Local Structure In IL-water Mixtures:A Theoretical Study

Ionic liquids?ILs?have been considered "green solvents" and "design solvents" in recent years,which and have also been seen as a good alternative to toxic and volatile organic solvents by academics and industry.The application of ILs is continually improving.Such as the application of ILs in environmental sciences,like capture and isolate CO2 and treat SO2.ILs can also be applied to fuel cells,fuel-sensitized solar cells,thermoelectric chemistry batteries,ILs-lithium,sodium and magnesium batteries.ILs can also be used in chemical synthesis,pharmaceutical fields,agriculture and some other cross-field applications.In recent years,we have paid more and more attention to the mixtures of ILs,especially with the water in nature.There are also an increasing number of studies based on theoretical calculations to explore a mixture of ILs,including binary,ternary ILs mixed system simulation calculations.Due to the universality of water and its particularity,the presence of water in ILs can lead to changes in its properties,such as solubility,polarity,viscosity,and electrical conductivity.It has been found that both hydrophilic and hydrophobic ILs can absorb different levels of water in the air and that the state of water molecules dissolved in the ionic liquid and the interaction between water and the anions and cations are less studied,It is necessary to understand the state of water dissolved in ILs at the molecular level to further understand ILs as a chemical synthesis and separation medium.In this paper,quantum chemical calculations and kinetic simulations were carried out for the first time to study the binary and ternary mixtures of [EMIM][Tf2N] and water,[BMIM][BF4],[BMIM][PF6] and water.In this paper,the structure of [Tf2N]-?W?n and [EMIM][Tf2N]?W?n is optimized by density functional theory based on B3LYP/6-311+G?d,p?level,where W is water Molecules,n = 1⁶.The influence of water molecules on the interaction of anions and cations in[EMIM][Tf2N] was investigated by analyzing the optimal structure of water in different water molecules.The ternary mixed system of [EMIM][Tf2N] and water and the ternary mixed systemof [BMIM][BF4],[BMIM][PF6] and water were studied by Tinker program under the AMBER force field.The model of [EMIM][Tf2N] and water was established by MS?1:1,1:6,1:20,6:1 and pure [EMIM][Tf2N]?,respectively.Simulations and analysis the presence and influence of water molecules.The density obtained by MD simulation is in good agreement with the experimental data.It is concluded from RDF that the addition of a small amount of water reduces the interaction of anions and cations in ILs.According to the RDF of the mixture of different water content systems,the water molecules act mainly with the anions and cations in ILs and destroy the hydrogen bond network in ILs,which reduces the interaction of anions and cations in ILs.When the water content in the mixture is large,the water mainly interacts with other water atoms and forms larger water molecules.We also simulated the kinetics of the [BMIM][PF6]/[BMIM][BF4]/H₂ O ratio of 1:1:6,1:1:8,1:3:8,1:5:8.The dynamic phase transition between the homogeneous mixture and the liquid-liquid biphasic phase was studied,and the interaction of the mixed system was studied.By considering the relationship between hydrophilicity/hydrophobicity and phase behavior of ions,we propose a reversible phase transition for[BMIM][PF6]/[BMIM][BF4]/H₂ O in the range of 1:3:8.The phenomenon was analyzed statistically by phase transition process,RDF analysis,water molecule size and morphology.