Conventional Ionic Liquids Research Articles

Aluminum-Ion Electrolytes with Weakly Coordinating Anions

The conventional chloroaluminate ionic liquid electrolytes for rechargeable aluminum (Al) batteries are challenged by intrinsic limitations including corrosivity and poor chemical stability due to the active chloride content. Here, we report the first synthesis and characterizations of an Al “simple salt” electrolyte composed of aluminum hexafluorophosphate (Al(PF6)3) in dimethyl sulfoxide (DMSO). Al(PF6)3 salt was synthesized via the reaction between triethylaluminium (Et3Al) and ammonium hexafluorophosphate, and purified via recrystallization. The single crystal X-ray diffraction reveals that the Al3+ cation is solvated with six DMSO molecules (Al(DMSO)6(PF6)3) in the salt crystal structure. The 0.25 M Al(PF6)3 solution in DMSO demonstrates high ionic conductivity at approximately 1.3×10-2 S cm-1. With characterizations including nuclear magnetic resonance spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy (XPS), we demonstrate the reversibility of Al deposition-stripping in the electrolyte, which can be improved by the addition of trace amount of Et3Al as the electrolyte additive. The side reaction involving the reductive decomposition of DMSO to form aluminum oxide during Al deposition is identified by a combination of XPS and gas chromatography/electron ionization-mass spectrometry. Another Al-ion electrolyte with weakly coordinating tetrakis(hexafluoroisopropyloxy) borate ((B[hfip]4)-) anion in DME was also synthesized and characterized. These Al-ion electrolytes with weakly coordinating anions exhibit distinct chemical and electrochemical properties comparing with chloroaluminate ionic liquid electrolytes. They create an opportunity to develop new Al electrolyte system.

Highly Efficient and Reversible Absorption and Oxidation of Low-Concentration Nitric Oxide by Functionalized Ionic Liquids

A novel method of using anion-functionalized ionic liquids (ILs) with high NO absorption capacity and reversibility for the capture and in situ oxidation of low-concentration NO was established. For the mixed gas containing 0.25% NO, the accumulation rate of nitric acid in these ILs was significantly higher than that in the conventional ILs; after absorption and oxidation reached equilibrium, the molar ratio of HNO₃ to [P₄₄₄₆][PhSO₃] was 0.86, which was 5 times as high as that of the conventional IL. Therefore, the problems of low efficiency and poor reversibility of traditional ILs in the absorption and oxidation process were solved. Through absorption and oxidation experiments, quantum chemical calculation, NMR, and time-resolved in situ ATR-FTIR spectroscopic investigation, the results demonstrated that such a high accumulation rate of HNO₃ originated from high uptake of NO through multiple-site interaction. Moreover, high reversibility is attributed to low volatility of conjugated acid of anions and decreased basicity of O sites on anions. We believe that such highly efficient and reversible conversion of low-concentration NO to HNO₃ by ILs provides a new strategy for improving atomic economy of fossil fuel combustion, that is, converting post-combustion pollutants to good valuable chemicals.

Ionic Liquid Mediated Decoration of Pt Nanoparticles on Graphene and Its Electrocatalytic Characteristics

In most of the conventional ionic liquid (IL) or poly-ionic liquid (PIL) mediated Pt carbon catalyst preparations, IL or PIL are covalently linked to the carbon involving complex reaction procedures. IL or PIL acts as the interface between Pt and carbon which increases the internal resistance of the material resulting in high overpotentials for electrocatalysis. In this regard we present a novel methodology to ionically tag IL to graphene that can easily be removed during the chemical reduction procedure for Pt decoration. We successfully prepared platinum nanparticles decorated on ionic liquid treated graphene (Pt-TMIm-rGO) material using a simple and scalable preparation method and systematically characterized. To understand the electrocatalytic efficiency of the material prepared, oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) characterization were studied and benchmarked with commercial counterparts. X-ray photoelectron spectroscopy results revealed a modulation of d-band centre of Pt and strong metal substrate interaction that reduced the over potential and increased durability. Pt-TMIm-rGO showed very high mass activity, low over potential compared to its counterparts in both ORR and MOR catalytic reactions. Pt-TMIm-rGO showed a high mass activity of ∼346 A g−1 at 0.9 V vs RHE in the case of ORR and 195.2 mA g−1 in case of MOR at 0.86 V vs RHE.

