How graphene oxide properties guide transport channel construction and impact desalination performance in composite membranes

Graphene oxide (GO) nanosheets are widely used for fabricating high-performance membranes due to self-assembled nanoscale/subnanoscale two-dimensional (2D) channels; however, the influence of GO physicochemical properties on the transport channels and desalination performance of GO membranes is not yet systematically investigated. Herein, GO membranes with different channel architectures and functional groups are prepared via ultrasonic and in situ thermal reduction methods. The 2D Fourier-transform infrared correlational spectroscopy analysis provides new insights into the dynamics of functional groups on GO nanosheets, and the quartz crystal microbalance with dissipation analysis further confirms the stability of smaller GO sheet (S-GO) membranes. The reduced S-GO (S-rGO) membrane has 86 % and 58 % rejection rates for 50 and 500 mM Na 2 SO 4 , respectively, and 97 % and 94 % for the methylene blue and orange II, respectively. The superior swelling resistance and elevated salt rejection is attributed to the GO nanosheets having a paucity of oxygen-containing functional groups and thus narrower interlayer spacing. A significant positive correlation is found between –COOH and GO membrane surface electronegativity, and between C–O–C and membrane hydrophilicity. A significant negative correlation is observed between the C/O ratio of the GO nanosheets and GO wet interlayer spacing, i.e., the fewer the oxygen-containing groups, the stronger the size-screening ability and swelling resistance of the GO membranes. Overall, GO separation layers with hydrophilic surfaces and weakly hydrophilic interior, could be designed so as to simultaneously enhance the permselectivity and swelling resistance of the GO membranes, which provides a roadmap for the development of high-performance GO membranes.