Zhijun Zhao ¹, Li Ding ², Richard Hinterding ¹, Alexander Mundstock ¹, Christopher Belke ⁴, Rolf J. Haug ⁴, Haihui Wang ^2,3 , Armin Feldhoff ¹

¹ Leibniz University Hannover, Institute of Physical Chemistry and Electrochemistry, 30167 Hannover, Germany

² South China University of Technology, School of Chemistry and Chemical Engineering, 510640 Guangzhou, China

³ Tsinghua University, Department of Chemical Engineering, 100084 Beijing, China

⁴ Leibniz University Hannover, Institute of Solid State Physics, 30167 Hannover, Germany

While many efforts have been made in improving the hydrogen separation performance of MOF (metal-organic framework) membranes over the last decades, attention about helium separation has been rarely raised despite the soar of helium price.

As a member of MOF family, ZIF-67 has a suitable pore size for helium separation. However, it prefers homogeneous nucleation, hindering the preparation of continuous membranes. MXene is a new family of 2D materials with the general formula M_n+1X_nT_x, where M is one or more early transition metals, X is carbon and/or nitrogen, T_x stands for the surface terminations (e.g. –OH), and n = 1 – 4.

well-intergrown ZIF-67 membranes (4.1 μm thick) were formed by the assistance of laminarly stacked Ti₃C₂T_x films, while only a few discrete ZIF-67 grains were present in the MXene-free area after solvothermal synthesis. Several analytic methods, including time-dependent in-situ XRD, HRTEM, and EELS, have found that the MXene films, despite being as thin as 90 nm, could host a high amount of Co (II) ions, which promote heterogeneous nucleation of ZIF-67.

Single-gas and mixed-gas permeation experiments showed that the ZIF-67 membranes exhibited excellent gas separation performance and long-term chemical and thermal stabilities, superior to the state-of-the-art MOF membranes.