Synthesis of TiO2 hollow spheres using binary ionic liquids as an electrocatalyst

Titanium dioxide (TiO₂ titania) hollow sphere was simply synthesized using various ionic liquids (ILs). The shape and size of TiO₂ particles were significantly different with the composition of ILs. This is mainly attributed to the interaction between organic solvent and IL at the interface leading to the formation of sphere. Among the binary ILs, [Bmim][BF₄] + [Omim][PF₆], [Bmim][BF₄] + [Omim][PF₆], and [Bmim][PF₆] + [Hmim][PF₆] were useful to prepare TiO₂ nanostructures with high surface area and anatase phase. Especially, [Bmim][BF₄] + [Omim][PF₆] was the most effective IL to synthesize an anatase TiO₂ hollow sphere.

     

Measurement and Correlation of the Ionic Conductivity of Ionic Liauid-Molecular Solvent Solutions

The ionic conductivity of the solutions formed from 1-n-butyl-3-methylimidazolium tetrafluoroborate （[Bmim][BF4]） or 1-n-butyl-3-methylimidazolium hexafluorophosphate （[Bmim][PF6]） and different molecular solvents （MSs） were measured at 298.15 K. The molar conductivity of the ionic liquids （ILs） increased dramatically with increasing concentration of the MSs. It was found that the molar conductivity of the IL in the solutions studied in this work could be well correlated by the molar conductivity of the neat ILs and the dielectric constant and molar volume of the MSs.     

Solubility of selected dibasic carboxylic acids in water,in ionic liquid of [Bmim][BF4], and in aqueous [Bmim][BF4] solutions

The solubilities of three dibasic carboxylic acids (adipic acid, glutaric acid, and succinic acid) in water, in the ionic liquid of 1-butyl-3-methyl-imidazolim tetrafluoroborate ([Bmim][BF₄]), and in the aqueous [Bmim][BF₄] solutions have been measured by a solid-disapperance method. The binodal curve of water + [Bmim][BF₄] was also determined experimentally from solid–liquid–liquid coexistence temperature up to near the upper critical solution temperature. Experimental results showed that each acid-containing binary behaved as a simple eutectic system. The solid–liquid equilibrium (SLE) data were correlated with the NRTL model for each binary system. The NRTL model with these determined binary parameters predicted the solid-disappearance temperatures of the aqueous ternary mixtures containing [Bmim][BF₄] and the dibasic acids to within an average absolute deviation of 2.0%.     

Synthesis of crosslinked PEG/IL blend membrane via one-pot thiol–ene/epoxy chemistry

Poly(ethylene glycol) (PEG)-based membranes have obtained considerable attentions for CO₂ separation for their promising CO₂ separation performance and excellent thermal/chemical resistance. In this work, a one-pot thiol–ene/epoxy reaction was used to prepare crosslinked PEG-based and PEG/ionic liquids (ILs) blend membranes. Four ILs of the same cation [Bmim]⁺ with different anions ([BF₄]⁻, [PF₆]⁻, [NTf₂]⁻, and [TCM]⁻) were chosen as the additives. The chemical structure, thermal properties, hydrophilicity, and permeation performance of the resultant membranes were investigated to study the ILs' effects. An increment in CO₂ permeability (~34%) was obtained by optimizing monomer ratios and thus crosslinking network structures. Adding ILs into optimized PEG matrix shows distinct influences in CO₂ separation performance depending on the anions' types, due to the different CO₂ affinities and compatibilities with PEG matrix. Among these ILs, [Bmim][NTf₂] was found the most effective in enhancing CO₂ transport by simultaneously increasing the solubility and diffusivity of CO₂. © 2020 The Authors. Journal of Polymer Science published by Wiley Periodicals LLC. J. Polym. Sci. 2020 , 58, 2575-2585     

Direct Ethanol Production from Ionic Liquid-Pretreated Lignocellulosic Biomass by Cellulase-Displaying Yeasts

Among the many types of lignocellulosic biomass pretreatment methods, the use of ionic liquids (ILs) is regarded as one of the most promising strategies. In this study, the effects of four kinds of ILs for pretreatment of lignocellulosic biomass such as bagasse, eucalyptus, and cedar were evaluated. In direct ethanol fermentation from biomass incorporated with ILs by cellulase-displaying yeast, 1-butyl-3-methylimidazolium acetate ([Bmim][OAc]) was the most effective IL. The ethanol production and yield from [Bmim][OAc]-pretreated bagasse reached 0.81 g/L and 73.4% of the theoretical yield after fermentation for 96 h. The results prove the initial concept, in which the direct fermentation from lignocellulosic biomass effectively promoted by the pretreatment with IL.     

