UV–vis absorption spectroscopy of carbon nanotubes: Relationship between the π-electron plasmon and nanotube diameter

The position and intensity of the π plasmon absorbance of a series of single-walled and multi-walled carbon nanotubes has been systematically investigated for the first time using ultraviolet–visible (UV–vis) absorption spectroscopy. All nanotube samples obey the Lambert–Beer law and exhibit similar extinction coefficients (∼50 mL/mg cm) regardless of their structure or method of preparation. The absolute wavelength (energy) of the π plasmon absorbance has been shown to vary with nanotube diameter as Eπ = 4.80 + 0.70/(dNT)2. This empirical relationship when correlated with nanotube pyramidalisation angle can be used to estimate the energy range for the π plasmon in a single sheet of graphene to be 4.8–4.9 eV.