Alkanethiolate-Protected Silver Nanoparticles and Clusters: Characterization, Synthesis Optimization and Formation Mechanism Investigation

Abstract

The primary objective of this thesis research was to investigate reaction process of silver nanoparticle (Ag NP) and nanocluster synthesis; to develop facile and efficient way to synthesize small and homogeneous silver nanoparticles; to explore method to preserve particle size and size distribution in the post-synthesis treatment; and to synthesize atomically precise Ag nanoclusters.

Brust-Schiffrin Method or BSM was the most popular route for obtaining sub 5-nm chalcogenolate-protected metal NPs. It was generally believed that metal salts interact with ligands to form polymer as the precursor for NP synthesis. Lennox and co-workers, however, showed NMR evidence that the precursor was actually a metal-halide complex. Our group used Raman to provide independent confirmation for the precursor status, and proposed reaction route for BSM. We showed that the reversed BSM gave better control to NP sizes, and discovered critical role of encapsulated water inside the reverse micelle.

Based on the BSM method and the new progress in mechanism studies, we investigated a series of conditions in each of the major reaction steps using octanethiol ligand as a model system, modified synthetic route, and proposed reaction process. By combining modified BSM with low and room temperature aging, highly homogeneous Ag NPs with small sizes have been obtained. A series of influential factors including Ag : ligand ratio, carbon chain length, and temperature etc were systematically investigated. Post-synthesis treatment, particularly purification process which was a key factor for particle growth after reduction, was extensively studied by using various kinds of precipitation solvents and considering different aspects of the reaction. Ag nanoclusters protected by alkanethiols were synthesized for the first time and the hypothesis for reaction route was proposed.

Our work has impacts in both reaction studies and practical applications. The effects of various conditions that were investigated in our work could serve as applicable model for optimizing ligand-protected Ag NPs and nanoclusters using BSM. The mechanism that we proposed will help understand the reaction process and guide the design of NP synthesis. Furthermore, our contribution will have potential applications in molecular electronics with particles possessing nicely controlled size and homogeneity.