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The separation of light hydrocarbons, including C2H6 and C3H8, is essential to natural gas upgrading. Meanwhile, N2 removal from CH4 is also crucial to concentrating low-quality coalbed methane, but the adsorption process is challenging because of the close kinetic diameter. This work reports two hydrogen-bonded metal-nucleobase frameworks (HOF-ZJU-201 and HOF-ZJU-202) capable of efficiently separating C3H8/CH4, C2H6/CH4, and CH4/N2. Due to strong affinity for C3H8 and C2H6, the low-pressure capacity for C3H8 (5 kPa) and C2H6 (10 kPa) of HOF-ZJU-201a exceeds most adsorbents. The ideal adsorbed solution theory (IAST) selectivity of C3H8/CH4 and C2H6/CH4 is 119 and 45 at ambient conditions. According to density functional theory calculations, surface polarization environments formed by electron-rich anions and electron-deficient purine heterocyclic rings contribute to the selective capture of C3H8 and C2H6 with greater polarizability. Furthermore, the high CH4 adsorption capacity (1.73 mmol/g for HOF-ZJU-201a and 1.50 mmol/g for HOF-ZJU-202a at 298 K and 1.0 bar) and excellent CH4/N2 selectivity (6.0 for HOF-ZJU-201 at 298 K), as well as dynamic breakthrough experiments of binary CH4/N2 gas mixture implied their efficacy in the concentration of low-quality coalbed methane.
We appreciate Dr. Wei Zhou and Dr. Hui Wu for their contribution to the structure analysis. We are grateful for the financial support by the National Natural Science Foundation of China (Nos. 21878260, 21978254, and 22141001).