Shape Evolution and Tunable Properties of Monodisperse Magnetite Crystals Synthesized by a Facile Surfactant-Free Hydrothermal Method

Monodisperse Fe3O4 crystals have been synthesized by a simple hydrothermal method. Reaction conditions are performed in an ethylene glycol (EG)/NaOH system using FeCl3 as the iron source without adding any surfactants. By adjusting the initial molar ratio of NaOH to Fe3+, several morphologies including solid spheres, hollow spheres, spherical chains, tetrakaidecahedrons, octahedrons, and some flower-like structures can be obtained. Further investigation reveals that all of the spherical structures are formed by the highly oriented assembly of Fe3O4 nanoparticles. The evolution of the morphology from spheres to octahedrons can be attributed to the competition effect between ethylene glycol and NaOH under the reaction conditions. The saturation magnetization, coercivity, and remanent magnetization of the as-synthesized samples vary as the morphology and grain size changes.