Zapping a ZIF improves its gas-separating properties

Exposing a membrane made of the metal-organic framework ZIF-8 to an external electric field transforms the material from one with a modest ability to separate propene from propane to a good separator of these gases. The finding, from a team led by Leibniz University Hannover scientists Jürgen Caro and Alexander Knebel, could be broadly applicable to different classes of framework materials that are similar to ZIF-8 (Science 2017, DOI: 10.1126/science.aal2456). ZIF-8 is a soft MOF crystal with zinc-coordinated imidazolate linker units that move in a manner described as “breathing.” Applying an external electric field of 500 V/mm to ZIF-8 reduces this motion and causes the material’s lattice to polarize, prompting a transition in its crystal structure. The zapped ZIF-8 has a 0.36-nm pore aperture, which is only slightly larger than the 0.34-nm opening in the unzapped material. However, because the linkers move less when electrified, the MOF’s ability to separate propene from propane improves. In a commentary that accompanies the paper, MOF expert Jorge Gascon of King Abdullah University of Science & Technology speculates that the work could lead to “catalysts where selectivity could be tuned for certain substrates by changing the coordination environment of the active site and even electrically actuated artificial organs and tissues.”