A novel zwitterionic polyelectrolyte grafted PVDF membrane for thoroughly separating oil from water with ultrahigh efficiency

TLDR

Oil–water separation is a worldwide challenge due to increasingly oily wastewater and frequent oil spill accidents. The study reports fabricating a zwitterionic polyelectrolyte brush–grafted PVDF membrane via surface‑initiated atom transfer radical polymerization to separate oil from water. The membrane was prepared by tuning the SI‑ATRP polymerization time to achieve superhydrophilic and underwater superoleophobic properties. It achieves >99.999 % oil rejection, leaving oil contents below 10 ppm (often <2 ppm), far below international wastewater standards, with an oil‑adhesion force <1 μN, giving excellent antifouling and recyclability.

Abstract

Oil–water separation is a worldwide challenge because of increasingly oily wastewater, as well as frequent oil spill accidents. We report in this work the fabrication of a zwitterionic polyelectrolyte brush (poly(3-(N-2-methacryloxyethyl-N,N-dimethyl) ammonatopropanesultone), abbreviated as PMAPS)-grafted poly(vinylidene fluoride) (PMAPS-g-PVDF) membrane via a surface-initiated atom transfer radical polymerization (SI-ATRP) technique for separating oil from water. By tuning polymerization time, a superhydrophilic and underwater superoleophobic PMAPS-g-PVDF membrane was successfully prepared. The membrane can be applied for thoroughly separating dispersed oil from water with ultrahigh separation efficiency >99.999% in terms of rejection coefficient. The oil contents after one-time separation of a selection of oil–water mixtures are all less than 10 ppm and some of them are even lower than 2 ppm. These values are much lower than the standard minimum requirements of the international regulations for wastewater discharging. The oil-adhesion force between an oil droplet and the membrane surface was measured to be less than 1 μN. Due to the ultralow oil adhesion, the membrane exhibits an excellent antifouling property to oil and is easily recyclable.