Galvanic replacement-mediated synthesis of hollow Cu₂O-Au nanocomposites and Au nanocages for catalytic and SERS applications

The galvanic replacement reaction (GRR) involves a corrosion process that is driven by the difference in the electrochemical potentials of two species. Here we demonstrate the synthesis of hollow Cu₂O-Au nanocomposites via a GRR process between Cu₂O and HAuCl₄, and subsequent conversion of the hollow Cu₂O-Au nanocomposites into Au nanocages that are actually assembled of ∼10 nm Au nanoparticles. It is interesting to find that Cu₂O nanocubes produced from reductive solution chemistry are actually transformed from Cu(OH)₂ nanowire precursors, and the Cu₂O particle size is inversely proportional to the reaction temperature. A time-dependent TEM study of the GRR process between Cu₂O and HAuCl₄ indicates that this reaction involves evolution of an internal hollow core and surface precipitation of Au nanoparticles, which allows the formation of hollow Cu₂O-Au nanocomposites. Comparing the properties of hollow Cu₂O-Au nanocomposites and Au nanocages, it is determined that the hollow Cu₂O-Au nanocomposites are more catalytically active in the reduction of 4-nitrophenol into 4-aminophenol in the presence of NaBH₄, and Au nanocages are two orders of magnitude more sensitive in SERS detection of the target molecule, methylene blue. We believe the findings in this work may render a better understanding of the preparation and GRR process of Cu₂O nanomaterials.