Flexible molecular sieving of C2H2 from CO2 by a new cost-effective metal organic framework with intrinsic hydrogen bonds

• A flexible molecular sieving strategy developed for efficient C 2 H 2 /CO 2 separation. • A new cost-effective MOF was prepared with unprecedented topological structure. • High C 2 H 2 capacity and high C 2 H 2 /CO 2 uptake selectivity achieved by ZNU-3. • Excellent C 2 H 2 /CO 2 separation performance confirmed by breakthroughs. The separation of C 2 H 2 /CO 2 is an important process in industry but challenged by the trade-off of capacity and selectivity owning to their close physical properties and identical kinetic molecular size. Herein, we reported a new metal organic framework ZNU-3 (ZNU = Zhejiang Normal University) with flexibility controlled by abundant hydrogen-bonds for highly selective molecular sieving of C 2 H 2 from CO 2 , CH 4 , C 2 H 4 and C 2 H 6 using commercially available cost-effective ligands. At 1.0 bar and 298 K, the uptake capacity of C 2 H 2 is 81.0 cm 3 (STP) g −1 , while the CO 2 , C 2 H 4 , C 2 H 6 , CH 4 , N 2 uptake capacities are only 5.4, 5.3, 1.0, 1.1, 1.1 cm 3 (STP) g −1 , respectively. Such high uptake ratios of C 2 H 2 over other C2 and C1 gases have rarely been achieved. Particularly, the C 2 H 2 /CO 2 uptake ratio of 14.9 is only secondary to that of the benchmark UTSA-300a and much higher than those of all other porous materials. Dynamic breakthrough experiments with equimolar C 2 H 2 /CO 2 mixtures showed that the retaining time of C 2 H 2 is nearly 2 fold of that of CO 2 , indicating the excellent practical separation performance of ZNU-3 for C 2 H 2 /CO 2 mixtures. Modeling studies indicated that C 2 H 2 is mainly trapped by two opposite carboxylic groups with additional small contribution from π···π packing between pyridine ring and planar C≡C moiety.