Graphene quantum dots engineered nanofiltration membrane for ultrafast molecular separation

In this study, we developed a new approach to designing and preparing NF membranes through pore engineering by graphene quantum dots (GQDs). An in-situ interfacial polymerization reaction between GQDs and trimesoyl chloride (TMC) took place within the pores of ultrafiltration (UF) membranes, which was followed by thermal treatment. The irreversible shrinkage of membrane bulk material by thermal treatment ensured the robust residence of the GQDs nanoaggregates. The pore structure of the resultant membranes was revealed by scanning electron microscope (SEM), positron annihilation spectroscopy (PAS), Brunner-Emmet-Teller (BET) measurements and neutral solutes rejection experiments. The voids among GQDs nanoaggregates formed the pores of resultant membranes, which radius can be tuned in range of 1.21-1.72 nm by the adding amount of GQDs. The resultant membranes exhibited ultrafast water permeation of 244.7 L/(m(2) h bar), which was about 5-6 times higher than the reported datas in previous literatures, and the rejection of Alcian blue and Congo red could attain 92.9% and 98.8%, respectively. Long-time operation and chemical exposure further demonstrated the stability of the resultant membranes. The approach reported in this study may open a new avenue for a variety of molecular/ionic separations by reconstructing membrane pore structure through the mediation of nanomaterials.