Structural and Mechanistic Differences in Mixed-Linker Zeolitic Imidazolate Framework Synthesis by Solvent Assisted Linker Exchange and de Novo Routes
Structural and Mechanistic Differences in Mixed-Linker Zeolitic Imidazolate Framework Synthesis by Solvent Assisted Linker Exchange and de Novo Routes
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DOI：
10.1021/jacs.7b01660
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发表时间：
2017-04-26
影响因子：
15
通讯作者：
Nair, Sankar
中科院分区：
文献类型：
--
作者：
Jayachandrababu, Krishna C.;Sholl, David S.;Nair, Sankar
混合连接体沸石咪唑酯骨架（ZIF）是金属有机骨架（M0 F）的子类，其通过改变咪唑酯连接体上的官能团而经受显著的性质调节。已经证明了混合接头ZIF的溶剂辅助接头交换（销售）和从头合成，但是这两种不同类型的杂合ZIF的结构特性（最重要的是接头分布和合成机制）的差异是未知的。在这项工作中，H-1 NMR结合旋转和多脉冲光谱（CRAMPS），水吸附和氮测量的组合揭示了销售和从头ZIF-8-90杂交体之间的连接体混合的明显差异。本机荧光共聚焦显微镜显示提供了一个直接的手段来可视化这些差异。详细研究了晶体尺寸、温度和销售持续时间的影响，并提出了ZIF中销售过程的一个可推广的机制。发现销售过程遵循导致核壳形态的扩散限制行为。在更苛刻的销售条件下，由于初始ZIF-8晶体的蚀刻和部分溶解，发现与扩散限制行为的偏差。通过选择适当的反应条件，销售方法似乎能够产生具有良好形态质量的受控核壳ZIF结构，其补充通过从头方法获得的良好混合结构。
Mixed-linker zeolitic imidazolate frameworks (ZIFs) are a subclass of metal organic frameworks (MOFs) amenable to significant property tuning by altering the functional groups on the imidazolate linkers. Solvent assisted linker exchange (SALE) and de novo synthesis of mixed linker ZIFs have been demonstrated, but the differences in structural properties most importantly the linker distributions and synthesis mechanisms of these two different types of hybrid ZIFs are unknown. In this work, a combination of H-1 NMR combined rotation and multiple pulse spectroscopy (CRAMPS), water adsorption, and nitrogen measurements reveal distinct differences in linker mixing between SALE and de novo ZIF-8-90 hybrids. Native-fluorescence confocal microscopy is shown to provide a direct means to visualize these differences. The effects of crystal size, temperature, and SALE duration were studied in detail, and a generalizable mechanism for SALE processes in ZIFs is proposed. The SALE process is found to follow a diffusion-limited behavior leading to core shell morphologies. Under harsher SALE conditions, deviations from diffusion-limited behavior are found due to etching and partial dissolution of the initial ZIF-8 crystals. With the selection of appropriate reaction conditions, SALE processes appear to be capable of generating controlled core shell ZIF structures of good morphological quality that complement the well-mixed structures obtained by de novo methods.