Hollow octahedral and cuboctahedral nanocrystals of ternary Pt–Ni–Au alloys

Hollow particles of Pt–Ni–Au alloys have been prepared through a two-step reaction with the synthesis of NiPt octahedral and cuboctahedral templates followed by a galvanic replacement reaction by Au(III). Metal etching presents an efficient method to yield hollow particles and investigate the Au diffusion in the metallic Pt–Ni framework through macroscopic (X-ray diffraction and SQUID magnetic measurement) and microscopic (HRTEM and STEM) measurements. The hollow particles retain the shape of the original nanocrystals. The nucleation of Au is found to be induced preferentially on the tip of the polyhedral nanocrystals while the etching of Ni starts from the facets leaving hollow octahedral particles consisting of 2 nm thick edges. In the presence of oleylamine, the Au tip grows and yields a heterogeneous dimer hollow-NiPt/Au. Without oleylamine, the Au nucleation is followed by Au diffusion in the Ni/Pt framework to yield a hollow single crystal Pt–Ni–Au alloy. The Pt–Ni–Au alloyed particles display a superparamagnetic behavior at room temperature.