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Title: Atomistic insight into adsorption, mobility, and vibration of water in ion- exchanged zeolite-like metal-organic frameworks
Authors: Nalaparaju, A.
Babarao, R.
Zhao, X.S. 
Jiang, J.W. 
Keywords: Adsorption
Atomistic simulation
Metal-organic frameworks
Issue Date: 22-Sep-2009
Citation: Nalaparaju, A., Babarao, R., Zhao, X.S., Jiang, J.W. (2009-09-22). Atomistic insight into adsorption, mobility, and vibration of water in ion- exchanged zeolite-like metal-organic frameworks. ACS Nano 3 (9) : 2563-2572. ScholarBank@NUS Repository.
Abstract: The adsorption, mobility, and vibration of water in ion-exchanged rho-zeolite-like metal-organic frameworks (ZMOFs) are investigated using atomistic simulations. Because of the high affinity for the ionic framework and nonframework ions, water is strongly adsorbed in rho-ZMOFs with a three-step adsorption mechanism. At low pressures, water is preferentially adsorbed onto Na+ ions, particularly at site II; with increasing pressure, adsorption occurs near the framework and finally in the large cage. Upon water adsorption, Na+ ions are observed to redistribute from site I to site II and gradually hydrated with increasing pressure. In Li-, Na-, and Cs- exchanged rho-ZMOFs, the adsorption capacity and isosteric heat decrease with increasing ionic radius attributed to the reduced electrostatic interaction and free volume. The mobility of water in Na-rho-ZMOF increases at low pressures but decreases upon approaching saturation. With sufficient amount of water present, the mobility of Na+ ions is promoted. The vibrational spectra of water in Na-rho-ZMOF exhibit distinct bands for librational motion, bending, and stretching. The librational motion has a frequency higher than bulk water due to confinement. With increasing loading and hence stronger coordinative attraction, the bending frequency shows a blue shift. Symmetric and asymmetric modes are observed in the stretching as a consequence of the strong water- ion interaction. This study provides a fundamental microscopic insight into the static and dynamic properties of water in charged ZMOFs and reveals the subtle interplay between water and nonframework ions. © 2009 American Chemical Society.
Source Title: ACS Nano
ISSN: 19360851
DOI: 10.1021/nn900605u
Appears in Collections:Staff Publications

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