Single and multi-walled carbon nanotubes as sorbents for air monitoring

Carbon nanotubes (CNTs) possess some highly desirable sorbent characteristics, which makes them attractive for a variety of applications including micro-scale preconcentration of organics. The main advantage of CNTs is that their high aspect ratio leads to large specific capacity. At the same time, unlike conventional carbon based sorbents, they are non-porous tubular structures, thus eliminating the mass transfer resistance related to diffusion into pores. In this paper we present sorption characteristics of select organics on single (SWNT) and multi-walled (MWNT) carbon nanotubes packed and self-assembled onto micro-sorbent traps. The data demonstrates that adsorption as well as desorption are highly favorable on the CNTs. The former is characterized by relatively large breakthrough volumes and isosteric heats of adsorption (AH_s close to 64 kJ/mole), while rapid recovery was demonstrated by narrow desorption band widths. The elimination of nontubular carbonaceous impurities from the CNT surface was important, because they reduced the performance of these sorbents. The sorption/desorption characteristics of the SWNT and the MWNT were quite similar and significantly better than a commercial sorbent studied here.