Development of a novel dual-bioinspired method for synthesis of a hydrophobic/hydrophilic polyethersulfone coated membrane for membrane distillation

This study presented a novel method for the surface modification of a hydrophilic polyethersulfone (PES) membrane via dip-coating. The performance of the new membrane was investigated in a membrane distillation process. The surface free energy (SFE) of the modified PES was studied by the Owens-Wendt method. A significant decrease of surface free energy from 36.1 mN/m to 16.4 mN/m was observed after modifying the membrane surface with fluoro-organothiol (1H, 1H, 2H, 2H-perfluorodecanethiol). The water contact angle of the membrane increased from 66 degrees for PES to 115 degrees for surface-modified membrane. This remarkable increase suggests a successful switch from hydrophilicity to hydrophobicity owing to the creation of hierarchical submicro/nanostructures on the surface of PES. This structure was achieved by depositing polydopamine and silver nanoparticles, followed by lowering the surface free energy by fluoro-organothiol treatment. The performance of the modified membranes was evaluated through a direct contact membrane (DCMD) process in the presence of anionic and non-ionic surfactants and high salt concentrations (4.5 wt%). The membranes reached a high and stable flux of approximately 39.37 kg/m(2)h after surface modification. Besides, the newly engineered membranes had excellent stability during long-term operation, showing a salt rejection rate of 99.80% after 36-h.