Nanopore structure analysis of single wall carbon nanotube xerogels and cryogels

Abstract

We fabricated two types of single wall carbon nanotube (SWCNT) gels prepared by freeze-drying (cryogels) and air-drying (xerogels) from the dispersed SWCNT hydrogels. The comparative pore structure analysis using N2 adsorption at 77 K and H2O adsorption at 298 K was applied to these SWCNT gels. The N2 adsorption isotherms of both SWCNT gels have a steep initial uptake, low-pressure adsorption hysteresis and adsorption hysteresis above P/P0 = 0.9, indicating the presence of pore mouth structures in addition to micropores and mesopores. The mesoporosity of the SWCNT cryogels was about twice higher than that of the SWCNT xerogels, while their microporosities were similar. The H2O adsorption isotherms of both SWCNT gels differ from each other along the whole P/P0 range. The H2O adsorption isotherm of the SWCNT xerogels shows an explicit adsorption below P/P0 = 0.1 and marked low-pressure adsorption hysteresis; the pore mouth volume of the SWCNT xerogels from the initial uptake of H2O was nearly three times larger than that of the SWCNT cryogels. The H2O adsorption isotherms of our SWCNTs gels give similar micropore volumes, being by ≈ 40% larger than that of N2 adsorption isotherms. The excess micropore volume evaluated by H2O adsorption comes from the pore mouth structures in which N2 cannot access. This work demonstrates that H2O adsorption and N2 adsorption analysis are crucial for elucidation of the pore mouth structure.