Robust porous polymers bearing phosphine oxide/chalcogenide ligands for volatile iodine capture

Porous polymeric materials (PPMs) with phosphine oxide/chalcogenide (P = X) ligands were exploited, for the first time, for efficient capture of iodine from the vapor phase. Using triphenylphosphine oxide/sulfide/selenide (TPPO/S/Se), P = X ligands were introduced onto polyhedral oligomeric silsesquioxane (POSS) skeleton via a facile Friedel-Crafts reaction. They show iodine loading capacities, 1.22 g/g to 1.37 g/g at 90 degrees C, and 0.76 g/g to 0.85 g/g at 160 degrees C. Once heated at 160 degrees C under vacuum, they can still keep a considerable iodine loading capacity, 0.41 g/g and 0.51 g/g for POSS-TPPS and POSS-TPPSe, respectively. After soaking in ethanol, the POSS-TPPS/Se retained iodine more than 50%, the highest ratio reported so far for iodine release from PPMs. Besides, the dynamic column experiments were carried out to WA their competitive adsorption performance of iodine from a mixed stream with water vapor (40% Relative humidity), and the results suggest that the elevated temperature (160 degrees C) can reduce the adverse effect of water adsorption remarkably. Moreover, the spectral evidence and DFT calculations reveal that a strong charge transfer through P = X to iodine originates from the three aromatic rings and the chalcogens. The adsorption energy for POSS-TPPSe complexing iodine can reach up to 66 kJ/mol I-2, higher than other PPMs. As the first study of adsorbents with P = X ligands for iodine capture, this work opens a new avenue for the adsorptive capture of radioiodine in vapor at elevated temperatures and provides new insights for the interaction mechanism between P = X ligands and iodine molecules.