Axial coordination-assisted interwoven isomerism in 3D hydrogen-bonded organic frameworks for efficient natural gas purification

Abstract

We investigated the interwoven isomerism in 3D hydrogen-bonded organic frameworks (HOFs) YSH-8_Ni and YSH-8_Zn, demonstrating their effectiveness in natural gas purification. These frameworks, constructed from 5,10,15,20-tetrakis(3,5-dicarboxyphenyl)porphyrins (TDCPP_Ms; M = Ni and Zn), exhibit 2-fold and 4-fold interwoven structures of 3D hydrogen-bonded networks. YSH-8_Ni exhibited a 4-fold interwoven structure with stabilisation of π–π interaction among porphyrin building blocks. YSH-8_Zn exhibited a 2-fold interwoven structure with axial coordination of oxygen species. Post solvent exchange to n-hexane, YSH-8_Zn/Hx exhibited improved stability through the connection by bridging ligand atoms between the 2-fold interwoven hydrogen-bonded networks. After activation, YSH-8_Zn/Hx* shows a BET surface area of 1665 m² g⁻¹, which is six times larger than that of YSH-8_Ni* (279.5 m² g⁻¹). YSH-8_Zn/Hx* exhibits outstanding selectivity for C₃H₈ over C₂H₆, C₃H₈ over CH₄, and C₂H₆ over CH₄, matching or exceeding the performance of leading benchmark materials. Dynamic breakthrough tests confirm its efficiency in separating CH₄ from C₃H₈/C₂H₆/CH₄ mixtures, C₂H₆ from C₃H₈/C₂H₆ mixtures, and CH₄ from C₂H₆/CH₄ mixtures. The stability of YSH-8_Zn/Hx* is evident from consistent breakthrough curves and PXRD patterns across three recycling cycles, underscoring its potential as a robust adsorbent for practical gas separation applications.