Synthesis and Magnetic Properties of Ferroferric Oxide in Supercritical Methanol.

Ferroferric oxide was prepared using Fe(NO₃)₃ · 9H₂O as the iron source under supercritical methanol conditions. Methanol was not only a solvent but also a reducing agent in the supercritical state. The effects of reaction temperature and time, and precursor concentration on product composition were investigated. In addition, ferromagnetic ferroferric oxide was synthesized in supercritical methanol with polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG) as surfactants. The as-synthesized products were characterized by XRD, SEM, FTIR techniques. Results showed that the addition of PVP and PEG had notable influences on the products. The findings also showed that ferroferric oxide of a loose flocculent structure and with a variable size (from several tens to a few hundred nanometers) had been prepared in supercritical methanol at 300 °C and 17.8 MPa for 15 min. Magnetic properties of the ferroferric oxide were detected by vibrating sample magnetometer. Its saturation magnetization was 50 emu/g, which was lower than the bulk value of 92 emu/g and showed that it had ferromagnetism.