Ionic Liquid Cations Research Articles

Bioconcentration potential of ionic liquids: New data on membrane partitioning and its comparison with predictions obtained by COSMOmic

Ionic liquids (ILs) have recently gained significant attention in both the scientific community and industry, but there is a limited understanding of the potential risks they might pose to the environment and human health, including their potential to accumulate in organisms. While membrane and storage lipids have been considered as primary sorption phases driving bioaccumulation, in this study we used an in vitro tool known as solid-supported lipid membranes (SSLMs) to investigate the affinity of ILs to membrane lipid - phosphatidylcholine and compare the results with an existing in silico model. Our findings indicate that ILs may have a strong affinity for the lipids that form cell membranes, with the key factor being the length of the cation's side chain. For quaternary ammonium cations, increase in membrane affinity (logMA) was observed from 3.45 ± 0.06 at 10 carbon atoms in chain to 4.79 ± 0.06 at 14 carbon atoms. We also found that the anion can significantly affect the membrane partitioning of the cation, even though the anions themselves tend to have weaker interactions with phospholipids than the cations of ILs. For 1-methyl-3-octylimidazolium cation the presence of tricyanomethanide anion caused increase in logMA to 4.23 ± 0.06. Although some of our data proved to be consistent with predictions made by the COSMOmic model, there are also significant discrepancies. These results suggest that further research is needed to improve our understanding of the mechanisms and structure-activity relationships involved in ILs bioconcentration and to develop more accurate predictive models.

Efficient extraction of Au(Ⅲ) by a piperidine-based ionic liquid and exploration of the mechanism driving force

Efficient gold extraction is of paramount importance, but how to improve the extraction efficiency and enhance the driving force of the extraction process is still to be explored. This study introduces an innovative approach using versatility ionic liquids (ILs) to overcome existing challenges. A tailored IL was synthesized and employed computational tools, including the Interaction Region Indicator, to predict its effectiveness in gold extraction. Quantum chemical calculations elucidated the interplay between hydrogen bonding capability and ion exchange properties of the ILs. Subsequent optimization of experimental conditions (0.1 mol/L HCl, 10.6 mg IL) yielded a remarkable 98.4 % extraction efficiency at 45 °C. Molecular dynamics simulations affirmed the IL's exceptional selectivity for Au(III) extraction, with analysis revealing that the extraction mechanism primarily hinged on electrostatic attraction and van der Waals interactions between ionic liquid cations and [AuCl4]−. This mechanism aligns with the established anion exchange mechanism, validated through Ultraviolet–visible spectrometer (UV–Vis), Nuclear Magnetic Resonance spectrometer (NMR), and Liquid Chromatograph Mass Spectrometer (LC-MS) analyzes. To complete the extraction cycle, 1.0 mol/L K2C2O4 was employed as a stripping agent for efficient Au(III) recovery from the loaded IL phase, facilitating repeated extraction cycles. This study underscores the sustainability of the IL-based Au(III) extraction process, maintaining consistently high extraction rates even after five cycles. In summary, this method does not use solvent, enabling environmentally friendly Au(III) extraction.

Bacterial Cellulose-Based ionogels with synergistically enhanced mechanical and thermoelectric performances for low-grade heat harvesting

Ionogels have a bright prospect for low-grade heat harvesting due to their advantages of non-volatility and high thermal stability. However, it is still challenging to develop ionogels with mechanical robustness and high thermoelectric properties. This work reports a carboxymethylated and Na+ doped bacterial cellulose-based ionogel (CBCIG-Na) with synergistically increased mechanical and thermoelectric performances. The enhancement of thermoelectric properties of ionogels is mainly attributed to the increase of ion transport pathways and the mobility difference between anions and cations in ionic liquid. After the modification, the CBCIG-Na ionogel with 0.5 mol% Na+ (CBCIG-Na0.5%) exhibits high Seebeck coefficient (45.02 mV K−1), ionic conductivity (21.2 mS cm−1) and ionic power factor (4296.82 μW m−1 K−2) when the relative humidity (RH) is 85 %. This is the highest ionic power factor ever reported for bacterial cellulose-based ionogels. Moreover, the CBCIG-Na0.5% shows high tensile strength (7.69 MPa) due to the larger 3D fiber network and enhanced intermolecular force, obvious adhesivity (9.28 kPa) and high transparence (76 %). After that, a flexible i-TE device containing 5 legs and packaged with polydimethylsiloxane (PDMS) was constructed. A high thermovoltage of 264.36 mV is generated when wearing the i-TE device (5 legs) on the forearm at room temperature (ΔT = 1.2 K). The outstanding performances, environmentally friendly and low-cost characters of CBCIG-Na0.5% ionogel indicating its great potential for low-grade heat harvesting.

