title: Probing Photosensitization by Functionalized Carbon Nanotubes.
abstract: Carbon nanotubes (CNTs) photosensitize the production of reactive oxygen species that may damage organisms by biomembrane oxidation or mediate environmental transformations of CNTs. Photosensitization by derivatized carbon nanotubes from various synthetic methods, and thus with different intrinsic characteristics (e.g., diameter and electronic properties), has been investigated under environmentally relevant aquatic conditions. We used the CNT-sensitized photoisomerization of sorbic acid ((2E,4E)-hexa-2,4-dienoic acid) and singlet oxygen formation to quantify the triplet states ((3)CNT*) 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. Results indicate that high-defect-density (thus well-stabilized), small-diameter, and semiconducting-rich CNTs have higher-measured excited triplet state formation and therefore singlet oxygen ((1)O2) yield. Derivatized SWCNTs were significantly more photoreactive than derivatized MWCNTs. Moreover, addition of sodium chloride resulted in increased aggregation and small increases in (1)O2 production of CNTs. The most photoreactive CNTs exhibited comparable photoreactivity (in terms of (3)CNT* formation and (1)O2 yield) to reference natural organic matter (NOM) under sunlight irradiation with the same mass-based concentration. Selected reference NOM could therefore be useful in evaluating environmental photoreactivity or intended antibacterial applications of CNTs.
authors.affiliation: National Research Council Associate, National Exposure Research Laboratory, Ecosystems Research Division, United States Environmental Protection Agency , Athens, Georgia 30605, United States.|Department of Environmental Engineering, National Chung Hsing University , Taichung City 402, Taiwan.
authors.forename: Chia-Ying
authors.initials: CY
authors.lastname: Chen
authors.affiliation: National Exposure Research Laboratory, Ecosystems Research Division, United States Environmental Protection Agency , Athens, Georgia 30605, United States.
authors.forename: Richard G
authors.initials: RG
authors.lastname: Zepp
mesh_terms: D000067493:Dynamic Light Scattering; D005663:Furans / Q000737:chemistry; D037742:Nanotubes, Carbon / Q000737:chemistry*; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D017382:Reactive Oxygen Species / Q000737:chemistry; D026082:Singlet Oxygen / Q000737:chemistry; D013011:Sorbic Acid / Q000737:chemistry; D013472:Sunlight; D014867:Water; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D005663:Furans; D037742:Nanotubes, Carbon; D017382:Reactive Oxygen Species; D014874:Water Pollutants, Chemical; D014867:Water; D026082:Singlet Oxygen; C012986:furfuryl alcohol; D013011:Sorbic Acid