The physicochemical properties of some imidazolium-based ionic liquids and their binary mixtures

The density, viscosity and conductivity of ionic liquids (ILs), 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF4]), 1-octyl-3-methylimidazolium chloride ([omim][Cl]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim] BF4]), 1-hexyl- 3-methylimidazolium chloride ([hmim][Cl]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF6]), and the [omim][BF4] + [omim][Cl], [hmim][BF4] + [hmim][Cl], and [hmim][PF6] + [hmim][Cl] binary mixtures were studied at dif- ferent temperatures. It was demonstrated that the densities of both the neat ILs and their mixtures varied linearly with temper- ature. The density sensitivity of a binary mixture is between those of the two components. The excess molar volumes (VE) of [hmim][BF4] + [hmim][Cl] and [hmim][PF6] + [hmim][Cl] mixtures are positive in the whole composition range. For [omim][BF4] + [omim][Cl], the VE is also positive in the [omim][Cl]-rich region, but is negative in the [omim][BF4]-rich re- gion. The viscosity or conductivity of a mixture is in the intermediate of those of the two neat ILs. For all the neat ILs and the binary mixtures studied, the order of conductivity is opposite to that of the viscosity. The Vogel-Tammann-Fulcher (VTF) equations can be used to fit the viscosity and conductivity of all the neat ILs and the binary mixtures. The neat ILs and their mixtures obey the Fractional Walden Rule very well, and the values of the Walden slopes are all smaller than unit, indicating obvious ion associations in the neat ILs and the binary mixtures.     

Experiments and model for the surface tension of (MDEA + [Bmim][BF4]) and (MDEA + [Bmim][Br]) aqueous solutions

The surface tension (γ) of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF₄]), 1-butyl-3-methylimidazolium bromide ([Bmim][Br]), (N-methyldiethanolamine(MDEA) + [Bmim][BF₄]) and (MDEA + [Bmim][Br]) aqueous solutions were measured by using the BZY-1 surface tension meter. The temperature ranged from (293.2 to 323.2) K. The mass fraction of MDEA ranged from 0.35 to 0.45. A thermodynamic equation was proposed to model the surface tension of (MDEA + ionic liquids) (ILS) aqueous solutions and the calculated results agreed well with the experiments. The effects of temperature, mass fractions of MDEA and ILS on the surface tension were demonstrated on the basis of experiments and calculations.     

Liquid–liquid equilibrium for binary and ternary systems containing di-isopropyl ether (DIPE) and an imidazolium-based ionic liquid at different temperatures

Liquid–liquid equilibrium (LLE) data were determined for two binary systems {di-isopropyl ether (DIPE) + 1-ethyl-3-methylimidazolium-ethylsulfate (EMISE)} and {DIPE + 1-butyl-3-methylimidazolium-tetrafluoroborate([Bmim][BF₄])}at temperatures between 293.15 K and 313.15 K. LLE data for six ternary systems {DIPE + water + EMISE} and {DIPE + water + [Bmim][BF₄]} at 293.15 K, 303.15 K, and 313.15 K were also reported. Experiments were carried out at atmospheric pressure using stirred and thermo-regulated cells. The experimental data were correlated with the well-known NRTL and UNIQUAC activity coefficient models. In addition, distribution coefficients and selectivities of the ionic liquids EMISE and [Bmim][BF₄] for water in the DIPE phase were measured.     

