Shape versus inverse-shape selective adsorption of alkane isomers in carbon nanotubes.
Simulation results are reported for the adsorption of pure pentane (C5) isomers and their ternary mixture in a series of open-ended armchair-type (m,m) single-walled carbon nanotubes (SWNTs). Inverse-shape selective adsorption occurs in the order of nC5<iC5<neoC5 only in the (7,7) SWNT as a result of the length entropy effect. In the larger (20,20) and (10,10) SWNTs, shape selective adsorption occurs in the order of nC5>or=iC5>neoC5 as a result of the configurational entropy effect. In smaller SWNTs, depending on the diameter, only nC5 adsorbs, or no adsorption at all occurs. The entropy effects are found to lead to a large adsorptive separation among the C5 isomers from their mixture. Using the ideal-adsorbed-solution theory with data on the adsorption of only the pure isomers, we predict mixture adsorption. The agreement between predictions and simulations deteriorates with decreasing diameter of the SWNT.
Jiang
Jianwen
J
Center for Molecular and Engineering Thermodynamics, Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716, USA. jiangj@che.udel.edu
Sandler
Stanley I
SI