Hierarchical nanostructures of cupric oxide on a copper substrate: controllable morphology and wettability

We have demonstrated a facile fabrication of CuO hierarchical nanostructures on copper substrates by the oxidation of copper in alkaline conditions at 60 °C. CuO flowerlike structures composed of hierarchical two-dimensional (2D) nanosheets and spherical architectures constructed by ultrathin nanowalls of ∼10 nm in thickness could be selectively generated by simply immersing a copper substrate into different alkaline solutions (NaOH and NH3·H2O). The continuous supply of Cu2+ from the substrate, as well as the reaction temperature, has shown its importance for the self-assembled growth of tiny 2D nanosheets and nanowalls into intricate hierarchical nanostructures. Optical absorption was used to determine the band gap energies of the nanostructures. Stable superhydrophobicity was firstly observed for these nanostructured films after modification. When the concentration of solution was changed, well-defined 2D nanosheet and nanowall arrays can accordingly be fabricated on a large scale. Our method might provide a general route towards the preparation of novel hierarchical films on metal substrates (Cu, Al, Zn, etc.), for which a number of promising applications in various fields can be envisioned.