Molecular dynamics studies of nanoconfined water in clinoptilolite and heulandite zeolites

The complete periodic series of alkali and alkaline earth cation variants ( Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, and Ba2+) of clinoptilolite ( Si : Al = 5) and heulandite ( Si : Al = 3.5) aluminosilicate zeolites are examined by large-scale molecular dynamics utilizing a flexible SPC water and aluminosilicate force field. Calculated hydration enthalpies, radial distribution functions, and ion coordination environments are used to describe the energetic and structural components of extra-framework species while power spectra are used to examine the intermolecular dynamics. These data are correlated to evaluate the impact of ion-zeolite, ion-water, and water-zeolite interactions on the behavior of nanoconfined water. Analysis of the correlated data clearly indicates that the charge density of extra-framework cations appears to have the greatest influence on librational motions, while the anionic charge of the framework (i. e. Si : Al ratios) has a lesser impact.