Polar triptycene-based non-metal organic frameworks show enhanced hydrogen adsorption

Abstract

Porous non-metal organic frameworks (N-MOFs) are an emerging class of porous materials that can have desirable properties such as stability for iodine capture, proton conductivity, and xenon / krypton separation. Here, we present the first experimental evidence of polymorphism in a porous N-MOFs, through the identification of two stable porous phases of a triptycene framework (T.Cl-α and T.Cl-β). We also report single crystal structures for two isostructural porous N-MOFs (T.Cl-α and T.Br-α). All three polymorphs are porous to carbon dioxide and nitrogen, and T.Cl-α exhibits a remarkable hydrogen uptake of 7.2 mmol g-1 at 77 K and 1 bar. This hydrogen sorption far exceeds most other porous crystals and compares favourably with many MOFs under the same condition. The hydrogen uptake for T.Cl-α is anomalously high for its relatively modest pore volume (0.198 cm3 g-1 from N2 isotherms at 77 K), which we attribute to London-dispersion interactions and geometric confinement within sub-nanometer pores.

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Identifiers

ORCID for Joseph Glover: orcid.org/0000-0002-5281-6664

ORCID for Roohollah Hafizi: orcid.org/0000-0001-6513-4446

ORCID for Graeme M. Day: orcid.org/0000-0001-8396-2771

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