Symmetry Breaking in the Transformation of Nanoporous Carbons Solids

Nanoporous carbons (NPC) or carbogenic molecular sieves (CMS) are unique materials that are able to produce shape selectivity for very precise molecular separations, such as that of oxygen from nitrogen on the basis of size. Surprisingly, the structure of NPC is globally amorphous. This seems at first irreconcilable, since regular transport behavior is expected to arise from regular porous solids such as zeolites and other crystalline molecular sieves. With this problem in mind as motivation, in this paper we describe some of the more intriguing aspects of the nanopore formation process. It is argued that at the nanoscale the NPC are both regular and structurally self similar, consisting of curved aromatic nanodomains that arise from the broken symmetry of hexagonal arrays. The symmetry breaking process is a direct result of the dissipation that takes place during pyrolysis leading to small molecules and a defect-laden carbogenic solid. In this context, some preliminary results illustrating how these NPC structures can be used to stabilize cesium for base catalysis and to prepare supported molecular sieve membranes for small molecule separations.

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