Nanocomposite Membrane with Polyethylenimine-Grafted Graphene Oxide as a Novel Additive to Enhance Pollutant Filtration Performance

Synthetic membranes often suffer ubiquitous fouling as well as a trade-off between permeability and selectivity. However, emerging materials which are able to mitigate membrane fouling and break the permeability and selectivity trade-off are urgently needed. A novel additive, GO-PEI, bearing a positive charge and hydrophilic nature was prepared by the covalent grafting of polyethylenimine (PEI) molecules with graphene oxide (GO) nanosheets, which later was blended with bulk poly(ether sulfone) (PES) to fabricate the graphene containing nanocomposite membranes (NCMs). Strong it pi-pi interactions contributed to the uniform dispersion of GO-PEI nanosheets in bulk PES to form the asymmetric structure of NCM without leaching. The ratio of the GO-PEI additive regulated the surface charge and hydrophilicity of NCMs. To filter charged proteins, the designed NCM exhibited a high permeability (flux) and high selectivity (retention) while showing resistance to fouling by the charged proteins, which could be attributed to the asymmetric structure and composition of the NCM that the porous internal and surface composited with the GO-PEI additive was responsible for the NCM's high flux; thereafter, the electrostatic attraction of the NCM surface to the charged pollutant enhanced the solute/water selectivity; finally, the synergistic effect of the hydrophilic and charged functional groups of the GO-PEI contributed to the formation of a dense hydration layer on the membrane surface thereby reducing membrane fouling. The NCM functionalized with the GO-PEI additive demonstrated potential for high-performance pollutant removal in water and wastewater treatments.