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Probing Photosensitization by Functionalized Carbon Nanotubes
Chen, C. AND R. Zepp. Probing Photosensitization by Functionalized Carbon Nanotubes. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 49(23):13835-13843, (2015).
Published in Environmental Science and Technology.
Carbon nanotubes (CNTs) photosensitize the production of reactive oxygen species that can damage organisms by biomembrane oxidation or mediate CNTs' environmental transformations. The photosensitized nature of derivatized carbon nanotubes from various synthetic methods, and thus with different intrinsic characteristics, has been investigated under sunlight exposure in environmentally- relevant aquatic conditions. We used the CNT-sensitized photoisomerization of sorbic acid (trans, trans- hexadienoic acid) and singlet oxygen formation to quantify the triplet states ecNT*) formed upon irradiation of selected single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs). The CNTs used in our studies were derivatized by carboxyl groups to facilitate their dispersion in water. Distinct photoreactivity was observed in four tested CNTs, correlating to intrinsic characteristics (e.g., diameter and electronic properties), solution chemistry (e.g., ionic strength) and colloidal stability. Results suggest that well-stabilized, small-diameter, semiconducting-rich CNTs correspond to higher-measured, excited triplet state formation and therefore 10 2 yield. Derivatized SWCNTs were significantly more photoreactive than derivatized MWCNTs. Moreover, addition of sodium chloride resulted in increased aggregation and small increases in singlet oxygen production of CNTs. The most photoreactive CNTs exhibited comparable photoreactivity (in terms of 3CNT* formation and 10 2 yield) to reference natural organic matter with the same mass-based concentration. Selected reference NOM could therefore be a useful indicator for evaluating CNTs' environmental photoreactivity or intended antibacterial applications.