Date of Award

Spring 2019

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

First Advisor

Hui Wang

Abstract

The dynamic interactions between capping ligands and nanoparticle surfaces play a critical role in guiding shape-controlled nanocrystalline growth, imparting unique physical and chemical properties to the nanoparticles. It has been well established that nanoparticles within the size regime of sub 5 nm possess unique heterogeneous catalytic properties, while sub wavelength metallic nanoparticles exhibit tunable plasmonic activity, when these properties are integrated into a single nanoparticle, it presents a significant opportunity to monitor, in real time, the molecular transformations associated with interfacial interactions at the nanoparticle surface. Using plasmon-enhanced Raman scattering as an ultrasensitive spectroscopic tool combining molecular fingerprinting with time resolving capabilities, I quantitatively demonstrated the correlation between local surface structures of Au nanoparticles with the interfacial adsorption, desorption, and exchange behaviors of thiol ligands by in situ measurements of these kinetic processes. These results provide mechanistic understanding of key thermodynamic, kinetic and geometric factors underpinning the surface curvature dependence of interfacial ligand dynamics and chemistry.

I next focused on understanding aryl grafting and polymerization on highly curved Au nanoparticle surfaces. This allowed for further real-time examination of unconventional coupling reactions between grafted aryl and thiophenol derivatives chemisorbed on Au nanoparticle surfaces that otherwise will not occur in the absence of the Au nanoparticles, revealing two distinct mechanistic pathways for dimerization and azo formation at the surface. Understanding that surface morphology of nanoparticles plays a crucial role for both interfacial dynamics, as well as, plasmonic enhancement associated with distinctive molecular fingerprinting capability is key to developing fundamental knowledge of interfacial chemical process between nanocrystals and ligands. To further, understand the structure property relationship of plasmonic nanocrystals, I presented experimental evidence detailing structural evolution dictated by the interdependence of oxidative etching and nanocrystalline growth. Deliberately controlling the nanocrystal surface topography allows fundamental insight towards better integration and optimization of desired plasmonic and catalytic properties.

Finally, I concluded my research with investigation into understanding the impact of surface coordination of isocyanide molecules to both Au and Au-Pd core shell nanocrystalline structures evaluating the associated kinetic binding events and thermodynamic stability onto those surfaces, precisely monitoring the different mechanistic pathways associated with interfacial ligand nanoparticle interactions. The insights gained from this investigation will improve understanding for optimizing plasmonic-enhanced catalysis.

The goal of this dissertation is to couple laser spectroscopic techniques with plasmonic nanocrystalline structures to understand molecular transformation kinetics and mechanistic pathways at the nanocrystal interface towards optimization of rational design principles for both plasmonic-enhanced catalysis and plasmon-driven photocatalysis. The fundamental insight gained from these studies will improve our ability to tailor and fine tune properties of metallic nanocrystals for use in environmental and energy applications.

Available for download on Tuesday, May 11, 2021

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