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Liquid-liquid extraction (LLE) is an important technique to separate aromatics from aliphatics since these compounds have very similar boiling points and cannot be separated by distillation. Ionic liquids (ILs) are considered as potential extractants to extract aromatics from aliphatics. In this paper, molecular dynamics (MD) simulations were used to predict the extraction property (i.e., capacity and selectivity) of ILs for the LLE of aromatics from aliphatics. The extraction properties of seven different ILs including [C 2 mim][Tf 2 N], [C 2 mim][TFO], [C 2 mim][SCN], [C 2 mim][DCA], [C 2 mim][TCM], [C 4 mim][Tf 2 N], and [C 8 mim][Tf 2 N] were investigated. Results show that ILs with shorter alkyl chain cations and [Tf 2 N] - anion exhibit better extraction efficiency than other ILs, which is in agreement with previously reported experimental data on the extraction of toluene from aliphatics and further validated the reliability of the proposed model. The binding energies between ILs and organic molecules were calculated by the density functional theory, which help explain the different extraction behaviors of different ILs. The symmetry-adapted perturbation theory analysis was performed to further understand the interaction mechanisms between ILs and organics. Our study shows that the [Tf 2 N] - anion also has the best extraction capability for heavier aromatics ( o -xylene, m -xylene, and p -xylene) from common aliphatics (heptane and octane). The MD modeling approach can be a low-cost in silico tool for the high-throughput fast screening of ILs for the LLE of aromatics from aliphatics.

Trace detection based on surface-enhanced Raman scattering (SERS) has attracted considerable attention, and exploiting efficient strategies to stretch the limit of detection and understanding the mechanisms on molecular level are of utmost importance. In this work, we use ionic liquids (ILs) as trace additives in a protein-TiO 2 system, allowing us to obtain an exceptionally low limit of detection down to 10 -9 M. The enhancement factors (EFs) were determined to 2.30 × 10 4 , 6.17 × 10 4 , and 1.19 × 10 5 , for the three systems: one without ILs, one with ILs in solutions, and one with ILs immobilized on the TiO 2 substrate, respectively, corresponding to the molecular forces of 1.65, 1.32, and 1.16 nN quantified by the atomic force microscopy. The dissociation and following hydration of ILs, occurring in the SERS system, weakened the molecular forces but instead improved the electron transfer ability of ILs, which is the major contribution for the observed excellent detection. The weaker diffusion of the hydrated IL ions immobilized on the TiO 2 substrate did provide a considerably greater EF value, compared to the ILs in the solution. This work clearly demonstrates the importance of the hydration of ions, causing an improved electron transfer ability of ILs and leading to an exceptional SERS performance in the field of trace detection. Our results should stimulate further development to use ILs in SERS and related applications in bioanalysis, medical diagnosis, and environmental science.

Reducing carbon dioxide emissions is one of the possible solutions to prevent global climate change, which is urgently needed for the sustainable development of our society. In this work, easily available, biodegradable amino acid ionic liquids (AAILs) with great potential for CO 2 absorption in the manned closed space such as spacecraft, submarines and other manned devices are used as the basic material. Molecular dynamics simulations and ab initio calculations were performed for 12 AAILs ([P4444][X] and [P66614][X], [X] = X = [GLy] - , [Im] - , [Pro] - , [Suc] - , [Lys] - , [Asp] 2- ), and the dynamic characteristics and the internal mechanism of AAILs to improve CO 2 absorption capacity were clarified. Based on structural analysis and the analysis of interaction energy including van der Waals and electrostatic interaction energy, it was revealed that the anion of ionic liquids dominates the interaction between CO 2 and AAILs. At the same time, the CO 2 absorption capacity of AAILs increases in the order [Asp] 2- < [Suc] - < [Lys] - < [Pro] - < [Im] - < [Gly] - . Meanwhile, the synergistic absorption of CO 2 by multiple-sites of amino and carboxyl groups in the anion was proved by DFT calculations. These findings show that the anion of AAILs can be an effective factor to regulate the CO 2 absorption process, which can also provide guidance for the rational and targeted molecular design of AAILs for CO 2 capture, especially in the manned closed space.

