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-8Ni and YSH-8Zn, demonstrating their effectiveness in natural gas purification. These frameworks, constructed from 5,10,15,20-tetrakis(3,5-dicarboxyphenyl)porphyrins (TDCPPMs; M = Ni and Zn), exhibit 2-fold and 4-fold interwoven structures of 3D hydrogen-bonded networks. YSH-8Ni exhibited a 4-fold interwoven structure with stabilisation of pi-pi interaction among porphyrin building blocks. YSH-8Zn exhibited a 2-fold interwoven structure with axial coordination of oxygen species. Post solvent exchange to n-hexane, YSH-8Zn/Hx exhibited improved stability through the connection by bridging ligand atoms between the 2-fold interwoven hydrogen-bonded networks. After activation, YSH-8Zn/Hx* shows a BET surface area of 1665 m2 g-1, which is six times larger than that of YSH-8Ni* (279.5 m2 g-1). YSH-8Zn/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-8Zn/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. Axial coordination caused interwoven isomerism of porphyrin-based 3D hydrogen-bonded organic frameworks. The axial coordination-assisted pore volume expansion enabled efficient gas separation of gaseous hydrocarbons.