Pressure-Induced Solidification of 1-Butyl-3-methylimidazolium Tetrafluoroborate

We have used Raman spectroscopy to investigate the high-pressure phase behavior of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]), a representative ionic liquid, at pressures up to ~7.5 GPa. We have also studied how increasing pressure leads to conformational changes in the [bmim]⁺ cation. We have found that liquid [bmim][BF₄] undergoes pressure-induced solidification (freezing) into a superpressed (metastable) state at 2.5 GPa; another structural change probably occurs at ~6 GPa. Remarkably, conformational changes in the [bmim]⁺ cation between trans and gauche conformers are concordant with the metastable structural changes of [bmim][BF₄]. As the pressure is increased from ambient, the fraction of gauche conformers increases, but the gauche fraction decreases above the solidification pressure (2.5 GPa), and slope of the gauche/trans ratio changes again above 6 GPa. We interpret these results in terms of the fragility of the ionic liquid.     

A novel method to prepare polymer-ionic liquid gel under high pressure and its electrochemical properties

Sol–gel transition behavior of ionic liquid gel based on poly (ethylene glycol) (PEG) and ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO₄] has been investigated under the pressure up to 250 MPa. The Temperature versus Pressure phase diagram of PEG/[EMIM][EtSO₄] gel is constructed, and it indicates that the melting point is an increasing function of pressure. Based on the phase diagram, the PEG/[EMIM][EtSO₄] gels are prepared by cooling under the pressure of 300 MPa and atmospheric pressure, respectively. From the differential scanning calorimetry result of the recovered samples, it is found that PEG/[EMIM][EtSO₄] gel prepared under high pressure has a higher crystallinity and smaller crystal size polymer network, comparing with under atmospheric pressure. The cyclic voltammograms and impedance spectra tests indicate that the PEG/[EMIM][EtSO₄] gel prepared under high pressure exhibit higher ionic conductivity comparing with atmospheric pressure. It could be speculated these excellent properties might be attributed to the loose gel structure and high ionic density induced by high pressure.     

A Novel Room Temperature Ionic Liquid Extraction Spectrophotometric Determination of Trace Germanium in Natural Water with Methybenzeneazosalicylfluorone

Abstract

This paper describes a highly sensitive and selective extraction spectrophotometric method for determination of trace germanium in natural water with new a chromogenic reagent methybenzeneazosalicylfluorone abbreviated as MBASF, in which a typical room temperature ionic liquid, 1‐butyl‐3‐methylimidazolium hexafluorophosphate abbreviated as [C₄mim][PF₆] was used as novel medium for liquid/liquid extraction of germanium(IV). In the presence of TritonX‐100, MBASF reacted with germanium(IV) to form a red complex rapidly, the complex was then extracted into the [C₄mim][PF₆] phase, the absorbance of the complex in ionic liquid at 496 nm was recorded and used to determine trace germanium(IV). The apparent molar absorptivity of the complex and the detection limit for the real sample were found to be 3.12×10⁶ L mol^?1 cm^?1 and 0.2 ng mL^?1, respectively. The absorbance of the complex at 496 nm increases linearly with the concentration up to 4 µg of germanium (IV) in 250 mL of aqueous solution. The interference study show the determination of germanium is free from the interference of almost all positive and negative ions found in the natural water samples. The determination of germanium in natural water was carried out by the present method and electrothermal atomic absorption spectrometry (AAS). The results were satisfactorily comparable so that the applicability of the proposed method was confirmed using the real samples. Moreover, the extraction mechanism with the ionic liquid system was also investigated. We think the extraction performance of the ionic liquid system is a combination of ion‐pairing effect between imidazolium cation and basic solute in the aqueous phase with the dissolution of polar molecule in ionic liquid phase. A wise choice of the appropriate combination of anion with imidazolium cation hydrophobicity allows playing with solute selectivity.     

A specialized apparatus for the study of liquid crystals at high pressures

Abstract

A pressure system specially designed for the study of liquid crystal materials at high pressures up to 4kbar is presented. The pressure system is based on a hydrostatic screw injector and uses either oil or gas as the pressure transmitting medium. The type of measurements which can be performed with the instrument include polarized microscopy, optical spectroscopy, electrooptic and electrical measurements. The different measurements performed place specific constraints on the design of the apparatus and the pressure cells, and details are given. A preliminary study of the smectic A modification of the twist grain boundary phase (TGB_A) at high pressures is presented. The pressure versus temperature phase diagram shows (i) a negative gradient of the TGB_A/isotropic phase boundary line and (ii) that the TGB_A phase does not exist at pressures above about 250 bar. Following Lubensky's analogy between the TGB_A phase and type II superconductors, the disappearance of the TGB_A phase at high pressure may imply that the Landau-Ginsburg parameter K decreases with pressure.     

