Journal of Ionic Liquids最新文献

Pyrrolidinium-based ionic liquids belong to the relatively common classes of these compounds; however, there are serious gaps in the knowledge and interpretation flaws of their physico-chemical properties, except for those containing the archetypal bistriflimide [NTf₂] anion. Compounds combining the 1-butyl-1-methylpyrrolidinium cation [C₄C₁Pyrr] with various fluorinated sulfonate anions exhibit vast polymorphism, rendering the thermodynamic description even more complicated. Four 1-butyl-1-methylpyrrolidinium ionic liquids, available commercially in high purities, were subjugated to a combined calorimetric and crystallographic study with a special emphasis on establishing a complete interpretation of their phase behaviour.

The samples were dried by vacuum heating and their purity was verified using the Karl Fischer titration and van't Hoff analysis of the melting peaks. Polymorphism was readily detected for all four compounds, but a complete description of their phase behaviour required an intensive and careful labour. Despite our experimental efforts, some of the polymorphs were found to be too elusive for a complete characterization by any of the used techniques. The obtained phase-transition temperatures and enthalpies were critically compared to the available literature with a variable agreement. While the existing thermodynamic data for [C₄C₁Pyrr][NTf₂] were found complete and sensible, literature data for the other compounds were incomplete or ambiguous. Heat capacities of the four compounds were determined using a Tian-Calvet calorimeter, the results of which were in a good agreement with the existing adiabatic-calorimetric data for [C₄C₁Pyrr][NTf₂]. Several crystal structures were newly resolved within the phase behaviour study and they are reported in the paper.

Exploring the polarity of ionic liquid phase composed of a ligand bonded to metal complex is essential for understanding the insights of solvent extraction. The normalized polarity of the ionic liquid phase composed of the tri-n‑butyl phosphate ligand and metal-ligand complex (metal = U, Nd, Th) was determined by a spectrophotometric technique using Reichardt’s dye as the polarity probe. The polarity was measured as a function of various parameters such as concentration of ionic liquid, concentration of nitric acid, ligand concentration and metal ion concentration of the system. The polarity increased with increase in the concentration of ionic liquid, nitric acid and metal ion in ionic liquid phase. The results are reported in this paper.

Sulfonic acid group functionalized 1,3-dialkyl imidazolium Brönsted acidic ionic liquids are shown as better catalysts in comparison to sulfuric acid with similar acid concentration for the depolymerization of poly(ethylene terephthalate) in hot compressed water. The highest activity was found by using 1.00 M aqueous 1-(3-propylsulfonic)-3-methylimidazolium chloride catalyst, where a practically complete decomposition of poly(ethylene terephthalate) could be achieved after 24 h at 210 °C with a 94% isolated yield of terephthalic acid. The superior catalytic activity of 1-(alkylsulfonic)-3-methylimidazolium chloride in comparison to sulfuric acid with similar acidic strength is explained as a result of charge-transfer and dipolar interactions between catalyst and poly(ethylene terephthalate).

All-atom molecular dynamics (MD) simulations of several different ionene chains solvated in an ionic liquid (IL) were conducted along with supporting experimental studies to understand the balance between the inter- and intramolecular interactions and their emergent structural properties. The imidazolium ionenes are comprised of a combination of linear butylimidazolium [C₄mim⁺] and decylimidazolium [C₁₀mim⁺] spacers, with 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C₂mim⁺][Tf₂N⁻] used as the IL solvent. Four ionenes have been considered, each with an incremental number of [C₄mim⁺] segments. There is an overall increase in the solvation metrics with an increase in [C₄mim⁺] segments per repeat unit, which can be traced to the favorable electrostatic interactions with the [Tf₂N⁻] anions. The solvation behavior trend is nonmonotonic with respect to the number of [C₄mim⁺] segments. These ionenes exhibit a contrasting balance of interactions, as compared to our previous investigation of IL-solvated ionenes where the polar ether linkages increased the intramolecular interactions, leading to strong contraction and coiling behavior.

Zinc oxide (ZnO) is a semiconductor with various physicochemical properties allowing its use in a wide range of technological applications. The aim of this work is to study nanocrystalline ZnO thin-film deposited using zinc salt which is dissolved in pure ionic liquids (ILs). The latter play a dual role: solvent and supporting electrolyte. Most of ILs have a large electrochemical window and sufficient ionic conductivity. In this work, four hydrophobic ILs, based on 1-alkyl-3-methylimidazoliums bis(trifluoromethylsulfonyl)imide were synthetized and characterized to highlight the effect of the length of the cationic alkyl chain on the morphological, structural and optical properties of nanocrystalline ZnO deposits. Grain growth and its arrangement are affected by the length of the cation alkyl chain of ILs, that act as model agents during electroplating. The electrochemical properties of the produced thin layers were also studied.

