Ionic Liquid bmimPF6 Research Articles

ATR-FTIR spectroscopic imaging with variable angles of incidence of crude oil deposits formed by flocculant flow

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging is a method for spatially resolved analysis of materials that combines the capabilities of ATR-FTIR spectroscopy with the use of a focal plane array detector. This paper presents the methodological aspects of adapting the ATR accessory with variable single reflection angle to the FTIR spectroscopic imaging method. The use of a variable reflection angle allows the image to be studied at different sample depths. Using examples of BMIMPF6 ionic liquid and crude oil droplets placed on the working surface of an internal reflection element, the characteristics of image acquisition as the angle of reflection is varied are discussed. The possibility of obtaining crude oil deposits directly on the working surface of the internal reflection element under the influence of a flocculant flow (n-heptane, acetone) and their study by ATR-FTIR spectroscopic image was demonstrated. Crude oil deposits were obtained under different formation conditions (flow rates of flocculant) and their spectroscopic images were also obtained at different single reflection angles. This information gives an indication of the composition of the deposit’s functional groups not only at spatial resolution but also at depth.

Hysteresis in the MD Simulations of Differential Capacitance at the Ionic Liquid-Au Interface.

In this Letter, we report the first observation of the capacitance-potential hysteresis at the ionic liquid | electrode interface in atomistic molecular dynamics simulations. While modeling the differential capacitance dependence on the potential scan direction, we detected two long-living types of interfacial structure for the BMImPF6 ionic liquid at specific charge densities of the gold Au(111) surface. These structures differ in how counterions overscreen the surface charge. The high barrier for the transition from one structure to another slows down the interfacial restructuring process and leads to the marked capacitance-potential hysteresis.

On the way to greener furanic-aliphatic poly(ester amide)s: Enzymatic polymerization in ionic liquid

The polymerization of 2,5-furandicarboxylic acid (FDCA), one of the key building blocks for the preparation of furan polymers, is often accompanied with side reactions (e.g. decarboxylation). Due to the mild reaction conditions, enzymatic polymerizations became an excellent candidate to address this issue. Here, we present a green and effective method to prepare different furanic-aliphatic poly(ester amide)s (PEAFs) by applying two different approaches. PEAFs with Mw‾ up to 21 kg mol−1 were successfully synthesized by a Novozyme 435-catalyzed polycondensation of dimethyl 2,5-furandicarboxylate (DMFDCA) with aliphatic diols, diamines or amino alcohols, using toluene at 90 °C. Additionally, we were able to enhance the sustainability of the entire process by performing the polymerization in ionic liquids – BMIMPF6 and EMIMBF4. Using the ionic liquids (ILs) BMIMPF6 and EMIMBF4 as solvents, we were able to produce PEAFs with Mw‾ up to 7 kg mol−1. The different polarity of the solvents affects the enzyme activity and product solubility, thus also the final molecular weight of the PEAFs. Despite the lower molecular weight, the tested ILs result products with similar characteristics. All obtained PEAFs are semi-crystalline materials and decompose at a temperature around 390 °C with a Tm of around 77–140 °C and Tg of around 11–46 °C. Although still exemplified on the proof-of-concept production of sustainable materials, these findings pave the way to promote the transition from fossil-to bio-based polymers, as well as more environmentally friendly synthetic routes.

Dynamics in the BMIM PF6/acetonitrile mixtures observed by femtosecond optical Kerr effect and molecular dynamics simulations.

We have performed the measurements of the optical Kerr effect signal time evolution up to 4 ns for a mixture of 1-alkyl-3-methyl-imidazolium hexafluorophosphate (BMIM PF6) ionic liquid and acetonitrile in the whole mole fractions range. The long delay line in our experimental setup allowed us to capture the complete reorientational dynamics of the ionic liquid. We have analysed the optical Kerr effect signal in the time and frequency domains with help of molecular dynamics simulations. In our approximation of the slow picosecond dynamics with a multi-exponential decay, we distinguish three relaxation times. The highest two are assigned to the reorientation of the cation and acetonitrile molecules that are in the vicinity of the imidazolium ring. The third one is recognized as originating from cation rotations and reorientation of acetonitrile molecules in the bulk or in the vicinity of the aliphatic chains of the cation. With help of the simulation we interpret the intermolecular band in the reduced spectral density, obtained from Kerr signal, as follows: its low-frequency side results from oscillations of one of the components in the cage formed by its neighbors, while the high-frequency side is attributed to the librations of the cation and acetonitrile molecule as well as the intermolecular oscillations of system components involved in specific interactions. We use this assignment and concentration dependence of the spectra obtained from velocity and angular velocity correlations to explain the mole fraction dependence of Kerr reduced spectral density.

