Rational synthesis of multimetallic nanocrystals for plasmonics and catalysis

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Ahn, Jae Wan
Qin, Dong
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Multimetallic noble-metal nanocrystals have attracted considerable attention owing to their broad structure-property relationship for applications in plasmonics and catalysis. However, it remains a major challenge to rationally synthesize these nanocrystals because most of the reported protocols lack a mechanistic understanding and often involve a trial-and-error approach when optimizing the experimental parameters. This dissertation demonstrates the use of facet-selective etching and deposition as a powerful method for the transformation of colloidal silver nanocrystals into multimetallic nanostructures with intricate properties. In particular, I leverage the metal-coordination ligands to direct the etching and deposition in an orthogonal manner. In the first case study, I transform silver nanocubes into bimetallic concave nanocubes encased by silver-gold alloy frames via selective removal of the silver atoms from side faces while co-depositing silver and gold atoms as an alloy on the edges and corners. I further subject the core-frame nanocubes to galvanic replacement for the fabrication of nanoscale, multimetallic, cage cubes by confining the drilling of silver to the center of each side face. In the second case study, I investigate the roles played by poly(vinylpyrrolidone) and cetyltrimethylammonium chloride in controlling the orthogonal deposition of gold on different facets of silver cuboctahedra for the fabrication of nanoboxes with complementary surface structures. To understand the interaction between the ligands noble-metal and nanocrystals, I develop an in situ platform based on surface-enhanced Raman spectroscopy for analyzing the competitive binding of thiol and isocyanide molecules to the surface of silver nanocubes. Collectively, this work offers insights into the rational synthesis of multimetallic nanocrystals for applications in plasmonics and catalysis.
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