Patterned surface with cactus plus desorption channels for fog collection by laser etching

Abstract Water scarcity has been a pressing crisis in quite a few cities globally. For addressing the urgent demand for water harvesting, a hybrid-wettability surface was fabricated on a copper-based substrate, integrating cactus spines, triangular cactus thorns, and pine needle-derived structures as primary water transport channels, secondary channels, and droplet shedding channels, respectively, for fog-water collection. The superhydrophobic part was fabricated through a two-step process involving rapid laser marking ablation and subsequent chemical modification with a fluorosilane coating, whereas the superhydrophilic patterns were obtained by subjecting the as-prepared superhydrophobic surface to secondary laser ablation. Compared with the untreated copper substrate, the pattern enhanced the fog collection efficiency by 105.21%, which reached 7.88 kg/(m 2 ·h). Additionally, the first drop time and the interval between each drop were 42.8 s and 5.25 s, respectively, which were reduced by 32.91% and 36.44%, respectively, compared to the reference. This was attributed to the cactus design plus the gradient desorption channel in particular, which solved the wall-hanging problem. Limited data regarding these values are available in the published literature. Meanwhile, freshwater fish survived in the harvested water for at least 7 days, and the limited chemical analyses revealed no acute biotoxicity or excessive concentrations of the specific ions examined. Temporal evolutions of the surface wettability and fog collection efficiency during one month of outdoor exposure were also investigated to evaluate their potential for practical application.