In the article we present our results regarding the obtaining and characterization of 20% Fe2O3 (target composition) iron oxide-silica nanocomposites, by using the differential thermal treatment of inorganic-organic hybrid xerogel based on Fe(acac)3-PVA-SiO2 . The hybrid xerogel was synthesized via sol-gel method at room temperature, using tetraethilortosilicate, TEOS, and iron (III) acetylacetonate as precursors, and polyvinyl alcohol as additive, where PVA molecular weight was 145000.
The thermal treatment at 180 ºC, 220 ºC, 260 ºC, 300 ºC, 400 ºC and 500 ºC of obtained hybrid xerogel resulted in six Fe2O3-SiO2 nanocomposite samples. All the samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Moessbauer spectroscopy, and magnetic measurements. The maghemite unique crystalline phase was obtained at 300 ºC along with a certain amount of amorphous iron oxide. Further rising the calcination temperature, it was observed that the transition process γ-Fe2O3 to α-Fe2O3 occurred and at 400 ºC and the maghemite and hematite are coexisting. At 500 ºC the only hematite crystalline phase was found. The structural and magnetic properties of the nanocomposite sample annealed at 260 ºC, namely, pure maghemite crystalline phase with superparamagnetic behaviour and ~10 nm average particle diameter, recommended it to be chosen in order to be tested as contrast agent in medical imaging (MRI) application.