Protic Ionic Liquids Research Articles

New hydroxylammonium-based protic ionic liquids: Influence of cation and anion structure on thermal, viscosity and conductive properties

In the research work, new protic ionic liquids (Pr-ILs) were synthesized by an acid-base neutralization reaction. The influence of IL chemical structure (i.e. anion and cation nature) on the thermal behavior, viscosity and ionic conductivity was evaluated. To confirm the chemical structure of synthesized Pr-ILs, nuclear magnetic resonance (1H and 19F) and Fourier transform infrared spectroscopy analyses were performed. Thermal analysis demonstrated that the influence of anion nature on the IL thermal stability was more pronounced than that of cation. The ionic liquids with trifluoromethanesulfonate anion showed the highest thermal stability (Tdeg ∼ 410–420 °C) as compared with other studied anions (i.e. phosphate and acetate anions). The trifluoromethanesulfonate-based Pr-ILs also demonstrated high ionic conductivity – between ∼58 and ∼64 mS·cm−1 at 150 °C and non-humid conditions. Despite the fact that phosphate-based Pr-ILs were more thermally stable (Tdeg ∼ 250–280 °C) than acetate-based ones (Tdeg ∼ 215 °C), acetate-based Pr-ILs revealed a higher ionic conductivity (∼15–19 mS·cm−1 at 80 °C) than phosphate-based Pr-ILs (∼0.2–1 and ∼0.4–2 mS·cm−1 at 80 and 120 °C, respectively). The obtained results confirm that the synthesized Pr-ILs are promising candidates for using them in electrochemical applications, namely, electrodialysis and fuel cells.

Exploring Solvation Properties of Protic Ionic Liquids by Employing Solvatochromic Dyes and Molecular Dynamics Simulation Analysis

Solvation properties are key for understanding the interactions between solvents and solutes, making them critical for optimizing chemical synthesis and biochemical applications. Designable solvents for targeted optimization of these end-uses could, therefore, play a big role in the future of the relevant industries. The tailorable nature of protic ionic liquids (PILs) as designable solvents makes them ideal candidates. By alteration of their constituent structural groups, their solvation properties can be tuned as required. The solvation properties are determined by the polar and non-polar interactions of the PIL, but they remain relatively unknown for PILs as compared to aprotic ILs and their characterization is non-trivial. Here, we use solvatochromic dyes as probe molecules to investigate the solvation properties of nine previously uncharacterized alkyl- and dialkylammonium PILs. These properties include the Kamlet–Aboud–Taft (KAT) parameters: π* (dipolarity/polarizability), α (H-bond acidity) and β (H-bond basicity), along with the ET(30) scale (electrophilicity/polarizability). We then used molecular dynamics simulations to calculate the radial distribution functions (RDF) of 21 PILs, which were correlated to their solvation properties and liquid nanostructure. It was identified that the hydroxyl groups on the PIL cation increase α, π* and ET(30), and correspondingly increase the cation–anion distance in their RDF plots. The hydroxyl group, therefore, reduces the strength of the ionic interaction but increases the polarizability of the ions. An increase in the alkyl chain length on the cation led to a decrease in the distances between cations, while also increasing the β value. The effect of the anion on the PIL solvation properties was found to be variable, with the nitrate anion greatly increasing π*, α and anion–anion distances. The research presented herein advances the understanding of PIL structure–property relationships while also showcasing the complimentary use of molecular dynamics simulations and solvatochromic analysis together.

Thermophysical insights and COSMO-RS study of triethylenetetramine-based protic ionic liquids with alkyl carboxylic acids

Protic ionic liquids (PILs) have increasing interest due to their potential application compared to conventional organic solvents. In the present study, new class of protic ionic liquids were developed by combining triethylenetetramine as cation and distinct carboxylic acids, specifically formic acid, butanoic acid, hexanoic acid, and octanoic acid employed as the anions. The products structures and purity were verified using 1H and 13C NMR as well as ESI-MS analysis. The structural variations effects on the thermophysical characteristics such as refractive index (nD), viscosity (η), density (ρ), and speed of sound (u) were evaluated throughout a broad temperature range. Temperatures between 293.15 and 333.15 K were used to calculate the viscosity and density values. It was also determined the thermal decomposition temperature (Td) and quantified the amount of water in the synthetic protic ionic liquids. Additional parameters such the expansion coefficient (α), standard entropy (S0), volume (V), lattice potential energy (UPOT), isentropic compressibility (βs), Intermolecular free length (Lf) of PILs were calculated using experimental values for sound speed and density. Furthermore, computation of activation energy employed the experimental viscosity values. In order to calculate the electronic polarizability and free volume present inside the ionic liquids, refractive indices of PILs were measured between the temperatures of 293.15 and 323.15 K. The study also explored the Conductor-like Screening Model for Real Solvents (COSMO-RS) computational approach to gain insights into the structural variation of TETA-based ionic liquids. The prepared PILs derived properties and linked with their structural moieties.

