Synthesis of Highly Crystalline and Monodisperse Maghemite Nanocrystallites without a Size-Selection Process

Abstract

The synthesis of highly crystalline and monodisperse γ-Fe₂O₃ nanocrystallites is reported. High-temperature (300 °C) aging of iron−oleic acid metal complex, which was prepared by the thermal decomposition of iron pentacarbonyl in the presence of oleic acid at 100 °C, was found to generate monodisperse iron nanoparticles. The resulting iron nanoparticles were transformed to monodisperse γ-Fe₂O₃ nanocrystallites by controlled oxidation by using trimethylamine oxide as a mild oxidant. Particle size can be varied from 4 to 16 nm by controlling the experimental parameters. Transmission electron microscopic images of the particles showed 2-dimensional and 3-dimensional assembly of particles, demonstrating the uniformity of these nanoparticles. Electron diffraction, X-ray diffraction, and high-resolution transmission electron microscopic (TEM) images of the nanoparticles showed the highly crystalline nature of the γ-Fe₂O₃ structures. Monodisperse γ-Fe₂O₃ nanocrystallites with a particle size of 13 nm also can be generated from the direct oxidation of iron pentacarbonyl in the presence of oleic acid with trimethylamine oxide as an oxidant.