A Zn−Ce Redox Flow Battery with Ethaline Deep Eutectic Solvent

Compared with conventional aqueous and ionic liquid electrolytes, deep eutectic solvent (DES) are considered as electrolyte for redox flow batteries because they have a wider electrochemical window and relatively low price. In this study, CeIV /CeIII and ZnII /Zn redox couples are used as the positive and negative active materials, respectively, in an electrolyte consisting of choline chloride ethylene glycol (ethaline). The structure of CeIII in the positive electrolyte is inferred through spectrum detection. CeIV /CeIII and ZnII /Zn redox couples show a stable potential difference of 2.2 V (vs. Ag) through cyclic voltammetry. The charge and discharge performance of battery was tested at different current densities. In addition, battery performance was evaluated at different temperatures and concentrations of cerium in the electrolyte. Consequently, at a current density of 0.5 mA cm-2 at room temperature and using 1.0 m CeIII , the battery performance reaches the best coulombic efficiency of 84 %.

Ionic polymer–metal composite actuators driven by methylammonium formate for high-voltage and long-term operation

Ionic liquids (ILs) have been exploited as the internal solvent in the development of ionic polymer–metal composite (IPMC) actuators capable of long-term operation. However, a major issue is that most IPMCs impregnated with conventional ILs are yet to be practically applied due to insufficient actuation performance. Herein, methylammonium formate (MAF), an IL with low viscosity, small ionic size, high ionic conductivity, and excellent electrochemical stability, is introduced as a new internal solvent for IPMCs to achieve both excellent operation characteristics and long-term stability. The actuation characteristics of a series of IPMCs impregnated with four types of ILs, including MAF, were analyzed. The MAF-based IPMCs had more than twice the displacement and three-fold higher blocking forces compared with other IL-based IPMCs. Moreover, unlike conventional water-driven IPMCs, the MAF-driven IPMCs operated even at high voltages (4V) without solvent loss and electrolysis. Their initial displacement remained above 81% even after operating for 2160 cycles (6h). This simple change of media in IPMC actuators is expected to advance the design of IPMCs with improved displacement, force generation, and stability.

Physical, thermal and structural properties of 1ChCl: 2 Urea based ionic liquids

Fourth generation of ionic liquids, relatively cheaper and environmental friendly, is called deep eutectic solvents (DESs). Generally, at present time are extensively recognized as novel remarkable as well as green alternative solvents to the conventional ionic liquids owing to their low cost and tolerance to moisture. DESs first came to the public vision in 2001, since then, researches and applications of deep eutectic solvents can cover, almost, all of the fields of science. In this study the physical, thermal and structural properties of 1ChCl: 2Urea based ionic liquids is reported. Firstly, the physical properties, in terms of viscosity, conductivity and density as a function of temperature are investigated intensively. Later, the microscopic structure of 1ChCl: 2Urea is studied by means of FTIR spectroscopy. Finally, the thermal properties, in terms of melting temperature and thermal stability, are also reported in this investigation. Overall, the obtained data and inspections are in an excellent agreement with the previous studies.

Synergistic Deep Eutectic Solvents for Lithium Extraction

Hydrophobic deep eutectic solvents (DESs) have attracted much attention as sustainable extraction media for various metals. However, in previously developed DESs, only one DES component is involved in metal complex formation, which has limited their extraction performance and selectivity. Here, we propose a novel synergistic DES concept for improving the performance of environmentally benign liquid–liquid extraction of lithium (Li). Two different conventional extractants, a beta-diketone and a neutral extractant, were effective for creating the synergistic DESs. When the two extractants were mixed, they formed a liquid DES. DESs have much lower viscosity than conventional hydrophobic ionic liquids. The Conductor-like Screening Model for Real Solvents method was used to estimate the formation of DESs with the melting point depressed by the intermolecular interaction between their components. The extraction performance of Li was greatly enhanced with the synergistic DESs. The extraction capacity of Li reached 4.4 g/L using the optimum DES combination because it was solvent-free and highly concentrated. Using the optimum DES, highly selective recovery of Li over Na and K was demonstrated with a model brine solution. This is the first report of efficient and selective extraction of Li with DES-based liquid–liquid extraction.

