Polyol synthesis of Cu2O nanoparticles:: use of chloride to promote the formation of a cubic morphology

We have employed the polyol method to synthesize copper(I) oxide (Cu2O) nanostructures with well-defined shapes and in large quantities. Transmission electron microscopy and X-ray powder diffraction studies show that polycrystalline colloidal spheres could be prepared in high yields by simply reducing copper nitrate with ethylene glycol heated to 140 degrees C in the presence of poly(vinyl pyrrolidone). When a small amount of sodium chloride was introduced, single-crystal nanocubes were obtained. In this case, chloride seems to play a pivotal role in controlling the formation of seeds and the growth rates of various crystallographic planes to shape the Cu2O nanostructures into nanocubes. Based on the structural analysis of samples obtained at different growth times, we also proposed a plausible mechanism to account for the formation of these two distinctive morphologies under different conditions.