Adsorption of pharmaceuticals and related compounds in cation-exchanged zeolites – A computational perspective

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Zeolites are porous inorganic framework materials that possess an intrinsic porosity due to the presence of channels or cavities in the crystal structure. In aluminosilicate zeolites, the negative framework charge is balanced through positively charged species, mostly protons or metal cations. Cation exchange has been established as a versatile technique to modify application-relevant properties of zeolite materials. Beyond established applications (e.g., catalysis, gas separation), zeolites could also find use in the adsorption of pharmaceuticals and related functional organic molecules, targeting applications in wastewater treatment (removal of “emerging contaminants”) or in drug delivery. So far, however, only a few experimental studies have studied cation-exchanged zeolites for these uses, and systematic insights into the impact of the cation type on the adsorption of functional organic molecules are largely lacking. In this project, atomistic simulations in the framework of dispersion-corrected density functional theory (DFT) will be used to study the interaction of pharmaceuticals and related compounds with zeolite adsorbents containing different cations. Focus will be on two large-pore zeolites of particular relevance to applications (FAU and MOR framework types), considering systems containing cations from different groups. The first part of the project will comprise a thorough validation of the DFT methodology, both in terms of preferred cation sites and adsorption energies. In the second part, the interaction between cationic zeolites and a set of “model compounds”, relatively simple pharmaceuticals containing representative functional groups, will be studied systematically, considering different cation species as well as variations in Si/Al ratio and framework type (FAU/MOR). A set of case studies will be performed in the third part: On the basis of published experimental studies, organic species of particular interest in the context of wastewater treatment or drug delivery will be identified. DFT calculations will then be employed to study their interaction with cationic zeolites, not only comparing different cation types, but also considering various additional aspect of relevance for real-world applications, such as the impact of temperature and the competitive adsorption of water. Altogether, the calculations performed in this project will lead to a better atomic-level understanding of the interactions between functional organic molecules and cationic zeolites, delivering valuable insights for the development of tailored zeolite adsorbents. While the project itself is of a purely computational nature, it is anticipated that it will stimulate more applied research activities by allowing the identification of zeolite-guest combinations that warrant a more comprehensive experimental investigation.