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Supramolecular modification of a metal–organic framework increases sorption switching: insights into reversible structural deformation of ZIF-8
Journal of Materials Chemistry A ( IF 10.7 ) Pub Date : 2022-09-13 , DOI: 10.1039/d2ta02962f
Al A. Tiba 1 , Jason A. Perman 2 , Leonard R. MacGillivray 1 , Alexei V. Tivanski 1
Affiliation  

Use of chemical modulators during the synthesis of coordination frameworks is an important strategy to affect and tune properties of porous materials. Herein, we introduce an approach to understanding structural modulation and deformation of porous nanocrystals in the context of gas adsorption by using atomic force microscopy (AFM) nanoindentation, scanning electron microscopy energy dispersive X-ray spectroscopy, and gas physisorption analysis. Modified nanocrystals of the prototypical zeolitic-imidazolate framework-8 (ZIF-8) were generated in triethylamine (Et3N) via in situ supramolecular modification in solution phase and compared to unmodified nanocrystals. The crystals of both samples had similar rounded morphologies with identical sizes ranging from 30–140 nm in diameter and height of 30–90 nm. We demonstrate that using Et3N as a modulator results in a conspicuous decrease in elastic modulus (0.7 ± 0.2 GPa) compared to unmodified nanocrystals of ZIF-8 (2.1 ± 0.8 GPa). Argon gas adsorption analysis also reveals that the more flexible, amine-modified framework exhibited gradual and cooperative gate-opening structural expansion at P/P0 = 0.33 ± 0.02 compared to the steeper and stepwise characteristics of unmodified samples of ZIF-8 at P/P0 = 0.45 ± 0.02. The lower Ar gas pressure required to induce reversible structural deformation during gas uptake corresponds to the decrease in elastic modulus of Et3N-modified nanocrystals of ZIF-8. Structural characterization suggests that Et3N contributed to lower relative numbers of hydrogen bonds and 2-methylimidazole linkers, creating more point defects in the modified framework while crystal structure remained unchanged. Our study also demonstrates how a combination of AFM nanoindentation, gas uptake, and spectroscopic characterization can be applied to understand structural and energetic changes upon adsorption in porous nanocrystals with modified supramolecular interactions.

中文翻译:

金属-有机框架的超分子修饰增加了吸附转换:ZIF-8可逆结构变形的见解

在合成配位框架过程中使用化学调节剂是影响和调整多孔材料性能的重要策略。在此,我们介绍了一种通过使用原子力显微镜 (AFM) 纳米压痕、扫描电子显微镜能量色散 X 射线光谱和气体物理吸附分析来理解气体吸附背景下多孔纳米晶体的结构调制和变形的方法。在三乙胺 (Et 3 N)中通过原位生成原型沸石-咪唑酯骨架 8 (ZIF-8) 的改性纳米晶体溶液相中的超分子修饰并与未修饰的纳米晶体进行比较。两种样品的晶体具有相似的圆形形态,尺寸相同,直径为 30-140 nm,高度为 30-90 nm。我们证明,与未改性的 ZIF-8 纳米晶体 (2.1 ± 0.8 GPa) 相比,使用 Et 3 N 作为调制剂会导致弹性模量 (0.7 ± 0.2 GPa) 显着降低。氩气吸附分析还表明,与未修饰的 ZIF- 8样品P / 0 _= 0.45 ± 0.02。在气体吸收过程中诱导可逆结构变形所需的较低 Ar 气体压力对应于ZIF-8的 Et 3 N 改性纳米晶体的弹性模量的降低。结构表征表明,Et 3 N 有助于降低氢键和 2-甲基咪唑接头的相对数量,在改性框架中产生更多点缺陷,而晶体结构保持不变。我们的研究还展示了如何将 AFM 纳米压痕、气体吸收和光谱表征相结合,以了解在具有修饰的超分子相互作用的多孔纳米晶体中吸附后的结构和能量变化。
更新日期:2022-09-13
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