Electrostatic Potential Optimization by Precise Tailoring of Amino Site Arrays in Isostructural Metal–Organic Frameworks for High‐Efficiency CH ₄ Purification

Abstract The modulation of binding sites and pore channel surfaces in adsorbents for advancing adsorptive separation is attracting considerable attention. In natural gas purification, the challenge of discriminating between homologous alkanes (C ₂ H ₆ and C ₃ H ₈ ) at low concentrations has been persistent, limiting the adsorption capacity and selectivity required for efficient CH ₄ separation. By leveraging the highly positive electrostatic potential of H atoms in C ₂ H ₆ and C ₃ H ₈ , a range of frameworks is synthesized in this study, and it is demonstrated that efficient CH ₄ separation can be achieved by optimizing the negative electrostatic potential of pore surfaces. The isostructural metal–organic framework, namely, Co‐3‐AIN, features an asymmetric rhombic cross‐sectional pore with inwardly directed amino sites, yielding exceptional C ₂ H ₆ and C ₃ H ₈ binding affinities (62 and 69 kJ mol ⁻¹ ). This design achieves outstanding low‐pressure uptakes of alkanes (58.7 cm ³ g ⁻¹ C ₂ H ₆ at 0.1 bar; 56.4 cm ³ g ⁻¹ C ₃ H ₈ at 0.05 bar) and unprecedented selectivities (C ₂ H ₆ /CH ₄ = 188; C ₃ H ₈ /CH ₄ = 2953) at 298 K. Breakthrough experiments using a ternary CH ₄ /C ₂ H ₆ /C ₃ H ₈ mixture (85:10:5, v/v/v) demonstrate the exceptional CH ₄ purification capability of Co‐3‐AIN, resulting in a high‐purity CH ₄ yield of 207.6 L/kg in a single separation cycle. The alkane sorption mechanism is clarified using in situ IR spectroscopy, DFT calculation, and Hirshfeld surface analysis.