Bimetallic Metal–Organic Framework Featuring Nitrogen/Oxygen Sites for Superior Methane/Nitrogen Adsorption Separation
Zhijie Zhou, Yanting Gao, Wei Xia, Wenbo Shi, Yizhou Liu, Zheng Fang, Zhiguo Zhang, Qiwei Yang, Qilong Ren, Zongbi Bao
Abstract
The development of advanced adsorbents for methane (CH 4 ) and nitrogen (N 2 ) separation is critical for the efficient utilization of coal-bed methane (CBM), which is a key alternative energy resource. Herein, we report a bimetallic copper–indium-based metal–organic framework (MOF), CuIn(3-ain) 4, featuring high-density nitrogen and oxygen sites distributed along its pore surface. These negatively charged atom sites, derived from CuN 4 and InO 8 clusters, form multiple hydrogen-bonding interactions with CH 4, significantly enhancing its adsorption affinity. CuIn(3-ain) 4 demonstrates a high CH 4 uptake of 1.56 mmol g –1 and excellent CH 4 /N 2 selectivity under ambient conditions, outperforming many reported materials. Dynamic breakthrough experiments confirm that over 90% purity methane can be obtained in a single adsorption–desorption cycle. Grand Canonical Monte Carlo (GCMC) simulations and density functional theory (DFT) calculations reveal that the nitrogen and oxygen sites play a crucial role in selectively recognizing CH 4 over N 2, leading to a superior separation efficiency. Moreover, the material exhibits excellent cyclic stability and scalability, making CuIn(3-ain) 4 a promising candidate for practical CH 4 /N 2 separation in CBM purification. This study provides valuable insights into the design of MOFs for challenging gas separations, emphasizing the role of polar sites in facilitating selective adsorption.