A biomimetic superwetting Bi2MoO6-dotted PAA/CS@CuC2O4 membrane with self-cleaning and self-healing ability to aggregate oil droplets for enhanced demulsification of O/W emulsion

Separation of thermodynamically-stable emulsions is of great significance, yet challenging due to the low efficiency and membrane fouling associated with existing methods. Inspired by the water-collection functionality of the hierarchically-structured back of desert beetles, we fabricated a novel inversely beetle-back-like copper mesh membrane, featuring superhydrophobic bumps on a superhydrophilic surface to facilitate the capture-aggregation of tiny oil droplets in oil-in-water (O/W) emulsions. Such membrane was composed of superhydrophobic (SH) Bi2MoO6 microparticles-dotted superhydrophilic polyacrylic acid/chitosan-coated CuC2O4 nanosheet arrays on copper mesh membranes. A cross-flow asymmetric filtration (CAF) device was constructed using the as-prepared membrane to continuously and efficiently separate O/W emulsions. The dispersed oil droplets were captured and coalesced by SH Bi2MoO6 on the superhydrophilic nanoarrays, then detached from the mesh membrane. Simultaneously, the continuous water phase could permeate freely through the mesh pores. The combination of the SH Bi2MoO6-dotted superhydrophilic membrane and CAF device ensured an excellent separation efficiency with an average water permeation flux of 2.7 kL m−2 h−1 for different surfactant-stabilized O/W emulsions and oil residual contents in the filtrate being less than 40 mg L−1. Moreover, the cross-flow of the feed solution in the CAF system strengthened the separation of the coalesced oil phase on the membrane surface, thus preventing the formation of a filter cake caused by the aggregation of emulsified oil droplets.