Selective Etching Induces Selective Growth and Controlled Formation of Various Platinum Nanostructures by Modifying Seed Surface Free Energy

Abstract

We present a strategy to achieve heterogeneous seeded growth on nanoparticle (NP) surfaces and construct various Pt nanostructures (cage- and ring-like) by using selective etching as surface-free-energy-distribution modifier. Preprepared Au polyhedron NPs (octahedron, decahedron, nanorod, and nanoplate) are mixed with KI, H(2)PtCl(6), and surfactant. Under heating, KI is first oxidized to I(2), which then selectively etches the edges of Au polyhedrons. Consequently, the partial removal of surface Au atoms creates highly active sites (exposed high-index facets, atom steps, and kinks) on the etched edges. Then the reduced Pt(0) atoms deposit on the etched edges preferentially and grow further, generating bimetallic nanostructures, Au octahedrons, or decahedrons with edges coated by Pt. The Pt layer protects the Au on the etched edges against further etching, changing the etching route and causing the Au on {111} facets without a Pt layer to be etched. After the Au is removed completely from the bimetallic nanostructures, ring-like, frame-like, and octahedral cage-like Pt nanostructures form. The evolution from Au polyhedrons to Pt ring or octahedron cage is investigated systematically by high-resolution transmission electron microscopy, transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray, scanning transmission electron microscopy, and high-angle annular dark field.

Face the Edges: Catalytic Active Sites of Nanomaterials

“…Subsequently etching the template would lead to a frame portraying the outline of the pristine NP. As for specific affinity on edges, this is usually realized in Au‐Ag system,128 they are easy to react in suitable position under controllable conditions. The specific affinity also exists in some other nonmetallic materials 129…”

“…e) Pt can grow on the edges of Au (up) and form NFs (down). Reproduced with permission 128. Copyright 2012, American Chemical Society.…”

“…When the edge sites of decahedra Au erode because of low CN, new facets are produced and Pt are preferentially deposited on the newly formed faces. After etching and annealing, smooth Pt NFs can be obtained (Figure 8e) 128. Pt octahedral frames can be fabricated by using Au octahedron as templates.…”

Facet selective etching of Au microcrystallites

“…All above examples pertain to particles with size well below 300 nm. Recently Fan et al have reported a versatile method for the selective etching of edges and {111} facets of various shaped Au nanocrystals [24]. Face selective etching is indeed interesting not only to understand the nature of the facets but also to produce various shapes with nearly same size.…”

Synthesis of Pd‐Rh Core–Frame Concave Nanocubes and Their Conversion to Rh Cubic Nanoframes by Selective Etching of the Pd Cores

“…Notable examples include nanocubes with concave side faces, nanocages (hollow cubes with pores in the walls), and nanoframes (hollow cubes only with ridges and no side faces). [2][3][4] Such nanocrystals have been reported for a number of metals, including Au, Ag, Pd, Pt, and Rh, [3][4][5] although most of them were made of a single metal. There are only a few reports on bimetallic systems, including core-shell concave nanocrystals in the composition of Pt@Rh, Au@Pd, and Pd@Au.…”