Structural Forces in Mixtures of Ionic Liquids with Organic Solvents.

Using molecular dynamics simulations, we study the impact of electrode charging and addition of solvent (acetonitrile, ACN) on structural forces of the BMIM PF6 ionic liquid (IL) confined by surfaces at nanometer separations. We establish relationships between the structural forces and the microscopic structure of the confined liquid. Depending on the structural arrangements of cations and anions across the nanofilm, the load-induced squeeze-out of liquid layers occurs via one-layer or bilayer steps. The cations confined between charged plates orient with their aliphatic chain perpendicular to the surface planes and link two adjacent IL layers. These structures facilitate the squeeze-out of single layers. For both pure IL and IL-ACN mixtures, we observe a strong dependence of nanofilm structure on the surface charge density, which affects the simulated pressure-displacement curves. Addition of solvent to the IL modifies the layering in the confined film. At high electrode charges and high dilution of IL (below 10% molar fraction), the layered structure of the nanofilm is less well defined. We predict a change in the squeeze-out mechanism under pressure, from a discontinuous squeeze-out (for high IL concentrations) to an almost continuous one (for low IL concentrations). Importantly, our simulations show that charged electrodes are coated with ions even at low IL concentrations. These ion-rich layers adjacent to the charged plate surfaces are not squeezed out even under very high normal pressures of ∼5 GPa. Hence, we demonstrate the high performance of IL-solvent mixtures to protect surfaces from wear and to provide lubrication at high loads.

Synthesis of porous graphene-like carbon materials for high-performance supercapacitors from petroleum pitch using nano-CaCO3 as a template

Porous graphene-like carbon materials (PGCMs) for supercapacitors were synthesized from petroleum pitch by a nano-CaCO3 template strategy combined with KOH activation. The PGCMs were characterized by TEM, XPS, Raman spectroscopy and N2 adsorption. Results show that their specific surface areas are 1542-2305 m2·g−1, depending on the template/pitch ratio, KOH/pitch ratio and activation temperature. The PGCMs feature interconnected graphene-like carbon layers with abundant small pores. The optimum supercapacitor electrode is produced when the PGCM is synthesized with a template/pitch ratio of 1.5, a KOH/pitch ratio of 1.5 at 850 °C for 1h. It has a specific capacitance of 293 F·g−1 at a current density of 0.05 A·g−1, an excellent rate capability with a capacitance of 231 F·g−1 at a current density of 20 A·g−1 and an outstanding cycling stability with a 97.4% capacitance retention after 7000 cycles in a 6 M KOH aqueous electrolyte. It also exhibits a high specific capacitance of 267 F·g−1 at a current density of 0.05 A·g−1, and a high energy density of 148.3 Wh·kg−1 at a power density of 204.2 W·kg−1 in a BMIMPF6 ionic liquid electrolyte. This is a possible method for the synthesis of PGCMs for high-performance supercapacitors.

On the role of BmimPF6 and P/F- containing additives in the sol-gel synthesis of TiO2 photocatalysts with enhanced activity in the gas phase degradation of methyl ethyl ketone

The role of phosphate and fluoride ions brought by the BmimPF6 ionic liquid via hydrolysis during the sol gel synthesis of TiO2 has been investigated by replacing BmimPF6 with phosphorous- and fluorine-containing additives, phosphoric acid (PA) and sodium fluoride (NaF), respectively. Correlation between the physico-chemical properties and the photocatalytic behavior of the synthesized TiO2 materials was established. High crystallinity anatase TiO2 photocatalysts with controlled crystallite size and shape resulting from P/F-induced modifications displayed strongly improved photocatalytic activity and mineralization yield under UV-A illumination in the degradation of methyl ethyl ketone (MEK) taken as model Volatile Organic Compound (VOC), compared to the TiO2 Aeroxide P25 reference and sol-gel TiO2 counterpart synthesized in absence of any BmimPF6. We showed that the BmimPF6 ionic liquid could be efficiently substituted by cheap PA and NaF additives in an adequate ratio in the sol-gel synthesis for synthesizing TiO2 photocatalysts without altering the main physico-chemical properties and the photocatalytic activity. We proposed a similar synthesis mechanism in both ionic liquid- and P/F-assisted sol-gel syntheses of TiO2, involving a combined role of phosphate and fluoride ions. The reaction of phosphates with titanium hydroxide network in the early stage of the sol-gel synthesis resulted in a size control of TiO2 crystallites and thus in higher specific surface area, in favor of a higher MEK conversion rate, while the fluoride ions were hypothesized to cause an anisotropic TiO2 crystal growth during the aging step of the sol gel synthesis, in favor of a higher selectivity to CO2 through a favored adsorption of intermediate products of MEK degradation on the exposed TiO2 {001} facets.

