Effects of Process Variables on Properties of CoFe₂O₄ Nanoparticles Prepared by Solvothermal Process

Controlling the morphology and magnetic properties of CoFe₂O₄ nanoparticles is crucial for the synthesis of compatible materials for different applications. CoFe₂O₄ nanoparticles were synthesized by a solvothermal method using cobalt nitrate, iron nitrate as precursors, and oleic acid as a surfactant. The formation of CoFe₂O₄ nanoparticles was systematically observed by adjusting synthesis process conditions including reaction temperature, reaction time, and oleic acid concentration. Nearly spherical, monodispersed CoFe₂O₄ nanoparticles were formed by changing the reaction time and reaction temperature. The oleic acid-coated CoFe₂O₄ nanoparticles inhibited the growth of particle size after 1 h and, therefore, the particle size of CoFe₂O₄ nanoparticles did not change significantly as the reaction time increased. Both without and with low oleic acid concentration, the large-sized cubic CoFe₂O₄ nanoparticles showing ferromagnetic behavior were synthesized, while the small-sized CoFe₂O₄ nanoparticles with superparamagnetic properties were obtained for the oleic acid concentration higher than 0.1 M. This study will become a basis for further research in the future to prepare the high-functional CoFe₂O₄ magnetic nanoparticles by a solvothermal process, which can be applied to bio-separation, biosensors, drug delivery, magnetic hyperthermia, etc.