STRUCTURE AND MAGNETIC PROPERTIES OF SiO 2 COATED Fe 2 O 3 NANOPARTICLES SYNTHESIZED BY CHEMICAL VAPOR CONDENSATION PROCESS

Magnetic nanoparticles for applications in separation and purification processes must satisfy several basic requirements. They should be superparamagnetic, i.e. possess low coercivity (H c ) and low retentivity (M r ), to enable re-dispersion after magnetic capture. In this study, the synthesis of SiO 2 coated γ-Fe 2 O 3 nanocomposite particles has been attempted to achieve the above magnetic properties. The synthesis method is based on the decomposition and oxidation of two metalorganic precursor, iron (III) acetylacetonate and tetraethylorthosilicate (TEOS) by the chemical vapor condensation process. The synthesized SiO 2 coated γ-Fe 2 O 3 nanoparticles consisted of large amount of amorphous SiO 2 phase shell enclosing the crystalline 20~30 nm γ- Fe 2 O 3 nanoparticle core. The H c and M r values of SiO 2 coated γ-Fe 2 O 3 nanoparticles were 34.5 Oe and 0.118 emu/g, respectively. These low H c and M r values were the results of very fine and spherical γ-Fe 2 O 3 particles well dispersed in the SiO 2 matrix. Also, from FT-IR analysis it was shown that the surface properties of the coated nanoparticles were similar to those of conventional fumed silica. Finally, the feasibility of SiO 2 coated γ-Fe 2 O 3 nanoparticle for magnetic separation media in various bio processes was discussed.