Fabrication of Ag-Pd concave nanocrystals through facet-selective oxidation of Ag atoms.

We report the fabrication of Ag-Pd concave nanocrystals by introducing the Pd(ii) precursor into an aqueous suspension of Ag nanocubes in the presence of cetyltrimethylammonium chloride (CTAC) under ambient conditions. Different from the previously reported work that involved the oxidation of Ag and deposition of Pd at random sites on the surface for the generation of Ag-Pd hollow nanocrystals, we demonstrate that the Cl- ions from CTAC can confine the oxidation of Ag atoms to the side faces of a nanocube while the resultant Pd atoms are deposited on the edges in an orthogonal manner. By controlling the amount of the Pd(ii) precursor involved in a synthesis, we can transform Ag nanocubes into Ag-Pd nanocrystals with different degrees of concaveness for the side faces and controllable Pd contents. We characterize the outermost layer of concave surfaces for the as-obtained Ag-Pd nanocrystals by surface-enhanced Raman scattering (SERS) through the use of an isocyanide probe. This facile approach would enable the fabrication of Ag-based concave nanocrystals for applications in plasmonics and catalysis.