Studies on ionic liquid-based corn starch biopolymer electrolytes coupling with high ionic transport number

Biopolymer electrolytes containing corn starch, lithium hexafluorophosphate (LiPF₆) and ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BmImTf) were prepared by solution casting technique. The ionic conductivity was found to increase with increasing ionic liquid concentration. Upon doping with 80 wt% of BmImTf, the ionic conductivity increased by three orders of magnitude. The highest ionic conductivity of (3.21 ± 0.01) × 10^?4 S cm^?1 was achieved at ambient temperature. The complexation between corn starch, LiPF₆ and BmImTf was further proven in attenuated total reflectance-Fourier transform infrared findings. The highest conducting biopolymer electrolyte was stable up to 230 °C, as proven in thermogravimetric analysis.     

Separation of no-carrier-added 109Cd from natural silver target using RTIL 1-butyl-3-methylimidazolium hexafluorophosphate

The room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate [C₄mim][PF₆] has various applications in the separation of a range of metal ions replacing volatile and toxic traditional organic solvents in liquid–liquid extraction systems. In this study, the RTIL [C₄mim][PF₆] was used to separate no-carrier-added (NCA) ¹⁰⁹Cd from α-particle irradiated Ag target. A natural Ag foil was bombarded by 30 MeV α-particles to produce ¹⁰⁹Cd. After the decay of all co-produced short-lived products, NCA ¹⁰⁹Cd was separated from the bulk Ag using [C₄mim][PF₆] as extractant from HNO₃ medium. Ammoniumpyrrolidine dithiocarbamate (APDC) was used as a complexing agent. At the optimum condition, 3 M HNO₃, 0.01 M APDC in presence of [C₄mim][PF₆], ~99 % bulk Ag was extracted to the IL phase, leaving NCA ¹⁰⁹Cd in the aqueous phase. The amount of Ag became negligibly small after re-extraction in the same condition. The ionic liquid was recovered by washing it with 1 M HCl.     

Synthesis of highly stable silver nanoparticles using imidazolium-based ionic liquid

Highly stable, aqueous dispersions, and hydrophilic ionic liquid-capped silver nanoparticles with positive surface charge were synthesized by in situ reduction of AgNO₃ with NaBH₄ in the presence of an imidazolium-based ionic liquid, viz., 1-dodecyl-3-methylimidazolium chloride ([C₁₂mim][Cl]) at room temperature. Prepared silver nanoparticles were characterized by UV–vis spectra, transmission electron microscopy (TEM), and zeta potential. UV–visible spectrum of the aqueous medium peaked at 407 nm corresponding to the plasmon absorbance of silver nanoparticles. TEM analysis revealed the spherical shape of the particles with sizes about 9 nm and low polydispersed. The surface charge of the synthesized silver nanoparticles was determined as +5.0 mV. The ionic liquid ([C₁₂mim][Cl]) capped silver nanoparticles were stable for at least 8 months.     

Atomistic Simulation of Structural and Mechanical Properties of the AMgF3 (A = K,Rb, and Cs) Compounds Under Hydrostatic Pressure

Structural, mechanical, elastic, and dielectric properties of the AMgF₃ (A = K, Rb, and Cs) compounds were investigated using classical atomistic simulation. A new set of interatomic potentials was developed for these compounds. Lattice parameters and interatomic distances have shown to accurately reproduce all structures, with very close agreement to the experimental data. In all cases, the relative error is below 0.5%. Effect of hydrostatic pressure in the structural, mechanical, elastic, and dielectric properties of these materials were studied from 0 up to 50 GPa. Compounds behavior and stability under pressure were analyzed. KMgF₃ and RbMgF₃ changed from brittle to ductile at approximately 2 GPa. These calculations play an important role in understanding the properties of the AMgF₃ (A = K, Rb, and Cs) compounds under pressure, and open up a new opportunity to study defects in this class of materials. © 2019 Wiley Periodicals, Inc.     

