Ionic Liquid Aqueous Solutions under Nanoconfinement

The nanoscale interactions of room temperature ionic liquids (RTILs) at uncharged (graphene) and charged (muscovite mica) solid surfaces were evaluated with high resolution X-ray interface scattering and fully atomistic molecular dynamics simulations. At uncharged graphene surfaces, the imidazolium-based RTIL ([bmim(+)][Tf(2)N(-)]) exhibits a mixed cation/anion layering with a strong interfacial densification of the first RTIL layer. The first layer density observed via experiment is larger than that predicted by simulation and the apparent discrepancy can be understood with the inclusion of, dominantly, image charge and π-stacking interactions between the RTIL and the graphene sheet. In contrast, the RTIL structure adjacent to the charged mica surface exhibits an alternating cation-anion layering extending 3.5 nm into the bulk fluid. The associated charge density profile demonstrates a pronounced charge overscreening (i.e., excess first-layer counterions with respect to the adjacent surface charge), highlighting the critical role of charge-induced nanoscale correlations of the RTIL. These observations confirm key aspects of a predicted electric double layer structure from an analytical Landau-Ginzburg-type continuum theory incorporating ion correlation effects, and provide a new baseline for understanding the fundamental nanoscale response of RTILs at charged interfaces.

Efficient removal of phenolic compounds from model oil using benzyl Imidazolium-based ionic liquids

Metal organic framework-ionic liquid hybrid catalysts for the selective electrochemical reduction of CO2 to CH4

Room temperature ionic liquids (RTILs) are unique in many respects. The preparation method reported here is based on their extremely low vapour pressure that allows for their usage in vacuum. By magnetron sputtering of nickel or by co-sputtering of Ni-Fe or Ag-Cu on a surface of several imidazolium-based RTILs, we prepared nanocolloids containing metallic nanoparticles ranging in size from 6 to 30 nm, depending on the kind of RTIL, with low size dispersion. The nanocolloids are stable in time, no sedimentation or agglomeration was observed after two years. The method can be used also for preparation of the nanoparticles from semiconducting or insulating materials. As the next step, nanocolloids prepared in this way can be used for decoration of thin-film gas sensors by proper nanoparticles aiming at enhancement of their sensitivity and selectivity. Two ways of immobilization are presented - mild heating of a drop of colloid containing Ni-Fe nanoparticles placed on TEM mesh, and Ag-Cu nanoparticles that were immobilized on the surface of gold thin-film electrode by electrophoresis.

Tribological characteristics of two imidazolium-based room temperature ionic liquids (RTILs), 1-hexyl-3-methylimidazolium tetrafluoroborate, and 1-hexyl-3-methylimidazolium hexafluorophosphate were investigated under high vacuum conditions. Viscosity–temperature characteristics and thermogravimetric characteristics of these compounds were also investigated. Imidazolium-based RTILs have relatively good viscosity–temperature characteristics that are comparable to those of multiply-alkylated cyclopentane (MAC). Thermogravimetric results showed that ionic liquids have high thermal stability and low vapor pressure. Ionic liquids showed low friction and low wear rate under high vacuum conditions, and high load-carrying capacity was observed.

The scientific interest in room-temperature ionic liquids (RTILs) became extraordinarily high over the last two decades. While in the earlier days most of the studies focused on the synthesis and chemical properties, recently the interest in there physical, dynamical and structural properties is increasing. This thesis is aiming at the dynamical properties using dielectric relaxation spectroscopy. The first part of the thesis presents the development of new experimental routes and mathematical routines to record the dielectric spectra of liquids at microwave to far-infrared frequencies. It is followed by the discussion of the dielectric spectra of the neat, mainly imidazolium-based RTILs. Beside the extraction of the static dielectric constants, detailed information on the dynamics is obtained, including activation parameters. At room-temperature, the spectra are extended to terahertz and far-infrared frequencies, to cover the whole frequencies range relevant for intermolecular dynamics. Additional insight is gained by comparing these broadband spectra to molecular-dynamics simulations as well as to optical Kerr effect spectra. Finally, binary mixtures of RTILs with polar solvents are investigated. The studies on mixtures with dichloromethane are indicating an expanded RTIL-like range, where the dielectric characteristics remain similar to the neat RTIL. Only at high dilutions, the mixtures behave rather like a conventional electrolyte solution with pronounced formation of contact ion-pairs. On the other hand the mixtures with water indicate a more complex, heterogeneous structure.

