 at 200 eV for [BMIM][Ac] and [EMIM][Ac], and 1.8 at 250 eV for [BMIM][BF4]. Molecular orbital calculations indicate that the acetate anion is the likely electron donor for [BMIM][Ac] and [EMIM][Ac], while in [BMIM][BF4], the electrons likely originate from the [BMIM]$^+$ cation. The differences in SEE yields are attributed to varying ionization potentials and molecular structures of the ionic liquids. These findings are essential for accurate modeling of plasma discharges and understanding SEE mechanisms in ionic liquids.

Development of an ionic liquid-based microextraction system (ILBME) for sensitive spectrophotometric analysis of neodymium(III) ions in environmental samples

ABSTRACT Introducing a precise, sensitive and simple system for determining neodymium(III) ions in aquatic samples could enhance the capabilities of routine instruments, particularly in terms of detection limits. Coupling a powerful preconcentration system, such as ionic liquid-based microextraction (ILBME), with a spectrophotometer can successfully achieve this goal. A sensitive and simple microextraction method based on a task-specific ionic liquid, designated [PDmim][Cl2], is described, in which the imidazolium-based ionic liquid served dual roles as both the chelating agent and the extraction phase. The ionic liquid was synthesized and characterized before being applied in microextraction procedure. The optimized microextraction results indicate that neodymium concentrations up to 5.10 µg L−1 can be successfully determined. The method characteristics, including the limit of detection (LOD), limit of quantification (LOQ), intra-day and inter-day relative standard deviations (RSDs), preconcentration factor (PF), enrichment factor (EF) and linear dynamic range (LDR), were found to be 1.53 µg L−1, 5.10 µg L−1, 3.83%, 4.44%, 123, 111.1 and 5.0–125.0 µg L−1, respectively. For method validation, the standard addition method using standard reference material (SRM) was employed, and the recovery range from real samples analyses was between 99.3% and 101.0%.

Wetting and interfacial behavior of imidazolium-based ionic liquids and water: A comprehensive review

Ionic liquids (ILs) have garnered considerable attention for their diverse applications, notably in controlling wettability on specific solid substrates, which holds ramifications for various processes reliant on interfacial behaviour encompassing adhesion and wetting. This review encompasses key advancements in IL wetting behavior and its implications. Factors such as drop size, temperature, alkyl chain structure, anion type, water concentration, and external electric fields influence the contact angle of ILs and their aqueous solutions. Despite challenges arising from IL property susceptibility to water content and wettability measurement sensitivity to solid surface, this review navigates the extent of IL wetting research, addressing line tension, surface tension measurement, and hydrogen bonding. The study aspires to furnish profound insights into IL wetting dynamics, informing IL-based fluidic technology design and elucidating intricate static and dynamic wetting attributes in analogous complex fluids.

Structural design and performance correlation of porous Poly(ionic liquid)S for 2-bromophenol adsorption

The demand for bromophenol is on the rise, driven by its extensive applications in industries, including human medicine. This surge in demand has spurred the development of eco-friendly methods for bromophenol recovery and the synthesis of new, low-toxicity compounds. In our study, we prepared a novel poly(ionic liquid) (PIL) featuring a benzene ring. The synthesis of this PIL involved using benzyl alcohol as the primary crosslinking agent, dimethoxymethane as an auxiliary crosslinking agent, and an imidazolium-based ionic liquid monomer, [Dimbb]Cl₂, for the adsorption of 2-bromophenol from aqueous solutions. We designed the PIL to be a high-performance and sustainable adsorbent by optimizing its specific surface area and pore structure. Structural analysis revealed that the PILs have a highly rich micro-mesoporous structure. The adsorption kinetics conformed to pseudo-second-order kinetics, reaching equilibrium in just 6 min. According to the Langmuir model, PIL-1 demonstrated a remarkable maximum adsorption capacity of 434.71 mg/g for 2-bromophenol. Quantum chemical calculations suggested that the adsorption mechanism involves processes such as pore filling, hydrogen bonding, electrostatic interactions, and π-π interactions. Furthermore, the adsorbent can be effectively recovered at least five times using anhydrous ethanol as the desorption agent, while maintaining an adsorption efficiency exceeding 90 %.

