Date of Award
Master of Science (MS)
Transformation of water-stable C60 clusters (nC60) to oxidized, soluble C60 derivatives via photoreactions (i.e., reactions in UV irradiation) and ground-state reactions (i.e., reactions in dark) with various oxidants, such as oxygen, ozone, free chlorine, among others, have been described as critical processes in understanding the ultimate environmental fate of fullerene-based materials. However, few studies have explored the oxidation of aqueous based C60 (as water stable nC60) with hydrogen peroxide (H2O2) / hydroxyl radical (.OH), which are common oxidants in both natural and engineered systems. Herein, the aqueous physicochemical transformations of C60 (as nC60 aggregates) in the presence of H2O2 / OH in both photo-excited state and ground state under environmentally relevant conditions are explored and described. Results show that nC60 undergoes facile oxidation in the presence of H2O2 under both UV irradiation and dark, and the oxidation reaction rates increase with H2O2 concentration, while being inversely related to solution pH. Further, Significant enhancement of nC60 transformation was observed under UV photo-irradiation. Resulting product characterization by DLS, FTIR, XPS, and TOC are described and collectively demonstrate that oxidized C60 derivatives (with addition of covalent oxygen functionality), are readily formed in the presence of H2O2 / OH. Increased hydrophilicity of products, as expected with increased (surface) oxidation, was quantified through classic octanol-water partition experiments (Kow). Taken together, this work emphasizes the significance of fundamentally understanding nanomaterial reactivity and identification of corresponding daughter products (and behaviors), as they are key for accurate material lifecycle assessments.
John Fortner, Marcus Foston, Brent Williams.