Highly monodisperse multiple twinned AuCu-Pt trimetallic nanoparticles with high index surfaces

Abstract

Trimetallic nanoparticles possess different properties than their mono- and bi-metallic counterparts, opening a wide range of possibilities for diverse potential applications with the notion to study possible morphology, atomic ordering, reduce precious metal consumption and many others. In this paper, we present a comprehensive experimental study on AuCu-Pt trimetallic nanoparticles with an average diameter of 15 ± 1.0 nm, synthesized in a one-pot synthesis method and characterized by the Cs-corrected scanning transmission electron microscopy technique that allowed us to probe the structure at the atomic level resolution. A new way to control the nanoparticle morphology by the presence of third metal (Pt) is also discussed by the overgrowth of Pt on the as prepared AuCu core by Frank-van der Merwe (FM) layer-by-layer and Stranski-Krastanov (SK) island-on-wetting-layer growth modes. With the application of this research, we are now a step closer to produce optimum catalysts in which the active phase forms only surface monolayers. In addition, the nanoalloy exhibits high index facet surfaces with {211} and {321} families that are highly open-structure surfaces and are interesting for the catalytic applications.

Figure 1

(a) TEM image of the Au nanoparticles and inset histogram represents the size distribution of the particles (mean size range 9.0 ± 1.0 nm.), (b) HRTEM images of the multiply twinned structure Au nanoparticles, (c) Representative TEM image of AuCu nanoparticles, histogram shows an average size range (13.0 ± 1.0 nm.), (d) and (e) shows the HRTEM images of multiple twinned particles at the five-fold and oriented along {112} zone axis.

Figure 2

(a) TEM image of AuCu/Pt trimetallic core-shell nanoparticles and the particle size ranging from 15.0 ± 1.0 nm. (b) and (c) HRTEM images of the multiple twinned structure nanoparticles which is oriented along the {001}zone axis.

Figure 3

(a) HAADF-STEM image of AuCu/Pt multiple twinned nanoparticles, (b–f) EDX elemental maps of nanoparticles – Au, Cu, AuCu alloy, Pt, and Overlay respectively, (g) Au, Cu and Pt elemental profiles along the red line across the particles (inset of g).

Figure 4

(a) Atomic resolution HAADF-STEM image of a penta-twinned AuCu/Pt core-shell nanoparticle. Each tetrahedron (R1, R2, R3, R4, and R5) is identified by white arrow and the angles measured between the {111} twinning plane are 72.1°, 72.4°, 70.8°, 71.7°, and 71.2° as indicated. (b) Close-up of the image as indicated by the square showing the crystalline planes and different contrasts of Pt, Cu and Au lattices are readily observed, (c) Corresponding fast Fourier transform (FFT) shows the [011] zone axis.

Figure 5

(a) Shows HAADF image of 16 nm penta-twinned nanoparticles on a [011] zone axis with high index exposed facets, (b and c) Atomistic model for high-index facets {211} and {321} with steps and terraces.