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Sunlight-induced Transformations of Graphene-based Nanomaterials in Aquatic Environments
Zepp, R., D. Bouchard, W. Hou, Chris Knightes, Matt Henderson, I. Chowdhury, C. Chen, H. Fairbrother, D. Goodwin, AND L. Kong. Sunlight-induced Transformations of Graphene-based Nanomaterials in Aquatic Environments. ACS National Meeting & Exposition, Boston, MA, August 17 - 20, 2015.
To be presented at the ACS Annual Meeting in Boston, MA.
Graphene-based nanomaterials and other related carbon nanomaterials (CNMs) can be released from products during their life cycles. Upon entry into aquatic environments, they are potentially transformed by photochemical reactions, oxidation reactions and biological processes, all of which affect their environmental transport. Release of CNMs from products such as plastic composites, as well as environmental transformation of the released CNMs, can be initiated by sunlight exposure. Direct and indirect processes are both competitively involved in the environmental phototransformation of CNMs. Like other CNMs, graphene oxide (GO) -- a promising precursor to graphene-based materials -- strongly absorbs sunlight in the ultraviolet and visible spectral regions, making direct photochemical reactions an important determinant of the persistence of these materials. In the case of GO in natural waters, direct photoreaction likely dominates the initial phototransformation of GO to form reduced graphene oxide species, LMW species and CO2; these photoproducts are significantly less photoreactive, however, and persist under direct photolysis conditions. Thus, indirect photolysis initiated by natural organic matter is likely to dominate the secondary phototransformation process, ultimately converting reduced graphene oxide and LMW species into CO2. During this mineralization process, the intermediate species exhibit decreasing size and higher carboxyl group concentrations, and greater stability against aggregation and reduced surface deposition, indicating they would be more mobile than parent GO. In this presentation, rates and mechanisms of these sunlight-induced transformations will be emphasized, and environmental modeling implications of these interesting processes will be discussed.