A microporous MOF with a polar pore surface exhibiting excellent selective adsorption of CO2 from CO2–N2 and CO2–CH4 gas mixtures with high CO2 loading

Abstract

A microporous MOF {[Zn(SDB)(L)_0.5]·S}_n (IITKGP-5) with a polar pore surface has been constructed by the combination of a V-shaped –SO₂ functionalized organic linker (H₂SDB = 4,4′-sulfonyldibenzoic acid) with an N-rich spacer (L = 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene), forming a network with sql(2,6L1) topology. IITKGP-5 is characterized by TGA, PXRD and single crystal X-ray diffraction. The framework exhibits lozenge-shaped channels of an approximate size of 4.2 × 5.6 Ų along the crystallographic b axis with a potential solvent accessible volume of 26%. The activated IITKGP-5a revealed a CO₂ uptake capacity of 56.4 and 49 cm³ g⁻¹ at 273 K/1 atm and 295 K/1 atm, respectively. On the contrary, it takes up a much smaller amount of CH₄ (17 cm³ g⁻¹ at 273 K and 13.6 cm³ g⁻¹ at 295 K) and N₂ (5.5 cm³ g⁻¹ at 273 K; 4 cm³ g⁻¹ at 295 K) under 1 atm pressure exhibiting its potential for a highly selective adsorption of CO₂ from flue gas as well as a landfill gas mixture. Based on the ideal adsorbed solution theory (IAST), a CO₂/N₂ selectivity of 435.5 and a CO₂/CH₄ selectivity of 151.6 have been realized at 273 K/100 kPa. The values at 295 K are 147.8 for CO₂/N₂ and 23.8 for CO₂/CH₄ gas mixtures under 100 kPa. In addition, this MOF nearly approaches the target values proposed for PSA and TSA processes for practical utility exhibiting its prospect for flue gas separation with a CO₂ loading capacity of 2.04 mmol g⁻¹.