Solubility of CO2 in imidazolium-based tetrafluoroborate ionic liquids

The solubility of CO₂ in imidazolium ionic liquids (ILs), 1-butyl-3-methyl imidazolium tetrafluoroborate ([bmim][BF₄]), 1-hexyl-3-methyl imidazolium tetrafluoroborate ([hmim][BF₄]) and 1-octyl-3-methyl imidazolium tetrtafluoroborate ([omim][BF₄]) was determined at 305-25 K and pressures from 1 to 9 MPa. The influence of chain length of alkyl substituents on the imidazolium cation on the solubility of CO₂ was investigated. The differences in solubility with chain length are in the sequence [omim][BF₄] > [hmim][BF₄] > [bmim][BF₄]. The solubility data were correlated by the extended Henry's law, and enthalpy, Gibbs free energy and entropy changes were obtained.     

Extraction and mechanism investigation of trace roxithromycin in real water samples by use of ionic liquid-salt aqueous two-phase system

The ionic liquid, as a green solvent, has several advantages over the organic solvents in traditional liquid-liquid extraction. Aqueous two-phase system (ATPS) consisting of a hydrophilic ionic liquid (1-butyl-3-methylimidazolium tetrafluoraborate, [Bmim]BF₄) and Na₂CO₃, which is a novel, simple, non-toxic and effective sample pretreatment technique coupled with molecular fluorescence spectrophotometry, was developed for the simultaneous separation, enrichment and rapid analysis of roxithromycin. The extraction yield of roxithromycin in [Bmim]BF₄-Na₂CO₃ aqueous two-phase system is influenced by the types of salts, concentrations of Na₂CO₃ and [Bmim]BF₄, as well as the extracting temperature. Under the optimum conditions, the average extraction efficiency is up to 90.7%. The mechanism of ionic liquid-salt ATPS formation was discussed by hydration theory, and the extraction mechanism of the [Bmim]BF₄-salt ATPS was investigated by FT-IR spectroscopy and UV-vis spectroscopy. The results demonstrate that no chemical (bonding) interactions are observed between ionic liquid and roxithromycin, while the nature properties of the roxithromycin are not altered. This method was practical when applied to the analysis of roxithromycin in real water samples with the detection limit of 0.03 μg mL⁻¹, relative standard deviation (RSD) of 1.9% (n = 13), and linear ranges of 1.00-20.00 μg mL⁻¹. The proposed extraction technique will be promising in the separation of other small biomolecules.     

Microwave-assisted separation of ionic liquids from aqueous solution of ionic liquids

Microwave-assisted separation has been applied to recover ionic liquid (IL) from its aqueous solution as an efficient method with respect to time and energy compared to the conventional vacuum distillation. Hydrophilic ILs such as 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([Bmim][TfO]) and 1-ethyl-3-methylimidazolium methylsulfate ([Emim][MS]) could be recovered in 6 min from the mixture of ILs and water (1:1, w/w) under microwave irradiation at constant power of 10 W while it took at least 240 min to obtain ILs containing same water content (less than 0.5 wt%) by conventional vacuum oven at 363.15 K with 90 kPa of vacuum pressure. Energy consumptions per gram of evaporated water from the homogeneous mixture of hydrophilic ILs and water (1:1, w/w) by microwave-assisted separation were at least 52 times more efficient than those in conventional vacuum oven. It demonstrated that microwave-assisted separation could be used for complete recovery of ILs in sense of time and energy as well as relevant purity.     

Microwave-Assisted Ionic Liquid-Catalyzed Selective Monoesterification of Alkylphosphonic Acids—An Experimental and a Theoretical Study

It is well-known that the P-acids including phosphonic acids resist undergoing direct esterification. However, it was found that a series of alkylphoshonic acids could be involved in monoesterification with C₂–C₄ alcohols under microwave (MW) irradiation in the presence of [bmim][BF₄] as an additive. The selectivity amounted to 80–98%, while the isolated yields fell in the range of 61–79%. The method developed is a green method for P-acid esterification. DFT calculations at the M062X/6–311+G (d,p) level of theory (performed considering the solvent effect of the corresponding alcohol) explored the three-step mechanism, and justified a higher enthalpy of activation (160.6–194.1 kJ·mol⁻¹) that may be overcome only by MW irradiation. The major role of the [bmim][BF₄] additive is to increase the absorption of MW energy. The specific chemical role of the [BF₄] anion of the ionic liquid in an alternative mechanism was also raised by the computations.     

