The Effects of Dynamic Transformation on the Formation of Pt-M (M = Ni, Fe) Nanocrystals
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.656
The Effects of Dynamic Transformation on the Formation of Pt-M (M = Ni, Fe) Nanocrystals Yiliang Luan1, Can Li1, Bo Zhao2, Amar Kumbhar3, Jun Zhang4, Jiye Fang1,* 1. Department of Chemistry, State University of New York at Binghamton, Binghamton, NY, USA 2. College of Arts & Sciences Microscopy, Texas Tech University, Lubbock, TX, USA 3. Chapel Hill Analytical and Nanofabrication Laboratory, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA 4. College of Chemical Engineering, China University of Petroleum (East China), Shandong, China
ABSTRACT In the synthesis of metallic nanocrystals (NCs) using a high-temperature colloidal approach, the competition between deposition and diffusion of “free atom (or clusters)” plays an important role as it can direct the morphology of NCs during their evolution. This competition is closely associated with some dynamic conditions such as heat and mass transfer. Stirring speed and ramp rate of heating are two factors that greatly impact the heat and mass transfer processes and consequently determine the morphology of the products but rarely discussed in most synthetic protocols. Herein, we study the syntheses of Pt-M (M = Ni, Fe) NCs as model reactions, showing that a low stirring speed and high ramp rate of heating result in ununiform pod-like NCs, whereas the inverse conditions promote NCs in a uniform shape. This observation can be plausibly explained using a competition mechanism between the deposition and diffusion of the newly reduced atoms during a stage of the NC’s growth.
INTRODUCTION Nanomaterials possess extensive applications[1-4] due to their unique properties compared with their bulk counterparts. High-temperature colloidal synthesis approach has been widely used in the preparation of NCs including metals[5-8], alloys[811], semiconductors[12, 13] and oxides[14-16], as it can produce size- and shapecontrolled nano-architectures. It is also one of the insightful strategies to produce NCs with exclusive facets in order to correlate a collective property such as the reaction activity or selectivity with a specific lattice plane[8, 17]. Compared with other wetchemical approaches such as the hydrothermal method, the high-temperature colloidal
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synthesis contains more variable factors that govern the formation of NCs and tune their shape through both the kinetic and thermodynamic controls. As an advantage, the growth of the particle products could be precisely controlled if these processing factors are successfully identified and controlled. For example, a competition between the deposition and diffusion of the “free atoms (or clusters)” released from the precursors during the growth of an NC[18] could steer the shape evolution of the NC a
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