Fluorine-containing Ionic Liquids Research Articles

Water flux enhancement of PVDF membrane by a facile coating method for vacuum membrane distillation

Vacuum membrane distillation (VMD) has received considerable attention from both academia and industry. During VMD, the liquid-vapor interface is supported by a porous hydrophobic membrane to prevent wetting of the membrane pores and allow only vapor to pass through. Therefore, it is advantageous for the production of high-purity water by desalination, and improving the membrane performance has attracted significant attention. In this work, we present a facile method of modifying polyvinylidene difluoride (PVDF) membranes with a fluorine-containing ionic liquid (BPPF6) to improve the membrane hydrophobicity and antiwetting and antifouling properties. The dynamic water contact angle of the membrane increased from 124.5 ± 0.3° to 136.7 ± 0.1°, and the VMD water flux increased by 14.2% for treating 3.5 wt% NaCl aqueous solution at 45 °C.

Are Ionic Liquids Suitable for Suppressing Coal Spontaneous Combustion?

Due to the reported fact that the active functional groups in coal can be dissolved and destroyed by ionic liquids, it is expected that the spontaneous combustion of coal can be affected from a thermodynamic perspective. However, ionic liquids with different thermal stabilities have distinct influences on coal combustion. Here, the thermal stability of long-flame coal in the presence of five pure ionic liquids ([Bmim][BF4], [Bmim][Ac], [Bmim][NO3], [Hoemim][BF4], and [Pmim][BF4]) was analyzed by thermogravimetric analysis, and the flammability of the raw coal, pure ionic liquids, and coal–IL mixtures (mass ratio of 1:1) were tested using a cone calorimeter according to the indexes of the time to ignition (TTI), mass loss rate (MLR), heat release rate (HRR), total heat release rate (THR), specific extinction area (SEA), and CO production. It is shown that the TTIs of mixtures containing coal-[Bmim][BF4], coal-[Hoemim][BF4], and coal-[Pmim][BF4] are relatively long, and the MLR, HRR, THR, and SEA values are relatively low, indicating that these fluorine-containing ionic liquids have a better flame-retardant effect than the other two fluorine-free ones, which may be ascribed to their similar role to halogen inhibitors. In addition, the endothermic process of [Bmim][BF4], [Hoemim][BF4], and [Pmim][BF4] can reduce the temperature of the coal surface and delay the ignition time of coal. In contrast, the TTI of coal-[Bmim][NO3] and coal-[Bmim][Ac] mixtures is much shorter than that of coal alone, and the MLR, HRR, and THR values are larger. This may be caused by the poor thermal stability of the two nonfluorine ionic liquids that began to decompose and release heat prior to coal, providing a large amount of heat for the low-temperature oxidation of coal and thus accelerating coal oxidation and combustion. Although the F-containing ionic liquids show the ability to inhibit spontaneous combustion of coal to some extent, their organic cations are potentially combustible and release large amounts of heat, smoke, and CO under high temperatures.

Study on the anodic behavior of AISI E52100 steel in two fluorine-containing ionic liquids

Ionic liquids have a number of excellent applications such as a kind of promising lubricants which have attracted considerable attention. In this work, we investigated corrosion properties which were found in the use of ILs formed by a 1-butyl-3-methylimidazolium cation and a fluorine-containing anion as lubricants of AISI E52100 steel. Electrochemical tests were used to study the anodic behavior of AISI E52100 steel, and surface analysis was performed to study the surface morphology. The electrochemical results showed that increasing temperature accelerates corrosion of the alloy in two kinds of ionic liquids. The data obtained from polarization curves and EIS suggested that the anodic process of the E52100 steel showed generally an active dissolution and increasing temperature can accelerate the corrosion of the steel. At the same time, the main difference as revealed by SEM–EDS plots was that localized corrosion with some irregular etch pits occurred in [Bmim]BF4 ionic liquid; however, a product layer covered uniformly on the surface of metal in [Bmim]PF6. The results of XPS spectrum indicated that the corrosion products formed on the surface of the AISI E52100 steel are mainly composed of FeO, Fe2O3, FeF2 and FeF3.

