A Scalable, Pollution-Free Protocol of Poly(vinylidene fluoride) In Situ Nanofibrillar Membranes for Effective Oil–Water Separation

The application of poly(vinylidene fluoride) (PVDF) nanofibrils in the membrane separation field has been extensively limited due to solvent toxicity and complex regulatory techniques of PVDF in the fabrication of nanofibrils. In this work, a scalable and environmental pollution-free protocol based on in situ nanofibrillation, followed by etching of the polymer matrix to fabricate PVDF nanofibrillar membranes for oil-water separation, has been successfully realized. Due to strong interfacial interactions with the poly(ethylene oxide) (PEO) matrix, PVDF nanofibrils with diameters ranging from 200 to 400 nm are obtained by shear and stretch stresses under the melt-stretching field. The low surface energy of PVDF and the rough surface of PVDF nanofibrillar membranes result in hydrophobic and under-oil superhydrophobic performances, making them strong candidates for application in oil-water emulsion separation. The high separation flux (5160 L m^-2 h^-1 bar^-1) and separation efficiency (97.5%) are achieved when the membrane thickness reaches 1.7 mm, surpassing the performance of other PVDF-based membranes. PVDF nanofibrillar membranes also display high durability, ascribed to a robust nanofibril-jointed structure, which maintains a good balance between permeability and separation efficiency after multiple separations. Moreover, PVDF nanofibrillar membranes also exhibit promising comprehensive performance, including good oil-absorption capacity, good reusability, resistance to acids/alkalis/organic solvents, and temperature resistance. This work offers insights into the construction of PVDF separation membranes via a scalable and pollution-free processing technology.