Influence of stirring velocity on the synthesis of magnetite nanoparticles (Fe3O4) by the co-precipitation method

Superparamagnetic magnetite nanoparticles (mean diameter ∼10 nm) were synthesized using the co-precipitation route from Fe2+/Fe3+ in aqueous solutions (molar ratio 1:2) by adding a base under mechanical stirring at 10,000 rpm. This stirring velocity was found to be suitable for obtaining nanoparticles of this mean size, and a decrease in stirring velocity resulted in a larger size (∼19 nm) and a wider size distribution. At 18,000 rpm, in addition to magnetite, goethite is also synthesized in the form of nanoparticles and nanorods are found. At higher stirring velocities (25,000 rpm), the solution's core temperature increased from 20° to 37 °C, generating a mixture of non-magnetic iron compounds.