Effect of the Confinement and Presence of Cations on Hydrogen Bonding of Water in LTA-Type Zeolite

The hydrogen bond is one of the most important intra- or intermolecular interactions for molecular systems, especially for those involving water, which have been systematically investigated. Although we deal with water in nanoporous materials in a number of applications, elucidating to what extent its structure is perturbed from the bulk is a virtually unexplored issue. We performed Monte Carlo simulations to compute the adsorption of water in pure silica and cation-containing LTA-type zeolites, namely, ITQ-29, LTA-4A, and LTA-5A, and evaluated the effect of the confinement and presence of cations on its structural properties. The high water stability and industrial impact of zeolites, with either hydrophobic or hydrophilic character, make them of great interest for the targeted purpose. The analysis was carried out in terms of the radial distribution functions and hydrogen bond statistics. Specifically, the percentages of water molecules engaged in i hydrogen bonds and the average number of hydrogen bonds per water molecule were computed on the basis of a geometric criterion for hydrogen-bonding definition. The water clustering was likewise evaluated in terms of the number and size of the aggregates. Results reveal a notable structural transformation with respect to bulk water and contribute insight into this problem.