Date on Master's Thesis/Doctoral Dissertation

5-2019

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Degree Program

Chemistry, PhD

Committee Chair

Zamborini, Francis

Committee Co-Chair (if applicable)

Baldwin, Richard

Committee Member

Baldwin, Richard

Committee Member

Grapperhaus, Craig

Committee Member

Sumanasekera, Gamini

Author's Keywords

nanoparticles; oxidation potential; hydroquinone; aggregation

Abstract

This dissertation describes how anodic stripping voltammetry (ASV) was used to study size-controlled electrophoretic deposition (EPD) and the aggregation-dependent oxidation properties of citrate-stabilized Au nanoparticles (NPs). EPD of citrate-coated Au NPs occurs in the presence of hydroquinone (HQ) onto indium-tin-oxide-coated glass electrodes (glass/ITO) at potentials positive of the HQ oxidation potential. HQ oxidation produces protons at the electrode surface, which serve to neutralize the citrate molecules that electrostatically stabilize the Au NPs. Neutralization leads to the loss of stabilization and deposition onto the electrode. EPD in the presence of ferrocyanide, a non-proton-producing molecule, at oxidation potentials resulted in no deposition of Au NPs, confirming the proton neutralization deposition mechanism. ASV provides information about the aggregation-dependent oxidation of 4 nm, 15 nm, and 50 nm diameter citrate-coated Au NPs. The oxidation potential for well-separated NPs decreases with decreasing size in the order 4 nm < 15 nm < 50 nm. As the 4 nm and 15 nm diameter Au NPs aggregate by decreasing the solution pH, their oxidation potential increases towards that of the 50 nm diameter Au NPs. The shift is due to a decrease in the surface area-to-volume ratio (SA/V) of the NPs upon aggregation. The positive shift depends on aggregate size, and the total positive shift is larger for 4 nm diameter compared to 15 nm diameter Au NPs.

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