Giant reversible swelling of nanoporous materials disovered - possible applications for storage of carbon dioxide and gaseous (bio)fuels

Scientists all over the world are participating in the quest for new materials with properties suitable for the environmentally friendly and economically feasible separation, recovery, and reuse of gaseous fuels, such as biogas and (bio-)hydrogen, and greenhouse gases like carbon dioxide, for which sequestration options are being researched. We follow developments surrounding carbon capture and storage (CCS), because they can be applied to biofuels and result in radically carbon-negative energy systems (here and here).

In this context, a team of scientists from France, the UK and the European Synchronotron Research Facility (ESRF) have recently discovered an unprecedented giant and reversible swelling of nanoporous materials with exceptional properties: huge flexibility and profound selectivity. They published their results [*abstract] in Science this week.

Porous hybrid solids are the new materials that could make the world more environmentally friendly (earlier post). The team from Institut Lavoisier at University of Versailles have developed metal-organic three-dimensional structures with cages and channels (known as MIL, for Material Institut Lavoisier). These compounds contain metal ions (in this case chromium and iron), with organic linkers and are very flexible, and hence, can change shape very easily. They can open up or close down in response to external factors such as pressure, temperature, light or influence of gases and solvents.

Crystals behaving like lungs
The French researchers, in collaboration with the staff of the Swiss-Norwegian experimental station (called beamline) at the ESRF, have tracked, for the first time, a reversible giant increase in volume of these solids (image, click to enlarge). It ranges from 85% of their size to up the unprecedented 230%. Such a large expansion in crystalline materials has not been observed before. This reversible “breathing” action is similar to the lungs’ function in humans: they grow in size when inhaling and go back to their original size when exhaling. The lungs expand, however, by only around 40%:
biomass :: bioenergy :: biofuels :: energy :: sustainability :: biogas :: biohydrogen :: carbon capture and storage :: CCS :: nanotechnology :: gas storage ::

The huge swelling effect has been achieved in a simple way: MIL materials were immersed into solvents, and their cavities were filled and thus opened by entering solvent molecules. This made the structures grow, without breaking bonds and retaining the crystallinity of the materials. This process was monitored at the ESRF, using high-quality synchrotron radiation and the experimental results were combined with computer chemistry simulations.

The swelling process can reversed by heating the solvated form and the dry form is then recovered. In this form, the material exhibited closed pores with almost no accessible porosity. Surprisingly, the same team published a paper last autumn where they showed that some gas molecules can close, but not open, the pores upon absorption. Moreover, the closed hydrated form demonstrates a remarkable selectivity in absorption of polar and nonpolar gases.

The next step for the team is to investigate how hydrogen or green-house gases can be stored in these kinds of materials. This may open a door to ecological applications such as (bio-)hydrogen and (bio-)methane-fuelled cars or the capture of carbon dioxide in the near future.

Image: Structures (along the c axis) of the MIL-88A, B, C, D series in their dry forms (top) and open forms (bottom). Credit: ESRF.

More information:
Serre, C. Mellot-Draznieks, S. Surblé, N. Audebrand, Y. Filinchuk, G. Férey , "Role of Solvent-Host Interactions That Lead to Very Large Swelling of Hybrid Frameworks" [*abstract], Science, 30 March 2007: Vol. 315. no. 5820, pp. 1828 - 1831, DOI: 10.1126/science.1137975.

P. L. Llewellyn, S. Bourrelly,C. Serre, Y. Filinchuk, and G. Férey, "Hydrogen Storage in the Giant-Pore Metal-Organic Frameworks MIL-100 and MIL-101" [*abstract], Angewandte Chemie International Edition, Volume 45, Issue 48, Date: December 11, 2006, Pages: 8227-8231

Philip L. Llewellyn, Sandrine Bourrelly, Christian Serre, Yaroslav Filinchuk, Gérard Férey, "How Hydration Drastically Improves Adsorption Selectivity for CO2 over CH4 in the Flexible Chromium Terephthalate MIL-53" [*abstract], Angewandte Chemie, Volume 118, Issue 46, Date: November 27, 2006, Pages: 7915-7918

On new, high-capacity and biobased methane storage tanks relying on nanoporous materials, see Biopact: The bioeconomy at work: methane storage tanks for cars made from corn cobs - February 18, 2007