Selective separation of oil-in-water emulsion with high efficiency by bio-inspired Janus membrane

The efficient and rapid separation of oil from stabilized oil-in-water emulsions with micro/nanometer size is a global challenge. Owing to the low oil content in oil-in-water emulsions, separating the oil by simply controlling the surface wettability is difficult. Controlling the pore size of the membrane surface to achieve separation will lead to a sharp decrease in flux. Herein, inspired by cell membrane transportation, a hydrophilic/hydrophobic bifunctional Janus membrane for stable oil-in-water separation was prepared by simple surface polymerization and vapor diffusion. The prepared Janus membrane contained a hydrophobic side and hydrophilic polyamine layer. When used for oil-in-water emulsion separation, the polyamine layer accumulated micro/nanometer oil droplets, forming an oil layer on the hydrophobic surface. Water was retained by the 1H,1H,2H,2H-perfluorooctyl trichlorosilane layer, allowing oil droplets to selectively permeate through the membrane, achieving the separation effect. As the pore size of the modified fabric was basically unchanged, the permeation flux was fast (1.53×103 Lm−2 h−1). Furthermore, the poly(N,N-dimethylaminoethyl methacrylate) layer destroyed the emulsion stability, making the emulsion droplets aggregate without affecting the separation efficiency with fast permeation flux. Therefore, the prepared bifunctional Janus membrane shows great potential for actual wastewater treatment.