Research On Conductivity And Separation Of Ionic Liquids Functionalized Porous Materials

As a new type of green solvents,ionic liquids(ILs)have shown great value in the area of electrochemistry,multicomponent-gas separation,etc.due to its extremely-low vapour pressure,noninflammability,nonexplosion,and structure-adjust ability.However,the fluidity of ILs and its high viscosity hinders the further application.Combined ILs and porous materials in order to regulate the latter's properties of porous materials,can not only enhance the mass transfer rate by sufficiently separate ILs and significantly increasing its contact area with gas,but also solve the problem of ILs loss by restricting ILs in the pores to solve the problems of ionic liquids leakage as liquid electrolytes.In this work,various normal and functionalized ILs were synthesized,and introduced into metal organic frameworks(MOFs)and molecular sieve to generate a series of composite materials(hybrid materials).Their application in conductive materials,CO₂ and NH₃ adsorption/separation were studied.Listing below were the primary research contents and results:(1)Ionic conductivity research of ILs functionalized MOFs(MIL-101)materials.A series of solid ionic conductive materials with different ILs and various amounts were designed and synthesized.ILs molecules were introduced into the pores of MIL-101under the demonstration of XRD,BET characterization and the comparison between the sizes of ILs and MIL-101.The influence of temperature,MIL-101 pores occupation percentage,ILs conductivity on the conductivity of IL@MIL-101 composite materials was studied.Activation energy was calculated.Recycling stability was tested.The results showed the conductivity rose significantly compare to MIL-101 the nonconductor.And the conductivity of IL@MIL-101 has a positive correlation with temperature and the ILs amount.For[Emim][SCN]@MIL-101,the conductivity of ES₁₀₀@M was two orders of magnitude higher than that of ES₂₅@M(6.21×10^–3 S·cm^–1 vs 4.35×10^–5 S·cm^–1)at 150°C.This indicates the increasing amount of ILs introduced into the pores of MIL-101 causes the increasing amount of charge carriers,and further leads to the rise of composite material conductivity.TGA and cycling conductivity test revealed a favourable thermal and recycling stability.(2)Ionic conductivity research of ILs functionalized MOFs materials doping with Na⁺.MIL-101-SO₃Na materials with abundant Na⁺on the framework was prepared through ion-exchange method.By regulating the concentrations of IL&Na-salts([Emim][BF₄]&Na BF₄,[Emim][NTf₂]&Na NTf₂,[Bmim][NTf₂]&Na NTf₂,[C₄Py][BF₄]&Na BF₄,and[Bmim][PF₆]&Na PF₆)and introducing IL&Na-salts into the pores of MIL-101-SO₃Na,5 types of IL&Na-salts functionalized MIL-101-SO₃Na solid conductive materials were synthesized.Crystal structure,pore property,surface morphology,and thermal stability were studied by XRD,BET,FT-IR,SEM,TEM,and TGA tests.Conductivity tests results indicated the ionic conductivity rose as the ILs introduction amount increased after the ILs was introduced into MIL-101-SO₃Na pores compared to that of MIL-101 the insulator.The result MDEAns adding sodium salts into IL&Na-salts@MOF can significantly enhance its conductivity.And the conductivity of sample EB-15(1.32×10^–2 S·cm^–1)is 0.72 times higher than that of sample EB-13(7.66×10^–3 S·cm^–1).(3)The CO₂ separation ability of ILs functionalized MOFs materials was studied.A series of IL@MOF hybrid materials loaded with different ILs were designed and prepared.The effect of ILs types,MOFs types,ILs loading amount,testing temperature on CO₂ adsorption were evaluated.The CO₂ recycling adsorption ability of IL@MOFs was also studied.The results showed a highest CO₂ adsorption ability of[Bmim][OAc]@ZIF-8 material among five kinds of hybrid materials(even higher than that of ZIF-8 itself).[Bmim][OAc]@MIL-101 absorb less CO₂ than MIL-101,which indicates CO₂ adsorption ability is a synergy effect that can be influenced by both ILs and MOFs.The higher the[Bmim][OAc]loading amount,the higher the CO2adsorption amount on[Bmim][OAc]@ZIF-8 hybrid material,and correspondingly the lower the CH₄ and N₂ adsorption amount,especially when the total pressure was low.When the total pressure is 5 k Pa.Temperature revealed little influence on CO₂adsorption ability of[Bmim][OAc]@ZIF-8 hybrid material,which indicates the CO2adsorption on[Bmim][OAc]is a chemical adsorption under low total pressure.On the other hand,CO₂ could be entirely desorbed from[Bmim][OAc]@ZIF-8,and the renewed[Bmim][OAc]@ZIF-8 material had a good recycling adsorption ability.(4)NH₃ adsorption ability of functional ILs hybrid material was studied.Two kinds of alcohol-ammonia type ILs([TEA][CF₃SO₃]and[MDEA][CF₃SO₃])which showed high NH₃ adsorption ability were designed and synthesized.Based on the fact these ILs are solid or show high viscosity and unable to transfer mass effectively,both ILs were loaded on four kinds of porous materials with large specific surface area to produce ILs hybrid materials.All these hybrid materials were characterized to study their NH₃ and CO₂ adsorption ability.The NH₃/CO₂ selectivity was also calculated.The results revealed[TEA][CF₃SO₃]had a NH₃ adsorption ability as high as 166.6 mg NH₃·g IL^–1 at 40°C,with a NH₃/CO₂ selectivity of 106.4.The higher the ILs loading amount,the larger the NH₃ adsorption amount of the ILs hybrid materials.Compared to pure ILs,[TEA][CF₃SO₃]hybrid materials had a faster adsorption rate,and a better adsorption performance at relatively low temperature and high total pressure.40%[TEA][CF₃SO₃]@MCM-41 material had a NH₃/CO₂ selectivity of 61.54,and a good recycling adsorption performance.