Room-temperature rapid synthesis of hierarchically porous ZIF-93 for effective adsorption of volatile organic compounds

Facile synthesis conditions, abundant hierarchical porosity, and high space-time yields (STYs) are prerequisites for the commercial application of zeolitic imidazolate frameworks (ZIFs). However, these prerequisites are rarely achieved simultaneously. Herein, a green and versatile strategy to rapidly synthesize hierarchically porous ZIFs (HP-ZIFs) was developed using an alkali as a deprotonating agent. The synthesis conditions were room temperature and ambient pressure in an aqueous solution, and the synthesis time could be reduced to 1 min. The produced HP-ZIFs had hierarchically porous structures with mesopores and macropores interconnected with micropores. The STY for HP-ZIFs was up to 9670 kg m^-3 d^-1, at least 712 times the previously reported values. In addition, the porosity and morphology of the produced HP-ZIFs could be fine-tuned by controlling the synthesis parameters (e.g., reaction time, molar ratios, metal source, and alkali source). Compared with conventional ZIFs, the adsorption performance of the as-synthesized HP-ZIFs for p-xylene and n-hexane was significantly improved. Positron annihilation lifetime spectroscopy (PALS) was utilized to study the pore properties, and the adsorption behavior of HP-ZIFs on guest molecules was investigated using density functional theory (DFT) simulations. This strategy shows significant promise for the large-scale industrial production of desirable HP-ZIFs for adsorption applications.