Ab Initio Simulations To Understand the Leaf-Shape Crystal Morphology of ZIF-L with Two-Dimensional Layered Network

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• 作者：Benyamin Motevalli ; Neda Taherifar ; Huanting WangJefferson Zhe Liu
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：February 2, 2017
• 年：2017
• 卷：121
• 期：4
• 页码：2221-2227
• 全文大小：429K
• ISSN：1932-7455

文摘

Two-dimensional porous coordination polymers are the perfect candidates as ultrathin membranes with superior gas separation performances. However, fundamental understanding on the crystal growth, which is vital for membrane applications, is very limited. Studies on the crystal morphologies could provide valuable clues. In this paper, we carried out an ab initio study to understand the crystal morphology of the two-dimensional ZIF-L. Several typical surfaces, such as (001), (100), (010), and (110) surface slabs, were generated by using our developed automated surface generation software package. The corresponding surface energies were calculated. Our results show that the surface relaxation is localized in the first Zn layer, but the magnitude of energy reduction is quite significant, about 60% of surface energy of the as-cut surfaces. We identified two important factors that determine the surface energetic orders of different crystal surfaces: number density and the types of dangling bonds. Particularly, we find that breaking the second coordination bond at one zinc center costs about 65% more energy than the first bond. Based on our surface energy results, the Wulff construction reproduces the smooth curvy leaf shape morphology very well. In the end, we show that our understanding could be extended to another well-known 2D ZIF crystal. Our study would provide valuable insights into the physical/chemical interactions inside such 2D crystals and the growth mechanisms.