Georgia Institute of Technology Materials Science and Engineering

Committee Members: 

Prof. Dong Qin, Advisor, MSE

Prof. Zhiqun Lin, MSE

Prof. Meilin Liu, MSE

Prof. Preet Singh, MSE

Prof. Angus Wilkinson, CHEM

"Bifunctional Metal Nanocrystals for Catalyzing and Reporting on Chemical Reactions by Surface-Enhanced Raman Scattering"

Abstract:

Noble-metal nanocrystals are of critical importance to an array of fundamental studies and a broad spectrum of applications in photonics, sensing, imaging, and catalysis. Thanks to the significant progress in controlling their colloidal synthesis, recent years have witnessed the successful development of bifunctional nanocrystals with integrated plasmonic and catalytic activities. Silver nanocrystals, in particular, could directly serve as bifunctional probes to catalyze reactions while reporting on the molecular species involved by in situ surface-enhanced Raman scattering (SERS). Although silver is an excellent catalyst for some oxidation reactions, it shows limited activities toward reduction reactions. This dissertation documents the discovery of Ag nanocrystals as a redox catalyst for the production of an aromatic azo compound. I unraveled the mechanistic insights by tracking and analyzing the vibrational bands of all chemical species involved in the reaction by in situ SERS. I established that surface functionalization with isocyanide allowed Ag nanocrystals to extract the oxygen atom from the nitro-group of a nitroaromatic compound for the oxidation of isocyanide to isocyanate. Concomitantly, the coupling between two adjacent deoxygenated nitroaromatic molecules produced an aromatic azo compound. In addition to demonstrating the feasibility of in situ SERS for monitoring chemical reactions, I further investigated the role of laser excitation wavelength in affecting SERS detection using Ag-Pd nanorods and Ag nanocubes with distinctive localized surface plasmon resonance (LSPR) properties as two bifunctional probes. I validated that Ag-Pd nanorods embraced stronger SERS activity when their longitudinal LSPR mode was at resonance with 785-nm laser excitation. In comparison, Ag nanocubes exhibited stronger SERS activity when their LSPR major peak of Ag nanocubes is closer to 532-nm laser excitation.