Synthesis of homogeneous NiO@SiO ₂ core-shell nanostructures and the effect of shell thickness on the magnetic Properties

We have developed a methodology to obtain NiO@SiO ₂ core-shell nanostructures for the first time. These nanostractures have a NiO core of 25-20 nm diameter and silica shell of 5-10 nm. The shell thickness could be increased to 25 nm with appropriate loading of tetraethylorthosilicate. The shell structure was confirmed by transmission electron microscopy, energy- dispersive X-ray analysis and zeta potential studies. Electron paramagnetic resonance studies indicate the presence of free radicals on the surface of the SiO ₂ shell. The increase in the magnetic susceptibility with shell thickness is explained by the enhancement of the free radicals associated with the silica shell. These magnetic core-shell nanostractures have potential as catalysts and in magnetic devices.