Nanostructured Pure γ-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‐Fe2O3. 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‐Fe2O3 samples revealed mesoporous particles with high surface areas in the range of 70–120 m2 g−1 after heat treatment at 300 °C. The γ‐Fe2O3 particles retained their γ‐phase as well as their mesoporous structure at relatively high temperatures, as high as 400 °C. Mesoporous materials were obtained with a significantly high surface area, specifically, nanometer‐sized particles of pure maghemite, γ‐Fe2O3, via forced precipitation in a solution of FeCl3 in 2‐propanol. The mesoporous microstructures as well as the γ‐phase (see figure) were retained at high temperatures. FeCl3 + NaOC(CH3)3${{{\longrightarrow{{\rm {\rm propanol}}}{}}}$ Fe5O7OH⋅4 H2O${{{\longrightarrow{\Delta ,\ 200-400\,^{{\rm o}}{\rm {\rm C}}}{}}}$γ‐Fe2O3