Transformation of 3D Polycatenated Framework to 2D Framework Promotes the Ethane-Selective C₂H₆/C₂H₄ Separation

Abstract

Ethane-selective adsorbents enable the direct production of high-purity C₂H₄ in a single step, showcasing substantial research potential. In this work, we report the synthesis of two hydrogen-bonded organic frameworks (HOFs), NKM-HOF-6 and NKM-HOF-7, featuring permanent microporosity. Upon treatment with hot acetone, NKM-HOF-6 undergoes a structural transformation into NKM-HOF-7, characterized by a transition from a 3D polycatenated framework to a 2D parallel displacement-stacked structure. This transformation leads to a reduction in the maximum pore size of NKM-HOF-7 and a decrease in the density of -CF₃ groups within its channels, thereby enhancing its preferential affinity for C₂H₆ over C₂H₄. The adsorption capacity difference between C₂H₆ and C₂H₄ in NKM-HOF-7 is 11.1 cm³·g^–1, with an IAST selectivity of 1.77, surpassing the corresponding values for NKM-HOF-6 (9.6 cm³·g^–1 and 1.56, respectively). Breakthrough experiments further reveal that NKM-HOF-7 achieves nearly twice the separation efficiency of NKM-HOF-6 for C₂H₆/C₂H₄ (10/90, V/V) mixtures. Theoretical calculations attribute this enhanced C₂H₆ affinity to the synergistic effects of optimized pore dimensions and functionalized pore surfaces in NKM-HOF-7. These findings provide critical insights for the rational design of highly efficient C₂H₆-selective adsorbents.

Keywords

Hydrogen-bonded organic frameworks / Structural transformation / C₂H₆/C₂H₄ separation / Crystal engineering / Pores / Weak intermolecular interactions

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2025 SIOC, CAS, Shanghai, & WILEY-VCH GmbH