Optical absorption response of chemically modified single-walled carbon nanotubes upon ultracentrifugation in various dispersants

Arc discharge single-walled carbon nanotubes (SWCNTs) were modified through different oxidative treatments and functionalization reactions. The modified SWCNT powders were dispersed in four different aqueous media and purified by ultracentrifugation. Extinction coefficients of the modified SWCNTs depended on the SWCNT type but did not depend on the dispersion medium. According to visible/near infrared spectroscopy, the purity of all the modified SWCNT dispersions substantially improved after ultracentrifugation; however, the spectrum profile, the degree of purity and the centrifugation yield were influenced by the SWCNT type, the surface functional groups and the dispersion medium. Semi-quantitative purity indexes calculated from optical absorption spectra were supported by transmission electron microscopy observations. Contents in metal impurities were analyzed by energy dispersive X-ray spectroscopy. SWCNT samples processed by oxidative acid treatments and ultracentrifugation showed metal contents of lower than 0.5 wt%.