Bio-inspired underwater superoleophobic PVDF membranes for highly-efficient simultaneous removal of insoluble emulsified oils and soluble anionic dyes

Exploiting high-performance polymer membranes, which can simultaneously remove of both highly-emulsified oils and water-soluble contaminants such as dyes, is urgently required, yet remains an arduous challenge due to the critical restrictions of single functionality and severe membrane fouling. Herein, a superior superwettable polyvinylidene fluoride/chitosan/dopamine (PVDF/CS&DA) membrane was developed via a facile one-step codeposition strategy. With the catalysis of tyrosinase, DA-based chemical modification was conducted in a weak acid environment (pH 5.8–6.0) rather than conventional alkaline environment (i.e., pH 8.5), providing an intriguing alternative route towards mussel-inspired functional modification. Owing to the synergistic effect of the hydrophilic components and nano-structure roughness, the resultant membrane exhibited remarkable underwater superoleophobicity (oil CA of 1, 2-dichloroethane, 163.9°) and oil-repellency properties. Accordingly, benefiting from the superwettability features, the composite membrane achieved superior separation (an enhanced permeation flux of 201.3 L m−2 h−1 and a high separation efficiency of up to 99.7%) and anti-fouling performances in separating oil-in-water emulsions. More interestingly, this membrane displayed an excellent in situ adsorption capability for water-soluble anionic dyes, showing a fairly high adsorption efficiency (96.8% and 92.7% for methyl blue and orange G, respectively) after merely one-time rapid filtration and a robust recyclability. Therefore, the resulting membrane integrating high-efficiency emulsions separation and synchronous dyes removal capabilities holds a great prospect for sophisticated oily wastewater decontamination.