Hierarchical Sandwich-Type Hetero-Wetting Nanofibrous Membrane toward Nano-Scaled Oil/Water Emulsion Separation

The ever-increasing discharge of oily sewage poses serious threats to marine ecosystem and human health, which has become a severe environmental problem globally. With high porosity, interconnected porous architectures and tunable surface wettability, superwetting nanofiber membranes have been proven effective in remediating oily sewage. However, constrained by their micron-scale pores, nanofiber membranes demonstrate insufficient separation efficiency for sub-150 nm emulsified oil droplets, making it difficult to meet the standards of regulations for discharging oily sewage in various countries and regions. Herein, a “sieving-repulsion-adsorption” mechanism was proposed to break the limitation of “trade-off” between permeability and selectivity via the designed hetero-wetting nanofiber membrane, which was engineered by intercalating discrete hydrophobic polydimethylsiloxane (PDMS) microdomains between hydrophilic polyethylene oxide (PEO)-based hydrogels modified polyacrylonitrile (PAN) nanofiber membranes. The hetero-wetting architecture improves water transport under the synergistic effect of hydrophobic/hydrophilic layers while captures the tiny oil droplets via hydrophobic/oleophilic PDMS microdomains, thereby achieving high emulsion permeance of 22,308 L⋅m−2⋅h−1⋅bar−1 with high separation efficiency of 99.97% and total organic carbon (TOC) content less than 3 ppm. Notably, the membrane demonstrates exceptional fouling resistance (94.6% permeance recovery) and cyclic stability, outperforming most previously reported state-of-the-art nanofiber membranes. This sandwich-type hetero-wetting nanofibrous membrane provides new insights into advanced membranes fabrication for low-carbon and efficient treatment of nano-scaled oil-in-water emulsions.