Molecular insight into the dissolution-degradation process of cellulose bunch in ionic liquids

Ionic liquids (ILs) as green solvents have been utilized in dissolving cellulose and fabricating regenerated cellulose fibers. Imidazolium-based ILs with acetate or phosphate anions present advantage, due to the low viscosity and melting point, as well as its excellent ability to form hydrogen bonds (H-bonds) with the hydroxyl groups of cellulose chains. In this work, the microscopic dissolution processes of a cellulose bunch in four ILs were reproduced via molecular dynamics (MD) simulations. The cellulose bunch dissolution capabilities of these four ILs are [Emim][OAc] > [Emim][DMP] > [Emim][DEP] > [Bmim][DMP], as verified through in-situ polarized optical microscope. It is important to note that cellulose may degrade in some ILs during dissolution, affecting the performance of regenerated cellulose, while the underlying mechanism is unclear, and the strength of H-bonds formed between ILs and cellulose chains can reflect their degradation strength Combined with density functional theory (DFT) calculations, the H-bonds formed between different anions and cellulose hydroxyl groups were analyzed in depth and the order of H-bond strength is [OAc]− > [DEP]− > [DMP]−, which is different from the dissolution order of cellulose bunch in [Emim][DEP] and [Emim][DMP]. Further analysis revealed that the difference in diffusion coefficients leads to faster dissolution of cellulose in [Emim][DMP]. This study elucidates the dissolution and degradation processes of cellulose in ILs at the molecular level, offering theoretical insights crucial for the development of novel ILs that are efficient in the process of cellulose spinning.

Optimizing Environmentally-Friendly oil Recovery: Synergies of Imidazolium-Based ionic liquids and carboxymethylcellulose hydrogels

This research focuses on the combined effectiveness of imidazolium-based ionic liquids (ILs) with triflate anion and carboxymethylcellulose-based hydrogels (CBHs) for environmentally friendly oil recovery. The selection of ILs was based on a review of existing literature, and their performance in extreme reservoir conditions was evaluated by studying parameters like concentration, salinity, temperature, and alkyl chain length. A new material,ionic liquid based CBH (CBHIL), was synthesized by incorporating ILs into hydrogels, and its structure was analyzed using various tests including FTIR, TGA, rheology, and SEM morphology tests. To evaluate the performance in EOR processes, particularly in carbonate rocks, a multilayer glass micromodel with permeabilities was designed. The objective was to determine the water-absorbing capacity, equilibrium swelling, and contact angle change, ultimately leading to increased oil recovery. The results indicated that 1-hexyl-3-methylimidazolium triflate (IL6) was able to reduce interfacial tension (IFT) to a minimum of 6.5 mN/m, surpassing 1-butyl-3-methylimidazolium triflate (IL4), especially at high temperatures and salinity. The emulsion stability of IL6 in the oil phase was also confirmed. CBH was used as a carrier for ILs, exhibiting thermal resistance up to 120 °C. Its porous structure and significant equilibrium swelling of up to 1550 % under harsh reservoir conditions were observed. By incorporating IL in the CBHIL-C6 structure, the linear viscoelastic range of CBH increased from 52.2 % to 170 % strain, and effectively altered carbonate rocks to become completely water-wet, reducing the contact angle from 115.4° to 44.62°. The combination of these two substances led to a maximum recovery of 79.85 % of the original oil in place, a significantly superior outcome compared to separate injection of the substances. Thus, these new compounds demonstrate promising potential for EOR applications in challenging reservoir conditions.

