THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Monday, April 6, 2020

10:00 AM
via

BlueJeans Video Conferencing

https://bluejeans.com/653757486

will be held the

DISSERTATION PROPOSAL DEFENSE

for

Shi Shi

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

Committee Members:

Prof. Dong Qin, Advisor, MSE

Prof. Meilin Liu, MSE

Prof. Zhiqun Lin, MSE

Prof. Preet Singh, MSE

Prof. Angus Wilkinson, CHEM

Abstract:

For nanocrystals made of the plasmonic metals, they could directly serve as bifunctional probes to catalyze reactions while reporting on the chemical species involved by in situ surface-enhanced Raman spectroscopy (SERS). These plasmonic metals, however, are only active towards a limited number of catalytic reactions when compared with the platinum-group metals. One approach to address this problem is to take one metal from each category for the development of a bimetallic system with integrated plasmonic and catalytic properties. Another possibility is to introduce an organic ligand to the surfaces of plasmonic nanocrystals for the creation of electronic perturbations toward the expansion of catalytic capabilities. In the first part of this proposal, I demonstrate the use of isocyanide compounds to functionalize the surface of Ag nanocubes for revitalizing their catalytic properties toward the reduction of 4-nitrothiophenol (4-NTP). I hypothesize that the s donation of electrons from isocyanide to Ag would make its surface atoms highly electron rich for a reaction with –NO2 of adsorbed 4-NTP molecules (an electron acceptor), leading to the creation of atomic oxygen toward the oxidation of isocyanide to isocyanate on the surface. My SERS results suggest that the presence of isocyanate can drive the reduction of 4-NTP for the production of trans-4,4’-dimercaptoazobezene (trans-DMAB). Different from Ag nanocubes where SERS signal is typically arising from the edges and sharp corners, namely SERS hot spots, nanospheres would provide uniform SERS signal across the surface, making it possible to monitor chemical reaction on the interests of entire surface. To achieve reproducible SERS signal with desired sensitivity, in the second part of this proposal, I will develop strategies to assemble Ag or Au nanospheres into 2-D closely packed structures on a solid substrate for the detection of biological species and chemical reactions with ligands that can’t chemically bind to the surface. In the third part of my proposal, I will use bimetallic Ag-Pd nanorods as a bifunctional probe for reporting chemical reactions by SERS. By tuning the dimensions of nanorods in two orthogonal directions, this class of bifunctional nanocrystal could resonate with two distinct incident lights and thus provide valuable information for understanding the wavelength-dependent behaviors in a catalytic reaction.