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 Kr-85 and I-129(2) due to their volatility and long half-life. Efficient capture of I-129(2) (t(1/2) = 15.7 X 10(6) years) from the nuclear waste stream can help reduce the risk of releasing I-2 radionuclide into the environment and/or potential incorporation into the human thyroid. Metal organic frameworks have the reported potential to be I-2 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 I-2 in the presence of water vapor are thus of great interest. Herein, we report on the I-2 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 I-2 within the pores in proximity to the phenyl- and phenol-based linkers stabilized by the I center dot center dot center dot pi and I center dot center dot center dot O interactions, which allow selective uptake of iodine.