化学
化学吸附
碘
水溶液
咪唑酯
吸附
沸石咪唑盐骨架
无机化学
结合能
物理化学
金属有机骨架
有机化学
物理
核物理学
作者
James T. Hughes,Dorina F. Sava,Tina M. Nenoff,Alexandra Navrotsky
摘要
For the first time, using aqueous solution calorimetry, we clearly identify the chemisorption of an unusually strong iodine charge-transfer (CT) complex within the cages of a metal–organic framework. Specifically, we studied the sorption of iodine gas in zeolitic imidazolate framework-8 (ZIF-8, Zn(2-methylimidazolate)2). Two iodine-loaded ZIF-8 samples were examined. The first, before thermal treatment, contained 0.17 I2/Zn on the surface and 0.59 I2/Zn inside the cage. The second sample was thermally treated, leaving only cage-confined iodine, 0.59 I2/Zn. The energetics of iodine confinement per I2 (relative to solid I2) in ZIF-8 are ΔHads = −41.47 ± 2.03 kJ/(mol I2) within the cage and ΔHads = −18.06 ± 0.62 kJ/(mol I2) for surface-bound iodine. The cage-confined iodine exhibits a 3-fold increase in binding energy over CT complexes on various organic adsorbents, which show only moderate exothermic heats of binding, from −5 to −15 kJ/(mol I2). The ZIF-8 cage geometry allows each iodine atom to form two CT complexes between opposing 2-methylimidazolate linkers, creating the ideal binding site to maximize iodine retention.
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