Quantitative Analysis of the Coverage Density of Br<sup>–</sup> Ions on Pd{100} Facets and Its Role in Controlling
the Shape of Pd Nanocrystals
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Abstract
We
report an approach based on a combination of inductively coupled
plasma mass spectrometry and X-ray photoelectron spectroscopy for
quantitative analysis of the role played by Br<sup>–</sup> ions
in the synthesis of Pd nanocrystals. The Br<sup>–</sup> ions
were found to adsorb onto Pd{100} facets selectively with a coverage
density of ca. 0.8 ion per surface Pd atom. The chemisorbed Br<sup>–</sup> ions could be removed via desorption at an elevated
temperature under reductive conditions. They could also be gradually
released from the surface when Pd cubic seeds grew into cuboctahedrons
and then octahedrons. On the basis of the coverage density information,
we were able to estimate the minimum concentration of Br<sup>–</sup> ions needed for the formation of Pd nanocubes with a specific size.
If the concentration of Br<sup>–</sup> ions was below this
minimum value, not all of the {100} facets could be stabilized by
the capping agent, leading to the formation of nanocubes with truncated
corners. The quantitative analysis developed in this study is potentially
extendable to other systems involving chemisorbed capping agents