Janus copper mesh with asymmetric wettability for on-demand oil/water separation and direction-independent fog collection

Traditional preparation methods of Janus membranes are either too complicated or cannot accurately control their characters such as surface wettability, layer thickness, and pore structure. Herein, asymmetric wettability and layer thickness on the copper mesh were successfully regulated by an interface-confined surface engineering strategy and applied for liquid manipulation. Water droplets can spontaneously infiltrate from the superhydrophobic side to the superhydrophilic side of the as-prepared Janus copper mesh (JCM), achieving unidirectional transportation. Besides, the separation efficiency of the JCM exceeds 99.2%, whether it is a combination of light or heavy oil-water mixtures. Moreover, compared to the corresponding superhydrophilic and superhydrophobic meshes, the JCM showed a 200% increase in fog collection. A fog collector with a sandwich structure was further developed, making up of a superhydrophilic inner layer and double-deck superhydrophobic external layers that always play a role of a Janus collector to allow a continuous and high-performance fog harvesting regardless of the direction of the fog flow. Overall, this work provides a new idea in the fabrication of Janus membranes, which could be extended to the transport of directional water, switchable oil/water separation, fog collection, and other fields.