Imidazolium-based Room Temperature Ionic Liquids Research Articles

Preparation and characterization of room temperature ionic liquid/single-walled carbon nanotube nanocomposites and their application to the direct electrochemistry of heme-containing proteins/enzymes

This work describes the formation and possible electrochemical application of a novel nanocomposite based on single-walled carbon nanotubes (SWNTs) and imidazolium-based room-temperature ionic liquids (RTILs) of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF 4, a hydrophilic RTIL) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF 6, a hydrophobic RTIL). The nanocomposites ([bmim]BF 4-SWNTs, and [bmim]PF 6-SWNTs) were formed by simply grinding the SWNTs with the respective RTIL. The results of the X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy indicated that the nanocomposites were formed by adsorption of an imidazolium ion on the surface of SWNTs via the “cation–π” interaction. SEM images showed that [bmim]BF 4-SWNTs (or [bmim]PF 6-SWNTs) nanocomposites could uniformly cover the surface of a glassy carbon (GC) electrode resulting in a RTILs-SWNTs/GC modified electrode with a high stability. The RTILs-SWNTs composite could be readily used as a matrix to immobilize heme-containing proteins/enzymes (myoglobin, cytochrome c, and horseradish peroxidase) without undergoing denaturation, as was verified by UV–vis and circular dichroic (CD) spectroscopic results. The voltammetric results showed that heme-containing proteins/enzymes entrapped in RTILs-SWNTs composites displayed a pair of well-defined, stable redox peaks, which were ascribed to their direct electron-transfer reactions. The results of controlled experiments showed that the positive charged imidazolium ion played a significant effect on the electrochemical parameters, such as the redox peak separation and the value of the formal potentials, etc., of the electron-transfer reaction of non-neutral species dissolved in solution or immobilized on the electrode surface. Further results demonstrated that the heme-containing proteins/enzymes entrapped in RTILs-SWNTs composites could still retain their bioelectrocatalytic activity toward the reduction of oxygen and hydrogen peroxide. The results depicted in this work may pave a new avenue to electrocatalysis, proteins/enzymes electrochemistry, and bioelectrochemical synthesis, etc.

Application of the transient grating method to the investigation of the photo-thermalization process of malachite green in room temperature ionic liquids

Transient grating spectroscopy has been applied to the investigation of the photo-thermalization process of malachite green (MG) in several imidazolium-based room temperature ionic liquids (RTILs). MG was simultaneously photo-excited to the S 2 state by two sub-picosecond laser pulses (390 nm) with an angle of 30°, and the time profile of the transient grating due to the population and energy dynamics of MG was monitored by the diffraction of a probe pulse (780 nm). The population grating signal in RTILs showed a fast decay component (ca. 4 ps). After the decay of the population signal, there appeared an acoustic oscillation signal mainly due to the heat dissipation from the photo-excited MG molecule. In the highly viscous ILs such as 1-butyl-3-methylimidazolium hexafluorophosphate, the TG signal showed an additional slower rise component, which cannot be explained by the fast heat dissipation process. The signal was analyzed in terms of the structure relaxation of RTILs, and the sound velocities at the high frequency have been determined.

Raman stpectroscopy of vibrational and rotational relaxation of acetonitrile molecules dissolved in ionic liquids

Vibrational and rotational relaxation processes of acetonitrile (AN) molecules as molecular probes dissolved in the imidazolium-based room-temperature ionic liquid (RTIL) 1-decyl-3-methyl-imidazolium bromide have been studied by Raman spectroscopy technique (the band shape analysis using different polarizations of the incident and scattered light). It has been shown that the vibrational relaxation processes are quickened in the RTIL surrounding. The corresponding vibrational correlation times decrease from about 3 ps in the neat AN to 1.5n2 ps in AN solution in RTIL (10 and 20 wt % of AN). The effect of RTIL environment on the rotational dynamics of AN, namely, on the tumbling motion of dipole moments, is rather small. However, the slow-down of AN reorientations in RTIL was distinguished, namely, the rotational correlation times increase from 1.0n1.5 ps (neat AN) to 1.6n1.9 ps (AN / RTIL solutions). The results have been discussed in terms of various molecular and media contributions to these processes (H-bonding, highly viscous media effect, intermode exchange of vibrational energy, etc). The demolition of structural effects (short-range order and mesoscopic structures in the nano-scale) in 1-decyl-3-methyl-imidazolium bromide by the mutual penetration of AN and RTIL species is suspected.

