Experimental and Theoretical Comparison of Gas Desorption Energies on Metallic and Semiconducting Single-Walled Carbon Nanotubes

Abstract

Single-walled carbon nanotubes (SWNTs) exhibit high surface areas and precisely defined pores, making them potentially useful materials for gas adsorption and purification. A thorough understanding of the interactions between adsorbates and SWNTs is therefore critical to predicting adsorption isotherms and selectivities. Metallic (M-) and semiconducting (S-) SWNTs have extremely different polarizabilities that might be expected to significantly affect the adsorption energies of molecules. We experimentally and theoretically show that this expectation is contradicted, for both a long chain molecule (n-heptane) and atoms (Ar, Kr, and Xe). Temperature-programmed desorption experiments are combined with van der Waals corrected density functional theory, examining adsorption on interior and exterior sites of the SWNTs. Our calculations show a clear dependence of the adsorption energy on nanotube diameter but not on whether the tubes are conducting or insulating. We find no significant experimental or theoretical difference in adsorption energies for molecules adsorbed on M- and S-SWNTs having the same diameter. Hence, we conclude that the differences in polarizabilities between M- and S-SWNTs have a negligible influence on gas adsorption for spherical molecules as well as for highly anisotropic molecules such as n-heptane. We expect this conclusion to apply to all types of adsorbed molecules where van der Waals interactions govern the molecular interaction with the SWNT.

Carbon nanotubes allow capture of krypton, barium and lead for multichannel biological X-ray fluorescence imaging

“…Although Kr can potentially condense inside open CNTs at temperatures <200 K (refs 24, 25), there are no reports of irreversible encapsulation. The SWCNTs were sealed into an silica ampoule under approximately atmospheric pressure of Kr, and then heated to 700 °C, before cooling slowly to permit closing of the open nanotube ends9.…”

Metal-free ferromagnetic metal and intrinsic spin semiconductor: two different kinds of SWCNT functionalized BN nanoribbons

“…8,9 In addition, due to the chemical activity of the graphene nanoribbon edges, [10][11][12] their electronic and magnetic properties can be modified by the termination and passivation of the edges. 18 On the other hand, SWCNTs can be considered to be rolled from graphene, [19][20][21][22] and thus, the geometric structure of a SWCNT can be described by its chiral indices (m,l) that define its perimeter vector (chiral vector) One of the most striking characteristics of SWCNTs is that their intrinsic electrical properties depend on the chiral indices (m,l), namely when m = l or m À l is divisible by 3, (m,l)SWCNTs belong to the nonmagnetic metals, otherwise they are nonmagnetic semiconductors, except the extremely small diameter SWCNTs which are all metallic. 18 On the other hand, SWCNTs can be considered to be rolled from graphene, [19][20][21][22] and thus, the geometric structure of a SWCNT can be described by its chiral indices (m,l) that define its perimeter vector (chiral vector) One of the most striking characteristics of SWCNTs is that their intrinsic electrical properties depend on the chiral indices (m,l), namely when m = l or m À l is divisible by 3, (m,l)SWCNTs belong to the nonmagnetic metals, otherwise they are nonmagnetic semiconductors, except the extremely small diameter SWCNTs which are all metallic.…”

“…[13][14][15][16][17] Recently, Tang et al have studied semiconductorhalf-metal transition in zigzag edge graphene nanoribbons supported on hybrid fluorographene-graphane nanoribbons. 19,20 Due to their fascinating thermal, mechanical, chemical, and electrical and magnetic properties, [22][23][24][25][26][27][28][29][30][31][32][33][34] SWCNTs have been applied to a wide range of scientific and technological fields, such as, chemical and biological sensors, [23][24][25][26][27] gas purification and adsorption, 22 scanning probe microscopy tips, 30 as well as photo electronic devices [31][32][33] etc. 19,20 Due to their fascinating thermal, mechanical, chemical, and electrical and magnetic properties, [22][23][24][25][26][27][28][29][30][31][32][33][34] SWCNTs have been applied to a wide range of scientific and technological fields, such as, ...…”

Semiconductor with intrinsic spin: a hybrid structure of zigzag edge graphene nanoribbon/single‐walled carbon nanotube

“…On the other hand, single‐walled carbon nanotubes (SWCNTs), which can be considered to be rolled from GNRs 16, can be either semiconducting or metallic, depending on their chiral indices, ( m , l ), which equivalently are identified by the tube diameter. Namely ( m , m )SWCNTs are metals, while ( m , l )SWCNTs with m ≠ l are semiconductors 17. Now they have been proposed for a wide range of scientific and technology applications, such as gas adsorption and purification 17, chemical sensors 18–22, hydrogen storage 23, 24, scanning probe microscopy tips 25, cathode field emitters 26, and electronic devices 27, 28.…”

“…Namely ( m , m )SWCNTs are metals, while ( m , l )SWCNTs with m ≠ l are semiconductors 17. Now they have been proposed for a wide range of scientific and technology applications, such as gas adsorption and purification 17, chemical sensors 18–22, hydrogen storage 23, 24, scanning probe microscopy tips 25, cathode field emitters 26, and electronic devices 27, 28. Moreover, SWCNTs are well‐known for their extremely high flexural rigidity 29.…”