Facile and Rapid Isolation of Oxypeucedanin Hydrate and Byakangelicin from Angelica dahurica by Using [Bmim]Tf2N Ionic Liquid

Ionic liquids (ILs) have sparked much interest as alternative solvents for plant materials as they provide distinctive properties. Therefore, in this study, the capacity of ILs to extract oxypeucedanin hydrate and byakangelicin from the roots of Angelica dahurica (A. dahurica) was investigated. The back-extraction method was examined to recover target components from the IL solution as well. Herein, [Bmim]Tf₂N demonstrated outstanding performance for extracting oxypeucedanin hydrate and byakangelicin. Moreover, factors including solvent/solid ratio, extraction temperature and time were investigated and optimized using a statistical approach. Under optimum extraction conditions (solvent/solid ratio 8:1, temperature 60 °C and time 180 min), the yields of oxypeucedanin hydrate and byakangelicin were 98.06% and 99.52%, respectively. In addition, 0.01 N HCl showed the most significant ability to back-extract target components from the [Bmim]Tf₂N solution. The total content of both oxypeucedanin hydrate (36.99%) and byakangelicin (45.12%) in the final product exceeded 80%. Based on the data, the proposed approach demonstrated satisfactory extraction ability, recovery and enrichment of target compounds in record time. Therefore, the developed approach is assumed essential to considerably reduce drawbacks encountered during the separation of oxypeucedanin hydrate and byakangelicin from the roots of A. dahurica.     

Bimodal molecular weight distribution of poly(styrene‐co‐acrylonitrile) formed by conventional free‐radical copolymerization of acrylonitrile and styrene in room temperature ionic liquids

Conventional free‐radical copolymerization of acrylonitrile (AN) and styrene (St) was realized in room temperature ionic liquids (RTILs), 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([Bmim][BF₄]) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([Bmim][PF₆]), under mild conditions. The copolymerization in RTILs was more rapid than that in traditional solvent DMF. Poly(styrene‐co‐acrylonitrile) (SAN) prepared in RTILs had higher molecular weight than that prepared in DMF or by bulk copolymerization. SAN with bimodal molecular weight distribution (MWD) were obtained in most of the reaction conditions in [Bmim][BF₄] and some conditions in [Bmim][PF₆]. By the analysis of reaction phenomena and fluorescence behavior, the reason of the difference in MWD could be attributed to the difference of reaction system compatibility mainly caused by the immiscibility of macromolecule with RTIL. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4420–4427, 2006     

LLE for (water + ionic liquid) binary systems using [Cxmim][BF4] (x = 6, 8) ionic liquids

Liquid–liquid equilibrium diagrams were determined for (IL + water) systems using the family of ILs 1-alkyl-3-methylimidazolium tetrafluoroborates, where the alkyl groups are hexyl and octyl ([C_xmim][BF₄] with x = 6 and 8). The gravimetric method was used to determine the equilibrium compositions at temperatures ranging from 278.15 to 340.15 K. Both systems present an upper critical solution temperature (UCST), which increases from [C₆mim][BF₄] to [C₈mim][BF₄]. The experimental data were correlated using the NRTL and eNRTL models. The binary interaction parameters were calculated for each system and model, and good agreement between experimental and calculated equilibrium compositions was obtained. Finally, the apparent Gibbs energy, enthalpy and entropy of water solution in the ILs were calculated using a modified van’t Hoff equation. The three thermodynamic functions were found to be positive for both ILs.     

Preparation of Nylon-6 Particles in Ionic Liquids

Summary: Utilizing the thermal stability of ionic liquid, micrometer-sized Nylon-6 particles were successfully prepared by hydrolytic polymerization of ε-caprolactam at high temperature with polyvinyl pyrrolidone as stabilizer in ionic liquids, 1-butyl-3-methyl imidazolium tetrafluoroborate, [Bmim][BF₄] and N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoro-methanesulfonyl)amide, [DEME][TFSA]. The obtained particles had a unique shape because Nylon-6 is a crystalline polymer. Viscosity-average molecular weights of Nylon-6 prepared in [Bmim][BF₄] and [DEME][TFSA] at 180 °C for 48 h were 4200 and 2200, respectively.     

