Polysulfone membranes clicked with poly (ethylene glycol) of high density and uniformity for oil/water emulsion purification: Effects of tethered hydrogel microstructure

•PEG tethered PSF membrane was fabricated for oil/water emulsion purification.•PEG was grafted densely and uniformly on membrane surface by click chemistry.•Higher hydrodynamic thickness leads to lower WCA values.•The grafting density has more impact on membrane properties than the PEG MW.•High grafting density and low grafting MW required achieving good performance.

Hydrogel-tethered polysulfone (PSF) membranes have been synthesized by grafting propargyl-poly(ethylene glycol) (pro-PEG) onto azide-functionalized PSF membrane surfaces via the copper (Ι) catalyzed azide-alkyne cycloaddition (CuAAC) reaction, and then used for oil/water emulsion purification. Three pro-PEGs (120, 750 and 1300 g/moL) and two PSF-azi membranes with different degrees of azide functionality were used to obtain a series of PSF-g-PEG membranes. The membranes were characterized in detail by FTIR, XPS, FESEM and the contact angle method. The click reaction was demonstrated to be effective, and PEG was densely and highly uniformly grafted on the membrane surfaces including the pore walls. A higher hydrodynamic thickness of the PEG layer leads to a lower contact angle. The grafting density has more impact on membrane properties than the PEG molecular weight. The membrane grafted with low-molecular weight PEG at high grafting density shows a better combination of antifouling performance and permeance. The best performance was 120 L m−2 h−1 emulsion flux with complete oil rejection and over 95% flux recovery in cycled fouling-rinsing tests. It is suggested that high grafting density should be pursued with strict control on the chain length to obtain good emulsion filtration membranes.