Driven by the potential applications of ionic liquids (ILs) in many emerging electrochemical technologies, recent research efforts have been directed at understanding the complex ion ordering in ...these systems, to uncover novel energy storage mechanisms at IL-electrode interfaces. Here, we discover that surface-active ILs (SAILs), which contain amphiphilic structures inducing self-assembly, exhibit enhanced charge storage performance at electrified surfaces. Unlike conventional non-amphiphilic ILs, for which ion distribution is dominated by Coulombic interactions, SAILs exhibit significant and competing van der Waals interactions owing to the non-polar surfactant tails, leading to unusual interfacial ion distributions. We reveal that, at an intermediate degree of electrode polarization, SAILs display optimum performance, because the low-charge-density alkyl tails are effectively excluded from the electrode surfaces, whereas the formation of non-polar domains along the surface suppresses undesired overscreening effects. This work represents a crucial step towards understanding the unique interfacial behaviour and electrochemical properties of amphiphilic liquid systems showing long-range ordering, and offers insights into the design principles for high-energy-density electrolytes based on spontaneous self-assembly behaviour.
Porous liquids can be prepared from the dispersion metal–organic frameworks (MOFs) in ionic liquids (ILs). Porous liquids prepared from 5 % of ZIF‐8 in a phosphonium‐based ionic liquid are capable of ...absorbing reversibly up to 150 % more nitrogen and 100 % more methane than the pure ionic liquid.
Gas absorbent: Porous liquids can be prepared from the dispersion metal–organic frameworks in ionic liquids. Porous liquids prepared from 5 % of ZIF‐8 in a phosphonium‐based ionic liquid are capable of absorbing reversibly up to 150 % more nitrogen and 100 % more methane than the pure ionic liquid.
The polarizable CL&Pol force field presented in our previous study, Transferable, Polarizable Force Field for Ionic Liquids (J. Chem. Theory Comput. 2019, 15, 5858, DOI: ...http://doi.org/10.1021/acs.jctc.9b0068910.1021/acs.jctc.9b00689), is extended to electrolytes, protic ionic liquids (PIL), deep eutectic solvents (DES), and glycols. These systems are problematic in polarizable simulations because they contain either small, highly charged ions or strong hydrogen bonds, which cause trajectory instabilities due to the pull exerted on the induced dipoles. We use a Tang–Toennies (TT) function to dampen, or smear, the interactions between charges and induced dipole at a short range involving small, highly charged atoms (such as hydrogen or lithium), thus preventing the “polarization catastrophe”. The new force field gives stable trajectories and is validated through comparison with experimental data on density, viscosity, and ion diffusion coefficients of liquid systems of the above-mentioned classes. The results also shed light on the hydrogen-bonding pattern in ethylammonium nitrate, a PIL, for which the literature contains conflicting views. We describe the implementation of the TT damping function, of the temperature-grouped Nosé–Hoover thermostat for polarizable molecular dynamics (MD) and of the periodic perturbation method for viscosity evaluation from non-equilibrium trajectories in the LAMMPS MD code. The main result of this work is the wider applicability of the CL&Pol polarizable force field to new, important classes of fluids, achieving robust trajectories and a good description of equilibrium and transport properties in challenging systems. The fragment-based approach of CL&Pol will allow ready extension to a wide variety of PILs, DES, and electrolytes.
Liquids with permanent porosity Giri, Nicola; Del Pópolo, Mario G; Melaugh, Gavin ...
