Zwitterionic Nanohydrogel Grafted PVDF Membranes with Comprehensive Antifouling Property and Superior Cycle Stability for Oil-in-Water Emulsion Separation

Fouling caused by oil and other pollutants is one of the most serious challenges for membranes used for oil/water separation. Aiming at improving the comprehensive antifouling property of membranes and thus achieving long-term cyclic stability, it is reported in this work the design of a kind of zwitterionic nanosized hydrogels grafted poly(vinylidene fluoride) (PVDF) microfiltration membrane (ZNG-g-PVDF) with superior fouling-tolerant property for oil-in-water emulsion separation. Sulfobetaine zwitterionic nanohydrogels with the diameter of approximate to 50 nm are synthesized by an inverse microemulsion polymerization process. They are then grafted onto the surface of PVDF microfiltration membrane, endowing the membrane a superhydrophilic and nearly zero oil adhesion property. This ZNG-g-PVDF membrane exhibits great tolerance and resistance to salts pH, especially an excellent antifouling property to oil-in-water emulsions containing various pollutants such as surfactants, proteins, and natural organic materials (e.g., humic acid). The comprehensive antifouling property of the membrane gives rise to the cyclic stability of the membrane greatly improved. A nearly 100% recovery ratio of permeating flux is achieved during several cycles of oil-in-water emulsion filtration. The ZNG-g-PVDF membrane shows great potential in treating practical oily wastewater containing complicated components in the effluent.