Uncovering chemical structure-dependency of ionic liquids as additives for efficient and durable perovskite photovoltaics

Ionic liquids (ILs) have garnered significant attention in the field of perovskite solar cells (PSCs) due to their versatile capabilities in manipulating the crystallization kinetics, optimizing the morphology, and effectively passivating defects, leading to high-efficiency and long-term stability. While previous studies have mostly focused on individual ILs or different anions and their application in PSCs, the distinctive distribution of cations and anions within ILs underscores the significance of optimizing cationic structures and elucidates the particular role of cations in ILs on device performance. In this work, the implications of juxtaposing ILs incorporating carboxyl-functionalized imidazolium cations against conventional imidazolium-based counterparts on the crystallization kinetics, perovskite film quality, and the photovoltaic performance of perovskite devices. This strategy involving carboxyl-functionalized cations in ILs with a higher affinity to coordinate Pb2+, supported by chemical spectroscopy testing and a quantitative measure of the bond strength via Crystal orbital Hamiltonian group (COHP) calculations. The modified ILs more prominently results in enhancing the degree of PbI2 conversion into perovskite, slowing down crystallization rates and inducting formation of higher-quality perovskite films. Benefitting from the strong chemical interaction provided carboxyl-functionalized cations and widespread distribution of carboxyl-functionalized cations throughout the perovskite films, accomplishing comprehensive synergistic passivation of defects in perovskite films. This led to the suppression of non-radiative recombination and enhanced carrier transport properties. The incorporation of carboxyl modified ILs with suitable chemical structures resulted in a remarkable enhancement of the champion power conversion efficiency (PCE) to 24.21% in the ILs-treated device, coupled with excellent long-term stability.

Simultaneous electropolymerization of pyrrole and anionic or cationic polymerizable monomeric ionic liquids. Linear actuation of the attained materials

The simultaneous galvanostatic electrogeneration of polypyrrole (PPy) and a polyanion, or a polycation, from the concomitant solutions of pyrrole and monomeric ionic liquids (PIL) give films of two interpenetrated polymeric networks: polyanion-PPy (PILA-PPy) and polycation-PPy (PILC-PPy), as corroborated by Fourier transform infrared (FTIR) spectroscopy. The linear actuation was characterized by cyclic voltammetry and chronoamperometry in aqueous electrolyte describing cation-driven actuation of the PILA-PPy actuators (cation exchange during oxidation/reduction) and anion-driven actuation of the PILC-PPy actuation. The exchange of a unique ion in each actuator, corroborated by energy dispersive X-ray (EDX) analysis of the oxidized and reduced materials, allows the control of the actuation direction. The concomitant driving electrochemical reactions are described. Coulovoltammetric responses present a closed loop in the studied potential range indicating that only those reactions (oxidation/reduction) are present in the studied potential range (0.65 V and − 0.6 V). The PILC-PPy strain was 8.7% and the stress gradient 1.45 MPa, overcoming 1.5 times those from PILA-PPy actuators, consuming also a higher charge density, having 2.1 times better conductivity and 1.3 times higher diffusion-coefficients. The stability of the actuators was studied by consecutive cycling. The PILA-PPy and PILC-PPy films are characterized by scanning electron microscopy (SEM), FTIR and EDX spectroscopy.

