Integrated asymmetric superwetting Janus membrane for the efficient separation of various surfactant-stabilized oil–water emulsions

Abstract

Water pollution caused by oil has seriously threatened the environment and human health. Janus membranes can separate oil–water emulsions efficiently but they suffer from high synthesis cost, poor stability, and complicated synthetic methods. Instead of commonly used carbon nanotubes or polymer nanofibers, in this work, a new Janus membrane with polydimethylsiloxane (PDMS)-modified ultra-long basic magnesium hydroxide chloride hydrate (MHCH) nanowires as the superhydrophobic side, and stainless steel mesh (SSM) coated by Co₃O₄ nanoneedles as the hydrophilic and underwater oleophobic side was successfully constructed by a simple clamping method. Cheap silica microspheres were used to control the pore size and surface roughness of the MHCH membrane. This integrated Janus membrane shows high separation flux (1100–3300 L m⁻² h⁻¹) and excellent separation efficiencies (>99.0%) for various surfactant-stabilized oil-in-water (O/W) and water-in-oil (W/O) emulsions, especially for those formed from highly viscous oil phases (kerosene, diesel). Water content in the filtrates after W/O emulsion separation and oil content in filtrates after O/W emulsion separation are less than 0.016% and 30 mg L⁻¹, respectively. Importantly, this integrated Janus membrane remains functional surface even in environments with high concentrations of acid or alkali. Using a simple clamping method to obtain an efficient and cheap Janus membrane would provide more convenience for membrane module cleaning and replacement. This novel integrated Janus membrane holds great promise as a candidate material in the design of porous membranes. Also, this work shows important potential for oily wastewater treatment.