Formation of Rh frame nanorods using Au nanorods as sacrificial templates

This report describes a new formation process of Rh frame structures using Au nanorods (NRs) as sacrificial templates. Initially, Au@Rh NRs were prepared by reducing Rh3+ in the presence of Au NRs, ascorbic acid, and cetyl trimethyl ammonium bromide (CTAB) in aqueous solution. After formation of Au@Rh NRs having an island-type of Rh shell, Rh NR frames, which consist of four side edges and top and bottom edges of NRs, were formed in one step through selective oxidative etching of an Au NR core and Rh shells over unstable facets such as {2 5 0} or {5 12 0} by X-(X = Br, Cl) + O-2. An alternative method for the formation of Rh NR frames was the separation between the formation process of Au@Rh NRs and Rh NR frames by oxidative etching. In this two-step process, after formation of Au@Rh NRs, a similar shape of Rh NR frames having {100} facets as major planes was prepared by the addition of HCl. No Rh frame structure was formed from decahedral Au@Rh particles because smooth Rh shells without interspace were formed; Rh shells over low-index {111} facets were not etched by X-(X = Br, Cl) + O-2. The results obtained from this study suggest a novel method for the formation of frame structures and constitute new information related to their formation mechanism.