Janus membrane decorated via a versatile immersion-spray route: controllable stabilized oil/water emulsion separation satisfying industrial emission and purification criteria

Abstract

Janus membranes with opposite wetting behavior on each side are of great significance in the oil/water separation field. However, most of the reported work only focuses on the separation of immiscible oil/water mixtures instead of emulsions. In addition, almost no previous work pays attention to whether the filtrate after the separation process can meet industrial emission standards. In order to achieve controllable stabilized emulsion separation with high efficiency, a polyaniline–silica nanoparticle (PANI–SiNP)-modified Janus membrane is prepared through a facile immersion-spray coating method. PANI polymer and SiNPs are modified on two sides of the substrate, just like Yin and Yang in Chinese Tai Chi, and have opposite but complementary properties. The PANI-coated surface is superhydrophilic with underwater superoleophobic wettability, which can separate oil-in-water emulsions (including different ionic types and crude oil-in-sea water emulsion) when it is facing up. Conversely, the SiNP-coated surface exhibits opposite wettability with superhydrophobicity and superoleophilicity, which can separate water-in-oil emulsions when this side is facing up. More importantly, this Janus material has high efficiency for both oil-in-water and water-in-oil emulsions, meeting the industrial emission and purification standards. The membrane shows excellent stability and recyclability, which means it can be applied in practical wastewater treatment.