Effect of the Silica Cover on the Properties of Co3O4 Nanoparticles

Cobalt oxide nanoparticles were functionalized with sodium citrate and coated with a silica shell (Co3O4@Q@SiO2). Different experimental configurations were tested in order to obtain low-sized cobalt oxide nanoparticles with high crystallinity, using the chemical reduction-oxidation method. Then, the nanoparticles were coated with silica using the Stober method, obtaining a silica cover on top of the cobalt oxide nanoparticle surface with a few nanometers thickness. This method permits the functionalization of the nanoparticles at the time of coating. Results show that with a heat treatment of 500 degrees C, high-crystallinity cobalt oxide nanoparticles are obtained with a spherical shape and an average diameter of 30 nm, whereas the silica cover has 5 nm thickness. Evidence of nanoparticle functionalization was obtained through the measurement of the absorption bands of the functional groups of the sodium citrate with a silica cover. In addition, coated nanoparticles show a reduction of their magnetic remanence as well as their coercivity with respect to the uncoated nanoparticles since silica acts as barrier avoiding superficial contact between magnetic nanoparticles.