Publication Date

April 2017

Advisor(s)

Michelle Personick

Major

Chemistry

Language

English (United States)

Abstract

Noble metal nanoparticles that possess distinct shapes are extremely promising as selective, environmentally friendly, and energy-efficient catalysts. Metal nanoparticles have large surface areas consisting of many active sites, which, in turn, increase their catalytic ability when compared to ordinary, macroscale bulk metals. Nanoparticles characterized by particular shapes possess a variety of well-defined surface facets that influence catalytic activity and selectivity. These facets improve catalytic activity and selectivity by controlling the binding strength and arrangement of specific reaction intermediates. Platinum-silver and platinum-gold nanoparticle alloys are especially important in catalysis, yet the formation of these particles is not well controlled or understood. This thesis focuses on the structure and composition of platinum nanoparticles using both a silver additive, as well as a gold additive, in aqueous based, seed-mediated syntheses. It was demonstrated that silver nitrate (AgNO3) promotes the formation of platinum nanoparticles below 50°C, but also gives rise to nanoparticles that have “fuzzy” surface structures. Above 50°C, however, it was determined that particles form with non-fuzzy surfaces and very little silver composition. Nevertheless, particles grown above 50°C become polydisperse in size and amorphous in shape. A few methods successfully altered the observed amorphous morphology of Pt-Ag nanoparticles. The addition of 30 µL of 1 M HCl at growth solutions of 30°C and 40°C resulted in octahedra-shaped particles. Moreover, the addition of 0.1 M NaCl in solution led to the formation of Pt-Ag nanoparticles with either {111} or {100} facets. The observed “fuzzy” surface structure was first hypothesized, and later confirmed in an article by Xia et al. to be, in part, the result of silver-platinum alloying by way of a co-reduction, underpotential deposition layering mechanism. The addition of 0.1 M NaCl in solution led to the formation of Pt-Ag nanoparticles with considerably less fuzziness. It was later proposed that this surface fuzziness could also be caused by the precipitation of AgCl nanoclusters, which can be solubilized by the addition of NaCl to the growth solution. With the addition of chlorauric acid (HAuCl4), in the absence of silver nitrate, Pt-Au nanoparticles formed in the shapes of decahedra, octahedra, and truncated triangular bipyramids. These Pt-Au particles have very little surface fuzziness, and resemble core-shell structures. In order to improve upon the current state of chemical catalysis, it is expected that these findings will be used to help control the shape, structure, and size of platinum-silver and platinum-gold nanoparticles.

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