First-principles study of structural and vibrational properties of crystalline silver azide under high pressure

A detailed first-principles study of the structural and vibrational properties of crystalline silver azide under hydrostatic pressure of 0–500 GPa has been performed with density functional theory in the generalized gradient approximation. The crystal structure is relaxed to allow ionic configurations, cell shape, and volume to change without any symmetry constraints. It is found that the silver azide crystal remains orthorhombic structure with Ibam space group for pressures up to 7 GPa, where there is a transition to an I4/mcm tetragonal symmetry. The lattice parameter and electronic structure are investigated as functions of pressure. The calculated vibrational frequencies at ambient pressure are in agreement with available experimental data. We also discuss the pressure-induced frequency shifts for the internal and lattice modes of silver azide crystal upon compression.     

Effect of addition of 1-butyl-3-methylimidazolium thiocyanate on conductivity of Na-containing polymer electrolyte

Research in the environmentally friendly energy field has grown rapidly due to severe problems such as global warming and climate change. Sodium-ion technology is one of the most promising alternatives to lithium-ion batteries. Use of ionic liquids containing thiocyanate anion has been considered because of their low cost, low viscosity, and nonhazardous nature. In this work, polyethylene oxide (PEO)–sodium perchlorate (NaClO₄) samples containing different amounts of 1-butyl-3-methylimidazolium thiocyanate ionic liquid were prepared by a solution casting method. Addition of the ionic liquid to the PEO–NaClO₄ electrolyte further increased the ionic conductivity. The electrolyte containing 30 wt% ionic liquid exhibited the maximum ionic conductivity of ~5.0 × 10^?4 S/cm at room temperature. Fourier-transform infrared (FT-IR) spectroscopy revealed the interaction between the polymer chain and salt ion complexes for various sodium salt contents. Differential scanning calorimetry (DSC) demonstrated that the crystallinity was reduced by addition of 1-butyl-3-methylimidazolium thiocyanate ionic liquid.     

Rubbery copolymer electrolytes containing polymerized ionic liquid for dye-sensitized solar cells

A novel type of random copolymer comprised of a polymerized ionic liquid, poly(1-((4-ethenylphenyl)methyl)-3-butyl-imidazolium iodide) (PEBII), and amorphous rubbery poly(oxyethylene methacrylate) (POEM) was synthesized and employed as a solid electrolyte in an I₂-free dye-sensitized solar cell (DSSC). The copolymer electrolytes deeply infiltrated into the nanopores of mesoporous TiO2 films, resulting in improved interfacial contact of electrode/electrolyte. The glass transition temperature (T _g) of the PEBII–POEM (?23 °C) was lower than that of PEBII homopolymer (?4 °C), indicating greater chain flexibility in the former. However, the DSSC efficiency of PEBII–POEM (4.5 % at 100 mW/cm²) was lower than that of PEBII (5.9 %), indicating that ion concentration is more important than chain flexibility. Interestingly, upon the introduction of ionic liquid, i.e., 1-methyl-3 propylimidazolium iodide, the efficiency of PEBII remained almost constant (5.8 %), whereas that of PEBII–POEM was significantly improved up to 7.0 % due to increased I^? ion concentration, which is one of the highest values for I₂-free DSSCs.     

Pressure Effect on the Crystal Structure of Na2C2O4: Deformation Anisotropy During Hydrostatic Compression and Phase Transition at 3.8 GPa

Variation of the unit cell parameters of Na₂C₂O₄ is investigated by powder diffractometry in diamond anvils when hydrostatic pressure is increased to 6.5 GPa. Anisotropic distortion of the structure was observed up to about 3.8 GPa, whereupon a transition to an unknown polymorphous modification occurred. Before the phase transition, the compression was maximal in the direction perpendicular to close-packed layers formed by oxalate ions. Minimal compression was observed in the direction of the specific crystallographic axis b. The anisotropy of compression at elevated pressure is similar, but not identical, to the anisotropy of compression of the same structure at reduced temperature.     

Green and efficient extraction strategy to lithium isotope separation with double ionic liquids as the medium and ionic associated agent

