A novel plasma-induced surface hydrophobization strategy for membrane distillation: Etching, dipping and grafting

Surface hydrophobic modifications of hydrophilic porous polyacrylonitrile (PAN) membranes for vacuum membrane distillation (VMD) desalination via dipping in fluorine-containing solution followed by plasma irradiation were studied. 1H, 1H, 2H, 2H-perfluorodecyl methacrylate (F8) was used as the monomer . The monomer was not vaporized in this work, which might make the modification process more economic and environment friendly. The surface hydrophobicity , morphology and VMD performance of the modified membranes were controlled by degree of grafting (DG), and a moderate DG value of 43.54   μg   cm −2 was optimal. Before grafting F8, Ar plasma etching pretreatment of the pristine PAN membrane was also studied, which increased the membrane’s surface pore size, roughness, thus improving the VMD performance and stability of the finally modified membrane (PAN-EM). When a 3.5   wt% NaCl solution was treated by the PAN-EM membrane at 80   °C under vacuum degree of 95.2   kPa, a flux of 59.42   kg   m −2   h −1 and a salt rejection of 99.93% were achieved. Moreover, the PAN-EM membrane showed a stable desalination performance during an 80   h intermittent VMD operation, indicating that the strategy consisting of etching, dipping and grafting developed in this study was very promising to fabricate porous and hydrophobic membranes with great application prospect for VMD desalination.