Facile fabrication of MOF-based composite membranes with liquid crystal ordered microstructure for effective dyes separation

Abstract

High-performance membranes for effective dye/water separation are urgently desired in chemical industrial manufacture, and Metal-organic frameworks (MOFs) with abundant microporous structures are considered suitable candidates for fabricating separation membranes. However, for MOF-based membranes, maintaining superior separation efficiency while ensuring high water flux remains a challenge. In this study, a series of novel MOF-based composite materials (TFNs) and membranes oriented by electric fields (fio-TFNs) were fabricated using NH₂-MIL-53(Fe), a thermotropic liquid crystal, poly (styrene-4-sulfonic acid), and polytetrafluoroethylene. The fio-TFN membranes exhibited characteristics of orientation and uniform distribution, and showed higher water flux and dye rejection compared with ordinary TFN membranes. This highlights the significant role played by the ordered orientation of liquid crystal molecules induced by the electric field in effective dye/water separation. High porosity is the basis of dye absorption, and the electrostatic interaction among structural charges and dyes is the dominant driving forces in these dye/water separation systems. The prepared fio-TFN membranes exhibited excellent performance in effective dye separation. For instance, the fio-TFN-1 membrane demonstrated high water flux (up to 255.9 L·m⁻² h⁻¹ bar⁻¹) and excellent dye rejection rates (≥97 %, 92 %, and 82 % for methyl blue, congo red, and rhodamine B, respectively). Moreover, these prepared membranes exhibited excellent long-term stability, reusability, and flexibility, indicating their potential as high-performance separation membranes for wastewater treatment.