Rapid room-temperature synthesis of hierarchical porous zeolitic imidazolate frameworks with high space-time yield

Abstract

Hierarchical porous zeolitic imidazolate frameworks (ZIFs) have potential for adsorption, catalysis and chemical sensing applications. Ultrafast synthesis of ZIFs at room temperature and pressure is particularly desirable for large-scale industrial production. Here, we developed a green and versatile method using organic amines as supramolecular templates (organic amine-template) to rapidly synthesize hierarchical porous ZIFs (ZIF-8, ZIF-61 and ZIF-90) at room temperature and pressure. The synthesis time was reduced dramatically to within 1 min, and the resulting ZIFs had multimodal hierarchical porous structures with mesopores/macropores interconnected with micropores. Notably, the space–time yield (STY) of hierarchical porous ZIF-8 was up to 1.29× 104 kg m–3 d–1, which is more than three times higher than that reported using other methods. Furthermore, the morphologies and porosities of the produced ZIFs could be readily tuned by controlling the synthesis time or type of organic amine. The organic amine played two roles in the synthesis: (1) a protonation agent to deprotonate organic ligands, facilitating the formation of ZIF crystals, and (2) an structure directing agent to direct mesopore/macropore formation. The resulting hierarchical porous ZIF-8 exhibited enhanced uptake capacities and diffusion rates for guest molecules relative to its microporous counterpart. This work provides a new direction for the green and efficient synthesis of various hierarchical porous ZIFs with high STYs for a wide range of applications.