New strategy to synthesis of hierarchical porous ZIF-8 for enhanced mass transport inside the pore

Metal–organic frameworks (MOFs), a new class of porous crystalline materials, have attracted significant interest for potential applications in gas separation, storage, and catalysis. The application of zeolitic imidazolate framework-8 (ZIF-8), a versatile MOF based on imidazolate ligands, is hindered by its structure. The microporous ZIF-8 structure has a negative effect on diffusion and mass transfer, which can lead to a low diffusion rate of reactants larger than 2 nm. To overcome these disadvantages, the concept of superstructured hierarchical porous ZIF-8 (HPZIF-8) micro-particle has been presented, which consists of two different pore structures (micropore and mesopore). We propose a simple aggregation method to enhance the controllability and performance of ZIF-8 in a water-based environment. Compared with the same-sized ZIF-8 particles, the HPZIF-8 particles can reach the higher mass transfer through the mesopores and lead to high diffusion rates. To demonstrate the performance enhancement, the fabricated HPZIF-8 was characterized as a photocatalyst for removing methylene blue from water. The two different pore structures of HPZIF-8 resulted in improved catalytic performance. These results could inspire MOFs research for applications such as carbon dioxide capture and catalysis.