Membrane separation technology offers great potential due to its low energy consumption and continuous operation availability. Metal-organic frameworks (MOFs) are promising in separation membranes due to their abundant species, high porosity, and precise regulation of pore architectures.
However, the development process of high-performance MOF membranes is time-consuming and costly, and the membrane is plagued by unavoidable problems such as heterogeneous nucleation, defects, cracks, etc., resulting in the actual separation performance of MOF membranes being far lower than the theoretical simulation value, and not accurately demonstrating the separation ability of the material intrinsic pore structure.
The MOF membrane amount to date is only a drop in the bucket compared to the material collections. The fabrication of an arbitrary MOF membrane exhibiting inherent separation capacity of the material remains a challenge.
Recently, a research group led by Prof. YANG Weishen and Assoc. Prof. PENG Yuan from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) has proposed a new strategy of modular customization and non-destructive regulation of MOFs for efficient membrane separations.
They have achieved rapid regulation of the MOF module and verified the corresponding membrane for highly accurate separation applications, which provided a solid scientific and technical foundation for the research and development of separation membranes to meet the high-efficiency separation requirements of today's bulk/specific industrial products.
This work was published in Angewandte Chemie International Edition on Oct. 16.
Diagrammatic illustrations of the MOF modular customization concept (Image by SHU lun and PENG yuan)
The researchers proposed a strategy to modularize custom defect-free MOF separation membranes. The membrane structure consisted of two parallel modules. One was a discrete MOF module based on the characteristics of heterogeneous mutually reinforcing nuclei, which led to the implementation of molecular mass transfer and separation by exploiting the intrinsic pore structure. The other was the highly cross-linked, ultra-low permeability polyamide module formed by the confined interface polymerization operation, which was responsible for the comprehensive blockade of defects between MOF modules.
Guided by this strategy, the MOF module could be randomly replaced to customize the corresponding MOF separation membrane, and high-performance MOF separation membranes could be rapidly produced. With the modified post-synthesis strategy, the MOF module skeleton in the membrane was controlled without loss and the separation accuracy was doubled.
The researchers selected four MOFs with different pore/channel sizes and functionalities for batch fabrication of defect-free MOF membranes. Each membrane fully displayed the separation potential according to the MOF pore size.
Among them, the NH2-Zn2Bim4 membrane exhibited a high H2/CO2 mixture separation factor of 1656 and H2 permeability of 964 gas permeation unit. Taking advantage of this strategy, the membrane performance could be further enhanced via application-oriented post-synthetic ligand exchange. The H2/CO2 selectivity of the regulated membrane was approximately 200% higher than that of the original membrane.
"This strategy provides a tractable route to customize a myriad of high-performance membranes to meet different separation requirements," said Prof. YANG.
This work was supported by the National Natural Science Foundation of China.