Thesis Format
Monograph
Degree
Master of Science
Program
Chemistry
Supervisor
Workentin, Mark S.
Abstract
Preparing atomically precise silver nanoclusters (Ag NC) modified with functional ligands capable of post-synthetic chemistry for use in potential applications like sensing, catalysis, and electrochemical processes remains a challenge. In this thesis, the synthesis of a novel stable free radical (TEMPO) functionalized Ag20 NC and some derivatives are presented, and their molecular structures are characterized by single crystal X-ray diffraction (SCXRD). The clusters were also characterized by multinuclear-NMR, IR, UV-vis, EPR and XPS spectroscopies, asserting the stability and novelty of free radical moieties in Ag NCs. The optical properties of the TEMPO-modified Ag20 NC, important for optical sensing applications, were probed using photoluminescence (PL) and electrochemiluminescence (ECL) spectroscopies. The electrochemical properties and catalytic behaviour of Ag20TEMPO6 NC were studied, exhibiting reversible redox behaviour with diffusion-controlled kinetics and displaying proof of concept of electrocatalytic activity in the oxidation of alcohols. Other post-synthetic reactions, like the regeneration of the nitroxide radical from a methoxyamine Ag20 NC derivative (Ag20MeTEMPO8 NC) with a nucleophile, were also investigated. The results contribute to a deeper understanding of the properties of atomically precise Ag NCs and expand the scope of post-synthetic cluster surface chemistry of functionalized Ag NCs.
Summary for Lay Audience
At the nanoscale, structures have small dimensions (10-9 m), being impossible to look with the naked eye. Due to their smaller size, silver-made nanostructures possess different and interesting properties compared to their bulk counterparts that are dependent on the size of the nanostructure, which opens opportunities for their use in various applications.
We prepare nanostructures composed of 20 silver (Ag) atoms, so-called atomically precise nanoclusters, since the structure obtained is identically formed of 20 Ag for every species. These clusters have a core-shell structure, where the Ag atoms form the core and surface ligands attached to it are the shell. In this work, I created new clusters with 20 Ag that are modified and protected by a moiety known as TEMPO (Ag20TEMPO), a functional group that has an unpaired free electron (free radical). A derivative of Ag20TEMPO was fabricated by removing the free radical and attaching another moiety, thus changing the reactivity and properties of the ligand (Ag20MeTEMPO). These clusters were analyzed using a variety of techniques to understand their properties, how they behave when interacting with UV and visible light, and to obtain information about their structures.
We explored how these nanoclusters behave when exposed to electrical currents, using a method called cyclic voltammetry, when a potential is applied in a cycle and the current response is measured. The results showed that the TEMPO-functionalized silver nanoclusters can be oxidized and reversibly reduced back to their original state, meaning they can easily lose and gain electrons. They also showed significant ability to catalyze chemical reactions, particularly in oxidizing alcohols (losing electrons) into other substances. Additionally, thanks to the Ag20MeTEMPO, we investigated other reactions that take place after the cluster synthesis. The regeneration of the free radicals is possible by applying the right potential and the interaction with nucleophile compounds, molecules that look to interact with positively charged molecules and donate their extra electrons to bond with them.
Recommended Citation
Ruiz Hernandez, Ali Roberto, "Nitroxide-functionalized Atomically Precise Ag20 Nanoclusters for Electrocatalytic Oxidations" (2024). Electronic Thesis and Dissertation Repository. 10466.
https://ir.lib.uwo.ca/etd/10466
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