Monodisperse iron oxide nanoparticles were prepared by thermal decomposition of iron carbonyl in octyl ether in the presence of oleic acid. The particle size could be tuned from 7 nm to 25 nm. The dual role of oleic acid as a surfactant and a boiling-point elevating agent was discussed. The impacts of varied reflux conditions were investigated and a new monodisperse mechanism was given. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) were used to study the oxidation states of iron oxide nanoparticles. The evolution of d-spacing values in HRTEM images and SAED patterns demonstrated the transition from γ-Fe2O3 to Fe3O4 with the increasing particle size. Superconducting quantum interference device (SQUID) and vibrating sample magnetometer (VSM) were used to reveal the superparamagnetic behavior of as-synthesized nanoparticles.
Fig. 1. TEM images of monodisperse iron oxide nanocrystals: (a) 7 nm; (b) 10 nm; (c) 15 nm; (d) 22 nm.