A dual-biomimetic surface with leaf-skeleton-based hierarchical structures for efficient atmospheric water harvesting

Atmospheric water harvesting (AWH) has been extensively researched as a sustainable solution to current freshwater scarcity. Various bioinspired AWH surfaces have been developed to enhance water-harvesting performance, yet challenges remain in optimizing their structures. In this work, we report a dual-biomimetic AWH surface that combines beetle-inspired heterogeneous wettability with leaf-skeleton-based hierarchical microstructures on a rigid substrate. An authentic leaf skeleton innovatively serves as the mask during photolithography complemented by O₂-plasma treatment, enabling precise design of superhydrophilic SiO₂ structures with a hierarchy of vein orders forming reticulate meshes on a hydrophobic Si substrate. This design facilitates enhanced water collection through intricate reticulate meshes and directional droplet transport along the abundant multi-order veins. Such AWH surface shows a water-harvesting efficiency of 172 mg cm⁻² h⁻¹, increasing up to 62% and 58% over the pristine SiO₂/Si wafer and Si wafer, respectively. Additionally, the role of structure orientation in the open-surface droplet transport is explored while the AWH surface is vertically placed during the water-harvesting process. This work highlights the potential of using meticulous natural designs, like leaf skeletons, to improve AWH surfaces, with broad applications in compact devices, such as on-chip evaporative cooling and planar microfluidics manipulation.