Syntheses of hematite and maghemite nanocrystals from a single metal-organic precursor for catalytic use

Iron(II) isonicotinate tetrahydrate has been used as the metal-organic precursor for the synthesis of the alpha and gamma phases of nanocrystalline Fe2O3. Solvothermal aging of an alkaline ethanolic solution of the precursor at 120 degrees C gives alpha-Fe2O3 (hematite) nanorods, while spherical gamma-Fe2O3 (maghemite) nanoparticles are obtained from its alkaline ethylene glycolic solution at 180 degrees C. Smaller maghemite nanoparticles have been prepared via poly(vinylpyrrolidone) (PVP) coating. Both forms of iron oxide materials have been characterized by XRD, TEM, and Raman, IR and UV-Vis spectroscopy. Single crystalline alpha-Fe2O3 nanorods of similar to 12 nm diameter are obtained at low precursor concentrations. The alpha-Fe2O3 materials are superparamagnetic while uncoated gamma-Fe2O3 and PVP-coated gamma-Fe2O3 samples are ferromagnetic and superparamagnetic respectively. Preliminary studies show that these iron oxides are active as magnetic nanocatalysts in the selective epoxidation of styrene with aqueous tert-butylhydroperoxide as the oxidant.