Fabrication of truncated rhombic dodecahedral Cu₂O nanocages and nanoframes by particle aggregation and acidic etching

We report a simple approach for the fabrication of cuprous oxide (Cu ₂O) nanocages and nanoframes possessing an unusual truncated rhombic dodecahedral structure. An aqueous solution containing CuCl₂, sodium dodecyl sulfate (SDS) surfactant, NH₂OH·HCl reductant, HCl, and NaOH was prepared, with the reagents introduced in the order listed. Rapid seed-particle aggregation and surface reconstruction of the intermediate structure resulted in the growth of type-I nanoframes, which have only {110} skeleton faces and empty {100} faces, 45 min after mixing the reagents. Continued crystal growth for additional 75 min produced nanocages with filled {100} faces. The nanocages have diameters of 350-400 nm, and their walls are thicker than those of the nanoframes. Selective acidic etching over the {110} faces of the nanocages by HCl via the addition of ethanol followed by sonication of the solution led to the formation of type-II nanoframes, which have elliptical pores on the {110} faces. The morphologies of these nanoframes were carefully examined by electron microscopy. Without addition of ethanol, random etching of the nanocages can occur at a slow rate. Octahedral gold nanocrystals and high-aspect-ratio gold nanorods were successfully encapsulated in the interiors of these Cu₂O nanocages by adding the gold nanostructures into the reaction solution. The formation process for such core-cage composite structures was studied. These composite materials should display interesting properties and functions.