Date Created

8-2026

Embargo Date

8-31-2027

Document Type

Thesis

Degree Name

Master of Science

Department

College of Natural and Health Sciences, Chemistry and Biochemistry, Chemistry and Biochemistry Student Work

First Advisor

Murielle Watzky

First Committee Member

Aaron Apawu

Second Committee Member

Corina Brown

Abstract

Controlling nanoparticle nucleation, colloidal stability, and surface chemistry remains a significant challenge in the aqueous synthesis of plasmonic gold nanoparticles (AuNPs). This study aimed to develop a reproducible aqueous synthetic strategy for thioether-functionalized ionic liquid (IL)-stabilized gold nanoparticles (AuNPs) and to investigate the mechanistic role of transient Au(III)-thioether coordination in nanoparticle nucleation, growth, and colloidal stabilization to establish optimal synthesis conditions. Specifically, the study examined whether 2-(ethylmercapto)ethyltributylphosphonium chloride, a short alkyl-chained ionic liquid, could effectively stabilize AuNPs in aqueous media, how Au(III)-IL interactions influence nucleation and growth, and which reaction conditions result in a highly reproducible approach for producing these stable and low-polydispersity nanoparticles.

The ionic liquid was synthesized and characterized by 1H and 13C NMR spectroscopy. Two synthetic approaches were evaluated: post-synthetic ligand exchange on citrate-capped AuNPs and a bottom-up reduction of HAuCl4 with NaBH4 in the presence of the ionic liquid. Reaction conditions, including the Au:IL:NaBH4 molar ratio, temperature, reagent addition mode, and aging time, were systematically optimized. The resulting nanoparticles were characterized using UV–visible spectroscopy and dynamic light scattering.

Cyclic voltammetry revealed that transient Au(III)-thioether ionic liquid interaction modifies the redox behavior of the gold precursor, stabilizing Au(III) ions and regulating reduction kinetics prior to nanoparticle formation. The bottom-up approach outperformed ligand exchange, producing more reproducible nanoparticles with improved colloidal stability. Optimal synthesis conditions consisted of an Au:IL:NaBH4 molar ratio of 1:4:0.5, controlled dropwise addition of NaBH4, and an aging period of 48–72 h, resulting in stable localized surface plasmon resonance, lower polydispersity, and positive zeta potentials. In contrast, lower Au:IL ratios, higher NaBH4 concentrations, and rapid reagent addition produced broader plasmon bands, higher PDI values, and increased bulk gold formation.

Overall, this study demonstrates that transient Au(III)-thioether coordination is a key mechanistic factor governing nanoparticle nucleation, growth, and colloidal stabilization. The findings establish thioether-functionalized phosphonium ionic liquids as effective stabilizing ligands for the reproducible bottom-up synthesis of plasmonic AuNPs in aqueous media and providing mechanistic insight about the synthesis and a foundation for future applications in biosensing, bioimaging, drug delivery, and nanomaterials engineering.

Abstract Format

html

Keywords

Gold nanoparticles; thioether-functionalized ionic liquids; localized surface plasmon resonance; cyclic voltammetry; nanoparticle nucleation and growth; colloidal stabilization

Subject Categories

Inorganic Chemistry | Materials Chemistry | Physical Chemistry

Language

English

Extent

189 pages

Rights Statement

Copyright is held by the author.

Digital Origin

Born digital

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Available for download on Tuesday, August 31, 2027

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