Studying the adsorption of emerging organic contaminants in zeolites with dispersion-corrected density functional theory calculations: From numbers to recommendations

Abstract

It has been established that adsorption energies obtained from dispersion-corrected density functional theory (DFT) calculations show a considerable dependence on the choice of exchange-correlation functional and dispersion correction. A number of investigations have employed different approaches to compute adsorption energies of small molecules like methane, ethane, or carbon dioxide in different types of zeolites (all-silica, protonated, cation-exchanged), using reference values from high-level calculations and/or experiments. Such comparative studies are lacking for the adsorption of larger functional organic molecules such as pharmaceuticals or personal care products in zeolites, despite the potential relevance for various applications, among them contaminant removal and drug delivery. The present study aims to fill this gap by comparing adsorption energies and, for selected cases, equilibrium structures of adsorption complexes of emerging organic contaminants in all-silica zeolites, employing a total of 13 dispersion-corrected DFT approaches. Methods using a pairwise (D3) dispersion correction as well as non-local van der Waals density functionals were included. A comparison of adsorption energies obtained for a variety of emerging organic contaminants in zeolites with the MOR and FAU topologies showed that the absolute values vary widely, whereas the qualitative trend across the set of zeolite-contaminant combinations are not strongly dependent on the choice of functional. For a few cluster models, DFT adsorption energies were compared to reference values obtained with the random phase approximation. When combining these results with observations of previous benchmarking studies, the rev-vdW-DF2 and PBE-D3 functionals emerge as approaches that should be (relatively) free from a systematic tendency to deliver too negative adsorption energies.

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

“…DFT calculations and AIMD simulations used the electronic structure module Quickstep of the CP2K package, version 9.1, which uses the Gaussian and plane wave method (VandeVondele et al 2005;Kühne et al 2020). The rev-vdW-DF2 exchange-correlation functional was used in all calculations (Hamada 2014), in line with earlier studies addressing the interaction of sizeable organics with zeolites (Fischer 2022;Fischer 2023). Core electrons were represented using Goedeker-Teter-Hutter (GTH) pseudopotentials devised by Krack (Krack 2005).…”

“…This indicates that such simulations could be employed to predict zeolite adsorbents having a high affinity towards a given PPCP prior to an experimental characterization. Subsequently, the adsorption energies were recomputed using periodic electronic structure calculations in the framework of dispersion-corrected density functional theory (DFT) with the purpose of identifying suitable DFT approaches for the study of functional organic molecules in zeolites (Fischer 2022). Several earlier DFT studies employed cluster models cut out from the zeolite structure in order to reduce the computational expense, with examples including investigations of sulfonamide antibiotics in all-silica FAU (Braschi et al 2010;Braschi et al 2013) and of salicylic acid, carbamazepine, and ciprofloxacin in cation-exchanged FAU (Wei et al 2017).…”

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

“…All calculations used the rev-vdW-DF2 functional, 45 which was found to perform well in previous studies of guest-free zeolite structures 46 and of adsorption complexes of different contaminants in all-silica zeolites. 40 Goedeker-Teter-Hutter pseudopotentials devised by Krack were employed to represent the core electrons. 47 The first Brillouin zone was sampled at the Γ-point, only.…”

“…48 The BFGS optimisations were considered converged when the maximal residual force was below 5•10 −6 Ha bohr −1 and, simultaneously, the maximal step size (displacement between optimisation steps) was below 2•10 −5 bohr. As double-zeta basis sets deliver systematically too negative adsorption energies, 40 single-point calculations employing triple-zeta (TZVP-MOLOPT) basis sets were used to compute the energies for the optimised structures. These single-point calculations used a cutoff energy of 900 Ry.…”

“…39 The adsorption energies were subsequently recomputed using density functional theory (DFT) calculations, aiming at a comparison of the results obtained with different exchange-correlation functionals. 40 While more comprehensive DFT investigations of CBZ adsorption in zeolites are lacking, a recent study addressed the adsorption at the surfaces of the mineral kaolinite, a sheet silicate. 41 Use of the dispersion-corrected PBE-D2 functional 42,43 resulted in an adsorption energy of −138 kJ mol −1 for the adsorption of CBZ at the aluminol surface of kaolinite.…”