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Adsorbed natural gas (ANG) systems involve using porous materials to increase the working capacity and/or reduce the storage pressure compared to compressed natural gas (CNG). Flexible metal-organic materials (FMOMs) are particularly interesting in this context since their stepped isotherms can afford increased working capacity if the adsorption/desorption steps occur within the proper pressure range. We report herein that metal doping in a family of isostructural FMOMs, ML 2 (M=Co, Ni or Ni x Co 1-x , L=4-(4-pyridyl)-biphenyl-4-carboxylic acid), enables control over the gate opening between non-porous (closed) and porous (open) phases at pressures relevant to methane storage. Specifically, methane-induced phase transformations can be fine-tuned by using different Ni/Co ratios to enhance methane working capacity. The optimal working capacity from 5 to 35 bar at 298 K (153 cm 3  cm -3 ) was found for Ni 0.89 Co 0.11 L 2 (X-dia-1-Ni 0.89 Co 0.11 ), which is greater than that of benchmark rigid MOFs., (© 2023 Wiley-VCH GmbH.)

In the electronics industry, the efficient recovery and capture of sulfur hexafluoride (SF 6 ) from SF 6 /N 2 mixtures is of great importance. Herein, three metal-organic frameworks with fine-tuning pore structures, Cu(peba) 2 , Ni(pba) 2 , and Ni(ina) 2 , were designed for SF 6 capture. Among them, Ni(ina) 2 has perfect pore sizes (6 Å) that are comparable to the kinetic diameter of sulfur hexafluoride (5.2 Å), affording the benchmark binding affinity for SF 6 gas. Ni(ina) 2 exhibits the highest SF 6 /N 2 selectivity (375.1 at 298 K and 1 bar) and ultra-high SF 6 uptake capacity (53.5 cm 3  g -1 at 298 K and 0.1 bar) at ambient conditions. The remarkable separation performance of Ni(ina) 2 was verified by dynamic breakthrough experiments. Theoretical calculations and the SF 6 -loaded single-crystal structure provided critical insight into the adsorption/separation mechanism. This porous coordination network has the potential to be used in industrial applications., (© 2022 Wiley-VCH GmbH.)

The enrichment and purification of coal-bed methane provides a source of energy and helps offset global warming. In this work, we demonstrate a strategy involving the regulation of the pore size and pore chemistry to promote the separation of CH 4 /N 2 mixtures in four nickel-based coordination networks, named Ni(ina) 2 , Ni(3-ain) 2 , Ni(2-ain) 2 , and Ni(pba) 2 , (where ina=isonicotinic acid, 3-ain=3-aminoisonicotinic acid, 2-ain=2-aminoisonicotinic acid, and pba=4-(4-pyridyl)benzoic acid). Among them, Ni(ina) 2 and Ni(3-ain) 2 can effectively separate CH 4 from N 2 with top-performing performance because of the suitable pore size (≈0.6 and 0.5 nm) and pore environment. Explicitly, Ni(ina) 2 exhibits the highest ever reported CH 4 /N 2 selectivity of 15.8 and excellent CH 4 uptake (40.8 cm 3  g -1 ) at ambient conditions, thus setting new benchmarks for all reported MOFs and traditional adsorbents. The exceptional CH 4 /N 2 separation performance of Ni(ina) 2 is confirmed by dynamic breakthrough experiments. Under different CH 4 /N 2 ratios, Ni(ina) 2 selectively extracts methane from the gaseous blend and produces a high purity of CH 4 (99 %). Theoretical calculations and CH 4 -loading single-crystal structure analysis provide critical insight into the adsorption/separation mechanism. Ni(ina) 2 and Ni(3-ain) 2 can form rich intermolecular interactions with methane, indicating a strong adsorption affinity between pore walls and CH 4 molecules. Importantly, Ni(ina) 2 has good thermal and moisture stability and can easily be scaled up at a low cost ($25 per kilogram), which will be valuable for potential industrial applications. Overall, this work provides a powerful approach for the selective adsorption of CH 4 from coal-bed methane., (© 2022 Wiley-VCH GmbH.)