Adsorption of the drug molecule carbamazepine in zeolites: Studying host-guest and guest-guest interactions with DFT calculations

In the past two decades, pharmaceuticals and personal care products (PPCPs) have been identified as environmental contaminants of considerable concern due to their significant hazard potential. The anticonvulsant drug carbamazepine (CBZ, C15H12N2O), widely prescribed in the treatment of epilepsy, is a particularly relevant PPCP contaminant: It is hardly removed by conventional wastewater treatment techniques, shows considerable persistence in environmental waters, and negatively affects different organisms. Currently, various technological options are being considered to remove CBZ and other PPCPs from wastewaters, including (photo)oxidation processes, membrane separations, and adsorption-based separations. Hydrophobic high-silica and all-silica zeolites have been identified as promising adsorbents for the removal of organic contaminants. In this contribution, the adsorption of CBZ in 11 all-silica zeolites having different pore sizes and connectivities was investigated using dispersion-corrected density functional theory (DFT) calculations (CP2K code, rev-vdW-DF2 functional). On the basis of calculations considering a single CBZ molecule per simulation cell, IFR- and AFI-type all-silica zeolites were identified as systems with the highest affinity towards CBZ. Both of these frameworks contain one-dimensional channels outlined by 12-membered rings of SiO4 tetrahedra. An analysis of the lowest-energy configurations showed that a “good fit” of CBZ into the pores, which maximises van der Waals interactions, is critical to achieve a high affinity, whereas hydrogen bonds are only of minor importance. Further calculations investigating the adsorption of two CBZ molecules per simulation cell indicated that attractive guest-guest interactions are more significant in zeolites with larger pores.

Funding by the German Research Foundation (project 455871835) is gratefully acknowledged.