Preparation and Characterization of a PVDF Membrane Modified by an Ionic Liquid

In order to enhance the hydrophobicity of polyvinylidene fluoride (PVDF) porous membranes, the blending of PVDF with a hydrophobic ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]) was carried out. The modified PVDF membranes with [Bmim][PF6] were fabricated through a non-solvent induced phase inversion using lithium chloride as a porogen in the PVDF casting solution. The effects of [Bmim][PF6] on the membrane characteristics were investigated. FT-IR analysis indicates that the IL is successfully retained by the PVDF membrane. Thermogravimetric analysis reveals that the optimum temperature of the modified membrane is below 300°C. Scanning electron microscopy pictures show that modified membranes have more homogeneous and larger diameter pores with a mean pore size of 0.521µm and porosity of 78%. By measuring the IL leaching during the membrane fabrication, it was found that the modified membrane does not lose IL. Atomic force microscopy shows that the roughness of the modified membrane surface increases slightly, but the contact angle of the modified membrane increases significantly from 88.1° to 110.1°. The reason for this is that the fluorine-containing IL has a low surface energy, which can enhance the hydrophobicity of the membrane. Finally, by comparing modified membranes with different IL concentrations, we draw a conclusion that the modified membrane with an IL concentration of 3 wt-% has the best properties of pore size, porosity, and hydrophobicity.

A Polyol-Mediated Fluoride Ions Slow-Releasing Strategy for the Phase-Controlled Synthesis of Photofunctional Mesocrystals.

There are only a few inorganic compounds that have evoked as much interest as sodium yttrium fluoride (NaYF4). Its extensive applications in various fields, including transparent displays, luminescence coding, data storage, as well as biological imaging, demand the precise tuning of the crystal phase. Controlling the emergence of the desired α-phase has so far remained a formidable challenge, especially via a simple procedure. Herein, we represented a polyol-assisted fluoride ions slow-release strategy for the rational control of pure cubic phase NaYF4 mesocrystals. The combination of fluorine-containing ionic liquid as a fluoride source and the existence of a polyalcohol as the reactive medium ensure the formation of uniform α-phase mesocrystallines in spite of a higher temperature and/or higher doping level.

Syntheses and Properties of Methoxy and Nitrile Functionalized Imidazolium Tris(pentafluoroethyl)trifluorophosphate Ionic Liquids

An alternative and more benign method was employed to synthesize tris(pentafluoroethyl)trifluorophosphate (FAP) ionic liquids (ILs). Ion exchange chromatography was used instead of the typical electrochemical fluorination developed by Ignat’ev and co-workers. The resulting procedure is simple and can be readily performed, as the use of corrosive hydrofluoric acid and the production of toxic and explosive byproducts were circumvented. Functionalization of the alkyl group of the imidazolium cation with a methoxy and a nitrile moiety was employed to observe changes in properties. The success of the synthesis was confirmed by 1H, 19F, and 31P NMR, IR, and UV–vis spectroscopy techniques. Quantitative product yields of approximately 80% (w/w) were obtained. The water content and viscosity values of the synthesized FAP-based ILs were found to be lower compared to other fluorine-containing ionic liquids. Thermal analyses resulted in high thermal degradation temperatures greater than 573.15 K. Electrochemical anal...

An Investigation on the Friction and Wear Properties of Perfluorooctane Sulfonate Ionic Liquids

The study aims to explore the physicochemical and tribological properties of perfluorooctane sulfonate ionic liquids (PSILs) C8F17SO3N4444 and C8F17SO3P4444. The results showed that C8F17SO3P4444 exhibited excellent friction-reducing and anti-wear properties at both room and high temperatures, and C8F17SO3N4444 presented excellent tribological properties at high temperature when they were used as lubricants for steel/steel, steel/copper, and steel/aluminum friction pairs. As compared with traditional fluorine-containing ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl) imide (L-F104), increasing the fluorocarbon chain length of the anion is proven to be an effective way to improve the performance of the PSILs in terms of hydrophobicity, corrosion resistance, and tolerance to extreme pressure, thereby making them more suitable to be used as lubricants under harsh conditions. The X-ray photoelectron spectroscopy analysis indicated that physical adsorption and tribochemical reactions occurred and generated protective films on the sliding surface during the rubbing process, which reduced the friction and elevated the anti-wear efficiency of the PSILs.

