A unidirectional water transport bilayer Janus membrane with gradient pore structure for effective oil-water separation

The development of high-performance oil-water separation membranes necessitates addressing the inherent challenges of high energy consumption while ensuring both high flux and durability. In this study, we propose an electrospun Janus membrane with an asymmetric structure, consisting of a hydrophilic layer made from polyacrylonitrile (PAN) and polyethylene glycol (PEG), and a hydrophobic layer composed of polycaprolactone (PCL), referred to as the PPCL membrane. By constructing a gradient pore structure within the bilayer membrane, we enhance capillary forces to achieve superior unidirectional water transport. This design allows water droplets to permeate the Janus membrane in just 0.05 s, with a diffusion rate of 217.6 mm 2 /s and a diffusion area of 1084.9 mm 2 . The separation efficiency is found to positively correlate with both the diffusion area and rate, while negatively correlating with time, thereby confirming the beneficial effect of unidirectional water transport on oil-water separation. Even after 9 oil-water separation cycles, the PPCL-16 % membrane maintains stable separation efficiencies of 92.5 ± 1.8 % for white mineral oil-water mixtures and 91.3 ± 1.2 % for dichloromethane emulsions, while consistently achieving an oil-in-water emulsion flux exceeding 205 L·m −2 ·h −1 . In summary, this study offers theoretical support for the design and optimization of unidirectional water transport membranes in oil-water separation applications, ensuring low energy consumption while emphasizing high separation flux and efficiency.