Date of Award

Summer 8-2022

Level of Access Assigned by Author

Open-Access Thesis

Language

English

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor

Mitchell R. M. Bruce

Second Committee Member

Alice E. Bruce

Third Committee Member

Carl P. Tripp

Additional Committee Members

Brian G. Frederick

Ahmed A. Mohamed

Abstract

Gold nanoparticles have been used in environmental remediation as catalysts through biological and chemical redox reactions of many types of industrial waste including nitroarenes, organic dyes, carbon monoxide, and others. These reactions occur in harsh environmental conditions (e.g. changing temperature, presence of salts, extreme pH solutions) which require robust nanoparticles that can keep their activity and resist aggregation. This thesis describes the synthesis, characterization, and investigation of the catalytic activity of gold-aryl nanoparticles. Gold–aryl nanoparticles (AuNPs-COOH) fabricated using a mild reduction process of a molecular aryldiazonium gold(III) salt [HOOC-4-C6H4N≡N]AuCl4 showed high stability in the presence of high ionic strength salt, acidic and basic pH values, commercial buffer solutions, and moderate temperature range (20-90 °C). In addition, AuNPs-COOH showed resistance for ligand exchange of the aryl organic shell on the gold core surface with alkane thiols. The

catalytic activity of the AuNPs-COOH was investigated by using two model reduction reactions. First, the reduction of 4-nitrophenol (4-NPh) with sodium borohydride was studied. AuNPs- COOH showed high catalytic activity (apparent rate constant, kapp = 2.26 x 10-2 s-1) and a relatively low Ea (25 kJ mol−1) compared to reported literature values of other gold nanomaterials systems. The second model reaction was the reduction of ferricyanide with sodium borohydride or sodium thiosulfate catalyzed with AuNPs-COOH. In the presence of AuNPs-COOH as a catalyst, the apparent rate constant of the reduction reaction with sodium borohydride is kapp = 0.142 s-1, and with sodium thiosulfate kapp = 0.045 min-1. The catalytic reduction of ferricyanide showed decreased Ea in both reducing agent systems (20 kJ mol-1 and 24 kJ mol-1 for NaBH4 and Na2S2O3, respectively) compared with the reported uncatalyzed reactions (30 kJ mol-1 and 38 kJ mol-1, respectively). AuNPs-COOH showed an increase in kapp value through a multicycles reduction experiment in the Na2S2O3 system with the formation of a gold-Prussian blue analog at the end.

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