Pore Space Partition Enabled by Lithium(I) Chelation of a Metal–Organic Framework for Benchmark C<sub>2</sub>H<sub>2</sub>/CO<sub>2</sub> Separation
Yi-Zhan Hao, Kai Shao, Xu Zhang, Yihong Yu, Di Liu, Hui‐Min Wen, Yuanjing Cui, Bin Li, Banglin Chen, Guodong Qian
Abstract
Adsorptive separation of acetylene (C 2 H 2 ) from carbon dioxide (CO 2 ) offers a promising approach to purify C 2 H 2 with low-energy footprints. However, the development of ideal adsorbents with simultaneous high C 2 H 2 adsorption and selectivity remains a great challenge due to their very small molecular sizes and physical properties. Herein, we report a lithium(I)-chelation strategy for pore space partition (PSP) in a microporous MOF (Li + @NOTT-101-(COOH) 2 ) to achieve simultaneous high C 2 H 2 uptake and selectivity. The chelation model of Li + ions within the framework was visually identified by single-crystal X-ray diffraction studies. The immobilized Li + ions were found to have two functions: (1) partitioning large pore cages into smaller ones while maintaining high surface area and (2) providing specific binding sites to selectively take up C 2 H 2 over CO 2 . The resulting Li + @NOTT-101-(COOH) 2 exhibits a rare combination of a simultaneous high C 2 H 2 capture capacity (205 cm 3 g –1 ) and C 2 H 2 /CO 2 selectivity (13) at ambient conditions, far surpassing that of NOTT-101-(COOH) 2 (148 cm 3 g –1 and 3.8, respectively) and most top-tier materials reported. Theoretical calculations and gas-loaded SCXRD studies reveal that the chelated Li + ions combined with the segmented small cages can selectively bind with a large amount of C 2 H 2 through the unique π-complexation, accounting for the improved C 2 H 2 uptake and selectivity. Breakthrough experiments validated its excellent separation capacity for actual C 2 H 2 /CO 2 mixtures, providing one of the highest C 2 H 2 productivities of 118.9 L kg –1 (>99.5% purity) in a single adsorption–desorption cycle.