Seeded Growth Of Pd Nanocrystals: The Influence Of Surface Capping Agent

Controlling the shape of metal nanocrystals is essential to the improvement of their applications in catalysis. One common approach is seed-mediated growth, in which newly formed atoms are added to the surface of pre-formed seeds under well-controlled conditions.  In previous studies of seed-mediated growth, the experiments were often conducted with seeds that whose surfaces are covered by capping agents while the influence of such capping agents was largely unknown.  Specifically, bromide ions can serve as an effective capping agent for the {100} facets of Pd and thus has been widely used for the synthesis of Pd nanocubes. The bromide ions could be removed through washing in a reductive environment. In this work, we demonstrated that the growth pathway of a Pd cubic seed was indeed affected by the capping agent adsorbed on the surface of the seed. Palladium atoms were randomly deposited on the surface of a Pd seed when there was no bromide on the surface. In the case of Pd seeds with bromide bound to the surface, the majority of atoms were deposited on the {111} and {110} facets, corresponding to the corners and edges. Our results suggest that the capping agents on the surface of seeds could alter the growth pathway of seeded growth, which could be used as an effective approach to manipulate the morphology of the final products.