Fabrication of PES-based membranes with a high and stable desalination performance for membrane distillation

Polyethersulfone (PES)-based membranes with a high and stable desalination performance for vacuum membrane distillation (VMD) were fabricated by spraying a dispersion containing hydrophobic-modified PES grafted copolymers onto porous PES membranes. The copolymer (PES-g-PFMA-C-8) with different degrees of grafting (DG) was synthesized by grafting 1H,1H,2H,2H-perfluorodecyl methacrylate (FMA-C-8) onto PES by simultaneous irradiation in a homogeneous system wherein the kinetics of the radiation-induced graft polymerization was studied. The copolymers, pristine PES membrane and fabricated PES-based membranes were also characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. After spraying, the hydrophobicity of the membrane increased and its maximum pore size reduced, which enhanced its desalination stability. During an intermittent 80 h VMD desalination operation, a flux of approximately 50.5 kg m(-2) h(-1) and a stable salt rejection of 99.98% were achieved when a 3.5 wt% NaCl solution was treated at 70 degrees C under vacuum of 92 kPa by the PES-based membrane using the copolymer with a DG of 20.3%, whereas salt leakage obviously occurred since the 52nd hour of operation when the pristine PES membrane was used. These results indicate that the modified PES membrane developed in this study is a promising candidate for VMD desalination due to its comparable flux.