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 °C, and 0.76 g/g to 0.85 g/g at 160 °C. Once heated at 160 °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 test 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 °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 I2, 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.