Date on Master's Thesis/Doctoral Dissertation

12-2023

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Degree Program

Chemistry, PhD

Committee Chair

Zamborini, Francis

Committee Member

Baldwin, Richard

Committee Member

Maurer, Muriel

Committee Member

Gupta, Gautam

Author's Keywords

Nucleation and growth; self assembled monolayers; single nanoparticle detection; electrophoretic deposition; redox reactions in hydrogel electrolytes; reactions in spatial confinement

Abstract

This dissertation investigates the electrochemical deposition (ECD) and electrophoretic deposition (EPD) processes involving citrate (cit)-stabilized Au nanoparticles (NPs) and calcium alginate (Ca-Alg-Au NP) hydrogel films. The first part of the dissertation investigates the influence of NP size, surface area (SA) coverage, and ligand stabilizers on the electrochemical growth of Au on Au NPs, aiming to enhance our understanding of the growth process during the nucleation and growth of metal NPs. The growth kinetics depend on Au NP size (4 nm > 15 nm > 50 nm) for a constant SA coverage, as determined by the overpotentials for ECD. The growth rate increases with increasing SA, showing reversible kinetics for all NP sizes above a threshold SA. In addition, alkanethiol self-assembled monolayers (SAM)-coated Au NPs show a decrease in growth kinetics as the SAM chain length increases while showing the same NP size dependence as cit Au NPs. Faster growth kinetics on Au NPs relative to glass/ITO allows for a two-step EPD/ECD amplification for electrochemical detection of fM solution concentrations of Au NPs by anodic stripping voltammetry (ASV). This approach is sensitive, simple, fast, low cost, and has the potential for automation and portability, making it promising for Au detection for mining, electronic waste, and bioassays. The second part of this dissertation explores the EPD of Ca-Alg and hybrid Ca-Alg-Au NP hydrogel films utilizing Au NP-catalyzed electrooxidation of hydroquinone (HQ). This approach induces a localized pH decrease at the electrode surface, facilitating Alg and Au NP deposition followed by Ca2+ gelation. The catalytic action of Au NPs reduces the EPD potential, presenting promising applications in sensors, biological studies, electrocatalysis, and energy-related research. Electrochemical understanding in Ca-Alg-Au NP films involves investigating the behavior of Fe(CN)63-/4- on Pt, Au, and glassy carbon electrodes coated with EPD-deposited Ca-Alg and Ca-Alg-Au NP hydrogel films. Reversible electrochemistry with decreased Fe(CN)63- diffusion follows an initial equilibration time. The amide-functionalized hydrogel impeded electrochemistry, likely due to hindered mass and ion transfer. Incorporating Au NPs initially enhances Fe(CN)63- redox activity but hampers it at higher loads, indicating a significant change in mass and ion transfer, likely altering hydrogel viscoelastic and fluid properties. Finally, EPD of Ca-Alg and Ca-Alg-Au NPs in pipette tips and Pt/Ir scanning tunneling microscopy (STM) tips enables electrochemical measurements (Fe(CN)63-, Au ECD, Au ASV, and Au NP EPD) in microscale hydrogel environments as small as 10 microns. Microscale electrochemistry differs significantly from bulk hydrogels, exhibiting reversible kinetics and the capability to form microscale metal patterns through ECD and EPD.

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