Adsorption of Carbamazepine in All‐Silica Zeolites Studied with Density Functional Theory Calculations**

Abstract

The anticonvulsant drug carbamazepine (À ) is an emerging contaminant of considerable concern due to its hazard potential and environmental persistence. Previous experimental studies proposed hydrophobic zeolites as promising adsorbents for the removal of carbamazepine from water, but only a few framework types were considered in those investigations. In the present work, electronic structure calculations based on dispersion-corrected density functional theory (DFT) were used to study the adsorption of CBZ in eleven all-silica zeolites having different pore sizes and connectivities of the pore system (AFI, ATS, BEA, CFI, DON, FAU, IFR, ISV, MOR, SFH, SSF framework types). It was found that some zeolites with one-dimensional channels formed by twelve-membered rings (IFR, AFI) exhibit the highest affinity towards CBZ. A "good fit" of CBZ into the zeolite pores that maximizes dispersion interactions was identified as the dominant factor determining the interaction strength. Further calculations addressed the role of temperature (for selected systems) and of guest-guest interactions between coadsorbed CBZ molecules. In addition to predicting zeolite frameworks of particular interest as materials for selective CBZ removal, the calculations presented here also contribute to the atomic-level understanding of the interaction of functional organic molecules with all-silica zeolites.

Density functional theory study of hydrophobic zeolites for the removal of triclosan from aqueous solution

“…Calculations of the adsorption energies for TCS in all-silica zeolites delivered very similar adsorption energies in the range of −153 to −160 kJ mol -1 for five of the six frameworks, with a weaker interaction being observed only for FAU, which possesses large supercages. This is a notably different finding compared to the previous DFT study of CBZ adsorption, where adsorption energies obtained for these five zeolites varied between −122 kJ mol -1 for BEA and −172 kJ mol -1 for IFR (Fischer 2023). This qualitative difference can be attributed to the higher flexibility of TCS, which allows it to adjust in a way that the interaction with the pore walls in differently shaped pores is maximized.…”

“…The largest deviation of about 20% occurs for all-silica FAU, followed by H-FAU (16%), whereas the differences for all-silica MOR (10%) and H-MOR (7%) are significantly smaller. As observed in the previous study of CBZ adsorption, where FAU, IFR, and MOR were compared (Fischer 2023), the deviation between "dynamic" and "static" results is directly correlated with the guest molecule's freedom of motion in the zeolite pores: Much more pronounced oscillations are possible in the large cages of FAU than in the comparatively narrow channels of MOR. This results in a larger impact of thermal motion on the internal energy of adsorption in the former system.…”

“…The deformation energies are always small, with the sum of the two ∆𝐸 term amounting to less than 5% of the total adsorption energy in all zeolites except MOR (where it reaches 6.5%). Rather different observations were made in the earlier DFT study of CBZ adsorption, where the sum of the deformation energies exceeded 10% of the total adsorption energies for some zeolites, notably BEA and MOR (Fischer 2023). Whereas the CBZ molecule is rather rigid, containing a tricyclic aromatic system, TCS can adjust much more easily to different pore environments because the two phenyl rings can rotate essentially independently.…”

“…The structures of the six all-silica zeolites (BEA, FAU, AFI, IFR, MOR, CFI frameworks, represented by the framework type codes [FTC] assigned in the structure database of the International Zeolite Associations IZA (Baerlocher and McCusker 2022)) are the same as in previous work (Fischer 2023). Sources of the experimental structure data and the corresponding cell parameters are given in the Supporting Information (Table S2).…”

“…With ongoing hardware and software developments, periodic calculations are now routinely feasible for unit cells of typical zeolites. A recent DFT investigation studied the adsorption of carbamazepine (CBZ) in eleven all-silica zeolites (Fischer 2023). In addition to the optimization of CBZ@Zeo adsorption complexes, DFT-based ab initio molecular dynamics (AIMD) simulations were carried out for selected zeolites to analyze the influence of temperature.…”