离子液体在溶解方面的研究进展

离子液体作为一种新型的“绿色溶剂”,广泛应用于化学反应、萃取分离等化工过程。介绍了绿色溶剂——离子液体发展状况,详细讨论了离子液体在溶解方面的研究进展,包括离子液体在萃取分离方面的研究、离子液体作为反应过程中的溶剂以及离子液体作为高分子溶剂的研究。     

Charge Dynamics and Bending Actuation in Aquivion Membrane Swelled with Ionic Liquids

The actuation strain and speed of ionic electroactive polymer (EAP) actuators are mainly determined by the charge transport through the actuators and excess ion storage near the electrodes. We employ a recently developed theory on ion transport and storage to investigate the charge dynamics of short side chain Aquivion^® (Hyflon^®) membranes with different uptakes of ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf). The results reveal the existence of a critical uptake of ionic liquids above which the membrane exhibits a high ionic conductivity (σ > 5 × 10⁻² mS/cm). Especially, we investigate the charge dynamics under voltages which are in the range for practical device operation (∼1 V and higher). The results show that the ionic conductivity, ionic mobility, and mobile ion concentration do not change with the applied voltage below 1 V (and for σ below 4 V). The results also show that bending actuation of the Aquivion membrane with 40wt% EMI-Tf is much larger than that of Nafion, indicating that the shorter flexible side chains improve the electromechanical coupling between the excess ions and the membrane backbones, while not affecting the actuation speed.     

Methanol-Water Solution Transport in Nafion Membranes with Different Cationic Forms

Measurements of liquid transport were made with a Nafion membrane at different cationic forms. The experimental data are used to estimate the alcohol permeability when the membrane is separating water and water-methanol solutions. The obtained permeability coefficient values were useful for analyzing the influence of the substituted cations on the transport process in the membranes. In the present article, the permeability coefficient of methanol in Nafion substituted by Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺, Ba²⁺, Fe²⁺, Fe³⁺, and Al³⁺ were reported at different methanol concentration values. The analysis of the results revealed that, in general, for ions with the same period in the periodic table, the alcohol permeability decreases with increasing the valence. In contrast, when ions with the same valence are compared, the alcohol permeability decreases when the atomic mass increases, with the exception of the Mg²⁺. As a general trend, similar alcohol permeability variation with the concentration is observed for all the cationic forms of the membrane. There is an initial increase in the permeability, and, when the methanol concentration in the solutions is about 60%, the permeability decreases with the alcohol concentration. However, in the case of trivalent ions, the methanol permeability decreases with the methanol concentration.     

离子液体及其应用进展

主要概述了离子液体及其发展概况,离子液体的种类特性以及合成方法.重点归纳了离子液体作为溶剂的优越性以及离子液体在化学反应、电化学、催化化学和分离纯化中的应用,并指出了离子液体在大规模工业应用方面存在的问题.     

功能型离子液体萃取氧化脱硫研究

合成了一系列含有不同阴离子的1-烷基-3-甲基咪唑型离子液体,以35％H2O2以及冰醋酸为氧化剂,分别考察了不同条件下离子液体对模拟油品和实际油品的脱硫效果.结果表明,离子液体阴离子的酸性以及阳离子烷基碳链的长度对脱硫效果具有显著影响,其中具有较长碳链的强酸性硫酸氢盐类离子液体在剂:油氧化剂=1∶25∶1,30 ℃条件下对模拟油品与实际油品均具有较高的脱硫率,对模拟油品一次脱硫率在90％以上,对抚顺石化公司石油二厂汽油、柴油一次脱硫率在80％以上,其中汽油含硫量降至10 mg/kg左右,达到欧V标准,显示了非常好的工业应用前景.     

