The Oriented Self‐Assembly of Magnetic Fe3O4 Nanoparticles into Monodisperse Microspheres and Their Use as Substrates in the Formation of Fe3O4 Nanorods

We describe a facile solvothermal route for the large‐scale preparation of ferromagnetic Fe3O4 sub‐micrometer spheres and nanorods by using FeCl3 as the iron source, oleic acid as the surfactant, and ethylene glycol as the reducing agent and solvent. The as‐synthesized Fe3O4 microspheres are composed of a mess of Fe3O4 nanoparticles with a size of 10 nm and have nearly monodisperse diameters that can be controlled in the range 100–410 nm. HRTEM images and SAED patterns show that these microspheres present a “single‐crystalline” nature, which can be attributed to the highly oriented assembly of the small Fe3O4 nanoparticles. Interestingly, by using the pre‐synthesized Fe3O4 microspheres as the growth substrate, single‐crystalline Fe3O4 nanorods can be formed on the surfaces of the microspheres. These nanorods are about 7–20 nm in diameter and 120–400 nm in length, and have smooth surfaces. The formation mechanisms of the Fe3O4 microspheres and nanorods have been investigated and discussed. Furthermore, the magnetic properties of the as‐synthesized microspheres and nanorods have also been investigated and the magnetization saturation values are 74.6 and 92.3 emu/g, respectively.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)