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 were grafted from graphene oxide (GO) nanosheets to prepare the nanofiltration membrane, and the electrostatic effect and Donnan effect in the membrane pores could be greatly improved. The GO was modified by introducing double bonds. Then, polyanionic poly(acrylic acid) (PAA) and polycationic diallyldimethylammonium chloride (PDDA) were grafted from GO nanosheets, which were employed to fabricate the nanofiltration membranes, respectively. Therefore, nanofiltration membranes GO-PAA and GO-PDDA with cross-linked structure and pH responsiveness were prepared. The separation effect of the anionic dyes was over 99%, and the membrane had perfect adsorption effect on cationic dyes. The cross-linked structure formed between GO nanosheets inhibited the change of the interlayer spacing of the nanofiltration membrane. The conformation of the graft chains could be adjusted by the pH value of the solution, by adjusting the size of the nanochannel. The rejection rates of the nanofiltration membranes for the cationic dyes could reach more than 98%, and the membrane had perfect adsorption effect on anionic dyes. 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.