the face of severe problems such as eIn nergy scarcity and greenhouse effect, especially under China's "double carbon" target, the development of membrane separation technologies with low energy consumption and low carbon emissions has attracted much attention in the fields of hydrogen preparation and purification, carbon dioxide capture and other important industrial gas separation.

Among them, metal-organic framework materials (MOFs) are expected to become a new generation of ideal separation membrane materials due to their structural diversity, regular pore channels, high porosity and rich surface chemistry.

Recently, a new concept of soft-solid defect-free metal-organic framework composite separation membrane has been proposed by the team of Wei-Shen Yang and Yuan Peng, an associate researcher at the Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences (hereinafter referred to as DICP), by designing a novel preparation strategy of simple in situ growth combined with domain-limited interfacial polymerization, which achieves high-precision separation of hydrogen and carbon dioxide (H2/CO2) with very small size difference. separation of hydrogen and carbon dioxide (H2/CO2) with very small size difference. The separation performance of the new MOFs membrane far exceeds that of all MOF-based separation membranes reported so far and has promising applications. The results were published in the German Journal of Applied Chemistry and selected as a "Very Important Paper".

How were the new MOFs membranes prepared? The research team introduced that they first grew micron-sized, quasi-vertical, discrete layered Zn2(Bim)4 solid MOF grains on commercially available inexpensive flexible porous organic carriers to achieve gas transfer by fully exposing the two-dimensional straight-through molecular sieve pore channels between the Zn2(Bim)4 grain layers.

Subsequently, the research team constructed a modular network structure of soft polyamide-solid Zn2(Bim)4 linked by a domain-limited interfacial polymerization operation. The nanometer-thick and highly cross-linked polyamide network can be tightly attached to the sides of adjacent Zn2(Bim)4 grains, resulting in full coverage of intergranular non-selective defects while guaranteeing full opening of Zn2(Bim)4 interlayer straight-through pore channels.

These defect-free separation membranes have unique advantages for gas separation applications. The results show that the quasi-perpendicular Zn2(Bim)4 intergranular two-dimensional straight-through pore channels are the main gas transfer channels, resulting in ultra-high (H2/CO2) sieving accuracy and separation selectivity that is one to two orders of magnitude higher than that of other reported MOF-based separation membranes, reaching 1084.

In addition, the membrane material has excellent thermal and hydrothermal stability and is resistant to condensable gas swelling; the membrane performance remains unchanged after 50 consecutive 90° bends or rolls into 3 mm diameter round tubes (the largest membrane bending curvature to date).

It is further found that the preparation strategy and the unique defect-free membrane structure concept are highly universal, and the formed ZIF-67, ZIF-8 and other soft-solid defect-free composite separation membranes show excellent (H2/CO2) separation selectivity, much higher than other ZIF-67 or ZIF-8-based separation membrane materials.

This work fully exploits the advantages of high molecular sieving ability of MOFs, excellent flexibility of polymers, cheap and easy availability of carriers, and simple and scalable preparation strategy, which opens a new path for creating MOF-based membranes with industrial applications. In the future, modular functional design strategies will enable the customization of specific separation membranes for the precise identification, separation and purification of specified separation systems.

The editors of the German Journal of Applied Chemistry described the work as "unanimously peer-reviewed as very important" and "less than 5% of all work receives such a positive rating."