Multi-Interactions in Ionic Liquids for Natural Product Extraction.

Natural products with a variety of pharmacological effects are important sources for commercial drugs, and it is very crucial to develop effective techniques to selectively extract and isolate bioactive natural components from the plants against the background of sustainable development. Ionic liquids (ILs) are a kind of designable material with unique physicochemical properties, including good thermal stability, negligible vapor pressure, good solvation ability, etc. ILs have already been used in pharmaceuticals for extraction, purification, drug delivery, etc. It has been reported that multi-interactions, like hydrogen bonding, hydrophobic interactions, play important roles in the extraction of bioactive components from the plants. In this review, recent progress in the understanding of scientific essence of hydrogen bonding, the special interaction, in ILs was summarized. The extraction of various natural products, one important area in pharmaceutical, by conventional and functional ILs as well as the specific roles of multi-interactions in this process were also reviewed. Moreover, problems existing in bioactive compound extraction by ILs and the future developing trends of this area are given, which might be helpful for scientists, especially beginners, in this field.

Computational Screening of the Physical Properties of Water‐in‐Salt Electrolytes**

AbstractWater‐in‐salts form a new family of electrolytes with properties distinct from the ones of conventional aqueous systems and ionic liquids. They are currently investigated for Li‐ion batteries and supercapacitors applications, but to date most of the focus was put on the system based on the LiTFSI salt. Here we study the structure and the dynamics of a series of water‐in‐salts with different anions. They have a similar parent structure but they vary systematically through their symmetric/asymmetric feature and the length of the fluorocarbonated chains. The simulations allow to determine their tendency to nanosegregate, as well as their transport properties (viscosity, ionic conductivity, diffusion coefficients) and the amount of free water, providing useful data for potential applications in energy storage devices.

Ionic thermoelectric materials for waste heat harvesting

Ionic thermoelectric polymers are a new class of materials with great potential for use in low-grade waste heat harvesting and the field has seen much progress during the recent years. In this work, we briefly review the working mechanism of such materials, the main advances in the field and the main criteria for performance comparison. We examine two types of polymer-based ionic thermoelectric materials: ionic conductive polymer and ionogels. Moreover, as a comparison, we also examine the more conventional ionic liquid electrolytes. Their performance, possible directions of improvements and potential applications have been evaluated.

Highly Luminescent 4H-1,2,4-Triazole Derivatives: Synthesis, Molecular Structure and Photophysical Properties.

An alternative approach to the Suzuki cross-coupling reaction is used to synthesize a series of new luminophores based on 4-alkyl-4H-1,2,4-triazole cores conjugated via 1,4-phenylene linker to fused-bicyclic and tricyclic aromatic, or heteroaromatic arrangements. The described methodology allows one to conduct the coupling reaction with the use of commercially available boronic acids in the presence of conventional solvents or ionic liquids and produced excellent yields. It was found that the use of ultrasounds or microwaves significantly accelerates the reaction. The obtained compounds exhibited high luminescent properties and a large quantum yield of emitted photons. The X-ray molecular structures of three highly conjugated 4H-1,2,4-triazole representatives are also presented.

Simulation study of deep eutectic solvent-based biogas upgrading process integrated with single mixed refrigerant biomethane liquefaction

Deep eutectic solvents (DESs) comprise ChCl/urea, in combination with water, have been considered in removing acid gases (CO2 and H2S) from biogas. The evaluation of DES for biogas upgrading at relatively high pressure (i.e., >8.0 bar) has not been reported before. The aqueous DES performance has also not been analyzed compared to conventional amines-based solvent (MEA) and ionic liquid (IL). To the best of our knowledge, this is the first study that presents the integration of DES-based biogas upgrading with a mixed refrigerant liquefaction process to facilitate the safe and economical transportation of biomethane over long distances. The biogas considered in this study consisted of 60% CH4, 39% CO2, and 1% H2S. The aqueous ChCl/urea (70 wt%) results in biomethane with ≥99.0 wt% purity and ≥97.0 wt% recovery. Then, this biomethane was liquefied with ≥90% liquefaction rate. Based on the results obtained herein, overall capital, operating, and total annualized cost savings of 2.8%, 25.82%, and 14.26% were achieved using the 70% DES-based integrated process in comparison with the MEA-based integrated process. Whereas 1.41%, 16.85%, and 8.71% capital, operating, and total annualized costs could be saved in comparison with the IL (i.e., [Bmim][PF6])-based integrated process. It could be deduced that the overall cost of the biomethane value chain can be reduced using the proposed approach.

