Babu Deepu J, He Guangwei, Hao Jian, Vahdat Mohammad Tohidi, Schouwink Pascal Alexander, Mensi Mounir, Agrawal Kumar Varoon
Laboratory of Advanced Separations (LAS), École Polytechnique Fédérale de Lausanne (EPFL), Valais Wallis, CH-1951, Sion, Switzerland.
Institut des Sciences et Ingénierie Chimiques, École Polytechnique Fédérale de Lausanne (EPFL), Valais Wallis, CH-1951, Sion, Switzerland.
Adv Mater. 2019 Jul;31(28):e1900855. doi: 10.1002/adma.201900855. Epub 2019 May 14.
Although polycrystalline metal-organic framework (MOF) membranes offer several advantages over other nanoporous membranes, thus far they have not yielded good CO separation performance, crucial for energy-efficient carbon capture. ZIF-8, one of the most popular MOFs, has a crystallographically determined pore aperture of 0.34 nm, ideal for CO /N and CO /CH separation; however, its flexible lattice restricts the corresponding separation selectivities to below 5. A novel postsynthetic rapid heat treatment (RHT), implemented in a few seconds at 360 °C, which drastically improves the carbon capture performance of the ZIF-8 membranes, is reported. Lattice stiffening is confirmed by the appearance of a temperature-activated transport, attributed to a stronger interaction of gas molecules with the pore aperture, with activation energy increasing with the molecular size (CH > CO > H ). Unprecedented CO /CH , CO /N , and H /CH selectivities exceeding 30, 30, and 175, respectively, and complete blockage of C H , are achieved. Spectroscopic and X-ray diffraction studies confirm that while the coordination environment and crystallinity are unaffected, lattice distortion and strain are incorporated in the ZIF-8 lattice, increasing the lattice stiffness. Overall, RHT treatment is a facile and versatile technique that can vastly improve the gas-separation performance of the MOF membranes.
尽管多晶金属有机框架（MOF）膜相比其他纳米多孔膜具有若干优势，但迄今为止，它们尚未展现出良好的CO分离性能，而这对于节能碳捕集至关重要。ZIF-8是最受欢迎的MOF之一，其晶体学确定的孔径为0.34纳米，非常适合CO₂/N₂和CO₂/CH₄分离；然而，其灵活的晶格将相应的分离选择性限制在5以下。据报道，一种新型的合成后快速热处理（RHT）方法，即在360℃下几秒钟内完成，可显著提高ZIF-8膜的碳捕集性能。通过温度激活传输的出现证实了晶格硬化，这归因于气体分子与孔径之间更强的相互作用，活化能随分子尺寸增加（CH₄ > CO₂ > H₂）。分别实现了前所未有的CO₂/CH₄、CO₂/N₂和H₂/CH₄选择性超过30、30和175，以及对C₂H₄的完全阻隔。光谱和X射线衍射研究证实，虽然配位环境和结晶度未受影响，但ZIF-8晶格中引入了晶格畸变和应变，从而提高了晶格刚度。总体而言，RHT处理是一种简便且通用的技术，可极大地提高MOF膜的气体分离性能。
