Water Adsorption Behavior on a Highly Dense Single-Walled Carbon Nanotube Film with an Enhanced Interstitial Space

In this study, we describe the adsorption behavior of water (H₂O) in the interstitial space of single-walled carbon nanotubes (SWCNTs). A highly dense SWCNT (HD-SWCNT) film with a remarkably enhanced interstitial space was fabricated through mild HNO₃/H₂SO₄ treatment. The N₂, CO₂, and H₂ adsorption isotherm results indicated remarkably developed micropore volumes (from 0.10 to 0.40 mL g^-1) and narrower micropore widths (from 1.5 to 0.9 nm) following mild HNO₃/H₂SO₄ treatment, suggesting that the interstitial space was increased from the initial densely-packed network assembly structure of the SWCNTs. The H₂O adsorption isotherm of the HD-SWCNT film at 303 K showed an increase in H₂O adsorption (i.e., by ∼170%), which increased rapidly from the critical value of relative pressure (i.e., 0.3). Despite the remarkably enhanced adsorption capacity of H₂O, the rates of H₂O adsorption and desorption in the interstitial space did not change. This result shows an adsorption behavior different from that of the fast transport of H₂O molecules in the internal space of the SWCNTs. In addition, the adsorption capacities of N₂, CO₂, H₂, and H₂O molecules in the interstitial space of the HD-SWCNT film showed a linear relationship with the kinetic diameter, indicating an adsorption behavior that is highly dependent on the kinetic diameter.