Isoreticular Microporous Metal-Organic Frameworks for Carbon Dioxide Capture

The isoreticular principle has been applied to construct two copper metal-organic framework (MOF) analogues with different porosities for the adsorptive capture of CO₂ from N₂ and CH₄ at 1 atm and 298 K. By using a 4-substituted isophthalate linker with a bulky nitro group, the microporous MOF [Cu(BDC-NO₂)(DMF)] (UTSA-93 or CuBDC-NO; H₂BDC-NO₂ = 4-nitroisophthalic acid and DMF = N,N'-dimethylformamide) has been synthesized with mot topology, showing a compact pore structure with a size of 6.0 × 7.0 Ų in contrast to that of 6.9 × 8.5 Ų in the prototypical MOF with a bromo group. The optimized pore structure allows the nitro-functionalized MOF to capture CO₂ with a higher capacity of about 2.40 mmol g^-1 under ambient conditions, in contrast to 1.08 mmol g^-1 in the bromo-functionalized analogue. The adsorption selectivity of CuBDC-NO-a for a CO₂/N₂ (15:85) mixture (28) under ambient conditions is also higher than that of the bromo-substituted prototype (25) and comparable with those of several MOF materials. Moreover, dynamic breakthrough experiments of the nitro-functionalized MOF have been performed to illustrate its separation potential toward a CO₂/N₂ mixture.