Preparation,Properties And Applications Of Ionic Liquid Gel Microspheres

Ionic liquid gels（IL-gels）are a new type of composite materials that confine ionic liquids（ILs）into solid space network matrices.To date,bulk IL-gels have been studied by many researchers and showed impressive potential in the fields of electronic technology,catalysis,biomedicine,and clean energy.However,the micro/nanoscale IL-gels,have rarely been reported so far to the best of our knowledge.Scale effects exist in almost all systems,which essentially depend on the mutual coupling of structures and forms at different scales.Reported microgels are all based on water or organic solvent as dispersion medium,and the inherent deficiencies of these dispersion media,such as volatility and lack of functionality,limit their applications.In view of the properties and functions of ILs,the independent spherical micron-scale IL-gels,which are designated as ionic liquid gel microspheres（ILG-microspheres）,were prepared for the first time in this paper.The ILG-microspheres were combined with active substances in various composite forms,and a series of high-efficiency microreactors based on ILG-microspheres have been developed to solve the problems of ILs including high viscosity,easy leakage and high cost in some applications.The research results show that ILG-microspheres,as the liquid compartment components of the microreactors,have excellent ability and selectivity of mass transfer,and can rapidly enrich substances.The internal ILs in ILG-microspheres can also build a microenvironment for enrichment of substrate and promotion of catalytic reaction tuning by chemical regulation.The microreactors constructed by ILG-microspheres have a synergistic effect of enrichment and nearby catalysis,which shows a broad application prospect in the fields of extraction separation,catalysis,flow chemistry and sensor.The specific research contents and results are as follows:1.Based on the summary of the current research status,and also inspired by the multi-compartmental structure,multi-phase structure and soft matter morphology of cells in bionics,the concept of“liquid compartment microreactor”was proposed for the first time,i.e.,in the micro/nano-solid–liquid composite based microreactors,there is at least one liquid phase other than the reaction medium phase,and especially in the case in which the liquid phase is divided into compartments,which provides a new strategy for the development of efficient composite materials based microreactors.2.Preparation and mass transfer properties of ILG-microspheres with hydrophobic ILs as dispersion medium.First,the independent IL（[BMIM]PF₆）-gel microspheres with sizes of 200–1500 nm and 200–800μm were prepared by emulsion polymerization and suspension polymerization,respectively,using methyl methacrylate（MMA）as monomer to form polymer network matrix and 1-butyl-3-methylimidazolium hexafluorophosphate（[BMIM]PF₆）as liquid dispersion medium,respectively.The results proved that secondary bonds are formed between[BMIM]PF₆ and ester group of PMMA in ILG-microspheres,and thus have excellent thermal stability.The three fluorescent dyes with different charge properties can be extracted from the solution into IL（[BMIM]PF₆）-gel microspheres,and can also be eluted,indicating that IL（[BMIM]PF₆）-gel microspheres have excellent mass transfer performance.The column chromatography with IL（[BMIM]PF₆）-gel microspheres as the fillers realized the chromatographic separation of dye mixture.The results demonstrate that IL（[BMIM]PF₆）-gel microspheres are suitable for the construction of liquid compartment microreactors and may also be employed as a new type of fillers of chromatographic column.3.Construction and flow chemistry of liquid compartment microreactors based on IL（[BMIM]PF₆）-gel microspheres.The IL（[BMIM]PF₆）-gel microspheres were embedded into Bi OBr spheres by a solvothermal method to prepare a novel liquid compartment microreactor（Bi OBr@ILG-microspheres）with a synergistic effect of extraction-catalysis,realizing interface integration between ILG-microspheres and functional substances.Under static photocatalysis,Bi OBr@ILG-microspheres exhibited significantly higher photocatalytic degradation rate constants and degradation efficiencies for Rh B compared to the reference microspheres,with 100%degradation of Rh B within 7 min.Furthermore,the Bi OBr@ILG-microspheres are embedded in a PVA hydrogel to build a multi-liquid phase photocatalytic membrane for continuous-flow photocatalytic degradation ciprofloxacin.Compared with the control groups,the degradation efficiency of the multi-liquid phase photocatalytic membrane was significantly improved,showing an～100%removal rate of ciprofloxacin for a long time.The excellent ciprofloxacin removal performance of the membrane with the Bi OBr@ILG-microspheres should be due to the rapid enrichment of ciprofloxacin by ILG-microspheres under flow conditions,and the efficient catalysis of nearby Bi OBr made the extraction of ciprofloxacin by ILG-microspheres always in an unsaturated state.The developed multi-phase catalytic membrane efficiently realizes substrate enrichment-nearby catalytic synergistic effect under flowing state,demonstrating the advantages of liquid compartment microreactors and the universality of the research strategy.4.Preparation of hydrophilic ILs type ILG-microspheres and their application in catalytic oxidation desulfurization.Since stable ILs-in-oil（IL/O）emulsions are rather difficult to be constructed using conventional emulsifiers,so it is impossible to prepare the independent ILG-microspheres with hydrophilic ILs as dispersion medium through the above methods.For this reason,this chapter developed a method to prepare hydrophilic ILs type ILG-microspheres through solution polymerization followed with high-temperature vacuum desolvation in porous support.The hydrophilic ILs type ILG-microspheres with mesoporous silica microspheres as the support matrix were successfully prepared,and heteropolyacid ionic catalyst（[BMIM]PW）was further embedded into ILG-microspheres with[BMIM]BF₄（1-butyl-3-methylimidazolium tetrafluoroborate）as the dispersion medium and PHEMA（poly（hydroxyethyl methacrylate））as the gel networks,which realized the efficient loading of functional substances inside the ILG-microspheres and construction of a novel solid-liquid composite liquid compartment microreactors（Si O₂@[BMIM]PW/ILG-microspheres）for catalytic oxidative desulfurization.The Si O₂@[BMIM]PW/ILG-microspheres have excellent desulfurization performance for the model oil with DBT 500 ppm,and the desulfurization ratio can reach 100%in 4 h.Moreover,due to the dual confinement effect of mesoporous silica pores and gel networks,Si O₂@[BMIM]PW/ILG-microspheres had excellent stability,and the confined catalysts（[BMIM]PW）and ILs（[BMIM]BF₄）would not leak during the application.5.The aggregation behavior of IL-gels nanospheres containing carbon dots（CDs）and the fluorescence properties of the aggregated microspheres.Nanostructured IL-gels are expected to have more excellent functions.However,nanoparticles,especially nanoparticles containing liquid,are prone to agglomeration due to their higher surface energy.Therefore,it is difficult to prepare independent nanoscale IL-gels by conventional emulsion polymerization and other methods.In this paper,a method for the preparation of IL-gels nanospheres by graft polymerization was developed.The IL-gels nanospheres containing CDs（CDs@IL（[EMIM]NTF₂）-gels,50 nm）were prepared by graft polymerization by modifying the initiator group onto the surface of CDs prepared with o-phenylenediamine as the carbon source,where the[EMIM]NTF₂（1-ethyl-3-methylimidazolium bis[（trifluoromethyl）sulfonyl]imide）as the dispersion medium and PMMA as the gel networks.The CDs@IL（[EMIM]NTF₂）-gels nanospheres can further aggregate to form microspheres during the preparation process,and the aggregation behavior of CDs@IL（[EMIM]NTF₂）-gels nanospheres can be modulated by changing the additive amount of CDs.Unlike conventional solid CDs,the isolated CDs in the gel have solid-state fluorescence properties.CDs@IL（[EMIM]NTF₂）-gels microspheres have selective extraction performance and sensitive fluorescence detection response to substances in solution,and are expected to be served as fluorescence sensors.