Real-Time Multiple Beam Interferometry Reveals Complex Deformations of Metal鈥揙rganic-Framework Crystals upon Humidity Adsorption/Desorption

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• 作者：Theodoros Baimpos ; Buddha Ratna Shrestha ; Qingyun Hu ; Georgi Genchev ; Markus Valtiner
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：July 23, 2015
• 年：2015
• 卷：119
• 期：29
• 页码：16769-16776
• 全文大小：412K
• ISSN：1932-7455

文摘

Gas adsorption in metal鈥搊rganic-frameworks (MOFs) can dramatically affect the size of the crystals (expansion and/or shrinkage) or lead to distortion of their porous structure/framework. This can strongly affect mechanical properties of MOFs potentially leading to loss or improvement of the performance of applications such as membranes, filters, or sensors. Here, we utilize white light multiple-beam-interferometry (MBI) in a surface forces apparatus (SFA) to measure in real-time the deformations taking place in HKUST-1 crystals during humidity adsorption/desorption cycles. MBI provides a real-time measurement of crystal deformations during guest molecule uptake with msecs time and 脜 distance resolution. We find unusual and unexpected dynamic and nonmonotonic deformation behavior upon humidity loading in HKUST-1 crystals, which we attributed to the gradual filling of the different adsorption sites in the MOF crystal framework. Also, the effect of the external mechanical pressure applied to hydrated/dehydrated crystals strongly affects the flexibility of HKUST-1 crystals and hence their deformation characteristics during guest molecule loading. Our results may have important implications for better understanding/modeling of the effect of gas adsorption on the mechanical properties of MOFs. MBI may be extended not only to other MOFs but also to any other guest鈥搈olecule systems in which adsorbate/adsorbent interactions affect structure鈥損roperty relationships.