Construction And Application Of Temperature-sensitive Ionic Liquid-based Two-liquid Phase System

Ionic liquids(ILs)are organic molten salts with a low melting point at or near room temperature.The aqueous two-phase system(ATPS)refers to two-phase systems with distinct interfaces due to the incompatibility between certain water-soluble organics or polymers when added to water.While the ionic liquid-based two-phase system(IL-TPS)is formed by ionic liquids and salting agents,which combines the advantages of ionic liquids and two-phase systems,and is widely used as an efficient and mild new green system.Compared with the traditional ATPS,IL-TPS has the advantages of low vapor pressure,non-volatility,good solubility,high electrical conductivity,good thermal stability and antioxidant properties,which leading to the rapid development and extensive research of IL-TPS in the separation of bioactive substances.Ionic liquid-based biphasic systems usually have the dynamic phase transitions with stimulated responses,the most common of which are temperature-driven phase transitions.Depending on the different effects of temperature on the phase state,it can be further subdivided into two types:upper critical solution temperature(UCST)and lower critical solution temperature(LCST).The property of changing the phase state by controlling the temperature is of great importance in the study of IL-based biphasic phases.Therefore,this thesis focuses on the mechanism and application of temperature-sensitive biphasic systems composed of ILs with specific structures.This thesis consists of three parts.:Part 1:The current status of research on ionic liquid-based two-phase systems with responsiveness was firstly introduced,especially the construction of temperature-sensitive ILbased two-phase systems and their application research.Part 2:In this study,a series of ILs were prepared using cis-and trans-dicarboxylic acid anions and tetrabutylphosphine cations,and the ATPS phase transition mechanism was investigated.It was found that conformational changes in the IL anion resulted in UCST behavior of fumaric acid-type IL([P4444][Fum])and LCST behavior of maleic acid-type IL([P4444][Mal])in aqueous solution.electrostatic interactions between ILs cations and anions competed with IL-water interactions,resulting in different critical solubility temperatures.When the anion-cation interaction is greater than the IL-water interaction,IL molecules favor aggregation to form a separated liquid-liquid phase.Otherwise,the IL-water system will form a homogeneous solution.In addition,it is shown that the dissociation of dicarboxylic acid in the anion and the spatial site resistance in the presence of hydrogen bonding have an effect on the phase separation behavior of ATPS.Finally,the reversible transformation of ATPS between homogeneous and two phases provides an effective platform for the separation of small amino acid molecules.Part 3:In this work,a two-liquid phase system composed of ionic liquid[C4mim][Tf2N]and organic solvent trichloromethane was constructed,which was determined to have UCST phenomenon by studying the IL content and temperature.Then the interfacial synthesis method of porous polymers(POP)was combined with such ionic liquid-based two-liquid phase to compare the differences of POP films synthesized by the same system at homogeneous and separated phases.In this study,two monomers,homophthalaldehyde and benzidine,were chosen to be dissolved in IL phase and slowly diffused into the interface under the action of an acidic catalyst,and finally a homogeneous film was formed at the liquid-liquid interface.The crystallinity and growth state of the porous materials were determined by scanning electron microscopy(SEM)and X-ray diffraction(XRD).The nitrogen adsorption and desorption curves of the synthesized POP materials also confirmed the formation of porous structures and exhibited mesoporous adsorption characteristics.Finally,the adsorption capacity of the porous materials for iodine in gas was investigated.