Adsorption behaviors of HiPco single-walled carbon nanotube aggregates for alcohol vapors

HiPco single-walled carbon nanotubes (HPNTs) containing Fe were purified by a one-step process with HCl-washing (D-method) and a two-step process with HCl-washing after air oxidation (GD-method). The HPNT samples before and after purification were characterized using the N-2 adsorption at 77 K, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The TGA results showed a decreased Fe content after purification. In addition, the XPS results provided evidence that oxygen-based functional groups were introduced to the nanotube surface by both purification methods. The purification treatments also altered the N2 adsorption isotherms from type II to type IV; this accompanied the development of microporosity. Thus, purification considerably affects the surface chemistry and pore structures of HPNT aggregates. The effects of purification on the adsorption properties of HPNT aggregates with regard to CH3OH and C2H5OH vapors were examined at 303 K. The purification greatly enhanced the adsorptivity for CH3OH and C2H5OH vapors at 303 K under a low relative pressure. We associated this with the enhanced microporosity and the oxygen-based functional groups introduced on the surface.