Quantitative analysis of dispersion and doping of individual carbon nanotubes in water based solutions using absorption and Raman spectroscopy

The concentration dependence of the dispersion of carbon nanotubes in water surfactant solution is monitored using absorption and Raman spectroscopy revealing a debundling below ~0.07 g/l. A quantitative analysis of the doping of individual carbon nanotubes in surfactant at this concentration is conducted by varying the pH from 1 to 13 and monitoring the Raman spectrum. Mixed Gaussian and Lorentzian line shapes were fitted to the radial breathing modes and using a simple protonation model, an equilibrium constant K_p was obtained for each RBM. The protonation rate was related to the optical band gap of the tubes and the number of protons acting per entity was also calculated.