Fabrication of a superhydrophilic/underwater superoleophobic PVDF membrane via thiol–ene photochemistry for the oil/water separation

The direct discharge of oily wastewater into the environment is considered one of the greatest threats to the ecological environment. Membrane technology is considered as an efficient strategy to treat oily wastewater. However, the membrane fouling caused by oil adsorption has intensively impeded its practical utilization in oil/water separation. This work aims to fabricate an anti-oil-fouling membrane for the effective separation of oil/water emulsions. The PEGylated poly(vinylidene fluoride) (PVDF) membrane was synthesized via thiol–ene photochemistry with poly(ethylene glycol) diacrylate (PEGDA) and 3,6-dioxa-1,8-octanedithiol (DOT) as the modifiers. The results of scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) mapping analysis revealed that the PEGylated layers show uniform distribution on the membrane surface by regulating the feed PEGDA concentration. The superhydrophilic and underwater superoleophobic characteristics of the PEGylated membrane provided oil-adhesion resistance to the membranes. The membrane grafted with a high amount of PEGylated layers shows a low pure water flux, due to the pore blockage. The PEGylated membrane possesses the stable surface wettability and permeation performance of emulsion. The separation efficiency of PEGylated membranes for multiple emulsions is greater than 99%, and the highest rejection value is as high as 99.9%. After the three-cycle filtration of emulsified pump oil solution, the flux recovery ratio of membranes still reaches 90%, indicating an outstanding fouling resistance to emulsified oily matters. This work provides a feasible strategy to prepare the antifouling PVDF membrane used for the oil/water separation.