Molecular Modeling of Univalent Cation Exchange in Zeolite N

Molecular dynamics simulations are used to investigate the hydration energy and ion-exchange properties of a synthetic zeolite, zeolite N with composition |K10(H2O)8Cl2|[Al12Si12O40]. The exchange of K+ ions with univalent ions such as NH4+, Na+, Rb+, and Cs+ is investigated under a range of simulation conditions using a three-dimensional membrane in an electrolyte box containing explicit water molecules. Hydration energy calculations indicate that zeolite N prefers eight water molecules per cage, which is consistent with X-ray and neutron diffraction determination of the structure. Ion density profiles and calculated self-diffusion coefficients show that univalent ion exchange by zeolite N is selective toward NH4+ in preference to other ions. The methodology used here to simulate the uptake of ions from an electrolyte within the zeolite N membrane produces results that are consistent with experimental data and implements a low computational overhead.