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Title: Molecular understanding for the adsorption of water and alcohols in hydrophilic and hydrophobic zeolitic metal-organic frameworks
Authors: Nalaparaju, A.
Zhao, X.S. 
Jiang, J.W. 
Issue Date: 8-Jul-2010
Citation: Nalaparaju, A., Zhao, X.S., Jiang, J.W. (2010-07-08). Molecular understanding for the adsorption of water and alcohols in hydrophilic and hydrophobic zeolitic metal-organic frameworks. Journal of Physical Chemistry C 114 (26) : 11542-11550. ScholarBank@NUS Repository.
Abstract: A molecular simulation study is reported for the adsorption of water and alcohols (methanol and ethanol) in two metal-organic frameworks (MOFs) topologically similar to rho-zeolite; one is a hydrophilic Na +-exchanged rho-zeolite-like MOF (Na-rho-ZMOF), and the other is a hydrophobic zeolitic-imidazolate framework-71 (ZIF-71). The adsorption isotherms in Na-rho-ZMOF are type I as a consequence of the high affinity of the nonframework Na+ ions and ionic framework. The adsorption capacity decreases in the order of water > methanol > ethanol. Water is adsorbed more closely in the window region, whereas methanol and ethanol are populated in the α cage due to steric effect. In water/methanol and water/ethanol mixtures, water adsorption increases continuously with increasing pressure and replaces alcohols competitively at high pressures. In ZIF-71, the framework-adsorbate affinity is relatively weaker and type V adsorption is observed. Water has vanishingly small adsorption at low pressures and a sharp increase in adsorption at 22 kPa due to capillary condensation. Methanol and ethanol exhibit cluster-growth adsorption, followed by continuous pore filling. The adsorption in ZIF-71 increases in the order of water < methanol < ethanol at low pressures; however, the opposite order is observed at high pressures because of entropy effect. In water/alcohol mixtures, alcohols are selectively more adsorbed at low pressures but surpassed by water with increasing pressure. The framework charges have a substantial effect on adsorption in Na-rho-ZMOF, but not in ZIF-71. This study provides a molecular understanding for the adsorption of water and alcohols in two zeolitic MOFs with the identical topology and reveals the significantly different adsorption mechanisms. © 2010 American Chemical Society.
Source Title: Journal of Physical Chemistry C
ISSN: 19327447
DOI: 10.1021/jp1033273
Appears in Collections:Staff Publications

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