Highly Connected Stable Metal-Organic Frameworks With Polyhedral Cage-Like Cavities for Natural Gas Upgrading

The development of efficient methane (CH₄) separation and purification technologies is essential for optimizing the efficiency of natural gas. Compared to conventional cryogenic distillation, adsorptive separation using porous materials offers significant advantages in terms of energy efficiency and operational simplicity. The construction of highly connected cage-like metal-organic frameworks (MOFs) provides suitable pore volume and functional space to enhance both adsorption capacity and selectivity, although their design and synthesis remain challenging. In this work, four MOFs featuring polyhedral cage-like cavities are synthesized via an isoreticular design strategy. Single-component adsorption experiments demonstrate that all prepared MOFs exhibit substantial uptake capacities for C₃H₈ and C₂H₆, while showing markedly lower adsorption for CH₄. Theoretical calculations and structural analysis elucidate the selective adsorption mechanisms, emphasizing the critical role of appropriate cage dimensions and polar pore surfaces. Breakthrough experiments confirm that the prepared MOFs effectively separate ternary natural gas mixtures (C₃H₈/C₂H₆/CH₄, 5/10/85, v/v/v) at 298 K, yielding CH₄ with a high purity exceeding 99.9%. Furthermore, these MOFs maintain good crystalline stability after 24-hour immersion in aqueous solutions across a pH range of 2-10. The combination of high adsorption capacity, exceptional selectivity, and remarkable stability renders these MOFs highly efficient adsorbents for natural gas upgrading.