Performance of Cu^II‐, Pb^II‐, and Hg^II‐Exchanged Mordenite in the Adsorption of I₂, ICH₃, H₂O, CO, ClCH₃, and Cl₂: A Density Functional Study

Abstract

Periodic dispersion-corrected DFT is used to investigate the adsorption of I and ICH , which may be released during a severe nuclear accident, for three divalent cation (Cu , Pb and Hg )-exchanged mordenites with an Si/Al ratio of 23. Gases such as H O, CO, ClCH , and Cl 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.

Porous sorbents for the capture of radioactive iodine compounds: a review

“…[163][164][165][166][167][168] In the particular case of the capture of iodine species, the adsorption properties and cation exchange capacities of zeolites make them interesting and remarkable candidates for this application. In the literature, several zeolites of different structural types have been studied for the capture of iodine species, such as mordenite (MOR structural type), 29,34,74,76,77,79,80,[169][170][171][172][173][174][175][176][177][178] NaX and NaY zeolites (FAU type), 5,60,75,77,78,88,132,179 ZSM-5 (MFI type), 74,77 ferrierite (FER type) and zeolite beta (*BEA type) 74,77 (ESI, Table 3 †).…”

“…Later, numerous studies were carried out on this topic, especially during the 1970s and 1980s 21,29,34,38,40,47,52,180 and then between 2000 and 2017. 5,8,71,[74][75][76][77][78][79][80][169][170][171][173][174][175][176][177][184][185][186][187][188] These studies focused on the determination of the inuence of various parameters such as the temperature ( C), silver content (wt%), Si/Al ratio, supercial velocity, and pretreatment of the material on the adsorption capacities of silver-exchanged zeolites (ESI, Table 3 †). Other works focused on issues such as aging of the material under different atmospheres (NO x , humidity).…”

“…for a better understanding of iodine capture and its performance. [74][75][76][77][78][79][80][81] In addition, new porous sorbents have been added to the list of potential sorbents for iodine trapping, including titanosilicates, 82,83 mesoporous silicas, 6,81,[84][85][86] silverimpregnated silica and alumina (Ag/SiO 2 and Ag/Al 2 O 3 , respectively), 19,35,52,61,65,70,[87][88][89][90][91][92][93][94][95][96][97] silver-functionalized aerogels, chalcogels, 7,98-108 macroreticular ion exchange resins, 16,39,41,42,[44][45][46]50,53,55 metal-and covalent-organic frameworks (MOFs and COFs, respectively) 6,14, and porous organic polymers (POPs). [133][134][135]…”

“…Aer these works, Staples et al 52 studied the effect of the exchanged cations (Na + , Ag + , Pb 2+ , Cd 2+ ) on the irreversibility of the capture of iodine (I 2 ) by the faujasite-type X zeolite at 150 C. Even though the iodine adsorption capacity of every cation was acceptable, only silver was capable of trapping iodine in an irreversible way. Recent studies, 75,76,79,80 especially those using density functional theory (DFT) simulations, enabled the determination of the inuence of the valence of cations on the selective adsorption of iodine species by zeolites. In an initial study, Chebbi et al 75 showed that copper (Cu + )-and silver (Ag + )exchanged faujasite zeolites (CuX and AgX, respectively) preferentially adsorbed iodine compounds rather than species such as water, chloromethane and chlorine.…”

Effects of the cation and Si/Al ratio on CH3I adsorption by faujasite zeolites

“…In the case of zeolites, the ease of exchange reactions and the cation size are also further important criteria. Recently, some DFT studies conducted on different monovalent cationexchanged faujasite and mordenite have shown new insights for the adsorption of both I 2 and CH 3 I [21,22]. It was found that soft cations, such as Cu + and Ag + , are able to adsorb iodine compounds with high adsorption energies, even in presence of some inhibitors (apart from CO and to a lesser extent NO) potentially present under severe accidental conditions.…”