In situ monitoring of the adsorption of Co2+ on the surface of Fe3O4 nanoparticles in high-temperature aqueous fluids
Abstract
Developing an understanding of the reaction processes occurring at the surface-fluid interface at the atomic level of nanostructured materials in high-temperature aqueous environments is necessary for establishing general principles of behavior of nanomaterials operating in such extremes. In situ Co K-edge X-ray absorption spectroscopy (XAS) measurements were made on Fe 3O4 nanoparticles in the presence of Co2+ ions in aqueous fluids to 500 °C and approximately 220 MPa. The results from analysis of the in situ EXAFS data, along with SEM-EDX spectra measured from reacted nanoparticles, indicate that adsorption of Co2+ ions on the surface of Fe3O4 nanoparticles is negligible at temperatures below 200 °C but becomes significant in the 250-500 °C temperature range. The low reaction temperature threshold of the Co2+ aqua ion with Fe3O4 nanoparticles is consistent with a relatively low value of the crystal field stabilization energy (CFSE) of Co 2+ in octahedral site symmetry in spinels. Modeling of the pre-edge feature of the XANES and analysis of the extended X-ray absorption fine structure (EXAFS) shows that Co2+ adsorbs predominantly on octahedral sites of the surface of nanoparticles in aqueous fluids. Structural analyses using EXAFS and high resolution TEM show that the inverse spinel structure is preserved in the Co-incorporated surface atomic layers of the Fe 3O4 nanoparticles. Our results suggest that the dissolved radioactive isotope 60Co in the primary cooling loop of supercritical water-cooled nuclear reactors have a high likelihood of precipitating on the surfaces of spalled ferrite nanomaterial.
Department(s)
Physics, Astronomy, and Materials Science
Document Type
Article
DOI
https://doi.org/10.1016/j.supflu.2013.05.017
Keywords
Adsorption, Electron microscopy, Nanostructures, Oxides, Surfaces, XAFS
Publication Date
7-8-2013
Recommended Citation
Yan, Hao, Robert A. Mayanovic, Joseph W. Demster, and Alan J. Anderson. "In situ monitoring of the adsorption of Co2+ on the surface of Fe3O4 nanoparticles in high-temperature aqueous fluids." The Journal of Supercritical Fluids 81 (2013): 175-182.
Journal Title
Journal of Supercritical Fluids
