Size-dependent thermal oxidation of copper: single-step synthesis of hierarchical nanostructures

Thermal oxidation of copper is a simple and scalable method to produce copper oxide nanowires. We report for the first time the formation of nanowires on copper powder during thermal oxidation and the resulting nanowire coverage that is dependent on the initial particle size. Systematic thermogravimetric analysis (TGA) and in situ X-ray diffraction (XRD) studies of thermal oxidation of particles of different sizes provide insights into the size-dependent process and evolution of the various phases of copper and copper oxide with time. Furthermore, we find that a large void is formed within these particles after oxidation and propose a mechanism based on the Kirkendall effect. The unique tunability of hierarchical features and hollow interior can be used to create new scalable structures for applications in a variety of areas including thermal management and catalysis.