Phase transformation and shape evolution of iron oxide nanocrystals synthesized in the ethylene glycol-water system

Iron oxide particles with various shapes, sizes and phase concentrations (including α-Fe₂O₃ and Fe₃O₄) have been synthesized through a simple hydrothermal method in the ethylene glycol (EG)-water system. In the preparation conditions, ferric chloride (FeCl₃•6H₂O) was used as the iron source in the presence of sodium hydroxide (NaOH) without any surfactants. By adjusting the experimental parameters (EG/H₂O ratio, base content, iron ions concentration, etc.), the shape, the size, the phase and the magnetic property of the products could be easily controlled. The products were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and a vibrating sample magnetometer (VSM). A further investigation revealed that high EG content and high alkaline condition favored the formation of Fe ₃O₄ phase. A possible growth mechanism was proposed based on the experimental results. The magnetic properties were deeply affected by the morphology and phase of the as-synthesized products. The controlled shape, size and phase structure of the iron oxides through simple synthetic procedures provides potential opportunities to realize the promising size and shape-dependent applications.