Date of Award

Fall 2025

Project Type

Thesis

Program or Major

Chemistry

Degree Name

Master of Science

First Advisor

Christine Caputo

Second Advisor

Roy Planalp

Third Advisor

Charles Zercher

Abstract

Exposure to ultraviolet radiation poses risks to human health while also damaging materials.Materials like plastics and wood experience degradation and discoloration when exposed to ultraviolet (UV) radiation, while humans can experience premature aging and wrinkling, skin cancer, and eye damage.1–4 Unfortunately, current UV protective materials in use today have several drawbacks including rapid degradation, toxicity and oxidative damage. These issues have made the development of non-toxic alternative UV filters highly sought after. Carbon dots are a group of carbon-based nanoparticles, first discovered in 2004 by Scrivens and coworkers while purifying single-walled nanotubes, then officially named in 2006. 5,6 Carbon dots are able to be made using a variety of methods beginning with either preexisting carbon materials or small compounds, polymers, or biomass which allows for sustainable precursors to be used. 7 Due to their eco friendliness, photostability, and versatility, carbon dots have become an area of significant interest in photocatalysis, sensors, biomedicine, and more recently, UV absorption for sunscreen applications. 8,9 Previous works have shown that carbon dots can serve as effective UV absorbers however the majority of these studies have used non-sustainable precursors, or even precursors with known toxicity. 10,10–13 Herein, carbon dots were prepared using sustainable precursors with either an aromatic structure or containing nitrogen atoms. Gallic acid, a naturally occurring polyphenol, was chosen to investigate aromatic character and carbon dots were formed at increasing temperatures to explore the impact of core conjugation of UV absorption. Chitosan, the second most abundant biopolymer on the planet, was chosen to explore nitrogen doping through the formation of two compositions of carbon dot-derived gels with different and nitrogen concentrations to compare their photophysical and materials properties. viii The effects of different solvents were investigated along with an attempt to modify the surface of those carbon dots to alter the solubility.14–16 Gallic acid-based carbon dots, were found to demonstrate solvent dependent fluorescence emission and absorbance profiles when solvent polarity and hydrogen bonding capabilities were altered. When solvent polarity decreased or hydrogen bonding increased, the absorbance spectrum experienced red shifting, and the emission spectrum experienced blue shifting. These carbon dots were heated in solution with chitosan to form amide bonds between the surface of the carbon dot and the chitosan framework. The reacted carbon dots were then extracted into an organic solvent and fluorescence was used to determine if hydrophobic carbon dots had been generated. We found that the surface modified carbon dots were partially soluble in organic nonpolar solvent, shown with the presence of fluorescence in the extracted organic solvent.

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