Structural parameters reduction in polyamide forward osmosis membranes via click modification of the polysulfone support

To reduce the structural parameter of composite polyamide (PA) forward osmosis membrane , the support polysulfone (PSf) was prepared by blending PSf/PSf-g-methoxypolyethylene glycol (PSf/PSf-g-mPEG) with the mPEG weight molecular weights of 200, 500, 1000 and 1900 g/mol at the PSf/PSf-g-mPEG weight ratios of 4:1 and 9:1, respectively. The composite membranes were prepared as the following steps: (1) propargyl mPEGs preparation; (2) chloromethylation and azidation of PSf; (3) PSf-g-mPEG preparation via click chemistry; (4) PSf/PSf-g-mPEG blended support membrane preparation by phase separation; (5) polyamide active layer formation through interfacial polymerization between phenylenediamine and 1,3,5-benzenetricarbonyl trichloride on the support membrane. The successful synthesis of the polymers and preparation of the composite membranes were certified with Fourier transform infrared spectroscopy , nuclear magnetic resonance, X-ray photoelectron spectroscopy analysis, field emission scanning electron microscope and energy dispersive spectrometer. The pure water fluxes of the blended support membranes were sharply increased; the maximum pure water flux was gained for the PSf/PSf-g-mPEG500 blended membrane. For the composite polyamide (PA) membrane, the water flux was improved drastically, while the rejection to the salt remained unchanged in the reverse osmosis system; the pure water flux rose dramatically and the structure parameter ( S ) dropped significantly in the forward osmosis system.