Screening ionic liquids based on COSMO-SAC model for extracting organic sulfur from coal and mechanism study

Screening suitable ionic liquids（ILs） for removing organic sulfur compounds from coal and discovering new, effective and environmentally friendly coal desulfurization additives is crucial. The solubility properties (SP) of six organic sulfur model compounds (OSMCs) in imidazole ILs were calculated based on the COSMO-SAC model. The results showed that 2-thiophenecarboxylic acid and 2-aminophenyl phenyl sulfone exhibited favorable solubility properties in certain ILs. The solubility properties of partial imidazole ILs consisting of [Cl]- were significantly better than other anions. Through the σ -profiles analysis of ILs anions, cations and OSMCs, it showed that [Cl]- had a higher tendency to be hydrogen bond acceptor than other anions. The polar groups in OSMCs increased the hydrogen bond donor or acceptor sites for interactions with ILs, while extended the optional range of ILs for hydrogen bond interactions with OSMCs. The extraction efficiencies of 2-thiophenecarboxylic acid by ILs were above 25%, with [DMIM][Cl] displaying the highest efficiency at 47.5%. Meanwhile, [DMIM][Cl] was the most effective extractant for removing all OSMCs except benzothiophene, which was basically consistent with the calculation results. Electrostatic potential analysis was used to obtain the sites where OSMCs are the most likely to form hydrogen bond interactions with [DMIM][Cl]. And characterization of hydrogen bond formation between ILs and OSMCs was obtained by FTIR analysis. The hydrogen bond formed by p-thiocresol with [DMIM][Cl] is weak, and the hydrogen bonds formed by 2-thiophenecarboxylic acid, 2-aminophenyl phenyl sulfone with [DMIM][Cl] are relatively strong. The analysis of intermolecular hydrogen bond interactions verified the mechanism underlying the excellent extraction performance for specific OSMCs by the selected ILs.

NMR investigation of multi-scale dynamics in ionic liquids containing Li+ and La3+: From vehicular to hopping transport mechanism

The dynamics in mixtures of ionic liquid and monoatomic cations has been studied at different time scales ranging from the nanosecond up to the second. The mixtures were composed of cholinium bis(trifluoromethanesulfonyl)imide ([Chol][TFSI]) and LiTFSI, with LiTFSI mole fraction, ▪, spanning from 0 to 0.5 (saturated solution), and [Chol][TFSI] and ▪ from 0 to 0.12. The translational self-diffusion coefficients of ▪, ▪ and ▪ have been measured, along with NMR their relaxation times at various magnetic fields, in order to decipher the intertwined dynamics between the ions, and to reveal how the local dynamics impact the long range translational diffusion. When the concentrations of lithium and lanthanum are increased in the liquid, the long range dynamics of all the ions drop. In the case of LiTFSI, the self-diffusion coefficient of lithium becomes higher than the one of TFSI at high concentration, revealing a change in lithium transport mechanisms. The NMR relaxation data confirm this change, showing a clearer transition at ▪. It is interpreted as a change from a vehicular transport mechanism of the lithium below ▪ to a hopping mechanism above. A similar crossover seems to occur in the lanthanum solutions. This phenomenon seems correlated to the departure of the hydroxyl group of the organic cation from the lithium solvation shell.

Vibrational mode of low-dimensional ionic liquid bismuth hybrid perovskite probed by FTIR and Raman Spectroscopy

Bismuth-based hybrid organic-inorganic perovskites (Bi-HOIPs) are developed as lead-free halide perovskites due to their low toxicity and good stability. In this study, the incorporation of ionic liquid (IL) cations in the Bi-HOIPs structure, namely 1-butyl-1-methylpyrrolidinium (BMP) and 1-(3-aminopropyl) imidazole (API), are investigated. Bi-based HOIPs are kept in ambient conditions (20–25 °C) to compare the structural differences in FTIR and Raman spectra between pristine and aged samples. The FTIR and Raman spectra of all aged samples are slightly shifted after being retrieved at the ambient conditions for four months (∼below 45 cm−1). Our work paves the way in developing Bi-based HOIPs for solar cells and photodetectors applications.

