Simultaneous anti-fouling and flux-enhanced membrane distillation via incorporating graphene oxide on PTFE membrane for coking wastewater treatment

To overcome the limitations of existing hydrophobic membranes for membrane distillation (MD) to treat industrial wastewater with complex contaminants, a composite membrane was developed in this study via incorporating graphene oxide (GO) on commercial polytetrafluoroethylene (PTFE) membrane. The dual-layer GO/PTFE membrane demonstrated asymmetric wettability, which transformed the membrane from in-air hydrophobic and underwater superoleophilic pristine surface to in-air hydrophilic and underwater oleophobic surface. The composite membrane displayed excellent salt rejection (>99.9%) and organic rejection (99.4%) during MD of bio-treated coking wastewater, outperforming the pristine PTFE membrane with apparent fouling and wetting phenomenon. The flux of GO/PTFE membrane reached 20.1 kg/m2·h, which is 44% higher than that of the pristine membrane. These improvements were attributed to the specific morphological and physicochemical characteristics of the composite membrane, such as high water affinity, strongly negative charges on membrane surface, reduced temperature polarization and screening effect to large molecules by the GO layer. This study suggests that GO/PTFE composite membrane has great potential in enhancing the permeate flux and fouling resistance simultaneously, which could be a competitive option for MD to treat challenging wastewaters enriched with salts and hydrophobic organics.