Insights into the effect of the spacer on the properties of imidazolium based AIE luminogens

With the aim to obtain organic salts with potential applications in high performance molecular electronics, we combined properties of π-conjugated spacers, like 1,4-diethynylbenzene and 1,6-diethynylpyrene, with the ones of both imidazole and imidazolium units. Physico-chemical properties of obtained fluorescent organic salts were investigated performing thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC) and cyclic voltammetry measurements (CV). Photophysical behavior of the salts was analyzed in conventional solvents and ionic liquids, by UV–vis and fluorescence investigation. Solution phase aggregation study revealed that these salts self-assemble in conventional solvents and ionic liquids, leading to aggregation induced emission processes. Notably, emission was maintained also in the solid state, with higher or lower intensity compared with the solution, depending on which spacer is present. This latter, also impacts on the morphology of the aggregates, allowing fine tuning the properties of the supramolecular materials formed.

Ag Electrodeposition from Silver Solvate Ionic Liquid

Ag electrodeposition technics have been used in many fields, such as jewelry, tableware, lead frame of semiconductors, and aerospace materials. The practical Ag plating aqueous baths contain highly toxic cyanides to suppress dendritic growth. Toward the realization of green industry, cyanide-free alternative baths are needed. Ionic liquids (ILs) attract attention as green solvents with less volatility and less flammability and also as functional liquids which enable non-dendritic Ag electrodeposition without cyanides [1,2]. However, there have still been few studies on “silver solvate IL baths”, composed of Ag(I)-oligoether cationic complex and counter anion like other solvate ILs [3-5]. Silver solvate ILs are expected to offer an advantage in mass transport due to high Ag(I) concentration. In this study, we synthesized glyme-based silver solvate IL and investigated Ag electrodeposition.An equimolar mixture of glyme (G2, G3, G4, or G5) and silver bis(trifluoromethylsulfonyl)amide (AgTf2N) resulted in a liquid-state only for G5 at room temperature, which became a colorless and transparent liquid using activated carbon. Electrochemical properties of Ag(G5)Tf2N were examined using Pt plate as working electrode (WE) and Ag wires as reference electrode (RE) and counter electrode (CE). Cyclic voltammogram demonstrates distinct redox waves of Ag plating and stripping, evidencing that Ag(I)-G5 complexes are an electroactive species and this solvate IL can work as an Ag-plating bath. Reductive wave does not show a peak owing to diffusion limitation even though cathodic potential limit is extended up to –3.0 V vs. Ag. The cathodic current density reaches –7.0 mA cm–2 at –3.0 V. For the previously-reported Ag deposition from conventional ILs, poor solubility of salts caused the low current density of deposition. Thus, the large reductive current density from Ag(G5)Tf2N is quite advantageous.A galvanostatic electrodeposition at 0.08 mA cm–2 was performed to investigate the morphology of Ag deposits. Figs. 1c,d demonstrates that the obtained electrodeposits were quite dense and smooth. For comparison, we plated Ag from a diluted AgTf2N-G5 solution (Figs. 1e,f). Unlike the case of Ag(G5)Tf2N, the deposits were coarse and faceted. It is also notable that Tf2N ions have a certain leveling effect in Ag electrodeposition [6]. Therefore, the extremely high concentration of Ag(I) ion and Tf2N– ion is an important factor to form the dense and smooth Ag deposits. Suppose the high concentration is the only determinant, other electrolytes with a high AgTf2N concentration such as aqueous solutions could give dense and smooth Ag deposits. We prepared diluted and saturated AgTf2N aqueous solutions and conducted Ag electrodeposition. From the saturated aqueous solution, however, the shape of Ag has no difference, although from the diluted aqueous solution the morphology of Ag is quite similar to that from the diluted G5 solution. Consequently, not only a high AgTf2N concentration but also solvent is the factor for realizing highly smooth Ag deposits (e.g. difference of Ag(I)-solvent complex, physicochemical property of electrolyte, or electrode/electrolyte interface). This work offers a guideline to design Ag plating baths that have extremely high Ag(I) concentration and can electrodeposit dense and smooth Ag.[1] S. Z. E. Abedin et al., Electrochim. Acta, 54, 5673 (2009).[2] B. H. R. Suryanto et al., Electrochim. Acta, 81, 98 (2012).[3] T. Mandai et al., Chem. Rec, 19, 708 (2019).[4] A. Kitada et al., J. Electrochem. Soc., 165, H121 (2018).[5] A. Kitada et al., J. Electrochem. Soc., 164, H5119 (2017).[6] N. Serizawa et al., Electrochim. Acta, 56, 346 (2010). Figure 1

