Fabrication of novel zwitterionic copolymer high performance membrane applied for oil/water mixtures and emulsions separation

The separation of oily wastewater is important for the ecological environment. Due to all kinds of defects in traditional methods, membrane technology shows outstanding merit for separating oil contaminants from water. In this work, a novel zwitterionic monomer 2-(3-carboxyacryloyloxy)-N-(Carboxyethyl)-N, N-dimethyl ethanaminium (DMAAA) was synthesized and characterized. Then, a novel zwitterionic copolymer, poly(2-(3-carboxyacryloyloxy)-N-(Carboxyethyl)-N, N-dimethyl ethanaminium-co-2-hydroxyethyl acrylate) (P(DMAAA-co-HEA)) was prepared by free radical polymerization. The superhydrophilic and underwater-superoleophobic membranes were prepared using stainless steel mesh (SSM) with different pore sizes as substrate, P(DMAAA-co-HEA) as superhydrophilic component, nano-silica (SiO2) as micro-nano porous structure, and tetraethyl orthosilicate (TEOS) as cross-linking agent by the one-step dip-coating method. P(DMAAA-co-HEA)-TEOS-SiO2 coated 400 mesh SSM(PTS-SSM400) exhibits ultra-high separation flux (243,600 L·m−2·h−1) and separation efficiency (>99.88%) in separating oil/water mixtures. And the coated 2000 mesh SSM (PTS-SSM2000) can separate various surfactant-stabilized emulsions with high water flux and efficiency only under gravity. Moreover, the membranes have excellent chemical stability and wear resistance. Even having been successively immersed for seven days in acidic, alkaline, and saline environments, respectively, and after 50 wear resistance cycle tests, the coated membranes can still effectively separate oil/water mixtures. The simple and facile preparation method is especially suitable for large-scale practical industrial applications.