Hierarchically porous metal–organic frameworks: rapid synthesis and enhanced gas storage

Abstract

Large pore sizes, high pore volumes, facile synthesis conditions, and high space–time yields are recognized as four crucial criteria in the fabrication of metal–organic frameworks (MOFs). However, these four objectives are rarely realized together. Herein, we have developed a simple and versatile method that employs 1,4-butanediamine (BTDM) as a template for rapidly fabricating four stable hierarchically porous MOFs (H-MOFs), including HKUST-1, ZIF-8, ZIF-67, and ZIF-90. The synthesis conditions are simple and facile at room temperature and ambient pressure, and the synthesis time can be shortened to 1 min. The resultant H-MOFs exhibit multimodal hierarchically porous structures with meso- and macropores interconnected with micropores, as well as high pore volumes (0.76 cm³ g⁻¹). The maximum space–time yield for the hierarchically porous HKUST-1 reaches 7.4 × 10⁴ kg m⁻³ d⁻¹, at least one order of magnitude higher than previous reported yields. Notably, the additive BTDM not only facilitates crystal growth but also guides the formation of meso- and macropores. The synthesis route is highly versatile, as analogues (e.g., tetramethyl-1,3-diaminopropane and tetramethyldiaminomethane) can also be employed as templates to prepare diverse H-MOFs. Furthermore, the porosities of the H-MOFs are readily tuned by controlling the metal source, template amount and type of template. The as-synthesized H-MOFs act as adsorbents with significantly improved performances relative to those of microporous MOFs used for CH₄ and CO₂ gas storage. This strategy may aid in the large-scale industrial synthesis of desirable H-MOFs for gas storage.