Ionic liquids boost gas uptake in MOFs

Modifying common metal-organic frameworks (MOFs) with ionic liquids is a simple way to boost the porous materials’ gas-uptake properties, according to a study (J. Am. Chem. Soc. 2018, DOI: 10.1021/jacs.8b05802). Endowed with extreme surface area and porosity, as well as the ability to be tuned chemically, MOFs draw widespread attention for use in gas separation and storage and other applications, some of which have been commercialized. To tailor the materials’ structures and properties, researchers have synthesized thousands of MOFs mainly by varying the building blocks. Some chemists opt instead to identify a promising MOF for a targeted application and then customize the material via postsynthesis modification. A team led by Seda Keskin and Alper Uzun of Koç University in Istanbul followed that approach to improve CO₂ uptake in ZIF-8, a common imidazolate framework. By treating hydrophobic ZIF-8 with a hydrophilic imidazolium ionic liquid in which CO₂ is highly soluble, the team formed a chemically selective shell on the MOF exterior. Tests show that CO₂ adsorption in the new material is 5.7 times as high as in untreated ZIF-8, and selectivity for CO₂ over methane jumped by a factor of 45—improvements that make ZIF-8 attractive for carbon capture and natural gas purification.