A group contribution model for prediction of the viscosity with temperature dependency for fluorine-containing ionic liquids

Abstract One of the barriers against application of ionic liquids (ILs) for industrial separations is their relatively high viscosity. The viscosity of the IL can however be decreased by inserting the fluorinated moieties into the anion structure. Hence, if one could find a relationship between chemical structure, temperature, and viscosity one could design fluorine-containing ILs (F-ILs) with desired specifications. In this communication, two extensive dataset of F-ILs were gathered; one with reliable sources consisting of 863 experimental viscosities for 85 F-ILs, and the other including unreliable sources consisting of 1160 experimental data points for 332 F-ILs. Using the reliable dataset an efficient group contribution (GC) model was developed, which employs a total of 35 functional groups to estimate the temperature-dependent viscosities of F-ILs. The proposed GC model produced a low average absolute relative deviation (AARD) of 3.23%, root-mean-square error (RMSE) of 0.19, and coefficient of determination (R 2 ) of 0.977. The other model developed using the second database only parameterized in supplementary materials.

A mild and environmentally benign strategy towards hierarchical CeO2/Au nanoparticle assemblies with crystal facet-enhanced catalytic effects for benzyl alcohol aerobic oxidation

The exposure of the crystallographic facets of CeO2 nanocrystals may alter their surface structure and composition, leading to significant discrepancies in their reactivity with respect to catalyzing different reactions. In this paper, a facile strategy of etching hollow CeO2 spheres (@CeO2) with a fluorine-containing ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), under hydrothermal conditions was developed to achieve surface-fluorinated @CeO2 nanoparticles with exposed active high-energy facets, which were further assembled in situ into @CeO2 nanoparticle assemblies. The IL, [Bmim][BF4], is believed to play an important role in determining the formation of CeO2 nanoparticles, and the mild release of fluorine species from [Bmim][BF4] may account for the surface-fluorination and the exposure of active high-energy facets of CeO2. The CeO2 nanoparticle assemblies are ideal model materials for studying crystal facet-dependent catalytic behavior. By loading well-dispersed Au nanoparticles via a sol-impregnation method, @CeO2/Au nanoparticle assemblies were achieved, which showed an enhanced catalytic performance for benzyl alcohol aerobic oxidation. In comparison with @CeO2/Au nanoparticle assemblies obtained by etching @CeO2 spheres with other fluorine-containing agents, NH4BF4, NaBF4, and NH4F, under identical reaction conditions, @CeO2/Au nanoparticle assemblies achieved by etching with [Bmim][BF4] exhibited the highest catalytic activity for benzyl alcohol aerobic oxidation. The surface-fluorination and the exposure of active high-energy facets of CeO2 nanoparticles are believed to be responsible for the enhancement of their catalytic activity. This methodology provides a robust strategy to create CeO2 materials with the active high-energy facets exposed and afford model materials for investigating crystal facet-dependent catalytic behavior, which currently represents an exciting issue in the nanocatalysis community.

Toward resolving anxiety about the accelerated corrosive wear of steel lubricated with the fluorine-containing ionic liquids at elevated temperature

Ionic liquids (ILs) have potential as high-temperature liquid lubricants based on their extremely low vapor pressure and chemical stability. There are many ILs that contain a fluorine atom in their anion moiety. However, since fluorine-containing liquid lubricants such as perfluoropolyether (PFPE) sometimes show very large wear of steel due to an excessive chemical reaction between their fluorine atom and the iron, similar excessive corrosive wear of steel is anticipated when fluorine-containing ILs are used at high temperature. Eight types of ILs with the same bis(trifluoromethanesulfonyl)amide (TFSA)-anion moiety were used as sample oils. Tribotests were carried out with a ball-on-disk-type reciprocating motion tribometer by changing the testing oil temperature from room temperature (RT) to 250°C. X-ray photoelectron spectroscopy (XPS) analyses were carried out to determine the extent of chemical reaction. All eight of the sample ILs tested showed increase in friction and wear with the rise in temperature, and decreasing friction and wear after that. A very marked increase in wear was observed at 250°C for all of the sample ILs, due to the deterioration of the ILs. We also found that the wear increase with increasing temperature was derived not from the excessive corrosive wear but from the reduction in the load–bearing capability of fluids due to the decrease in viscosity. In this region, the formation of metal fluoride and sulfide increased very slightly with the temperature. In the temperature range in which the friction and wear were decreased with temperature, the formation of metal fluoride and sulfide increased. A high degree of fluoride formation was detected by XPS with the PFPE lubricant, with which the level of wear was very much larger than that with the TFSA-based ILs. It can be concluded that there is no need to worry about the accelerated corrosive wear of the TFSA-based ILs up to 200°C.

