Mixed Ionic Liquids: The Case of Pyridinium-Based Fluids

We report in this work a combined experimental and computational study on the molecular level structuring of binary ionic liquid mixtures comprising pyridium cations. The effect of anions on liquid structure was analyzed from the mixing (mixture 1) of [b3mpy]­[BF₄] and [b3mpy]­[N­(CN)₂] ionic liquids, in the full composition range, leading to [b3mpy]­[BF₄]_<i>x</i>[N­(CN)₂]_1–<i>x</i> mixed ionic liquids. The effect of the length of alkylic chains in cations was studied with mixtures (mixture 2) of [b3mpy]­[BF₄] and [o3mpy]­[BF₄] ionic liquids, also studied in the full composition range, leading to [b3mpy]_<i>x</i>[o3mpy]_1–<i>x</i>[BF₄] ionic liquids. Fourier transform infrared–attenuated total reflection spectra were recorded and analyzed as a function of anionic and cationic composition for the two studied mixture types. Classical molecular dynamics simulations were also performed for mixtures 1 and 2 as a function of anionic and cationic composition. The reported experimental and computational results show that the properties of the studied mixed systems change in an almost linear way, leading to almost ideal mixtures from the thermodynamic viewpoint, and thus pointing to simple dilution effects of the involved ions controlling the mixture properties

Theoretical Study of Low Viscous Ionic Liquids at the Graphene Interface

The interaction of 1-ethyl-3-methylimidazolium dicyanamide ionic liquid with graphene was studied using computational chemistry methods with quantum chemistry and classical dynamics approaches. The adsorption of this ionic liquid at the graphene surface, the structure at the interfaces, and layering were analyzed. The arrangement of ions and composition at adsorbed layers was determined together with the strength of ion–graphene interactions. Likewise, the disrupting effect of graphene on ionic liquid structure and interionic interactions was considered. The effect of ionic liquid on graphene–graphene interactions was studied and potential of mean force calculated to infer the possible screening effect of this ionic liquid and its relationship with its graphene exfoliation ability

Molecular Dynamics Simulations of Metal Nanoparticles in Deep Eutectic Solvents

A molecular dynamics study on the solvation of metal nanoparticles in deep eutectic solvents is reported in this work. The solvation process was analyzed in terms of the type of metal, geometry of the nanoparticles and properties of the deep eutectic solvent. Simulations results in the microsecond range allowed to infer the properties of the solvation shells and the effects of the nanoparticles on the liquid structuring. The possible aggregation of metal nanoparticles in the studied solvents was analyzed and discussed in terms of the screening effect of the solvents and the efficient nanoparticle–solvent intermolecular forces. The reported results show deep eutectic solvents acting as metal nanoparticle stabilizers, thus providing a new platform for nanoparticles technologies

Molecular Dynamics Study of Carbon Nanostructures in <i>N</i>‑Methylpiperazinium Lactate Ionic Liquid

The results of classical molecular dynamics simulations on the behavior and properties of the new <i>N</i>-methylpiperazinium lactate ionic liquid with regard to a wide collection of carbon nanostructures including nanotubes, graphene sheets, graphene nanoribbons, nanotube junctions, and nanopores are reported in this work. Ionic liquid confinement in the studied nanostructures and nanostructure solvation by the ionic liquid are studied. Spatial arrangements, encapsulation processes, energy evolution, and diffusion are analyzed. Likewise, diffusion of the studied ionic liquid through carbon nanopores is also analyzed with the aim of studying its feasibility as membrane systems. The reported results show the outstanding properties of the studied systems, in terms of encapsulation, solvation, and interfacial behavior on the studied interfaces, which led to a valuable platform for developing new nanomaterials very useful in a wide collection of possible applications

Choline-Based Ionic Liquids on Graphite Surfaces and Carbon Nanotubes Solvation: A Molecular Dynamics Study

The microscopic structure of choline benzoate and choline salicylate at uncharged hydrophobic graphite surfaces, and around and inside single-walled carbon nanotubes with (10,10) and (15,15) armchair configurations, was analyzed using molecular dynamics simulations. The reported results show remarkable structural differences in the vicinity of graphite surfaces (up to 20 Å) in comparison with bulk ionic liquids. A remarkable increase of density in the region up to 6 Å close to graphite surface is inferred, which is more remarkable for benzoate and salicylate anions than for choline cation. Aromatic rings in benzoate and salicylate anions lie flat at the graphite surface. Choline-based ionic liquids show cylindrical distributions around carbon nanotubes, with the filling of the nanotube depending on the nanotube diameter. The distributions inside the nanotubes rely on the nanotube diameter and are not uniform for the studied anions and cations. Aromatic rings in benzoate and salicylate cations stay parallel to nanotube surfaces

On the Properties of CO₂ and Flue Gas at the Piperazinium-Based Ionic Liquids Interface: A Molecular Dynamics Study