Water-Doped Brønsted Acidic Protic Ionic Liquids for Enhanced Tributyl Citrate Synthesis in a Two-Phase Esterification System.

Tributyl citrate (TBC) plays a crucial role as a plasticizer, enhancing the flexibility of polymers such as polyvinyl chloride. Its biodegradability and non-toxic nature contribute to eco-friendly appeal, making it a preferred additive in diverse industries, including food packaging, medical devices, toys, and consumer goods. Herein, a method for the synthesis of TBC using inexpensive Brønsted acidic protic ionic liquids (ILs) in a two-phase reaction system is presented. The esterification process is carried out with high yield (>99 %), selectivity (up to 98 %) and short reaction time of 2 h. The catalyst in the form of IL shows excellent performance and stability, desirable for industrial applications.

Nonstoichiometric Protic Ionic Liquids: The Role of Excess Acid in Charge Transport Mechanisms.

A study of charge transport mechanisms in an electric field was conducted on nonstoichiometric protic ionic liquids (PIL) based on triethylamine (TEA), in combination with an excess of either trifluoroacetic acid (TFA) or trifluoromethanesulfonic acid (TfO). The addition of excess precursor acid adds proton-donor sites to the system to support potential structural proton transport, which could, for example, enable the use in fuel cells. Transport measurements by pulsed field gradient (PFG) NMR diffusion and, in particular, electrophoretic NMR (eNMR) are supported by NMR chemical shifts and Raman spectroscopy, where the latter techniques elucidate the local solvation structures. Migration of the acidic proton of the excess acid in the electric field occurs toward the cathode with a velocity larger than that of the anions. This intriguing feature of a rapid drift of a neutral molecule is explained by the interplay of strong correlations between anion and cation as well as between anion and acid. The neutral acid is subject to vehicular transport with the anion, while the anion is partitioning between anion-acid and anion-cation clusters, resulting in a lower average drift velocity. The negative drift direction of the neutral acid and its proton is superimposed to and thus counteracts the vehicular transport of protons with the cation. The study sheds light on the role of excess acid in PIL and reveals the versatile interactions between anion, cation, and excess acid within a PIL determining its charge transport properties.

Modulating CO2 electroreduction to syngas by protic-nonprotic ionic liquid composite electrolytes

CO2 electroreduction reaction (CO2RR) to syngas with a tunable CO/H2 ratio and high current density is a promising but challenging application. Here, we report a novel electrolyte, including protic ionic liquid (IL) [Bim][NTf2], nonprotic IL, acetonitrile (MeCN) for CO2RR to syngas. When the concentration of [Bim][NTf2] increased from 0.005 to 0.12 mol·L-1, the CO/H2 ratio dropped from 30 to 0.1 and the current density increased from 26.4 to 113.4 mA·cm-2 at -2.3 V vs. Ag/Ag+ in H-cell. The [Bim][NTf2] not only can generate H+ to accelerate HER, but also increases the CO2 solubility to promote CO2RR to CO. Meanwhile, the [Bmim][NTf2] mainly increased the current density for CO2RR. By varying the concentration of [Bim][NTf2], the CO/H2 ratio could be modulated in ternary electrolyte. This work offers a novel method to modulate the CO/H2 ratio for enhancing the efficiency of CO2RR to syngas with a high current density in H-cell.

Molecular Interactions between Ionic Liquid Lubricants and Silica Surfaces: An MD Simulation Study.

