Constructing Nano‐Trap of CO ₂ and C ₂ H ₆ in an Anion Pillared MOF for Efficient One Step CH ₄ Purification

ABSTRACT High purity methane is highly necessary for improving its conversion efficiency, but the one‐step purification faces significant challenges due to the presence of bottleneck effects. In the present work, an anion‐pillared MOF (HBU‐26) was synthesized by self‐assembly of organic ligand ( L = 1,1,2,2‐tetra(pyridin‐4‐yl)ethene) and CdSO ₄ ·8/3H ₂ O. In HBU‐26, ligands coordinate with Cd ²⁺ ions to form two‐dimensional planes, and adjacent two‐dimensional planes are connected by SO ₄ ²⁻ ions to form a three‐dimensional framework. It can capture more CO ₂ (44.0 cm ³ /g), C ₃ H ₈ (42.6 cm ³ /g), and C ₂ H ₆ (47.2 cm ³ /g) than CH ₄ (21.3 cm ³ /g) at ambient conditions. Even at lower pressure, the adsorption capacities of CO ₂ , C ₃ H _8, and C ₂ H ₆ rapidly reach saturation. Further research shows that HBU‐26 exhibits higher CO ₂ /CH ₄ (109.8, v/v: 5:85), C ₃ H ₈ /CH ₄ (1209.6, v/v: 5:85), and C ₂ H ₆ /CH ₄ (146.9, v/v: 10:85) adsorption selectivity at 100 kPa, suggesting it may achieve one‐step CH ₄ purification. DFT calculations show that the C‐H···π and C‐H···O interactions should be responsible for the efficient separation selectivity. Furthermore, breakthrough experiments further verify that HBU‐26 can separate high purity CH ₄ from a dry or humid CO ₂ /C ₃ H ₈ /C ₂ H ₆ /CH ₄ mixture. The research results contribute to the rational design of novel gas adsorbents.