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

Magnetic single-domain gamma-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 similar to 4 nm and lengths of 10-20 nm were found in the porous sulfonated gel matrix Magnetization and Mossbauer studies indicated that the gamma-Fe2O3/SiO2 nanocomposites are superparamagnetic. The magnetic properties can be manipulated via the matrix structure and synthesis conditions. (C) 1997 Acta Metallurgica Inc.