Low temperature hydrothermal synthesis of octahedral Fe3O4 microcrystals

Octahedral Fe3O4 crystals in the size range of 200-300 nm have been prepared with a high yield at a low temperature of 90 degrees C using a simple polyethylene glycol (PEG)-mediated hydrothermal approach. It is found that both PEG molecules and NaOH content are crucial for the formation of Fe3O4 octahedrons because of the selective adsorption of PEG molecules on the ( 1 1 1) planes of Fe3O4 at higher NaOH concentrations, delaying the crystal growth along the [ 1 1 1] axis. The formation mechanisms related to Fe3O4 nuclei, octahedral crystals, and their linear self-assembly structures are discussed. Magnetization measurements show that the Fe3O4 octahedrons have a relatively high magnetic saturation value of 85.5 emu g(-1) and a coercive field of 118 Oe, which is ascribed to the high crystalline perfection and chain-like structures of the sample.