Carboxylate Ionic Liquids Research Articles

Effective elimination of multiple heavy metal ions from wastewater using circular liquid-liquid extraction based on trioctylammonium carboxylate ionic liquids

The widespread discharge of effluents containing heavy metal ions (HMIs) from various industries into natural water bodies has become an alarming concern due to their harmful effects. Recently, ionic liquid (IL)-assisted liquid–liquid extraction (LLE) has emerged as a rapid and facile method for treating industrial effluents, effectively reducing the risk of secondary pollution. The primary objective of this study was to design novel hydrophobic ILs for the extractive removal of toxic HMIs from aqueous media. These hydrophobic ILs were designed by incorporating cyclic carboxylic acids (thiobenzoic acid, pyridine dicarboxylic acid, and pyrimidine dicarboxylic acid) with trioctylamine. The aim was to evaluate the effect of different coordinating atoms in the cyclic carboxylic acids on HMI extraction, while the trioctylamine moiety was chosen to provide the necessary hydrophobicity. The synthesized ILs were evaluated for their efficiency in the extractive removal of toxic HMIs, including Cu(II), Cd(II), Ni(II), and Pb(II), both individually and from their mixtures, under simulated industrial conditions. Thorough optimization was performed to identify the key parameters affecting extraction efficiency. The HMI concentrations were adjusted to their reported maximum contamination limits to ensure real-time applicability, and the ILs demonstrated successful extraction under these conditions. Experimental studies showed that the ILs were able to effectively remove HMIs even from mixtures, confirming their practical relevance. A detailed comparison with literature data revealed that the extraction mechanism primarily relied on the preferential coordination of metals, following the HSAB principle. Furthermore, metal ions were stripped back using disodium EDTA solution, facilitating the regeneration of the ILs for multiple reuse cycles and supporting a sustainable, circular process.

Structural effect on physicochemical properties of ethanolamine carboxylate ionic liquids by experimental and theoretical study

The hydroxylammonium ionic liquids (ILs) falling within the category of protic ionic liquids (PILs) have garnered attention from researchers, owing to their outstanding solubility properties. A one-step method was employed to synthesize a series of ethanolamine ILs. The thermodynamic properties of the ILs, including surface tension, density, and electrical conductivity, were measured across varying temperatures. Essential parameters such as thermal expansion coefficient, molecular volume, surface entropy, and surface energy were estimated using empirical equations. In order to elucidate the intermolecular interactions within the ethanolamine carboxylate ILs, the sigma profiles of ILs were determined using COSMO-RS. It was observed that the ethanolamine cation has a strong potential as a H-bond donor, while the carboxylate anion demonstrates significant capability as a hydrogen bond acceptor. By DFT calculations, it was observed that the NH in the ethanolamine cation can form H-bonds with the oxygen atom in the carboxylate anion.

Experimental and In Silico Comparative Study of Physicochemical Properties and Antimicrobial Activity of Carboxylate Ionic Liquids.

The COVID-19 pandemic highlighted the need to create and study new substances with improved lipophilicity and antimicrobial properties, such as ionic liquids (ILs), with easily tunable physicochemical properties. Most ILs possess strong antibacterial effects, but ILs containing the imidazolium cation are even more effective than the positive control. Thus, in this study, three ionic liquids with 1-butyl-3-methylimidazolium cation and various carboxylate anions (phenylacetate, benzoate, and 4-methoxyphenylacetate) were synthesized and fully characterized. The interactions between the cations and anions were discussed based on the experimental density, viscosity, and electrical conductivity. From the measured electrical conductivity and viscosity, the Walden plot is constructed and ionicity of the studied ILs is discussed. The similarities and dissimilarities among the studied ILs and their physicochemical properties are analyzed by applying the hierarchical cluster analysis and in silico calculated properties. The antimicrobial activity of the studied ionic liquids is tested on two bacterial (E. coli and P. aeruginosa) and three fungi (P. verrucosum, A. flavus, and A. parasiticus) strains, finding that they showed improved antimicrobial activity compared to the individual components.