离子液体及其在电化学中的应用

离子液体即在室温或接近室温下呈液态的完全由离子构成的物质,作为环境友好和“可设计性”溶剂正在引起越来越多的重视。它具有熔点低、蒸汽压小、酸性可调及良好的溶解度、粘度和密度等特点。综述了离子液体的组成、分类、性质、制备和纯化,就离子液体在电池技术、电合成、电沉积、电容器等电化学方面的应用和研究进展加以阐述,并对该领域的研究前景作了展望。     

High-resolution imaging of ion conductivity of Nafion membranes with electrochemical atomic force microscopy

Conductive electrochemical AFM images demonstrating the complex nature and structure of Nafion surface conductivity are presented. Nanoscale regions with high currents determining the overall total membrane current can be distinguished from majority domains with lower currents and non-conductive areas. The different conductive domains form ordered structures and show a specific dynamic behaviour. These observations were compared to the structural and electrical models in the literature. None of the models is able to explain all aspects of the current images. The existence of inverted micelles seems to be quite probable since the formation of agglomerates like chains and larger ordered clusters is clearly visible. This aspect is best described by the model of Schmidt-Rohr and Chen. In addition, the highly dynamic behaviour and distribution of conductive channels of Nafion leading to the formation of new current pathways also indicates the formation of different meso-phases with a high local fluctuation rate. The other discussed models also predict structural features which are in agreement with our observations like the formation of super-structures and agglomeration of fibers.The structural characterisation reflects the situation at or near the membrane surface and might differ from the bulk structure since the surface energy may have a large influence on the formation of structures during the membrane solidification process. The quite large dynamics of conductivity changes of Nafion reflected in the formation of new current pathways even at room temperature leads to the assumption that the internal structure of Nafion is subject to significant changes due to humidity and temperature variations. The local variation of individual structures may reflect the variation of concentration of hydrophilic and hydrophobic groups during membrane solidification. The minimization of surface free energy during a self-assembling process is essential for the formation of different phases and subsequent structures like chains, etc. as well as higher order clustering.     

Study of lithiated Nafion ionomer for lithium batteries

Lithiated Nafion 112 ionomer was characterized by FT-IR spectroscopy, AC impedance, and cyclic voltammetry. The ionomer swollen with mixed solvents of propylene carbonate (PC) and ethylene carbonate shows ionic conductivity of 8.18×10^–5Scm^–1 at 25°C and good electrochemical stability to allow operation in Li/ionomer/LiCoO₂ cells. The discharge capacity of the first cycle is 126mAhg^–1. Significant capacity loss occurs during cycling due to the presence of PC. AC impedance shows that the passive layer formed at the Li/ionomer interface dominates the cycling performance of the cell.     

Modification of Nafion membranes by incorporation of cationic polymers for reduction of methanol permeability

A small amount of basic polymer was incorporated in the Nafion membrane. Compared with the re-cast Nafion membrane, the Nafion/basic polymer membrane reduced the methanol permeability considerably. The equilibrium water uptake and proton conductivity decreased, but the thermal and mechanical stability was enhanced with increasing concentration of basic polymer. These property changes were caused by formation of cation/anion complex between acidic Nafion and basic polymer molecules. The effects of the types and molecular weights of basic polymers on the methanol permeability and proton conductivity were not significant.     

Continuous Transesterification with Acidic Ionic Liquids as Homogeneous Catalysts

Ionic liquids (ILs) are recyclable acid catalysts for transesterification reactions. In the present study, different acidic ILs were examined in this reaction, with special focus on their recyclability. Furthermore, the IL‐catalyzed transesterification reaction was realized in continuous operation. A miniplant reactor with technically representative design and operating characteristics was used for this study. The applied rig has a volume of 5 L and an external thermosyphon reboiler. The miniplant reactor can be operated in batch and in continuous mode. ILs functionalized with a sulfonic acid group were found to be the most suitable IL catalysts for the transesterification reactions under investigation. Using these ILs, reaction rates as high as for H₂SO₄ could be realized. Moreover, the IL catalyst was demonstrated to be active for at least 1000 h of operation time.     

