Synthesis of ZIF-93/11 hybrid nanoparticles via post-synthetic modification of ZIF-93 and their use for H₂/CO₂ separation

The present work shows the synthesis of nano‐sized hybrid zeolitic imidazolate frameworks (ZIFs) with the rho topology based on a mixture of the linkers benzimidazole (bIm) and 4‐methyl‐5‐imidazolecarboxaldehyde (4‐m‐5‐ica). The hybrid ZIF was obtained via post‐synthetic modification of ZIF‐93 in a bIm solution. The use of different solvents, MeOH and DMAc, and reaction times led to differences in the quantity of bIm incorporated to the framework, from 7.4 to 23% according to solid‐state NMR spectroscopy. XPS analysis showed that the mixture of linkers was also present at the surface of the particles. The inclusion of bIm to the ZIF‐93 nanoparticles improved the thermal stability of the framework and also increased the hydrophobicity according to water adsorption results. N₂ and CO₂ adsorption experiments revealed that the hybrid material has an intermediate adsorption capacity, between those of ZIF‐93 and ZIF‐11. Finally, ZIF‐93/11 hybrid materials were applied as fillers in polybenzimidazole (PBI) mixed matrix membranes (MMMs). These MMMs were used for H₂/CO₂ separation (at 180 ⁰C) reaching values of 207 Barrer of H2 and a H₂/CO₂ selectivity of 7.7 that clearly surpassed the Robeson upper bound (corrected for this temperature).