Preparation of γ-Fe2O3 nanopowders by direct thermal decomposition of Fe-urea complex: reaction mechanism and magnetic properties

In this work, a novel method of producing maghemite (γ-Fe2O3) nanopowders has been developed, which can be performed by the direct thermal decomposition of an Fe–urea complex ([Fe(CON2H4)6](NO3)3) in a single step. The reaction mechanism, particle morphology, and the magnetic properties of the γ-Fe2O3 nanopowders have been studied by using thermogravimetric (TG), differential scanning calorimetry (DSC), fourier transformed infrared (FTIR) spectroscopy, elemental analysis, X-ray powder diffraction (XRD), transmission electron micrograph (TEM) observations, and magnetic measurements. Thermal analyses together with the results of XRD show that the formation of γ-Fe2O3 occurs at ~200 °C through a two-stage thermal decomposition of the [Fe(CON2H4)6](NO3)3 complex. The resulting iron oxide phases (i.e., γ-Fe2O3 and α-Fe2O3) are strongly dependent on the synthesis conditions of the [Fe(CON2H4)6](NO3)3. When the molar ratio of Fe(NO3)3 · 9H2O to CON2H4 that is used for the synthesis of [Fe(CON2H4)6](NO3)3 is 1:6 (i.e., molar ratio in stoichiometry), a mixed phase of γ-Fe2O3 and α-Fe2O3 is formed. When the molar ratio is 1:6.2 (i.e., using an excess CON2H4), on the other hand, a pure γ-Fe2O3 is obtained. Magnetic measurements show that resulting nanopowders exhibit a ferromagnetic characteristic and their maximum saturation magnetization increases from 47.2 to 67.4 emu/g with an increase in the molar ratio of Fe(NO3)3 · 9H2O to CON2H4 from 1:6 to 1:6.2.