Adsorption-Induced Structural Transition of ZIF-8: A Combined Experimental and Simulation Study

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• 作者：Hideki Tanaka ; Shuji Ohsaki ; Shotaro Hiraide ; Daigo Yamamoto ; Satoshi Watanabe ; Minoru T. Miyahara
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：April 24, 2014
• 年：2014
• 卷：118
• 期：16
• 页码：8445-8454
• 全文大小：525K
• 年卷期：v.118,no.16(April 24, 2014)
• ISSN：1932-7455

文摘

Zeolitic imidazolate framework-8 (ZIF-8) has a 鈥済ate-opening鈥?framework with narrow pore apertures that swing open by reorientation of 2-methylimidazolate (MeIM) linkers enforced by guest adsorption. The present study aimed to employ free energy analysis to provide insight into the mechanism of the adsorption-induced structural transition that results from the reorientation of the MeIM linkers. We combined experimental Ar adsorption at cryogenic temperatures with grand canonical Monte Carlo simulations to determine the free energy profiles as functions of the rotational angle of the MeIM linker (胃_IM) and bulk gas pressure. We also estimated the energy fluctuation of the system, which is crucial to discussing the structural transition from a metastable state. The results from the free energy analysis, for example, at 91 K, suggest the following conclusions: A gradual reorientation of the MeIM linkers up to 胃_IM = 10.5掳 occurs with increasing gas pressure that is followed by a spontaneous structural transition to 胃_IM = 25.5掳 during the adsorption process (gate opening), and then, during the desorption process, an equilibrium structural transition occurs with the opposite reorientation of the MeIM linkers from 胃_IM = 25.5掳 to 胃_IM = 10.5掳 (gate closing).