Exquisite manipulation of two-dimensional laminar graphene oxide (GO) membranes via layer-by-layer self-assembly method with cationic dyes as cross-linkers

Herein, we propose one novel strategy by layer-by-layer (LBL) self-assembly method to prepare two-dimensional (2D) laminar membranes assembled between sulfonated graphene oxide (S-GO) nanosheets and various cationic dyes on the polyethyleneimine (PEI) -modified Nylon-6 (PA6) substrate. The membrane performances are manipulated exquisitely by the charge of substrate, the assembled dye type, dye size, self-assembly layer number etc. The water permeance positively correlates with the height of assembled cationic dyes. The amido bonds or sulfamide bonds and π–π conjugation endow the resulted membrane with strong performance stability. Furthermore, by precisely selecting the size and charge the assembled dye, the prepared LBL GO membranes can efficiently separate mixed dyes in aqueous solution via charge repulsion or/and size sieving mechanism. For example, the separation selectivity of 39.2 for the mixed Rhodamine B/Ethyl Violet (RB/EV) dyes can be achieved with the LBL MV-0.25-2-2 membrane (it was assembled by 2 mmol L−1 Methyl violet solution for two S-GO layers with the Nylon-6 substrate modified with 0.25 wt % PEI aqueous solution). Simultaneously, the introduced cationic dyes endow these membranes with extra antibacterial capacity to both E. coli and S. aureus.