Fast Gas Adsorption Kinetics in Supraparticle-based Mof Packings with Hierarchical Porosity.

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. Here, we address this problem by forming materials with structural hierarchy, using a supraparticle-based approach. We fabricate spherical supraparticles composed of nanosized MOF particles by emulsion templating and use them as the structural component forming a macroscopic material. We use zeolitic imidazolate framework-8 (ZIF-8) particles as a model system and compare the gas adsorption kinetics of our hierarchical material with conventional pellets without structural hierarchy. We demonstrate that a pellet packed with supraparticles exhibits a 30 times faster adsorption rate than unstructured ZIF-8 powder. These results underline the importance of controlling structural hierarchy to maximize the performance of existing materials. In our 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. This article is protected by copyright. All rights reserved.