Development of Highly Efficient Oil–Water Separation Carbon Nanotube Membranes with Stimuli-Switchable Fluxes

In this work, a carbon nanotube (CNT)-based membrane [(4-((4-((11-ferroceneundecyl)oxy)phenyl)diazenyl)phenoxy)-diethylene triamine (FADETA)/polyethyleneimine (PEI)-decorated CNT membrane] with stimuli-switchable separation fluxes was developed. The multiwalled CNTs were modified by a pH-, light-, and redox stimuli-responsive surfactant FADETA initially, and then the FADETA-decorated CNTs were further cross-linked by PEI and finally coated on the polypropylene membrane. Interestingly, the particular membrane was successfully applied in emulsion systems to separate oil and water with high efficiency. First, the FADETA-/PEI-decorated CNT membrane showed highly porous microstructural characteristics owing to the overlapped and cross-linked CNTs as confirmed by the scanning electron microscopy observation. Then, it showed strong hydrophilicity to water in the air and high oleophobicity to oil underwater, thereby endowing the membrane with the potential to separate oil and water. Owing to the modified multiple stimuli-responsive FADETA on CNTs, the separation fluxes were stimuli-switchable, which could be adjusted reversibly by environmental factors including pH, light, and redox.