Surface Modification of Polyimide Oil-Water Separation Membrane by Fe3+ Cross-Linked Tannic Acid Coating to Enhance Flux

Due to the frequent occurrence of marine oil spill accidents, the ecological environment is facing severe threats. However, some traditional oil-water separation methods suffer from issues such as high cost, environmental unfriendliness and low efficiency. Therefore, there is an urgent need to develop a simple and efficient oil-water separation membrane. Leveraging the non-toxicity and abundance of hydrophilic groups (such as -carboxyl and -OH) in tannic acid, this study, for the first time, forms a hydrophilic coating on the surface of polyimide membrane (PI) through the complexation of tannic acid with ferric chloride hexahydrate, thus fabricating a superhydrophilic/superoleophobic membrane for oil-water separation. The water contact angle (WCA) of the modified membrane drops to 0° within 5 s, while the underwater oil contact angle (UOCA) reaches up to 142°. Moreover, under the action of gravity, the membrane not only achieves a high water flux of 2100 L·m -2 ·h -1 but also attains a removal rate of over 90 % for various oil-in-water emulsions. In addition, the modified membrane exhibits excellent resistance to acids, alkalis, and salts, as well as outstanding oil-fouling resistance. This promising material offers a universal modification strategy with broad applications in wastewater treatment.