Improved Reversible and Selective SO2 Absorption by a Stable Phosphonium Carboxylate Ionic Liquid

Improved Reversible and Selective SO₂ Absorption by a Stable Phosphonium Carboxylate Ionic Liquid

Hydrated carboxylate ionic liquids as chemical CO2 sorbents of high capacity and moderate enthalpy of absorption

Tetralkylphosphonium carboxylate ionic liquids are herein presented as efficient carbon dioxide chemisorbents in the presence of water. The ionic liquids tetrabutylphosphonium formate and acetate, tributylmethylphosphonium formate and a series of triethylalkylphosphonium formates and acetates, have been prepared by various synthetic procedures either from hydroxide or methylcarbonate precursors, or via multiple steps starting from the parent triethylphosphine. Their physicochemical properties, namely melting or glass transition temperatures, thermal decomposition behaviour, densities and viscosities have been determined. As dry substances, they are viscous liquids or low-melting solids, whereas they show little tendency to solidify in their hydrated forms. They were used mostly as monohydrates in CO2 solubility measurements, exhibiting highest capacities (3 mol L−1, i.e. ≈ 0.9 molCO2 molIL−1, at 5 bar, 25 °C) at equimolar H2O/ionic liquid ratios, approaching those of commercial aqueous amine sorbents. Carbon dioxide chemisorption into hydrogencarbonate takes place, as demonstrated by infrared spectroscopy with isotopic labelling. CO2 absorption isotherms were recorded at various temperatures and the data used to estimate the heat of absorption according to three different thermodynamic models. Enthalpies of CO2 absorption depended heavily on the model used. Rationalisation of this was done on the grounds of the expected relevance of physical and chemical sorption processes. Average heats of CO2 absorption lie between −40 and −45 kJ mol−1, in accordance with mild chemical absorption albeit significantly lower than those for typical chemical sorbents such as amines. This reinforces the feasibility of hydrated carboxylate ionic liquids for CO2 capture technologies of low regeneration energies.

Ionic liquids based on carboxylate anions: Auto and hetero assembly with methylcellulose in diluted and semi-diluted regime

This study explores the impact of carboxylate ionic liquids (ILs) on the phase transition properties of methylcellulose (MC) in the diluted and semi-diluted regime. Conductivity measurements were used to examine the aggregation of ILs 1-decyl-3-methylimidazolium butanoate ([C10MIM][BUT]), 1-decyl-3-methylimidazolium crotonate ([C10MIM][CRO]), and 1-decyl-3-methylimidazolium pentanoate ([C10MIM][PEN]) in the presence and absence of MC. The interaction between ILs and MC was confirmed using 1H NMR spectroscopy. The effect of ILs on the phase transition of MC was investigated through UV–vis spectroscopy and oscillatory rheometry. Results indicated that the carboxylate ILs studied tend to interact with MC, reducing polymer-polymer interactions and the apparent viscosity of MC solutions. Furthermore, carboxylate ILs were observed to modulate the sol-gel transition temperature of MC to higher temperatures, while weakening the resulting gel compared to pure MC gels.

Design, synthesis, analgesic, antibacterial and docking studies of novel 8-piperazinylcaffeine carboxylate ionic liquids.

This paper presents a comprehensive evaluation of novel 8-piperazinylcaffeine carboxylate ionic liquids, including their design, synthesis, characterization, analgesic and antibacterial properties, as well as docking studies. These unique salts were produced by combining 8-piperazinyl caffeine (8-PC) with various carboxylic acids, some of which are commonly used nonsteroidal anti-inflammatory drugs (NSAIDs). Through in vivo experiments on female mice using the formalin test, the analgesic efficacy of different 8-PC salts with various NSAIDs was assessed. Results demonstrated that a majority of these salts exhibited significant analgesic activity when compared to NaIBP, a standard reference drug. Particularly noteworthy was the enhanced analgesic effect of the 8-PC's NSAIDs salts (11a, 11c-e, and 11k) compared to their corresponding sodium salts, which was attributed to the presence of the 8-PC cation (synergistic effect). Furthermore, all synthesized salts were subjected to in vitro testing against Gram-positive Staphylococcus aureus (PTCC 1133), Gram-negative Pseudomonas aeruginosa (ATCC 27853), and Escherichia coli (PTCC 1330) bacteria. Among them, salt 11k displayed notable antibacterial activity, especially against P. aeruginosa, a dangerous opportunistic pathogen. Additionally, docking analysis revealed strong binding of the synthesized 8-PC and NSAID salts to the active site of the COX-2 enzyme.