CO₂ capture using ionic liquids is among the most promising alternatives for flue gases treatment; in particular, piperazine-based fluids have attracted great attention both in industry and in academia. The reported results obtained in this work using molecular dynamics simulations allow analyzing the behavior of CO₂ and a model flue gas at the interface of <i>N</i>-alkylpiperazinium-based ionic liquids. Density profiles across the boundary show changes in the orientation and ordering of involved ions at the interface, thus leading to changes in surface tension. Likewise, CO₂ and ionic liquids systems show strong accumulation of CO₂ molecules at the interface in short times, whereas crossing the interface and diffusing to the bulk ionic liquids is a slower process. For flue gas and ionic liquid systems, CO₂ molecules accumulate at the interface and water molecules also tend to form a layer out of the interface, whereas the effect of the remaining flue gas components is not remarkable. The behavior of the studied systems shows the prevailing role of interfacial behavior on the dynamic of CO₂ absorption processes for the studied ionic liquids

Computational Study of Hexamethylguanidinium Lactate Ionic Liquid: A Candidate for Natural Gas Sweetening

Considering the technological and economical importance of natural gas sweetening, new methods have to be developed to replace the aqueous amine processes currently used in most of the gas processing industry, with the objective of improving the treatment of sour gases, avoiding the problems arising from the amine technologies to fulfill the present technological, economical, and environmental requirements of the natural gas industry. Ionic liquids have been proposed in the literature as a suitable alternative for sour gas capture through physical/chemical absorption mechanisms. Guanidinium/lactate ionic liquids have showed adequate absorption ability, leading to low Henry’s constants, for both CO₂ and H₂S. Moreover, this ionic liquid shows very favorable economical, technological, and environmental properties that would make it suitable for sour gas absorption on a large scale. Nevertheless, the mechanism of the interaction between the considered acid compounds and the ionic liquid is still not fully understood. Therefore, we report in this work a computational study, using classical molecular dynamics methods, to characterize the properties and molecular level structure of hexamethylguanidinium lactate ionic liquid, [HMG]LAC, pure and after absorption of CO₂, H₂S, and CH₄, to infer the mechanism of interaction between these gases and the ionic liquid, leading to the absorption of these compounds, and to analyze the effect of absorbed gases on the ionic liquid structure from a molecular viewpoint. Results show a strong interaction between CO₂, H₂S, and the LAC anion, arising from the presence of hydroxyl and carboxylate groups, which govern the absorption of these gases on the studied ionic liquid. The reported results should stimulate further studies, including accurate experimental measurements, on the absorption ability of the considered ionic liquid and the related family of compounds

Interfacial Properties of Double Salt Ionic Liquids: A Molecular Dynamics Study

The behavior of ionic liquids containing more than one cation or anion, double salt ionic liquids, at the interfaces with vacuum and relevant acid gases (CO₂ and SO₂) was studied using classic molecular dynamics simulations. The [1-butyl-3-methylimidazolium]­[Cl]_1–<i>x</i>[Tf₂N]_<i>x</i> double salt ionic liquids were considered in which the effect of ionic molar ratio was investigated in the entire composition range. Molecular dynamics simulations using large model systems and simulation times of 200 ns allowed a detailed characterization of the structuring at the investigated interfaces, showing the possibility of tuning the interfacial behavior through the ratios of involved ions in double salt ionic liquids, which opens a new option for controlling relevant industrial processes involving ionic liquids, such as acid gas capture

Water Effect on Acid-Gas Capture Using Choline Lactate: A DFT Insight beyond Molecule–Molecule Pair Simulations

The suitability of CO₂ and SO₂ capture by using choline lactate ionic liquid as a sorbent and the effect of water content for acid-gas absorption were investigated through density functional theory (DFT) simulations in this work. Simulations that contain model systems considering up to four molecules (cholinium, lactate, water, and CO₂/SO₂) have been analyzed, and compositional effects on small cluster(s) formed by four ionic pairs and variable number of water molecules have been studied in this work. Assessment of the effect of water content on acid-gas capture that uses exotic ionic liquids is a rare study, and our results showed that water presence hinders CO₂/SO₂ affinity and solubility dramatically, mainly due to the dominated affinity between the ionic pair and water molecule rather than the CO₂/SO₂ molecule. Moreover, our studies also showed that affinity between ionic liquid and CO₂ is hindered by more than ionic liquid and SO₂ rich system with the presence of water in the environment

Interfacial Properties of Deep Eutectic Solvents Regarding to CO₂ Capture

The interfacial properties of deep eutectic solvents based on choline cloride plus urea, glycerol, or malonic acid in contact with gas phases composed by pure CO₂, pure SO₂, and a model flue gas, along with the liquid–vacuum interface, were studied using molecular dynamics simulations. The works provide insights on the mechanisms of acid gases capture at relevant interfaces and at atomistic level. The structural rearrangements on the molecules and ions composing the solvents at the solvent upon contact with the studied gas phases is studied together with the adsorption of gas molecules at the surface, the diffusion rates across the surface boundary, and the strength of intermolecular forces in the surface. This work provides a detailed analysis on the interfacial mechanism controlling acid gases captured by deep eutectic solvents