Hierarchical Hydrophilic/Hydrophobic/Bumpy Janus Membrane Fabricated by Femtosecond Laser Ablation for Highly Efficient Fog Harvesting

The shortage of freshwater is threatening sustainable economic development and ecological security worldwide. Janus membrane, as a highly efficient method to collect the invisible fog water in the wet environment, is still hindered by some inherent limitations: (1) poor condensation of fog droplets on the superhydrophobic side due to the ultralow adhesive force of droplets with substrate and (2) insufficient detachment of droplets from the superhydrophilic side in time, which hampers the continuous water transport in the micropores. Herein, inspired by the desert beetle's back with alternating hydrophobic/hydrophilic bumps and the cactus thorn with an asymmetric geometry, we design and fabricate a kind of hierarchical hydrophilic/hydrophobic/bumpy Janus (HHHBJ) membrane by femtosecond laser ablation on an aluminum membrane to achieve the self-driven fog collection, which achieves over 250% enhancement in the water collection efficiency over the conventional Janus membrane. Even when the mist flow is applied to the surface at an incident angle of 45°, the collection efficiency increases by 600%. The mechanism of the HHHBJ film with excellent fog collection efficiency is mainly related to the continuous efficient fog condensation on the top surface and droplet removal on the bottom surface in time. We believe the proposed multi-bioinspired HHHBJ film with droplet self-driven collection ability provides insights to conceive and construct a highly efficient fog collection system in broad fields.