Ionic liquids (ILs) are promising nonderivatizing solvents for the dissolution of cellulose and lignin in biomass pretreatment processes, which are, however, retarded by sluggish dynamics. Recent investigations showed that cosolvents such as dimethyl sulfoxide (DMSO) can accelerate the dissolution dramatically. On the other hand, water is used as a common antisolvent to regenerate cellulose from solutions. To understand the co-/antisolvent effects in dissolving cellulose by ILs, we performed molecular dynamics simulations of the interfaces between an Iβ cellulose crystal and different solvent systems, including ILs, DMSO, water, and mixed solvent systems. The density profiles and pair energy distributions (PEDs) show that the anions interact much more strongly with the cellulose surface than the cations, which is responsible for the dissolution of cellulose. It was found that the number of chloride ions in contact with cellulose does not cause the co-/antisolvent effect. In contrast, the cellulose-chloride PEDs are sensitive to the addition of molecular solvents, such as DMSO and water. Detailed analyses show that multiple hydrogen-bond (HB) patterns are formed between chloride and the hydroxyl groups of cellulose that are noticeably changed in the presence of DMSO or water. A combined analyses of both the PEDs and HB patterns can provide valuable information about the enhancement of cellulose dissolution. The simulation results in this work present useful knowledge for the design of solvent systems for dissolving cellulose or other types of biomass.

Understand the structure of the ILs/air interface on a molecular level is significant. In this work, the liquid-air interface of a class of ILs containing 1-alkyl-3-methylimidazolium cations ([Cnmim]+, n = 4, 6 and 8) was investigated by a sum-frequency generation vibrational spectroscopy experiment. The length of the alkyl chain of cations and anion type (tetrafluoroborate ([BF4]−), thiocyanate ([SCN]−), dicyanamide ([DCA]−), hexafluorophosphate ([PF6]−)) were varied to determine their intrinsic effects to the micro-structure on the interface. Meanwhile, combining with the experiment, the orientation angle and surface density for cations and anions of ILs at the air interface was analyzed by molecular dynamics simulation. It is found that the butyl side chain of cations protrudes out into the air as well as the orientation angle between the side chain and interface is 30°–50°. Meanwhile, the anion volume of ILs has almost no influence on the butyl side chain and the methyl on the side chains tend almost planar to the interface with the increased chain length. This research is highly significant for the theoretical and quantitative understanding of the interface chemistry of imidazole-based ILs. [ABSTRACT FROM AUTHOR]

Evaporation power generation (EPG), hailed as a promising clean power generation technology, has garnered significant attention. Nonetheless, achieving consistent and replicable performance of EPG remains a major challenge, hampering its practical application potential. Herein, we present the design of a tri-layered poly-ionic membrane (TL-PIM) inspired by transpiration processes in plants, that can not only continuously output electricity with an average voltage of ∼0.6 V for over 8 consecutive days with a maximum power density of 1.6 µW cm−2, but can also be reused for at least 70 cycles (> 350 h) with a stable voltage, demonstrating superior repeatability over most previous works. The excellent long-lasting and repeatable performance of EPG in the TL-PIM can be attributed to the stable nanochannels constructed by a hydrophilic polymer, 2D nanosheets, and poly-ionic liquids (PILs), where the bromide ions (Br-) in the PILs can shuttle back and forth selectively and efficiently during the power generation and discharge processes. More importantly, the TL-PIM can be integrated linearly to generate electricity within a wide range of temperatures and humidity, even outdoors, showcasing remarkable environmental adaptability. These findings on EPG indicate that the bio-inspired TL-PIM offers a promising venue for continuous and reproducible electricity generation by harnessing thermal energy from moisture, which holds significance for the sustainable utilization of EPG as a renewable energy source in the future. [Display omitted] • A novel three-layer multi-ion membrane inspired by the plant transpiration process is prepared. • Stable nanochannels lead to long-lasting and repeatable evaporation power performance. • The evaporation power generation can continuously supply electricity with 0.6 V for 180 h. [ABSTRACT FROM AUTHOR]

Ionic liquids with stimuli‐responsive characteristics are an essential branch in the comprehensive ionic liquids' family, which can meet the controllable and reversible needs in practical applications with different stimulation means. In this review, we summarize the recent research progress of these stimuli‐responsive ionic liquids, mainly focusing on their chemical structures, properties, responsive mechanism, aggregation structures, and phase behaviors, which were driven by external stimuli, such as CO2, magnetism, light, temperature, redox, and pH. Then, the particular or potential applications of stimuli‐responsive ionic liquids are expounded in various fields of science, including catalytic reaction, extraction, separation, nanomaterial preparation, and gas absorption. In the end, the challenges and strategies of the subject are briefly presented. It is expected that this review will contribute to the rational design and applications of stimuli‐responsive ionic liquids in the future. [ABSTRACT FROM AUTHOR]