Nature (London),
11/2015, Letnik:
527, Številka:
7577
Journal Article
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Porous solids such as zeolites and metal-organic frameworks are useful in molecular separation and in catalysis, but their solid nature can impose limitations. For example, liquid solvents, rather ...than porous solids, are the most mature technology for post-combustion capture of carbon dioxide because liquid circulation systems are more easily retrofitted to existing plants. Solid porous adsorbents offer major benefits, such as lower energy penalties in adsorption-desorption cycles, but they are difficult to implement in conventional flow processes. Materials that combine the properties of fluidity and permanent porosity could therefore offer technological advantages, but permanent porosity is not associated with conventional liquids. Here we report free-flowing liquids whose bulk properties are determined by their permanent porosity. To achieve this, we designed cage molecules that provide a well-defined pore space and that are highly soluble in solvents whose molecules are too large to enter the pores. The concentration of unoccupied cages can thus be around 500 times greater than in other molecular solutions that contain cavities, resulting in a marked change in bulk properties, such as an eightfold increase in the solubility of methane gas. Our results provide the basis for development of a new class of functional porous materials for chemical processes, and we present a one-step, multigram scale-up route for highly soluble 'scrambled' porous cages prepared from a mixture of commercially available reagents. The unifying design principle for these materials is the avoidance of functional groups that can penetrate into the molecular cage cavities.
The dissolution of microcrystalline cellulose in 1-butyl-3-methylimidazolium acetate C sub(4)C sub(1)ImOAc was studied using a solid-liquid equilibrium method based on polarized-light optical ...microscopy from 30 to 100 degree C. We found that C sub(4)C sub(1)ImOAc could dissolve as much as 25 wt% of cellulose at temperatures below 100 degree C. The structure of the composite phase obtained after cooling a solution of 16 wt% of cellulose in C sub(4)C sub(1)ImOAc was analyzed by low angle X-ray diffraction showing the absence of microcrystalline cellulose, but depicting an extensive long range isotropic ordering. With the aim of improving the dissolution of cellulose in the ionic liquid, dimethyl sulfoxide, DMSO, was added as a co-solvent. It was observed that it enhances the solvent power of the ionic liquid by decreasing the time needed for dissolution, even at low temperatures. In order to understand what makes DMSO a good co-solvent, two approaches were followed. Firstly, we studied experimentally the mass transport properties (viscosity and ionic conductivity) of C sub(4)C sub(1)ImOAc + DMSO mixtures at different compositions and, secondly, we assessed the molecular structure and interactions around glucose, the structural unit of cellulose, by means of molecular dynamics simulations. As expected, DMSO dramatically decreases the viscosity and increases the conductivity of the mixtures, but without inducing cation-anion dissociation in the ionic liquid. These results were confirmed by molecular simulation as it was found that the presence of a 0.5 mole fraction concentration of DMSO does not significantly affect the hydrogen-bond network in the ionic liquid. Furthermore, molecular dynamics shows that in the C sub(4)C sub(1)ImOAc + DMSO equimolar mixture, DMSO does not interact specifically with glucose. We conclude that DMSO improves the solvation capabilities of the ionic liquid because it facilitates mass transport by decreasing the solvent viscosity without significantly affecting the specific interactions between cations and anions or between the ionic liquid and the polymer. The behavior of DMSO as a co-solvent was compared with that of water and it was found that water molecules are more probably found near glucose than those of DMSO, thus interfering with ionic liquid-glucose interactions, which might explain the unsuitability of water as a co-solvent for cellulose in ionic liquids.
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•Determination of partition coefficients of VOCs alone or in mixtures.•Hydrophilic and hydrophobic DESs present high affinity towards various VOCs.•Evaluation of DESs absorption ...capacities using a bubble method under various conditions.•DESs can be easily regenerated and maintain their high absorption capacities.•DESs are promising absorbents to capture VOCs from industrial exhaust.
Volatile organic compounds (VOCs) are primary air pollutants emitted directly from industries with adverse health effects and environmental impacts. Absorption is an attractive method to treat industrial exhaust loaded with VOCs, but most actual absorbents are often toxic and non-biodegradable. This work aims to evaluate deep eutectic solvents (DESs) as absorbents for VOCs using static and dynamic processes. The determination of vapour-liquid partition coefficient was performed for nine VOCs, from different chemical families, in eight hydrophilic and hydrophobic DESs, at different temperatures. The influence of VOC mixtures on DESs absorption capacities was determined for two different mixtures. DESs showed high absorption capacities for a variety of VOCs, without saturation even at high VOC concentration. The absorption capacities of DESs were also evaluated using a dynamic set-up which simulated an industrial absorption column. This set-up allows the modulation of the VOC flow rate, water content and column temperature. Both static and dynamic results are in good agreement. The DES based on tetrabutylammonium bromide and decanoic acid displayed high absorption capacities and versatility for the different tested VOCs, with a maximum enhancement of absorption reaching 60000-folds for 1-decene at 303 K, compared to water. The regeneration of the absorbent was carried out by several absorption/desorption cycles or after water removal, without loss of absorption capacity. The overall results show that DESs have characteristics that allow them to be considered as promising solvents for VOCs absorption.