The unique physicochemical properties of ionic liquids (ILs) attracted interest in their application as lubricants of micro/nano-electromechanical systems. This work evaluates the feasibility of using the protic ionic liquids [4-picH][HSO4], [4-picH][CH3SO3], [MIMH][HSO4], and [MIMH][CH3SO3] and the aprotic ILs [C6mim][HSO4] and [C6mim][CH3SO3] as additives to model lubricant poly(ethylene glycol) (PEG200) to lubricate silicon surfaces. Additives based on the cation [4-picH]+ exhibited the best tribological performance, with the optimal value for 2% [4-picH][HSO4] in PEG200 (w/w). Molecular dynamics (MD) simulations of the first stages of adsorption of the ILs at the glass surface were performed to portray the molecular behavior of the ILs added to PEG200 and their interaction with the silica substrate. For the pure ILs at the solid substrates, the MD results indicated that weak specific interactions of the cation with the glass interface are lost to accommodate the larger anion in the first contact layer. For the PEG200 + 2% [4-picH][HSO4] system, the formation of a more compact protective film adsorbed at the glass surface is revealed by a larger trans population of the dihedral angle -O(R)-C-C-O(R)- in PEG200, in comparison to the same distribution for the pure model lubricant. Our findings suggest that the enhanced lubrication performance of PEG200 with [4-picH][HSO4] arises from synergistic interactions between the protic IL and PEG200 at the adsorbed layer.

Lyotropic ionic liquid crystal gels derived from polyimidazolium hydrogen sulfate for enhanced proton conductivity

AbstractAnisotropic gels developed from polymer networks accommodating lyotropic liquid crystals are promising electrolytes but electrochemically inert polymers prevent ions from being conducted efficiently. In this work, we synthesized protic ionic liquid polymer in lyotropic ionic liquid crystal to improve proton conduction across the polymer skeleton in anisotropic gels. In situ polymerization of 1‐vinylimidazolium hydrogen sulfate ionic liquid dissolved in aqueous 1‐tetradecyl‐3‐methylimidazolium hydrogen sulfate lyotropic liquid crystal gave chemical liquid crystal gels exhibiting both dynamic order and mechanical strength. The protic ionic liquid polymer bridged the hydrogen bond chains between neighboring ionic lyotropic liquid crystal domains to give a proton conductivity of 117 mS cm−1 at 25°C. Macroscopic alignment of the liquid crystal gel achieved by mechanical shearing promoted proton conductivity to 137 mS cm−1. The macroscopically aligned liquid crystal gel acted stably in a fuel cell device, delivering a peak power density 2.95 times higher than the unaligned one. Gelation of lyotropic ionic liquid crystals with protic ionic liquid polymer provides an effective strategy to develop anisotropic gel electrolytes for electrochemical devices.

Exploiting Cation Structure and Water Content in Modulating the Acidity of Ammonium Hydrogen Sulfate Protic Ionic Liquids.

In this paper, we investigated the effect of cation structure and water content on proton dissociation in alkylammonium [HSO4]- protic ionic liquids (ILs) doped with 20 wt % water and correlated this with experimental Hammett acidities. For pure systems, increased cation substitution resulted in a reduction in the number of direct anion-anion neighbors leading to larger numbers of small aggregates, which is further enhanced with addition of water. We also observed spontaneous proton dissociation from [HSO4]- to water only for primary amine-based protic ILs, preceded by the formation of an anion trimer motif. Investigation using DFT calculations revealed spontaneous proton dissociation from [HSO4]- to water can occur for each of the protic ILs investigated; however, this is dependent on the size of the anion aggregates. These findings are important in the fields of catalysis and lignocellulosic biomass, where solvent acidity is a crucial parameter in biomass fractionation and lignin chemistry.

Enzymatic hydrolysates of Agave tequilana bagasse pretreated with protic ionic liquids: Saccharification efficiency and hydrogen production

This work demonstrated for the first time that hydrogen (H2) can be generated from Agave tequilana bagasse (ATB) after ionic liquid (IL) pretreatment up to 111.1 L H2/kg hydrolyzed biomass in only 20 h. It is shown that the low-cost protic IL [EOA][OAc] (ethanolamine acetate) can effectively pretreat ATB at two different scales (bench and lab) using 2 and 250 g (dry basis) at 20% solids loading and 160 °C for 90 min resulting in significant structural changes followed by FTIR spectroscopy. The lignin content of the pretreated ATB was reduced by 28.6% after lab-scale pretreatment which ultimately improved the sugar yield with the different saccharification strategies (batch vs. fed-batch). Up to 0.643 g TS (total sugars)/g ATB were obtained in a fed-batch strategy with fixed enzymatic loading, representing an enhancing 2.8-fold when compared to the untreated biomass. Models of enzymatic saccharifications were included for both, untreated and pretreated ATB, in terms of TS concentration (g/L) and fiber length (mm) to confirm differences in accessibility and availability of both substrates. The results successfully revealed that 1.1 kg or 14 m3 of H2 can be produced from 100 kg of dry ATB after pretreatment with [EOA][OAc] indicating the feasibility of improved sugar and H2 yields where either a low-cost pretreatment agent or an adequate saccharification strategy contributes to the biorefinery scheme.

