Nanostructured Pure ψ-Fe₂O₃ via Forced Precipitation in an Organic Solvent

Pure maghemite, γ-Fe₂O₃, was prepared as ultra fine particles in the nanometer-sized range via the forced precipitation method in an organic solvent. The precipitation of iron(III) ions, from iron(III) chloride in 2-propanol led selectively to highly dispersed particles of ferrihydrite, which upon treatment with temperatures higher than 200°C under dynamic vacuum resulted in high-surface-area particles of γ-Fe ₂O₃. Precipitation in water also led to ferrihydrite, but the final product, after heating at 300°C, contained a mixture of γ-Fe₂O₃ and α-Fe₂O₃ (hematite). The precipitation from iron(III) nitrate in water resulted in goethite which was converted to hematite upon heating. On the other hand, the final product in 2-propanol was a mixture of maghemite and hematite. The products were characterized by FTIR, TGA, XRD, and gas sorption analysis. Nitrogen gas adsorption studies for the pure γ-Fe₂O ₃ samples revealed mesoporous particles with high surface areas in the range of 70-120 m²g^-1 after heat treatment at 300°C. The γ-Fe₂O₃ particles retained their y-phase as well as their mesoporous structure at relatively high temperatures, as high as 400°C.