Ether-functionalized Ionic Liquid Research Articles

Combined thermodynamic and theoretical study on ether-functionalized ionic liquid mixture systems of [MOEmim][TFSI] with ACN/GBL

Ether-functionalized ionic liquids (ILs) have a higher fluidity and are widely used in a variety of applications due to the introduction of the ether group. In order to better understand the relationship between properties and internal interactions of ether-based ILs, we prepared two ether-functionalized ILs 1–2-methoxyethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide ([MOEmim][TFSI]) with acetonitrile (ACN) or γ-butyrolactone (GBL) mixture systems, and investigated the changes of their thermodynamic properties and internal interaction behaviors over the entire concentration range. First, the thermodynamic properties such as dynamic viscosity, density and electrical conductivity of the two mixture systems were measured from 288.15 K to 343.15 K. The excess molar volume (VE), and viscosity deviation (Δη) were calculated by using the measured experimental density and dynamic viscosity data, which can provide microscopic information on the interactions. Further, the intermolecular interactions of the mixture systems were evaluated by density functional theory (DFT) calculations. The sigma–profile (σ–profile) provided insight into the hydrogen bonds (H-bonds) and molecular surfaces interactions. We also used molecular dynamics simulations (MD) to study ILs mixtures in many different solvent concentrations, thereby providing a microscopic and macroscopic characterization of fluid structure, molecular aggregation, and intermolecular forces.

Experimental determination of viscosity for the binary mixtures of the ether-functionalized ionic liquids [C22O1IM][TfO] with monohydric alcohols

In order to apply ionic liquids in various fields, it is necessary to understand their physical and chemical properties. Viscosity, in particular, is an important parameter of multicomponent solutions and plays a decisive role in mass transfer, heat transfer and fluid flow in industrial process. In this work, the ether-functionalized ionic liquid [C22O1IM][TfO] was synthesized and characterized by 1H NMR, 13C NMR, ESI mass spectrometry and elemental analysis. The viscosity of the binary mixture of ionic liquid [C22O1IM][TfO] with ethanol, 1-propanol and 2-propanol in the full concentration range of T = (288.15–318.15) K were measured. The relationships between the viscosity of the binary system and concentration and temperature were investigated. By Vogel–Tamman–Fulcher (VTF) equation and Arrhenius equation, the temperature dependences of the viscosities for the binary system were described and the VTF equation showed better correlation for the binary system. The viscosity deviation that expresses the difference between the actual value and the ideal value of the mixture viscosity, Δη, was calculated. At the same time, the Gibbs energy of activation for viscous flow of the relative viscosity for the mixture, ΔG≠r, was also calculated based on the relative viscosity, ηr, and ΔG≠r is negative that is consistent with the results of, Δη, it means that the interaction between ions becomes weak due to the solvation. The viscosity deviation, Δη, and the Gibbs energy of activation for viscous flow of the relative viscosity for the mixture, ΔG≠r, could be well fitted by the Redlich–Kister equation. In addition, the related entropies and enthalpies were also calculated and discussed.

The molar surface Gibbs free energy and estimate of polarity for a new ether-functionalized ionic liquid [C22O1IM][DCA

A new ether-functionalized ionic liquid (IL), 1-ethyl-3-(2-methoxyethyl)-imidazolium dicyanamide, [C22O1IM][DCA], was prepared and characterized. The values of density, surface tension and refractive index of the IL were measured at T=(298.15–338.15)K by using standard addition method (SAM) and the values of the molar surface Gibbs free energy were also calculated so that the molar surface entropy and the molar surface enthalpy of the IL were obtained. Using the concept of the molar surface Gibbs free energy, the traditional Eötvös equation was transformed into a modified Eötvös equation which can be well applied to the IL. In terms of the new scale of polarity for ILs, the polarity of [C22O1IM][DCA] and 11 molecular liquids were estimated. The results show that the polarity order of these molecular liquids predicted by the dielectric constant is consistency with its estimated by the new scale of polarity for ILs.

Ether-functionalized ionic liquid based composite membranes for carbon dioxide separation

The cellulose acetate and ether-functionalized pyridinium-based ionic liquid composite membranes has been designed to improve CO2 separation performance.