Nafion/PTFE Composite Membranes for Fuel Cell Applications

The composite membranes were prepared by impregnation of porous poly(tetrafluoroethylene) membranes with a 5 wt% Nafion solution. Scanning electron microscope micrographs of composite membranes show the surface and cross section of poly(tetrafluoroethylene) membranes were covered and filled with Nafion resin. Comparison of physical properties and fuel cell performance of composite membranes with those of Nafion membranes (DuPont Co) is presented. The composite membrane has better thermal stability and gas barrier property but worse ionic conductivity than Nafion membrane. Though the composite membrane has a lower conductivity than Nafion membrane, however, owing to the thinner thickness of composite membrane (in thickness of 20±5µm) than Nafion-115 (in thickness of 125µm) and Nafion-117 (in thickness of 175µm) membranes, the composite membrane has a shorter H⁺ ion transporting pathway and thus a higher conductance (conductance = conductivity/membrane thickness) than Nafion-115 and Nafion-117 membranes. Thus the composite membrane has a better fuel cell performance than Nafion-117 and Nafion-115 membranes. In this report, we show that our composite membrane has a fuel cell performance similar to Nafion-112 membrane (in thickness of 50µm).     

咪唑类离子液体的制备与合成

离子液体作为一类新型绿色介质,近年来获得了突飞猛进的发展。本文简单介绍了离子液体的种类及性质,列举了常用的常规法、微波法、超声法和电化学法等辅助合成方法;重点介绍了目前主要的功能化和手性咪唑离子液体合成方法。     

Solid polymer electrolytes V: microstructure and ionic conductivity of epoxide-crosslinked polyether networks doped with LiClO4

A crosslinked polyether network was prepared from poly(ethylene glycol) diglycidyl ether (PEGDE) cured with poly(propylene oxide) polyamine. Significant interactions between ions and polymer host have been observed for the crosslinked polyether network in the presence of LiClO₄ by means of FT-IR, DSC, TGA, and ⁷Li MAS solid-state NMR. Thermal stability and ionic conductivity of these complexes were also investigated by TGA and AC impedance measurements. The results of FT-IR, DSC, TGA and ⁷Li MAS solid-state NMR measurements indicate the formation of different types of complexes through the interaction of ions with different coordination sites of polymer electrolyte networks. The dependence of ionic conductivity was investigated as a function of temperature, LiClO₄ concentration and the molecular weight of polyether curing agents. It is observed that the behavior of ion transport follows the empirical Vogel-Tamman-Fulcher (VTF) type relationship for all the samples, implying the diffusion of charge carrier is assisted by the segmental motions of polymer chains. Moreover, the conductivity is also correlated with the interactions between ions and polymer host, and the maximum ionic conductivity occurs at the LiClO₄ concentration of [O]/[Li⁺]=15.     

A Method for Improving Ionic Conductivity of Nafion Membranes and its Application to PEMFC

In this paper, we show that proton conductivity and PEMFC performance of Nafion membranes prepared by solutions casting can be improved by aligning the side cahin ionic aggregations along the membrane thickness direction using an electric field. The nano-structures of Nafion membranes prepared by solutions casting with applying an electric field were investigated using transmission electron microscopy (TEM), which clearly shows fibril-like structures of Nafion molecular aggregations aligned along the electric field. The alignment of ionic aggregations along the membrane thickness direction causes linear and less curved proton transferring pathways across the membrane cross section and thus a higher proton conductivity and a better PEMFC performance.     

[Bmim]Cl-xAlCl_3催化合成十二烷基苯

采用AlCl3和[Bmim]Cl不同摩尔比的[Bmim]C1-xA1C13离子液体为催化剂,研究了不同条件下1-十二烯与苯的烷基化反应。实验结果表明,以A1Cl3和[Bmim]Cl的摩尔比为2.0([Bmim]Cl-2A1C13)的离子液体为催化剂,在反应温度25℃、反应时间30 min,苯、烯及离子液体的摩尔比为5︰1︰0.03的条件下,正十二烯的转化率可达98.32%,2-LAB的选择性可达36.76%。离子液体和产物可形成易于分离的双液相,简化了催化剂与产物的分离操作。     

Investigation on Aggregate Formation of Ionic Liquids

Understanding the behavior of ionic liquids on the molecular level is essential for explaining solubilizing or reaction processes, including catalytic reactions in ionic liquids or with ionic liquids as co‐solvent. Using mass spectrometry techniques it is possible to characterize their aggregate formation behavior, which depends on the used solvent. With increasing polarity of the solvent and decreasing ionic liquid concentration, the size of the formed aggregates decreases. From conductivity measurement curves “critical aggregate concentrations” were calculated, which confirm the results of mass spectrometry measurements. Addition of ionic liquids increases the solubility of acetophenone in water. This effect can be explained by the aggregate formation ability of ionic liquids. The findings can be used to explain the outstanding solubility and solvation properties of ionic liquids.     

