Evaluation of Carbonaceous Impurities in As-Produced Single-Walled Carbon Nanotubes by Solution-Phase Spectrophotometry

This paper will describe a practical procedure and a simple data analysis method for the evaluation of the carbonaceous impurities in the as-produced (AP) single-walled carbon nanotube (SWNT) samples. This procedure starts with dispersing an AP-SWNT sample in an aqueous surfactant by using a sonicator. Then the optical absorption spectrum of the suspension is measured in the visible and the near-infrared regions by using a spectrophotometer. This spectrum features the superposition of the structures originating from the inter-band transitions in the electronic density of states (DOS) of the SWNTs and the structures originating from the pi-plasmons in both SWNTs and carbonaceous impurities. With multiple AP-SWNT samples, the obtained optical absorption spectra are converted into a single plot that can directly indicate the relative levels of the carbonaceous impurities. In this approach, the discrepancy in the concentrations of the SWNT suspensions does not affect the evaluation