A Dual-Biomimetic Surface with Leaf-Skeleton-Based Hierarchical Structures for Efficient Atmospheric Water Harvesting

Atmospheric water harvesting (AWH) is a sustainable strategy to mitigate current freshwater scarcity. Recent developments lie in regulating surface properties inspired by numerous natural creatures. However, it remains challenging to design a surface capable of fast water capture and directional droplet transport, both of which are essential for efficient AWH applications. Here, we proposed a novel approach for designing the water-harvesting surfaces (i.e., a tailored microstructured surface), inspired by the heterogeneous wettability of the Namib Desert beetle and the hierarchical structures of <i>Ficus religiosa</i> leaf skeleton. Unlike conventional oversimplified structural optimization, our approach directly employs the natural designs of the leaf skeleton to distribute heterogeneous wettability and optimize the structural increments without adjustments. Within the leaf-skeleton-based structure of superhydrophilic SiO₂, the superior water-capture capability is enabled by the novel intricate venules within reticulate meshes, which is also the critical factor in facilitating directional droplet transport along the abundant hierarchical veins. The proposed water-harvesting surface has shown exceptional efficiency, demonstrating a 62% increase over pristine SiO₂/Si wafers and a 58% increase over pristine Si wafers. Furthermore, the impact of leaf-skeleton-based structure orientation in the open-surface droplet transport is investigated. When most veins are pointing downward, aligned with the direction of gravity, our surface achieves the highest water-harvesting efficiency, showing a 17% increase compared with its horizontal orientation and a 10% increase compared with its flipped orientation. The innovative dual-biomimetic surface structures are expected to have wide applications in other water-related research, such as evaporative cooling of electronic devices.