Preliminary Assessment of Imidazolium-Based Room-Temperature Ionic Liquids for Extraction of Organic Contaminants from Soils

Alternative solvents known as room-temperature ionic liquids (RTILs) were considered for extraction of organic soil contaminants. A hydrophobic RTIL, 1-butyl-3-methyl imidazolium hexafluorophosphate ([bmim]PF6), and a hydrophilic RTIL, 1-butyl-3-methyl imidazolium chloride ([bmim]Cl), were selected as representative imidazolium-based RTILs to assess the extraction of several organic contaminants (OCs) from two model soils. The two soils were montmorillonite (clay minerals, high surface area, and no organic matter) and glacial till (organic matter). The soils were spiked separately with DDT, dieldrin, hexachlorobenzene, and pentachlorophenol. With the exception of DDT, extractions of OCs from montmorillonite using [bmim]PF6 (79-92%) were nearly as effective as extractions with acetone and ethanol (85-100%). The extraction of OCs from glacial till with RTILs (15-61%) was less effective than extraction with organic solvents (59-100%). The [bmim]Cl was as efficient as [bmim]PF6 for extraction of OCs from glacial till, while [bmim]PF6 was more efficient than [bmim]Cl for extraction of OCs from montmorillonite. The two RTILs were most effective for the extraction of dieldrin (the heaviest OC) from both soils. The extraction results for glacial till showed dependence of OC extraction on the viscosity and melting point of RTILs.

Superlong Polypyrrole Nanowires Aligned within Ordered Mesoporous Silica Channels

Polymer-encapsulated silica: An imidazolium-based room-temperature ionic liquid (PyC12MIM+Br−) bearing a terminal pyrrole group was synthesized. Using this novel polymerizable surfactant as a template in a sol–gel process, highly ordered hexagonal mesoporous silica, containing aligned superlong polypyrrole nanowires, was successfully fabricated within the silica channels (see picture).

Electrolytic conductivity of four imidazolium-based room-temperature ionic liquids and the effect of a water impurity

The electrolytic conductivities ( κ) of four hydrophobic room-temperature ionic liquids (RTILs) were measured at temperatures from (288.15 to 323.15) K. The measurements were made with a commercial conductivity cell with platinum black electrodes. In order to exclude atmospheric moisture, the conductivity cell was modified so that it could be sealed during measurements. The RTILs studied were 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and 1-butyl-3-methylimidazolium hexafluorophosphate. The RTILs were dried under vacuum until the mass fraction of water ( w H 2 O ) was ⩽10 −5. Coulometric Karl Fischer titration was used to determine w H 2 O in each RTIL before and after measurements of κ. Most measurements were made on dried RTILs, but some measurements were performed intentionally at higher w H 2 O in order to study the effect of a water impurity on κ. For {water + 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide}, κ was found to increase dramatically with increasing w H 2 O ; for example, in going from w H 2 O = 10 - 5 to 10 - 2 , the fractional increase in κ was 0.36 {=( κ wet − κ dried)/ κ dried}. This work illustrates the importance of measuring the water content in RTILs both before and after measurements of κ.

