New applications for materials called metal-organic frameworks (MOFs) could emerge through a method that produces them as transparent glasses.
Worldwide intense study into MOFs is taking place across the world as researchers investigate the dense network of pores that allows them to selectively take up and store many specific types of gas molecules. But they are generally crystalline and brittle, limiting capacity for them to be fabricated into complex shapes. Now, KACST researcher, Omar Yaghi, and colleagues have developed a process that allows glassy MOFs to solidify from a liquid mixture.
MOFs are hybrid organic-inorganic materials with metal ions or clusters held in place by carbon-based linker groups. They contain a network of internal cavities that gives them an astonishing capacity for taking up and retaining gas molecules. The internal surface area within one gram of a MOF can be greater than the area of an entire football field. Researchers vary the metal and linker groups to exploit this surface area to bind to many different gases for potentially significant applications. MOFs have been created that can store fuel molecules, such as hydrogen and methane. Others can separate molecules from gas mixtures, to purify selected gases or remove pollutants. Still others have been produced that can absorb and retain water molecules to dry gases. MOFs with catalytic properties might catalyze key industrial reactions efficiently and in a highly compact form.
Previous attempts to make useful glassy MOFs have been thwarted because the processes closed access to the porous interior so gases could no longer enter. The new procedure, which Yaghi developed in collaboration with researchers in the US, retains full access to the interior. This offers the potential to combine all the advantages of existing MOFs with the new possibilities offered by glassy forms. The key innovation was the development of a solvent mixture that would support the formation of the glassy MOF while much of the solvent was gradually evaporated.
One incentive for making glassy MOFs is to make it possible to mold them into complex shapes, perhaps to coat the contours of machines, for example. Making transparent glasses, such as this new research has achieved, also offers possibilities in thin film applications where transmission of light may be advantageous.
It is too early to say which commercialized applications may be found for MOF glasses. The researchers, however, see potential in the petrochemical and environmental industries, in medical devices, and food packaging.
- Zhao, Y., Lee, S.-Y. , Becknell, N., Yaghi, O. M. & Angell, C. A. Nanoporous transparent MOF glasses with accessible internal surface. J. Am. Chem. Soc.138, 10818–10821 (2016). | article