Tailored carbon dioxide capacity in carboxylate-based ionic liquids.

We have used a library of thermally stable tetraalkylphosphonium carboxylate ionic liquids that were easily prepared from available carboxylic acids. Depending on the pKa in water of the precursor acids, the resulting ionic liquids either dissolve or reversibly chemically absorb CO2, with some exhibiting notable gas capacities, reaching a CO2 mole fraction of 0.2 at 1 bar and 343 K. While equilibrium constants and ionic liquid capacities generally correlate with the pKa of the acids, certain exceptions underscore the influence of liquid structure and physical properties of the ionic liquids, elucidated through molecular dynamics simulations and density functional theory calculations. Unlike the trends observed in other CO2-absorbing ILs, phosphonium carboxylates do not experience increased viscosity upon gas absorption; instead, enhanced diffusivities are observed, facilitating efficient gas-liquid transfer.

Thermal decomposition kinetics and mechanisms of long alkyl chain ionic liquids with carboxylate anions

This work presents the synthesis and analysis of the thermal decomposition kinetics and mechanisms of long alkyl chain ionic liquids (ILs) with cations 1-decyl-3-methylimidazolinium ([C10MIM]+), 1-dodecyl-3-methylimidazolinium ([C12MIM]+), and 1-hexadecyl-3-methylimidazolinium ([C16MIM]+) and butanoate ([C3COO]−) and heptanoate ([C6COO]−) anions. The kinetics analysis was performed using the Kissinger-Akahira-Sunose isoconversional methodology. The results indicated that the carboxylate ILs are less thermally stable than their bromide analogues and the order of thermal stability was explained by the values of the kinetic parameters (Ea and lnA) and their variation with α. For most of the studied carboxylate ILs there was a considerable variation in Ea as the decomposition progressed, indicating multiple decomposition steps. The thermal decomposition mechanism was studied by analyzing the thermal degradation residue from 1H NMR spectroscopy.

Investigation on Asphaltene Dispersion Activity of Tetrabutylammonium Carboxylate Ionic Liquids

Asphaltene destabilization is still known as one of the main problems of the petroleum industry and imposes many costs on this industry during crude oil production, transportation, and refining. The most important solution to control this problem is using chemical compounds to disperse asphaltene aggregates. Ionic liquids, as an emerging industrial solvent and catalyst, have been used for this purpose in the last two decades. In this work, three ionic liquids having a tetrabutylammonium cation and oleate, stearate, and cinnamate anions were synthesized and used as asphaltene dispersants. The efficiency of the synthesized ionic liquids on the stability of asphaltene aggregates was investigated using cluster size, polydispersity index, zeta potential, and ultraviolet spectroscopy data. It was found that tetrabutylammonium cinnamate and tetrabutylammonium oleate (dispersion indices of 82.5 and 60.2, respectively) have a much higher efficiency than tetrabutylammonium stearate (dispersion index of 20.6). The results of cluster size, polydispersity index, and zeta potential analysis were confirmed by ultraviolet spectroscopy and optical microscopy data. For instance, the mean radius of asphaltene clusters was 2179.8 nm, reduced to 253, 680, and 1402 nm after adding tetrabutylammonium salt of cinnamate, oleate, and stearate, respectively. The same trend was observed in the results of the polydispersity index (0.417, 0.470, and 0.624) and zeta potential analysis (31.4, 1.81, and −0.56). The cinnamate, oleate, and stearate anions have four, one, and no carbon–carbon π bonds, respectively. It seems that the presence of π bonds that can form π–π interactions with π bonds of the asphaltene molecules is an essential factor in asphaltene stabilization by these ionic liquids. In addition, the results showed that the higher the net negative charge of the anion, the greater the ability of the anion to stabilize asphaltene aggregates. This stabilization, which was mainly done through electrostatic interactions between polar groups of asphaltene and the carboxylate anions, was confirmed by zeta potential data.

