A thin and high loading two-dimensional MOF nanosheet based mixed-matrix membrane for high permeance nanofiltration

The performance of mixed matrix membranes (MMMs) is usually limited by thick separation layer, low filler loading, and boundary defect between polymer and filler. Herein, a new two-dimensional metal-organic framework (2D MOF), named BUT-203, is designed and synthesized. Remarkably, the micron-sized crystals of this MOF could be readily delaminated into nanosheets with thickness of ca. 3 nm and lateral size of hundreds of nanometers to several microns. This delaminated nanosheets with high dispersibility in ethanol have a good compatibility with the polycation polymer polyethyleneimine (PEI). Under the optimum condition, a thin (ca. 70 nm) and high filler loading (up to ca. 73%) MMM, named BUT-203/PEI-HPAN(73) can be fabricated on macroporous hydrolyzed polyacrylonitrile (HPAN) substrate by a simple blending-spin coating method. This membrane shows a high water permeance up to 870 L/(m2·h·MPa) and high rejections (over 97.9%) for anionic dye molecules. In addition, this membrane exhibits a long term running stability, high dye desalination ability, and excellent antifouling property. These results suggest the usefulness of the membrane in nanofiltration, and simultaneously this work demonstrates that rationally designed 2D MOFs have great potential as filler materials in fabricating MMMs for various applications.