Synthesis, Characterization, Polycrystalline Structure And Application Research Of Polyhydroxypyridinium Ionic Liquid

Global warming,energy shortage,environmental pollution and other problems are becoming more and more prominent,the technology industry green low-carbon upgrade,new energy revolution and energy storage technology development is imperative.Ionic liquids show very broad application prospects in the fields of new energy,new materials,catalytic separation,carbon capture and utilization due to their excellent characteristics such as ionic designability,synergistic properties and low vapor pressure.Based on these,we present an exploratory study on cold crystallization energy storage applications and crystal structure change-driven CO₂ capture and separation of ionic liquids by designing and synthesizing a series of polyhydroxypyridine functional ionic liquids and thoroughly investigating their polycrystalline structures,thermal behaviors and influence laws in order to expand the application fields of ionic liquids.The main research contents are as follows:（1）Design,synthesis and characterization of polyhydroxypyridine ionic liquids.Seven polyhydroxypyridine ionic liquids,numbered as IL-1 to IL-7,were designed and synthesized by modifying the cation chain length and anion species through quaternization and anion exchange.Respectively,the synthesized polyhydroxypyridine ionic liquids were characterized by ESI-MS,¹H NMR,¹³C NMR,etc.,which proved that we successfully synthesized the target ionic liquids with structures consistent with those designed.（2）Exploration of thermal behavior and thermal storage of polyhydroxypyridine ionic liquids.The thermochemical properties of polyhydroxypyridine ionic liquids were investigated,and it was demonstrated that the introduction of hydroxyl and hydroxyethyl functional groups on ionic liquid cations could enhance the thermal stability of ionic liquids,while the introduction of hydroxyethoxy groups would decrease the thermal stability.Based on the thermochemical behavior analysis and structural analysis,a cold crystallization material of ionic liquids for thermal energy storage is proposed,which can store thermal energy in the form of latent heat and show melting temperature values suitable for application in the intermediate temperature range（40～100°C）.The sample does not crystallize during the cooling process after the first melting,but changes from liquid to glassy state via the supercooled liquid.Cold crystallization occurs during reheating and the thermodynamic stability of cold crystallization is lower than that of the initial crystals.In-situ temperature-varying powder XRD demonstrated that different crystalline phases were formed throughout the thermal cycle.Crystal polymorphism is the basis of cold crystallization behavior.The results of enthalpy change analysis of the phase change process show that this ionic liquid cold crystallization material has a very small heat loss during the heat storage and release process,and has great potential in thermal energy storage.（3）Exploration of CO2 capture and separation driven by crystal structure change of ionic liquids.The crystal structure of 1-（2-hydroxyethyl）-4-（2-hydroxyethoxy）pyridine bromide ionic liquid was obtained by single crystal XRD.The changes of crystal forms induced by pressure were measured by Raman spectroscopy using diamond anvil cell（DAC）,which proved that there were reversible crystal polymorphs in the process of pressurization and depressurization.We explored the synthesis of CO₂-ionic liquid clathrate compounds through a high pressure in situ Raman monitoring system with a sapphire viewable window.It is preliminarily proved that CO₂-ionic liquid clathrate compounds are realistic and feasible.Ionic liquid clathrate compounds have great development potential in CO₂ capture and separation,hydrogen storage,gas separation and purification.