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Posted: Jul 09, 2012
Rational design of molecular gas storage architectures
(Nanowerk News) Metal organic frameworks (MOFs) are well suited to storage of gas molecules. EU-funded researchers developed novel forms of these structures that enable their frame to open and accommodate molecules that should not otherwise fit.
MOFs, as their name suggests, consist of metal oxide joints bonded to organic struts. The result is very porous structures consisting of cavities separated by windows and exhibiting very high surface areas. MOFs are generally quite rigid and chemically stable due to the strength of their chemical bonds.
The modularity of MOFs supports rational design of custom-made pore systems. When combined with microporous zeolites, sharing many of the same properties and already used in a variety of applications worldwide, the result is nanoporous zeolitic imidazole frameworks (ZIFs).
ZIFs have gained wide acclaim for their potential in gas storage, including that related to energy applications such as hydrogen (H2) or methane (CH4) storage and those related to carbon dioxide (CO2) for CO2 sequestration and storage.
However, while great potential exists, discovery of novel ZIFs for gas adsorption (adherence of gas molecules to the surface of the ZIF) is largely occurring by trial and error.
European researchers sought to bring rational design to the field of ZIF production via funding of the DASZIF project. Molecular simulations led to identification of optimal ZIF structures which were then synthesised and characterised with respect to their adsorption of various gases.
The reason for differences in expected versus obtained adsorption profiles was then explained by simulation studies. Scientists identified the cause as the balance between the strength of fluid-fluid interactions and fluid-solid interactions, itself a function of fluid type and pore size.
One of the most exciting findings built on previous results indicating the adsorption of gas molecules larger than the windows between cavities. Following this lead, scientists experimentally demonstrated structural flexibility in the ZIF framework due to a change in the imidazolate linkers. The alterations resulted in an enlargement of the pore window. The team further characterised this effect with respect to adsorption of a variety of energy-related gases.
Development of new ZIFs, detailed characterisation of their adsorption characteristics and the demonstration of structural flexibility could have an important positive impact on gas storage for energy usage and for carbon sequestration systems.