Performance of Cu II -, Pb II -, and Hg II -Exchanged Mordenite in the Adsorption of I 2 , ICH 3 , H 2 O, CO, ClCH 3 , and Cl 2 : A Density Functional Study.

Periodic dispersion-corrected DFT is used to investigate the adsorption of I2 and ICH3 , which may be released during a severe nuclear accident, for three divalent cation (Cu2+ , Pb2+ and Hg2+ )-exchanged mordenites with an Si/Al ratio of 23. Gases such as H2 O, CO, ClCH3 , and Cl2 present in the containment atmosphere can inhibit the selective adsorption of iodine species. To identify the most promising adsorbents, a systematic study is performed in which all the possible cationic sites in the main channel of the mordenite structure are considered. For the energetically most stable sites, the divalent cation is located in the small rings (five- or six-membered) containing two Al atoms, while in the energetically less stable configurations, the two Al atoms are far apart (>7 Å) and the cation is close to only one Al atom. Upon adsorption of the various molecules, the coordination number of the cation decreases with increasing interaction energy, as the molecules can attract the divalent cations from the framework. Finally, the computed interaction energies show that Hg-mordenite (MOR) could be a suitable material for selective adsorption of volatile iodine species, contrary to Cu-MOR and Pb-MOR.