Low Temperature Synthesis of Magnetite and Maghemite Nanoparticles

We report on the synthesis of iron oxide nanoparticles below 100 °C by a simple chemical protocol. The uniqueness of the method lies in the use of Ferrous ammonium sulphate (in conjugation with FeCl₃) which helps maintain the stability of Fe²⁺ state in the reaction sequence thereby controlling the phase formation. Hexamine was added as the stabilizer. The nanoparticles synthesized at three different temperatures viz, 5°, 27°, and 95 °C are characterized by several techniques. Generally, when a mixture of Fe³⁺ and Fe²⁺ is added to sodium hydroxide, α-Fe₂O₃ (the anti-ferromagnetic phase) is formed after the dehydration process of the hydroxide. In our case however, the phases formed at all the three temperatures were found to be ferro (ferri) magnetic, implying modification of the formation chemistry due to the specifics of our method. The nanoparticles synthesized at the lowest temperature exhibit magnetite phase, while increase in growth temperature to 95 °C leads to the maghemite phase.