Crystal structure of iron-oxide nanoparticles synthesized from ferritin

We have investigated the crystal structure of nanosized iron-oxide by X-ray diffraction (XRD), extended X-ray absorption fine structure measurements at the iron K-edge as well as by transmission electron microscopy (TEM). Iron-oxide nanoparticles were produced by thermal treatment of horse spleen ferritin molecules. The structure of these particles was compared to alpha-Fe2O3 and gamma-Fe2O3 nanopowder references. The thermal treatment of a submonolayer film of ferritin molecules results in pure gamma-Fe2O3 nanoparticles, while for films above a certain thickness alpha-Fe2O3 and gamma-Fe2O3 coexist, exhibiting two different crystallite sizes. TEM shows a characteristic particle diameter of similar to 7 nm for gamma-Fe2O3 resulting from thermal treatment of monolayers, consistent with the crystallite size of the gamma-phase as obtained from XRD measurements on multi-layered samples. XRD shows the alpha-Fe2O3 phase to be characterized by a crystallite size of similar to 34 nm.