A Quantitative Analysis of Anions and pH on the Growth of Bimetallic Nanostructures

Symmetrically branched and shape-controlled alloyed nanocrystals composed of Au and Pd are synthesized via seed-mediated coreduction, in which the two metals are simultaneously deposited onto Au seeds. Here, a qualitative evaluation of morphology development (obtained via SEM of product from reaction aliquots) is coupled with a quantitative analysis of metal deposition rates (obtained via ICP-MS of the same samples) to elucidate the roles of anions and pH in bimetallic nanostructure formation. Different anion environments and total precursor concentration were found to influence metal deposition rates and nanostructure morphology. In contrast, reaction pH did not alter the deposition rates significantly despite dramatic changes in morphology. The latter is surprising given the often-cited pH-dependent reduction process in similar systems. These experiments are a first effort at quantitatively analyzing the kinetics of metal deposition in a bimetallic system, where understanding the shape-directing effects of synthetic conditions will facilitate design of new nanostructures.