Biomolecule-Free, Selective Detection of o-Diphenol and Its Derivatives with a Screen-Printed Electrochemical Sensor

We report here biomolecule-free, selective detection of o-diphenol and its derivatives with a screen-printed electrochemical sensor. It is based on the preparation of a highly stable slurry made of 2,2-diphenyl-1-picrylhydrazyl (DPPH) dissolved in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) room temperature ionic liquid for use as screen-printed ink in fabricating the proposed sensor. A detailed investigation by scanning electron microscope (SEM) along with UV-visible and FT-IR spectroscopic studies indicates that DPPH is well dispersed and stabilized by BMIMPF6 ionic liquid. Enhanced current response is observed using the as-printed electrode (designated as SP-DPILE) in electrochemical measurements of o-diphenols with good sensitivity and selectivity. Its selectivity is proved through the discrimination of catechol signal from resorcinol and hydroquinone in the absence of biomolecule auxiliary. This is valuable in real sample analysis, and the feasibility of the SP-DPILE is demonstrated for the detection of gallic acid in green tea by flow injection analysis.

The Application of Ionic Liquid Composite Materials in Denitrification from Flue Gas

In this paper, ionic liquid BMIMPF6 was synthesized and characterized by IR and 1H NMR, and the properties, such as melting point, density, viscosity conductivity and the solubility with common solvents were detected. The NO2 solubility in composite materials composed of ionic liquid and organic base was also discussed, the absorption process was optimized and the absorption mechanism was speculated. The results showed that the purity of ionic liquid is 99% by 1H NMR. The properties of ionic liquid are basically identical with literature reported data. Under the optimum experimental conditions, the composite material composed of the ionic liquid and the organic alkali showed a high NO2 absorption amount of 0.311gNO2/g ionic liquid composite material, and the absorption process is a physical and chemical process. The ionic liquid composite material can be recycled for 4 times, and the absorption effect is basically unchanged.

Free-standing oligo(oxyethylene)-functionalized polythiophene with the 3,4-ethylenedioxythiophene building block: electrosynthesis, electrochromic and thermoelectric properties

A free-standing ordered polymer of P(EDT-E5-EDT) based on oligo(oxyethylene)-functionalized polythiophene with two 3,4-ethylenedioxythiophene units as building blocks was electrosynthesized successfully at a low oxidation potential, and comparatively investigated in three electrolytes of ACN/LiClO4, PC/LiClO4 and ionic liquid BmimPF6. Interestingly, one ordered film obtained from PC/LiClO4 resulted in its electrical conductivity up to 40Sm−1 depending on the mild growth condition. Among the fabricated P(EDT-E5-EDT) system, electronic transport is an important factor to receive a highest Seebeck coefficient of 35.9μVK−1. P(EDT-E5-EDT) films also exhibited favorable electroactivity and remarkable redox stability in especial. Moreover, the resultant films were demonstrated the electrochromic nature by color changing from salmon pink to blue, and broad absorption can be observed in near infrared region with the band gaps of 1.88–1.93eV. Further switching transmittance revealed that polymers had reasonable contrast ratios (17.35–52.36%), high coloration efficiencies (151.6–363.5cm2C−1), excellent switching stability and color persistence. The effective EDOT moieties in the chain plays a great role in the advanced properties, which could be developed to be semiconducting polymers in many electronic application areas.

Electrosynthesis of electroactive and fluorescent polyphenanthrenes via electropolymerization in BmimPF6

Poly(9,10-dihydrophenanthrene) (PDHP) and polyphenanthrene (PPhe) were synthesized electrochemically by direct anodic oxidation of their corresponding monomers in an ionic liquid BmimPF6. The electropolymerization performances of 9,10-dihydrophenanthrene (DHP) and phenanthrene (Phe), together with the properties of both polymers, including electrochemistry, optical properties, thermal degradation, and morphology were comparatively illustrated. FT-IR spectral analysis manifested that the polymerization of DHP occurred primarily at C(2) and C(7) positions, while Phe mainly through the coupling at C(9) and C(10) sites, in good agreement with previous results. Both PDHP (Eg=2.55eV) and PPhe (Eg=2.18eV) were electroactive and exhibited moderate redox stability, as well as good thermal stability. Furthermore, two polymers could emit yellow–green light, while PDHP showed higher fluorescence quantum yield of 0.14.