Studies on Thermal Properties of Selected Aprotic and Protic Ionic Liquids

Abstract

We describe herein the thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) investigations of the thermal properties of selected room-temperature ionic liquids (RTILs). The dependence of the thermal properties on both cation and anion structures of RTILs was systematically studied. The ionic liquids (ILs) investigated here include 28 different imidazolium-based ILs, 22 ammonium-based ILs, and 16 amide-based ILs. In general, these three cation classes exhibit different thermal behaviors but follow a quite systematic trend as expected from the corresponding structural variation. The ILs with bromide as the conjugate anion have lower thermal stabilities than those with bis(trifluoromethane sulfonyl) imide or bis(perfluoroethyl sulfonyl) imide as the conjugate anion. The mass of TGA samples and scan rate were found to have a systematic effect on the decomposition temperature of ILs, highlighting the caution needed in reporting TGA results.     

All solid electric double layer capacitors based on Nafion ionomer

The aim of the present work is to demonstrate that an efficient all solid electric double layer capacitor (EDLC) may be realised with electrolyte membrane and carbon based electrodes prepared by using a Nafion ionomer solution. Polymer membrane was prepared by a casting method. Electrodes were prepared with two overlapped layers formed of a carbon-Nafion layer and a carbon paper substrate. Three different electrolyte separators in capacitor configuration have been tested and compared: (1) a commercial Nafion 115 membrane (N115), (2) a membrane prepared by casting the Nafion 1100 solution (NRG50) and (3) a porous glass fibre matrix impregnated with a 1 M H₂SO₄ solution (FVH2SO4). The membrane and electrodes assemblies (MEA) had thickness of 0.6-0.8 mm and geometric area of 4 cm². The EDLCs characteristics have been studied by conductivity, cyclic voltammetry and DC charge-discharge methods. Proton conductivities of 5.7×10⁻² and 3.1×10⁻² S cm⁻¹ have been measured at room temperature for the N115 and the NRG50, respectively. Specific capacity of 13.2 F g⁻¹ has been obtained by capacitor utilising the cast Nafion membrane. This value is 70% of specific capacity obtained from the capacitor using sulphuric acid and about 140% of that using Nafion 115.     

Agar-based films for application as polymer electrolytes

New types of polymer electrolytes based on agar have been prepared and characterized by impedance spectroscopy, X-ray diffraction measurements, UV-vis spectroscopy and scanning electronic microscopy (SEM). The best ionic conductivity has been obtained for the samples containing a concentration of 50 wt.% of acetic acid. As a function of the temperature the ionic conductivity exhibits an Arrhenius behavior increasing from 1.1 × 10⁻⁴ S/cm at room temperature to 9.6 × 10⁻⁴ S/cm at 80 °C. All the samples showed more than 70% of transparency in the visible region of the electromagnetic spectrum, a very homogeneous surface and a predominantly amorphous structure. All these characteristics imply that these polymer electrolytes can be applied in electrochromic devices.     

离子液辅助制备二氧化锰及催化性能研究

以高锰酸钾和三乙醇胺型离子液为原料合成了二氧化锰,采用X射线衍射技术和扫描电子显微镜考察了二氧化锰的相组成和形貌,并以酸性品红为降解对象考察了二氧化锰的催化性能.结果表明:催化剂的加入量,双氧水的加入量,pH值和焙烧温度对于催化剂的降解活性都有显著的影响,酸性品红降解的最佳条件为:0.05 g的二氧化锰,pH等于7,双氧水的加入量为2 mL.实验还表明催化剂高温煅烧后活性会下降.