An ultramicroporous multi-walled metal–organic framework for efficient C2H2/CO2 separation under humid conditions

Abstract

The removal of carbon dioxide (CO₂) from acetylene (C₂H₂) is not only industrially important for acetylene purification but also scientifically challenging owing to their high similarities in physical properties and molecular sizes. Multi-walled and ultramicroporous metal–organic frameworks (MOFs) can provide multiple specific interactions with C₂H₂ supplied to form a cooperative effect for efficient separation properties. Herein, we report a new strategy involving the extension of vertices to create an infinite multi-walled MOF (In-TATB) from 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine (H₃TATB) and In(III) ions. Two 3D frameworks built from In(III) chains and TATB³⁻ molecules interpenetrate through strong π–π interactions between triazine rings. Taking advantage of the confined ultramicroporous space (3.8 Å × 4.1 Å) and accessible sites of multiple walls, In-TATB shows a high adsorption enthalpy of C₂H₂ (36.6 kJ mol⁻¹ at 298 K and low-coverage) and excellent separation of C₂H₂/CO₂ mixtures with an IAST selectivity of 11.8 (at 298 K and 1 bar). More importantly, both dry and wet breakthrough results validated its exceptional separation performance for C₂H₂/CO₂ mixtures, affording a high dynamic separation factor. This work provides a novel and powerful approach to address this extremely challenging gas separation in industry.