A bifunctional ligand-derived anionic metal-organic framework with 9-connected Ni3(μ3-OH) SBUs for efficient C2H6/C2H4 separation

An anionic 3D MOF featuring 9-connected Ni 3 ( μ 3 -OH) secondary building units (SBUs), (Me 2 NH 2 ) 2 [Ni 6 (OH) 2 (Bpdc) 3 (4-Ptz) 6 ]·11H 2 O (NJTU-Bai90; NJTU-Bai denotes Nanjing Tech University Bai’s group), was hydrothermally synthesized using the bifunctional ligands bicyclo[1.1.1]pentane-1,3-dicarboxylic acid (H 2 Bpdc) and 4-(2H-tetrazol-5-yl)pyridine (4-HPtz). This MOF crystallizes in I-43 m space group and possesses intersecting 3D channels packed by trigonal-pyramidal and tetrahedral cages. Tailored for reversible C 2 H 6 adsorption and one-step purification of polymer-grade C 2 H 4 , NJTU-Bai90 not only has a high BET surface area of 1465.7 m 2 g −1 but also exhibits excellent stability in aqueous solutions at room temperature for at least one month. NJTU-Bai90 exhibits superior C 2 H 6 uptake (97.6 cm 3 g −1 at 298 K and 82.5 cm 3 g −1 at 308 K, both measured at 1 bar) in comparison with C 2 H 4 (85.5 cm 3 g −1 at 298 K and 68.4 cm 3 g −1 at 308 K, both measured at 1 bar). Remarkable IAST selectivity values (1.51 and 1.56, respectively) are maintained even at elevated temperatures. Furthermore, dynamic breakthrough experiments demonstrate that a C 2 H 6 /C 2 H 4 mixture (1/15, v/v) can be efficiently separated in one step and that polymer-grade C 2 H 4 yielding with a productivity of 19.1 mL g −1 at 298 K and 1 bar. The distinct retention times of C 2 H 6 and C 2 H 4 on NJTU-Bai90-packed separation columns further highlight the material’s great potential for industrial gas separation applications.