Calcium Vapor Adsorption on the Metal–Organic Framework NU-1000: Structure and Energetics

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• 作者：James M. Lownsbury ; Iván A. Santos-López ; Wei Zhang ; Charles T. Campbell ; Haoyu S. Yu ; Wei-Guang Liu ; Christopher J. Cramer ; Donald G. Truhlar ; Timothy Wang ; Joseph T. Hupp ; Omar K. Farha
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：August 4, 2016
• 年：2016
• 卷：120
• 期：30
• 页码：16850-16862
• 全文大小：830K
• 年卷期：0
• ISSN：1932-7455

文摘

The nature and energy of the reactions between calcium vapor and the internal surfaces of the metal–organic framework (MOF) NU-1000 have been studied by adsorption microcalorimetry, low energy He⁺ ion scattering spectroscopy (LEIS), X-ray photoelectron spectroscopy (XPS), and Kohn–Sham density functional theory (DFT). NU-1000 is one of the most stable MOFs with transition-metal-oxide nodes, and thus it is of interest as a potential catalyst or catalytic support when modified with other metals. The reaction heats of Ca with NU-1000 are high below 2 monolayers (ML) Ca coverage (570–366 kJ/mol), attributed (based on DFT) to Ca reacting first with free benzoic acid functionalities or water impurities, then with H₂O and OH groups on the Zr₆ nodes to produce Ca(OH)₂ clusters. With higher Ca doses, the heat of Ca reaction decreases asymptotically to the sublimation enthalpy of bulk Ca (178 kJ/mol), attributed to the formation of Ca(solid) nanoparticles on the external surface, which only occurs after all of the H₂O and OH groups are titrated deeply enough (∼20 nm) such that slow Ca diffusion prevents further reaction.