Physicochemical Properties of Tri-n-butylalkylphosphonium Cation-Based Room-Temperature Ionic Liquids

Unexpected Energy Applications of Ionic Liquids

Ionic liquids and their various analogues are without doubt the scientific sensation of the last few decades, paving the way to a more sustainable society. Their versatile suite of properties, originating from an almost inconceivably large number of possible cation and anion combinations, allows tuning of the structure to serve a desired purpose. Ionic liquids hence offer a myriad of useful applications from solvents to catalysts, through to lubricants, gas absorbers, and azeotrope breakers. The purpose of this review is to explore the more unexpected of these applications, particularly in the energy space. It guides the reader through the application of ionic liquids and their analogues as i) phase change materials for thermal energy storage, ii) organic ionic plastic crystals, which have been studied as battery electrolytes and in gas separation, iii) key components in the nitrogen reduction reaction for sustainable ammonia generation, iv) as electrolytes in aluminum-ion batteries, and v) in other emerging technologies. It is concluded that there is tremendous scope for further optimizing and tuning of the ionic liquid in its task, subject to sustainability imperatives in line with current global priorities, assisted by artificial intelligence.

Molecular Insight into the Ionic Conduction of Quaternary Ammonium and Phosphonium Cation-Based Ionic Liquids Using Dielectric and Spectroscopy Analyses

We analyzed the primary properties of ionic liquids (ILs) comprising quaternary phosphonium cations and bis(trifluoromethylsulfonyl) amide anions and compared them with those of corresponding quaternary-ammonium-cation-based ILs. Broadband dielectric spectroscopy was used to confirm the coupling between the translational and orientational motions of ions, and our results demonstrated that the high ionic conductivity of the phosphonium-based ILs was attributed to their fast rotational dynamics. The differences between ILs with different cations were further evaluated using vibrational (Raman and terahertz) spectroscopy. The Raman spectroscopy data revealed that the cation structure affected the conformation and flexibility (conformational change) of the anion. Furthermore, terahertz spectroscopy allowed us to evaluate the relationship between ion transport and intermolecular interactions between the cation and anion of ILs.

Electron Microscopy Imaging Applications of Room Temperature Ionic Liquids in the Biological Field: A Review

For biological imaging using electron microscopy (EM), the use of room-temperature ionic liquids (RTILs) has been proposed as an alternative to traditional lengthy preparation methods. With their low vapor pressures and conductivity, RTILs can be applied onto hard-to-image soft and/or wet samples without dehydration - allowing for a more representative, hydrated state of material and opening the possibility for visualization of in situ physiological processes using conventional EM systems. However, RTILs have yet to be utilized to their full potential by microscopists and microbiologists alike. To this end, this review aims to provide a comprehensive summary of biological applications of RTILs for EM to bridge the RTIL, in situ microscopy, and biological communities. We outline future research avenues for the use of RTILs for the EM observation of biological samples, notably i) RTIL selection and optimization, ii) applications for live cell processes and iii) electron beam and ionic liquid interaction studies.

Epoxy-Containing Ionic Liquids with Tunable Functionality

New types of ionic liquids (ILs) with an epoxy group on a piperidinium-type cation were successfully synthesized by the simple anion exchange reaction of a solid 1-allyl-1-(oxiran-2-ylmethyl)piperidinium bromide, which was designed in this study. Unfortunately, the physicochemical properties, e.g., viscosity and ionic conductivity, of the ILs were inferior to those of common ILs such as 1-ethyl-3-methylimidazolium tetrafluoroborate ([C₂mim][BF₄]) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C₄mim][Tf₂N]). However, the resulting ILs are of great interest as reaction intermediates: For example, the epoxy group on the cation could react with various reagents, including CO₂. Consequently, the modification of the cation structure in the ILs was possible. This is particularly interesting because it is very difficult to modify commonly used ILs. The approach established in this article will provide a favorable synthetic route for creating novel functional ILs in the future.