Comparative evaluation on the thermal properties and stability of MWCNT nanofluid with conventional surfactants and ionic liquid

Conventional surfactants such as CTAB (cetrimonium bromide), SDS (sodium dodecyl sulphate), SDBS (sodium dodecyl sulphonate) are combined with nanofluids to improve the stability and thermal conductivity of nanofluids. These nanofluids are mainly used for heat transfer applications where heating and cooling are usual courses of action which result in surfactants producing foams and polluting the heat transfer media, affecting the total system performance. Besides, the common surfactant molecules that augment the thermal resistance between the nanoparticles and base fluid also affect the thermophysical properties of the nanofluid. In this paper, [Bmim][Cl] (1-butyl-3-methylimidazolium chloride), a high purity ionic liquid (IL) with higher thermal stability was used to provide a comparative study on the stability and thermal properties with that of the conventional surfactants (CTAB, SDS, SDBS) on multiwalled carbon nanotubes (MWCNT)/propylene glycol (PG) nanofluid. The transient hot-wire based KD2-Pro and zeta potential results demonstrated that the inclusion of ionic liquid improved the thermal conductivity and stability of the formulated nanofluid. However, much like the conventional surfactants, the strong electrostatic repulsive force created by the ionic liquid was found to decrease when the temperature is increased. The outcome demonstrated the most extreme thermal conductivity upgrade of 33.7% at 303 K and maximum dispersion stability of more than one month without any aggregation for the nanofluid containing ionic liquid.

Performance of p-Toluenesulfonic Acid-Based Deep Eutectic Solvent in Denitrogenation: Computational Screening and Experimental Validation.

Deep eutectic solvents (DESs) are green solvents developed as an alternative to conventional organic solvents and ionic liquids to extract nitrogen compounds from fuel oil. DESs based on p-toluenesulfonic acid (PTSA) are a new solvent class still under investigation for extraction/separation. This study investigated a new DES formed from a combination of tetrabutylphosphonium bromide (TBPBr) and PTSA at a 1:1 molar ratio. Two sets of ternary liquid–liquid equilibrium experiments were performed with different feed concentrations of nitrogen compounds ranging up to 20 mol% in gasoline and diesel model fuel oils. More than 99% of quinoline was extracted from heptane and pentadecane using the DES, leaving the minutest amount of the contaminant. Selectivity was up to 11,000 for the heptane system and up to 24,000 for the pentadecane system at room temperature. The raffinate phase’s proton nuclear magnetic resonance (1H-NMR) spectroscopy and GC analysis identified a significantly small amount of quinoline. The selectivity toward quinoline was significantly high at low solute concentrations. The root-mean-square deviation between experimental data and the non-random two-liquid (NRTL) model was 1.12% and 0.31% with heptane and pentadecane, respectively. The results showed that the TBPBr/PTSADES is considerably efficient in eliminating nitrogen compounds from fuel oil.

