Hierarchically porous MOF@COF structures with ultrafast gas diffusion rate for C2H6/C2H4 separation

Abstract

For ethylene purification, C₂H₆-selective metal-organic frameworks (MOFs) show great potential to directly produce polymer-grade C₂H₄ from C₂H₆/C₂H₄ mixtures. Most C₂H₆-traping MOFs are ultra-microporous structures so as to strengthen multiple supramolecular interactions with C₂H₆. However, the narrowed pore channels of C₂H₆-traping MOFs cause large guest diffusion barriers, greatly hampering their practical applications. Herein, we present a feasible strategy by precisely constructing hierarchically porous MOF@COF core-shell structures to address this issue. Additional mesoporous diffusion channels were incorporated between MOF crystals through the construction of the COF shell, thereby enhancing the gas adsorption kinetics. Notably, designing a core-shell MOF@COF structure with an optimal coating amount of mesoporous COF shell will further improve the gas diffusion rate. Breakthrough experiments reveal that the tailored MOF@COF composites can effectively achieve C₂H₆/C₂H₄ separation and maintain its separation performance over five continuous measurement cycles. This investigation opens up a new avenue to solve the diffusion/transfer issues and provides more opportunities and potentials for MOF@COF composites in practical separation applications.

Keywords: Adsorption kinetics; C(2)H(6)/C(2)H(4) separation; Core–shell structure; Hierarchically porous; MOF@COF.