N-Nitrosodimethylamine (NDMA), which is a carcinogenic and toxic N-nitrosamine, can be found in water resources associated with a multitude of processes in various industrial facilities or merely as a by-product of water or wastewater treatment. Therefore, the removal of NDMA from drinking water represents an important human safety and public health concern. The present paper presents a density functional theory study of NDMA adsorption in all-silica MFI, Na-ZSM-5 and H-ZSM-5 zeolites. The stability of NDMA inside the zeolite pores was investigated by calculating the amount of energy released during adsorption. Various configurations of adsorbed NDMA to the zeolites were investigated, predominantly at the intersection of straight and sinusoidal channels. The strength of the adsorption energies followed the order H-ZSM5 > Na-ZSM-5 > all-silica MFI. NDMA has a dipole moment and the strongest binding of NDMA occurred through the interactions of the negatively charged O atom of the molecule to positive atoms of the zeolite. Similar calculations were performed for water adsorption in these three zeolites. The adsorption energy of water to these three structures followed the order Na-ZSM5 > H-ZSM-5 > all-silica MFI. We also incorporated van der Waals corrections in the simulations, which had the effect of stabilizing NDMA within the zeolite channels, but did not significantly change the relative stability of the different adsorption geometries. It was concluded that H-ZSM-5 is the best choice to remove NDMA because it is strong enough to adsorb NDMA and it is not too strong in adsorption of water molecules.
Worcester Polytechnic Institute
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Kamaloo, Elaheh, "Molecular Modeling of Adsorbed NDMA in MFI Zeolites" (2013). Masters Theses (All Theses, All Years). 299.
Zeolite, Molecular Modeling, N-nitrosamines, NDMA, DFT