The paper reported a green and efficient extraction strategy to lithium isotope separation. A 4-methyl-10-hydroxybenzoquinoline (ROH), hydrophobic ionic liquid—1,3-di(isooctyl)imidazolium hexafluorophosphate ([D(i-C₈)IM][PF₆]), and hydrophilic ionic liquid—1-butyl-3-methylimidazolium chloride (ILCl) were used as the chelating agent, extraction medium and ionic associated agent. Lithium ion (Li⁺) first reacted with ROH in strong alkali solution to produce a lithium complex anion. It then associated with IL⁺ to form the Li(RO)₂IL complex, which was rapidly extracted into the organic phase. Factors for effect on the lithium isotope separation were examined. To obtain high extraction efficiency, a saturated ROH in the [D(i-C₈)IM][PF₆] (0.3 mol l^?1), mixed aqueous solution containing 0.3 mol l^?1 lithium chloride, 1.6 mol l^?1 sodium hydroxide and 0.8 mol l^?1 ILCl and 3:1 were selected as the organic phase, aqueous phase and phase ratio (o/a). Under optimized conditions, the single-stage extraction efficiency was found to be 52 %. The saturated lithium concentration in the organic phase was up to 0.15 mol l^?1. The free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) of the extraction process were ?0.097 J mol^?1, ?14.70 J mol K^?1 and ?48.17 J mol^?1 K^?1, indicating a exothermic process. The partition coefficients of lithium will enhance with decrease of the temperature. Thus, a 25 °C of operating temperature was employed for total lithium isotope separation process. Lithium in Li(RO)₂IL was stripped by the sodium chloride of 5 mol l^?1 with a phase ratio (o/a) of 4. The lithium isotope exchange reaction in the interface between organic phase and aqueous phase reached the equilibrium within 1 min. The single-stage isotope separation factor of ⁷Li–⁶Li was up to 1.023 ± 0.002, indicating that ⁷Li was concentrated in organic phase and ⁶Li was concentrated in aqueous phase. All chemical reagents used can be well recycled. The extraction strategy offers green nature, low product cost, high efficiency and good application prospect to lithium isotope separation.     

Electrodeposition of americium on the stainless steel support for the purpose of radiochemical assay

The kinetics of uranium, plutonium and americium electrodeposition on steel targets from organic solutions of diphenyl-(N,N-dibutyl) carbamoylmethylphosphine oxide supplemented with the ionic liquid of trihexyltetradecylphosphonium hexafluorophosphate ([PH₄]⁺PF₆ ^?) in ethanol or N,N-dimethylformamide has been studied. When running a process in a dimethylformamide medium, and 0.05 M concentration of [PH₄]⁺PF₆ ^? americium deposition degree exceeds 95 % at the electrolysis time of 2 h. Alpha-spectra resolution of obtained target does not exceed 40 keV.     

Volumetric Properties of the {x 1[C4mim][MeSO4] + (1 − x 1)MeOH} System at Temperatures from (283.15 to 333.15) K and Pressures from (0.1 to 35) MPa

Densities of pure 1-butyl-3-methylimidazolium methylsulfate, [C₄mim][MeSO₄], and its mixtures with methanol have been measured. Measurements were made with an accuracy of ±0.2 kg·m^?3, using a vibrating-tube densimeter, over the temperature and pressure ranges (283.15–333.15) K and (0.1–35) MPa, respectively. The experimental densities for the pure ionic liquid and alcohol have been correlated by the Tait equation. The results for the {x ₁[C₄mim][MeSO₄] + (1 ? x ₁)MeOH} system have been correlated by a van Laar equation involving parameters that are dependent on temperature and pressure. Excess volumes have been obtained directly from the experimental densities, while isobaric expansivities, isothermal compressibilities, and related excess properties were calculated from the correlation equation. Exceptionally strong pressure and temperature influences on these properties were observed.     

Pressure effects on a dimetallic ferrimagnet [Mn(en)]3[Cr(CN)6]2 · 4H2O

We have investigated pressure effects on a dimetallic ferrimagnet [Mn(en)]₃[Cr(CN)₆]₂ · 4H₂O (en; ethylenediamine) through the magnetic measurements using a diamond anvil cell in the pressure region up to P = 4.7 GPa. This ferrimagnetic compound has an eminent high transition temperature (Tc) of 69 K at ambient pressure in the structurally characterized molecule-based magnet system. Under hydrostatic pressure, Tc linearly increases against pressure, and exceeds 130 K at P = 4.7 GPa. The amount of the saturated moment hardly changes in the considered pressure region. This pressure experiment might become a prototype of artificial material control for the high-Tc molecule-based magnet.     

Measuring structural inhomogeneity of a helical conjugated polymer at high pressure and temperature

We report on X‐ray scattering measurements of helical poly[9,9‐bis(2‐ethylhexyl)‐fluorene‐2,7‐diyl] by mapping the sample with 10 μm spatial resolution from 0.3 GPa to 36 GPa. We follow the strongest 00l reflection, which moves toward higher scattering angles with pressure indicating planarization of helical polyfluorene. Lateral inhomogeneity is increased for >10 GPa concomitant with the solidification of the pressure transmitting medium (a 4:1 mixture of methanol and ethanol). We also follow the 00l reflection with increasing temperature at the constant pressure of 4.3 GPa in neon. We observe a sharp shift toward higher scattering angles indicative of a phase transition at 167–176 °C. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 392–396     