Multiple Ether-Functionalized Phosphonium Ionic Liquids as Highly Fluid Electrolytes

Ionic liquids (ILs) are promising electrolytes, although their often high viscosity remains a serious drawback. The latter can be addressed by the introduction of multiple ether functionalization. Based on the highly atom efficient synthesis of tris(2-ethoxyethyl) phosphine, several new phosphonium ionic liquids were prepared, which allows studying the influence of the ether side chains. Their most important physicochemical properties have been determined and will be interpreted using established approaches like ionicity, hole theory, and the Walden plot. There is striking evidence that the properties of phosphonium ionic liquids with the methanesulfonate anion are dominated by aggregation, whereas the two triple ether functionalized ILs with the highest fluidity show almost ideal behavior with other factors being dominant. It is furthermore found that the deviation from ideality is not significantly changed upon introduction of the ether side chains, although a very beneficial impact on the fluidity of ILs is observed. Multiple ether functionalization therefore proves as a powerful tool to overcome the disadvantages of phosphonium ionic liquids with large cations.

Liquid phase microextraction based on the solidification of a floating ionic liquid combined with high-performance liquid chromatography for the preconcentration of phthalate esters in environmental waters and in bottled beverages

Liquid-phase microextraction based on the solidification of floating ionic liquids.

Detection of triazole pesticides in environmental water and juice samples using dispersive liquid–liquid microextraction with solidified sedimentary ionic liquids

The solidification of a sedimentary ionic liquid, [P₄₄₄₈][PF₆], was used to simplify the extraction process for the detection of triazole pesticides.

Effect of Cation on Physical Properties and CO2 Solubility for Phosphonium-Based Ionic Liquids with 2-Cyanopyrrolide Anions

A series of tetraalkylphosphonium 2-cyanopyrrolide ([Pnnnn][2-CNPyr]) ionic liquids (ILs) were prepared to investigate the effect of cation size on physical properties and CO2 solubility. Each IL was synthesized in our laboratory and characterized by NMR spectroscopy. Their physical properties, including density, viscosity, and ionic conductivity, were determined as a function of temperature and fit to empirical equations. The density gradually increased with decreasing cation size, while the viscosity decreased noticeably. In addition, the [Pnnnn][2-CNPyr] ILs with large cations exhibited relatively low degrees of ionicity based on analysis of the Walden plots. This implies the presence of extensive ion pairing or formation of aggregates resulting from van der Waals interactions between the long hydrocarbon substituents. The CO2 solubility in each IL was measured at 22 °C using a volumetric method. While the anion is typically known to be predominantly responsible for the CO2 capture reaction, the [Pnnnn][2-CNPyr] ILs with shorter alkyl chains on the cations exhibited slightly stronger CO2 binding ability than the ILs with longer alkyl chains. We attribute this to the difference in entropy of reaction, as well as the variation in the relative degree of ionicity.

Ionic liquid regioisomers: structure effect on the thermal and physical properties

Effects of side group placement was studied on triazolium ionic liquids and how a minor change in alkyl group placement results in very different properties.

SEM observation of hydrous superabsorbent polymer pretreated with room-temperature ionic liquids

Room-temperature ionic liquid (RTIL), which is a liquid salt at or below room temperature, shows peculiar physicochemical properties such as negligible vapor pressure and relatively-high ionic conductivity. In this investigation, we used six types of RTILs as a liquid material in the pretreatment process for scanning electron microscope (SEM) observation of hydrous superabsorbent polymer (SAP) particles. Very clear SEM images of the hydrous SAP particles were obtained if the neat RTILs were used for the pretreatment process. Of them, tri-n-butylmethylphosphonium dimethylphosphate ([P_{4, 4, 4, 1}][DMP]) provided the best result. On the other hand, the surface morphology of the hydrous SAP particles pretreated with 1-ethyl-3-methylimidazolium tetrafluoroborate ([C₂mim][BF₄]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄mim][BF₄]) was damaged. The results of SEM observation and thermogravimetry analysis of the hydrous SAP pretreated with the RTILs strongly suggested that most water in the SAP particles are replaced with RTIL during the pretreatment process.