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Local Microstructural Organization in Carbogenic Molecular Sieves

Published online by Cambridge University Press:  10 February 2011

Michael S. Kane  and
Henry C. Foley
Michael S. Kane
Affiliation:
Center for Catalytic Science and Technology, Department of Chemical Engineering, University of Delaware, Newark, DE 19716
Henry C. Foley
Affiliation:
Center for Catalytic Science and Technology, Department of Chemical Engineering, University of Delaware, Newark, DE 19716
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Abstract

The microstructure of nanoporous, carbogenic molecular sieves (CMS) was studied using high resolution electron microscopy and neutron diffraction. The narrow range of pore sizes observed in these complex materials suggests that although these materials are globally amorphous, the local microstructural features are more organized. Our work, focused on poly(furfuryl alcohol)-derived CMS, is aimed at characterizing the evolution of this microstructure. Microscopy results show that materials synthesized at low temperature have some degree of organization but that the microstructure is featureless and symmetric at longer length scales. This symmetry is broken at higher synthesis temperatures as thermodynamic driving forces lead to further organization of the carbon atoms into more ordered structures but the length scales remain short. Micrographs of high temperature CMS show a high degree of curvature and features reminiscent of fullerene. The connectivity of the carbon atoms in the CMS has been probed using powder neutron diffraction. This data suggests that the atoms in the CMS form ordered structures on the length scale of 15Å which are distinctly different from the structure of graphite. These observed changes in the microstructure directly impact the adsorptive and molecular sieving characteristics of the CMS as illustrated by the marked differences between the diffusivities of oxygen and nitrogen. This property is crucial for the very demanding separation of nitrogen from oxygen in air.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 431: Symposium P – Microporous and Macroporous Materials , 1996 , 9
Copyright
Copyright © Materials Research Society 1996

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