Synthesis of Monodisperse Magnetic Iron Oxide Nanoparticles from Submicrometer Hematite Powders

Abstract

This study identifies submicrometer hematite (α-Fe2O3) powder as a cost-effective and efficient starting material for the synthesis of monodisperse magnetic iron oxide nanoparticles (MMIONPs). The feature of this process is the slow dissolution of hematite powder in a mixture of unsaturated fatty acids and organic solvents. The hematite particles are dissolved by the complexation of their iron with the unsaturated fatty acid ligands to give iron acid salt as a soluble compound. This method presents an interesting example for the production of monodisperse oxide NPs from bulk oxide powder with a moderate solubility in fatty acids. Conceptually, it can be simply viewed as a controlled dissolution−recrystallization process. The relatively low solubility of magnetic iron oxides (maghemite and magnetite) in the reaction condition determines their appearance in the recrystallization process. Moreover, the monodispersity of the formed NPs is sustained during the whole process, which results from the slow supply and the fast consumption of growing units by the slow dissolution of hematite and the fast enough growth rate of magnetic iron oxide NPs. The compositions of the MMIONPs were determined by Mössbauer spectroscopy. It appears that γ-Fe2O3 is preferentially precipitated out at lower ligand concentrations, while the Fe3O4 appears along with γ-Fe2O3 at higher ligand concentrations.