Free-standing graphene oxide membrane works in tandem with confined interfacial polymerization of polyamides towards excellent desalination and chlorine tolerance performance

We explored a unique concept in this study to develop a membrane containing a hierarchical porous architecture derived by etching a specific component from a demixed UCST blend as the support layer and a free-standing GO and a polyamide (PA) layer as functional surfaces. To selectively sieve ions and improve chlorine tolerance performance, three different strategies were proposed here. In the first case, the free-standing GO membrane was used as the active layer. In the second case, the free-standing GO was positioned in tandem with the PA layer formed in situ. In the third case, GO was added during the formation of the active PA layer in situ. The support layer with a gradient in pore sizes (realized by varying the composition in the blends) was fabricated via crystallization induced phase separation in a classical UCST system (PVDF/PMMA) and etching out the amorphous component (here PMMA). A gradient in the pore sizes was obtained by rationally stitching the various membranes obtained by varying the blends' composition. Pure water flux and rejection experiments were carried out to evaluate the performance of this composite membrane. This unique strategy resulted in excellent salt rejection (more than 95% for a monovalent ion), improved fouling resistance (more than 85%), excellent dye removal performance (more than 96% for a cationic dye), and outstanding chlorine tolerance performance and antibacterial activity. Thus, this study emphasizes that the free-standing GO membrane's positioning controls the membranes' overall performance.