Hydrothermal Growth of Fatty Acid Stabilized Iron Oxide Nanocrystals

Seed nanocrystals formed by the coprecipitation of ferric and ferrous ions with oleate modification, at the molar ratios of sodium oleate and Fe ion [SO]/[Fe] from 0.05 to 0.5, were subjected to a hydrothermal treatment at 100−230 °C to initiate the crystal growth. Fourier transform infrared spectroscopy revealed that these nanocrystals were stabilized by a surface oleate that formed a stable colloidal solution in various nonpolar solvents such as cyclohexane and benzene. An X-ray diffraction analysis showed that the higher hydrothermal temperatures and lower oleate concentration promoted the Ostwald ripening process to produce highly crystallized iron oxide nanocrystals based on a cation deficient magnetite polymorph. Transmission electron microscopy revealed that the oleate concentrations played an important role in controlling the nucleation and growth process; it was found that the lower oleate concentration was the preferable growth condition to produce uniformly sized and shaped nanoparticles with high saturation magnetization.