Janus Composite Porous Structure with Asymmetric Selective-Wettability for Unidirectional Liquid Transportation and High-Efficiency Oil–Water Separation

Selective-superwetting surfaces exhibiting diametrically opposed superwettability toward oil and water have been widely used in the filtration-based separation of oil-water mixtures. But further reducing energy consumption and improving separation flux and separation efficiency still remain challenges. Janus composite porous structures with asymmetric wettability have capacities of driving liquid unidirectional penetration and blocking liquid opposite transmission. This "liquid diode" functionality has proven to be effective for high-efficiency separation in past studies. However, most of the existing Janus porous structures exploit only the capacity of blocking liquid opposite transmission, leaving their capacity of driving liquid unidirectional penetration underutilized. Herein, we propose a selective (super)wetting surface-based configuration of Janus composite porous structure and fabricate two kinds of Janus composite porous structures. The Janus composite porous structures with asymmetric selective (super)wettability exhibit capacities of driving water/oil unidirectional penetration and blocking water/oil opposite transmission. The oil-water separation efficiency is over 99%, and the separation flux is significantly higher than conventional homogeneous selective-superwetting porous structures. This work provides insights into the design of Janus porous structures with significant potential applications in selective unidirectional actuation of multiphase liquids, oil-water separation, wastewater treatment, and marine oil spill recovery. Furthermore, this scalable fabrication methodology opens avenues for developing next-generation smart membranes for osmotic energy harvesting and adaptive interface materials.