Superwetting rape pollen layer for emulsion switchable separation with high flux

Abstract

The treatment of various kinds of oil-in-water and water-in-oil emulsions is increasingly desired but is still a considerable challenge. Although traditional two-dimensional superwetting separation materials have been widely studied, they still suffer from disadvantages such as single wettability and low separation flux. In this work, three-dimensional hollow porous rape pollen with switchable wettability was fabricated via simple solvent extraction and subsequent calcination using the pristine rape pollen as starting material. The obtained rape pollen was developed into a superwetting rape pollen layer, which achieves controllable wettability transition between hydrophobicity/underwater superoleophilicity and superhydrophilicity/underoil superhydrophilicity via calcination and steam modification alternately, without the addition of toxic modification reagents. Moreover, the wettability of rape pollens could be reversibly switched for many times. The obtained rape pollen layer can be used for on-demand separation of various oil-in-water and water-in-oil emulsions in one single device. After calcination, the hydrophobic/underwater superoleophilic rape pollen layer can absorb tiny oil droplets from oil-in-water emulsion, and the wetting properties can be rapidly switched to be superhydrophilicity/underoil superhydrophilicity to capture the water droplets from water-in-oil emulsion, with both high separation efficiency and separation flux. This work not only provides a novel emulsion separation approach that is different from membrane separation, but also has high potential in practical applications relating to wastewater treatment, fuel purification, microfluidics, and so on.