CO2 Absorption by Solvents Consisting of TMG Protic Ionic Liquids and Ethylene Glycol: The Influence of Hydrogen Bonds

Herein, the absorption of CO2 by the TMG-based (TMG: 1,1,3,3-tetramethylguanidine) ionic liquids (ILs) and the absorbents formed by TMG ILs and ethylene glycol (EG) is studied. The TMG-based ILs used are formed by TMG and 4-fluorophenol (4-F-PhOH) or carvacrol (Car), and their viscosities are low at 25 °C. The CO2 uptake capacities of [TMGH][4-F-PhO] and [TMGH][Car] are low (~0.09 mol CO2/mol IL) at 25 °C and 1.0 atm. However, the mixtures [TMGH][4-F-PhO]-EG and [TMGH][Car]-EG show much higher capacities (~1.0 mol CO2/mol IL) than those of parent ILs, which is unexpected because of the low CO2 capacity of EG (0.01 mol CO2/mol EG) in the same conditions. NMR spectra and theoretical calculations are used to determine the reason for these unexpected absorption behaviors. The spectra and theoretical results show that the strong hydrogen bonds between the [TMGH]+ cation and the phenolate anions make the used TMG-based ILs unreactive to CO2, resulting in the low CO2 capacity. In the Ils-EG mixtures, the hydrogen bonds formed between EG and phenolate anions can weaken the [TMGH]+–anion hydrogen bond strength, so ILs-EG mixtures can react with CO2 and present high CO2 capacities.

Effective superlubricity behavior triggered by interfacial tribochemical reactions from simple protic ionic liquids aqueous

Superlubricity technology is one of the fastest growing fields of tribology in recent years because it can fundamentally reduce friction and wear. However, the current challenges for liquid superlubricity are the bearing capacity of lubricants and the stable superlubricity behavior at high shear rates. In this work, four imidazole-phosphate ionic liquids (ILs) with different chain lengths were prepared and used as pure water additives to achieve stable superlubricity with the friction coefficient of 0.008 under high loading (300 N) and high speed (0.461 m/s) between steel interfaces. The evoluation progress and tribochemical reaction of superlubricity is explored by the staged experiment. The results showed that a key factor of achieving superlubricity is the running-in period, in which, on the one hand, the contact pressure greatly reduce to maintain a suitable bearing range. On the other hand, the ordered accumulation of hydrogen ions, organic anions and cations, and ion of hydration formed a multi-layer electrostatic layer at the interface of the friction pair, which not only provides a protective layer to avoid serious corrosion, but also enhances the bearing capacity of the lubricating film attributed to the electrostatic repulsion. In addition, the tribochemical reaction between ILs and the surface of metal forms a functional tribofilm composed of carbides, iron oxides, nitrides and phosphides, which prevents the direct contact of the friction pair and reduces wear. Consequently, this research offers valuable insights into the optimal IL structure, revealing the tribochemical reaction of the superlubricity process and holding the significant potential of water-based superlubricity systems for practical applications.

Interfacial structures and dissociation reactions of protic ionic liquids on Li metal surface: A combined first-principles and ab initio molecular dynamics investigation

Interfacial structures and dissociation reactions of protic ionic liquids (PILs) comprising five protic cations with two common sulfonylimide anions on the Li(001) surface were investigated using first-principles calculations and ab initio molecular dynamics simulations. Both the anions rapidly decompose, yielding LiF, Li2O and Li2S species as well as large fragments, e.g. NSO2CF3 and NSO2. Particularly, the proton attached to the N atom generally segregates from the cations and generates LiOH with the O atom from the anions and the surface Li atom. In addition, detailed comparisons of reaction mechanisms between PIL-based and AIL-based systems were also made.