Formation of ether-functionalized ionic-liquid-based aqueous two-phase systems and their application in separation of protein and saccharides.

Ionic-liquid (IL)-based aqueous two-phase systems (ATPSs) have attracted much attention in the separation technology. In this work, we synthesized five novel ether-functionalized ILs and studied their applications in ATPS formation. The phase diagrams for several systems were determined at 298.15 K. An as-prepared IL (1-(2-butoxy-ethyl)-3-methylimidazolium chloride) was chosen as a representative to construct ATPSs for separation of bovine serum albumin (BSA) from aqueous saccharide solutions. Results showed that 76.1-94.3% of BSA was enriched into the IL-rich top phase and almost all the saccharides were extracted into the salt-rich bottom phase in a one-step separation process. The main factors affecting the separation process, such as kinds of saccharides and the amount of inorganic salts, were discussed. Furthermore, the size distributions of aggregates in the IL-rich top phase were determined by dynamic light scattering (DLS), and accordingly the possible mechanism for the separation was investigated.

Compatibility of LiMn2O4 cathode with electrolyte based on low-viscosity ether-functionalized pyrazolium ionic liquid

One new ether-functionalized ionic liquid (IL) composed of pyrazolium cation with one 2-ethoxyethyl group and bis(trifluoromethylsulfonyl)imide anion was synthesized and characterized. The IL showed the lowest viscosity among all the reported pyrazolium ILs, and the value was 38.9 mPa s at room temperature. The conductivity of the IL was 3.48 mS cm−1 at 25 °C, and its electrochemical window was 4.4 V. Cycling performance of symmetric lithium cell was investigated for the IL electrolyte with 0.6 mol kg−1 of LiTFSI. Li/LiMn2O4 cell using the IL electrolyte owned good cycling and rate performances, and it was found for the first time that LiMn2O4 cathode was compatible with electrolyte based on ether-functionalized IL. By the characterizations of X-ray diffraction and scanning electron microscopy for fresh and cycled LiMn2O4 electrodes, it was inferred that the slow dissolution of LiMn2O4 in the IL electrolyte might happen during the charge–discharge processes.

Spectroscopic Study of the Structural Heterogeneity and Microviscosity of [bmim][PF<sub>6</sub>] and [moemim][PF<sub>6</sub>] Ionic Liquids

Room temperature ionic liquids (RTILs), which have several special properties such as negligible vapor pressure, high thermal and chemical stability, good molecular structure and property designability, have received a great deal of attention, and have emerged as potential environmentally benign solvents. Therefore, a deep understanding of the solvent properties of RTILs, especially the microenvironment properties, is crucial to design new RTILs and extend their applications. The structural heterogeneities and local viscosities of the microenvironments of the ionic liquid [bmim][PF6] and the ether-functionalized ionic liquid [moemim][PF6] were investigated by the rotational dynamics of coumarin 153 (C153) and the excimer-to-monomer fluorescence emission intensity ratio (I-E/I-M) of 1,3-bis(1-pyrenyl)propane (BPP). The rotational dynamics of C153 shows that there are incompact and compact domains within the heterogeneous structure of [bmim][PF6], resulting in fast and slow components of C153 rotational dynamics. The rotational dynamics of C153 shows that there is mainly one type of microenvironment in [moemim][PF6]. The C153 rotation time constants show that the microviscosity of [moemim][PF6] is lower than that of [bmim][PF6], and this result is confirmed by steady-state fluorescence measurement with the BPP microviscosity probe. The side chain of [moemim][PF6] is more polar and more flexible than that of [bmim][PF6], and the oxygen of the ether group could act as a hydrogen bond acceptor and interact with the cations of the ionic liquid, which possibly reduces the electrostatic attraction between the cations and anions in the ionic liquid and leads to the lower structural heterogeneity and microviscosity of [moemim][PF6].