Deep eutectic solvents in separations: Methods of preparation, polarity, and applications in extractions and capillary electrochromatography

Deep eutectic solvents (DESs) have emerged as alternatives to conventional organic solvents and ionic liquids (ILs). Their tunable and designer physio-chemical properties, low cost, and ease of preparation make them attractive solvent systems for use in extractions and additives to chromatographic separations. However, due to the diverse range of hydrogen bond acceptors and donors that comprise DESs, choosing the appropriate solvent for separations can be challenging. This review discusses all methods of DES preparation and details their advantages and disadvantages. Since polarity is an important aspect in their use in separations, the classification of DESs based on the betaine dye and nile red scales as well as Kamlet-Taft parameters is also discussed. Finally, a summary of applications of DESs in various extraction processes (phenolics, fuels, metals, proteins, carbohydrates), solid-phase extraction, solid-phase microextraction, as well as capillary electrochromatography is provided.

A Review of the Use of Eutectic Solvents, Terpenes and Terpenoids in Liquid–liquid Extraction Processes

Diverse and abundant applications of the eutectic solvents have appeared in the last years. Their promising tunable properties, eco-friendly character and the possibility of being prepared from numerous compounds have led to the publication of numerous papers addressing their use in different areas. Terpenes and terpenoids have been employed in the formulation of eutectic solvents, though they also have been applied as solvents in extraction processes. For their hydrophobic nature, renewable character, low environmental impact, cost and being non-hazardous, they have also been proposed as possible substitutes of conventional solvents in the separation of organic compounds from aqueous streams, similarly to hydrophobic eutectic solvents. The present work reviews the application of eutectic solvents in liquid–liquid extraction and terpenes and terpenoids in extraction processes. It has been made a research in the current state-of-the-art in these fields, describing the proposed applications of the solvents. It has been highlighted the scale-up feasibility, solvent regeneration and reuse procedures and the comparison of the performance of eutectic solvents, terpenes and terpenoids in extraction with conventional organic solvents or ionic liquids. Ultimately, it has been also discussed the employ of predictive methods in extraction, the reliability of thermodynamic models in correlation of liquid–liquid equilibria and simulation of liquid–liquid extraction processes.

Processing of Functional Composite Resins Using Deep Eutectic Solvent

Deep eutectic solvents (DESs)—a promising class of alternatives to conventional ionic liquids (ILs) that have freezing points lower than the individual components—are typically formed from two or more components through hydrogen bond interactions. Due to the remarkable advantages of biocompatibility, economical feasibility and environmental hospitality, DESs show great potentials for green production and manufacturing. In terms of the processing of functional composite resins, DESs have been applied for property modifications, recyclability enhancement and functionality endowment. In this review, the applications of DESs in the processing of multiple functional composite resins such as epoxy, phenolic, acrylic, polyester and imprinted resins, are covered. Functional composite resins processed with DESs have attracted much attention of researchers in both academic and industrial communities. The tailored properties of DESs for the design of functional composite resins—as well as the effects of hydrogen bond on the current polymeric systems—are highlighted. In addition to the review of current works, the future perspectives of applying DESs in the processing of functional composite resins are also presented.

Comprehensive Utilization of Marine Microalgae for Enhanced Co-Production of Multiple Compounds.

Marine microalgae are regarded as potential feedstock because of their multiple valuable compounds, including lipids, pigments, carbohydrates, and proteins. Some of these compounds exhibit attractive bioactivities, such as carotenoids, ω-3 polyunsaturated fatty acids, polysaccharides, and peptides. However, the production cost of bioactive compounds is quite high, due to the low contents in marine microalgae. Comprehensive utilization of marine microalgae for multiple compounds production instead of the sole product can be an efficient way to increase the economic feasibility of bioactive compounds production and improve the production efficiency. This paper discusses the metabolic network of marine microalgal compounds, and indicates their interaction in biosynthesis pathways. Furthermore, potential applications of co-production of multiple compounds under various cultivation conditions by shifting metabolic flux are discussed, and cultivation strategies based on environmental and/or nutrient conditions are proposed to improve the co-production. Moreover, biorefinery techniques for the integral use of microalgal biomass are summarized. These techniques include the co-extraction of multiple bioactive compounds from marine microalgae by conventional methods, super/subcritical fluids, and ionic liquids, as well as direct utilization and biochemical or thermochemical conversion of microalgal residues. Overall, this review sheds light on the potential of the comprehensive utilization of marine microalgae for improving bioeconomy in practical industrial application.