Silicon oxide in an iron(III) oxide matrix: the sol–gel synthesis and characterization of Fe–Si mixed oxide nanocomposites that contain iron oxide as the major phase

The synthesis of Fe–Si mixed oxide nanocomposite materials in which the iron(III) oxide is the major component is described. In a typical synthesis, the iron oxide precursor, FeCl3 · 6H2O, was mixed with a silica precursor, tetramethyl- or tetraethylorthosilicate, in ethanol and gelled using an organic epoxide. The composition of the resulting materials was varied from Fe/Si (mol/mol)=1–5 by adjusting the amount of silica precursor added to the FeCl3 · 6H2O solution. Further processing of the gels in supercritical CO2 resulted in monolithic, porous aerogel nanocomposite materials with surface areas ranging from 350–450 m2/g. The bulk materials are composed of iron(III) oxide/silica particles that vary in size from 5–20 nm depending on the epoxide used for gelation. Iron(III) oxide and silica dispersion throughout the bulk material is extremely uniform on the nanoscale. The synthesis method presented is general for the synthesis of several other metal oxide/silicon oxide nanocomposite materials.