Abstract
Ferrihydrite (Fe5O7(OH)·4H2O) is poorly crystalline hydrated ferric oxyhydroxide. Using a treatment in a mixed FeCl2/NaOH solution, we attempted to prepare magnetic nanoscale particles from ferrihydrite. During the treatment, the concentration of FeCl2 was fixed at 0.1 M, and the concentration of NaOH was varied from 0.09 to 0.26 M. The as-prepared products were characterized using X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. The experimental results showed that under the FeCl2/NaOH solution treatment, the ferrihydrite transformed into nanoscale γ-Fe2O3 via an α-FeO(OH) intermediate phase. The as-prepared products contained rod-type α-FeO(OH), sphere-type γ-Fe2O3, and flake-type γ-Fe2O3 particles. A mechanism for a coupling of the aggregation and the transition was proposed to interpret the formation of highly crystalline nanoscale particles from the poorly crystalline smaller particles.
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