AbstractThe construction of functional three-dimensional covalent organic frameworks (3D COFs) for gas separation, specifically for the efficient removal of ethane (C₂H₆) from ethylene (C₂H₄), is significant but challenging due to their similar physicochemical properties. In this study, we demonstrate fine-tuning the pore environment of ultramicroporous 3D COFs to achieve efficient one-step C₂H₄ purification. By choosing our previously reported 3D-TPB-COF-H as a reference material, we rationally design and synthesize an isostructural 3D COF (3D-TPP-COF) containing pyridine units. Impressively, compared with 3D-TPB-COF-H, 3D-TPP-COF exhibits both high C₂H₆ adsorption capacity (110.4 cm³ g⁻¹ at 293 K and 1 bar) and good C₂H₆/C₂H₄ selectivity (1.8), due to the formation of additional C-H···N interactions between pyridine groups and C₂H₆. To our knowledge, this performance surpasses all other reported COFs and is even comparable to some benchmark porous materials. In addition, dynamic breakthrough experiments reveal that 3D-TPP-COF can be used as a robust absorbent to produce high-purity C₂H₄ directly from a C₂H₆/C₂H₄ mixture. This study provides important guidance for the rational design of 3D COFs for efficient gas separation.