Facile construction of polyzwitterion membrane via assembly of graphene oxide-based core-brush nanosheet for high-efficiency water permeation

Zwitterions with super-hydrophilic feature are promising membrane materials for water-selective permeation process. However, the applications of zwitterionic materials in membrane are mainly restricted to surface modification or acting as minor additive, while the construction of zwitterionic membrane matrix remains challenging. Herein, we proposed a facile approach to constructing polyzwitterion membrane via direct assembly of graphene oxide (GO)-based core-brush nanosheets. The in situ free radical polymerization of sulfobetaine methacrylate (SBMA) monomer on GO surface ensures the ultra-high grafting amount of poly(sulfobetaine methacrylate) (PSBMA) brushes and then results in the polymer-dominated structure of PSBMA@GO membrane (polymer content high to 83%) instead of the ordered laminar structure in common GO-based membranes. Meanwhile, the original functional groups on GO can be retained after grafting PSBMA, which act as reactive sites for subsequent cross-linking and structural manipulation. Because of the exceptionally high hydration ability and water affinity of PSBMA brushes from the high-density ionic groups, and the densified membrane structure through incorporating the optimized amount of ethylenediamine (EDA) cross-linker, the as-prepared polyzwitterion membrane obtains an excellent water/ethanol separation performance with the separation factor of 1420 and the permeate flux of 5.20 kg/m²·h (70 °C, 20 wt% water in feed), which shows remarkable superiority compared with the reported polymeric membranes. The strategy proposed here provides a novel pathway for constructing polyzwitterion membranes with high separation efficiency, and can be applied with a greater scope of monomers.