Hydrophilicity reversal by post-modification: Hydrophobic zeolite FAU and LTA coatings on stainless-steel-net for oil/water separation

Because of the increase of industrial wastewater containing insoluble oil and oil discharged accidents, oil/water separation has turned out an exceedingly crucial and urgent issue in environmental protection. Therefore, it is terribly significant to develop a simple and effective technology for oil/water separation. Membrane separation has been well known as a promising method to remove oils from water due to its energy-efficiency and cost-effectiveness. In the present work, we report the synthesis of a hydrophobic zeolite FAU named F-FAU through a simple and effective post-synthetic modification. Firstly, a thin zeolite FAU layer is grown on the 3-aminopropyltriethoxysilane (APTES) modified stainless steel net (SSN) to form SSN supported FAU (SSN@FAU) coating. And then, a hydrophobic SSN@F-FAU coating is prepared through post modification of SSN@FAU coating with perfluorooctyltriethoxysilane (POTS). After POTS modification, the water contact angle (CA) of the SSN@FAU coating increases from 15° to 132° for SSN@F-FAU coating, while both morphology and structure of the SSN@FAU coating keep unchangeable. Attributing to the high hydrophobicity of the F-FAU coating, the SSN@F-FAU coating shows a wonderful oil/water separation performance, with oil/water separation efficiency of above 98.8 % and oil flux of up 50,000 L m⁻² h^-1. After 50 cycles successive separation of hexane/water mixture, the separation efficiency of the SSN@F-FAU coating keeps constant (over 99.1 %), showing potential application for oil/water separation in industries. Further, hydrophobic SSN@F-LTA coating can be consistently prepared through post modification of SSN@LTA coating with POTS, and also shows a high oil/water separation performance, with oil/water separation efficiency above 99.0 % and oil flux over 40,000 L m⁻² h^-1, confirming the universality of the preparation strategy.