Robust superwetting polytetrafluoroethylene membranes with interlayer-bridged inorganic nanocoating for efficient oil/water separation

Abstract

Treating oily wastewater is of great importance and urgency worldwide. The superhydrophilic and underwater superoleophobic (SUS) membrane is an effective alternative to realize such a goal. However, most SUS membranes are vulnerable in harsh environments, such as strong acidic/alkaline solutions or physical abrasion, resulting in a limited lifespan. In this work, a robust SUS membrane was developed by depositing in situ a TiO2 nanocoating onto the polytetrafluoroethylene (PTFE) porous membrane with (3-[(perfluorohexyl sulfonyl) amino] propyltriethoxy silane) (PFSS) as an intermediate layer. In the preparation process, the fibrils and nodes of the PTFE membrane were integrally enclosed with the chemical networks generated by hydrolysis and self-condensation of the PFSS. Then, the nano-TiO2 was in situ bonded with the sulfonyl amide group of the PFSS via bidentate coordination. As a result, an ultrathin and continuous nano-TiO2 coating (∼20 nm) was created, and the coating covered throughout the porous PTFE matrix. The resultant PTFE membranes demonstrated typical SUS characteristics, while their pore structure was almost unchanged. The PTFE SUS membranes exhibited a high emulsion permeance (up to 18,700 L m–2h−1 bar−1) with a separation efficiency above 99.3%. Attributed to the soldering effect of the PFSS between TiO2 nanoparticles and the PTFE membrane, the developed SUS membranes exhibited excellent stability against strong acid/alkali washing and hydraulic shearing, all of which outperformed the majority of current SUS membranes.