Survey of the multi-stage mass spectrometry of common ionic liquid cations and some polyfluorinated ions

Ionic liquids are useful for many applications and the structural diversity as a class is ever increasing. Knowledge of gas-phase dissociation pathways can inform analytical method development for the characterization of novel syntheses, degradation products, or environmental contaminants, and can inform our knowledge of the fate of ionic liquid species in the gas phase (e.g., after ejection by electrospray spacecraft thrusters). In this work, the N-heterocyclic (NHC) ions:1-butyl-1-methylpiperidinium (BMPi), 1-methyl-1-propylpiperidinium (MPPi), 1-butyl-1-methylpyrrolidinium (BMPyr), 1-ethyl-1-methylpyrrolidinium (EMPyr), 1-butylpyridinium (BPy), and 1-Butyl-1-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl) imidazolium (BFIm) were studied. An additional fluorinated anion, nonafluorobutanesulfonate (NFBS), was also studied. Collision-induced dissociation mass spectrometry (CID-MS), as MS2 and MS3 using an ion trap mass spectrometer and energy-resolved breakdown curves using a quadrupole time-of-flight mass spectrometer, were used to determine dissociation patterns. Assignment of proposed dissociation pathways were made based on the experimental results and complementary computational chemistry. It was observed that for aromatic NHCs, cleavage at the C–N bond was preferred, to generate alkene-based neutral losses. Non-aromatic NHCs typically generated both alkane- and alkene-based neutral losses. Breakdown curves, supported by theoretical thermodynamic calculations, suggest that the loss of the alkane is the favorable dissociation pathway. Additionally, some ring-opening and ring contraction reactions via C–C bond cleavage were observed in non-aromatic species, whereas the intact aromatic NHC is typically a stable terminal ion. The polyfluorinated imidazolium fragmented via the breaking of C–N, C–C, and C–F bonds. The fluorinated anion, NFBS, fragmented by C–C and C–S bond cleavage to generate fluoroalkene, sulfur dioxide, and sulfur trioxide neutral losses. Beyond these broad stroke findings, the dissociation pathways of the seven ionic liquid ions were mapped using evidence from MS3, breakdown curves, and computational chemistry together assigning product ions as either arising from competitive or sequential pathways and proposing tentative structures. Some of the ionic liquid ions showed class-based product ions which will be useful in analytical development for their characterization. Finally, these results were contextualized within previous literature reports on other ionic liquid species.

Ecotoxicity studies reveal that organic cations in dicamba-derived ionic liquids can pose a greater environmental risk than the herbicide itself

The following research provides novel and relevant insights into potential environmental consequences of combination of various organic cations with commercial systemic herbicide (dicamba), in accordance with a ‘herbicidal ionic liquids’ (HILs) strategy. Toxicity assays of five dicamba-based HILs comprising different hydrophobic and hydrophilic cations, namely choline [CHOL][DIC], ethyl betainate [BETC2][DIC], decyl betainate [BETC10][DIC], hexadecyl betainate [BETC16][DIC] and didecyldimethylammonium [DDA][DIC]), have been tested towards bacteria (Pseudomonas putida, Escherichia coli, Bacillus subtilis), algae (Chlorella vulgaris), fresh and marine water crustaceans (Daphnia magna, Artemia franciscana). The structure of respective substituents in the cation emerged as a decisive determinant of toxicity in the case of tested species. In consequence, small ions of natural origin ([CHOL] and [BETC2]) demonstrated toxicity numerous orders of magnitude lower compared to fully synthetic [DDA]. These results emphasize the role of cations' hydrophobicity, as well as origin, in the observed acute toxic effect. Time-dependent toxicity assays also indicated that betaine-type cations comprising an ester bond can rapidly transform into less harmful substances, which can generally result in a reduction in toxicity by even several orders of magnitude. Nonetheless, these findings challenge the concept of ionic liquids with herbicidal activity and give apparent parallels to adjuvant-dependent toxicity issues recently noted in typical herbicidal formulations.

High-Safety Electrolytes with an Anion-Rich Solvation Structure Tuned by Difluorinated Cations for High-Voltage Lithium Metal Batteries.

