Fabrication of hierarchically porous ZIF-8 using a competitive ligand via a one-step method in supercritical CO2 and its application for CO2 adsorption

Abstract

Hierarchically porous metal–organic frameworks (HP-MOFs) possess the advantages of the high porosity of MOFs and unique properties, such as a wide pore size range. Hierarchically porous ZIF-8 (HP-ZIF-8) was facilely fabricated via a one-step method in supercritical CO₂ (scCO₂) using a competitive ligand. The mesoporous structure and morphology of HP-ZIF-8 can be easily adjusted by changing the dosage of competing ligands and the reaction temperature. When the molar ratio of zinc acetylacetonate, 2-methylimidazole, and 2-butyl-1H-imidazole was 1 : 1 : 6, the HP-ZIF-8 with micropores (1.7 nm) and mesopores (3.9–30 nm) was synthesized at 50 °C and 30 MPa for 3 hours with excellent reproducibility. The as-synthesized ZIF-8 shows a high activity for CO₂ adsorption, and the CO₂ equilibrium adsorption capacity reached up to 1.49 mmol g⁻¹ sorbent at 25 °C and 0.1 MPa. Moreover, the CO₂ equilibrium adsorption capacity of HP-ZIF-8 was maintained at 1.36 mmol g⁻¹ sorbent after 7 cycles.