Pouring-type gravity-driven oil–water separation without water bridge

Oil pollution brings great challenge to environmental protection. Utilising oil–water separation device to separate and recycle oils is an environment-friendly approach to dispose mixtures containing oils. Pouring-type gravity-driven oil–water separation method based on extremely wettable materials is an interesting area of research because of its high separation velocity, selectivity and purity. However, the presence of water bridge results in low separation efficiency. Herein, the authors first synthesised a facile etching method and a dip-coating method to fabricate contrary extreme wettability sponges including superhydrophilic–underwater-superoleophobic (SHI–U-SOO) sponge and superhydrophobic–superoleophilic (SHO–SOI) sponge. Accordingly, they designed a three-way oil–water separation system whose left and right bottom tubes were installed with the SHI–U-SOO sponge and the SHO–SOI sponge, respectively. Water and oil separately flow out from the left and right tubes, thereby eliminating the water bridge and increasing separation efficiency, and still having ideal separation selectivity and separation purity. The developed three-way oil–water separation system has promising application prospects in disposing oil spills, oil leakage from factories and industrial effluents.