Covalent organic framework (COF) membranes have emerged as promising candidates for hydrogen purification due to their tunable pore sizes and robust structures. However, achieving high selectivity and permeability simultaneously remains a challenge due to the inherent pore size distribution of COF materials. In this study, we fabricated two distinct COF membranes, TpPa-1 and TpTGCl, with pore sizes of 1.8 nm and 0.39 nm, respectively, using tailored synthesis methods. The TpTGCl membrane, synthesized via room temperature interfacial polymerization and vacuum-assisted filtration, exhibits an ultrathin nanosheet structure with an interlayer π–π stacking distance of 0.33 nm. This unique architecture, combined with its affinity for CO2 adsorption, enables exceptional hydrogen separation performance, achieving a H2/ CO2 selectivity of 52.5 and a H2 permeability of 3.49 × 10– 7 mol m− 2 s− 1 Pa− 1. Molecular dynamics simulations confirmed the steric hindrance effect as the primary mechanism for the selective permeation of hydrogen. The TpTGCl membrane effectively sieves larger gas molecules ( CO2, N2, CH4, etc.) without the need for material modification or excessive membrane thickness. This study demonstrates the potential of COF membranes with tailored pore sizes for high-performance hydrogen purification and offers valuable insights for the development of advanced separation technologies.

Sub-nanoporous COF-TpTGCl membranes for enhanced H2CO2 separation via steric sieving
    Abstract
    1 Introduction
    2 Experimental section
        2.1 Materials
        2.2 Preparation of COF-TpTGCl membrane
        2.3 Gas permeance tests of membranes
        2.4 Characterization
    3 Theoretical model section
        3.1 Model construction
        3.2 Molecular dynamics simulations (MD)
        3.3 Adsorption energy
        3.4 Self-diffusion coefficient (Dself) of gases in the membrane
    4 Results and discussion
        4.1 Characterization of COF-TpTGCl nanosheets
        4.2 Structure and morphology of membranes
        4.3 Gas separation performance of COF-TpTGCl membranes
    5 Conclusion
    Acknowledgements 
    References

• Xuechun Li(School of Chemistry and Chemical Engineering, Shandong University of Technology, Zibo 255000, People’s Republic of China)
• Desheng Xu(School of Chemistry and Chemical Engineering, Shandong University of Technology, Zibo 255000, People’s Republic of China)
• Yun Jin(School of Chemistry and Chemical Engineering, Shandong University of Technology, Zibo 255000, People’s Republic of China) Corresponding author
• Tingting Du(School of Chemistry and Chemical Engineering, Shandong University of Technology, Zibo 255000, People’s Republic of China)
• Jian Song(School of Chemistry and Chemical Engineering, Shandong University of Technology, Zibo 255000, People’s Republic of China)
• Yuxin Wei(School of Chemistry and Chemical Engineering, Shandong University of Technology, Zibo 255000, People’s Republic of China)
• Xiuxia Meng(School of Chemistry and Chemical Engineering, Shandong University of Technology, Zibo 255000, People’s Republic of China)
• Naitao Yang(School of Chemistry and Chemical Engineering, Shandong University of Technology, Zibo 255000, People’s Republic of China) Corresponding author