In situ XANES Study of Co2+ Ion Adsorption on Fe3O4 Nanoparticles in Supercritical Aqueous Fluids

In situ x-ray absorption spectroscopy (XAS) measurements were made on Fe 3 O 4 nanoparticles in supercritical aqueous fluids to 500 °C in order to study their reactivity with Co 2+ aqua ions and to investigate the structural properties of the reacted nanoparticles. The analyses of the x-ray absorption near edge structure (XANES) of XAS indicate that reactivity of Fe 3 O 4 nanoparticles with Co 2+ ions is minimal to 200 °C but becomes significant in the 250–500 °C temperature range. XANES and angular momentum projected density of states ( l -DOS) calculations were carried out using the FEFF8.2 code and analyses were made using multi-peak fitting to determine the origin of the features exhibited in the spectra.