Date of Award

Spring 2025

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

Gonghu Li

Second Advisor

Christopher Bauer

Third Advisor

Christine Caputo

Abstract

Solar fuel generation from photocatalytic carbon dioxide (CO2) reduction is a growing area of interest to mitigate global energy and climate crises. Graphitic carbon nitride (C3N4) is a light-absorbing semiconductor with a promising outlook for solar fuels, gaining popularity in recent years due to its low cost and appropriate band positions for many environmentally relevant reactions. The addition of atomically dispersed single atom catalysts (SACs) to semiconducting materials is a viable strategy for creating active sites to improve photocatalytic performance of the semiconductors studied. Designing C3N4 materials as a support for SACs with well-defined binding motifs and sufficiently high concentrations remains a challenge. In this thesis, modifications of C3N4 are investigated to improve their performance in photocatalytic CO2 reduction to carbon monoxide in the presence of cobalt SACs.In Chapter 2, C3N4 materials were modified via pre- and post-synthetic processes to investigate their surface area and how the materials respond to doping under different conditions. In Chapter 3, a series of functionalized dopants were used to modify C3N4 during its synthesis, and the use of dianhydride dopants was found to greatly enhance the photocatalytic performance of the cobalt SACs bound on C3N4 surfaces. Work done in Chapter 4 further investigated these dianhydride dopants by varying their size and π conjugation and studying their ability to modify the structural and electronic characteristics of the semiconductor. Studies included in Chapter 5 utilized the same dianhydrides to generate cobalt SAC binding sites in the form of polymeric phthalocyanine units that are then used as dopants in C3N4. These cobalt sites remained dispersed as single atoms after they were included in C3N4 and show improved activity in CO2 reduction. Research presented in Chapter 6 studied the combination of cobalt and magnesium SACs on C3N4, which successfully enhanced the CO2 reduction of these materials. Additionally, in situ X-ray absorption spectroscopy (XAS) was performed under photocatalytic CO2 reduction conditions to investigate structural changes during photochemical reactions. Finally, an examination of the binding environment of molecular cobalt catalysts deposited on C3N4 surfaces and their catalytic performance is presented in Chapter 7. Overall, this work outlines a careful approach to the design and study of photocatalysts to optimize performance by modifying structure. Each project outlines a particular variation of the C3N4 structure and analyzes surface and spectroscopic techniques, including XAS, to characterize the semiconductor itself and the SACs. This analysis works to connect those structural changes with the activity of those materials in photocatalysis.

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