Selective separation Al3+/Gd3+ by designed carboxylic acid-ionic liquid with low acid and alkali consumption

As the associated element of ion-adsorbed type rare earth ores, aluminum ion (Al3+) has a great influence on the purification of gadolinium ion (Gd3+). In this paper, six carboxylic ionic liquids were synthesized with methyltrioctylammonium ([N1888]+) as cation and carboxyl group as anion, and optimized for selective separation of Al3+/Gd3+. The extraction capability, separation factor, stripping property and recycling stability of the ionic liquid on the separation of Al3+ and Gd3+ were systematically investigated. In addition, the loaded Al3+ can be totally stripped by 0.08 mol‧L−1 HCl solution. A particularly high separation factor of 923 can be obtained for removing Al3+ from industrial GdCl3 feed solution (762 mg‧L−1 Al3+ and 146 g‧L−1 Gd3+). The removal rate of Al3+ was up to 98.69% and the recovery rate of Gd3+ achieved at 92.47% by carboxylic ionic liquid ([N1888][C7H11O2]) in one-step extraction. After 0.6 mol‧L−1 HCl solution stripping and 0.5 mol‧L−1 NaOH solution regenerating, the extraction efficiency of Al3+ was only reduced by 3% after 5 cycles of organic phase. With the low acid and base concentration, it greatly reduced the chemical consumption and significantly the emission of high ammonia–nitrogen wastewater inindustry. This work provides a low-carbon process for efficient removal of Al3+ from industrial GdCl3 feed by carboxylic ionic liquids.

Self-separation ionic liquid catalyst for the highly effective conversion of H2S by α,β-unsaturated carboxylate esters under mild conditions

The deep-processing utility of pure hydrogen sulfide (H2S) is a significant direction in natural gas chemical industry. Herein, a brand-new strategy of H2S conversion by α,β-unsaturated carboxylate esters into thiols or thioethers using task-specific carboxylate ionic liquids (ILs) as catalyst has been developed, firstly accomplishing the phase separation of product and catalyst without introducing the third component. It can be considered as a cascade reaction in which the product selectivity can be controlled by adjusting the molar ratio of H2S to α,β-unsaturated carboxylate esters. Also, the effects of ILs with different anions and cations, intermittent feeding operations, as well as pressure−time kinetic behaviors on cascade reaction were investigated. Furthermore, the proposed interaction mechanism of H2S conversion using butyl acrylate catalyzed by [Emim][Ac] was revealed by DFT-based theoretical calculation. The approach enables the self−phase separation promotion of catalyst and product and achieves 99% quantitative conversion under mild conditions in the absence of solvent, making the entire process ecologically benign. High-efficiency reaction activity can still be maintained after ten cycles of the catalyst. Therefore, the good results, combined with its simplicity of operation and the high recyclability of the catalyst, make this green method environmentally friendly and cost−effective. It is anticipated that this self-separation method mediated by task-specific ILs will provide a feasible strategy for H2S utilization, which will guide its application on an industrial scale.

Readily regenerable amine-free CO2 sorbent based on a solid-supported carboxylate ionic liquid

Accumulation of anthropogenic CO2 is undoubtedly the major cause of global warming. In addition to reducing emissions, minimising the threatening effects of climate change in the near future might also require the capture of enormous amounts of CO2 from point sources or from the atmosphere. In this regard, the development of novel affordable and energetically attainable capture technologies is greatly needed. In this work, we report rapid and greatly facilitated CO2 desorption for amine-free carboxylate ionic liquid hydrates as compared to a benchmark amine-based sorbent. Complete regeneration was achieved at moderate temperature (60 °C) over short capture-release cycles using model flue gas on a silica-supported tetrabutylphosphonium acetate ionic liquid hydrate (IL/SiO2), whereas the polyethyleneimine counterpart (PEI/SiO2) only recovered half its capacity after the first cycle in a rather sluggish release process under the same conditions. The IL/SiO2 sorbent achieved a slightly superior working CO2 capacity than PEI/SiO2. The easier regeneration of carboxylate ionic liquid hydrates, which behave as chemical CO2 sorbents leading to bicarbonate in a 1:1 stoichiometry, is due to their relatively low sorption enthalpies (≈40 kJ mol−1). The faster and more efficient desorption from IL/SiO2 fits a first-order kinetic model (k = 0.73 min−1), whereas a more complex process was observed for PEI/SiO2 (pseudo-first order initially, k = 0.11 min−1, pseudo-zero order at later stages). The remarkably low regeneration temperature, the absence of amines and the non-volatility of the IL sorbent are favourable assets to minimise gaseous stream contamination. Importantly, regeneration heats —a crucial parameter for practical application— are advantageous for IL/SiO2 (4.3 kJ g (CO2)−1) vs. PEI/SiO2, and fall within the range of typical amine sorbents indicating a remarkable performance at this proof-of-concept stage. Further structural design will enhance the viability of amine-free ionic liquid hydrates for carbon capture technologies.

