Mechanistic Study on the Replacement Reaction between Silver Nanostructures and Chloroauric Acid in Aqueous Medium

Abstract

The replacement reaction between silver nanostructures and an aqueous HAuCl(4) solution has recently been demonstrated as a versatile method for generating metal nanostructures with hollow interiors. Here we describe the results of a systematic study detailing the morphological, structural, compositional, and spectral changes involved in such a heterogeneous reaction on the nanoscale. Two distinctive steps have been resolved through a combination of microscopic and spectroscopic methods. In the first step, silver nanostructure (i.e., the template) is dissolved to generate gold atoms that are deposited epitaxially on the surface of each template. Silver atoms also diffuse into the gold shell (or sheath) to form a seamless, hollow nanostructure with its wall made of Au-Ag alloys. The second step involves dealloying, a process that selectively removes silver atoms from the alloyed wall, induces morphological reconstruction, and finally leads to the formation of pinholes in the walls. Reaction temperature was found to play an important role in the replacement reaction because the solubility constant of AgCl and the diffusion coefficients of Ag and Au atoms were both strongly dependent on this parameter. This work has enabled us to prepare metal nanostructures with controllable geometric shapes and structures, and thus optical properties (for example, the surface plasmon resonance peaks could be readily shifted from 500 to 1200 nm by controlling the ratio between Ag and HAuCl(4)).

Ambient-stable tetragonal phase in silver nanostructures

“…The Ag nanowires can react with an aqueous solution of HAuCl 4 through a galvanic replacement reaction, leading to the formation of epitaxial Ag-Au alloy nanotubes ( Supplementary Fig. S12a) 29,30 . The resulting nanotubes maintain the pentagonal cross-section of the Ag nanowires and also have fivefold twin planes that do not cross ( Supplementary Fig.…”

“…were maintained throughout the entire synthesis. Silver nanocubes with size of ~120 nm were synthesized through a modified polyol process described in our previous work 29 . In a typical synthesis, 5 ml of anhydrous ethylene glycol (99.8%, Sigma-Aldrich) was heated in a 100-ml threeneck flask that was immersed in an oil bath setting at 160 °C for 1 h. A 3-ml aliquot of an ethylene glycol solution of 0.25 M AgNO 3 and a 3-ml aliquot of an ethylene glycol solution of 0.19 M PVP were simultaneously added to the hot ethylene glycol using a two-channel syringe pump at a rate of 0.375 ml min − 1 .…”

Gold Nanocages for Biomedical Applications

“…Figure 1, A-C, shows SEM and TEM images of samples derived from Ag nanocubes with sharp corners. [19] This work shows that the replacement proceeds through the following steps: i) initiation of Ag dissolution by pitting at a specific site on the surface of a Ag nanocube; ii) formation of a pinhole-free nanobox consisting of thin, uniform walls through a combination of galvanic replacement and Au-Ag alloying; and iii) generation of pores in the wall through a dealloying process. A schematic of this mechanism is shown in Figure 2A.…”

Nanostructured Pt-alloy electrocatalysts for PEM fuel cell oxygen reduction reaction

“…In a similar approach, Ag and Cu nanowires have been used as a template to generate Au (Fig. 20), 128 Pd and Pt nanotubes through a galvanic replacement reaction.…”