Porous Organic Cages for Sulfur Hexafluoride Separation

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Abstract

A series of porous organic cages is examined for the selective adsorption of sulfur hexafluoride (SF ₆) over nitrogen. Despite lacking any metal sites, a porous cage, CC3, shows the highest SF ₆/N ₂ selectivity reported for any material at ambient temperature and pressure, which translates to real separations in a gas breakthrough column. The SF ₆ uptake of these materials is considerably higher than would be expected from the static pore structures. The location of SF ₆ within these materials is elucidated by X-ray crystallography, and it is shown that cooperative diffusion and structural rearrangements in these molecular crystals can rationalize their superior SF ₆/N ₂ selectivity.

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Methane storage in flexible metal-organic frameworks with intrinsic thermal management.

Jarad A Mason, Julia Oktawiec, Mercedes Taylor … (2015)

As a cleaner, cheaper, and more globally evenly distributed fuel, natural gas has considerable environmental, economic, and political advantages over petroleum as a source of energy for the transportation sector. Despite these benefits, its low volumetric energy density at ambient temperature and pressure presents substantial challenges, particularly for light-duty vehicles with little space available for on-board fuel storage. Adsorbed natural gas systems have the potential to store high densities of methane (CH4, the principal component of natural gas) within a porous material at ambient temperature and moderate pressures. Although activated carbons, zeolites, and metal-organic frameworks have been investigated extensively for CH4 storage, there are practical challenges involved in designing systems with high capacities and in managing the thermal fluctuations associated with adsorbing and desorbing gas from the adsorbent. Here, we use a reversible phase transition in a metal-organic framework to maximize the deliverable capacity of CH4 while also providing internal heat management during adsorption and desorption. In particular, the flexible compounds Fe(bdp) and Co(bdp) (bdp(2-) = 1,4-benzenedipyrazolate) are shown to undergo a structural phase transition in response to specific CH4 pressures, resulting in adsorption and desorption isotherms that feature a sharp 'step'. Such behaviour enables greater storage capacities than have been achieved for classical adsorbents, while also reducing the amount of heat released during adsorption and the impact of cooling during desorption. The pressure and energy associated with the phase transition can be tuned either chemically or by application of mechanical pressure.

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Separation of rare gases and chiral molecules by selective binding in porous organic cages.

Linjiang Chen, Paul S Reiss, Samantha Y C Chong … (2014)

The separation of molecules with similar size and shape is an important technological challenge. For example, rare gases can pose either an economic opportunity or an environmental hazard and there is a need to separate these spherical molecules selectively at low concentrations in air. Likewise, chiral molecules are important building blocks for pharmaceuticals, but chiral enantiomers, by definition, have identical size and shape, and their separation can be challenging. Here we show that a porous organic cage molecule has unprecedented performance in the solid state for the separation of rare gases, such as krypton and xenon. The selectivity arises from a precise size match between the rare gas and the organic cage cavity, as predicted by molecular simulations. Breakthrough experiments demonstrate real practical potential for the separation of krypton, xenon and radon from air at concentrations of only a few parts per million. We also demonstrate selective binding of chiral organic molecules such as 1-phenylethanol, suggesting applications in enantioselective separation.

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Organic cage compounds--from shape-persistency to function.

Gang Zhang, Michael Mastalerz (2014)

Defined cavities are found in biological systems, such as in enzymes to accelerate specific reactions with specific molecular targets, or as transport containers for molecular cargoes. Chemists have been inspired by those phenomena found in nature and synthesized defined cage compounds for different purposes, such as for stabilizing reactive intermediates, running reactions within the cavities or studying recognition events. However, most cage compounds are based on the coordination of metal ions, and only a few are charge neutral. Purely organic cages are usually charge neutral and more stable due to existing covalent bonds. Covalent bonds can be made in two ways, applying irreversible reactions or reversible reactions. By introducing dynamic covalent chemistry (DCC), cages have become accessible in good yields from rather simple precursors. Here, we compare both methods and highlight those that give very good yields. Furthermore, the use of organic cage compounds in sorption, recognition, sensing, separation and stabilization of molecules will be discussed.

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Author and article information

Journal

Journal ID (nlm-ta): J Am Chem Soc

Journal ID (iso-abbrev): J. Am. Chem. Soc

Journal ID (publisher-id): ja

Journal ID (coden): jacsat

Title: Journal of the American Chemical Society

Publisher: American Chemical Society

ISSN (Print): 0002-7863

ISSN (Electronic): 1520-5126

Publication date (Electronic): 13 January 2016

Publication date (Print): 10 February 2016

Volume: 138

Issue: 5

Pages: 1653-1659

Affiliations

[† ]Department of Chemistry and Centre for Materials Discovery, University of Liverpool , Crown St., Liverpool L69 7ZD, United Kingdom

[‡ ]Department of Chemistry, Imperial College London , South Kensington, London SW7 2AZ, United Kingdom

[§ ]Atomistic Simulation Centre, Department of Physics and Astronomy, Queen’s University Belfast , University Road, Belfast BT7 1NN, United Kingdom

Author notes

[* ] aicooper@ 123456liv.ac.uk

Article

DOI: 10.1021/jacs.5b11797

PMC ID: 5101576

PubMed ID: 26757885

SO-VID: 5c0da642-bfaa-4435-9027-78bc64977590

License:

This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.

History

Date received : 17 November 2015

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document-id-new-14 ja-2015-11797s

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ScienceOpen disciplines: Chemistry

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ScienceOpen disciplines: Chemistry

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