Fabrication of a Superhydrophilic and Underwater Superoleophobic Membrane via One-Step Strategy for High-Efficiency Semicoking Wastewater Separation

Hydrophilic polyvinylidene fluoride (PVDF) membranes can effectively separate the low oil content in semicoking wastewater. It is important to develop a stable superhydrophilic PVDF membrane with high oil rejection. Here, we developed a one-step strategy based on a polyphenol netlike structure coating to achieve the conversion of commercial membranes from hydrophobic to superhydrophilic; namely, the codeposition of 2-propenamide, N-[2-(3,4-dihydroxyphenyl)­ethyl] (DMA) and 3-aminopropyltriethoxysilane (APTES) in aqueous solution. ATR-FTIR and XPS technologies proved that the coating successfully adhered to the PVDF membrane. The pure water flux of the developed membrane was 17 270 L m^–2 h^–1 bar^–1. When treating simulated semicoking wastewater with low oil content, the permeate flux and the oil content of the filtrate were 5500 L m^–2 h^–1 bar^–1 and <6.5 mg L^–1, respectively. The modified PVDF membrane showed perfect wetting performance. The permeation flux of the real semicoking wastewater cycled 9 times was stable at 4530 L m^–2 h^–1 bar^–1 and the oil content of the filtrate was <12.5 mg L^–1. This work emphasizes a simple way to design superhydrophilic membranes for the separation of low-oil content emulsion, which will be promising for treating semicoking wastewater.