Equilibration Time:  Kinetics of Gas Adsorption on Closed- and Open-Ended Single-Walled Carbon Nanotubes

Abstract

We have explored the adsorption kinetics of argon and methane on chemically opened and on as-produced carbon nanotubes. We monitored the evolution of the adsorbate pressure after each gas dose was added to the cell during the performance of adsorption isotherms. We found significant differences between the equilibration times measured on these two groups of nanotubes. We propose an explanation for our experimental observations that makes use of recent computer simulations conducted for similar adsorbed systems.

Carbon nanotubes as adsorbents in environmental pollution management: A review

“…The observed adsorption energies (E ads ) follow the order: E ads (channels) > E ads (grooves) > E ads (pores) > E ads (surfaces) [106]. For the adsorption on groove sites, the E ads values of methane were 4.37 kcal mol −1 [38,107] and 5.8 kcal mol −1 [50,108,109], whereas external E ads were determined to be 2.68 kcal mol −1 by Muris et al [38] and 2.5 kcal mol −1 by Talapatra and Migone [110]. Internal adsorption energy of methane for small diameter (0.7-1.1 nm) SWCNTs is 8.44 kcal mol −1 [81].…”

“…It is interesting to note that the adsorption reaches equilibrium much faster on external sites (grooves and outer surfaces) than on the internal sites (interstitial channels and inside the tube) under the same pressure and temperature conditions. The external sites are directly exposed to the adsorbing material; the adsorption process on internal sites has to be initiated on the ends of the pore, followed by diffusion to the sites at the interior [49,50]. Second, the fraction of opened and unblocked nanotubes can greatly influence the overall adsorption capacity.…”

Non-Monotonic Kinetics of Alkane Adsorption on Single-Walled Carbon Nanotubes

“…Specifically, we have determined how the time it takes for equilibrium to be reached after a dose of gas is added to the cell containing a substrate (i.e., the equilibration time) depends on sorbent loading and on the size of the molecules used in the adsorption process. 4,5 The substrate used in these measurements was bundles of close-ended single-walled carbon nanotubes. 6 The adsorbates utilized were a sequence of five alkane chains, from methane to pentane.…”

Effect of the adsorption of oxygen on electronic structures and geometrical parameters of armchair single-wall carbon nanotubes: A density functional study

“…For the (4,4), (5,5), (6, 6), (7,7), (8,8), (9,9), and (10, 10) tubes, different adsorption sites, O2-(4, 4) O2-(5, 5) O2- (6,6) O2-(7, 7) O2- (8,8) O2-(9, 9) O2-(10, 10) Here, h is the angle between the O-C dummy atoms. A dummy atom is located at the centre of the tubes (see Fig.…”

“…Carbon nanotubes (CNTs), seamlessly rolled-up graphene sheets of carbon, are one of the most promising molecular structures for a wide range of future technological innovations. CNTs, in particular, because of their size, large surface area, and hollow geometry, are being considered as prime materials for gas adsorption [4][5][6][7][8], containers for molecules [9][10][11], salts, and metals [12][13][14]; biological, chemical and electromechanical sensors [15,16]; nanoelectronic device; filled carbon nanotubes, used for magnetic recording, etc [17]. Band structure calculations carried out by different quantum mechanical and semi-empirical methods [18][19][20] have predicted that the electronic transport properties of SWCNTs are highly dependent on their helicity, and range from large band-gap semi-conducting to metallic.…”