Date of Graduation

Fall 2022

Degree

Master of Science in Chemistry

Department

Chemistry and Biochemistry

Committee Chair

Adam Wanekaya

Abstract

Carbon dots (CDs) are a subclass of carbon nanomaterials that exhibit unique properties of fluorescence, photostability, low toxicity, and biocompatibility. These unique properties have enabled numerous applications including biosensing, heavy-metal detection, and pH-sensing, among others. Their optical properties can be modified via doping to produce increasingly fluorescent CDs after appropriate purification. Herein, doped CDs were synthesized in four bottom-up methods for comparison using sucrose or citric acid as carbon precursors. Varying hetero-atom dopants (N, S, B) were used in differing molar ratios. The pH-dependent fluorescence and fluorescent quantum yield (QY) were measured for each sample. Characterization was conducted using Fourier-Transform Infrared Spectroscopy (FT-IR) for functional group identification, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) for sizing, and Ultraviolet-visible Spectroscopy (UV-vis) and fluorescence spectroscopy for optical properties. The digestive microwave method was determined to be the best performing, with nitrogen as the hetero-atom dopant which produced the highest fluorescing CDs. All nitrogen-doped carbon dots (NCDs) demonstrated pH-dependent fluorescence with increased fluorescence from pH 7-13. Overall, citric acid-based nitrogen-doped carbon dots (NCD-ca) with a carbon-to-dopant molar ratio of 1:6 demonstrated the highest QY of 19% in pH 11. Therefore, NCDs, as prepared, may serve as cost-effective fluorescent pH sensors.

Keywords

carbon dots, doping, nanoparticles, pH-sensing, fluorescence, nanomaterials, quantum yield

Subject Categories

Analytical Chemistry

Copyright

© Megan B. Prado

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