Synthesis of Fe₃O₄ nanoparticles with various sizes and magnetic properties by controlled hydrolysis

Nanoparticles of Fe₃O₄ were synthesized by hydrolysis in an aqueous solution containing ferrous and ferric salts at various ratios with 1,6-hexanediamine as a base. It was found that the ferrous to ferric ratio influences the reaction mechanism for the formation of Fe₃O₄. When the ratio of ferrous to ferric ions was increased, the formation of large hydroxide particles as a precursor of Fe₃O₄ was promoted, which resulted in an increase in the size of Fe₃O₄ nanoparticles. As a result, the mean diameter of Fe₃O₄ nanoparticles increased from ∼9 to ∼37 nm as the molar percentage of ferrous ions with respect to the total iron ions was increased from 33 to 100%. Furthermore, it was demonstrated that magnetic properties of Fe₃O₄ nanoparticles can be controlled by adjusting the molar ratio of ferrous to ferric ions as well as the particle diameter.