Multipurpose Zwitterionic Polymer-Coated Glass Fiber Filter for Effective Separation of Oil–Water Mixtures and Emulsions and Removal of Heavy Metals

Oil–water separation is crucial to treat industrial oily wastewater and manage oil spill pollution. Because of complex environments in real applications, it is challenging to develop multifunctional filter membranes that can not only effectively separate oil and water but also fulfill other practical requirements such as reducing toxic contaminants and operating under extreme circumstances. Here, we report a superhydrophilic and underwater superoleophobic filter membrane with high oil–water separation efficiency under a variety of harsh conditions (i.e., high acidity, high alkalinity, and hypersalinity) and unique capability of removing heavy metal ions. Zwitterionic poly(ornithine methacrylamide) (pOrnAA) is superhydrophilic, interacting strongly with water via electrostatic interactions. The filter was fabricated by chemically modifying glass fibers with cross-linked pOrnAA hydrogel coatings via a facile in situ free radical polymerization method. Not only it successfully separated free oil–water mixtures under both mild and extreme (highly acidic, alkaline, or salty) conditions, but also it effectively separated oil-in-water emulsions, with an oil separation efficiency above 99% for all cases. The coating also improved the water flux and flux recovery ratio while maintaining excellent oil separation efficiency for repeated use of the membrane. Furthermore, the filter membrane demonstrated effective heavy metal removal by chelation, with adsorption capacities of 36.3 and 6.9 mg/g for Cu2+ and Ni2+, respectively, attributed to ornithine methacrylamide (OrnAA) being derived from amino acid, which chelates heavy metals by nature. The outstanding performance of the zwitterionic pOrnAA-coated glass fiber filter membrane proves its multifunctionality, offering considerable potential for practical applications including oil–water separation and heavy metal removal.