As next-generation energy storage devices, lithium metal batteries (LMBs) must offer high safety, high-voltage resistance, and a long life span. Electrolyte engineering is a facile strategy to tailor the interfacial chemistry of LMBs. In particular, the solvation structure and derived solid electrolyte interphase (SEI) are crucial for a satisfactory battery performance. Herein, a novel middle-concentrated ionic liquid electrolyte (MCILE) with an anion-rich solvation structure tuned by difluorinated cations is demonstrated to achieve ultrahigh safety, high-voltage stability, and excellent ternary-cathode compatibility. Novel gem-difluorinated cations first synthesized for prestoring fluorine on positively charged species, not only preferentially adsorb in the inner-Helmholtz layers, but also participate in regulating the Li+ solvation structure, resulting in a robust interphase. Moreover, these weak interactions in the Li+ solvation structure including anion-solvent and ionic liquid (IL) cation-solvent pairs are first revealed, which are beneficial for promoting an anion-dominated solvation structure and the desolvation process. Benefiting from the unique anion-rich solvation structure, a stable hetero-SEI structure is obtained. The designed MCILE exhibits compatibility with Li metal anode and the high-voltage ternary cathode at high temperatures (60°C). This work provides a new approach for regulating the solvation structure and electrode interphase chemistry of LMBs via difluorinated IL cations.

Ionic Liquids Microenvironment Modulates the Interface Properties of g-C3N4 for Boosting the Performance of Photodegradation and Infected Wound-Healing Therapy.

The improvement of photocatalytic activity of g-C3N4 is expected for its advanced applications but remains a challenge due to the limitations of current strategies, such as single function, inefficiency, and uneconomical. Herein, a modified g-C3N4 with improved interface properties is constructed through the modulation of the ionic microenvironment affected by ionic liquids (ILs) and exhibits a 2.3-fold enhanced photodegradation efficiency and a 3.5-fold enhanced reaction rate relative to pristine g-C3N4. It has demonstrated excellent performance in photo-therapy bacterial-infected wounds. Theoretical calculation indicated that the precursor can be regulated by designing the specific ILs microenvironment to form "ILs-Mel" clusters due to the diversity of interaction energy and electrostatic potential. The cluster results in uneven stress on the 2D plane, further inducing the reconstruction of the microstructure. The synergistic effect of cations and anions of ILs on regulating the interface properties of g-C3N4 due to the change of skeleton structure during thermolysis of ILs. The microstructure, surface, and optical-electrical properties can be adjusted by selecting different cations of ILs, and the custom-made band structure and wettability can be obtained by selecting different anions. This work provides a facile strategy to modulate the interface properties of g-C3N4 by building specific a microenvironment of precursor.

A novel synergistic intensification method for CO2 absorption by metal salt and task-specific ionic liquids hybrid solvent in microchannel reactor

A novel metal salt-promoting mass transfer intensification method for CO2 absorption into task-specific ionic liquids aqueous solution was proposed. The mass transfer intensification and intrinsic mechanisms of different concentrations of metal salts (NaBF4, KBF4, KCl, and CuCl2) with task-specific ionic liquids (1-aminopropyl-3-methylimidazolium tetrafluoroborate [Apmim] [BF4]) aqueous solutions for CO2 capture process were visually investigated using a microchannel reactor. The results showed that adding metal salts could remarkably enhance the interaction between metal cations and ionic liquid anions, thereby decreasing the interaction between anions and cations within the ionic liquid molecules and promoting the chemical reaction between ionic liquid cations and CO2. Under the condition of the same salt concentration, the addition of KBF4 has more obvious enhancement for mass transfer in CO2 absorption process. The mass transfer coefficient increases as the gas-liquid phase flow rate rise under slug flow condition. In addition, based on the effects of metal salt concentration, absorbent density, and gas-liquid phase flow rate on the CO2 volumetric mass transfer coefficient kLa, a new correlation for predicting the volumetric mass transfer coefficient of CO2 absorption into the hybrid solvent in microchannel reactor was proposed and validated.