Ionic liquids increase the catalytic efficiency of a lipase (Lip1) from an antarctic thermophilic bacterium.

Lipases catalyze the hydrolysis and synthesis of triglycerides and their reactions are widely used in industry. The use of ionic liquids has been explored in order to improve their catalytic properties. However, the effect of these compounds on kinetic parameters of lipases has been poorly understood. A study of the kinetic parameters of Lip1, the most thermostable lipase from the supernatant of the strain ID17, a thermophilic bacterium isolated from Deception Island, Antarctica, and a member of the genus Geobacillusis presented. Kinetic parameters of Lip1 were modulated by the use of ionic liquids BmimPF6 and BmimBF4. The maximum reaction rate of Lip1 was improved in the presence of both salts. The highest effect was observed when BmimPF6 was added in the reaction mix, resulting in a higher hydrolytic activity and in a modulation of the catalytic efficiency of the enzyme. However, the catalytic efficiency did not change in the presence of BmimBF4. The increase of the reaction rates of Lip1 promoted by these ionic liquids could be related to possible changes in the Lip1 structure. This effect was measured by quenching of tryptophan fluorescence of the enzyme, when it was incubated with each liquid salt. In conclusion, the hydrolytic activity of Lip1 is modulated by the ionic liquids BmimBF4 and BmimPF6, improving the reaction rate and the catalytic efficiency of this enzyme when BmimPF6 was used. This effect is probably due to changes in the structure of Lip1 induced by the presence of these ionic liquids, stimulating its catalytic activity.

Prediction and measurement of phase equilibria for the extraction of BTX from naphtha reformate using BMIMPF6 ionic liquid

New Liquid–Liquid Equilibrium (LLE) data for three ternary systems namely; hexane+benzene+BMIMPF6, heptane+toluene+BMIMPF6, octane+o-xylene+BMIMPF6, and a fourth system consisting of synthetic naphtha reformate which is composed of hexane/heptane/octane+benzene/toluene/o-xylene+BMIMPF6 were obtained. The LLE were determined at T=298.15K and atmospheric pressure. Effect of the number of substituted methyls attached to aromatic rings was evaluated in terms of selectivity and extractive capacity of the ionic liquid BMIMPF6. The results showed a decrease of the extracted amount of aromatics by the ionic liquid as the increase of the number attached methyl groups in the corresponding aromatic systems. Thus, the extraction capability of aromatics by BMIMPF6 was in the order of benzene>toluene>o-xylene, either present in individual ternary systems or as mixture in one pseudo ternary system. Five thermodynamics models were used to correlate satisfactorily the LLE data for the four studied ternary systems. These are T-K-Wilson, Dortmund UNIFAC, ASOG, NRTL, and UINQUAC. Different strategies and modifications are made to the group contribution models UNIFAC and ASOG. These modifications showed an improved prediction compared to their original expressions. However, among all models considered in this study, the UINQUAC model gave the best predictions.

Structural and Dynamic Features of Candida rugosa Lipase 1 in Water, Octane, Toluene, and Ionic Liquids BMIM-PF6 and BMIM-NO3

Ionic liquids (ILs) and organic chemicals can be used as solvents in biochemical reactions to influence the structural and dynamic features of the enzyme, sometimes detrimentally. In this work we report the results for molecular dynamics simulations of Candida rugosa lipase (CRL) in ILs BMIM-PF6 and BMIM-NO3, as well as organic solvents toluene and octane in an effort to explore the role of solvent on the structure and dynamics of an enzyme known to be active in many nonaqueous media. Simulations of CRL in water were also included for comparison, bringing the aggregate simulation time to over 2.8 μs. At both 310 and 375 K the ILs significantly dampen protein dynamics and trap the system near its starting structure. Structural changes in the enzyme follow the viscosity of the solvent, with the enzyme deviating from its initial structure the most in water and the least in BMIM-PF6. Interactions between the enzyme surface and the solvent in the IL simulations show that contacts are dominated by the IL anion, which is ascribed to a broader spatial distribution of positively charged protein residues and reduced mobility of the cation due to the size of the imadazolium ring.

Nano-crystals of various lanthanide fluorides prepared using the ionic liquid bmimPF6

Lanthanide fluorides are important materials for a wide spectrum of applications. In this work, nano-sized crystalline fluorides of nearly all of the lanthanides were prepared via a one-pot reaction using the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) as both the solvent and as the fluorination agent and the appropriate lanthanide nitride as the source of the trivalent ion. The phase compositions of the samples (hexagonal, orthorhombic or a mixture of these) as well as the sizes of the nanocrystals were characterised by X-ray diffraction (XRD) and confirmed by high resolution transmission electron microscopy (HR-TEM). Fluorescence measurements were performed for all of the samples to gain insight into the optical properties of the samples.

