Capture of Volatile Iodine, a Gaseous Fission Product, by Zeolitic Imidazolate Framework-8

Here we present detailed structural evidence of captured molecular iodine (I₂), a volatile gaseous fission product, within the metal–organic framework ZIF-8 [zeolitic imidazolate framework-8 or Zn(2-methylimidazolate)₂]. There is worldwide interest in the effective capture and storage of radioiodine, as it is both produced from nuclear fuel reprocessing and also commonly released in nuclear reactor accidents. Insights from multiple complementary experimental and computational probes were combined to locate I₂ molecules crystallographically inside the sodalite cages of ZIF-8 and to understand the capture of I₂ via bonding with the framework. These structural tools included high-resolution synchrotron powder X-ray diffraction, pair distribution function analysis, and molecular modeling simulations. Additional tests indicated that extruded ZIF-8 pellets perform on par with ZIF-8 powder and are industrially suitable for I₂ capture.