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.