Controllable synthesis of monodispersed iron oxide nanoparticles by an oxidation-precipitation combined with solvothermal process

As an important magnetic inorganic nanomaterial, iron oxide nanoparticles have exceptionally outstanding physical and chemical properties for bio-medicine and chemistry applications. Traditional Fe3O4 nanopowders normally have heavy aggregation problems, which may limit their applications. In this study, we made monodispersed Fe3O4 nanoparticles with an average size of 5-12 nm using a combination of oxidation-precipitation with solvothermal method. The Fe2+ in the reaction system can be partially oxidized to Fe3+ by the ambient air as an oxidizing agent, therefore, the precipitation process does not require nitrogen and other oxidants or reductants. The monodispersed Fe3O4 nanoparticles can be successfully modified and steadily dispersed in cyclohexane or n-hexane. The effects of different types of surfactants and alcohols, addition amount of surfactants and alkali, and ratio of ethanol-water solution were explored to obtain the optimum synthesis conditions. In addition, the different phase composition and morphology of final product can be simply adjusted using different addition amount of alkali to get Fe3O4, alpha-Fe3O4, gamma-Fe3O4 and alpha-FeOOH nanoparticles. We believe that the monodispersed Fe3O4 nanoparticles with a good dispersibility and magnetic response may have great application prospects in biological medicine, chemocatalysis and magnetic recording for future research.