In situ investigation of morphological and phase changes during thermal annealing and oxidation of carbon-encapsulated copper nanoparticles

In situ electron microscope and X-ray investigations of the morphological and phase characteristics of copper nanoparticles encapsulated in a carbon shell were carried out. It was found that oxidation of the copper nanoparticles starts at a temperature of 200 oC. The formation of oxide phases occurs on the surface of the carbon shells, with the Cu2O phase appearing first followed by the formation of the CuO phase. Upon heating to just below its melting point, the copper sublimes resulting in the formation of hollow carbon nanocapsules. Treatment of the initial or oxidized encapsulated copper nanoparticles with nitric acid and annealing can be used to obtain hollow carbon nanocapsules.