Researchers Visualize and Measure the Morphological Phases of Platinum
Nanocrystals
summary written by Raven Hanna
Crystals of different sizes and shapes have different functional properties. This is certainly true in the case of platinum nanocrystals, which can be used to increase catalytic reactions including hydrogen cell fuel oxidation. Understanding crystallization processes will allow researchers to fine-tune the shape, size, and quality of crystals for specific, tailored applications.
An international team of researchers led by Richard Tilley from Victoria University in Wellington, New Zealand investigated the crystallization process of platinum nanocrystals. They set up reactions with two precursor concentrations (low and high) and took measurements over time. Real time in situ X-ray diffraction (XRD), using SSRL Beam Line 7-2, measured the crystallinity of the nanocrystals during the reactions, while transmission electron microscopy (TEM) revealed the morphology of the crystalline material. Combining the information from these two techniques allowed the researchers to discern the processes of crystallization.
The researchers found that the low concentration reactions create slow-growing, faceted crystals by laying down each platinum atomic layer in a thermodynamically controlled manner. In striking contrast, the high concentration reactions are kinetically controlled and go through distinct morphological phases over time, starting with a cuboctahedral faceted structure, growing into quasi-octapods, further evolving through simultaneous growth and dissolution of different parts of the nanocrystals into etched-octapods, and finally becoming porous nanocrystals.
The researchers conclude that combining the TEM and in situ XRD techniques creates a powerful tool for understanding crystal growth and structure. This research was published in the October 14, 2009, issue of the Journal of the American Chemical Society.
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Cheong, S., Watt, J., Ingham, B., Toney, M. F. & Tilley, R. D. In situ and ex situ studies of platinum nanocrystals: growth and evolution in solution. J. Am. Chem. Soc. 131, 14590-14595 (2009).
