Fabrication of oriented metal-organic framework nanosheet membrane coated stainless steel meshes for highly efficient oil/water separation

Due to frequent oil spill accidents, the efficient separation of oil/water mixtures is attracting one's attention. In this work, we adopt a direct growth strategy for preparing continuous and highly oriented Zn-2(bIm)(4) (bIm = benzimidazole) ZIF nanosheet membranes on stainless steel meshes (SSMs) as substrate by the self conversion of vertically arranged ZnO nanorods grown on the SSMs. This kind of perpendicularly oriented nanosheet membrane has superhigh hydrophobicity and special microstructure and thus is very promising for fabricating membrane separators and application in oil removal. On the SSMs with different meshes (500 mesh and 2000 mesh), the corresponding ZIF nanosheet membranes were successfully fabricated by the oriented growth of nanosheets to form different separators called as ZNM-SSM-500 and ZNM-SSM-2000, respectively. They were applied in the separation of different oil/water mixtures by using dichloromethane, petroleum ether, n-hexane, toluene, nitrobenzene and cyclohexane as model oils, and could demonstrate excellent separation performance. The ZNM-SSM-500 separator shows a separation efficiency of 99.8% with high flux of over 100,000 L m(-2) h(-1) for free oil/water mixtures containing 50 wt% water, while the ZNM-SSM-2000 separator exhibits a water rejection of as high as 99.95% for water-in-oil emulsions containing 2 wt% water. Moreover, the resulting nanosheet membrane could also demonstrate excellent thermal stability and recyclability. Therefore, the oriented nanosheet membrane is of great application potential in practical oil/water separation.