Coupled Regulation of Interfacial Wettability and Pore Architecture in Carbon-Coated Polyethylene Membranes for Efficient Oil-Water Separation

Abstract

Efficient oil-water separation is essential for oily wastewater treatment, especially for surfactant-stabilized water-in-oil emulsions, where dispersed water droplets are difficult to reject without compromising oil permeation. Membrane-based separation offers a promising route for oily wastewater treatment, but many reported membranes still rely on complex fabrication procedures, specialized substrates, or multistep surface modification. Herein, a commercially available polyethylene membrane was directly converted into a carbon-coated polyethylene membrane (CPEM) through sequential sanding and vacuum-assisted nanocarbon deposition. This simple physical treatment simultaneously regulates the interfacial wettability and pore architecture of the membrane. The resulting CPEM exhibits a hierarchical micro/nano-rough surface with underoil water contact angles above 160°, while its average pore diameter decreases from 173.56 to 150.67 nm. Together, these features create an oil-wettable and water-repellent interface with a tightened but connected pore network. The CPEM achieves gravity-driven separation of immiscible oil-water mixtures with separation efficiencies above 99.9% and a maximum flux of 3723 ± 141 L m–2 h–1. It also efficiently separates surfactant-stabilized water-in-oil emulsions, with fluxes of up to 1201 ± 30 L m–2 h–1 and separation efficiencies of up to 98.8 ± 0.3%, while retaining a separation efficiency of 98.2 ± 0.2% after 30 cycles. In addition, the membrane exhibits good antifouling performance, chemical stability, thermal stability, and mechanical flexibility. This work provides a facile and low-cost strategy for upgrading commercial polymer membranes for efficient oil-water separation.