Cooperative Ligand Engineering Enabling Stepwise Optimization of Metal–Organic Frameworks for Improved C2H2 Separation from CO2 and CH4

Abstract

Acetylene (C₂H₂), a critical chemical feedstock, is indispensable in numerous industrial processes. To satisfy the stringent demands for high-purity acetylene, adsorption-based separation techniques have become highly efficient strategies for purifying acetylene from mixtures containing methane and carbon dioxide. In this study, we introduce a novel cooperative ligand engineering strategy that integrates low-symmetry functionalized auxiliary ligands. This innovative approach enables the stepwise synthesis of three zinc-based metal–organic frameworks (MOFs), specifically ZJNU-406, ZJNU-407, and ZJNU-408, which exhibit distinct structural characteristics transitioning from 2D to 3D frameworks. The incorporation of functional groups and framework transformation optimizes the pore environments, thereby creating specific adsorption sites for target gases. Notably, ZJNU-408 demonstrates superior separation performance, with a C₂H₂ adsorption capacity of 44.8 cm³ g^–1 at 298 K, and selectivities of 4.28 for C₂H₂/CO₂ and 18.6 for C₂H₂/CH₄ at 298 K and 1.0 bar. Postsynthetic modification with copper ions further enhances its C₂H₂ selectivity, achieving values of 6.8 for C₂H₂/CO₂ and 20.7 for C₂H₂/CH₄. These results outperform those of many previously reported MOF adsorbents, highlighting the substantial potential of these materials for industrial C₂H₂ purification.