Surface Oxidation of Cu₂O Nanoparticles by Adsorbed Ammonia

Copper-based nanoparticles have been intensively studied owing to their superior antibacterial activity. In this study, cuprous oxide (Cu₂O) nanoparticles were synthesized using two different methods. In particular, two methods for synthesizing copper oxide from NaOH, namely, with and without the addition of NH₃, were used to adjust the morphology of the nanoparticles. The nanoparticles from the NH₃ and NaOH samples possessed an octahedral morphology. The crystal structure of the samples was confirmed by X-ray diffraction. The size distribution of the NH₃ sample was narrower than that of the NaOH sample. Furthermore, the average size of the NH₃ sample was smaller than that of the NaOH sample. Unexpectedly, the antibacterial activity of the NH₃ sample was found to be lower than that of the NaOH sample. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy revealed that the adsorbed NH₃ caused the surface oxidation of Cu₂O nanoparticles with azide (N₃) formation on surface.