title: Separation of CO2-CH4 mixtures on defective single walled carbon nanohorns--tip does matter.
abstract: Using realistic models of single-walled carbon nanohorns and their single-walled carbon nanotube counterparts, we study the equilibrium separation of CO2-CH4 mixtures near ambient operating conditions by using molecular simulations. We show that regardless of the studied operating conditions (i.e., total CO2-CH4 mixture pressures and mole fractions of mixture components in the bulk phase), single-walled carbon nanohorns maximize the CO2-CH4 equilibrium separation factor. Optimized samples of single-walled carbon nanohorns consisting of narrow tubular parts capped with horn-shaped tips show highly selective adsorption of CO2 over the CH4 mixture component, with the CO2-CH4 equilibrium separation factor of ~8-12. A large surface-to-volume ratio (i.e., enhanced surface forces) and unique defective morphology (i.e., packing of adsorbed molecules in quasi-one/quasi-zero dimensional nanospaces) of single-walled carbon nanohorns are their key structural properties responsible for the excellent separation performance. Our theoretical simulation results are in quantitative agreement with a recent experimental/theoretical study of the CO2-CH4 adsorption and separation on oxidized single-walled carbon nanohorns [Ohba et al., Chem. Lett., 40, 2011, 1089]. Both experiment and theory showed that the CO2-CH4 equilibrium separation factor of oxidized samples of single-walled nanohorns measured near ambient operating conditions is ~2-5. This reduction in the separation efficiency as compared to optimized samples of single-walled carbon nanohorns is theoretically justified by their lower surface-to-volume ratio (i.e., larger diameters of tubular parts and horn-shaped tips).
authors.affiliation: N. Copernicus University, Department of Chemistry, Physicochemistry of Carbon Materials Research Group, Gagarin Street 7, 87-100 Toruń, Poland. aterzyk@chem.umk.pl.
authors.forename: Sylwester
authors.initials: S
authors.lastname: Furmaniak
authors.forename: Artur P
authors.initials: AP
authors.lastname: Terzyk
authors.forename: Piotr
authors.initials: P
authors.lastname: Kowalczyk
authors.forename: Katsumi
authors.initials: K
authors.lastname: Kaneko
authors.forename: Piotr A
authors.initials: PA
authors.lastname: Gauden
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D003198:Computer Simulation; D008697:Methane / Q000737:chemistry*; D037742:Nanotubes, Carbon / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D037742:Nanotubes, Carbon; D002245:Carbon Dioxide; D008697:Methane