Surface modification of thin film composite nanofiltration membrane with graphene oxide by varying amine linkers: Synthesis, characterization, and applications

We report surface modifications of thin film composite nanofiltration (TFC NF) membrane with amine and the characterization of the resulting membrane for anti-biofouling properties. Graphene oxide (GO) was grafted on the surface of the TFC NF membrane using three linkers, ethylene diamine, diethylene triamine and triethylene tetraamine. Grafting of GO on the surface was successfully validated through Raman Spectroscopy and XPS. Ring-like structures were observed on the surface of the dense polyamide layer of TFC NF membranes under SEM after modification with GO. A slight increase in the roughness, and hydrophilicity was noticed in the membranes modified with GO. GO-grafted membranes demonstrated enhanced chlorine stability, lower biofouling tendency, lower flux decline during filtration of seawater and improved hexavalent chromium rejection in the basic pH. The improved chlorine stability is attributed to intermolecular hydrogen bonding between GO and polyamide structure, while the enhanced biofouling resistance and lower flux decline is ascribed to hydrophilic GO. The membranes were further evaluated for rejection of heavy metal ions, in particular hexavalent chromium, which showed about 97% rejection in basic pH attributed to the rise in negative character of the membrane surface due to the grafting of GO. Na2SO4 rejection for control TFC was reduced by 9.6%, while a reduction between 1 and 5.5% was found in fGO grafted membranes after 1 h exposure to 1000 ppm NaOCl.