Molecular dynamics study on effects of the synergistic effect of anions and cations on the dissolution of cellulose in ionic liquids

This work systematically explores the interaction between cellulose and various ionic liquids (ILs) formed by the pairing of glycine cations with diverse anions. Results show that the interaction of anions with cellulose decreases in the order of [CH3COO]− > [Im]− > [SCN]− > Cl− > [PF6]−, differing from imidazole-based ionic liquids. The synergistic effect of anions and cations is crucial for cellulose dissolution. Moreover, the electronegativity of anions can enhance their interaction with cellulose. Short alkyl chains (n = 1, 3, 5) reduce hydrogen bonding due to steric hindrance, while longer chains (n = 9) promote diffusion and hydrogen bond formation. The introduction of electron-withdrawing groups to anions weakens their interaction with cellulose, while marginally strengthening the association between cations and cellulose. Overall, a delicate balance among anion-cation-cellulose interactions is essential for effective cellulose dissolution. The obtained results are anticipated to be of significant importance in the rational design of innovative amino acid-based ionic liquids, aiming to achieve efficient cellulose dissolution.

Emission based response of Er3+, Tb3+, and Er3+-Tb3+ co-doped 1393 bioactive glasses along with HPTS towards CO2

The HPTS serves as a versatile tool in pH and CO2 sensing studies, as well as in cell biology studies of various processes. However, the long-term photostability of HPTS as a fluorescent dye is an important consideration in its use, especially for long-term applications. In this work, sol–gel synthesized Er3+, Tb3+ and Er3+: Tb3+ co-doped 1393 bioactive glass particles were incorporated with the HPTS in the presence of ionic liquid in an ethyl cellulose matrix. The interaction of the bioactive glasses with the HPTS was investigated by steady-state luminescence and excited-state lifetime measurements. The prepared composites showed linearizable responses when exposed to different CO2 concentrations. High I0/I100 values (87, 109 and 115) were obtained for the binary blends of HPTS and bioactive glasses. When the imidazolium-based IL was used together with the offered composites, we observed improved stability and longevity for the HPTS up to 315 days. The incorporation of imidazolium-based ionic liquids as additives in HPTS-based fluorescence assays together with the bioactive glasses holds promise for enhancing the photostability of the HPTS and improving the reliability and longevity of fluorescence signals in various research applications.

Design and Characterization of Epoxy Resin Systems Based on Mixtures of Imidazolium-Based Ionic Liquids with Docusate and Dicyanamide Anions

This study focuses on the synthesis, characterization, and application of four ionic liquids (ILs), three of which are being reported for the first time, with unique thermal properties and diverse anion-cation combinations, specifically in the context of epoxy resin polymerization. 1-3-Didodecylimidazolium dicyanamide (dDDIM DCA), 1-3-Didodecylimidazolium docusate (dDDIM DOSS), 1-ethyl-3-methylimidazolium dicyanamide (EMIM DCA), and 1-ethyl-3-methylimidazolium docusate (EMIM DOSS) were used to prepare six different mixtures with the same cation and with varying concentrations of DCA components, which is the main factor of an efficient polymerization, while the other component is intended to modify the properties of the cured resin. Mixtures based on EMIM cation demonstrated increased enthalpy and lower onset polymerization temperatures, indicating more efficient curing processes. The hardness of cured epoxy resins can be adjusted by altering the curing temperature and IL composition, with EMIM DCA and EMIM DOSS mixtures displaying high Shore A hardness, suitable for durable surface applications. In contrast, mixtures with higher dDDIM DCA proportions offered a balance between rigidity and flexibility, ideal for applications requiring both mechanical strength and elasticity.

