Superhydrophilic/underwater superoleophobic PVDF ultrafiltration membrane with pH-responsive self-cleaning performance for efficient oil-water separation

The treatment of various oily wastewaters generated in human production and life has been a huge challenge in recent years. Responsive materials for controlled wettability surface have a great potential for oil-water separation. Inspired by the superior pH-responsive of poly (2-(N, N′-dimethylamino) ethyl methacrylate) (PDMAEMA), a pH-responsive self-cleaning PVDF ultrafiltration membrane containing both carboxyl and tertiary amine groups were prepared by a simple grafting and co-blending method. The membrane fabrication process consisted of introducing 3-Dimethylaminopropylamine (DMPA) into the SMA side chain, resulting in the creation of the amphiphilic polymer DMPA@SMA. This polymer was then mixed with PVDF to produce DMPA@SMA/PVDF membranes. The optimized DMPA@SMA/PVDF membranes showed excellent superhydrophilicity/underwater superhydrophobicity, with a water contact angle of 0° and an underwater oil contact angle higher than 150° for crude oil. These endowed the as prepared membrane with a high pure water flux of 852 L·m−2·h−1 and anti-crude-oil-adhesion property. The separation efficiency exceeded 98% for various surfactant-stabilized oil-in-water emulsions, whether it's positively charged emulsion or negatively charged emulsion. More interestingly, the carboxyl and tertiary amine groups presented the membrane with pH responsivity, and the membrane surface can be triggered by acid or alkali with self-cleaning performance. Strategy proposed in the present work offers a convenient and effective way to prepare membranes treating oil-in-water emulsions with either negative or positive charges.