Zeolitic imidazolate framework
Zeolitic imidazolate frameworks (ZIFs) are a class of metal-organic frameworks that are topologically isomorphic with zeolites. ZIFs are composed of tetrahedrally-coordinated transition metal ions (e.g. Fe, Co, Cu, Zn) connected by imidazolate linkers. Since the metal-imidazole-metal angle is similar to the 145° Si-O-Si angle in zeolites, ZIFs have zeolite-like topologies. As of 2010, 105 ZIF topologies have been reported in the literature.
Properties and potential applications
One potential application of ZIFs is as scrubbers for removing carbon dioxide from gas streams. One litre of the crystals could store about 83 litres of CO2. The crystalline solids are usually non-toxic and are easily prepared, making them an attractive possibility for carbon capture and storage. "The porous structures can be heated to high temperatures without decomposing and can be boiled in water or solvents for a week and remain stable, making them suitable for use in hot, energy-producing environments like power plants."
ZIFs are chemically and thermally stable materials. "Study of the gas adsorption and thermal and chemical stability of two prototypical members, ZIF-8 and -11, demonstrated their permanent porosity (Langmuir surface area = 1,810 m2/g), high thermal stability (up to 550°C), and remarkable chemical resistance to boiling alkaline water and organic solvents."
Like zeolites and other porous materials, zeolitic imidazolate framework membranes are potentially attractive for the separation of gases because of their highly porous structure, large accessible pore volume with fully exposed edges and faces of the organic links, pore apertures in the range of the kinetic diameter of several gas molecules, and high CO2 absorption capacity. ZIF-8 membranes display high CO2 permeances for equimolar mixtures of CO2 and CH4."
- Park, KS; et al. (2006). "Exceptional chemical and thermal stability of zeolitic imidazolate frameworks" (PDF). PNAS 103 (27): 10186–10191. Bibcode:2006PNAS..10310186P. doi:10.1073/pnas.0602439103.
- Phan, A.; Doonan, C. J.; Uribe-Romo, F. J.; Knobler, C. B.; O'Keeffe, M.; Yaghi, O. M. "Synthesis, Structure, and Carbon Dioxide Capture Properties of Zeolitic Imidazolate Frameworks" Acc. Chem. Res. 2010, 43, 58-67. doi:10.1021/ar900116g
- Zhang, J.-P.; Zhang, Y.-B.; Lin, J.-B.; Chen, X.-M., "Metal Azolate Frameworks: From Crystal Engineering to Functional Materials", Chem. Rev. 2012, vol. 112, pp. 1001-1033. doi:10.1021/cr200139g
- CBC News article New materials can selectively capture CO2, scientists say published February 15, 2008
- Journal of American Chemical Society article "Highly Permeable Zeolite Imidazolate Framework-8 Membranes for CO2/CH4 Separation" JACS,2010, Volume 132, page 76-78.