Abstract

A unique oil-in-water emulsion route has been devised to synthesize nanosized magnetite (Fe₃O₄) particles using a small amount of cyclohexane as the oil phase, NP5 + NP9 as the surfactant phase, and a Fe(II)/Fe(III) salt solution as the aqueous phase. The Fe₃O₄ powder thus derived from the emulsion containing 88 wt% 0.3 M FeSO₄ + Fe(NO₃)₃ in the aqueous phase possesses an equiaxial morphology and an average particle size of <10 nm. Studies on the electrical conductivity of the emulsions as a function of Fe²⁺/Fe³⁺ concentration in the aqueous phase revealed the complexation effect of the NP5 + NP9 surfactant towards Fe²⁺/Fe³⁺ ions. The resulting particle size and morphology are therefore dependent on the amounts of surfactant and aqueous phase in the emulsion. A strongly alkaline aqueous phase favors the formation of Fe₃O₄, while a low alkalinity favors the formation of α-FeOOH. Magnetic property measurements and Mössbauer spectroscopic studies indicate that the emulsion-derived iron oxide powder is superparamagnetic, which becomes ferrimagnetic with decreasing measurement temperature.