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Photochemistry of Aqueous C60 Clusters: Wavelength Dependency and Product Characterization
Hou, W. C., L. Kong, K. A. Wepasnick, R. G. ZEPP, D. H. Fairbrother, AND C. T. Jafvert. Photochemistry of Aqueous C60 Clusters: Wavelength Dependency and Product Characterization. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 44(21):8121-8127, (2010).
To construct accurate risk assessment models for engineered nanomaterials, there is urgent need for information on the reactivity (or conversely, persistence) and transformation pathways of these materials in the natural environment. As an important step toward addressing this issue, we have characterized the products formed when aqueous C60 clusters (nC60) are exposed to natural sunlight and also have assessed the wavelengths primarily responsible for phototransformation. Long-wavelength light isolated from sunlight, was shown to be important in both the phototransformation of nC60 and in the production of 1O2. The significance of visible light in mediating the phototransformation of nC60 was supported by additional experiments with monochromatic light in which the apparent quantum yield at 436 nm was comparable to that at 366 nm. LDI-TOF mass spectrometry indicated that most of the photoproducts formed after 947 h of irradiation in natural sunlight retain a 60 atom carbon structure. A combination of 13C NMR analysis of 13C-enriched nC60, X-ray photoelectron spectroscopy and FTIR indicated that photoproducts have olefinic carbon atoms as well as a variety of oxygen-containing functional groups, including vinyl ether and carbonyl or carboxyl groups, whose presence destroys the native π-electron system of C60. Thus, the photoreactivity of nC60 in sunlight leads to the formation of water-soluble C60 derivatives.