Supercritical Hydrogen Adsorption of Ultramicropore-Enriched Single-Wall Carbon Nanotube Sheet

Abstract

Ultramicropore-enriched single-wall carbon nanotube (SWCNT) sheet was prepared by a filtration process after acid treatment using HNO3/H2SO4 solution. Field emission scanning electron microscopic observation showed that a highly dense entangled structure of SWCNT bundles was formed by acid treatment. The pore structure of the SWCNT sheet was evaluated from adsorption isotherms of N2 at 77 K and CO2 at 273 K. The SWCNT sheet gave remarkably developed uniform ultramicroporosity and reduced mesoporosity through formation of the highly packed sheet. The acid treatment remarkably increased the adsorption amount of supercritical hydrogen at 77 K by about three times. The enhancement of hydrogen adsorption by acid treatment came mainly from the increase in the ultramicropores because the increase in isosteric heat of hydrogen adsorption by acid treatment was only 0.1−0.2 kJ mol-1.