Photoenhanced oxidation of nC60 in water: Exploring H2O2 and hydroxyl radical based reactions

Abstract

The transformations of water-stable C60 clusters (nC60) to oxidized C60 derivatives via photoreactions and ground-state reactions have been described as critical processes in understanding the ultimate environmental fate of fullerene-based materials. However, (photo)oxidation of aqueous-based C60 (as water stable, nanoscale aggregates termed nC60) with hydrogen peroxide (H2O2) and/or hydroxyl radical (OH), common environmental oxidants, has not been fully explored. To address this, the aqueous physicochemical transformations of C60 (as nC60 aggregates) in the presence of H2O2 and/or OH in both photoexcited-state and ground-state under environmentally relevant conditions are quantitatively described. Results show that nC60 undergoes facile oxidation in the presence of H2O2 under UVA irradiation but not under dark conditions, and the oxidation reaction rates increase with effective OH concentration (via photodecomposition of H2O2), while being inversely related to solution pH. Product characterization via dynamic light scattering, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, total organic carbon, high-performance liquid chromatography, and octanol-water partition experiments collectively describe resulting C60 derivatives with new covalent oxygen functionality which are also relatively more hydrophilic. For all cases, photoirradiation was observed to significantly enhanced the rates and extent of C60 oxidation.