High flux nanofiltration membranes prepared with a graphene oxide homo-structure

High flux nanofiltration (NF) membranes with a unique homo-structure were prepared from 0D graphene oxide quantum dots (GO QDs) and 2D GO sheets via a facile vacuum filtration process. Our study revealed that laminated GO sheets functionalized as molecular sieving while GO QDs acted as nano wedges to prevent the stacking of GO sheets, which resulted in a significantly improved permeability of the membranes. With the increase in GO QDs content, the layered structure of the membranes was well preserved, and the average interlayer spacing of the membranes increased. Moreover, the intercalation of GO QDs also improved the hydrophilicity of the membranes to some extent. Furthermore, transmission electron microscopy was employed to characterize the relative distribution of the two components, which indicated that GO QDs were uniformly buried in GO sheets. NF performance of the membranes was then evaluated regarding their permeability and retention for dye macromolecules, proteins, natural organic matters, and metal nanoparticles (NPs). With GO QDs, the permeability of the membranes was markedly improved in all the testing solutions (2-4 times) without compromising their retention for direct yellow, bovine serum albumin, humic acid, and Au NPs (> 99%). This work demonstrates that the homo-structure of 0D GO QDs buried in 2D GO sheets can effectively improve the separation efficiency of GO-based NF membranes.