Polyphenol zwitterionic nanohydrogel modified polyvinylidene difluoride membrane for separating oil-in-water emulsions with superior cycle stability

Numerous strategies have been proposed for the superwetting membranes application in the separation of oily wastewater. Here, benefiting from the hydrophilic properties of hydrogel and the adhesive properties of plant polyphenols, we proposed a polyphenol zwitterionic hydrogel coating Poly(DMA-co-SPP) to modify hydrophobic PVDF membranes by a one-step co-deposition method. The polyphenol zwitterionic nanohydrogel, Poly(DMA-co-SPP), were prepared by polymerization of ethanol-aqueous solution. The characterization of fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy demonstrated the successful fabrication of the PVDF-Poly(DMA-co-SPP) membrane. The PVDF-Poly(DMA-co-SPP) membranes were designed with superhydrophilic/submerged superoleophobic surfaces, which exhibited excellent oil rejection rate (99%) and flux (2100 L·m−2·h−1·bar−1) for up to 30 separation cycles. The experimental results showed that the oil rejection rate (>99%) of iso-octane, dodecane and toluene emulsions was attributed to the low oil adhesion and hydration layer on the PVDF-Poly(DMA-co-SPP) membrane surface. The introduction of hydrogel particles improved the resistance of membranes to chemical and mechanical damage because of the interwoven hydrogen bonding and cross-linked network. This may stimulate advanced research into novel membrane materials for oily wastewater treatment. [Display omitted] •A strategy to deposit polyphenol zwitterionic nanohydrogels with PVDF membranes.•Strong resistance to mechanical damage and chemical attack.•The removal rates of isoctane, dodecane and toluene emulsions were all > 99%.•Excellent cycling stability as the flux 2100 L·m−2·h−1·bar−1 for separating soybean oil-in-water emulsions.