The influence of a hierarchical porous carbon network on the coherent dynamics of a nanoconfined room temperature ionic liquid: A neutron spin echo and atomistic simulation investigation

Recent studies show that Ionic Liquids (ILs) have the ability to improve oil recovery. In this experimental study, an imidazolium-based Room-Temperature Ionic Liquid (RTIL), 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]), was used to extract heavy oil (14 °API) from unconsolidated packed sand samples. The RTIL was injected as slug, with different concentrations and sizes. The [EMIM][OAc] results were compared with the efficiency of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]) and 1-dodecyl-3-methylimidazolium chloride ([DMIM][Cl]) ILs. The results indicate that the efficiency of IL depends mainly on the type of IL. A comparison with a well-known commercial surfactant (Sodium Dodecyl Sulfate, SDS) was performed, and the results confirmed the higher efficiency of the ionic liquids. Changes in Interfacial Tension (IFT), Surface Tension (SFT), and Zeta Potential (ZP) in the solution supported the recovery factor results. Finding the optimum concentration and slug size are significant factors in making the oil extraction process more economical.

Transport properties of imidazolium-based room temperature ionic liquids in confinement of slit charged carbon nanopores: New insights from molecular simulations

Raman spectroscopy study of water confinement in ionic liquid 1-butyl-3-methylimidzolium nitrate

Electrolytes in Li-ion batteries play a significant role as they influence different aspects directly related to the battery performance, such as safety, voltage window, electrochemical stability, and the formation of solid-electrolyte interphase (SEI). Conventionally, these electrolytes are composed of a lithium salt dissolved in an organic solvent such as ethylene carbonate and propylene carbonate. Regarding safety, these organic electrolytes can be replaced by room-temperature ionic liquids (RTILs), which present lower vapor pressure and non-flammability.1 Moreover, adding polymer to these liquid electrolytes to form polymer gel electrolytes has proven to be a good strategy to avoid dendritic growth and increase electrolyte stability.2 The properties of RTIL electrolytes containing Li salts have been studied in the last decade. Still, the scope has been limited primarily to simple RTILs consisting of one cationic and one anionic species. Inspired by the success of high-entropy alloys (HEAs) for forming stable solid solutions with excellent mechanical properties,3 the concept of high-entropy materials has been recently transferred to electrolytes, where the effect of mixing multiple Li salts is explored.4 However, the number of compositional combinations increases rapidly when multiple salts, cationic and anionic species are introduced, and the explorable compositional space increases even more when polymers are added to the mixture.Automating the electrolyte preparation and characterization can be the key feature to allow the exploration of all the possible electrolyte combinations. In this work, we explain the first preliminary results obtained from an autonomous preparation and characterization of high-entropy electrolytes composed of a mixture of two different lithium salts in ionic liquids consisting of multiple anionic and cationic species. In addition, the adaptation of the autonomous system of preparation and characterization of liquid electrolytes to polymer gel electrolytes is also proposed and explained. References. (1) Niu, H.; Wang, L.; Guan, P.; Zhang, N.; Yan, C.; Ding, M.; Guo, X.; Huang, T.; Hu, X. Recent Advances in Application of Ionic Liquids in Electrolyte of Lithium Ion Batteries. J. Energy Storage 2021, 40, 102659. https://doi.org/10.1016/j.est.2021.102659.(2) Chen, J.; Wu, J.; Wang, X.; Zhou, A.; Yang, Z. Research Progress and Application Prospect of Solid-State Electrolytes in Commercial Lithium-Ion Power Batteries. Energy Storage Mater. 2021, 35, 70–87. https://doi.org/10.1016/j.ensm.2020.11.017.(3) Yeh, J.-W.; Chen, S.-K.; Lin, S.-J.; Gan, J.-Y.; Chin, T.-S.; Shun, T.-T.; Tsau, C.-H.; Chang, S.-Y. Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes. Adv. Eng. Mater. 2004, 6 (5), 299–303. https://doi.org/10.1002/adem.200300567.(4) Wang, Q.; Zhao, C.; Wang, J.; Yao, Z.; Wang, S.; Kumar, S. G. H.; Ganapathy, S.; Eustace, S.; Bai, X.; Li, B.; Wagemaker, M. High Entropy Liquid Electrolytes for Lithium Batteries. Nat. Commun. 2023, 14 (1), 440. https://doi.org/10.1038/s41467-023-36075-1.