Synthesis of gold nanoparticles in sol–gel glass porogens containing [bmim][BF4] ionic liquid

The [bmim][BF₄] ionic liquid effect on gold nanoparticles formation in silica sol–gel materials is studied in order to produce gel-derived glasses with optical properties. The characteristic red color from gold nanoparticles is observed for transparent glass monoliths obtained sintering, between 365 and 425 °C, a silica sol–gel precursor containing HAuCl₄·3H₂O and [bmim][BF₄], under normal atmospheric conditions. The effect of sintering the ionogel at different temperatures (T_sint) or times (t_sint) on the optical properties, shape, size, and distribution of gold nanoparticles is discussed. Presence of the gold particles is observed using transmission electron microscopy images followed by energy dispersive X-ray spectroscopy analysis. The thermal decomposition of [bmim][BF₄] in the ionogel is investigate using calorimetric and spectroscopic techniques, and by analysis of volatile compounds released by the sol–gel material during sintering. With these results a mechanism for the formation of the gold nanoparticles is proposed, where a first ionic liquid degradation step provides the reductive environment that enables the gold nanoparticles production at the range of temperatures between 350 and 425 °C. Upon sintering the synthesized materials the ionic liquid acts as a sacrificial additive and the ionic liquid thermal decomposition products enables the formation of gold nanoparticles in the sol–gel matrix.     

Encapsulation of silica nano-spheres with polymerized ionic liquid for selective isolation of acidic proteins

A nanocomposite is prepared by encapsulating silica nano-spheres with polymerized ionic liquid in aqueous medium without use of any organic solvents. Vinyl groups are covalently introduced on to the surface of silica nano-spheres, which are then encapsulated by copolymerization of 1-vinyl-3-ethylimidazolium bromide (monomer) and 1,4-butanediyl-3,3′-bis-l-vinylimidazolium dibromide (cross-linker) at room temperature. The derived nanocomposite, PIL@SiO₂, provides a green adsorbent for protein sorption. PIL@SiO₂ is selective toward acidic proteins, and its selectivity can be controlled via varying the amount of monomer used in the copolymerization process. At pH 6.0, use of 5 mg PIL@SiO₂ nanocomposite results in a sorption efficiency of up to 95 % for 200 mg L^?1 ovalbumin in 1 mL sample solution. Electrostatic and hydrophobic interactions between PIL@SiO₂ and protein species dominate the adsorption process. The ovalbumin adsorption behavior is consistent with the Langmuir model, giving a sorption capacity of 333.3 mg g^?1. The retained ovalbumin is recovered by elution with 0.2 % SDS solution. Circular dichroism spectra reveal virtually no change to the α-helix content of ovalbumin after elimination of SDS by use of dialysis. In summary, high-purity ovalbumin is isolated from chicken egg-white by use of the PIL@SiO₂ nanocomposite as adsorbent.     

Quantitative High Performance Liquid Chromatography Determination of Alkanolamines in Ionic Liquid Absorbents

The development of modern absorption media suitable for CO₂ scrubbing, such as ionic liquids and their mixtures, requires appropriate analytical protocols. In this paper, the application of high-performance liquid chromatography to the determination of alkanolamine at various concentrations in ionic liquid solutions was investigated. Both hydrophilic and hydrophobic commercial ionic liquids, such as 1-butyl-3-methylimidazolium acetate [bmim][OAc], 1-ethyl-3-methylimidazolium octylsulfate [emim][OcSO₄], and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [bmim][NTf₂], were studied in this paper and different sample preparation procedures were used for each class of solvent. A simple extraction step was necessary prior to HPLC analysis for hydrophobic ionic liquids. This step was performed using five times more 0.05 M KH₂PO₄ than needed for the ionic liquid sample. Hydrophilic ionic liquid solutions could be analyzed after diluting the sample with water. The general procedure involved separation at room temperature using a cation-exchange HPLC with 0.05 M KH₂PO₄ as the mobile phase and refractometric detection without derivatizing the amines. The influence of the temperature and mobile phase composition on alkanolamine retention was investigated. The relationship between the peak area and alkanolamine concentration was linear over 3 orders of magnitude (2–200 nmol). The detection limit (LOD) for monoethanolamine (MEA) and diethanolamine (DEA) was 1.5 and 2 nmol, respectively. For hydrophobic ionic liquids, which require extraction, it was possible to analyze a 0.004% MEA solution. The quantity of the sample required for analysis was 0.1 g, and the analysis time did not exceed 20 minutes.