The transport behavior of CO2 at the ionic liquids (ILs)‐electrode interface was revealed from the thermodynamic view via molecular dynamics simulations. The hopping and self‐diffusive mechanisms were identified in the interfacial and bulk region, and thereafter a hopping‐diffusion model was developed to evaluate the transport resistance of CO2 from bulk to the interface. Meanwhile, the vibrational spectrum and entropy change of CO2 at the interface were calculated using the thermodynamic analysis method. For ILs with the same cation ([Emim]+), both transport resistance and entropy decrease follow the order: [BF4]− < [AC]− < [NO3]−, indicating [BF4]− possesses the faster CO2 transport efficiency across the electrical double layer. Furthermore, the methyl substitution effect on transport and thermodynamic properties was clarified, indicating the coupling relation between the transport process and thermodynamic advantage. These findings can lay the ground for the molecule design of ILs‐electrode interface in the applications in the chemical engineering field. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotubes (SWNTs) tend to aggregate to heavily tangled bundles due to the strong van der Waals attraction. Ionic liquids (ILs) are a kind of newly proposed solvents in which SWNT can be physically well dispersed. In this article, the cylindrical interface has been investigated by molecular dynamics simulation between IL of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) and an infinite long armchair (6,6) SWNT. The highly ordered structure of the cations and anions is elucidated by the simulation results. Two evident dense layers are found for both the cations and anions along the surface normal direction of the SWNT. In addition, we have observed two different orientation patterns of the cations in the first layer. In sublayer 1A, which is the nearest to the surface, the imidazolium rings of the cations prefer to be parallel to the surface, with a slight tilt angle less than 15°. In sublayer 1B, they tend to be perpendicular to the surface, with their butyl chains appearing in sublayer 1A. The [BF4]− anions are found to cling to the nanotube surface with three fluoride atoms, also indicating a highly ordered orientation. The simulation results in this work provide a clue to understand the stabilisation and dispersion of SWNT bundles in ILs. [ABSTRACT FROM AUTHOR]

• Three low viscous protic ionic liquids were synthesized for CO 2 absorption. • The ionic liquids with larger basicity show higher CO 2 absorption capacity. • Addition of H 2 O influences greatly the CO 2 absorption performance of [TMGH][Im]. • Different products were obtained in [TMGH][Im] and [TMGH][Im]-H 2 O systems. Protic ionic liquids (PILs) are considered as potential solvents for CO 2 capture due to their simple synthetic routes and unique properties. In this work, three low viscous PILs, tetramethylgunidinium imidazole ([TMGH][Im]), tetramethylgunidinium pyrrole ([TMGH][Pyrr]) and tetramethylgunidinium phenol ([TMGH][PhO]) were synthesized and the effect of anions, temperature, CO 2 partial pressure and water content on CO 2 absorption performance of PILs was also systematically studied. It was found that the PILs with larger basicity show higher CO 2 absorption capacity, and [TMGH][Im] simultaneously shows relatively high absorption rate and CO 2 absorption capacity of 0.154 g CO 2 /g IL at 40 °C, 1 bar. The addition of H 2 O has a positive effect on gravimetric absorption capacity of CO 2 at the range of 0–20 wt% H 2 O, and the highest capacity of 0.186 g CO 2 /g IL was achieved as the water content was 7 wt%. In situ FTIR, 13C NMR and theoretical calculations verified that more stable bicarbonate are produced during CO 2 absorption by [TMGH][Im]-H 2 O system. However, neat [TMGH][Im] can react with CO 2 to form the reversible carbamate, leading to excellent recyclability after four absorption-desorption cycles. The results implied that neat [TMGH][Im] shows great potentials in CO 2 absorption applications. [ABSTRACT FROM AUTHOR]

