Highly permeable PA@GO loose nanofiltration membranes enabled by hierarchical transport channels for efficient dye removal

Graphene oxide (GO) membranes exhibit ultrafast water permeation properties, which have been employed in various membrane-based separations including nanofiltration for dye removal from textile wastewater. However, it's still a great challenge to achieve precise control over the microstructure of GO membranes and obtain ultrathin GO membranes with exceptional separation efficiency and robust membrane structure. Herein, in-situ confined interfacial polymerization (IP) is proposed for fabricating loose polyamide (PA)@GO hybrid membranes with high permeance and dye rejection as well as robust membrane stability. A new diamine of sulfadiazine (SA) with intrinsic hydrophilic and conjugated sulfonamide groups is employed as cross-linker of GO membranes and monomer of PA in IP process, simultaneously. PA is in-situ synthesized in confined GO interlayer via IP process and intercalated into GO interlayer, which enlarges the interlayer spacing of GO membranes gradiently. The combination of hydrophilic PA nanofiltration layer on GO membrane surface and the PA intercalated GO membrane with varying interlayer spacing creates hierarchical transport channels for water molecules, which contributes to the high water permeance. Moreover, the less reactive SA monomer endows PA@GO selective layer with appropriate negative charge and loose transport channels, which contributes to both of high permeance and dye rejection due to Donnon effect and size exclusion effect. The PA@GO hybrid membrane exhibits high permeance of 75.5 L/(m2·h·bar) with TB dye rejection of 99.8 %, and exhibits low NaCl rejection of 11.6 %. Moreover, PA@GO hybrid membrane shows good fouling resistance and long-term stability as well as stable separation performance under harsh conditions. Both of high permeance and dye rejection of PA@GO hybrid membrane suggests that the integration of PA nanofiltration layer and GO membrane via in-situ confined interfacial polymerization can achieve the delicate control over the interlayer channel structure and the physicochemical properties of the membrane surface of GO membranes, which offers a promising method to break through the trade-off effect between permeability and selectivity of GO membranes.