Bioinspired Fog Harvesting Surface Based on Aluminum Functionalization

Limited access to fresh water is a growing global challenge, and atmospheric water harvesting offers a promising approach for supplementing conventional water resources. Inspired by the fog-capturing spines of cacti, aluminum surfaces with controlled wettability were developed to investigate how surface chemistry, morphology, and wettability affect fog collection. Surfaces were prepared by sequential NaOH and HCl treatments followed by functionalization with several carboxylic acids: three oxygenated acids and four fatty acids from hexanoic to octadecanoic. FT-IR supported surface functionalization, while SEM and profilometry showed broadly similar morphology and roughness across functionalized samples. Oxygenated acids gave highly hydrophilic surfaces (θ < 10°), whereas fatty acids gave highly hydrophobic surfaces (θ up to 156.7°) with parahydrophobic features (strong water adhesion). Surfaces functionalized with fatty acids (from decanoic to octadecanoic) exposed to artificial fog collected approximately 1.6 to 2 times more water than untreated aluminum. Over five 1 h collection cycles, C10- and C14-functionalized surfaces maintained relatively stable collection performance despite decreasing contact angles. C18-functionalized surfaces showed the highest initial performance, but both contact angle and collected water mass decreased over successive cycles. These results demonstrate that long-chain fatty acid functionalization improves fog collection, with chain length influencing collection performance and its retention during repeated use.