Solute- solvent interactions between ethanolamine-based protic ionic liquids and lithium bromide in aqueous media using volumetric, acoustic and transport properties

The use of protic ionic liquids (PILs) as environmentally friendly green solvents has gained increasing interest in recent years for a variety of applications, including absorption refrigeration systems that use lithium bromide (LiBr). In this study, to gain a comprehensive understanding of the thermophysical properties of LiBr in water and aqueous solutions containing three different PILs (composed of the cations 2-hydroxyethylammonium, bis(2-hydroxyethyl)ammonium, and tris(2-hydroxyethyl)ammonium, with the acetate anion), a thorough investigation was conducted using ultrasonic, volumetric, viscometric, and electrical conductivity methods.Key thermophysical parameters such as apparent molar volume, apparent molar isentropic compressibility, viscosity B coefficient, and molar conductivity were calculated for the mentioned systems. Analyzing these thermophysical properties is essential for understanding the underlying forces in these liquid mixtures. The results revealed a significant influence of solute–solvent interactions in the studied systems, which were observed to increase with increasing PIL concentrations. Also, the co-sphere overlap model was employed to interpret the relation between hydrophilic-hydrophilic and ion-hydrophilic interactions, between PILs and LiBr along with a detailed analysis of the associated thermodynamic parameters.

Impedance Analysis of Capacitive and Faradaic Processes in the Pt/[Dema][TfO] Interface.

The electrochemical reaction kinetics, especially the oxygen reduction reaction (ORR) at the cathode, is crucial for the performance of a fuel cell. In this study, the electrochemical processes on a polycrystalline Pt electrode in the presence of protic ionic liquid (PIL) electrolyte diethylmethylammonium triflate [Dema][TfO] are investigated by means of cyclic voltammetry and electrochemical impedance spectroscopy. Since water is continually produced during fuel cell operation, the effect of the water content in the PIL has been intensively analyzed. In order to reveal the dependence of the interfacial reaction characteristics on the electrode potential, the impedance spectra were simulated by an equivalent circuit whose parameters can be related to both Faradaic and capacitive processes. Two interfacial resistances were identified, which differ by about 3 orders of magnitude. The larger one is a charge transfer resistance that can be associated with slow Faradaic processes like the ORR and platinum oxidation/oxide reduction. The smaller resistance is probably linked with fast processes that involve water molecules, such as hydrogen deposition and oxidation. The high- and midfrequency capacitive processes are attributed to "classical" double layer and pseudocapacitive behavior, similar to those identified under nitrogen atmosphere.

Ionogels based on protic ionic liquid - lithium salt mixtures

The effect of the addition of lithium nitrate on the liquid range and electrical conductivity of mixtures of a protic ionic liquid, ethylammonium nitrate (EAN) with LiNO3 is reported in this work. Moreover, changes in these properties upon confinement in silica-based matrices are also analysed and related to variations on the microstructure of the mixtures. Our results show that gelation of the mixtures induces amorphous behaviour in all the samples, but no significant changes in the thermal stability are detected. However, important differences on the electrical conductivity of the liquid and gel states of the mixtures were observed. While this magnitude decreases with the addition of salt in the liquid samples for all the temperatures it increases at low concentrations of LiNO3 up to a maximum in the gelled samples with the lowest concentration of added salt (0.1 mol of salt by kg of EAN). High resolution magic angle spinning (HRMAS) NMR shows that the addition of lithium nitrate increases the mobility (both rotational and translational motion) of the cation EA+ within the ionogel and the diffusion of the cation provides evidence of the presence of two different populations of the same molecules experiencing two distinct apparent diffusion coefficients (bi-exponential decay of magnetization in diffusion NMR experiments), while it is mono-exponential in the pure ionic liquid. The Li+ cation is shown to display a higher mobility (both rotational and translational motion) in the ionogel than in the neat ionic liquid. The frustration of the formation of solvation complexes due to the confinement is suspected to be behind this behaviour.

Optimization of cost-effective enzymatic saccharification using low-cost protic ionic liquid as pretreatment agent in Agave bagasse

This work studied the optimization of enzymatic saccharification of Agave tequilana bagasse (ATB) pretreated with the low-cost protic ionic liquid (PIL) ethanolamine acetate ([EOA][OAc]) using the highly available and cost-effective mixture of the enzymatic cocktails Celluclast 1.5L-Viscozyme L. Response surface methodology (RSM) was employed to maximize the sugars concentration and yield. The RSM optimization conditions of the enzymatic saccharification of pretreated ATB that achieved the maximum reducing sugars (RS) concentration were: 11.50 % w/v solids loading, 4.26 pH with 0.76 and 1.86 mg protein/mL buffer of Viscozyme L and Celluclast 1.5L, respectively. Similarly, the conditions that maximize the sugar yield (SY) were solids loading of 5.62 % w/v, and 4.51 pH as well as 1.07 and 2.03 mg protein/mL buffer of Viscozyme L and Celluclast 1.5L, respectively. Saccharification performance of the first-generation and low-cost enzyme mixture Celluclast 1.5L-Viscozyme L was compared with that reached by a second-generation and higher-cost CTec2, where Celluclast 1.5L-Viscozyme L achieved 60.86 ± 2.66 % y 79.25 ± 3.34 % of the sugars released by CTec2 at the same hydrolysis time (12 h) for the sugar concentration and yield models, respectively. These results are encouraging since they positively contribute to cost reduction and availability issues, which are key parameters to consider when thinking about scaling-up the process.

