Water is essential for human life, yet roughly two billion people worldwide still lack access to safely managed drinking water. With increasing pressure from rapid population growth and climate change, there is a critical need for water generation technologies that are low-cost, scalable, and environmentally sustainable. Passive atmospheric water harvesting offers a promising solution by capturing moisture from the air without continuous energy input, but current approaches are often limited by low efficiency or high cost.

This study aims to optimize a bioinspired mixed-wettability surface to enhance passive water collection by promoting both droplet nucleation and rapid transport of condensed water. The surface is fabricated using superhydrophobic zinc oxide nanowire (ZnO NW) arrays synthesized via a scalable sol-gel/chemical bath deposition method, followed by functionalization with a non-fluorinated silane agent. Here, we propose a novel “double-structured” ZnO NW array with hierarchical surface roughness. This novel morphology is assessed for its superhydrophobic property and benchmarked against other ZnO NW morphologies. Hydrophilic silica nanoparticles are then deposited on the superhydrophobic NW arrays to create the mixed wettability effect for water harvesting. Material performance is optimized by varying NW morphology, surface wettability, and nanoparticle concentration to maximize water collection rates and the stability of the material is tested over time to monitor for any degradation in performance.

To induce condensation without energy input, this mixed-wettability surface is coupled with a passive daytime radiative cooling (PDRC) coating composed of bicontinuous interfacially jammed emulsion gels (bijels). Bijels are formed through the kinetic arrest of spinodal decomposition of two immiscible liquids by jamming nanoparticles at the liquid-liquid interface. These porous polymer films exhibit high solar reflectance and strong infrared emissivity which enables sub-ambient cooling by using cold outer space as a heat sink. The PDRC layer is optimized by adjusting the domain size and film thickness to achieve maximum cooling performance. In parallel, a life cycle assessment (LCA) is conducted to evaluate the environmental impacts of material fabrication and identify key contributors to categories such as global warming potential, water use, and ozone depletion. This integrated approach informs design choices that minimize environmental burden. The results of this study show promise in developing a sustainable material with the ability to passively collect atmospheric water, potentially aiding in providing clean water globally in the face of the climate crisis.

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