Post-synthetic structural processing in a metal-organic framework material as a mechanism for exceptional CO₂/N₂ selectivity
Date
2013
Authors
Bloch, W.
Babarao, R.
Hill, M.
Doonan, C.
Sumby, C.
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Journal article
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Journal of the American Chemical Society, 2013; 135(28):10441-10448
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Witold M. Bloch, Ravichandar Babarao, Matthew R. Hill, Christian J. Doonan, Christopher J. Sumby
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Abstract
Here we report the synthesis and ceramic-like processing of a new metal-organic framework (MOF) material, [Cu(bcppm)H2O], that shows exceptionally selective separation for CO2 over N2 (ideal adsorbed solution theory, S(ads) = 590). [Cu(bcppm)H2O]·xS was synthesized in 82% yield by reaction of Cu(NO3)2·2.5H2O with the link bis(4-(4-carboxyphenyl)-1H-pyrazolyl)methane (H2bcppm) and shown to have a two-dimensional 4(4)-connected structure with an eclipsed arrangement of the layers. Activation of [Cu(bcppm)H2O] generates a pore-constricted version of the material through concomitant trellis-type pore narrowing (b-axis expansion and c-axis contraction) and a 2D-to-3D transformation (a-axis contraction) to give the adsorbing form, [Cu(bcppm)H2O]-ac. The pore contraction process and 2D-to-3D transformation were probed by single-crystal and powder X-ray diffraction experiments. The 3D network and shorter hydrogen-bonding contacts do not allow [Cu(bcppm)H2O]-ac to expand under gas loading across the pressure ranges examined or following re-solvation. This exceptional separation performance is associated with a moderate adsorption enthalpy and therefore an expected low energy cost for regeneration.
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© 2013 American Chemical Society