Sandwiched Copper Foam with Symmetrical Wettability for Direction-Independent Fog Collection

The Janus membrane demonstrates its advantages in timely drainage and directional water transport properties for efficient fog water collection, which helps alleviate global water shortages. However, the direction-dependent collection and inefficient directional water transport properties limit its widespread application. Herein, a single-layered sandwich-structured copper foam that features a superhydrophilic inner layer and double-deck external hydrophobic layers is prepared by a simple method. This innovative architecture demonstrates direction-independent fog harvesting capabilities through the synergistic integration of symmetric wettability gradients and robust structural integrity. Such sandwiched copper foam shows its superiority in rapid directional water transport and timely drainage properties which can quickly regenerate the fresh outer hydrophobic surface as well as the direction-independent unidirectional water transport properties. The rapid directional water transport property combined with the timely drainage of the sandwiched copper foam benefits the continuous better performance of fog collection compared to that of conventional Janus membranes. Clearly, the development of such sandwiched copper foam with a direction-independent unidirectional water transport property enables the effective and durable collection of fog droplets in environments with dynamically changeable winds. Overall, this work provides a new idea for the fabrication of advanced materials for direction-independent fog collection.