Synthesis of Homogeneous NiO@SiO2 Core-shell Nanostructures and the Effect of Shell Thickness on the Magnetic Properties

We have developed a methodology to obtain NiO@SiO2 core-shell nanostructures for the first time. These nanostructures 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 SiO2 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 nanostructures have potential as catalysts and in magnetic devices.