Ultrafast Achievement of a Superhydrophilic/Hydrophobic Janus Foam by Femtosecond Laser Ablation for Directional Water Transport and Efficient Fog Harvesting

Water scarcity is a serious global challenge, especially in arid and desert regions. Functional devices for directional water transport and fog collection have received increasing attention. Existing methods and technologies suffer from low fog-collecting efficiencies, complicated fabrication processes, and high fabrication costs. Herein, we report a simple and low-cost method to rapidly fabricate nanoparticle-covered microstructures on one side of a copper foam surface, using one-step femtosecond laser direct writing technology, which enormously improved processing efficiency. The resulting foam exhibits superhydrophilic/hydrophobic Janus properties. The foam allows water droplets to pass from the hydrophobic side to the superhydrophilic side, but not in the opposite direction. The Janus foam can therefore be used for harvesting water in fog environments, and the maximum water-collecting efficiency is 3.7 g cm-2 h-1, which is much better than existing data. The Janus foam exhibits excellent stability during abrasion and hydraulic wash tests. This water-collecting design may provide an efficient route for overcoming future water shortages.