Novel method to evaluate the carbon network of single-walled carbon nanotubes by hydrogen physisorption

Physical and chemical properties of single-walled carbon nanotubes (SWCNTs) are sensitive to the defects in the tubular graphene. To date, however, the method to characterize the defect of SWCNTs has been limited to transmission electron microscopy (TEM) and atomic force microscopy (AFM), which can only be used to observe the local structure of SWCNTs. In an effort to explore the evaluation method of SWCNTs, physisorption of H₂ on high-quality SWCNTs was investigated by cryogenic thermal-desorption spectroscopy (cryo-TDS), which revealed particular sensitivity to the defects of SWCNTs. TDS showed a sharp desorption peak at 20 K (α) for as-purified SWCNTs, and additional desorption signals were observed at 27 and ∼24 K (β and γ) for air-oxidized SWCNTs. The α, β, and γ peaks were attributed to H2 at the groove site and interstitial channel of a SWCNT bundle and inside of SWCNT, respectively. The sharpness of the a peak and the ratio of α to βand γ were found to depend strongly on the sample preparation condition. With this cryo-TDS technique, the perfectibility of the carbon network of SWCNTs can be reliably and sensitively evaluated.