Cobalt oxide (Co 3 O 4) nanoparticles were prepared by reducing cobalt sulfate heptahydrate with sodium borohydride using functionalized S BA-15 mesoporous silica as a hard template. Functionalization of both external and internal silica walls leads to the infiltration and reaction of the reagents inside the silica framework. Heat treatment of the impregnated silica at 500 °C in air resulted in formation of cobalt oxide nanoparticles inside silica pores. Cobalt oxide nanoparticles with an

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... e diameter of 2.9 ±0.5 nm were obtained by dissolution of the silica template using a solution of NaOH. The Co 3 O 4 nanoparticles were characterized by X-ray diffraction, and transmission electron microscopy. Magnetic properties of Co 3 O 4 nanoparticles were determined with a Quantum Design MPMS SQUID magnetometer. The blocking temperature (T B) observed at 6 K indicates a superparamagnetic behavior.