Influence of potential contaminants on I2 and CH3I adsorption onto zeolitic imidazolate frameworks (ZIFs) using GCMC simulations

Abstract

Zeolitic imidazolate frameworks (ZIFs) are one type of promising volatile radioiodine sorbents due to their chemical/thermal stability, tunable structures, and high iodine adsorption capacity. However, the inhibiting effect of contaminants on volatile iodine adsorption onto ZIFs remains unclear. Herein, the adsorption of volatile iodine (I2 and CH3I) onto five different ZIFs (SALEM-2, ZIF-8, ZIF-Cl, ZIF-90, and ZIF-65) and adsorption selectivity over ten contaminants were investigated by using grand canonical Monte Carlo (GCMC) methods. It is found that the I2 adsorption isotherm could be accurately described by the Langmuir-Freundlich model. Furthermore, the adsorption quantity of CH3I is much smaller than that of I2 at the same partial pressure. Ten potential gaseous contaminants that existed in a reprocessing plant or nuclear reactor accident, including CO, NO, H2O, CH4, C2H6, CH3OH, CH3CH2OH, Cl2, CH3Cl, and C6H6, were considered for calculation of binary adsorption. The results show that C6H6 has the largest adsorption enthalpy among all contaminants, whereas CO, NO, H2O, and CH4 have the smallest. Moreover, CO, NO, H2O, and CH4 have negligible effects on volatile iodine adsorption onto ZIFs. In contrast, except for CH3I adsorption onto ZIF-65, C6H6 has the strongest inhibiting effect since benzene could occupy the adsorption sites of iodine in ZIFs. This work not only provided the fundamental knowledge of volatile iodine adsorption on ZIFs but also proposed a new strategy to evaluate the inhibiting effect of contaminants. It could be helpful for future screening and design of better sorbents.