New Crystalline Solids Can Reversibly Increase Their Volume More Than 3x; Possible Impact for Hydrogen Storage

2 April 2007

Structure of chromium (III) diphenyl dicarboxylate, one of the new crystalline solids, in its crude form following synthesis (middle), with all traces of solvent removed (on the left), and after absorption of solvent and increase in volume (on the right). Click to enlarge. Source: G. Férey, CNRS 2007

A team of scientists from France, UK and the European Synhrotron Radiation Facility (ESRF) have recently discovered an unprecedented giant and reversible swelling of nanoporous crystalline solids with exceptional properties: huge flexibility and profound selectivity.

The team from Institut Lavoisier at Université de Versailles developed metal-organic three-dimensional structures with cages and channels. These compounds contain metal ions (in this case chromium and iron), with organic linkers. The materials are very flexible and can change shape easily. They can open up or close down in response to external factors such as pressure, temperature, light or influence of gases and solvents.

Lead by Gérard Férey, 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. It ranges from 85% of their size to up an 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%.

This reseach is published in the current issue of the journal Science.

Upon immersion into solvents, the cavities of the materials were filled and thus opened by entering solvent molecules. The structures grew without breaking bonds and while 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. 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 greenhouse gases can be stored in these kinds of materials. This discovery may be applicable for mobile hydrogen storage for vehicles or the capture of carbon dioxide in the near future.

In 2005, Férey and his team developed a new nanoporous material—chromium terephthalate—which far outperformed the best materials known to date. With pores 2.9 and 3.4 nanometers in diameter and a specific adsorbing surface area of 6,000 square meters per gram, this solid was a strong nanomaterial for storing hydrogen at the temperature of liquid nitrogen.

Resources:

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

• “How Hydration Drastically Improves Adsorption Selectivity for CO₂ over CH₄ in the Flexible Chromium Terephthalate MIL-53”; Philip L. Llewellyn, Sandrine Bourrelly, Christian Serre, Yaroslav Filinchuk, Gérard Férey; Angewandte Chemie International Edition, Volume 45, Issue 46 , Pages 7751 - 7754

• “A Chromium Terephthalate-Based Solid with Unusually Large Pore Volumes and Surface Area”; G. Férey, C. Mellot-Draznieks, C. Serre, F. Millange, J. Dutour, S. Surblé, I. Margiolaki; Science 23 September 2005: Vol. 309. no. 5743, pp. 2040 - 2042 DOI: 10.1126/science.1116275