An X-ray absorption spectroscopy study of the FeK edge in nanosized maghemite and in Fe2O3-SiO2 nanocomposites

The structural evolution of Fe2O3-SiO2 nanocomposite samples prepared using the sol-gel method have been studied by EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) techniques in comparison with pure nanosized and microcrystalline maghemite samples. EXAFS data show that the difference between nanosized and microcrystalline maghemite is due to an increase of disorder of the superficial sites while no decrease of coordination numbers was detected. EXAFS and XANES data of the nanocomposite thermally treated at 900 degrees C indicate that the sample is constituted by maghemite nanoparticles embedded into amorphous silica while the sample thermally treated at 300 degrees C contains an amorphous precursor which is very likely to be ferrihydrite. No interactions between the metal oxide nanoparticles and the silica network are present since the EXAFS spectra of the nanocomposite samples can be interpreted as only having Fe-O and Fe-Fe interactions.