“Colloidal silver nanocrystals and their derivatives: Synthesis, properties, and applications”

Abstract

Silver nanocrystals have received growing interests owing to their fascinating localized surface plasmon resonance (LSPR) properties and spectacular applications in surface-enhanced Raman scattering (SERS). Despite remarkable success, Ag nanocrystals are highly susceptible to oxidative etching and only exhibit limited catalytic activities. To address these issues, the first part of my thesis documents the development of synthetic approaches to enrich Ag nanocrystals with a second noble metal for the generation of Ag@Pd-Ag core-frame nanocubes and Ag@SiO2/Au nanoparticles. I also demonstrated these bimetallic nanocrystals as bifunctional probes for in situ monitoring the catalytic reactions by SERS. In the second part of this thesis, I turned the synthesis of Ag@Pd-Ag core-frame nanocubes into a model system for investigating the heterogeneous nucleation in nanocrystal growth with a molecular probe. I demonstrated that 2,6-dimethylphenyl isocyanide was a sensitive probe for in situ atomic-level tracking of the heterogeneous nucleation of Pd on Ag nanocubes by SERS. I discovered that the isocyanide group could bind to one, two, and three adjacent Pd atoms to generate the atop, bridge, and hollow binding configurations, respectively, and give different vibrational frequencies, making it possible to characterize Pd atoms being deposited onto different facets of Ag nanocubes. This in situ SERS offers an opportunity to investigate the role of reaction temperature and the type of Pd(II) precursor in affecting the reduction, deposition, and surface diffusion involved in heterogeneous nucleation. Collectively, my thesis opens up new possibilities for the rational design and synthesis of bimetallic nanocrystals involving Ag and another noble metal such as Pt, Ru, Rh, and Ir.