Date of Award

Summer 2025

Document Type

Open Access Thesis

Department

Chemistry and Biochemistry

First Advisor

Olja Simoska

Abstract

The growing global demand for energy, ongoing reliance on fossil fuels, and increasing water pollution from industrial and anthropogenic sources present significant environmental challenges. In response to these issues, renewable and sustainable energy sources offer substantial potential for reducing dependence on fossil fuels and ensuring access to clean water. Microbial electrochemical systems (MESs) have emerged as promising, eco-friendly solutions for energy-efficient wastewater treatment and bioremediation. A key challenge in MESs development is facilitating effective electron transfer between microorganisms and electrode surfaces. The first chapter of this thesis discusses the fundamentals of MES types, explains mechanisms of extracellular electron transfer, and explores microorganisms and electron mediators commonly used in MESs. The second chapter of this thesis presents a comprehensive review of soluble, redox-active quinones used as exogenous electron shuttles to help facilitate electron transfer from bacteria to electrode surfaces, providing insight on how mediator properties influence quinone-mediated bioelectrocatalytic performance. Specifically, this thesis examines a quinone-based mediator system for extracellular electron transfer (EET) in Escherichia coli during glucose metabolism. A library of 12 quinone redox mediators was evaluated through electrochemical measurements, revealing variations in mediated current densities based on mediator structure and concentration. Among the tested quinones, tetrahydroxy-1,4-benzoquinone produced the highest mediated current density of 11.7 ± 1.1 μA cm−2. Additional electrochemical characterization of quinone mediator reduction potentials in aqueous and aprotic media showed that redox properties in aqueous environments correlate with the observed mediated current densities in E. coli. These findings suggest that the critical electron transfer step occurs either within the bacterial cell or outside its membrane. This thesis offers valuable insights into the rational design of mediated bioelectrocatalytic systems, highlighting the importance of microorganism type, metabolic processes, and electrochemical mediator behavior in both aqueous and aprotic environments.

Rights

© 2025, Megan Danielle Whisonant

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