Novel polyethersulfone-functionalized graphene oxide (PES-fGO) mixed matrix membranes for wastewater treatment

In this study, three routes of nucleophilic substitution of graphene oxide (GO) were compared for the fabrication of novel polyethersulfone-functionalized GO (PES-fGO) mixed matrix membranes. These routes were: cross-linking of GO with maleic acid containing nucleophilic dicarboxyl groups (M1); co-polymerization of GO with hyperbranched polyethyleneimine (HPEI) with excess amino group (M2); and nucleophilic modification of GO with naturally-derived chitosan containing amino and hydroxyl groups (M3). These membranes were then characterized and tested for the treatment of electrokinetically remediated wastewater. Membrane properties such as mechanical strength, morphology, chemical functionalities, hydrophilicity and pore structures were measured to assess the membranes in relation to their performance. M2 membrane displayed the least open and densest structure due to the abundance of nucleophilic amino groups on HPEI. The flexible N-H chains increased the resistance of the active layer to water and contributed to the lowest water fluxes provided by M2 membrane. Regardless of viscous hindrance, intermolecular bonds with higher energies (C-O in M1 and O-H in M2) promoted thermodynamic instability which increased the pore sizes and water fluxes through M1 and M3. Therefore, the highest tensile strength and allowable load were exhibited by M2 membrane. The CO-NH linkages in M2 contributed to the highest overall pollutant removal efficiencies: 97.1% Fe2+, 95.3% Zn2+, 92.7% Cd2+, 99.9% Cr6+, 99.9% bacteria, and 98% chemical oxygen demand (COD) due to stronger repulsive electrostatic force and nano-sized membrane pores.