Two highly stable and selective solid phase microextraction fibers coated with crown ether functionalized ionic liquids by different sol–gel reaction approaches

In this work, two novel crown ether functionalized ionic liquid (FIL)-based solid phase microextraction (SPME) fibers were prepared by sol–gel technology using the synthesized 1-(trimethoxysily)propyl 3-(6′-oxo-benzo-15-crown-5 hexyl) imidazolium bis(trifluoromethanesulphonyl)imide ([TMSP(Benzo15C5)HIM][N(SO2CF3)2]) and 1-allyl-3-(6′-oxo-benzo-15-crown-5 hexyl) imidazolium bis(trifluoromethanesulphonyl)imide ([A(Benzo15C5)HIM][N(SO2CF3)2]) as selective stationary phases. Owing to the introduction of trimethoxysilypropyl to the imidazole cation, the [TMSP(Benzo15C5)HIM][N(SO2CF3)2] could be chemically bonded to the formed sol–gel silica substrate through the hydrolysis and polycondensation reaction. Similarly, the [A(Benzo15C5)HIM][N(SO2CF3)2] was able to participate in the formation of the organic–inorganic copolymer coatings through the free radical crosslinking reaction. These two fibers were determined to have “bubble-like” surface characteristics analogous to a previously prepared [A(Benzo15C5)HIM][PF6]-based fiber. Their thermal stabilities were much higher than that of the [A(Benzo15C5)HIM][PF6]-based coating. They were capable of withstanding temperatures as high as 400°C without evident loss of the crown ether FILs. They also had strong solvent, acid and alkali resistance, good coating preparation reproducibility and high selectivity for medium polar to polar compounds. The high selectivity of these two fibers could be attributed to the strong ion-dipole, hydrogen bonding and π–π interactions provided by the synergetic effect of ILs and benzo-15-crown-5 functionalities. Moreover, the selectivity of these two fibers was rather different although the structures of these two crown ether FILs were very similar. This is maybe because the relative contents of the crown ether FILs chemically bonded to the organic–inorganic copolymer coatings were quite different when prepared by different sol–gel reaction approaches.

Ether-functionalized ionic liquid electrolytes for lithium-air batteries

Ionic liquids composed of N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium (DEME), N-methyl-N-methoxyethylpiperidinium (PP1.1o2) cations functionalized with ethers, N-methyl-N-propylpiperidinium (PP13), and N-butyl-N-methylpyrrolidinium (P14) cations and the bis(trifluoromethanesulfonyl)amide (TFSA) anion are investigated for application as electrolytes in non-aqueous lithium–oxygen (Li–O2) batteries. The PP13–TFSA, P14–TFSA and DEME–TFSA ionic liquids have high oxygen radical stability. A comparison of the lithium supply capacity measured using pulse-gradient spin-echo NMR for 7Li nuclei and the oxygen supply capacity measured using electrochemical methods indicates that the oxygen supply is the rate-limiting step for the generation of lithium–oxygen compounds (LiOx) in these ionic liquids with supporting electrolytes. The DEME–TFSA system has the highest LiOx generation activity among the ionic liquid systems examined. We demonstrate the improved performance (output power, discharge–charge capacity and coulombic efficiency) of a Li–O2 battery using the DEME–TFSA system compared with that using the PP13–TFSA system. The improvements observed for the DEME–TFSA system are attributed to the high LiOx generation properties and lithium ion supply.

Evaluation and analysis of Li-air battery using ether-functionalized ionic liquid

Li-air battery using ionic liquids, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) amide (DEME-TFSA) and N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)amide (PP13-TFSA), as the solvents for electrolyte have been studied. A significant improvement of discharge capacity has been observed for DEME-TFSA (4315 mAh g−1-electrode at current density of 0.1 mA cm−2), compared with PP13-TFSA. As a discharged product, aggregates reaching 4 μm diameter in size are formed on the surface of cathode, almost 80% of the products are decomposed after charge. By using Raman spectroscopy, two typical peaks attributed to Li2O2 were detected from the discharged aggregates. From the cross sectional SEM images, vacancy occupation ratios of discharged and charged electrodes are estimated, and they are in good agreement with the theoretical calculations. The discharged products formed inside of the cathode are not decomposed completely by charge.