Information regarding possible transformation pathways of carbon nanotube in the environment is required in order to evaluate environmental and health consequences of these materials. Photochemical processes investigated include both direct and indirect photochemical reactions under solar spectrum light. Unfunctionalized single walled carbon nanotubes (SWCNTs) are much less reactive under sunlight than functionalized SWCNTs. As a result, indirect photochemical reactions of these materials has been investigated. It is well known that very low (� 10-15 M) concentrations of hydroxyl radicals occur in many natural waters due to photochemical reactions involving humic acids. As a result, solar irradiation has been used to generate a low steady-state concentrations of hydroxyl radicals (from H2O2) to study indirect photochemical reactions of unfunctionalized SWCNTs in water. Unfunctionalized SWCNTs containing a high fraction of semiconducting (6, 5 chirality) tubes (SG65 from SouthWest Nano Technologies) were dispersed in aqueous solutions containing sodium dodecyl sulfate (SDS) and H2O2, and exposed to light (300-410 nm). Upon irradiation, the ultraviolet and visible absorbance of the solutions decreased, an increase in the Raman I(D) band relative to the I(G) band occurred, and the near infrared fluorescence decreased, all indications that photo-chemical transformation of the unfunctionalized nanotubes occurred. Additional experiments in the absence of the surfactant with added H2O2 also showed a decrease in the fluorescence signals after 68 and 93 days. X-ray photoelectron spectroscopy (XPS) analysis on the same SG65 samples without added surfactant shows an increase in total oxygen to 16.5% from 4.4% in the as-received sample. In aqueous suspensions of carboxylated single walled carbon nanotubes, there is evidence that the reactive oxygen species (ROS) singlet oxygen (1O2), superoxide anion (O2-�), and �OH occur upon irradiation with light within the solar spectrum. Therefore, direct photochemical reactions of these functionalized SWCNTs have been investigating. The Raman I(D) band initially decreased relative to the I(G) band during the first 5 days of irradiation under lamps that emit light in the solar spectrum (300-410 nm), followed by an increase in the I(D)/I(G) ratio for the next 33 days. Potential mineralization and changes in surface functional group composition of some carboxylated carbon nanotubes are currently under investigation.

Photochemical fate of single-walled carbon nanotubes in the aquatic environment

248th National Meeting (2014)

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