Ultrathin metal-organic framework (MOF) based membranes have the potential to achieve high-performance gas separations, but current fabrication methods still face challenges in the simultaneous improvement of selectivity and permeance. Prof. Wang Zhi’s team from the School of Chemical Engineering and Technology introduced new design strategies to fabricate ultra-thin MOF-based gas separation membranes.

One work is to construct ultrathin unobstructed gas transport channels through the membrane selective layer in mixed matrix membranes (MMMs) by using gravity-induced interface self-assembly of poly (vinylamine) and polymer modified MIL-101(Cr). The MOF nanoparticles were imbedded in the polymer matrix in the form of a single layer. The fabricated membranes showed excellent CO₂/N₂ separation performance.

The Scheme of membrane fabrication and gas transport process

This design concept and approach for constructing ultrathin unobstructed gas transport channels can be used to fabricate other MMMs with different porous materials and polymer matrices for achieving high gas separation performance.

This work is completed by Prof. Wang Zhi in collaboration with Prof. Michael D. Guiver. Wang Bo, a PhD candidate of Tianjin University, is the first author of this work. This work has been published on Advanced Materials (2020, 32, 1907701).

Prof. Wang Zhi and Prof. Michael D. Guiver also participated in another work to fabricate ultrathin and low-crystallinity-state pure MOF (LC-MOF) membranes by interface layer polarization induction of metal ions and ligands. This is achieved using an interface layer having metal ions with dense and uniform distribution, resulting in the creation of abundant open metal sites. Three types of LC-MOF membranes (45-150 nm) are fabricated, among which ZIF-8 membranes modified in situ with diethanolamine (DZIF-8) display the best performance for propylene/propane separation.

(A) Representation of the formation process of supported ultrathin LC-MOF membranes. (B) SEM surface images, SEM cross-sectional images and AFM images of (a) DZIF-8-1, (b) DZIF-8-2 and (c) DZIF-8-3 LC-MOF membranes.

This work provides a practical approach for the preparation of ultrathin membranes, not only for MOFs, but also applicable to other porous materials.

Prof. Zhong Chongli at Tiangong University worked with Prof. Wang Zhi and Prof. Michael D.Guiver at Tianjin University. Dr. Qiao Zhihua at Tiangong University is the first author, and Liang Yueyao and Dr. Zhang Zhengqing from the same University are the co-first authors. This work has been published on Advanced Materials (2020, DOI: 10.1002/adma.202002165).

By the School of Chemical Engineering and Technology

Editor: Eva Yin