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 CO 2 from N 2 and CH 4 at 1 atm and 298 K. By using a 4-substituted isophthalate linker with a bulky nitro group, the microporous MOF [Cu(BDC-NO 2 )(DMF)] ( UTSA-93 or CuBDC-NO 2; H 2 BDC-NO 2 = 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 Å 2 in contrast to that of 6.9 × 8.5 Å 2 in the prototypical MOF with a bromo group. The optimized pore structure allows the nitro-functionalized MOF to capture CO 2 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 2 -a for a CO 2 /N 2 (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 CO 2 /N 2 mixture.