(684c) Liquid Phase Modeling for Removal of Contaminants of Emerging Concerns and Zeolite Catalysis

Contaminants of emerging concerns (CECs), such as pesticides (clofibric acid), pharmaceuticals (aspirin and carbamazepine), personal care products (caffeine), and plastics (bisphenol A), are increasingly found in groundwater sources, and remediation strategies are imperative for food security and human health. A new computational approach for removing sub-ppm level amounts of CECs from irrigation water sources has been developed with highly selective nanoporous adsorbents like acidic zeolite H-MFI.

First, a hybrid quantum mechanical/molecular mechanical (QM/MM) method was developed to describe the adsorption characteristics over acidic sites of zeolite under vapor phase conditions. The role of several cluster sizes containing 5-90 tetrahedral (T) atoms is examined for non-periodic QM cluster optimization calculations with several hybrid functionals (wb97 and wb97x), triple-ζ quality basis set, and in the presence of an extended zeolite framework described by standard force fields (electrostatic interactions and Lennard-Jones potential). This QM/MM method was designed for potential water sampling within the zeolite in mind. As model adsorption process with known experimental heat of adsorption, we computed both methanol and ethanol adsorption (free) energies on Bronsted sites in H-MFI zeolite with our QM/MM method and compared our data against experimental and periodic DFT data (see Figure 1).

To understand the adsorption characteristic of CECs from water, an explicit water solvent model has been used together with the free energy perturbation technique to analyze the adsorption of various CECs from water in zeolites. For water sampling within the zeolite pore network (a required step for our free energy perturbation calculations), Grand Canonical Monte Carlo (GCMC) simulations have been performed.