A Novel Side-Selective Galvanic Reaction and Synthesis of Hollow Nanoparticles with an Alloy Core

Hollow nanoparticles with an alloy core (HNACs) have been prepared by a novel side-selective galvanic reaction. Seeding growth first is used to synthesize Au@Ag nanoparticles (NPs), which react with HAuCl4 to form HNAC NPs. Through adjusting the core size, the amount of HAuCl4, and the diameter of Au@Ag, fabrications of various HNACs are achieved. By using high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry, field emission scanning electron microscopy, and UV-vis spectroscopy, the galvanic etching process is observed. We find the galvanic reaction is side-selective compared to previously reported reactions. Three features are believed to play important roles: (1) interfacial alloying between the Au core and Ag shell, (2) the structure of Au@Ag (the Au core is not right center), and (3) the Au-content-dependent galvanic reaction. Prepared HNACs have a rough surface and porous structure, which indicates they can capture more molecules with affinity. Also, these hydrophobic HNACs can assemble into ordered 3-dimensional organizations. All these features are important to surface-enhanced Raman scattering (SERS). 2-Naphthalenethiol is used as a probe molecule to investigate their SERS activity, and the results demonstrate their good performance. In addition, during the galvanic reaction, interestingly, the Ag+ from oxidization can react with a Cl- of HAuCl4 to form size-controlled AgCl NPs with a uniform diameter.