Size-controlled synthesis of monodisperse superparamagnetic iron oxide nanoparticles

dMonodisperse 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.

► The dual role of oleic acid in capping the nanoparticle and elevating the boiling point was discovered.
► γ-Fe2O3 is the dominant phase of small-sized iron oxide nanoparticles and the proportion of the Fe3O4 component gradually increases with the particle size.
► Using aeration or (CH)3NO made little difference in oxidation state.
► The regulation of the reflux states was found crucial in monodisperse mechanisms.