Graphene oxide/PVDF VIPS membranes for switchable, versatile and gravity-driven separation of oil and water

In what follows, we incorporated graphene oxide (GO) into poly(vinylidene fluoride) (PVDF) membranes prepared by vapor-induced phase separation (VIPS), in order to achieve gravity-driven separation of versatile water-in-oil (W/O) and oil-in-water (O/W) emulsions. Membranes were first fully characterize to evidence the presence of GO at the interface, using XPS, FT-IR, Raman, and XRD spectroscopy, while SEM permitted to describe the porous structure of the microfiltration (MF) membranes. An in-depth study of the wettability of the membranes was carried out through the determination of water contact angles in air and oil, and oil contact angles in air and water, using 4 different oils including toluene, hexane, diesel and soybean oil. It was found that GO did not significantly affect the wettability of the membranes. However, gravity-driven filtration tests performed after pre-wetting the membranes with the dispersing phase forming the emulsion at play revealed that GO could accelerate 8-10 times the separation of both O/W and W/O emulsions. The nature of the dispersing phase probably dictates the selective wetting of the functional groups of the GO particles, which in turn favors the permeation of the dispersing phase and accelerates the whole separation. Besides, GO strengthens the interactions with the wetting liquid contributing to totally eliminate air pockets, which prevents the dispersed phase in complex emulsions (involving diesel or soybean oil) to permeate through the pores, and so, improves the separation efficiency despite larger pores.