Fujiwara Atsushi, Wang Junwei, Hiraide Shotaro, Götz Alexander, Miyahara Minoru T, Hartmann Martin, Apeleo Zubiri Benjamin, Spiecker Erdmann, Vogel Nicolas, Watanabe Satoshi
Department of Chemical Engineering, Kyoto University, Katsura, Nishikyo, Kyoto, 615-8510, Japan.
Institute of Particle Technology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058, Erlangen, Germany.
Adv Mater. 2023 Nov;35(44):e2305980. doi: 10.1002/adma.202305980. Epub 2023 Sep 26.
Metal-organic frameworks (MOFs) are microporous adsorbents for high-throughput gas separation. Such materials exhibit distinct adsorption characteristics owing to the flexibility of the crystal framework in a nanoparticle, which can be different from its bulk crystal. However, for practical applications, such particles need to be compacted into macroscopic pellets, creating mass-transport limitations. In this work, this problem is addressed by forming materials with structural hierarchy, using a supraparticle-based approach. Spherical supraparticles composed of nanosized MOF particles are fabricated by emulsion templating and they are used as the structural component forming a macroscopic material. Zeolitic imidazolate framework-8 (ZIF-8) particles are used as a model system and the gas-adsorption kinetics of the hierarchical material are compared with conventional pellets without structural hierarchy. It is demonstrated that a pellet packed with supraparticles exhibits a 30 times faster adsorption rate compared to an unstructured ZIF-8 powder pellet. These results underline the importance of controlling structural hierarchy to maximize the performance of existing materials. In the hierarchical MOFs, large macropores between the supraparticles, smaller macropores between individual ZIF-8 primary particles, and micropores inherent to the ZIF-8 framework collude to combine large surface area, defined adsorption sites, and efficient mass transport to enhance performance.
金属有机框架材料（MOFs）是用于高通量气体分离的微孔吸附剂。由于纳米颗粒中晶体框架的灵活性，这类材料呈现出独特的吸附特性，这可能与它们的块状晶体不同。然而，对于实际应用，需要将此类颗粒压实成宏观颗粒，这会造成传质限制。在这项工作中，通过基于超粒子的方法形成具有结构层次的材料来解决这一问题。由纳米尺寸的MOF颗粒组成的球形超粒子通过乳液模板法制备，并用作形成宏观材料的结构组分。沸石咪唑酯骨架-8（ZIF-8）颗粒用作模型体系，并将这种具有层次结构的材料的气体吸附动力学与没有结构层次的传统颗粒进行比较。结果表明，与无结构的ZIF-8粉末颗粒相比，填充有超粒子的颗粒吸附速率快30倍。这些结果强调了控制结构层次以最大化现有材料性能的重要性。在具有层次结构的MOFs中，超粒子之间的大孔、单个ZIF-8初级颗粒之间较小的孔以及ZIF-8框架固有的微孔共同作用，结合了大表面积、明确的吸附位点和高效的传质，从而提高了性能。
