The Role of Surface Nonuniformity in Controlling the Initiation of a Galvanic Replacement Reaction

Abstract

The use of silver nanocrystals--asymmetrically truncated octahedrons and nanobars--characterized by a nonuniform surface as substrates for a galvanic replacement reaction was investigated. As the surfaces of these nanocrystals contain facets with a variety of different areas, shapes, and atomic arrangements, we were able to examine the roles of these parameters in different stages of the galvanic replacement reaction with HAuCl(4) (e.g., pitting, hollowing, pit closing, and pore formation), and thus obtain a deeper understanding of the reaction mechanism than is possible with silver nanocubes. We found that the most important of these parameters was the atomic arrangement, that is, whether the surface was capped by a {100} or {111} facet, and that the area and shape of the facet had essentially no effect on the initiation of the reaction. Interestingly, through the reaction with asymmetrically truncated octahedrons, we were also able to demonstrate that even when pitting occurred over a large area, this region would be sealed through a combination of atomic diffusion and deposition during the intermediate stages of the reaction. Consequently, even if pitting occurred across a large percentage of the nanocrystal surface, it was still possible to maintain the morphology of the template throughout the reaction.

Ex Situ and in Situ Surface Plasmon Monitoring of Temperature-Dependent Structural Evolution in Galvanic Replacement Reactions at a Single-Particle Level

“…16 The standard reduction potential of the AuCl 4 − /Au pair (0.99 V vs standard hydrogen electrode (SHE)) is higher than that of the Ag + /Ag pair (0.80 V vs SHE); thus, the Au ions are reduced to Au atoms, while the Ag atoms are oxidized to Ag ions and are dissolved in the aqueous solution, as follows:…”

25th Anniversary Article: Galvanic Replacement: A Simple and Versatile Route to Hollow Nanostructures with Tunable and Well‐Controlled Properties

“…A similar trend was also observed for Ag octahedrons solely covered by eight {111} facets. [ 45,58 ] When more than one type of facets are present on the surface of a template, galvanic replacement can proceed with facet selectivity, [ 59,60 ] allowing for rational design and engineering of the fi nal nanostructure. In this case, galvanic replacement tends to start from the facet(s) with the highest surface free energy, whereas the deposition of newly formed atoms preferentially occurs on the remaining facets with lower surface free energies.…”

“…[ 61,62 ] When a clean polyhedron with no capping agent on the surface is employed as the sacrifi cial template for a galvanic replacement reaction, the dissolution of atoms should begin from the {110} and {100} facets due to their higher surface free energy, while deposition of the newly formed atoms should occur on the {111} facets regardless of the area and shape of the facets. [ 60 ] In the solution-phase synthesis of nanocrystals, however, a facet-specifi c capping agent is often intentionally introduced into the reaction system to promote the formation of desired facets. [63][64][65][66][67][68] As such, the surface of a nanocrystal is often covered by the capping agent.…”

Synthesis and Catalytic Activities of Metal Shells (Monolayer, Bilayer, and Alloy Layer)-Coated Gold Octahedra toward Catalytic Reduction of Nitroaromatics

“…Galvanic replacement reaction takes place immediately when HAuCl 4 is added to Ag NPs in aqueous condition even at 0 °C . Galvanic replacement reactions for various MNPs with different shapes have been reported. − Both Au and Ag NPs show unique and well-separated surface plasmon resonance (SPR) absorption bands in the visible region . Studies on the optical properties of alloy shell (AS) on core (Au@AgAu) and multishells on core (Au@Ag@Au@Ag) have been reported. − However, a systematic investigation on the catalytic effect of different types of metal shells (monolayer, bilayer, and alloy layer of Au, Ag, and AuAg alloy on AuOh) will shed light on the choice of best catalysts to be designed.…”