Alkylphosphonium carboxylate ionic liquids with tuned microscopic structures and properties.

Eleven pure alkylphosphonium carboxylate ionic liquids (ILs) were synthesised following a reliable and accessible route. Tetrabutylphosphonium and tetradecyltrihexylphosphonium cations were associated to a variety of [R-COO]- anions with R varying from shorter to longer linear alkyl chains; smaller to bulkier branched alkyl chains; cyclic saturated aliphatic and aromatic moieties; and one heterocyclic aromatic ring containing nitrogen. A combined experimental and molecular simulation study allowed the full characterization of the physico-chemical properties, the structure and the thermal stability of the synthesized ILs. Although slightly more viscous than their imidazolium counterparts, the viscosities of the prepared salts decrease dramatically with temperature and are comparable to other ILs above 50 °C, a manageable temperature as they are thermally stable up to temperatures above 250 °C, even under an oxidizing atmosphere. The microscopic structure of the phophonium ILs is rich and has been studied both experimentally using SAXS and by molecular dynamics simulation using state of the art polarizable force fields whose parameters were determined when necessary. Unique and surprising anion-anion correlations were found for the tetrazolate-based IL allowing to explain some of the unique physical-chemical properties of this phosphonium salt.

Triprotic Ammonium Oleate Ionic Liquid Crystal Lubricant for Copper-Copper Friction and Wear Reduction

The triprotic ammonium carboxylate ionic liquid crystal (2-hydroxyethyl)ammonium oleate (MO) has been studied as a neat lubricant and as a lubricant additive in two base oils, PAO6 and 100N. The lubricants have been used in commercially pure copper-OFHC copper balls on disk reciprocating sliding contact at room temperature. Neat MO presents a very good lubricating performance, with a friction coefficient of 0.06 and a wear rate of OFHC copper disk of 4.15 × 10−7 mm3/N·m. These results are, respectively, 94% and 98% lower than those obtained for PAO6, with similar reductions obtained with respect to 100N. MO has also been studied as an additive in 2wt.% proportion. The severe abrasive wear mechanism that takes place in the presence of neat base oils is reduced by the MO additive.

Gelatin and Tannic Acid Based Iongels for Muscle Activity Recording and Stimulation Electrodes.

Iongels are soft ionic conducting materials, usually composed of polymer networks swollen with ionic liquids (ILs), which are being investigated for applications ranging from energy to bioelectronics. The employment of iongels in bioelectronic devices such as bioelectrodes or body sensors has been limited by the lack of biocompatibility of the ILs and/or polymer matrices. In this work, we present iongels prepared from solely biocompatible materials: (i) a biobased polymer network containing tannic acid as a cross-linker in a gelatin matrix and (ii) three different biocompatible cholinium carboxylate ionic liquids. The resulting iongels are flexible and elastic with Young's modulus between 11.3 and 28.9 kPa. The morphology of the iongels is based on a dual polymer network system formed by both chemical bonding due to the reaction of the gelatin's amines with the polyphenol units and physical interactions between the tannic acid and the gelatin. These biocompatible iongels presented high ionic conductivity values, from 0.003 and up to 0.015 S·cm-1 at room temperature. Furthermore, they showed excellent performance as a conducting gel in electrodes for electromyography and electrocardiogram recording as well as muscle stimulation.

