Structural Stability of Metal Organic Framework MOF-177

Journal of Physical Chemistry Letters (Impact Factor: 7.46). 11/2009; 1(1). DOI: 10.1021/jz900028u


Metal organic framework MOF-177 is one of the most promising crystalline porous adsorbents for hydrogen adsorption. The effects of oxygen and water on the structural stability of MOF-177 are investigated by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). A MOF-177 sample is exposed to ambient air for 5 weeks and monitored for its structural changes by XRD. The crystal structure of MOF-177 gradually changes from hexagonal to orthogonal, and then to monoclinic in the 5-week period. The crystal structure of MOF-177 is completely destroyed after it is immersed in water. The weight loss of MOF-177 is negligible at temperatures below 330 °C in the presence of oxygen. However, MOF-177 totally converts to zinc oxide at 420 °C.Keywords (keywords): MOF-177; structural stability; XRD; TGA; crystal structure

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    • "The surface area and pore volume of MOF-177 after immersing in water or exposure to air for 3 days were much smaller than that of the fresh MOF-177 [34] [35]. Therefore, MOF-177 should not be exposed a long time (e.g., 3 days reported at a nominal RH of 40% [35]) to air at relatively high RH in the application although it is a better adsorbent with larger adsorption capacity for VOCs than adsorbents such as activated carbons at relatively high RH conditions. "
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    ABSTRACT: Adsorption of volatile organic compounds (VOCs) including acetone, benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene and ethenylbenzene in air on a synthesized MOF-177 and the influence of humidity on adsorption were examined at 25 ± 0.5 °C. Larger adsorption capacity of VOCs on MOF-177 was observed even at relatively high humidity, suggesting that the porous MOF-177 material could be a potential adsorbent for sorptive removal of the unwanted VOCs from air due to its large surface area and pore volume. Adsorption of VOCs on MOF-177 is captured by a pore filling mechanism, showing a negative linear relationship between the volume adsorption capacity and the molecular cross-sectional area of VOCs. Adsorption of VOCs on MOF-177 in humid air will be suppressed by the competition of water molecules and the decomposition of MOF-177 framework structure with water. It was suggested that MOF-177 should not be exposed a long time to air at relatively high RH and pre-drying of gas is required to avoid the competition suppress of water on adsorption and the decomposition of MOF-177 framework structure in the applications of MOF-177 as adsorbents.
    Preview · Article · Dec 2013 · Journal of Environmental Chemical Engineering
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    ABSTRACT: Metal organic frameworks (MOFs) are an important class of material which has a potential to be used for variety of applications such as in storage materials, pollution control, etc. Here we report a molecular dynamics simulation study investigating dynamical behaviour of the smallest and linear hydrocarbon, acetylene, adsorbed in CuBTC MOF. CuBTC has complex network structure consisting of large pores and tetrahedral pockets connected by windows. Calculated mean squared displacements of the acetylene molecules adsorbed in CuBTC showed anomalous behaviour with change in concentration. This has been understood by studying the evolution of the trajectories and free energy map. There are two pathways for an acetylene molecule to diffuse inside CuBTC. One is through tetrahedral pockets and other is through large pores. It is found that tetrahedral pockets are potential minima sites and most of the molecules reside there at low concentration. Free energy map also showed that there exists a higher energy barrier if diffusion occurs through tetrahedral pockets rather than large pores. Relative population of acetylene molecules in large pores is found to increase with the concentration and since energy barrier is less while diffusing through large pores, it leads to increase in the average diffusivity at higher concentration. It is found that relative population of acetylene molecules diffusing through different pathways and collision between the molecules decide the average diffusivity of the molecules inside CuBTC. Analysis of intermediate scattering function indicated that there exist three time scales associated with the centre of mass diffusion of the acetylene molecules in CuBTC framework.
    No preview · Article · Apr 2013 · Physics of Condensed Matter
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    ABSTRACT: Metal–organic framework (MOF-177) was synthesized, characterized and evaluated for hydrogen adsorption as a potential adsorbent for hydrogen storage. The hydrogen adsorption equilibrium and kinetic data were measured in a volumetric unit at low pressure and in a magnetic suspension balance at hydrogen pressure up to 100 bar. The MOF-177 adsorbent was characterized with nitrogen adsorption for pore textural properties, scanning electron microscopy for morphology and particle size, and X-ray powder diffraction for phase structure. The MOF-177 synthesized in this work was found to have a uniform pore size distribution with median pore size of 12.7 Å, a higher specific surface area (Langmuir: 5994 m2/g; BET: 3275 m2/g), and a higher hydrogen adsorption capacity (11.0 wt.% excess adsorption, 19.67 wt.% absolute adsorption) than previously reported values on MOF-177. Freundlich equation fits well the hydrogen adsorption isotherms at low and high pressures. Diffusivity and isosteric heat of hydrogen adsorption were estimated from the hydrogen adsorption kinetics and equilibrium data measured in this work.
    No preview · Article · Dec 2008 · International Journal of Hydrogen Energy
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