[COF@ZIF-8]: Enhanced Lattice Rigidity in MOF–COF "Alloy" Membranes for Superior Propylene/Propane Separation
The research is from Adv. Mater. 2022, 34(24), 2201423, completed by Prof. Zhongyi Jiang of Tianjin University and coworkers
Abstract
1) The development of molecular-sieving membranes from metal–organic frameworks (MOFs) for olefin/paraffin mixtures is crucial for sustainable chemical processes. However, the flexibility of MOF lattices affects their sieving ability. This study introduces "alloy" membranes (AMs), combining quaternary ammonium (QA)-functionalized covalent organic frameworks (COFs) with a zeolitic imidazolate framework-8 (ZIF-8) matrix, to enhance lattice rigidity.
2) The incorporation of COFs into the ZIF-8 matrix leverages Coulomb forces to restrict linker rotation in ZIF-8, creating an alloying effect that adjusts lattice rigidity. This results in a propylene/propane separation factor exceeding 200 and a propylene permeance of 168 GPU, surpassing previous MOF-based membranes.
3) The study presents a new approach to tuning MOF lattice rigidity, offering a potential breakthrough in the design of mixed matrix membranes for energy-efficient gas separations.
2) Background Summary
1) Industry Problems: The chemical industry relies heavily on energy-intensive processes for olefin/paraffin separation, contributing significantly to global energy consumption and carbon emissions. Alternative separation technologies, such as non-thermal membrane processes, are needed.
2) Previous Solutions: MOFs have been considered for their tunable pore sizes and high porosity. However, their framework flexibility due to linker rotation has limited their use in precise molecular sieving.
3) Innovations: The authors propose "alloy" membranes that integrate QA-functionalized COFs into ZIF-8, creating a new alloying effect that enhances lattice rigidity and improves separation performance.
Experiment
1) Synthesis of Monomers: EBCOF nanosheets were synthesized via an interfacial crystallization method, characterized by AFM, HRTEM, and other techniques.
2) Fabrication of AMs: EBAMs were fabricated using an electro-driven co-deposition process, combining reductive electrosynthesis and electrophoretic deposition.
3) Incorporation of COFs: Varying amounts of EBCOF nanosheets were added to the ZIF-8 synthesis precursor, resulting in a series of EBAMs with tailored rigidity.
Analysis and Test Results
1) Characterization Techniques: XRD, FTIR, and XPS were used to assess the crystalline structure, lattice rigidity, and chemical composition of the AMs. The unit-cell parameters of ZIF-8 were refined to evaluate lattice changes.
2) Gas Separation Performance: EBAMs demonstrated superior C3H6/C3H8 separation performance, with the optimized EBAM-2 showing a separation factor of 203 and a C3H6 permeance of 168 GPU.
3) Stability Tests: EBAM-2 showed stable performance over a 120-hour operation test and maintained its selectivity under varying feed pressures.
Conclusion
1) The concept of "alloy" membranes has been successfully demonstrated through the fabrication of MOF–COF AMs, offering a new strategy for tuning MOF lattice rigidity.
2) The integration of QA-functionalized COFs into ZIF-8 resulted in a record-high separation performance for propylene/propane mixtures, with potential applications in energy-efficient gas separations.
3) The study opens up new possibilities for the design of advanced membranes, leveraging the vast potential of MOFs, COFs, and other framework materials for precise molecular or ionic sieving.
4) To study the long-term stability of AMs under industrial conditions and the scalability of the electro-driven co-deposition method for large-scale production.
MOF–COF “Alloy” Membranes for Efficient Propylene/Propane Separation
Yutao Liu, Hong Wu, Runlai Li, Jianyu Wang, Yan Kong, Zheyuan Guo, Haifei Jiang, Yanxiong Ren, Yunchuan Pu, Xu Liang, Fusheng Pan, Yu Cao, Shuqing Song, Guangwei He, Zhongyi Jiang
DOI: 10.1002/adma.202201423
Links：https://onlinelibrary.wiley.com/doi/10.1002/adma.202201423
