Biomimetic bumpy and eco-friendly slippery surfaces for enhanced dew and fog water harvesting

Abstract

As global water scarcity intensifies, atmospheric water harvesting (AWH), such as fog and dew collection using surfaces, offers a cost-effective and scalable solution. Although fog and dew harvesting on surfaces operate through different processes, both approaches rely on efficient droplet transfer, with dew harvesting further benefiting from dropwise condensation for enhanced performance. Here, nature-inspired millimetric bumpy patterns were fabricated on an aluminum surface using selective laser melting 3D printing to enhance dropwise condensation. Investigation showed the geometry significantly influenced droplet growth, with droplets at the apex of bumps growing approximately three times larger than those on flat areas. Following this, a nanometric two-layer was applied by coating the substrate in a silicon-based solution and exposing it to methylchlorosilane vapor. This process created an environmentally friendly, covalently bonded liquid-like polymer on the surface, forming a smooth, durable lubricating thin layer with ultralow contact angle hysteresis (CAH <3°), facilitating rapid droplet shedding and transport. Water harvesting performance tests under different environmental conditions showed that the patterned surface outperformed a flat one in both dew and fog harvesting. In dew harvesting, surface cooling increased specific water production (SWP), with the patterned surface reaching a maximum of 55 mg cm⁻² h⁻¹ with 72 % efficiency. In fog harvesting, SWP was significantly higher, with the patterned surface reaching 3055 mg cm⁻² h⁻¹ with 45 % efficiency. Furthermore, the coating's stability and resistance to high temperatures and humidity make it well-suited for industries requiring efficient condensation. This study helps improve water harvesting systems, contributing to a sustainable future.