Direct synthesis of Au–Ag nanoframes by galvanic replacement via a continuous concaving process

Controlled synthesis of noble-metal nanoframes is of great interest due to their promising applications in plasmonics and catalysis. However, the synthesis is largely limited to a multiple-step approach involving selective deposition followed by selective etching. Here we report a facile and general strategy to synthesize Au-Ag nanoframes based on a direct galvanic replacement reaction between Ag nanoparticles and a gold(I) complex, sodium aurothiosulfate, without an extra etching process. The formation of Au-Ag nanoframes in our approach undergoes a continuous concaving and hollowing-out process from Ag templates, which is related to selective Au deposition and the Kirkendall effect. As a proof-of-concept, it was shown that Au-Ag nanoframes with different dimensions can be prepared from the corresponding Ag nanocolloids using our strategy. The prepared wire-like Au-Ag nanoframes show superior single-particle surface-enhanced Raman scattering due to the linear narrow nanogaps within the nanoframes. We believe this study signifies a new approach by mediating galvanic replacement to prepare noble-metal nanoframes with precise controllability, which may enable a variety of applications in plasmonics and catalysis.