Effect of linker hybridization on the wetting of hydrophobic metal-organic frameworks

Wetting-dewetting of nanoporous materials is of key importance for a wide range of natural and technological cases, which include separation, chromatography, ionic channels. Heterogeneous lyophobic systems (HLS) consisting of a lyophobic nanoporous material and a non-wetting liquid are attractive for thermomechanical energy storage, conversion and dissipation under pressure/temperature variations. In recent years, metal-organic frameworks (MOFs) are entering many fields, including those mentioned above due to their wide structural diversity, structural flexibility and high tunability. In this work, we investigate the hitherto unexplored effects of forced wetting (intrusion-extrusion) of a hybrid mixed-linker ZIF-7-8 MOF (Zn-methylimidazole_0.794–benzimidazole_0.206) with water. Surprisingly, despite its structural similarity to ZIF-8, the hybrid ZIF-7-8 MOF demonstrates a non-hysteretic water intrusion-extrusion cycle that is in strong contrast to both ZIF-8 and ZIF-7 MOFs, which have pronounced intrusion-extrusion hysteresis. We used a combination of high-pressure intrusion-extrusion experiments, neutron diffraction structural analysis and atomistic simulations to put forward several hypotheses regarding the observed transformation from shock absorber/bumper behavior of ZIF-8 and ZIF-7 to molecular spring behavior of hybrid ZIF-7-8. These results open a new route for tuning the intrusion-extrusion (wetting-dewetting) hysteresis for numerous applications.