Physicochemical Characterization of Two Protic Hydroxyethylammonium Carboxylate Ionic Liquids in Water and Their Mixture

Physicochemical Characterization of Two Protic Hydroxyethylammonium Carboxylate Ionic Liquids in Water and Their Mixture

Green synthesis of acetylated maize starch in different imidazolium carboxylate and choline carboxylate ionic liquids

This work demonstrates that acetylated maize starches (AMS) with varied degree of substitution (DS, 0.26–2.63) was synthesized in ionic liquids (ILs) (imidazolium chloride, imidazolium carboxylate and choline carboxylate) at 85 °C without catalyst. The DS of AMS and reaction efficiency increased with decreasing alkyl chain length of cations or anions, while decreased as the choline cation replaced the imidazolium cation and the chloride anion replaced the acetate anion. The AMS synthesized in imidazolium-based ILs exhibited much higher hydrophobicity and thermal stability than the native starch. Rheological properties of ILs and ATR-FTIR analysis of acetic anhydride/ILs mixtures indicated that a shorter alkyl side chain or the combination of an imidazolium cation and an acetate anion gave ILs lower viscosities and weaker interactions between acetic anhydride molecules, which favored the acetylation of starch. These findings provide insights into the design of green processes to modify starch and the application of acetylated starch.

Influence of the cation partner on levulinate ionic liquids properties

In the context of bio-based ionic liquids (ILs), in recent years levulinate ILs have been explored in various applications with appreciable performances. To expand their scope of use, seven selected levulinate ILs featuring different cationic moieties have been prepared and their physico-chemical properties compared. While all the ILs generated displayed only glass transitions at low temperature (<−60 °C), [C4C1Pyr]Lev presented melting and crystallization events. The thermal stability determined by TGA decreased in the order [P8881]Lev > [C2C1Im]Lev ≈ [C4C1Im]Lev > [C2C1Pip]Lev > [C2C1Pyr]Lev ≈ [C4C1Pyr]Lev > [N8881]Lev, and is in good agreement with the general trend observed for carboxylate ILs. In terms of viscosity, the LevILs showed a Newtonian behaviour when considering the shearing rates range, with a marked reduction of the viscosity at increasing temperatures. The glassy behaviour of LevILs was further ascertained applying the MYEGA viscosity-based model for the determination of the fragility index.The density of the LevILs was found to vary in the vicinity of 1g/cm3, and the systematic refractive index increase with increasing density was identified as a general trend. The refractive index was experimentally determined at five different wavelengths and several temperatures between 80 °C and 130 °C and followed the order [C2C1Im]Lev > [C2C1Pip]Lev > [C4C1Im]Lev > [C2C1Pyr]Lev > [C4C1Pyr]Lev > [P8881]Lev > [N8881]Lev. Overall, the possibility to tune the physico-chemical properties of ILs through structural variations of the cationic part has been proven valid for the LevIL family. When compared with the carboxylate ILs described in the literature, LevILs show great potential for further applicative studies.

Newly synthesized Ionic Liquids as potent lubricants and additives to existing lubricant oils

Ionic Liquids are promising candidates for next generation green lubricants. We have synthesized 39 Tetraalkylammonium Alkyl Ether Carboxylate Ionic Liquids and tested them for their lubricant capabilities. We measured friction coefficient to assess the transition from the boundary to the hydrodynamic lubrication, the hydrodynamic area and the minimum friction value. Some Ionic Liquids are capable of forming a hydrodynamic layer fully separating two specimens. Compounds with short C-chain of the cationic part show poor tribological behaviour. Similarly, increasing the PO-degree of the anionic part lowers the lubrication power. An increase of the C-chain length improves the tribological behaviour, i.e. the minimum friction value becomes lower. This is due to the formation of a uniform tribolayer of the long-chain carboxylic acids. Higher viscosity of the Ionic Liquids results in low friction coefficients and the development of a hydrodynamic layer. This is due to a strong hydrodynamic pressure, which is formed by the more viscous compound. Addition of small amounts of Ionic Liquids to low performance oils increases their capability to from tribolayers and thus improves their lubricant capability.