Influence of imidazole-based ionic liquid surfactants on the wetting effect of long-flame coals

In order to study the wetting effect of C12MImBF4, C12MImBr and C12MImCl on long-flame coal, and their mechanism of action on coal-water bonding, physical experiments, molecular dynamics simulation and DFT theoretical calculation were combined in this work. It is confirmed that the imidazole ionic liquid surfactant optimizes the wetting effect by forming hydrogen bonds, reducing the surface tension of water, and increasing the number of free hydroxyl groups in coal. After the wettability test, the concentration of 4 g/L of the three ionic liquid surfactants had the best wetting effect on long-flame coal, and the contact angle at this concentration was reduced by more than 40 % compared with water within 0.2 s after dripping on the coal. Due to the difference in the anionic head group of the three surfactants, there are differences in the number and strength of hydrogen bonds formed between the three surfactants and water molecules, the results of wettability C12MImBF4 > C12MImCl > C12MImBr were presented. Combined with these characteristics of imidazole ionic liquids on long-flame coal, the reasonable application in the wet dust removal process of actual coal mine production can optimize the efficiency of droplet capture of coal particles, so as to effectively improve the dust removal capacity.

An electrochemical and theoretical approach towards the efficient microwave synthesis of imidazolium-based ionic liquids for unprecedented mild steel corrosion inhibition in 0.5 M H2SO4 solution

The inhibition potential of newly synthesized imidazolium-based ionic liquids (IL-1 and IL-2) on mild steel corrosion in a 0.5 M H2SO4 solution has been comprehensively investigated using gravimetric analysis, potentiodynamic polarization, and electrochemical impedance spectroscopy across various temperatures. Gravimetric analysis indicated that the adsorption of these inhibitors adhered to the Langmuir adsorption isotherm. Significantly, IL-2, featuring a longer alkyl chain, demonstrated superior inhibition efficiency (92.51 % at 303 K) compared to IL-1 (88.71 % at 303 K). Potentiodynamic polarization studies revealed a mixed-type inhibitory behavior, impacting both anodic and cathodic reactions. Surface morphological analyses via SEM and EDX confirmed the formation of a protective film on the mild steel surfaces, substantiating the corrosion inhibition capabilities of IL-1 and IL-2. The novelty of this research lies in the application of density functional theory (DFT) using the B3LYP method, which elucidated that the alkyl chain length at the N-3 position in imidazolium cation-based ionic liquids significantly enhances their inhibition potential. This mechanistic insight suggests that these ionic liquids effectively obstruct both anodic and cathodic sites, providing robust corrosion protection in a 0.5 M H2SO4 solution.

Formation of Uranyl Peroxide Compounds via Dissolution of Studtite, [(UO2)(O2)(H2O)2](H2O)2, in Ionic Liquids.

Four uranyl peroxide compounds with novel structures were formed following the dissolution of studtite, [(UO2)(O2)(H2O)2](H2O)2, in imidazolium-based ionic liquids. The compounds were characterized using single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), Raman and infrared (IR) spectroscopy, and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). The ionic liquids used in the experiments were 1-ethyl-3-methylimidazolium (EMIm) diethyl phosphate, EMIm ethyl sulfate, and EMIm acetate. Each of the four uranyl peroxide compounds contain components from the ionic liquids as terminal ligands on uranyl peroxide molecular units, bridging ligands in uranyl peroxide sheet structures, or charge balancing cations located in the interstitial space. The studtite dissolved in and reacted with the ionic liquids, producing unique crystal structures depending on the anionic component of the ionic liquid, the temperature at which the synthesis was performed, and the introduction of additional ionic species into the solution. This is the first report of studtite dissolving in and reacting with ionic liquids to form uranyl peroxide compounds, which has the potential to vastly increase the number of synthetic routes for the formation of uranyl peroxide clusters and uranyl peroxide cage clusters.

Using Diglycolamide Extractants in an Imidazolium-Based Ionic Liquid for Rare Earth Element Extraction and Recovery.

