Layer-by-layer assembled GO-based membranes with high long-standing stability and chemical resistance applied in dye separation and desalination

Abstract

The Graphene oxide (GO) membranes, as the most studied and accessible two-dimensional (2D) membranes, have performed their expected separation performance, but instability of these delicate membranes still hinders their development. Layer-by-layer (LBL) self-assembly is one smart method for preparing versatile 2D membranes with stable structure by chemical bonds or other forces. Herein, the 2D GO laminar membranes were prepared on the modified Nylon-6 substrates via LBL method by employing positively charged P–GO (guanidine modified GO nanosheets) and negatively charged S–GO (sulfonated GO nanosheets) as assembly flakes. This smart strategy was established on the superiority of LBL method by adjusting the assembly layer number and outermost charge when faced up with the different targeted contaminants. Benefited from the compact structures and intense charge, the LBL membranes can almost remove all the employed dyes (above 98% rejection for ML11 membrane). Furthermore, these membranes also show the high selectivity to water molecular in desalination (93.4% rejection to Na2SO4 and 72.7% rejection to NaCl for ML11 membrane). The membranes can endure the filtration of dye wasterwater and salt solution for above 168 h under cross-flow mode without rejection decline. Also, these versatile LBL membranes reveal high resistance to both chemical corrosion and bacterial attack, which is suitable for the continuous separation even under hostile external environment.