Abstract A large number of NH 3 emissions from industries, such as ammonia plant purge gas, tail gases of urea plants and ammonium molybdate plants, inevitably cause serious air pollution problems, such as fog and haze, which has raised extensive attentions worldwide. However, the commercial methods, like water scrubbing and acid scrubbing, substantially transfer the NH 3 pollute from gas phase to liquid or solid phase, which does not mean total elimination. How to realize efficiently separate and recover NH 3 form NH 3 -containing gas mixtures is still a great challenge. In order to develop efficient absorbents for NH 3 removal, a series of metal (copper (Cu), stannum (Sn), nickel (Ni), manganese (Mn), cadmium (Cd), zinc (Zn), ferrum (Fe)) ionic liquids (MILs) were synthesized, and their physicochemical properties and NH 3 absorption performance were systematically investigated. The results implied that the incorporation of metal center into ILs has a great effect on NH 3 absorption. Among the investigated MILs, bis(1-butyl-3-methyl imidazolium) copper tetrachloride salt ([Bmim] 2 [CuCl 4 ]) and bis(1-butyl-3-methyl imidazolium) stannum tetrachloride salt ([Bmim] 2 [SnCl 4 ]) show excellent NH 3 absorption capacities up to 0.172 gNH 3 ·gIL−1 and 0.106 gNH 3 ·gIL−1, respectively, which are far more than most of the conventional ILs. Moreover, the high selectivity for NH 3 /N 2 , NH 3 /CO 2 and NH 3 /O 2 of [Bmim] 2 [CuCl 4 ] and [Bmim] 2 [SnCl 4 ] indicated that these MILs can selectively separate NH 3 from NH 3 -containing gases. The absorption mechanism was further studied using Fourier transform infrared (FT-IR) spectroscopy and quantitative chemical calculations. It was demonstrated that the chemical complexation between [Bmim] 2 [CuCl 4 ] and NH 3 plays a dominant role in NH 3 absorption, but the stronger hydrogen bonding between [Bmim] 2 [SnCl 4 ] and NH 3 enhances the absorption performance. In addition, [Bmim] 2 [SnCl 4 ] can keep good stability after five absorption and desorption cycles, implying this MIL shows great potentials as an efficient and reversible absorbent for NH 3 capture applications. Graphical abstract Novel metal chloride anion-based ionic liquids have been designed for efficient separation of NH 3 , and both high NH 3 absorption capacity and excellent recyclability were simultaneously achieved by stannum ionic liquids [Bmim] 2 [SnCl 4 ]. Image Highlights • The incorporation of metal center into ILs can obviously enhance NH 3 absorption capacity in metal ionic liquids (MILs). • [Bmim] 2 [CuCl 4 ] and [Bmim] 2 [SnCl 4 ] have higher NH 3 capacity and NH 3 selectivity towards other gases. • The chemical complexation plays a dominant role in NH 3 absorption in [Bmim] 2 [CuCl 4 ], resulting in its irreversibility. • NH 3 absorption occurs in [Bmim] 2 [SnCl 4 ] through the strong hydrogen bonding, therefore showing great recyclability. [ABSTRACT FROM AUTHOR]

Abstract In this study, we have developed an all-atom force field with three-body hydrogen bond model for 1‑ethyl‑3‑methyl‑imidazolium chloride ([Emim][Cl]), predicted the experimental dynamic viscosity successfully and calculated the relationship between dynamic properties and ion pair (IP) structures relaxation time. The partial atom charges and parameters of Lennard-Jones and hydrogen bond model are derived from ab initio molecular dynamic (AIMD) simulations. The strategy is that charges are fitted by AIMD structures and parameters are adjusted to make structure consistent between molecular dynamic (MD) and AIMD. The dynamic viscosities were calculated by Green-Kubo (GK) relation and were in excellent agreement with experiments results. Structure of ionic liquids was studied by using several distribution functions and IP time response was calculated. The calculated IP lifetime was found in linear correlation with viscosity and self-dynamic coefficient. Highlights • Hydrogen bond model improves simulation structures and properties calculation. • Atom charges were assigned by fitting electric density of the multi ion pairs. • Reliable sheer viscosities of ILs were computed by Green-Kubo relations. • Transport properties are related to ion pair's lifetime. [ABSTRACT FROM AUTHOR]

The recovery of carboxylic acids from dilute aqueous solution is necessary but difficult in chemical industry. Methacrylic acid (MAA) is an important chemical widely used in polymer industry. In this work, the recovery of carboxylic acid from diluted aqueous solution by liquid-liquid extraction using ionic liquids (ILs) as extractants was studied. MAA was employed as model carboxylic acid. The partition coefficients of MAA in biphasic system and the extraction efficiencies of MAA were determined for imidazolium-based ILs and quaternary ammonium salt ILs with different structure of cation and anion. The extraction conditions such as extraction time, extraction temperature, mass ratio of ILs to MAA aqueous solution, initial concentrations of MAA, and water content were evaluated. An internal mechanism of the MAA extract by ILs was revealed by combining solvatochromic study, FT-IR and quantum chemical calculations. The results show that the strong hydrogen bond basicity (β) of ILs results in the high partition coefficient of MAA, which provides guidance to molecular design of ILs for the high efficient extractive separation of MAA from diluted aqueous solution. Based on this, IL with strong hydrogen bond basicity ([N 8881 ]Cl) was used to extract MAA from dilute aqueous solution. Compared with hexane which is conventional solvent used in MAA extractive separation, [N 8881 ]Cl can get 49 times higher of partition coefficient value and the extraction efficiency reach 94.57% for the single-stage extraction. [ABSTRACT FROM AUTHOR]