Growing demands for rare earth elements (REEs) have prompted sustainability concerns worldwide. Given the need for sustainable extraction methods amidst REEs, ionic liquids (ILs) have been investigated as tunable extraction substitutes for conventional organic solvents, offering negligible volatility and diverse physical and chemical properties. Recent reports have shown that the introduction of extractants, like N,N,N',N'-tetraoctyldiglycolamide (TODGA) or N,N-dioctyldiglycolamic acid (DODGAA), into ILs can provide high selectivity and affinity for REE capture. Precipitate formation has been observed in IL-extractant systems across several studies; however, the molecular interactions that drive this phenomenon have yet to be explored. This study investigates the coordination environment in the precipitate formed between [Yb3+], DODGAA, and the 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM+][PF6 -]) IL. The composition of the precipitate was confirmed using several spectroscopic techniques and revealed an underlying hydrogen bonding interaction between the fluorine atom of [PF6 -] anion and -OH of the Yb-DODGAA complex. Computational studies were also conducted to examine the coordination environment of the Yb-TODGA and Yb-DODGAA complexes. The binding affinity of the extractants toward [Yb3+] is analyzed by calculating the associated binding energy values. The results clearly show a stronger binding affinity of the extractants toward [Yb3+], supporting the observed high extraction efficiencies of DODGAA and TODGA.

Prediction of solubility of CO2, H2S, and their mixture in ionic liquids using the Cubic Two State equation of state

In this work, the capability of the Cubic Two State (CTS) equation of state (EoS) has been evaluated using the solubility of carbon dioxide (CO2), hydrogen sulfide (H2S), and their mixture in ionic liquids (ILs). The imidazolium-based ILs with [BF4], [PF6], and [Tf2N] anions have been studied. The self-association between IL molecules, CO2, and H2S molecules has been considered to optimize the pure model parameters. In addition to self-association between similar molecules, the cross-association between CO2-IL and H2S-IL in the binary mixtures has been considered. The results show that the CTS EoS can predict (kij=0.0) the solubility of H2S and CO2 in ILs ranging from 1 to 1000 bar satisfactory. The average ARD value for binary CO2-IL and H2S-IL systems has been obtained 20.3 % and 9.02, respectively. The CTS model has been used to predict the phase behavior of ternary systems containing CO2H2S-[C4mim][PF6], CO2H2S-[C8mim][PF6], and CO2H2S-[C8mim][Tf2N] at various temperatures. Finally, the CTS results have been compared to soft-SAFT and PC-SAFT EoSs. The results show that simple association contribution and the cubic term of the CTS EoS can model the molecular interactions between gases and ILs satisfactory. The CTS model can be considered as a robust and efficient thermodynamic model for the prediction of separation of CO2 and H2S using ILs.

Factorial Analysis and Thermal Kinetics of Chemical Recycling of Poly(ethylene terephthalate) Aided by Neoteric Imidazolium-Based Ionic Liquids.

Poly(ethylene terephthalate) (PET) waste accumulation poses significant environmental challenges due to its persistent nature and current management limitations. This study explores the effectiveness of imidazolium-based neoteric solvents [Emim][OAc] and [Bmim][OAc] as catalytic co-solvents in the glycolysis of PET with ethylene glycol (EG). Reaction thermal kinetics showed that both ionic liquids (ILs) significantly enhanced the depolymerization rate of PET compared to traditional methods. The use of [Emim][OAc] offered a lower activation energy of 88.69 kJ·mol-1, thus making the process more energy-efficient. The contribution of key process parameters, including temperature (T), plastic-to-ionic liquid (P/IL) mass ratio, and plastic-to-solvent (P/S) mass ratio, were evaluated by means of a factorial analysis and optimized to achieve the maximum PET conversion for both neoteric solvents. The relevance sequence for both ionic liquids involved the linear factors T and P/S, followed by the interaction factors T×P/S and T×P/IL, with P/IL being the less significant parameter. The optimal conditions, with a predicted conversion of 100%, involved a temperature of 190 °C, with a P/IL of 1:1 and a P/S of 1:2.5, regardless of the IL used as the catalytic co-solvent.

Advancements in Ti3C2Tx MXene Stability: Synergistic Antioxidant Strategies and Their Impact on Long-Lasting Flexible Sensors.

