Microemulsion Synthesis of Iron Core/Iron Oxide Shell Magnetic Nanoparticles and Their Physicochemical Properties

Iron magnetic nanoparticles were synthesized under an inert atmosphere via the reaction between FeCl₃ and NaBH₄ in droplets of water in a microemulsion consisting of octane with cetyl trimethylammonium bromide and butanol as surfactants. A thin Fe₃O₄ layer was produced on the iron nanoparticles using slow, controlled oxidation at room temperature. A silica shell was deposited on the Fe₃O₄ using 3-aminopropyltrimethoxysilane following the method of Zhang et al. [Mater. Sci. Eng. C 30 (2010) 92-97]. The structure and chemistry of the resulting nanoparticles were studied using variety of methods and their magnetic properties were determined. The diameter of the iron core was typically 8-16 nm, while the thickness of the Fe₃O₄ shell was 2-3 nm. The presence of the silica layer was confirmed using Fourier transform infra-red spectroscopy and the number of NH₂-groups on each nanoparticle was determined based on colorimetric tests using ortho-phthalaldehyde.