In this work, the alkylation of isobutane and butene, catalyzed by sulfuric acid in the presence of the fluoride–containing ionic liquids [Bmim][PF 6 ] and [Bmim][SbF 6 ], was investigated. The use of the binary mixture catalysts brought to a higher C 8 selectivity and longer catalyst lifetime, compared with the results obtained when working with sulfuric acid only. This was attributed to the formation of new species when [Bmim][PF 6 ] or [Bmim][SbF 6 ] are added to sulfuric acid. The acidolysis of [Bmim][PF 6 ] and [Bmim][SbF 6 ] was accompanied by the release of hydrogen fluoride (HF) and the decomposition of anions to [PF 6−x−2y (HSO 4 ) x (SO 4 ) y ] − and [SbF 6−x−2y (HSO 4 ) x (SO 4 ) y ] − , respectively. The presence of these new species after acidolysis was measured and confirmed by ion chromatography, 1 H–Nuclear Magnetic Resonance (NMR), 19 F–NMR and 31 P–NMR. The production of HF and the complexation of anions and carbenium ions both play an important role in stabilizing the carbenium ion and improving the catalytic performance. [ABSTRACT FROM AUTHOR]

• MD simulations of electrokinetic nanoconfined ionic liquids flow were performed. • The perpendicular configuration of cation at the silica surface was identified. • Modulating mechanism of external stimuli on electrokinetic flow of ionic liquids. • Developed quantitative relation between streaming current and external stimuli. The electrokinetic flow of ionic liquids (ILs) is widely used in electrochemical engineering applications. Herein, flow behavior and controlling mechanism of ILs driven by electrical field were investigated via molecular dynamics simulations. During the flow process, the cations prefer to allocate at the interface in a perpendicular configuration, while the anions tend to distribute randomly. In the interface region, the perpendicular cations and accumulated ILs would significantly enhance the local viscosity of ILs, which dominates the velocity distribution and total flux of the electrokinetic flow of confined ILs. Compared with the pressure and surface charging density, the nanochannel size would induce a larger impact on the average velocity, total flux, and streaming current of the electrokinetic flow of confined ILs. These quantitative results on the electrokinetic flow are crucial for the rational design of ILs-based devices or other chemical engineering processes. [ABSTRACT FROM AUTHOR]

• COSMO-RS is used for screening > 103 ILs with highly efficient in lignin dissolving. • Calculations and experiment prove the dissolving of IL is mainly modulated by H-bond. • [PMpyrr][OAC] ILs with the ability to dissolve lignin strongly. • The solubility of lignin in IL is related to the structure of lignin model. As the second most abundant terrestrial polymer, lignin has emerged as a major sustainable source for the production of fuels, chemicals, and materials. However, efficient screening of solvents for lignin dissolving faces great challenges. In this work, COSMO-RS was used to screen 3886 ionic liquids (ILs) composed of 58 cations and 67 anions, to find out the most effective ones for lignin dissolving by considering the critical items of logarithmic infinite dilution activity coefficient (lnγ∞) and σ-profiles. The substantial improvement of lignin dissolution was achieved in [PMpyrr][OAc] IL by both simulations and experiments validations. Moreover, it was found that the anions dominate the dissolution process and the strongly polar anions exhibit better dissolution ability. Furthermore, the underlying mechanism originated from the hydrogen bond (H-bond) between ILs and lignin was also revealed and systemically analyzed from donor and acceptor ability, indicating that high lignin solubility is reached in the ILs with stronger ability to form H-bond acceptors. This work leads to possible ways toward developing more selective and efficient lignin dissolution methods based on solvent properties. [ABSTRACT FROM AUTHOR]

• A novel coarse-grained model for poly (ionic liquids) system was developed. • The potential parameters of coarse-grained model are obtained by Boltzmann and iterative Boltzmann inversion method. • The structural and thermodynamic properties could been reproduced under the CG model comparing with the AA force field. A novel coarse-grained (CG) model for poly (1-vinyl-3-ethylimidazolium) tetrafluoroborate ([PVEim][BF 4 ]) was developed with the all-atom (AA) molecular dynamics simulations as a benchmark. In this model, the bonded and non-bonded potential parameters of CG force field were obtained by Boltzmann and iterative Boltzmann inversion, respectively. The simulation results show that the novel CG model can accurately describe the structural characteristics and reproduce the thermodynamic properties comparing with the AA force field model. The deviation of densities values between CG model and experiment was within 5% at 298 K. This work can be a useful guide to the computational for large-scale PILs systems. [ABSTRACT FROM AUTHOR]