Preparation And Characterization Of Single-hole Hollow Magnetic Composite Microspheres

Due to its special structure and excellent magnetic response performance, single-hole hollow magnetic composite microspheres exhibit potential applications in many fields, such as separation and purification of biomaterials, carriers of drug or catalyst etc. Therefore, the preparation of single-hole hollow magnetic composite microspheres with controllable struc-ture has great research significance.The key point of preparation of single- hole hollow magnetic composite microspheres is the produce of single hole structure. Herein, our strategy can be described as follows: first, Fe3O4 hollow magnetic composite microspheres is prepared, then Si O2 shell is partially coat-ed on the surface of Fe3O4 microspheres, at last, a single-hole can be produced by corrosion Fe3O4. In this thesis, we proposed two novel methods to fabricate single- hole hollow magnet-ic composite microspheres: Pickering emulsion template method and PS-Fe3O4 composite microspheres template method. The main contens and rensults as follows:(1)Single-hole hollow magnetic composite Fe3O4/Si O2 microspheres with Fe3O4 inner shell and Si O2 outer shell can be preparaed successfully by Pickering emulsion template method.The size of microspheres and holes are 438±19nm and 245~412nm respectively, and the hole size and its magnetic response performance can be controlled by oxalate acid dissolution time. Stable Pickering emulsion particles can be prepared when the ratio of para f-fin/ Fe3O4 between 4:1 to 8:1. Different surfactants has little influence on particles dispersion on the surface of wax.The thickness of silica shell can be changed by the concentration of TEOS, and the optimal concentration of TEOS is 6.74 mmol/L.(2)The problem of microspheres aggregation can be well resolved by adding disperse nanoparticles in the process of making Pickering emulsion. Three kinds of particles-Fe2O3 nanoparticles, Ca CO3 nanoparticles and Ca CO3-Fe3O4 composite nanoparticles were studies, and the results indicated that Ca CO3-Fe3O4 composite nanoparticles was the best among them to solve the problem of microspheres aggregation.(3)Fe3O4/Si O2 mcirospheres were used to prepare Pickering emulsion, and then Si O2 shell which exposed to the outside of wax were removed by Na OH solution, at last, holes can be produced by corrosion Fe3O4. This method can be produce non-aggreation Si O2/ Fe3O4 hollow mcirospheres with holes. Usually, the prepared microspheres exhibit porous structrure rather than single hole. The hole size is 50~60 nm.(4)Composite microspheres produced by negatively charged PS spheres and posi-tively charged Fe3O4 microspheres were utilized as template to prepare successfully sin-gle-hole hollow Fe3O4/Si O2 magnetic composite microspheres..When the PS/Fe3O4 micro-spheres ratio ranges between 50:1 to 100:1,the prepared Fe3O4/Si O2 microspheres exhibt well dispersion. The size of PS particles e ffect on the size of holes. When the size of PS micro-spheres is 200 nm, Fe3O4/Si O2 microspheres exhibit porous structure, while the size of PS microspheres is 2 μm, Fe3O4/Si O2 microspheres exhibit sing-hole structure.