Improved performance and antifouling properties of thin-film composite polyamide membranes modified with nano-sized bactericidal graphene quantum dots for forward osmosis

Abstract

Forward osmosis (FO) has applications in desalination, water purification, and wastewater treatment. A major problem in FO is membrane fouling (especially biofouling), which affects adversely the flux efficiency, operating costs, and membrane lifespan. Here, this work addresses this problem via incorporating graphene quantum dots (GQDs) in the active polyamide layer of thin film composite (TFC) membranes. The incorporation of GQDs leads to the development of thin film nanocomposite (TFN) membranes that have improved surface hydrophilicity, antimicrobial activity, and FO performance. The functionalization of the polyamide layer by GQDs is verified by XPS and ATR-FTIR. The properties and FO performance evaluation of the TFN membranes are compared with those of the TFC membranes, in terms of membrane morphology, structural properties, permeability, separation ability, and antifouling properties. The TFN membranes exhibited considerable antibacterial activity (about 90–95% reduction in the proliferation of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) as attached live bacteria). This significant antimicrobial activity is due to the unique structure of GQD-functionalized polyamide selective layer (i.e., its higher number of active edges representing oxidation stress). The TFN membranes also exhibited improved water flux in a range of GQD loading, and satisfactory long term stability due to strong covalent interactions between the GQDs and the polyamide active layer. The higher antibacterial activity, better antifouling properties, and the same transport properties of the TFN membranes point to the great FO potential of this new generation of membranes.