Effect of the functional groups in ionic liquid molecules on the friction and wear behavior of aluminum alloy in lubricated aluminum-on-steel contact

Four imidazolium-based room temperature ionic liquids containing phosphonyl functional groups, i.e. 1-(3′- O, O-diethylphosphonyl- n-propyl)-3-alkylimidazolium tetrafluoroborates and hexafluorophosphates, were synthesized. The physical properties of the resulting synthetic products were evaluated, and their tribological behaviors as the lubricants for an aluminum-on-steel sliding system were evaluated on an oscillating friction and wear tester, with the emphasis being placed on the effect of the O, O-diethylphosphonyl groups in the ionic liquid molecules on the tribological behaviors. Thus the friction and tests were conducted at a frequency of 25 Hz, a sliding amplitude of 1 mm, and for a duration of 30 min. The worn aluminum surface was analyzed by means of scanning electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy. It was found that the synthesized ionic liquids had better friction-reducing and anti-wear ability for the aluminum-on-steel system than their nonfunctionalized courterparts (1-ethyl-3-hexylimidazolium tetrafluoroborate, coded as L206, and 1-propyl-3-octylimidazolium hexafluorophosphate, coded as LP308). Especially, they had much better load-carrying capacity than L206 and LP308. The tribological behaviors of the synthetic lubricants were dependent on both the anions and the side-substituted alkyl chains attached to the imidazolium cations. Moreover, physical adsorption and complicated tribochemical reactions were involved during the sliding process of the Al-on-steel system under the lubrication of the synthetic functionalized ionic liquids, which led to the generation of physically adsorbing and chemically reacting films composed of five-member-ring complex compounds, metal fluorides, nitrogen oxide, and FePO 4 on the rubbed Al surface. Those physically adsorbing and chemically reacting films contributed to effectively decrease the friction and wear of the aluminum sliding against steel.

Low-Pressure Solubility of Carbon Dioxide in Room-Temperature Ionic Liquids Measured with a Quartz Crystal Microbalance

The solubility of carbon dioxide in a series of imidazolium-based room-temperature ionic liquids has been determined using a quartz crystal microbalance. Henry's constants were obtained for CO2 in nine different ionic liquids: 1-methyl-3-propylimidazolium bis[trifluoromethylsulfonyl]amide (C3mimTf2N), 1-n-butyl-3-methylimidazolium bis[trifluoromethylsulfonyl]amide (C4mimTf2N), C4mimTf2N with polyethylenimine, 1-n-hexyl-3-methylimidazolium bis[trifluoromethylsulfonyl]amide (C6mimTf2N), 1-methyl-3-n-octylimidazolium bis[trifluoromethylsulfonyl]amide (C8mimTf2N), 1-methyl-3-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)imidazolium bis[trifluoromethylsulfonyl]amide (C8F13mimTf2N), 1,4-dibutyl-3-phenylimidazolium bis[trifluoromethylsulfonyl]amide, 1-butyl-3-phenylimidazolium bis[trifluoromethylsulfonyl]amide, and 1-methyl-3-propylimidazolium hexafluorophosphate (C3mimPF6). All results were obtained at 25 °C with CO2 pressures at or less than 1 bar. A comparison of results helps in understanding the role of chemical structure on the separation capabilities of these materials. Notable among the results is a significantly greater measured CO2 solubility in the ionic liquid having the fluorine-substituted cation as compared to the corresponding ionic liquid with a nonfluorinated cation. CO2 solubility was found to be lower in the ionic liquid containing PF6- than for the corresponding liquid with Tf2N- anion. Addition of an imine polymer to the ionic liquid did not significantly change CO2 solubility characteristics. The presence of water had a minor effect on CO2 solubility for C8mimTf2N for environments with a relative humidity of 40% or less. Henry's constant for CO2 in C3mimPF6 obtained in this study is in good agreement with previously reported Henry's constant values for CO2 in C4mimPF6 that were obtained by other means. This study not only provides some important thermodynamic property information for these unique materials but also illustrates the utility of using a quartz crystal microbalance to obtain this information.

The Importance of Imidazolium Substituents in the Use of Imidazolium-Based Room-Temperature Ionic Liquids as Solvents for Palladium-Catalyzed Telomerization of Butadiene with Methanol

Room-temperature ionic liquids are used as cosolvents in the palladium-catalyzed telomerization of butadiene with methanol. The basic catalyst is palladium(II) acetate with either triphenylphosphin...