Effect of ionic liquids on structure and electromechanical properties of plasticized polyvinyl chloride (PVC) gels

Polyvinyl chloride (PVC) gels, as electroactive polymers, have various applications in the fields of soft actuators and sensors. The relationship between the structure and electromechanical properties of PVC gels, however, has not been fully understood so far. In this work, the effect of different alkyl chain length of 1-allyl- imidazolium cations of tetrafluoroborate (BF4)-based ionic liquid (IL) on structure, mechanical and dielectric properties, bending actuation, sensing and electroadhesion properties of plasticized polyvinyl chloride/dibutyl adipate (PVC/DBA) gel were investigated. The interaction between DBA and ILs in PVC/DBA/IL gels leads to the disruption of interactions between inter-DBA molecules and subsequent formation of DBA-rich phases with DBA/IL complexes. The number of DBA-rich phases in PVC/DBA/IL gels increases as the alkyl chain length of the cation in IL increases, due to an enhanced interaction between DBA and ILs with an increase in the alkyl chain length of the cation in IL. The Young's modulus of the PVC/DBA gel was slightly reduced, while the dielectric constant significantly increased when IL was added. Additionally, the bending actuation properties and capacitance pressure sensing sensitivity of the PVC/DBA/IL gel increased with an increase in the alkyl chain length of the cation of IL. However, there was an opposite trend observed for electroadhesion peel strength. Among the studied PVC/DBA/IL gels, the bending displacement, pressure sensing sensitivity, and electroadhesion peel strength of PVC/DBA/IL gel with 3.2 wt% of 1-allyl-3-butylimidazolium tetrafluoroborate ([ABIM]BF4) increased by 2.6 times, 7.5 times, and 1.7 times compared to PVC/DBA gel, respectively. These results provide new insights into understanding the relationship between structure and electromechanical properties of PVC gels for their application in actuation, sensing, and electroadhesion integrated soft grippers.

Charge transfer across the ionic liquid/oil interface: Facilitated ion transfer and electron transfer

Facilitated ion transfer (FIT) and electron transfer (ET) across the ionic liquid (IL)/oil (O) interface between ethylamine nitrate (EAN) and 1,4-dichlorobutane (DCB) have been electrochemically studied. Cyclic voltammograms (CVs) for the FIT of Li+ cation in IL by dicyclohexano-18-crown-6 (DCH18C6) across the IL/O interface formed at a micropipette tip show that the onset of the FIT current is significantly shifted due to the facilitation beyond the potential window limit and that the current is proportional to the concentration of DCH18C6 in O limited by the diffusion of DCH18C6 inside the micropipette. CVs for the ET from supporting electrolyte anions in O to NO3−, the IL anion of EAN, across the IL/O interface studied using a closed-bipolar cell show that NO3− in EAN has an ability to oxidize tetraphenylborate ions in O but not tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ions, the latter of which have more oxidation resistance.

A machine learning-based QSAR model reveals important molecular features for understanding the potential inhibition mechanism of ionic liquids to acetylcholinesterase

The broad application of ionic liquids (ILs) has been hindered by uncertainties surrounding their ecotoxicity. In this work, a Quantitative Structure-Activity Relationship (QSAR) model was devised to predict the inhibition of ILs towards the activity of AChE, employing both Random Forest (RF) and eXtreme Gradient Boosting (XGBoost) machine learning approaches. Fourteen kings of essential molecular feature descriptors were screened from an initial roster of 244 descriptors through the application of a feature importance index and they showed a significant impact on the activity of AChE activity. The two models based solely on the 14 most critical molecular descriptors could maintain model's robustness and reliability. The correlation analysis between these 14 descriptors and the inhibition of AChE activity revealed the potential impact of the molecular characteristics on ILs toxicity. The results underscored the main influence of cations in ILs on the inhibitory activity towards the AChE enzyme. Specifically, cations exhibiting hydrophobicity properties were found to exert more potent inhibitory effects on the AChE enzyme. In addition, some other properties of the cations, such as the degree of branching, atomic weight and partial charge also modulated their inhibition potential. This study enhances the comprehension of the structure-activity relationship between ILs and AChE inhibition, providing a reference for designing safer and greener ILs.

