Pressure promoted low-temperature melting of metal-organic frameworks
Pressure promoted low-temperature melting of metal-organic frameworks
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DOI：
10.1038/s41563-019-0317-4
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发表时间：
2019-04-01
期刊：
影响因子：
41.2
通讯作者：
Bennett, Thomas D.
中科院分区：
文献类型：
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作者：
Widmer, Remo N.;Lampronti, Giulio, I;Bennett, Thomas D.
金属有机骨架（MOFs）是一种具有巨大化学应用潜力的微孔材料。近年来，在沸石咪唑盐骨架（ZIF）家族的mof中发现了高压下结构崩溃和高温下向液态转变的现象。在这里，我们发现同时高压和高温条件导致ZIF-62和ZIF-4的复杂行为，在压力-温度相图的不同区域出现明显的高密度和低密度非晶相。原位粉末x射线衍射、拉曼光谱和光学显微镜显示，在中等工业压力下，液态MOF状态的稳定性在较低温度下大幅扩大，第一性原理分子动力学表明，框架配合压力的软化使热力学上更容易熔化。此外，熔体淬火高温液体形成的MOF玻璃具有永久的、可接近的孔隙。因此，我们的研究结果暗示了在低温下合成功能性MOF玻璃的途径，避免了在环境压力下加热时的分解。
Metal-organic frameworks (MOFs) are microporous materials with huge potential for chemical processes. Structural collapse at high pressure, and transitions to liquid states at high temperature, have recently been observed in the zeolitic imidazolate framework (ZIF) family of MOFs. Here, we show that simultaneous high-pressure and high-temperature conditions result in complex behaviour in ZIF-62 and ZIF-4, with distinct high-and low-density amorphous phases occurring over different regions of the pressure-temperature phase diagram. In situ powder X-ray diffraction, Raman spectroscopy and optical microscopy reveal that the stability of the liquid MOF state expands substantially towards lower temperatures at intermediate, industrially achievable pressures and first-principles molecular dynamics show that softening of the framework coordination with pressure makes melting thermodynamically easier. Furthermore, the MOF glass formed by melt quenching the high-temperature liquid possesses permanent, accessible porosity. Our results thus imply a route to the synthesis of functional MOF glasses at low temperatures, avoiding decomposition on heating at ambient pressure.