Cyphos nitrate (Trihexyl(tetradecyl)phosphonium nitrate: [P₆₆₆₁₄][NO₃]) is a well-known ionic liquid which is strongly hydrophobic and sustainable for the recovery of metal ions from waste matrix. In the present study, the ionic liquid was explored for the selectively separation of plutonium(IV) from uranium(VI), zirconium(IV), americium(III) and europium(III) present in the nitric acid medium in conjunction with 1,3-diisopropyl benzene (DIPB) as the diluent. The extraction factors of Pu(IV) were evaluated as a function of various experimental parameters such as the concentration of feed acidity, the concentration of ionic liquid, equilibration time, temperature, type of ionic liquid ions, etc. Facile formation of the anionic nitrato complex of Pu(IV) in the ionic liquid phase was found to be the driving force for the preferential extraction of Pu(IV) over other metal ions. Effect of radiation dose suggested the stability of the proposed ionic liquid by acquiring the similar extraction factors like that in the unirradiated ionic liquid phase. Remarkable separation factors of Pu(IV) over the aforementioned metal ions were computed and presented in the paper. Various thermodynamic parameters accompanied by the extraction as well as the back extraction processes of Pu(IV) from the loaded ionic liquid phase have been presented in detail.

In comparison to the clean conditions of ultrahigh vacuum (UHV), we investigate the influence of ambient conditions on the potential screening (PS) at the interfaces of Au and Pt electrodes with the ionic liquids [C₈C₁Im][Tf₂N] and [C₈C₁Im]Cl. Our study is based on a proof-of-principle experiment that shows that PS measurements performed by XPS yield the same results as measurements using a specific 3-electrode sample holder setup, both in UHV. Based on this, we compare PS measurements under ultraclean conditions by XPS with PS measurements with a 3-electrode setup in N₂ and in air. We demonstrate that there is indeed an influence of the ambient gas atmosphere, which depends on applied voltage and combination of IL and electrode material. For Pt electrodes, there is a pronounced influence of the ambient conditions on the PS for both [C₈C₁Im][Tf₂N] and [C₈C₁Im]Cl, while for Au electrodes hardly any influence is seen. We attribute the observed effects mainly to water affecting the electrical double layers at the IL/electrode interfaces. In addition, we observe that reaction products formed under faradaic conditions can lead to a contamination of the 3^rd electrode (reference electrode), yielding time-dependent deviations from the true behavior.

A combination of molecular dynamics simulations, quantum chemical calculations, and vibrational spectroscopy is employed to study ionic interactions in 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C_2OHmim]NTf₂, 1-methyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide [C₃mim]NTf₂, and their double salt mixtures. Ionic liquids containing hydroxy groups are unique in their ability to form unconventional hydrogen bonds between neighboring cations, despite the strong repulsive forces these ions exert upon one another. Our computational and spectroscopic data reveal a rich array of ionic interactions in pure [C_2OHmim]NTf₂. The hydrogen bonding network inherent to [C_2OHmim]NTf₂ is partially disrupted when [C₃mim]NTf₂ is added to the ionic liquid to produce [C_2OHmim]_0.5[C₃mim]_0.5NTf₂. This leads to increased amounts of uncoordinated hydroxy groups and minor changes in the distribution functions for side chain orientations. Furthermore, OH groups from [C_2OHmim]⁺ are shown to hydrogen bond with the acidic hydrogen atoms attached to the [C₃mim]⁺ or [C_2OHmim]⁺ imidazolium rings. Cation-cation hydrogen bonding is not restricted solely to situations where both cations contain hydroxy groups (i.e., homo-aggregation of cations through OH‧‧‧OH interaction motifs). Rather, hetero-aggregation of chemically distinct cations may also occur through CH‧‧‧OH hydrogen bonds, where the CH hydrogen atom is directly connected to the imidazolium ring. Taken together, our data shows the cationic interactions that occur in the ionic liquid mixtures are controlled by competitive interactions originating from the hydrophobic propyl groups and hydrophilic hydroxyethyl groups.

Ionic Liquids are often characterized by multiple length scales and these tend to be well separated. As an example, for 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide apolar pockets or domains are separated by a characteristic distance that is different from that of positive-negative charge alternation along a charge network. Accordingly, these structural features have their own well separated signatures in the reciprocal space structure function. Each of these well separated structural features of prototypical ionic liquids relaxes on its own time scale and we have explored this in a set of recent articles. The overarching goal of the current work is to explore what happens when the structural motifs are still present, but the length scale difference between these is small. Specifically, for ionic liquids containing ether tail functionalities such as 1-(2-(2-ethoxyethoxy)ethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, the separation between cationic head subspecies intercalated by anions (or anions sharing a cationic head counterion) is not that different from that of cationic heads or anions intercalated by tail regions and the time scale for relaxation of these structural motifs are also similar. For the ether-tail containing system, the slowest liquid relaxation scale associated with tail region-charge network correlations is about an order of magnitude faster than for its alkyl-tail isoelectronic analog.