Computational investigation on interaction mechanism of sulfur mustard adsorption by zeolitic imidazolate frameworks ZIF-8 and ZIF-67: Insights from periodic and cluster DFT calculations

Zeolitic imidazolate frameworks (ZIFs) have attracted significant attention as excellent materials for removing toxic substances from wastewater. Herein, a comprehensive first-principles and cluster DFT study was performed to investigate the interaction mechanism of sulfur mustard (HD) simulant, 2-chloroethyl ethyl sulfide (CEES) with ZIF-8 and ZIF-67. The primitive cell of ZIF-8 was optimized using some exchange functional methods, and excellent agreement between experimental and computed cell parameters was found using revised PBE functional. The optimization of several conformations by first-principles DFT calculations showed that the CEES molecule is favorably adsorbed into ZIFs. The adsorption was found to be due to long-range interactions between the CEES molecule and ZIFs' framework. The charge density difference (CDD) iso-surfaces showed no evidence of coordination between CEES molecule and ZIFs, confirming the physisorption mechanism. The ZIF-67 framework showed more negative adsorption energy compared to ZIF-8. On the other hand, cluster DFT calculations showed that clusters with open metal defects could electrostatically interact with the CEES molecule through electron-deficient metal centers. The present conclusions can be used as a reference for the future design of ZIF-based adsorbents.