Graft- Crosslinked Graphene Oxide Nanofiltration Membrane with Ph-Responsive Nanochannels

Electrostatic effect and Donnan effect could effectively improve the separation performance of nanofiltration membrane. Polyions was grafted onto graphene oxide (GO) nanosheets to prepare the nanofiltration membrane, the electrostatic effect and Donnan effect in the membrane pores could be greatly improved. The GO was modified by introducing double bonds. Then, nanofiltration membranes GO-PAA, GO-PDDA and GO-P(ATA-co-AM) with crosslinked structure and pH responsiveness were prepared. The pure water flux of the anionic GO-PAA nanofiltration membrane was 320.06 L·m-2·h-1·bar-1, the separation effect of the anionic dyes was over 99 %. The cross-linked structure formed between GO nanosheets inhibited the change of the interlayer spacing of the nanofiltration membrane. In an acidic environment, the electrostatic repulsion of the PAA chains were weakened, the PAA chains shrank, and the membrane rejection rate was poor; in a neutral or alkaline environment, the electrostatic repulsion increased, the PAA chains stretched, and the membrane rejection rate was superior. The pure water fluxes of GO-PDDA and GO-P(ATA-co-AM) were 199.04 L·m-2·h-1·bar-1 and 326.43 L·m-2·h-1·bar-1, respectively. The rejection rates of these two nanofiltration membranes for the cationic dyes could reach more than 98%. Similar to the grafted polyanion, the grafted polycation also formed a cross-linked structure between the graphene nanosheets, thereby inhibiting the change of the nanochannels with the pH value to a certain extent. Polyionic nanofiltration membranes have excellent selectivity and could be widely used in the treatment of dye wastewater and other fields.