Radioactive iodine capture by metal organic frameworks in liquid and vapour phases: An experimental, kinetic and mechanistic study

For environmental protection, the effectual capture of radioiodine produced or released as nuclear fission products, is of utmost importance. In this aspect, metal-organic frameworks (MOFs) may be a kind of promising material to address this hazardous environmental issue. Herein, four different MOFs, [Co_1.5(PhCOO)₃(bpy)0.5]_n (KQ-1), [Co(HCOO)₂(bpy)]_n (KQ-2), [Co(HCOO)₂]_n (KQ-3) and [Mn(HCOO)₂]_n (KQ-4) have been synthesized via solvothermal method by using benzoic acid (PhCOOH) or formic acid (HCOOH) as organic linker, 4,4′-bipyridine (bpy) as spacer and salts of Co(II) and Mn(II). The as-prepared MOFs were characterized in detail and their iodine (I₂) adsorption/release performance was also investigated in vapor and solution phase by UV-Vis spectroscopy with the adsorption capacity being KQ-1 >KQ-2 >KQ-3 ≈ KQ-4. The highest sorption capacity of about 551 and 131.05 mg/g was observed for KQ-1 in vapor and solution phase, respectively, and with recyclability upto five cycles. Raman and XPS spectra indicate that iodine binds to MOF as I₂ and I₃^- species. The plenty of aromatic rings form iodine-π charge transfer complex thus stabilizing the interaction to effect the iodine sorption (as evidenced in KQ-1). Henceforth, the iodine sorption is observed to depend on the presence of aromatic rings in the structure of MOFs.