A composited sponge with dual oil-water channels by heterogeneous stepped-interlocking superwettability structure for continuous separation of oil-in-water and water-in-oil emulsions

Petroleum operations produce emulsified oil-water mixtures that pollute the environment. Efficient oil recovery and wastewater purification are crucial. Extreme-wettability single-channel separators often form barrier layers from intercepted phases, reducing efficiency and flux stability. In this study, a composited sponge (HO-HL@MS) with dual oil-water channels was constructed by stepped-interlocking of a superoleophilic/superhydrophobic torus frustum sponge and a superhydrophilic/oleophobic circular frustum sponge. During the demulsification separation of oil-in-water emulsions, the superhydrophilic/oleophobic component facilitates emulsion demulsification and allows the aqueous phase to permeate, while the superoleophilic/superhydrophobic section enables timely discharge of clogging oil phases, conversely for during water-in-oil emulsions. This synergistic “demulsification-removal” mechanism allows simultaneous oil and water discharge, fundamentally resolving the issues of clogging and flux attenuation caused by the retention of the intercepted phase in traditional single-channel systems. It demonstrates excellent demulsification efficiency for both water-in-oil and oil-in-water emulsions. For water-in-oil emulsions, a permeation flux above 3000 L·m −2 ·h −1 with a separation efficiency exceeding 97.9 % after continuously processing 800 mL was achieved. For oil-in-water emulsions, a flux over 6000 L·m −2 ·h −1 with efficiency higher than 98.9 % was obtained. When treating industrial emulsions with high water content (60 % aqueous phase), it retained 98.37 % separation efficiency and a flux of 1803 L·m −2 ·h −1 for water-in-oil systems, and 98.6 % efficiency with a flux of 7279 L·m −2 ·h −1 for oil-in-water systems, demonstrating exceptional anti-fouling capability and industrial application potential. The composited sponge achieves efficient, stable, and long-term separation of various oil-water mixtures, emulsions, and industrial-grade emulsions, thus providing a new strategy for complex emulsion separation.