Ionic liquids as porogens in the microwave-assisted synthesis of methacrylate monoliths for chromatographic application

Several imidazolium-based ionic liquids (ILs) with varying cation alkyl chain length (C₄–C₁₀) and anion type (tetrafluoroborate ([BF₄]⁻), hexafluorophosphate ([PF₆]⁻) and bis(trifluoromethylsulfonyl)imide ([Tf₂N]⁻)) were used as reaction media in the microwave polymerization of methacrylate-based stationary phases. Scanning electron micrographs and backpressures of poly(butyl methacrylate-ethylene dimethacrylate) (poly(BMA-EDMA)) monoliths synthesized in the presence of these ionic liquids demonstrated that porosity and permeability decreased when cation alkyl chain length and anion hydrophobicity were increased. Performance of these monoliths was assessed for their ability to separate parabens by capillary electrochromatography (CEC). Intra-batch precision (n = 3 columns) for retention time and peak area ranged was 0.80–1.13% and 3.71–4.58%, respectively. In addition, a good repeatability of RSD_{Retention time} = <0.30% and ∼1.0%, RSD_{Peak area} = <1.30% and <4.3%, and RSD_Efficiency = <0.6% and <11.5% for intra-day and inter-day, respectively exemplify monolith performance reliability for poly(BMA-EDMA) fabricated using 1-hexyl-3-methylimidazolium tetrafluoroborate ([C₆mim][BF₄]) porogen. This monolith was also tested for its potential in nanoLC to separate protein digests in gradient mode. ILs as porogens also fabricated different alkyl methacrylate (AMA) (C4–C18) monoliths. Furthermore, employing binary IL porogen mixture such as 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄mim][BF₄]) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₄mim][Tf₂N]) successfully decreased the denseness of the monolith, than when using [C₄mim][Tf₂N] IL alone, enabling a chromatographic run to be performed with 1:1 ratio produced baseline separation for the analytes. The combination of ILs and microwave irradiation made polymer synthesis very fast (∼10 min), entirely green (organic solvent-free) and energy saving process.     

Density and Refractive Index for Binary Systems of the Ionic Liquid [Bmim][BF<Subscript>4</Subscript>] with Methanol, 1,3-Dichloropropane,and Dimethyl Carbonate

Refractive indices at 298.15 K and densities in the temperature interval 293.15 to 318.15 K were determined at atmospheric pressure over the whole composition range for the binary systems [Bmim][BF₄]+(methanol, or 1,3-dichloropropane, or dimethyl carbonate). Due to the high viscosity of the samples, which would produce a wrong density if a classical vibrating-tube densimeter were used, a densimeter was employed that automatically corrects the data for the viscosity effect. Because at room temperature some [Bmim][BF₄]+dimethyl carbonate mixtures showed partial immiscibility, liquid-liquid equilibrium was determined for this system. Excess molar volumes and deviations of refractive index from linear mixing behavior were calculated from the experimental data. An erratum to this article can be found at     

Densities and viscosities for ionic liquids mixtures containing [eOHmim][BF4], [bmim][BF4] and [bpy][BF4]

Densities and viscosities of binary ionic liquids mixtures, 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([eOHmim][BF₄]) + 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]), 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([eOHmim][BF₄]) + N-butylpyridinium tetrafluoroborate ([bpy][BF₄]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) + N-butylpyridinium tetrafluoroborate ([bpy][BF₄]) were measured over the entire mole fraction from T = (298.15 to 343.15) K. The excess molar volumes were calculated and correlated by Redlich–Kiser polynomial expansions. The viscosities for pure ionic liquids were analyzed by means of the Vogel–Tammann–Fulcher equation and ideal mixing rules were applied for the ILs mixtures.     

Palladium‐Catalyzed Enyne Cyclization of 2′‐Alkenyl 2‐Alkynoates in Imidazolium‐Type Ionic Liquids

The use of [bmim][BF₄], [bmim][PF₆], and [bmim][Cl] ILs as the solvents in Pd(II)‐catalyzed enyne cyclization of 2′‐alkenyl 2‐alkynoates in the presence of cupric chloride has been investigated. The Z/E stereoselectivity of the reaction could range from 90:10 to 4:96 by tuning the amount of LiCl in ILs. After the separation of the product, the IL–catalyst mixture could be recovered by treatment with hydrochloric acid and recycled several times without an obvious loss of catalytic activity.