Minimising non-selective defects in ultrathin reduced graphene oxide membranes with graphene quantum dots for enhanced water and NaCl separation

Abstract

• Ultrathin GQDs/rGO membranes are prepared through a two-step assembly method. • The strong π–π interaction between GQDs and rGO enables the coverage of defects. • GQDs/rGO membranes achieve both high water permeance and high NaCl rejection. Reduced graphene oxide (rGO) membranes have been intensively evaluated for desalination and ionic sieving applications, benefiting from their stable and well-confined interlayer channels. However, rGO membranes generally suffer from low permeability due to the high transport resistance resulting from the narrowed two-dimensional (2D) channels. Although high permeability can be realized by reducing membrane thickness, membrane selectivity normally declines because of the formation of non-selective defects, in particular pinholes. In this study, we demonstrate that the non-selective defects in ultrathin rGO membranes can be effectively minimised by a facile posttreatment via surface-deposition of graphene quantum dots (GQDs). The resultant GQDs/rGO membranes obtained a good trade-off between water permeance (14 L⋅m −2 ⋅h −1 ⋅MPa −1 ) and NaCl rejection (91%). This work provides new insights into the design of high quality ultrathin 2D laminar membranes for desalination, molecular/ionic sieving and other separation applications.