Alkoxy-Functionalized Three-Dimensional Microporous Covalent Organic Frameworks for Efficient Xenon/Krypton Separation

Abstract

Efficient Xe/Kr adsorption-based separation is highly desirable as an energy-saving alternative to cryogenic distillation for producing high-purity xenon. However, the similar physicochemical properties of xenon and krypton make selective separation challenging, requiring precise regulation of pore size and host-guest interactions. Herein, a series of alkoxy-functionalized three-dimensional covalent organic frameworks (COFs) with a 7-fold interpenetrated pts topology are designed and synthesized. By varying the alkoxy chain length, the sub-nanometer pore environment and xenon-binding sites are systematically tuned, leading to COFs with adjustable Xe/Kr separation performance. Gas adsorption results show an enhanced xenon affinity with increasing alkoxy chain length. Among them, 3D-TAPB-(OEt)₃-COF exhibits the highest Xe/Kr selectivity of 9.92 at 273 K and 1 bar, which is attributed to its optimized micropore size and abundant alkoxy groups. Theoretical calculations suggest that multiple alkoxy groups and extended alkyl chains strengthen xenon adsorption through enhanced van der Waals interactions. Dynamic breakthrough experiments further confirm the effective separation of Xe/Kr mixtures. This study highlights alkoxylation-based functional group regulation as an effective strategy for tailoring sub-nanometer pore environments in COFs toward noble gas separation.

Keywords

Xe/Kr adsorption-based separation / 3D covalent organic frameworks / 7-Fold interpenetrated pts topology / Alkoxy-functionalized strategy / Sub-nanometer pore environment / Xe/Kr selectivity / Van der Waals interaction / Dynamic breakthrough experiment

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