Supercritical Hydrogen Adsorption of Ultramicropore-Enriched Single-Wall Carbon\nNanotube Sheet

Abstract

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