Effects Of Water On The Structure And Properties Of Imidazole And Pyridine Ionic Liquids

As a novel green solvent, ionic liquids (ILs) have many advantages such as low melting point, negligible vapor pressure, wide liquidus range, well electrical conductivity, thermal stability, remarkable dissolution capacity and recycling. ILs have been become one of the hottest research in the world. However, the large-scale synthesis and purification are key problem in the application of ILs. Water is one of the most common impurities in ILs. The presence of water will greatly affect the structure, physical and chemical properties of ILs, and also has a large effect on the rate and selectivity of reaction. Therefore, it is very important to study the effect of water on the structure and properties of ILs.The effect of water on the structure and properties of1-ethyl-3-methyl-imidazolium triflate ([Emim]CF3SO3) were studied by molecular dynamics (MD) simulations. It was found that the radial distribution functions (RDFs) of different components in the mixture change regularly. The spatial distribution functions (SDFs) obtained from simulations are visualized to depict the microscopic structures of different components in the system. As the water mole fraction increasing, the interaction between the cation and anion are weakened, whereas the interaction of water with anion, cation and other water molecules increase respectively. The coordination numbers of the anion which surrounded with the cation decreases, whereas the coordination numbers of water surrounded with cation, anion, water increase with the increasing of water mole fraction. The viscosity decreases with the increasing of water mole fraction, whereas the electrical conductivity and the self-diffusion coefficients of the cation and anion increase respectively.The simulation study on the effect of temperature on the structure and properties of [EmimJCFaSO3/water was performed. With the temperature increasing, the distribution of water around cation and water around anion reduce. It was shown that the interaction of water-cation, water-anion are weakened and thermal motion of particles become quicker in the system. The self-diffusion coefficients of the cation, anion and water increase, the viscosity decreases whereas the electrical conductivity increases.The effect of water on the structure and properties of alkylimidazolium tetrafluoroborate ([Cnmim]BF4) and ethylimidazolium ([Emim]X) were studied by MD simulations, respectively. It was found that the sequence of the interaction between cation and water is [Emim]+>[Bmim]+>[C6mim]+>[C8mim]+with the increasing of alkylimidazolium side chain length. But the strength of hydrogen bonding interaction between cation and anion is enhanced. The self-diffusion coefficients of the cation, anion and water increase respectively, the viscosity decreases whereas the electrical conductivity increases. With the increasing of anionic volume, the strength of the interaction between water and anion is BF4->CF3SO3->bis(trifluoromethylsulfonyl)-imide (NTf2-). It was shown that the self-diffusion coefficients of the cation and anion decrease, the viscosity increases whereas the electrical conductivity decreases.MD simulations were used to explore the effect of water on the structure and properties of1-butylpyridinium tetrafluoroborate ([Bpy]BF4). It was found that the first peak position of cation-anion RDFs decrease and shift to the right. It was shown that the interaction between cation and anion are weakened. RDFs and coordination numbers of analysis were shown that the interaction of water and cation, water and anion increase respectively. With increasing water mole fraction, the self-diffusion coefficients of the cation, anion and water increase gradually, the viscosity decreases whereas the electrical conductivity increases.The effect of temperature on the structure and properties of [Bpy]BF4/waterwas performed. With the temperature increasing, the distribution areas of water around cation and anion reduce. It was shown that the interaction of water and cation, water and anion are weakened and thermal motion of particles become faster in the system. And the self-diffusion coefficients of the cation, anion and water increase, the viscosity decreases and the electrical conductivity increases.The effect of water on the structure and properties of1-butyl-pyridinium ILs ([Bpy]X) were studied by simulations. With the increasing of anionic volume, the strength of the interaction between water and anion is BF4->CF3SO3->NTf2-. It was shown that the self-diffusion coefficients of the cation and anion decrease, the viscosity increases whereas the electrical conductivity decreases.