Ultrathin nanofiltration membrane assembled by polyethyleneimine-grafted graphene quantum dots

Embedding nanofillers into the selective layer to creating moderate nanopores is a promising strategy to obtain high-performance nanofiltration membranes. Herein, we synthesized polyethyleneimine (PEI) functionalized graphene quantum dots (GQDs) as the water phase monomers and prepared an ultrathin desalination membrane through interfacial polymerization (IP). The in situ embedded GQDs with superiorly uniform dispersion generate abundant nanopores in the membrane, and PEI chains fill the introduced nanopores, avoiding the formation of overlarge nanopores. Besides, the PEI-grafted GQDs (NGQDs) display a reduced diffusion rate during IP, rendering an ultrathin selective layer. Benefiting from the ultrathin thickness (∼6.5 nm), the abundant water pathways (specific surface area: 6.73 m2/g), and the increased pore size (∼0.82 nm), the PA-NGQD600 membrane exhibits competitive pure water permeance (38.5 L m-2 h-1 bar-1) and inorganic salt rejection (95.5% for Na2SO4). The permeance exceeds those of the most desalination membranes reported so far and is ∼3 times higher than that of the reported GQD-based desalination membrane. This work provides a facile strategy for creating abundant nanopores in membranes with ultrathin thickness by interfacial polymerization.