Lithium salts used in batteries have poor solubility in many common room temperature ionic liquids, such as 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI). Lithium salt solutions in ionic liquids that contain the thiocyanate anion, in contrast, can be prepared at concentrations as high as 4 M. The solubility of three common lithium salts (LiClO4, LiSCN and LiTFSI) used in lithium batteries were measured for four room temperature ionic liquids including 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), 1-butyl-3-methylimidazolium acetate (bmimACET), 1-butyl-3-methylimidazolium thiocyanate (bmimSCN) and EMITFSI. The solubility was determined using Fourier Transform Infrared Attenuated Total Reflectance spectroscopy (FTIR-ATR), which was an efficient method for determining electrolyte solubility in electrolyte solvents. The ionic conductivity of room temperature ionic liquids with thiocyanate containing anions with high concentrations of lithium salts was determined using AC impedance. There was an optimal lithium salt concentration in the ionic liquid in terms of maximum ionic conductivity for the solutions.

Room-temperature ionic liquids (RTILs), i.e. organic molten salts with melting points below 100 ◦C, have been intensively developed for electrolytic media in various electrochemical systems due to the fact that RTILs have unique physicochemical properties such as favorable solubility of organic and inorganic compounds, relatively high ionic conductivity, no measurable vapor pressure, high thermal stability, low flammability, etc. Particularly, RTILs have been regarded as potential electrolytic media for electropolymerization processes.1 Many kinds of RTILs have been investigated for the electropolymerizations; however, highly conductive and stable RTILs based on quaternary phosphonium cations2 have been rarely employed for this application. In this work, we report the electrooxidative polymerization of aniline in triethylpentylphosphonium bis(trifluoromethylsulfonly)amide (P2225-TFSA) and tributylmethylphosphonium bis(trifluoromethylsulfonly)amide (P4441-TFSA) in comparison with the other type of RTILs, characterizing the obtained polyaniline films. The preparation of the phosphonium RTILs was performed by aqueous ion exchange reaction of the precursor quaternary phosphonium halides with lithium TFSA. The electrooxidative polymerization of aniline in phosphonium RTILs containing 0.1 M H-TFSA was carried out by cyclic voltammetry (CV) method using a three-electrode cell equipped with a Pt disk working electrode. The electrochemical activity of the polyaniline films were evaluated by extended CV scanning technique.Figure 1 shows typical cyclic voltammograms for the electrooxidative pocesses of aniline. As shown in Fig. 1, it was found that relatively large voltammetric response was observed in P2225-TFSA when compared to that in P4441-TFSA. This seems to be attributed to the relatively low viscosity and high conductivity of P2225-TFSA. In addition, the voltammetric responses were enhanced by cycling, which indicates that ionic species could be efficiently doped into the polyaniline film. The surface morphology based on SEM images of the polyaniline films will be also discussed.References 1 K. Sekiguchi, et al, J. Electroanal. Chem. , 557, 1 (2003).2 K. Tsunashima, et al, Electrochem. Commun., 9, 2353 (2007). Figure 1

Charge transport and glassy dynamics in a room temperature ionic liquid- [BMPyr][TFSI

The mechanism of solvation of ions by ionic liquids is more complex than solvation in most molecular solvents as the ionic liquid itself provides the counter ion. Solvation and ion pairing of anionic substrates in room-temperature ionic liquids (RTILs) were investigated using resonance Raman spectroscopy and DFT calculations. The purpose of this study was to differentiate between the formation of discrete cation/anion structures and a double-layer cloud of counter ions without specific atomic interactions between the ionic species. In acetonitrile/RTIL mixtures, the radical anion and dianion of dinitrobenzene (DNB) are stabilized by RTILs through solvation and ion pairing. The formation of the lowest-energy ion pair led to the largest shifts in the Raman band in DNB-·, while significantly smaller shifts were predicted for general solvation. The effect of general solvation and ion pair formation was studied using DFT with the implicit solvation model. Identification of the bands most sensitive to tight ion pairing allowed for the interpretation of the observed vibrational changes. The formation of tight ion pairs between the anionic solutes depends on both cation-solute and RTIL cation-anion interactions. Tight ion pairs were observed in RTILs, but general solvation was also important. This work establishes the advantageous use of vibrational spectroscopy to provide detailed structural information not accessible from voltammetry alone.