Effect of Water on Interfacial Chemical Properties of Nonionic Surfactants in Hydrophobic Ionic Liquid bmimPF6

We studied the effect of water addition on interfacial properties and aggregate behavior of nonionic surfactants (polyoxyethylene alkyl ether; CnEm) in an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate; bmimPF₆). When a small amount of water was added to mixtures of CnEm and bmimPF₆, two breaking points (cac1, cac2) were observed in the surface tension/CnEm concentration plots, suggesting the formation of two kinds of aggregates. This two-step aggregate formation was also confirmed by the fluorescence probe method using pyrene. The particle size of the aggregates measured by dynamic light scattering (DLS) was around 200 nm at cac1, and decreased to 4 nm above cac2. These results, together with freeze-fracture TEM observations, showed that the aggregate formed at cac1 was water in bmimPF₆ emulsions, which then transformed to micelles solubilizing water in the palisade layer above cac2. This concentration-dependent aggregate formation was supported thermodynamically by studying the dependence of cacs on temperature and alkyl and POE chain lengths of the surfactant.

Supercapacitor based on electropolymerized polythiophene and multi-walled carbon nanotubes composites

Polythiophene (PTh) was electropolymerized onto multi-walled carbon nanotubes (MWCNT) modified glassy carbon (GC) electrode in ionic liquid bmimPF6 solution successfully. The different electrochemical behavior of thiophene in bmimPF6 solution was studied by cyclic voltammetry. The different morphologies of PTh films on MWCNT/GC and GC electrodes were characterized by scanning electron microscopy. Cyclic voltammetry test displays that PTh/MWCNT composites have better capacitive property than pure MWCNT and pure PTh. The galvanostatic charge–discharge and electrochemical impedance microscopy tests show that the PTh/MWCNT composites possess good capacitive characteristics. The specific capacitance of the supercapacitor is 110Fg−1. The long-term stability of the supercapacitor was also tested, and the result indicates that the specific capacitance still keeps 90% of the initial capacitance after 1000 consecutive charge–discharge cycles.

Lamellar Liquid Crystals of Brij 97 Aqueous Solutions Containing Different Additives

Lamellar liquid crystals of Brij 97 aqueous solutions were investigated by means of rheological techniques and SAXS at 25 °C, in the presence of various additives including isopropyl myristate, oleic acid, ionic liquid bmim-PF6 and bmim-BF4. The lamellar phases show high elasticity as indicated by their mechanical and discrete relaxation spectra, which is expected to be an advantage when they are used as drug delivery vehicles. It is noted that in comparison with other systems, the lamellar phase formed in the Brij 97/water/IPM system has the lowest storage and loss moduli, implying that it has a weak network strength and less stable internal structure. The Brij 97/water/oleic acid system is the most shear resistance, whereas the Brij 97/water/bmim-PF6 system exhibits fluid-like viscoelastic properties to some extent. These differences are analyzed through SAXS data for the different location of the additive in the lamellar phase.

Features of spin exchange in nitroxide biradicals in the ionic liquid bmimPF6

The intramolecular electron spin exchange has been studied by electron paramagnetic resonance (EPR) spectroscopy in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) for various nitroxide biradicals as a function of temperature and the nature of the connecting bridge between two >NO· centers. Temperature variations of the isotropic nitrogen hyperfine splitting constant a and exchange integral values |J/a| were measured from EPR spectra and analyzed. Thermodynamic parameters of the conformational rearrangements were obtained. The spin exchange in rigid and flexible biradicals dissolved in the ionic liquid bmimPF6 was compared with that in toluene solutions. Interesting features of the spin exchange in biradicals in ionic liquid were observed and explained as a result of the specific intramolecular conformational transitions. The first example of a rather rigid biradical molecule becoming flexible under the influence of an ionic liquid is reported.

Increased Conversion to 2,4,6‐Triarylpyrylium Salt: Aldol Cyclotrimerization of Acetophenone in BMImPF6 Ionic Liquid

AbstractSubstituted acetophenone 1 in BMImPF6 ionic liquid, heated at 120 °C for 24 h, produces β‐methylchalcone 2, triarylbenzene 3, and triarylpyrylium salt 4. BMImPF6 catalyzes the self‐aldol condensation of 1, whose cyclotrimerization gives an increased conversion to 4 at the expense of 3 normally obtained from the cyclotrimerization of 1 in common organic solvent.