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Liquids with permanent porosity


Porous solids such as zeolites1 and metal–organic frameworks2,3 are useful in molecular separation and in catalysis, but their solid nature can impose limitations. For example, liquid solvents, rather than porous solids, are the most mature technology for post-combustion capture of carbon dioxide because liquid circulation systems are more easily retrofitted to existing plants. Solid porous adsorbents offer major benefits, such as lower energy penalties in adsorption–desorption cycles4, but they are difficult to implement in conventional flow processes. Materials that combine the properties of fluidity and permanent porosity could therefore offer technological advantages, but permanent porosity is not associated with conventional liquids5. Here we report free-flowing liquids whose bulk properties are determined by their permanent porosity. To achieve this, we designed cage molecules6,7 that provide a well-defined pore space and that are highly soluble in solvents whose molecules are too large to enter the pores. The concentration of unoccupied cages can thus be around 500 times greater than in other molecular solutions that contain cavities8,9,10, resulting in a marked change in bulk properties, such as an eightfold increase in the solubility of methane gas. Our results provide the basis for development of a new class of functional porous materials for chemical processes, and we present a one-step, multigram scale-up route for highly soluble ‘scrambled’ porous cages prepared from a mixture of commercially available reagents. The unifying design principle for these materials is the avoidance of functional groups that can penetrate into the molecular cage cavities.

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Figure 1: Preparation of the porous liquid.
Figure 2: Molecular simulations for the porous liquid show unoccupied molecular-sized pores.
Figure 3: Dissolution of methane in the porous liquid.
Figure 4: Porous liquids based on scrambled cages.

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This work was funded by the Leverhulme Trust (F/00 203/T) and by EPSRC (EP/C511794/1). M.G.D.P. acknowledges financial support from ANPCyT (PICT-2011-2128) and from the EC-H2020, MSCRISE-2014 programme, through project 643998 ENACT. L.P. and M.C.G. acknowledge support from the Contrat d’Objectifs Partagés (CNRS, Blaise Pascal University, and the Auvergne Regional Government, France). A.I.C. acknowledges the European Research Council under the European Union’s Seventh Framework Programme/ERC Grant Agreement no. 321156 for financial support. We thank M. E. Briggs for assistance with the cage syntheses.

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Authors and Affiliations



N.G. and R.L.G. synthesized the porous crown cage. M.D.P. and G.M. carried out the molecular simulations. K.R. and T.K. performed the PALS measurements. M.C.G. and L.P. measured the methane gas solubilities for the crown cage porous liquid. R.L.G. and A.I.C. conceived the synthesis of the scrambled porous imine cages. R.L.G synthesized and characterized the scrambled cage porous liquid and measured its gas solubilities. S.L.J. led the project overall and conceived the design of the porous liquid based on the crown-ether cage together with N.G. S.L.J. and A.I.C. led the writing of the manuscript with contributions from all co-authors.

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Correspondence to Stuart L. James.

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Supplementary information

Supplementary Information

This file contains Synthetic and analytical methods, with full synthesis details and characterisation. Molecular Simulations, positron annihilation lifetime spectroscopy (PALS), gas solubility and guest selectivities. (PDF 4891 kb)

Guest selectivity in ‘scrambled’ porous liquids

Two batches of porous liquid prepared in vials (200 mg scrambled cage dissolved in 1 mL hexachloropropene) and both were saturated with xenon (5 mins bubbling at 50-60 mL/min), followed by the addition of a stirrer bar. To one sample was added chloroform (16 μL, 1.0 mol. eq. based on cage) and to the other was added 1-t-butyl-3,5-dimethylbenzene (36 μL, 1.0 mol. eq.), in both cases being careful not to mix the solvents. Stirring was started to mix the solvent layers – as can be observed in the video, chloroform displaces the xenon gas whereas the large, bulky solvent does not. (MP4 29264 kb)

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Giri, N., Del Pópolo, M., Melaugh, G. et al. Liquids with permanent porosity. Nature 527, 216–220 (2015).

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