Anti-Wear Effect of Graphene Oxide in Lubrication by Fluorine-Containing Ionic Liquid for Steel

Anti-Wear Effect of Graphene Oxide in Lubrication by Fluorine-Containing Ionic Liquid for Steel

Extractive Desulfurization of Fuel Oils with Dicyano(nitroso)methanide-based Ionic Liquids

The inability of traditional hydrodesulfurization (HDS) to effectively remove aromatic sulfur compounds such as thiophene (TS) and dibenzothiophene (DBT) has called for alternative methods to be studied, among which extractive desulfurization using ionic liquids (ILs) has attracted increasing interest. In this work, we prepared a new IL, 1-butyl-3-methylimidazolium dicyano(nitroso)methanide ([C4mim][dcnm]), and investigated its extractive desulfurization for both model oils and real FCC gasoline, where model diesel fuel was composed of n-hexane and droplets of DBT and model gasoline was composed of n-hexane, toluene and droplets of TS. Other three [dcnm]-based ILs, 1-ethyl-3-methylimidazolium dicyano(nitroso)methanide ([C2min][dcnm]), N-ethyl-N-methylpyrrolidinium dicyano(nitroso)methanide ([C2mpyr][dcnm]), and N-butyl-N-methylpyrrolidinium dicyano(nitroso)methanide ([C4mpyr][dcnm]), were also comparatively investigated. These [dcnm]-based ILs have low viscosity which favors the mass transfer and reduces the extractive equilibrium time, also are fluorine-free which avoids the corrosion by hydrogen fluoride from anion decomposition that occurs generally in fluorine-containing ILs. The desulfurization ability follows the order [C4min][dcnm] > [C4mpyr][dcnm] > [C2min][dcnm] > [C2mpyr][dcnm]. Typically, [C4min][dcnm] is capable of removing 66% DBT and 53% TS from their respective model oils after one cycle (initial 500 ppm S, 25°C, 15 min, mass ratio of IL:oil 1:1), and < 10 ppm S-content can be obtained after 4 cycles. It was observed interestingly that the S-content in real FCC gasoline can be reduced from initial 250 ppm to < 30 ppm after 6 cycles using [C4min][dcnm] as extractive reagent, which is better than some previous results for real feedstocks. Mutual solubility, extractive temperature, IL:oil mass ratio, multiple extraction, initial S-content, and regeneration were also studied. These dcnm-based ILs are competitive extractive reagents compared with some other ILs to remove those aromatic S-compounds from fuel oils.

Synthesis of new fluorinated imidazolium ionic liquids and their prospective function as the electrolytes for lithium-ion batteries

Two fluorine-containing ionic liquids, 1-(2,2,2-trifluoroethyl)-3-methylimidazolium tosylate and 1-(2,2,2-trifluoroethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (TFSI anion), were obtained in good yields and high purity via a green pathway procedure free of solvent and hazardous catalyst. The incorporation of CF3 moieties in imidazolium structure decreases the ILs TFSI melting point. The preliminary electrochemical results are very promising, a wide electrochemical stability up to 5.7V vs Li+/Li for the fluorinated imidazolium with TFSI anion.

