Enhancing dye removal and antifouling properties of conductive polyethersulfone nanocomposite membranes by analogous zwitterion-functionalized separation layers with tunable surface-charge orientation

Membrane separation has been demonstrated to have enormous potential for alleviating the global scarcity of clean water. However, membrane fouling extremely limits its applications, and on-demand and precise molecular separation is very challenging for traditional membranes. Here, a novel smart voltage-gated membrane with an analogous zwitterion-functionalized separation layer is prepared by combining blending, surface segregation and co-deposition. Intriguingly, amphiphilic sodium styrene-maleic anhydride copolymer (SMANa) anchored on CNTs not only promotes their dispersion in the membrane but also enhances the electroconductivity through the synergistic ionic-electronic conducting effect. More importantly, positively and negatively charged molecular chains mounted on the membrane surface could form different “electric double” layers in response to the voltage stimuli. Consequently, the optimized membrane as the cathode exhibits superior permeations and separations of Congo red (99.9 %, 313.6 L/m2·h·bar) and indigo carmine (96.9 %, 420 L/m2·h·bar), and as the anode displays outstanding permeations and separations of methyl green (98 %, 381.6 L/m2·h·bar), crystal violet (95.7 %, 368.2 L/m2·h·bar) and methyl orange (94.6 %, 166.4 L/m2·h·bar) due to the effective combination of size sieving, electro-enhanced electrostatic repulsion and adsorption-induced electrostatic repulsion effects. Simultaneously, high flux recovery ratios are also achieved due to the superposition of a stable hydration layer and electrochemistry, indicating excellent antifouling properties.