A novel microporous hydrogen-bonded organic framework with electron-rich alkynyl groups for highly efficient C2H6/C2H4 separation

Abstract

Microporous hydrogen-bonded organic frameworks (HOFs) have been considered promising materials for ethane/ethylene (C₂H₆/C₂H₄) separation owing to their native nonpolar pores. However, the absence of functional binding sites on nonpolar pore surfaces commonly limits their separation performance. Herein, we report and construct a novel HOF material (termed as ZJU-HOF-60a) by incorporating electron-rich alkynyl groups into its pore surfaces to achieve highly efficient C₂H₆/C₂H₄ separation. The incorporated alkynyl groups not only serve as functional binding sites to provide multiple supramolecular interactions with the C₂H₆ molecule, but also do not participate in the formation of any hydrogen bonds in order to obtain the desired HOF framework. Alkynyl-functionalized ZJU-HOF-60a thus exhibits both a top-tier C₂H₆ uptake capacity of 3.79 mmol g⁻¹ and C₂H₆/C₂H₄ uptake ratio of 1.58 at 296 K and 1 bar, surpassing most of the previously reported C₂H₆-selective HOFs. Theoretical calculations indicate that the incorporated alkynyl groups combined with the surrounding carboxylic groups provide stronger and more number of C–H⋯π and C–H⋯O interactions to bind with C₂H₆ over C₂H₄, thus accounting for efficient C₂H₆/C₂H₄ separation. The actual separation performance of ZJU-HOF-60a was confirmed using breakthrough experiments for 50/50 (v/v) C₂H₆/C₂H₄ gas mixtures, affording a highly pure C₂H₄ productivity of 7.8 L kg⁻¹ under ambient conditions.