Porous materials are important in a wide range of applications including catalysis and storage of gases such as carbon dioxide, a major contributor to climate change. Finding new ways to synthesise these materials will enable more control over their properties and performance. A group from the University of Liverpool has developed a technique for assembling prefabricated organic cage structures into crystalline materials where controlling how the cages connect determines whether the material is porous or non-porous. The group used powder diffraction on beamline I11 to help determine the structure of some of these new materials with different guest molecules and how they respond to variable temperature. This work has been published in the journal Nature Materials.
Most molecules in the solid state pack efficiently to form structures with minimal void volumes. As a result covalent organic molecules are rarely permanently porous. Porous materials have been used before in the adsorption of harmful pollutants. For example, activated charcoal has been used in gas mask technology for many years. Activated charcoal is a highly porous network structure derived from natural biomass. By contrast, small synthetic molecules are typically not porous because they pack together efficiently to fill space like bricks in a wall.
The new cage molecules are hollow and assemble to form structures that are permeated by pore channels. The cages are remarkable because they adsorb large volumes of gases such as hydrogen, methane, and carbon dioxide. Unlike most other porous materials, the porous organic cages dissolve in common solvents and can be handled and purified using conventional chemical methods.
|Porous organic cage structures|
Professor Andrew Cooper is from the University’s Chemistry Department and Centre for Materials Discovery.
“There are a number of ways to make porous materials but most are based on extended networks or polymers, not small molecules. In this new paper, we suggest a different approach where prefabricated organic cages are treated as modules for the construction of porous solids. We believe that combining different cages in a single material will lead to complex structures with chemical functions that cannot presently be accessed. A future goal will be to design molecules which pack even less effectively and which are therefore even more porous. We also plan to construct solids that trap particular guests – for example, to capture carbon dioxide produced by combustion before it reaches the atmosphere.”
Professor Andrew Cooper, University of Liverpool
Porous organic cages, Tomokazu Tozawa, James T. A. Jones, Shashikala I. Swamy, Shan Jiang, Dave J. Adams, Stephen Shakespeare, Rob Clowes, Darren Bradshaw, Tom Hasell, Samantha Y. Chong, Chiu Tang, Stephen Thompson, Julia Parker, Abbie Trewin, John Bacsa, Alexandra M. Z. Slawin, Alexander Steiner and Andrew Cooper, Nature Materials, October 2009
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