Phase Evolution and Growth of Iron Oxide Nanoparticles: Effect of Hydrazine Addition During Sonication

The phase evolution of iron oxide was monitored by carefully controlling the addition of hydrazine monohydrate (N₂H₄·H₂O) during ultrasonication. The manner in which hydrazine was added affected the hydrolysis of iron­(III) nitrate resulting in two different phases of iron oxides such as maghemite (γ-Fe₂O₃) or goethite (α-FeOOH) as the major products. The formation of ferric hydroxide and Fe²⁺ during the addition of hydrazine monohydrate to iron salt solution at low pH was confirmed by structure analysis and 1,10-phenanthroline tests, respectively. Synchrotron X-ray diffraction analysis confirmed the formation of spherical maghemite (γ-Fe₂O₃) during the dropwise addition of hydrazine, whereas the formation of rod-shaped goethite (α-FeOOH) was confirmed by the instantaneous addition of hydrazine. Through these experiments, we were able to unequivocally establish the importance of hydrazine addition in controlling the phase formation and growth of iron oxide nanoparticles during sonication