Jumping Diffusion of Water Intercalated in Layered Double Hydroxides

Our molecular dynamics simulation study shows water in the nanoconfined monolayer in Cl^–-Mg₂Al-layered double hydroxides (Mg₂Al­(OH)₆Cl·<i>m</i>H₂O) diffuses in a similar way as atoms in solid lattice. A water molecule is mostly fixed in a hydroxyl group site, as an acceptor of hydrogen bonds donated by the upper and lower hydroxyl groups simultaneously. Because of exchange of acceptors, it loses hydrogen bonds from the two hydroxyl groups and accepts hydrogen bonds from another two groups in an adjacent site. Thus, a water molecule jumps from one site to another, which is rapid but rare. On average it takes ∼10⁴ ps for a jump to happen on a water molecule. The diffusion coefficient derived by the jump model is of the same order (∼10^–9 cm²/s) as that obtained by fitting the mean-square displacement, revealing water diffusion in the confined monolayer is largely contributed by a series of jump events