Chaudhery Mustansar Hussain, Chutarat Saridara, and Somenath Mitra

pp. 505 - 511

Abstract

Micro-sorbent traps referred to as microtraps serve as integrated concentration-injection devices for continuous
monitoring in gas phase streams. The application of carbon nanotubes as unique sorbents for the fabrication of microtraps
for the nano-scale adsorption/desorption of volatile organic molecules is presented in this paper. The microtrap application
requires high adsorption capacity as well as easy desorbability; the latter being critical for injection mode of these integrated
devices. The micro-sorbent characteristics of single and multi-walled carbon nanotubes for gas phase adsorption/desorption
of several volatile organic compounds like DCM, ethanol and benzene etc. has been studied. The nonporous nature of carbon
nanotubes (CNTs) eliminates the mass transfer resistance related to diffusion into pore structures, thus allowing easy
desorbability. At the same time, their high aspect ratios lead to large breakthrough volumes. As compared to a commercial
sorbent carbopack^TM, the breakthrough volume was as much as an order of magnitude higher in the CNTs, while the higher
rate of desorption measured as the peak width at half height of the desorption band was found nearly eight times lower (i.e.,
0.26 seconds with SWNT and 1.89 seconds with carbopack^TM). The trapping and desorption characteristics of single and
multi walled nanotubes were found to be comparable. We also found that the presence of disordered carbon impurities,
which could be removed by controlled oxidative annealing, could greatly degrade the performance of CNTs. This research
has suggested that CNTs can be used in micro-sorbent traps and surprisingly enhance the efficiency of the integrated concentration-injection devices. Consequently, this will open the doors to the application of high-capacity, CNTs-based sorbents
as a better alternative to conventional sorbent in continuous monitoring devices.