Insight into the separation mechanism of graphene oxide membrane by designing dual layered structure

Graphene oxide (GO) membrane, made by self-assembly method, has been extensively studied. Various modification methods are used to improve the membrane performance. In order to make different modification methods work together and further study the separation mechanism of self-assembled GO membrane, a two-step self-assembly method, concluding filtration and subsequent evaporation, was used to fabricate dual-layered membrane with different nanosheets on the surface and inside the membrane. As control, simply laminated membranes were fabricated by filtration GO solution containing nanosheets with different properties. Comparing various self-assembled membranes, including dual layered membranes and simply laminated membranes, it can be found that dual layered membranes have higher permeability than simply laminated membranes. The structure with hydrophilic surface, hydrophobic interior and low permeability resistance, like a water trap on the back of some beetles for collection of water from air, has the highest water flux. The dense layered structure and highly charged nanosheets are very important to maintain high salt rejection and ion selectivity. The channels inside the membrane are very important for desalination. By designing the layered structure composed of nano materials, it is possible to obtain membrane structure with better permeability and separation performance.