Hydrophilicity-controlled MFI-type zeolite-coated mesh for oil/water separation

MFI-type zeolite was prepared on porous stainless steel mesh by in situ and secondary growth method, respectively. The zeolite mesh consisting of well-grown polyhedral crystals showed great hydrophilicity, which absorbed water passing through the mesh driven by gravity and rejected oil simultaneously. In order to obtain better oil/water separation performance, Al³⁺ ions were introduced into the zeolite structure to control the hydrophilicity of the zeolite-coated mesh. With increasing aluminum content in the coated zeolite, the contact angle measurement demonstrated that the hydrophilicity of the membrane increased with the oil contact angle changing from 136.8° to 163.5°. When the Al/Si ratio was 0.04, the zeolite-coated mesh showed super-hydrophilicity and underwater super-oleophobicity. The oil rejection rate of the membrane reached >99% with the water flux of >80,000 L m⁻² h⁻¹ at this ratio. The zeolite-coated mesh showed high chemical stability in an oil rejection rate, when the filtrations were repeated 15 times successively with the same membrane. The zeolite-coated meshes were successfully reproduced by a simple re-calcination step due to their thermal stability. When the re-calcination step had been carried out for three times on the same membrane, the oil rejection performance was slightly reduced only less than 1%. The MFI-type zeolite-coated mesh were also used to separate various oils such as n-hexane, cyclohexane, mineral oil and vegetable oil. The oil rejection rates were above 96% for all these oils.