Hermetically-Coated Superparamagnetic Fe2O3 Particles with SiO2 Nanofilms

Magnetic nanoparticles are frequently coated with SiO2 to improve their functionality and bio-compatibility in a range of biomedical and polymer nanocomposite applications. In this paper, a scalable flame aerosol technology is used to produce highly dispersible, superparamagnetic iron oxide nanoparticles hermetically coated with silica to retain full magnetization performance. Iron oxide particles were produced by flame spray pyrolysis (FSP) of iron acetylacetonate in xylene/acetonitrile solutions, and the resulting aerosol was in situ coated with SiO2 by oxidation of swirling hexamethlydisiloxane vapor. The process allows independent control of the core Fe2O3 particle properties and the thickness of their silica coating film. This ensures that the non-magnetic SiO2 layer can be closely controlled and minimized. The optimal SiO2 content for complete (hermetic) encapsulation of the magnetic core particles was determined by isopropanol chemisorption. The magnetization of Fe2O3 coated with about 2 nm thin SiO2 layers was nearly identical to that of uncoated, pure Fe2O3 nanoparticles.