Introduction of multiple pore size regimes into metal-organic frameworks (MOFs) to form hierarchical porous structures can lead to improved performance of the material in various applications. In many cases, where interactions with bulky molecules are involved, enlarging the pore sizes of typically microporous MOF adsorbents or MOF catalysts is crucial for enhancing both mass transfer and molecular accessibility. In this review, we examine the range of synthetic strategies which have been reported thus far to prepare hierarchical MOFs or MOF composites with added macroporosity. These fabrication techniques can be either pre- or post-synthetic and include use of structural templating agents, gelation, defect formation, routes involving supercritical CO2 and 3D printing. We also discuss some challenges involved in the current techniques, which must be addressed if any of these approaches are to be taken forward for large-scale application.
This review was published in Nano-Micro Letters 11, 54 (2019)