Fluorescence Labeling and Quantification of Oxygen-Containing Functionalities on the Surface of Single-Walled Carbon Nanotubes

Fluorescence labeling of surface species (FLOSS) was applied to identify and determine the concentration of oxygen-containing functionalities on single-walled carbon nanotubes (SWCNTs), subjected to two different purification processes (air/HCl and nitric acid treatments) and compared to as-received (nonpurified) SWCNTs. The fluorophores were selected for their ability to covalently bind, with high specificity, to specific types of functionalities (OH, COOH, and CHO). FLOSS revealed that even as-received SWCNTs are not pristine and contain similar to 0.6 atomic % oxygen functionalities. FLOSS showed that, after nitric acid treatment, SWCNTs are similar to 5 times more functionalized that SWCNTs after air/HCl purification (5 versus 1 atomic % oxygen functionalities), supporting the idea that the former purification process is more aggressive than the latter. FLOSS demonstrated that carbonyls are the major functionalities on nitric-acid-purified SWCNTs, suggesting that chemical derivatization strategies might consider exploiting aldehyde or ketone chemistry.