Structural and magnetic properties of ferrihydrite nanoparticles

Abstract

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_2,3 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 Mössbauer spectroscopy results performed on the same ferrihydrite samples.