Octanuclear Cobalt(II) Cluster-Based Metal–Organic Framework with Caged Structure Exhibiting the Selective Adsorption of Ethane over Ethylene

Abstract

A novel metal− organic framework (MOF) of [Co 8 (OH) 4 (TCA) 4 (H 2 O) 4 ] n (abbreviation: JXNU-9) based on the unique octanuclear Co 8 (μ 3 -OH) 4 clusters linked by 4,4′,4″-nitrilotribenzoate (TCA 3− ) ligands featuring small caged structures and one-dimensional channels was prepared and characterized. JXNU-9 shows a high C 2 H 6 uptake capacity of 3.60 mmol g −1 (4.46 mmol cm −3 ) at 298 K and 1 atm with a small isosteric heat of adsorption ( 23.6 kJ mol −1 ) and a moderate C 2 H 6 /C 2 H 4 adsorption selectivity of 1.7, resulting in excellent C 2 H 6 /C 2 H 4 separation performance. The pore walls decorated by plenty of aromatic rings provide π-electron-cloud-surrounding environments to accommodate the large polarizable C 2 H 6 molecules. The calculations demonstrate that the rich πsystems in JXNU-9 facilitate an adsorption affinity for large C 2 H 6 molecules through multiple C−H•••π interactions. Additionally, the open metal sites located in the concave pores with a close Co•••Co separation (4.21 Å) in octanuclear Co 8 (μ 3 -OH) 4 clusters make the open metal sites inaccessible for the C 2 H 4 molecule with a kinetic diameter of 4.163 Å. Thus, the annihilation of open metal sites in this structure is achieved, which further facilitates the C 2 H 6 -selective C 2 H 6 /C 2 H 4 separation.

One-Step Ethylene Purification by an Ethane-Screening Metal–Organic Framework

“…By comparison, the value was lower than the pioneering Fe 2 (O 2 ) (dobdc) (3.7), Cu­(Qc) 2 (3.75), but was obviously higher than that of many top-performing C 2 H 6 -selective MOFs such as CPM-733 (1.25), MUF-15 (1.96) JNU-2 (1.6) (SI Table S4). When the pressure increased to 1 bar, 2 remained the higher selectivity of 2.5 at 298 K, still surpassing that of other benchmark materials, that is, JXNU-9 (1.7), NUM-7a (1.76), and Fe 2 (BDP) 3 (2.1) (SI Figure S9 and Table S4), etc. Noted that the IAST calculation was just for the qualitative analysis, we thus assessed the value at the 10/90 of C 2 H 6 /C 2 H 4 mixtures.…”

Improving Ethane/Ethylene Separation Performance of Isoreticular Metal–Organic Frameworks via Substituent Engineering

“…At the temperature of 298 K, the K H values of C 2 H 6 and C 2 H 4 are 0.344 and 0.239 mmol g −1 kPa −1 for NJU-Bai7 (Figure S18), 0.503 and 0.338 mmol g −1 kPa −1 for ZJNU-21 (Figure S19), 0.322 and 0.254 mmol g −1 kPa −1 for ZJNU-22 (Figure S20), and 0.467 and 0.403 mmol g −1 kPa −1 for ZJNU-23 (Figure S21), respectively. 4g), such as MUF-15 (1.95), 38 DUT-52(Hf) (1.9), 33 PCN-250 (1.9), 39 NUM-7 (1.764), 40 Dia-4-Ni (1.76), 34 Ca(H 2 tcpb) (1.67), 41 CPM-233 (1.64), 42 NUM-9 (1.61), 43 JNU-2 (1.6), 44 SNNU-40 (1.58), 45 LIFM-63 (1.56), 46 JXNU-9 (1.53), 47 MIL-53-NDCA (1.53), 48 Sc-BPDC (1.5), 49 MIL-142A (1.5), 50 Azole-Th-1 (1.44), 51 UPC-612 (1.41), 52 In-soc-MOF-1 (1.4), 53 NPU-1 (1.32), 54 MOF-545 (1.31), 55 and CPOC-301 (1.3), 56 but is inferior to that of a few high-performance C 2 H 6 -selective coordination framework compounds like Fe 2 O 2 (dobdc) (4.4), 36 Cu(Qc) 2 (3.4), 57 Co(AIN) 2 (2.96), 30 ZJU-120 (2.74), 58 MAF-49 (2.7), 29 and NKMOF-8-Br (2.65). 59 As shown in Figures S26−S29, the adsorption selectivity of C 2 H 6 over C 2 H 4 increases with the decreasing measurement temperatures.…”

“…Under the conditions of 298 K and 109 kPa, the adsorption selectivity of C 2 H 6 over C 2 H 4 , respectively, reaches 1.7, 1.4, 1.3, and 1.2 for ZJNU-21 , NJU-Bai7 , ZJNU-22 , and ZJNU-23 . The selectivity value of ZJNU-21 is similar to and even surpasses that of many coordination framework compounds reported for C 2 H 6 /C 2 H 4 separation (Figure g), such as MUF-15 (1.95), DUT-52­(Hf) (1.9), PCN-250 (1.9), NUM-7 (1.764), Dia-4-Ni (1.76), Ca­(H 2 tcpb) (1.67), CPM-233 (1.64), NUM-9 (1.61), JNU-2 (1.6), SNNU-40 (1.58), LIFM-63 (1.56), JXNU-9 (1.53), MIL-53-NDCA (1.53), Sc-BPDC (1.5), MIL-142A (1.5), Azole-Th-1 (1.44), UPC-612 (1.41), In- soc -MOF-1 (1.4), NPU-1 (1.32), MOF-545 (1.31), and CPOC-301 (1.3), but is inferior to that of a few high-performance C 2 H 6 -selective coordination framework compounds like Fe 2 O 2 (dobdc) (4.4), Cu­(Qc) 2 (3.4), Co­(AIN) 2 (2.96), ZJU-120 (2.74), MAF-49 (2.7), and NKMOF-8-Br (2.65) . As shown in Figures S26–S29, the adsorption selectivity of C 2 H 6 over C 2 H 4 increases with the decreasing measurement temperatures.…”

Selectivity Tuning of Adsorbents for Ethane/Ethylene Separation: A Review

“…Likewise, C–H···π interactions in MOF (Hf)­DUT-52a resulted in ethane selectivity with H···π distances of 3.188–3.757 Å and 3.250–3.761 Å for ethane and ethylene, respectively, indicating the strong interaction of ethane molecules with the aromatic framework . There are several other MOFs reported to be ethane selective, resulting from the interactions between aromatic ligands and ethane molecules, such as JXNU-9, NI­(IN) 2 , and ZJU-HOF-10­(sc), with an ethane selectivity of 1.6 (273 K, 1 bar), 2.45 (298 K, 1 bar), and 1.9 (296 K, 1 bar) respectively.…”