Temperature-Dependent Structure and Dynamics of Water Intercalated in Layered Double Hydroxides with Different Hydration States
M Chen and RL Zhu and JX Zhu and HP He, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 23752-23762 (2017).
Properties of water confined in layered double hydroxides (LDH) are relevant with hydration, dehydration, and protonic conduction in interlayer galleries. Evolutions of structure and dynamics of water in LDHs (Mg2Al(OH)(6)Cl center dot mH(2)O) with temperature are disclosed through molecular dynamics simulations performed in the range from 300 to 430 K. LDHs with m = 0.78 and 1.44 which characterize two different hydration states are investigated. Water in the lower hydration state is characterized with higher ordered structure. Irrespective of water content, water becomes less hydrogen bonded and more disordered as temperature increases. This leads to a large decrement in dehydration enthalpy, which facilitates dehydration energetically. Irrespective of temperature or water content, water exhibits the preference for being fixed in hydroxyl sites and it diffuses through jumping between neighbor sites. Jump diffusion approximately exhibits an Arrhenius dependence on temperature. A jump is a collective process consisting of water translation and hydroxyl group reorientation, which is reflected in the high activation energy and low attempt frequency. Hydronium ions may be transported through jumping between neighbor sites, making a contribution to proton transfer in interlayer galleries.
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