(353g) Fine-Tuning of Rigid Zeolitic Imidazole Framework Membrane with Graphene Nanoribbons for Gas Separation

Due to the well-defined crystalline pore structures, metal-organic frameworks (MOFs) have been studied for gas separation membrane materials. MOFs are particularly effective for the membrane fabrication because of relatively mild synthesis process. The ideal aperture size of a MOF can be predicted based on its rigid framework structure, but the movement of organic-linker molecules of MOF made the unpredictable gas molecular transport of MOF. For example, zeolitic imidazolate framework (ZIF)-8 has an ideal aperture size of 3.4 Å; however, its molecular cutoff is observed at two ranges of 3.4 Å and 4.0 Å. While the flexible properties of MOF are beneficial depending on the target molecules, such as hydrocarbon separation, controlling the pore structure of MOF can help predict the molecular sieving properties of MOF materials.

Therefore, to control the gas transport of ZIF-type membrane, we introduced graphene nanoribbon (GNRs) into ZIF layer. Because the sp² carbon edge domain induces strong anchoring effects with the metal ion of the MOF, the synthesized hybrid ZIF/GNR layer can form the intrinsic aperture size by suppressing the flexible modulation of the framework. Depending on the exposure area of sp² carbon edge domain, the molecular cut-off is different. The pore size of ZIF-8 membrane with embedded GNR layer was observed at 3.4 Ã…, while the expected pore size of ZIF-8 membrane with bilayer GNR layer was observed at 3.6 Ã… (CO₂-N₂)¹⁾. In particular, the embedded ZIF-8 membranes showed sharp H₂/CO₂ separation with an H₂ permeance of 7 × 10^−7 mol/m²Â·Pa·s and an H₂/CO₂ selectivity of 130 for binary mixed gases²⁾. Moreover, using simulated steam methane reforming system with H₂/CO₂/CH₄, the ternary gas separation was conducted and the results of ternary gas separation supported the possibility of application for industrial steam methane reforming system. In addition, the gas transport through the intrinsic ZIF-8 framework was also investigated using molecular dynamics simulations.

1) Adv. Funct. Mater. 17, 2011146 (2021).

2) Angew. Chem. Int. Ed.61, 49, e202214269 (2022).