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Roles of Direct and Indirect Light-Induced Transformations of Carbon Nanomaterials in Exposures in Aquatic Systems
Citation:
Zepp, R., D. Bouchard, W. Hou, C. Chen, B. Acrey, X. Chang, Matt Henderson, S. Martin, AND Chris Knightes. Roles of Direct and Indirect Light-Induced Transformations of Carbon Nanomaterials in Exposures in Aquatic Systems. SETAC North America 37th Annual Meeting, Orlando, FL, November 06 - 10, 2016.
Impact/Purpose:
Presented at SETAC North America 2016, Orlando, FL, November, 2016
Description:
Carbon nanomaterials (CNMs) such as fullerenes, carbon nanotubes and graphene-based nanomaterials have a variety of useful characteristics such as extraordinary electron and heat conducting abilities, optical absorption and mechanical properties, and potential applications in transistors and polymer nanocomposites. CNMs often are used in consumer and industrial products as composites with other materials such as polymers. The release of CNMs such as multiwalled carbon nanotubes (MWCNT) from the composites is stimulated by weathering induced by light exposure. Release can be followed by using ICP-MS to measure metal residues that are associated with the nanotubes, by UV-visible techniques or by TEM images of particles that can be leached from the weathered surfaces. In most cases the released CNMs are associated with fragments of the polymer matrix. Little is known about the fate of these unusual CNT-containing fragments but recent studies of microplastic residues in lakes and the ocean suggest that they may accumulate in aquatic organisms. Other studies haveshown that rapid sunlight absorption by CNMs such as graphene oxide and carboxylated nanotubes leads to rapid conversions to carbon dioxide and persistent, low-molecular weight photoproducts. Indirect pathways also are available for light-induced transformations of CNMs in natural waters. The indirect pathways are driven by reactive transients such ashydroxyl radicals that are produced by photoreactions of natural organic matter (NOM) and inorganic species such as nitrate, metals and peroxides. The objectives of this presentation are to compare both direct and indirect photochemical pathways for selected CNM transformations driven by sunlight exposure, focusing on structural changes and other factors that influence exposure to the CNMs and their photoproducts in natural waters. We will emphasize carbon nanotubes and graphene oxide in the presentation. Another objective is to define relationships and data that can be used to predictively model effects of CNMs on sunlight-induced photoproduction of reactive transients such as excited triplet states and reactive oxygen species that mediate toxic effects of CNMs and their photoproducts.