Two-dimensional (2D) transition metal carbides (Ti3C2Tx MXene) have demonstrated substantial application potential across various fields, owing to their excellent metallic conductivity and solution processability. However, the rapid oxidation of Ti3C2Tx in aqueous environments, leading to a loss of stability within mere days, poses a significant obstacle for its practical applications. Herein, we introduce an antioxidant strategy that combines free radical scavenging with surface passivation, culminating in the design and synthesis of imidazolium-based ionic liquids (ILs) incorporating siloxane groups. By deploying a straightforward hydrolysis-addition reaction, we successfully fabricated IL-modified Ti3C2Tx materials (Ti3C2Tx-IL). The Ti3C2Tx -IL not only displayed exceptional conductivity exceeding 3.85 × 104 S/m and hydrophilic contact angles below 45° but also showcased its superior chemical stability and antioxidation mechanisms through various analyses, including visual color change experiments, spectroscopic and energy spectrum characterization, free radical scavenging tests, and density-functional-theory-based molecular simulations. Furthermore, when utilized as a conductive filler in the fabrication of a poly(vinyl alcohol)/nanocellulose fiber (PVA/CNF) composite hydrogel (PCMIL), the resultant sensors exhibited remarkable mechanical performance with up to 535% strain, 1.59 MPa strength, 4.35 MJ/m3 toughness, and a conductivity of 3.40 mS/cm, as well as a high sensitivity gauge factor of 3.3. Importantly, even after 45 days of storage, the PCMIL retained most of its functionalities, demonstrating superior performance in human-machine interaction applications compared to hydrogels made from unmodified Ti3C2Tx. This research establishes a robust antioxidant protection strategy for Ti3C2Tx, offering substantial technical reinforcement for its prospective applications in the realm of flexible electronics and sensing technologies.

Effects of Heterogeneous Mixing of Imidazolium-Based Ionic Liquids with Alcohols on Complex Formation of Ni(II) Ion.

Understanding the complex formation of metal ions in room-temperature ionic liquids (ILs) is essential for the application of ILs in solvent extraction. Nevertheless, the research on metal complex formation in ILs lags behind other applications. The complex formation equilibria may be influenced by specific interactions among the metal ion, ligand molecule, and IL cation and anion. In the present investigation, the complex formation of Ni2+ with ethanol (EtOH) and methanol (MeOH) molecules in ILs, 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([CNmim][TFSA], where N represents the alkyl chain lengths of 2 and 8) was discussed in terms of the microscopic interactions among alcohol molecules, [CNmim]+ and [TFSA]-, and the mesoscopic mixing states of alcohols in [CNmim][TFSA], with N = 2-12. The microscopic interaction of alcohol molecules with the imidazolium ring H atoms in the ILs was evaluated by using ATR-IR and 1H and 13C NMR spectroscopies. The self-hydrogen bonding of alcohol molecules was clarified from the O-H stretching vibration of alcohol molecules. MeOH molecules can be more strongly hydrogen-bonded with themselves than EtOH molecules due to the less steric hindrance and the weaker dispersion force of MeOH with the IL cation's alkyl chain. In fact, small-angle neutron scattering (SANS) experiments revealed the more heterogeneous mixing of MeOH with the ILs by the self-hydrogen bonding among MeOH molecules than EtOH. The longer the IL cation's alkyl chain, the more the MeOH clusters significantly form. In contrast, the formation of EtOH clusters becomes weaker with elongating the alkyl chain. Ultraviolet (UV)-visible spectroscopic measurements on Ni2+-[CNmim][TFSA]-alcohol solutions with N = 2 and 8 revealed that di-, tetra-, and hexa-alcohol-Ni2+ complexes are formed in both the ILs. With N = 2, the stabilities of Ni2+-EtOH and Ni2+-MeOH complexes are comparable in the IL. However, with N = 8, the complexes are more stable in the EtOH solutions than in the MeOH solutions. This is because the less heterogeneous mixing of EtOH molecules with the IL results in the larger enthalpic contribution in the complex formation, as shown by the thermodynamic parameters estimated by the van't Hoff plots on the stability constants at several temperatures.