Smart Janus membrane for on-demand separation of oil, bacteria, dye, and metal ions from complex wastewater

Oil spills and oily wastewater discharged from industries and households have resulted in environmental and economic concerns. Therefore, emerging Janus membranes with anisotropic wettability have attracted significant attention as next-generation oil/water separation membranes owing to their specific, on-demand separation ability. However, the one-step separation of complex wastewater has not yet been achieved. Herein, a pH-responsive siloxane modified polystyrene microsphere/zinc oxide/carbon nanotube/polyvinylidene fluoride (S/PS/ZnO/CNTs/PVDF) membrane was rationally designed with Janus surfaces for providing hydrophilicity/underwater lipophobicity and lipophilicity/underoil hydrophobicity functionality. This study demonstrates that the underlying mechanism of on-demand separation of water-in-oil and oil-in-water emulsion is related to wettability, adhesive forces, and intrusion pressure. The proposed Janus membrane can achieve one-step separation of complex wastewater comprising oil, bacteria, organic dye, and metal ions. The effective removal of dyes is due to synergistic effects of electrostatic adsorption and photodegradation. This facile strategy for fabricating smart Janus separation membranes has application potential in on-demand oil/water separation and practical complex wastewater separation.