Another way to produce porous liquids is to dissolve cage molecules in solvents that consist of bulky molecules (or in ionic liquids that consist of bulky ion pairs), so that the solvent cannot enter ...the cages3. The authors found that their colloids have a lower density than that of pure liquid water, indicating that the pores in the solids do not fill with water molecules in the aqueous suspensions. ...proof of this was obtained from molecular simulations, which showed that water molecules forced into the pores are spontaneously expelled. ...the simulations showed that oxygen is rapidly adsorbed from aqueous solution by the suspended porous solids.
The synthesis of ionic liquids can generate large amounts of waste and use toxic or expensive raw materials. In this short review, we focused on one of the most promising pathways to large scale ...environment-friendly productions of ionic liquids. The "dialkylcarbonate route" has already allowed the preparation of more than one hundred original ion pairs, avoiding the use of pollutant alkylating agents and non-sustainable anion exchange materials, in a halide-free and water-free process.
The synthesis of ionic liquids can generate large amounts of waste and use toxic or expensive raw materials.
The absorption of carbon dioxide by the pure ionic liquids 1-ethyl-3-methylimidazolium acetate (C1C2ImOAc) and 1-butyl-3-methylimidazolium acetate (C1C4ImOAc) was studied experimentally from 303 to ...343 K. As expected, the mole fraction of absorbed carbon dioxide is high (0.16 at 303 K and 5.5 kPa and 0.19 at 303 and 9.6 KPa for C1C2ImOAc and C1C4ImOAc, respectively), does not obey Henry’s law, and is compatible with the chemisorption of the gas by the liquid. Evidence of a chemical reaction between the gas and the liquid was found both by NMR and by molecular simulation. In the presence of water, the properties of the liquid absorber significantly change, especially the viscosity that decreases by as much as 25% (to 78 mPa s) and 30% (to 262 mPa s) in the presence of 0.2 mol fraction of water for C1C2ImOAc and C1C2ImOAc at 303 K, respectively. The absorption of carbon dioxide decreases when the water concentration increases: a decrease of 83% in CO2 absorption is found for C1C4ImOAc with 0.6 mol fraction of water at 303 K. It is proved in this work, by combining experimental data with molecular simulation, that the presence of water not only renders the chemical reaction between the gas and the ionic liquid less favorable but also lowers the (physical) solubility of the gas as it competes by the same solvation sites of the ionic liquid. The lowering of the viscosity of the liquid absorbent largely compensates these apparent drawbacks and the mixtures of C1C2ImOAc and C1C2ImOAc with water seem promising to be used for carbon dioxide capture.
In this study, we have focused on binary mixtures composed of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)-imide, C4C1imNtf2, and a selection of six molecular components (acetonitrile, ...dichloromethane, methanol, 1-butanol, t-butanol, and water) varying in polarity, size, and isomerism. Two Kamlet–Taft parameters, the polarizability π* and the hydrogen bond acceptor β coefficient were determined by spectroscopic measurements. In most cases, the solvent power (dipolarity/polarizability) of the ionic liquid is only slightly modified by the presence of the molecular component unless large quantities of this component are present. The viscosity and electrical conductivity of these mixtures were measured as a function of composition and the relationship between these two properties were studied through Walden plot curves. The viscosity of the ionic liquid dramatically decreases with the addition of the molecular component. This decrease is not directly related to the volumetric properties of each mixture or its interactions. The conductivity presents a maximum as a function of the composition and, except for the case of water, the conductivity maxima decrease for more viscous systems. The Walden plots indicate enhanced ionic association as the ionic liquid gets more diluted, a situation that is the inverse of that usually found for conventional electrolyte solutions.
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