Synthesis of Nanocrystalline Iron Oxide Particles in the Iron(III) Acetate/Alcohol/Acetic Acid System

Abstract

AbstractNanosized iron oxide particles were synthesised without the addition of water by autoclaving iron(III) acetate/alcohol and iron(III) acetate/acetic acid/alcohol solutions at 180 °C for different time periods. Magnetite was formed in iron(III) acetate/ethanol, whereas hematite was formed in the iron(III) acetate/acetic acid/ethanol system. The average crystallite sizes of 11.1 and 22.6 nm and the stoichiometry of Fe2.89O4 were found for the nanosized magnetite particles. The primary magnetite particles aggregated into regular spheres 5 to 10 μm in size, which can be explained by the specific character of the small, reactive and polar molecules of ethanol. In the iron(III) acetate/octanol system, a mixture of magnetite and hematite was obtained. The average crystallite size of magnetite was up to 22 nm and that of hematite was up to 46.7 nm. In the iron(III) acetate/acetic acid/ethanol system, nanosized hematite particles were exclusively formed. 13C NMR spectroscopy revealed the presence of ethyl acetate ester in the supernatants. The formation of ester in the iron(III) acetate/ethanol system was explained by the catalytic oxidation of ethanol in the presence of acetate groups bonded to iron. Thus, in the oxidative dehydrogenation of ethanol into ethyl acetate, coordinated Fe3+ served as an electron acceptor that was reduced to Fe2+, and exclusively magnetite was formed. With the addition of acetic acid to the iron(III) acetate/ethanol system, the free acetic acid directly participated in an esterification reaction with ethanol. Water molecules generated in situ in this esterification reaction hydrolysed iron(III) acetate, and thus hematite was formed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)