A Water-Stable Twofold Interpenetrating Microporous MOF for Selective CO₂ Adsorption and Separation

Self-assembly of bent dicarboxylate linker 4,4'-sulfonyldibenzoic acid (H₂SDB) and flexible N,N-donor spacer 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (L) with Co(NO₃)₂·6H₂O forms a twofold interpenetrated {[Co₂(SDB)₂(L)]·(H₂O)₄·(DMF)}_n, (IITKGP-6) network via solvothermal synthesis with sql(2,6L1) topology, which is characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, powder X-ray diffraction (XRD), and single-crystal XRD. The framework is microporous with a solvent-accessible volume of 25.5% and forms a one-dimensional channel along [1-1 0] direction with the dimensions of ∼3.4 × 5.0 Ų. As the stability of metal-organic frameworks (MOFs) in the presence of water is a topic of significant importance while considering them for practical applications, this framework reveals its high stability toward water. The desolvated framework shows modest uptake of CO₂ (50.6 and 37.4 cm³ g^-1 at 273 and 295 K under 1 bar pressure, respectively), with high selectivity over N₂ and CH₄. Ideal adsorbed solution theory calculations show that the selectivity values of CO₂/N₂ (15:85) are 51.3 at 273 K and 42.8 at 295 K, whereas CO₂/CH₄ (50:50) selectivity values are 36 at 273 K and 5.1 at 295 K under 100 kPa. The high CO₂ separation selectivity over N₂ and CH₄ along with its water stability makes this MOF a potential candidate for CO₂ separation from flue gas mixture and landfill gas mixture as well.