Enhancement of H 2 and CH 4 adsorptivities of single wall carbon nanotubes produced by mixed acid treatment

Abstract

Single wall carbon nanotubes (SWCNTs) were treated with a HNO 3/H 2SO 4 mixed solution to increase the number of narrow micropores. The mixed acid treatment increased the micropore volume from 0.13 to 0.35 mL g −1 as measured by N 2 adsorption at 77 K. The micropore volume evaluated with CO 2 adsorption at 273 K increased from 0.06 to 0.27 mL g −1. This remarkable micropore volume increase was ascribed to the formation of a highly packed and ordered SWCNT assembly with the acid treatment, which was confirmed by field emission scanning electron microscopy. The adsorption amount of supercritical H 2 at 77 K under 5 MPa pressure increased twofold as a result of the acid treatment, while the supercritical CH 4 adsorption amount at 303 K and 5 MPa pressure increased by 40%. These remarkable increases were caused by increased amount of narrow micropores as a result of the acid treatment.