Forced intrusion of water and aqueous solutions in microporous materials: from fundamental thermodynamics to energy storage devices

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Forced intrusion of water and aqueous solutions in microporous materials: from fundamental thermodynamics to energy storage devicesChem. Soc. Rev., 8, 2017

 

Porous materials such as activated carbons, carbon nanotubes, zeolites and other open framework inorganic materials have been the subject of an intense research effort in the past two or three decades, owing to their practical importance in such processes as fluid separation, ion exchange, strategic gas storage, catalysis, biosensing and controlled drug delivery. The last decade has seen the emergence of new classes of crystalline porous framework materials, based on relatively weaker chemical bonds compared to inorganic materials such as oxides and zeolites. The most studied of these new materials today are the hybrid metal–organic frameworks (MOFs).

 

Most of these materials display narrow pore size, and the IUPAC recommendations state that pore size under 2 nm should be called micropores, pore size between 2 and 50 nm mesopores, and pores 450 nm macropores. Sometimes microand meso-pores are gathered together under the name of nanopores. Tailored nanoporous materials are still designed and synthesized at a furious pace today.

 

 

In real life ‘‘hydrophobic’’ surfaces are geometrically, chemically and electrically heterogeneous objects. Pure graphite surfaces for instance are believed to be hydrophobic, but nanoporous activated carbons exhibit a various amount of local functionalization of the pore surface (hydrophilic oxygenated sites). This is known to have a strong effect on the water uptake in porous carbon materials. The fundamental question is thus: ‘‘How does confined water behave in response to heterogeneous surfaces?’’. This question is common to a wide variety of nanoporous media, from biological cavities and porous polymers to inorganic materials such as porous carbons, zeolites, micelle-templated materials and other open framework porous materials. In addition to the experimental methodologies reviewed in the present article, extended osmotic molecular simulations will be needed in order to take into account the deformation of the framework materials upon fluid intrusion.

 

Résumé: 

Chem. Soc. Rev., 8, 2017

 

We review the high pressure forced intrusion studies of water in hydrophobic microporous materials such as zeolites and MOFs, a field of research that has emerged some 15 years ago and is now very active. Many of these studies are aimed at investigating the possibility of using these systems as energy storage devices. A series of all-silica zeolites (zeosil) frameworks were found suitable for reversible energy storage because of their stability with respect to hydrolysis after several water intrusion–extrusion cycles. Several microporous hydrophobic zeolite imidazolate frameworks (ZIFs) also happen to be quite stable and resistant towards hydrolysis and thus seem very promising for energy storage applications. Replacing pure water by electrolyte aqueous solutions enables to increase the stored energy by a factor close to 3, on account of the high pressure shift of the intrusion transition. In addition to the fact that aqueous solutions and microporous silica materials are environmental friendly, these systems are thus becoming increasingly interesting for the design of new energy storage devices.

 

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Références: 

Forced intrusion of water and aqueous solutions in microporous materials: from fundamental thermodynamics to energy storage devices

 

Guillaume Fraux, François-Xavier Coudert, Anne Boutin  and Alain H. Fuchs

 

Chem. Soc. Rev., 8, 2017

 

doi : 10.1039/C7CS00478H