Constructing Nano-Trap of CO₂ and C₂H₆ in an Anion Pillared MOF for Efficient One Step CH₄ Purification

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 CdSO₄·8/3H₂O. In HBU-26, ligands coordinate with Cd²⁺ ions to form two-dimensional planes, and adjacent two-dimensional planes are connected by SO₄ ^2- ions to form a three-dimensional framework. It can capture more CO₂ (44.0 cm³/g), C₃H₈ (42.6 cm³/g), and C₂H₆ (47.2 cm³/g) than CH₄ (21.3 cm³/g) at ambient conditions. Even at lower pressure, the adsorption capacities of CO₂, C₃H_8, and C₂H₆ rapidly reach saturation. Further research shows that HBU-26 exhibits higher CO₂/CH₄ (109.8, v/v: 5:85), C₃H₈/CH₄ (1209.6, v/v: 5:85), and C₂H₆/CH₄ (146.9, v/v: 10:85) adsorption selectivity at 100 kPa, suggesting it may achieve one-step CH₄ 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 CH₄ from a dry or humid CO₂/C₃H₈/C₂H₆/CH₄ mixture. The research results contribute to the rational design of novel gas adsorbents.