Construction And Application Of Porous Silica Microspheres Derived From Pickering Emulsions

Microspherical materials with specific sizes and structures,like hollow nanospheres,yolk@shell or multi-chamber structured materials,can be utilized as excellent carriers for catalytic active units,drug delivery etc.therefore,showing great potentials in catalysis,drug delivery,environmental protection and other fields.In this thesis,Pickering emulsion was used as a template to prepare complex silica microspheres through regulated sol-gel process under different conditions.The main achievements were as follows:(1)Hierarchical porous silica microspheres were constructed using a triple templates methods,which involves Pickering emulsion droplets,polystyrene spheres(PS),and cetyltrimethylammonium chloride(CTAC)micelles as templates.During this process,an aqueous solution containing CTAC and PS spheres was used as the aqueous phase,and the n-octane solution as the oil phase,while methyl-modifiedsilica nanospheres(MTMT-SiO2)was used as the emulsifier.A stable water-in-oil Pickering emulsion was formed under high-speed stirring.Subsequently,tetramethoxysilane(TMOS)was added for polymerization and cross-linking in the droplets to form composite microspheres of PS/SiO2 with a hierarchical porous structure.The interior structure of such microspheres was regulated through tuning the contents of PS and the dosage of NH3·H2O.The structure and morphology of fabricated microspheres were fully characterized by scanning electron microscope(SEM),transmission electron microscope(TEM),N2 adsorption and desorption,Fourier infrared spectroscopy(FTIR),and thermogravimetry(TG),and the specific surface was 47 m2/g,with pore volume of 0.1 cm2/g and an average pore diameter of 3 nm.(2)A application of the hierarchical porous silica microspheres.The formed silica microspheres could be utilized to immobilize CALB enzyme,forming CALB@PS/SiO2 solid catalyst,which exhibits excellent catalytic performance in the transesterification of alcohols.After 300 hours of continuous flow reaction,a high conversion rate and enantioselectivity was well maintained,and the microspheres showed no apparent damage after the reaction.After calcination,the microspheres have a large cavity structureand can be used to host organic amine solution(tetraethylenepentamine,TEPA),forming a solid adsorbent,which showed high CO2 adsorption capacity up to 5.44 mmol·g-1,and after 11 cycles of adsorption,the adsorbent could still obtain a CO2 adsorption capacity up to 5.36 mmol·g-1.(3)Construction of solid-liquid hybrid microspheres.A Pickering emulsion with 1-butyl-3-methylimidazole bromide as the dispersed phase was utilized as a template for the sol-gel process of methyl orthosilicate(TMOS),forming a hybrid microsphere with high ionic liquid-loading.The structure and morphology of the fabricated materials were characterized by optical morphology,SEM,N2 adsorption,and their permeability properties were studied by a molecular diffusion test.Moreover,the hybrid microspheres can be adjusted by controlling the amount of emulsifier,pH value of water phase,the type and amount of cross-linking agent.With suitable emulsifier content,pH=3 and TMOS as the silicon source solid-liquid hybrid microspheres formed which have good morphology and permeability.