engleski

Synthesis of nanocrystalline iron oxide particles in the iron(III)acetate/alcohol/acetic acid system

Nanosize iron oxide particles were synthesised without adding water by autoclaving iron(III) acetate/alcohol/ and iron(III) acetate/acetic acid/alcohol solutions at 180oC for different time periods. Magnetite was formed in iron(III) acetate/ethanol, while hematite was formed in the iron(III) acetate/acetic acid/ethanol system. The average crystallite size of 11.1 and 22.6 nm as determined by Rietveld analysis of XRD patterns and the stoichiometry of Fe2.89O4 (Mössbauer) were found for nanosize magnetite particles. FE-SEM showed that primary magnetite particles aggregated into regular spheres 5 to 10 mm in size, which can be explained by the specific character of the small, reactive and polar molecules of ethanol. In the system iron(III) acetate/octanol, a mixture of magnetite and hematite was obtained. The average crystallite size of magnetite was up to 22 nm and that of hematite up to 46.7 nm as determined by Rietveld analysis. In the iron(III) acetate/acetic acid/ethanol system nanosize hematite particles were exclusively formed. 13C NMR spectroscopy revealed the presence of ethyl acetate ester in 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 that was not bound to iron, directly participated in an esterification reaction with ethanol. Water molecules generated in situ in this esterification reaction hydrolysed iron(III) acetate, and hematite was formed.

acetate ; magnetite ; hematite ; esterification ; solvothermal

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