Transformation
of Ag Nanocubes into Ag–Au Hollow Nanostructures with Enriched
Ag Contents to Improve SERS Activity and Chemical Stability
- Publication date
- Publisher
Abstract
We report a strategy to complement
the galvanic replacement reaction between Ag nanocubes and HAuCl<sub>4</sub> with co-reduction by ascorbic acid (AA) for the formation
of Ag–Au hollow nanostructures with greatly enhanced SERS activity.
Specifically, in the early stage of synthesis, the Ag nanocubes are
sharpened at corners and edges because of the selective deposition
of Au and Ag atoms at these sites. In the following steps, the pure
Ag in the nanocubes is constantly converted into Ag<sup>+</sup> ions
to generate voids owing to the galvanic reaction with HAuCl<sub>4</sub>, but these released Ag<sup>+</sup> ions are immediately reduced
back to Ag atoms and are co-deposited with Au atoms onto the nanocube
templates. We observe distinctive SERS properties for the Ag–Au
hollow nanostructures at visible and near-infrared excitation wavelengths.
When plasmon damping is eliminated by using an excitation wavelength
of 785 nm, the SERS activity of the Ag–Au hollow nanostructures
is 15- and 33-fold stronger than those of the original Ag nanocubes
and the Ag–Au nanocages prepared by galvanic replacement without
co-reduction, respectively. Additionally, Ag–Au hollow nanostructures
embrace considerably improved stability in an oxidizing environment
such as aqueous H<sub>2</sub>O<sub>2</sub> solution. Collectively,
our work suggests that the Ag–Au hollow nanostructures will
find applications in SERS detection and imaging