Tannic Acid-Assisted Surface Coating of Peptides on the Poly(vinylidene fluoride) Membrane for Oil/Water Emulsion Separation

The membrane separation of oil/water emulsions has drawn much attention in recent years. The goal of present work is to develop a facile, cost-effective modification method to improve the hydrophilicity and antifouling of polyvinylidene fluoride (PVDF) membrane. Inspired by the plant polyphenol with strong anchoring ability on the various substrates, we report a two-step polyphenol chemistry strategy to achieve the hydrophobic-to-hydrophilic transformation of PVDF membrane via coordination assembly of tannic acid and Fe3+ ion followed by grafting of glutathione (GSH). The successful coating of GSH onto the PVDF membrane was confirmed by X-ray photoelectron spectroscopy. The modified PVDF membrane has good wettability (the water contact angle is 24.8 o and the underwater oil contact angle of 144.4 o) and high antifouling ability (the BSA rejection ratio is 87.7 %). More importantly, the modified membrane has a high water filtration flux up to 5,822 L m-2 h-1 at 0.09 MPa, and the separation efficiency is more than 99 % for the various surfactant stabilized oil-in-water emulsions. It is also successfully used to separate the high viscous crude oil-in-seawater emulsion, achieving a separation efficiency of > 95 %. The results showed that the simple and versatile method is promising for the modification of PVDF membranes with the ability of emulsion separation.