Study On The Preparation Of Single-hole Hollow SiO₂and Fe₃O₄@SiO₂Microspheres

The hollow microspheres with single holes in thier shell have numerous potentialapplications, such as controlled drug delivery, medical diagnosis, and the protection ofbiologically active agents and catalysis, due to their high uptake capacity for drugs andpollutants, and high effective diffusivity for large molecules and nanoparticles. Developingsimple, efficient preparation methods of single-hole hollow microspheres, and preparing ofsingle-hole hollow microspheres with controllable structure, are the basis of their applications,but also challenges in the search of microsphere-materials.In this paper, we proposed two kinds of novel methods to fabricate single-hole hollowSiO2and Fe3O4@SiO2microspheres by using a precipitation-phase separation process and aPickering template process. The process of controlling the structure such as pore size, particlesize and shell thickness, and magnetic content of the microspheres were investigated; Theproducts were characterized using scanning electron microscopy (SEM), transmissionelectron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), Fourier Transforminfrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA)and vibrating sample magnetometry (VSM). The main contents and results are as follow:(1) The single-hole hollow SiO2microspheres with controllable hole size were preparedby a precipitation-phase separation method. The results showed that preparaed the single-holehollow microspheres by using a mixed polymer, the hole size of the microspheres increasedwith the content of PMMA in mixed polymer; when the mixed polymer was contain PMMAand PS, adjusting the content of PMMA in PS/PMMA form0%to60%, the single-hole sizecould be tuned from57to450nm; when the mixed polymer was contain PMMA andP(St-co-MMA), adjusting the content of PMMA in P(St-co-MMA)/PMMA form0%to80%,the single-hole size could be tuned from188to360nm.(2) The single-hole hollow Fe3O4@SiO2microspheres with controlled structure andmagnetic property were also prepared by a precipitation-phase separation method. Themodification of Fe3O4-NPs is essential for these microshperes. We considered that Fe3O4-NPsmodified with n-dodecyltrimethoxysilane (DTMS-Fe3O4-NPs) do not effected the phase separation of polymer and TEOS, besides, they could dispersed onto the TEOS phase, whichis the formation reason of single-hole hollow Fe3O4@SiO2microspheres. By adjusting themix polymer content, the the single-hole size could be tuned from0-166nm. The size of themicrospheres could be tailored from240to1270nm by modulating the process parameters,such as the amount of ammonia, the volume ratio of the aqueous solution and organic solution,et. al. The Fe3O4@SiO2microspheres exhibited superparamagnetic properties, and thecorresponding Ms values varied from9.5to44.6emu/g by adjusting the content ofDTMS-Fe3O4-NP in the microspheres.(3) The single-hole hollow SiO2microspheres were fabricated by a Pickering emulsionroute using partly embedded CaCO3as template.The results showed that, the arrangement ofthe CaCO3microspheres on the surface of the wax particles could be tuned by ajustingCaCO3-to-paraffin wax mass ratio. The penetrating depth of CaCO3microspheres on the waxparticles and the single-hole size could be adjusted by the kinds of and the concentration ofsufactant (CTAB or DDAB) and the concentration of the sufactan. By optimizing theexperimental conditions, the single-hole hollow microspheres with a hole size of221-584nmwere sythesised, and the particle size as well as the thickness of SiO2microspheres could betailored from890nm to1890nm, and221nm to399nm, respectively.