Lubricity and corrosiveness of ionic liquids for steel-on-steel sliding contacts

Ionic liquids are expected to be used as new high-performance lubricants because of their low volatility, high thermal stability, and high oxidation stability. It is well known that some ionic liquids exhibit excellent lubricity for metals. On the other hand, there is concern about the corrosiveness of ionic liquids caused by tribo-chemical reactions. In this study, the lubricating properties of seven kinds of commercially available ionic liquids were evaluated under steel-on-steel sliding contacts using an SRV oscillating sliding tester. The worn surfaces were analyzed by optical microscopy, confocal laser scanning microscopy, scanning electron microscopy with energy dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy. The halogen-containing ionic liquids exhibited excellent lubricity for steel compared with the halogen-free ionic liquids. The X-ray photoelectron spectroscopy analytical results showed the formation of iron fluoride on sliding surfaces lubricated with the fluorine-containing ionic liquids. Formation of this iron-fluoride boundary layer reduced friction; however, corrosion occurred on the worn surfaces after the sliding. On the other hand, less corrosive damage was observed on the worn surfaces that slid under the dry-nitrogen atmospheric condition. These results suggested that the hydrofluoric acid, which was produced by the reaction between iron fluoride and contaminated water from the atmosphere, caused the corrosion on the worn surface. The halogen-free ionic liquids showed inferior lubricity compared with the halogen-containing ionic liquids, though they did not cause any remarkable corrosion. The corrosion-inhibition effect of the phosphorus element was shown in the halogen-containing ionic liquids composed of a phosphate anion or phosphonium cation. The friction-reduction effect was, however, inferior to that of the phosphorus-free ionic liquids. The tribo-chemical reaction of the phosphorus contained in the ionic liquids yielded a phosphate boundary layer that prevented the formation of iron halide on the sliding surface and enhanced the wear resistance.

Fluoride ion yield and absorption spectral analysis of irradiated imidazolium-based room-temperature ionic liquids

The radiation chemical yields of F ions (G(F−) values) were measured for a group of imidazolium-based room-temperature ionic liquids following 60Co gamma ray irradiation. The G(F−) values of ionic liquids: hexafluorophosphate, bis[(trifluoromethyl)sulfonyl]imide, trifluoromethanesulfonate and tetrafluoroborate anions associated with 1-butyl-3-methylimidazolium cations were determined to be 0.227, 0.136, 0.101 and 0.008μmolJ−1, respectively. The G(F−) value is dependent on the F–X (X=B, P, etc.) bond energy and the anion structure and can be considered as an indicator of the radiation stability of fluorine-containing ionic liquids. In addition, as confirmed by UV–Vis absorption measurement, the radiolytic products with strong photoabsorption and color darkening depend on the structures of both the cation and the anion.

Synthesis, Stabilization, Functionalization and, DFT Calculations of Gold Nanoparticles in Fluorous Phases (PTFE and Ionic Liquids)

Gold nanoparticles (Au-NPs) were reproducibly obtained by thermal, photolytic, or microwave-assisted decomposition/reduction under argon from Au(CO)Cl or KAuCl(4) in the presence of n-butylimidazol dispersed in the ionic liquids (ILs) BMIm(+)BF(4)(-), BMIm(+)OTf(-), or BtMA(+)NTf(2)(-) (BMIm(+) = n-butylmethylimidazolium, BtMA(+) = n-butyltrimethylammonium, OTf(-) = (-)O(3)SCF(3), NTf(2)(-) = (-)N(O(2)SCF(3))(2)). The ultra small and uniform nanoparticles of about 1-2 nm diameter were produced in BMIm(+)BF(4)(-) and increased in size with the molecular volume of the ionic liquid anion used in BMIm(+)OTf(-) and BtMA(+)NTf(2)(-). Under argon the Au-NP/IL dispersion is stable without any additional stabilizers or capping molecules. From the ionic liquids, the gold nanoparticles can be functionalized with organic thiol ligands, transferred, and stabilized in different polar and nonpolar organic solvents. Au-NPs can also be brought onto and stabilized by interaction with a polytetrafluoroethylene (PTFE, Teflon) surface. Density functional theory (DFT) calculations favor interactions between IL anions instead of IL cations. This suggests a AuF interaction and anionic Au(n) stabilization in fluorine-containing ILs. The (19)F NMR signal in BMIm(+)BF(4)(-) shows a small Au-NP concentration-dependent shift. Characterization of the dispersed and deposited gold nanoparticles was done by transmission electron microscopy (TEM/HRTEM), transmission electron diffraction (TED), dynamic light scattering (DLS), UV/Vis absorbance spectroscopy, scanning electron microscopy (SEM), electron spin resonance (ESR), and electron probe micro analyses (EPM, SEM/EDX).

Ionic Liquids with Fluorine‐Containing Cations

AbstractFor Abstract see ChemInform Abstract in Full Text.