ZnO nanoparticles coated mesh with switchable wettability for on-demand ultrafast separation of emulsified oil/water mixtures

Due to frequent discharge of oily wastewater and oils spill accident, oil/water separation has attracted worldwide attention. Nowadays, the on-demand separation of emulsified oil/water mixtures is urgent. Herein, the ZnO nanoparticles (NPs) coated mesh was prepared successfully by a simple spraying method. Reversible wettability conversion of the coated mesh between superhydrophobicity/superoleophilicity and superhydrophilicity/underwater superhydrophobicity was rapidly achieved by the alternation treated the coated mesh with stearic acid ethanol and NaOH solution for 15 min. Combined with the nanoscale pore size (smaller than the emulsion), the coated mesh could separate various kinds of emulsions whether water or oil is the continuous phase. Gravity is the only driving force for the entire separation process. The separation efficiency of emulsified oil/water mixtures was larger than 99.0%. Moreover, the coated mesh still showed high separation efficiency greater than 98.0% after 8 times cycle operations of wettability transition and separation, indicating a good stability and excellent recyclability. The developed ZnO NPs coated mesh should be a potential candidate for on-demand emulsions separation.