Inverse desert beetle-like ZIF-8/PAN composite nanofibrous membrane for highly efficient separation of oil-in-water emulsions

Abstract

Purification of highly emulsified oily wastewater is of significance but challenging due to the critical limitations of low efficiency and serious membrane blocking. Herein, inspired by the desert beetle's capability of water-collection in air, we first constructed an inverse desert beetle-like membrane to achieve oil capture in water, thus improving the separation performances of the surfactant-stabilized oil-in-water emulsion. The as-prepared nanofibrous membrane consists of hydrophobic/oleophilic ZIF-8 bumps and underlying underwater superoleophobic polyacrylonitrile (PAN), and possesses a similar structure to desert beetles but with opposite wettability. In the process of emulsion demulsification, besides the sieving effect of the underlying traditional underwater superoleophobic PAN membrane, the bumpy oleophilic ZIF-8 particles of the composite membrane can capture oil, thus strengthening the demulsification ability of the membrane. Furthermore, the separation efficiency of the inverse desert beetle-like membrane is up to 99.92% for surfactant-stabilized oil-in-water emulsion, which is superior to that of traditional single underwater superoleophobic PAN membranes lacking the hydrophobic bump structure. Moreover, for light oil-in-water emulsion, the permeation flux also increases because the captured tiny oil droplets can aggregate subsequently and grow large enough to detach from the underlying surface which greatly reduces the incidence of filter cake formation and congestion. This inverse desert beetle-like membrane opens up new avenues for designing advanced membranes in the oil/water emulsion separation field.