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Title: Molecular Simulations of Biofuel and Water Purification in Metal-Organic Frameworks
Keywords: Liquid-phase separations, Metal-organic frameworks, biofuel purification, water purifcation, ion exchange
Issue Date: 3-Jan-2012
Citation: ANJAIAH NALAPARAJU (2012-01-03). Molecular Simulations of Biofuel and Water Purification in Metal-Organic Frameworks. ScholarBank@NUS Repository.
Abstract: In the last decade, metal-organic frameworks (MOFs) have emerged as versatile nanoporous materials for widespread applications. To date, most experimental and theoretical studies on MOFs have focused on gas storage and separation. Recently, attention is particularly turning towards employing MOFs in liquid-phase separation. In this thesis, the objectives are to investigate biofuel and water purification in chemically and thermally stable MOFs by molecular simulation. As an initial step, the microscopic properties of water and alcohols in MOFs are examined. Because of the high affinity for nonframework ions, water is strongly adsorbed in rho-ZMOF with a three-step adsorption mechanism. Upon water adsorption, Na+ cations are redistributed among different favorable sites and the mobility of ions is promoted, which reveals the subtle interplay between water and nonframework ions. The adsorption isotherms of water and alcohols (methanol and ethanol) in Na-rho-ZMOF are type I as a consequence of the high affinity of adsorbates with framework. 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. Alcohols are selectively more adsorbed at low pressures from water/alcohol mixtures, but surpassed by water with increasing pressure. Biofuel (water/ethanol mixtures) purification is studied in two MOFs, hydrophilic Na-rho-ZMOF and hydrophobic Zn4O(bdc)(bpz)2 at both pervaporation (PV) and vapor permeation (VP) conditions. In Na-rho-ZMOF, water is preferentially adsorbed over ethanol and the diffusion selectivity of water/ethanol increases in Na-rho-ZMOF with increasing water composition. In contrast, ethanol is adsorbed more in Zn4O(bdc)(bpz)2 and the diffusion selectivity of ethanol/water decreases slightly with increasing water composition. The permselectivities in the two MOFs at both PV and VP conditions are largely determined by the adsorption selectivities. In addition, ion exchange in Na-rho-ZMOF is investigated towards water purification. Ion exchange between toxic Pb2+ ions in water and Na+ ions in Na-rho-ZMOF is observed from simulation. This study presents microscopic insights into the separation of water-ethanol mixtures and ion exchange process in MOFs, and suggests that MOFs might be intriguing candidates for biofuel and water purification.
Appears in Collections:Ph.D Theses (Open)

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