Structural and magnetic properties of ferrihydrite nanoparticles

Ferrihydrite is a short range ordered iron(III) oxyhydroxide that has been recently recognized as a good catalyst for Fischer-Tropsch synthesis of liquid hydrocarbons. Despite the critical role of ferrihydrite in many disciplines, its mineral structure remains a topic of debate. The main aspect of its structure which has been debated is the presence or absence of tetrahedrally coordinated Fe3+ in its mineral structure. In this work, electron energy-loss spectroscopy (EELS) was used to probe the Fe L-2,L-3 edges of ferrihydrite and reference spectra of different iron oxide compounds and the percentage of Fe3+ in T-d symmetry was estimated from non-linear least squares (NLLS) fitting coefficients. EELS results demonstrate that Fe3+ in T-d coordination is present in substantial amounts in the structure of ferrihydrite. These findings were supported by Mossbauer spectroscopy results performed on the same ferrihydrite samples.