Improving MFC efficiency in power generation and COD removal by using protic ionic liquid in MWCNT-CS-2-aminothiazole-SO3H nanoparticle-infused sulfonated PES

This study exhibits a novel nanofiller, functionalized multi-walled carbon nanotube (MWCNT)/chitosan (CS) by 2-aminothiazole/SO3H. This synthesized nanofiller was incorporated with a fabricated sulfonated polyethersulfone (SPES) to manufacture a composite proton exchange membrane (PEM), SPES/MWCNT-CS-2-aminothiazole-SO3H. The composite membranes were fabricated by different percentage amounts of nanofiller (0.1 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%). The trait comparison of SPES/MWCNT-CS-2-aminothiazole-SO3H, SPES, and Nafion 117 membrane is performed to investigate their application in the microbial fuel cell (MFC). The fabricated composite membrane SPES/MWCNT-CS-2-aminothiazole-SO3H 0.5 wt% illustrated superior water uptake (WU) of 90.41 %. Moreover, the maximum power density (PD) (66.04 mW.m−2) was produced by SPES/MWCNT-CS-2-aminothiazole-SO3H 0.5 wt%, which demonstrated a considerable increase (approximately 20 times) compared to SPES (3.19 mW.m−2). Furthermore, the power density generated by the Nafion 117 membrane was 15.78 mW.m−2. In addition, the statistics in MFC usage presented that prepared composite membrane combined with MWCNT-CS-2-aminothiazole-SO3H 0.5 wt% had the optimum chemical oxygen demand (COD) removal, and the coulombic efficiency (CE), with 90.46 % and 80.68 %, respectively. Due to the high efficiency and remarkable power generation achieved by the MFC with SPES/MWCNT-CS-2-aminothiazole-SO3H 0.5 wt%, this modified membrane can be considered as a promising cost-effective alternative separator in MFC.

Lyotropic liquid crystal phases of monoolein in protic ionic liquids.

Monoolein-based liquid crystal phases are established media that are researched for various biological applications, including drug delivery. While water is the most common solvent for self-assembly, some ionic liquids (ILs) can support lipidic self-assembly. However, currently, there is limited knowledge of IL-lipid phase behavior in ILs. In this study, the lyotropic liquid crystal phase behavior of monoolein was investigated in six protic ILs known to support amphiphile self-assembly, namely ethylammonium nitrate, ethanolammonium nitrate, ethylammonium formate, ethanolammonium formate, ethylammonium acetate, and ethanolammonium acetate. These ILs were selected to identify specific ion effects on monoolein self-assembly, specifically increasing the alkyl chain length of the cation or anion, the presence of a hydroxyl group in the cation, and varying the anion. The lyotropic liquid crystal phases with 20-80 wt. % of monoolein were characterized over a temperature range from 25 to 65 °C using synchrotron small angle x-ray scattering and cross-polarized optical microscopy. These results were used to construct partial phase diagrams of monoolein in each of the six protic ILs, with inverse hexagonal, bicontinuous cubic, and lamellar phases observed. Protic ILs containing the ethylammonium cation led to monoolein forming lamellar and bicontinuous cubic phases, while those containing the ethanolammonium cation formed inverse hexagonal and bicontinuous cubic phases. Protic ILs containing formate and acetate anions favored bicontinuous cubic phases across a broader range of protic IL concentrations than those containing the nitrate anion.

Unveiling protic amino acid ionic liquids for the efficient capture of carbon dioxide.

A series of novel protic amino acid ionic liquids (PAAILs) are designed and synthesized for the first time through acid-base neutralization and an ion exchange reaction. Among the synthesised PAAILs, the [DBNH][Maba] PAAIL has the largest CO2 absorption capacity of 0.78 mol mol-1 (0.142 g g-1) at 313.2 K. The PAAILs are found to be efficient, reversible, and selective CO2 absorbents.