Crystal-Phase- and Morphology-Controlled Synthesis of Fe₂O₃ Nanomaterials

α- and γ-Fe2O3 nanorods have been prepared from a β-FeOOH precursor that was obtained by aqueous-phase precipitation of ferric chloride. The oxyhydroxide precursor had a rodlike shape with a diameter of 30–40 nm and a length of 400–500 nm. Calcination at 500 °C of the rod-shaped oxyhydroxide in air yielded α-Fe2O3 nanorods, whereas heating to reflux in polyethylene glycol (PEG) at 200 °C resulted in the formation of γ-Fe2O3 nanorods. Both oxides inherited the rodlike morphology of the precursor but exposed different crystalline facets. When being used to catalyze NO reduction by CO, an environmentally important reaction in NO abatement, the γ-Fe2O3 nanorods were much more active than the α-Fe2O3 nanorods and showed an apparent crystal-phase effect. This was because the γ-Fe2O3 nanorods simultaneously exposed iron and oxygen ions on their surfaces, which facilitated the adsorption and activation of NO and CO molecules