Shape-Dependent Evolution of Au@Ag Core−Shell Nanocrystals by PVP-Assisted N,N-Dimethylformamide Reduction

Abstract

Shape-dependent Au@Ag core−shell nanocrystals have been successfully synthesized by using a two-step method. First, Au nanocrystal seeds with various shapes including single-crystal octahedron, single-twinned triangle or hexagon plate, and multiple-twinned decahedron were prepared by reducing HAuCl4 in ethylene glycol (EG) in the presence of polyvinylpyrrolidone (PVP) as a polymer surfactant under the condition of microwave heating. Subsequently, thus-obtained Au seeds were added into N,N-dimethylformamide (DMF) solution containing Ag+ ions for overgrowth of Ag shells by an oil-bath heating. Transmission electron microscope (TEM) observation demonstrates that shapes of formed Ag shells strongly depend on shapes of initiated Au seeds. These newly produced triangular or hexagonal platelike, octahedral, and multiple-twinned decahedral Au@Ag nanocrystals are mainly dominated by the Ag shells having {111} facets. This case is completely different from that previously investigated by us in EG system where formed triangular-bipyramidal, cubic, and pentagonal rod/wire Au@Ag core−shell nanostructures are surrounded by the Ag shells with {100} facets. Our studies reveal that it is possible to controllably prepare the Au@Ag core/shell nanocrystal structures with optional uniform crystalline planes by the same Au seed source and different reaction solvent.

Gold Coating of Silver Nanoprisms

“…For example, Au@Ag core-shell nanocrystals with various morphologies have been synthesized through an epitaxial growth process involving conformal Ag deposition on the surface of Au seeds. [29,30] However, the formation of a structure with an Ag core and an Au shell remains challenging due to the significant etching of Ag cores by Au salt precursors, which is known as galvanic replacement and typically leads to the generation of nanoframes, [31] or hollow nanoboxes, [32] or other irregular nanoparticles with random optical responses. In particular, when the core is a very thin silver prism (<10 nm), the tip is so vulnerable to oxidation that the flat (111) faces tend to be preferentially etched through the galvanic process.…”

Nucleation and growth mechanisms for Pd-Pt bimetallic nanodendrites and their electrocatalytic properties

“…Recently, heterogeneous, seeded growth has emerged as a powerful tool for precisely controlling the morphology and composition of bimetallic nanostructures [1][2][3][4][5][6][7][8][9][10][11][12][13]. This technical approach has enabled the preparation of a wide variety of bimetallic nanostructures that cannot be achieved otherwise.…”

Addendum: Plasmonic nanosensors with inverse sensitivity by means of enzyme-guided crystal growth

“…The reduction of silver ions on gold nanoparticles can also be affected by the presence of PVP because PVP can selectively adsorb silver nanostructures. Indeed, in gold-silver core-shell nanoparticles with cubic, triangularbipyramidal, and rod or wire silver shells, {100}-type dominant facets were formed upon epitaxial growth on the {111}-type facets of the gold core 10,11 . The morphology change between the Au core and Ag shells may have its origin in the change of adsorption selectivity of PVP molecules from Au{111}-type facets to Ag{100}-type ones in ethylene glycol solvent.…”