ZIF-8 based porous liquids with high hydrothermal stability for carbon capture

Abstract

Porous liquids (PLs), a novel material that combines both permanent porosity and fluidity, show enormous potential in gas capture and separation applications. However, MOF nanoparticles, as permanent porosity providers in PLs, have poor hydrothermal stability limiting their use in industries with the presence of water. In this study, the shell-ligand exchange reaction (SLER) was employed to replace the 2-methylimidazole on the surface of ZIF-8 crystals with 5,6-dimethylbenzimidazole, which improved the hydrothermal stability of ZIF-8 efficiently. The adsorption kinetic results showed that first-order kinetics could better predict the behavior of ZIF-8-based PLs in CO2 capture. Compared with ZIF-8-PLs, the CO2 capture capacity of ZIF-8-SLER-PLs was increased 30 % at 40 °C. When exposed to water at 80 °C for 20 days, ZIF-8-SLER retains its intact crystal morphology, high surface area and hydrothermal stability. Meanwhile, the 83 % CO2 adsorption capacity of ZIF-8-SLER (20 days) was retained. However, the pore structure of pristine ZIF-8 was collapsed seriously after hydrothermal experiment, and the CO2 adsorption capacity of ZIF-8 (20 days) was decreased by 40.6 % due to the lack of protection by hydrophobic ligands. This study opens a new pathway to use MOFs-based porous liquids for CO2 capture in industrial applications with the presence of water.