Novel γ-Fe₂O₃/SiO₂ magnetic nanocomposites via sol-gel matrix-mediated synthesis

Magnetic single-domain γ-Fe₂O₃ nanoclusters have been prepared by (i) coprecipitation of ferrous and ferric salts encapsulated within sol-gel derived silica (SiO₂), and (ii) oxidation of ferrous cations incorporated in a sulfonated, ion-exchange porous silica matrix. In the first method, a SiO₂ coating was formed on the Fe₂O₃ nanoclusters by hydrolysis and condensation of tetraethoxysilane. In the second route, sulfite (SO₃^-) functionalized silica was synthesized from a modified sol-gel precursor resulting in a porous gel with a narrow pore size distribution. The SiO₂ coating and sulfonated SiO₂ matrix provide the means for homogeneous dispersion of Fe₂O₃ clusters. The SiO₂-coated Fe₂O₃ nanoclusters are spherical with 4-5 nm diameters. Acicular crystalline Fe₂O₃ nanoclusters with diameters of ∼4 nm and lengths of 10-20 nm were found in the porous sulfonated gel matrix. Magnetization and Mössbauer studies indicated that the γ-,Fe₂O₃/SiO₃ nanocomposites are superparamagnetic. The magnetic properties can be manipulated via the matrix structure and synthesis conditions.