TY - JOUR
T1 - Adsorption of light alkanes and alkenes onto single-walled carbon nanotube bundles: Langmuirian analysis and molecular simulations
AU - Cruz, Fernando J. A. L.
AU - Esteves, Isabel A.A.C.
AU - Mota, José P. B.
N1 - F.J.A.L. Cruz and I.A.A.C. Esteves gratefully acknowledge financial support from F.C.T./M.C.T.E.S. (Portugal) through grants SFRH/BPD/45064/2008 and SFRH/BPD/14910/2004.
PY - 2010/3/20
Y1 - 2010/3/20
N2 - Grand canonical Monte Carlo (GCMC) simulations are employed to study the adsorption equilibrium properties of methane, ethane, ethylene, propane, and propylene onto homogeneous bundles of single-walled carbon nanotubes, at room temperature, from 10-4 bar up to 90% vapor pressure. Individual adsorption isotherms for the internal volume of a bundle and for its external adsorption sites are separately calculated for individual nanotube diameters in the range 11.0 Å ≤ D ≤ 18.1 Å. External adsorption is further decomposed into the contributions from its two main adsorption sites - external grooves and exposed surfaces of the peripheral tubes - based on a geometrical model for the average groove volume that takes into account the molecular nature of the adsorbate. Both intrabundle confinement and adsorption onto the grooves lead to type I isotherms, which are modeled with Langmuirian-type equations. Adsorption on the exposed surfaces of the peripheral tubes in a bundle gives rise to a type II isotherm, which is described by the BET model with a finite number of adsorbed layers. The linear combination of the Langmuir isotherm model for adsorption onto groove sites and the BET isotherm model produces a composite isotherm that is in good agreement with the GCMC isotherm for overall adsorption onto the external sites of a bundle. The influence of adsorbate molecular length and existence of an unsaturated chemical bond in its molecular skeleton are studied by monitoring the dependence of the Henry constant and zero-coverage isosteric heat of adsorption with the dispersive energy for the solid-fluid pair potential of each adsorbate. Our results show that the adsorptive properties are especially influenced by the presence of a double bond in the case of small molecules, such as the ethane/ethylene pair.
AB - Grand canonical Monte Carlo (GCMC) simulations are employed to study the adsorption equilibrium properties of methane, ethane, ethylene, propane, and propylene onto homogeneous bundles of single-walled carbon nanotubes, at room temperature, from 10-4 bar up to 90% vapor pressure. Individual adsorption isotherms for the internal volume of a bundle and for its external adsorption sites are separately calculated for individual nanotube diameters in the range 11.0 Å ≤ D ≤ 18.1 Å. External adsorption is further decomposed into the contributions from its two main adsorption sites - external grooves and exposed surfaces of the peripheral tubes - based on a geometrical model for the average groove volume that takes into account the molecular nature of the adsorbate. Both intrabundle confinement and adsorption onto the grooves lead to type I isotherms, which are modeled with Langmuirian-type equations. Adsorption on the exposed surfaces of the peripheral tubes in a bundle gives rise to a type II isotherm, which is described by the BET model with a finite number of adsorbed layers. The linear combination of the Langmuir isotherm model for adsorption onto groove sites and the BET isotherm model produces a composite isotherm that is in good agreement with the GCMC isotherm for overall adsorption onto the external sites of a bundle. The influence of adsorbate molecular length and existence of an unsaturated chemical bond in its molecular skeleton are studied by monitoring the dependence of the Henry constant and zero-coverage isosteric heat of adsorption with the dispersive energy for the solid-fluid pair potential of each adsorbate. Our results show that the adsorptive properties are especially influenced by the presence of a double bond in the case of small molecules, such as the ethane/ethylene pair.
KW - Adsorption
KW - Alkanes
KW - Alkenes
KW - Henry constant
KW - Molecular simulation
KW - Single-walled carbon nanotubes
UR - http://www.scopus.com/inward/record.url?scp=77049113746&partnerID=8YFLogxK
U2 - 10.1016/j.colsurfa.2009.09.002
DO - 10.1016/j.colsurfa.2009.09.002
M3 - Article
AN - SCOPUS:77049113746
SN - 0927-7757
VL - 357
SP - 43
EP - 52
JO - Colloids and Surfaces A: Physicochemical and Engineering Aspects
JF - Colloids and Surfaces A: Physicochemical and Engineering Aspects
IS - 1-3
ER -