Abstract
We have prepared Pd nanocrystals with systematic shape evolution from octahedral to cubic structures through a one-pot synthesis approach. Octahedral, cuboctahedral, and cubic structures can be synthesized by using cetyltrimethylammonium chloride (CTAC) surfactant as capping agent, H2PdCl4, ascorbic acid as reducing agent and a very small amount of KBr. Fine tuning in the amount of KBr added to the growth solution enabled the fine control of nanocrystal morphology. Structural characterization confirmed that octahedra are bounded by {111} facets, whereas the cubes are bounded by {100} facets. The final shapes of Pd nanocrystals resulted from the different growth rates in the <100> direction to that of <111> direction. We have successfully used a systematic method to synthesize Pd nanocrystals with entirely {111} and {100} facets and found the relationships among these shapes. These nanocrystals should allow the examination of their various properties as a function of particles shapes and surfaces. According to our experiments regarding the study of growth mechanism of the Pd nanocrystals, we found that bromide ions play a critical role to influence the reduction kinetics of Pd precursors and relative rates of Pd addition on the surfaces of nanoparticles. With the increase of KBr added to the growth solution, the whole reaction rate was increased. Furthermore, the accelerated growth rate in the <111> direction suppressed that of <100> direction to increase the proportion of {100} facets of Pd nanocrystals. In the future, we will apply these nanoparticles with specific facets as catalysts for the facet-dependent organic reactions.