Yazar "Wang, Jun" seçeneğine göre listele

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    Hydration Energetics of a Diamine-Appended Metal-Organic Framework Carbon Capture Sorbent
    (Amer Chemical Soc, 2020) Wang, Jun; Yilmaz, Esra; Zhang, Xianghui; Li, Houqian; Zhang, Renqin; Guo, Xiaofeng; Wu, Di
    mmen-Mg-2(dobpdc) (mmen = N,N'-dimethylethylenediamine, dobpdc = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) is a diamine-appended metal-organic framework (MOF) material with promising future as an efficient CO2 capture sorbent for industry applications. Here, using adsorption calorimetry, the energetic landscape of mmen-Mg-2(dobpdc) hydration has been revealed. Specifically, at near-zero water coverage, hydration results in the most exothermic differential enthalpy of adsorption of -110.9 +/- 3.1 kJ/mol water. A differential enthalpy plateau at -65.8 +/- 4.7 kJ/mol water is observed at the intermediate degree of hydration, which corresponds to water-diamine chemisorption through hydrogen bonding. Eventually, mmen-Mg-2(dobpdc) hydration is concluded at the second differential enthalpy plateau at -44.2 +/- 1.8 kJ/mol water suggesting condensation of water within the internal channel space of mmen-Mg-2(dobpdc). the position of the second plateau at about -44.0 kJ/mol water strongly suggests formation of liquid-like water clusters within the hydrophilic nanoconfinement environment. This comprehensive study energetically distinguishes the guest-host interfacial bonding and guest-guest intermolecular interactions for the water-mmen-Mg-2(dobpdc) system, which provides fundamental thermodynamic data to enhance our understanding of the behavior of CO2 capture sorbents in the presence of moisture.
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    Thermodynamic, Thermal, and Structural Stability of Bimetallic MIL-53 (Al1-xCrx)
    (Amer Chemical Soc, 2021) Mertsoy, Esra Y.; Zhang, Xianghui; Cockreham, Cody B.; Goncharov, Vitaliy G.; Guo, Xiaofeng; Wang, Jun; Wei, Nian
    Understanding the stability of porous materials, especially metal-organic frameworks ( MOFs), is central to defining their applications in gas storage, separation, and catalysis. Herein, integrating high-temperature drop combustion calorimetry as well as simultaneous thermal and in situ structural analyses, we performed a comprehensive study on the thermodynamic, thermal, and structural stabilities of MOF in air. A family of MIL-53 (Al1-xCrx) with systematically tuned metal contents was intentionally chosen considering their unique property that H2BDC species serve as both coordinated linkers and guest species confined. The results suggest that as temperature increases, all samples underwent (1) a phase transition from the pore-filled Pnma to the Imma with empty pores, (2) structural degradation, and (3) complete oxidation (burning). At the same temperature, as the chromium (Cr) content increases, the thermal and structural stability of MIL-53 (Al1-xCrx) in air decreases. In contrast, interestingly, the intrinsic thermodynamic stability systematically increases as a function of Cr content, evidenced by the more exothermic enthalpies of formation, ranging from 92.8 +/- 73.4 kJ/mol (slightly metastable) to -1593.2 +/- 60.8 kJ/mol (stable). Such a phenomenon is likely due to enhanced H2BDC-MIL-53 guest-host interactions upon Cr substitution, which energetically neutralize the metastability of MIL-53 open frameworks. This study highlights that the thermal, structural, and energetic stabilities are different and have equal importance in governing the synthesis and applications of MOFs.