Iodine Adsorption in Metal Organic Frameworks in the Presence of Humidity

Used nuclear fuel reprocessing represents a unique challenge when dealing with radionuclides such as isotopes of ⁸⁵Kr and ¹²⁹I₂ due to their volatility and long half-life. Efficient capture of ¹²⁹I₂ (t_1/2 = 15.7 × 10⁶ years) from the nuclear waste stream can help reduce the risk of releasing I₂ radionuclide into the environment and/or potential incorporation into the human thyroid. Metal organic frameworks have the reported potential to be I₂ adsorbents but the effect of water vapor, generally present in the reprocessing off-gas stream, is rarely taken into account. Moisture-stable porous metal organic frameworks that can selectively adsorb I₂ in the presence of water vapor are thus of great interest. Herein, we report on the I₂ adsorption capacity of two microporous metal organic frameworks at both dry and humid conditions. Single-crystal X-ray diffraction and Raman spectroscopy reveal distinct sorption sites of molecular I₂ within the pores in proximity to the phenyl- and phenol-based linkers stabilized by the I···π and I···O interactions, which allow selective uptake of iodine.