title: Applying Alkyl-Chain Surface Functionalizations in Mesoporous Inorganic Structures: Their Impact on Gas Flow and Selectivity Depending on Temperature.
abstract: Porous inorganic capillary membranes are prepared to serve as model structures for the experimental investigation of the gas transport in functionalized mesopores. The porous structures possess a mean pore diameter of 23 nm which is slightly reduced to 20 nm after immobilizing C16-alkyl chains on the surface. Gas permeation measurements are performed at temperatures ranging from 0 to 80 °C using Ar, N2, and CO2. Nonfunctionalized structures feature a gas transport according to Knudsen diffusion with regard to gas flow and selectivity. After C16-functionalization, the gas flow is reduced by a factor of 10, and the ideal selectivities deviate from the Knudsen theory. CO2adsorption measurements show a decrease in total amount of adsorbed gas and isosteric heat of adsorption. It is hypothesized that the immobilized C16-chains sterically influence the gas transport behavior without a contribution from adsorption effects. The reduced gas flow derives from an additional surface resistance caused by the C16-chains spacially limiting the adsorption and desorption directions for gas molecules propagating through the structure, resulting in longer diffusion paths. In agreement, the gas flow is found to correlate with the molecular diameter of the gas species (CO2< Ar < N2) increasing the resistance for larger molecules. This affects the ideal selectivities with the relation [Formula: see text]. The influence on selectivity increases with increasing temperature which leads to the conclusion that the temperature induced movement of the C16-chains is responsible for the stronger interaction between gas molecules and surface functional groups.
authors.affiliation: Advanced Ceramics, University of Bremen , Am Biologischen Garten 2, 28359 Bremen, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Besser
authors.affiliation: Advanced Ceramics, University of Bremen , Am Biologischen Garten 2, 28359 Bremen, Germany.
authors.forename: Atiq
authors.initials: A
authors.lastname: Ahmed
authors.affiliation: Center for Environmental Research and Sustainable Technology (UFT), University of Bremen , Leobener Strasse 1, 28359 Bremen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Baune
authors.affiliation: Advanced Ceramics, University of Bremen , Am Biologischen Garten 2, 28359 Bremen, Germany.|Centre for Materials and Processes (MAPEX), University of Bremen , Bibliothekstraße 1, 28359 Bremen, Germany.
authors.forename: Stephen
authors.initials: S
authors.lastname: Kroll
authors.affiliation: Center for Environmental Research and Sustainable Technology (UFT), University of Bremen , Leobener Strasse 1, 28359 Bremen, Germany.|Centre for Materials and Processes (MAPEX), University of Bremen , Bibliothekstraße 1, 28359 Bremen, Germany.
authors.forename: Jorg
authors.initials: J
authors.lastname: Thöming
authors.affiliation: Advanced Ceramics, University of Bremen , Am Biologischen Garten 2, 28359 Bremen, Germany.|Centre for Materials and Processes (MAPEX), University of Bremen , Bibliothekstraße 1, 28359 Bremen, Germany.
authors.forename: Kurosch
authors.initials: K
authors.lastname: Rezwan
keywords: Knudsen diffusion; carbon dioxide adsorption; gas permeation; mesoporous ceramic membrane; surface functionalization