Liquid–liquid extraction of strontium from acidic solutions into ionic liquids using crown ethers

90Sr is one of the most monitored fission products. New efficient methods for strontium separation are therefore sought. Over the past 20 years, crown ethers solutions in ionic liquids (ILs) have been confirmed to efficiently extract strontium from acidic solutions. Despite all the work done in this field, the extraction mechanism is still not completely clear. Depending on experimental conditions, the extraction is believed to proceed either in the form of an ion-association complex [Sr·CE·(NO3)2] or via exchange between [Sr·CE]2+ and two IL cations. This work aims to study the influence of several extraction parameters and compare them with the presumed mechanisms.

Electric field induced associations in the double layer of salt-in-ionic-liquid electrolytes.

Ionic liquids (ILs) are an extremely exciting class of electrolytes for energy storage applications. Upon dissolving alkali metal salts, such as Li or Na based salts, with the same anion as the IL, an intrinsically asymmetric electrolyte can be created for use in batteries, known as a salt-in-ionic liquid (SiIL). These SiILs have been well studied in the bulk, where negative transference numbers of the alkali metal cation have been observed from the formation of small, negatively charged clusters. The properties of these SiILs at electrified interfaces, however, have received little to no attention. Here, we develop a theory for the electrical double layer (EDL) of SiILs where we consistently account for the thermoreversible association of ions into Cayley tree aggregates. The theory predicts that the IL cations first populate the EDL at negative voltages, as they are not strongly bound to the anions. However, at large negative voltages, which are strong enough to break the alkali metal cation-anion associations, these IL cations are exchanged for the alkali metal cation because of their higher charge density. At positive voltages, we find that the SiIL actually becomes more aggregated while screening the electrode charge from the formation of large, negatively charged aggregates. Therefore, in contrast to conventional intuition of associations in the EDL, SiILs appear to become more associated in certain electric fields. We present these theoretical predictions to be verified by molecular dynamics simulations and experimental measurements.

An ionic liquid containing arsonium cation.

Cations in ionic liquids (ILs) are typically derived from ammonium or phosphonium structures with long alkyl chains, and it is well established that the central atom significantly influences the properties of the resulting ILs. In this study, an arsonium-based IL, trihexylmethylarsonium bis(trifluoromethylsulfonyl)amide, was synthesized. The arsonium cation was found to contribute to lower viscosity and higher ionic conductivity, while maintaining sufficient stability compared to its phosphonium counterpart.

Does the active hydrogen atom in the hydantoin anion affect the physical properties, CO2 capture and conversion of ionic liquids?

Compared to the effect of the active hydrogen atom in the cation in protic ionic liquids (ILs) on their properties and applications, there are very few reports on the role of the active hydrogen atom in the anion. In order to better understand the role of the active hydrogen atom in the anion, the physical properties, CO2 capture and conversion of three hydantoin-based anion-functionalized ILs ([P4442][Hy], [P4442]2[Hy], and [HDBU][Hy]) have been investigated via experiments, spectroscopy, and DFT calculations in this work. The results show that the active hydrogen atom in the anion can form anionic hydrogen bonding networks, which significantly increase the melting point and viscosity and decrease the basicity of the IL, thereby weakening its ability to capture and convert CO2. Interestingly, [P4442][Hy] undergoes a solid/liquid two-phase transition during CO2 absorption/desorption due to the formation of quasi-intramolecular hydrogen bonding between the active hydrogen atom and the O- atom of the absorbed CO2, suggesting that the presence of the active hydrogen atom gives [P4442][Hy] the potential to be an excellent molecular switch. As there is no active hydrogen atom in the anion of [P4442]2[Hy], it shows excellent CO2 capture and conversion performance through the double-site interaction. [HDBU][Hy] shows the weakest catalytic CO2 conversion due to the presence of active hydrogen atoms on both its anion and cation. Therefore, the active hydrogen atom in the anion may play a more important role in the properties and potential applications of ILs than the active hydrogen atom in the cation.