Preparation of a Bioinspired Conical Needle for Rapid Directional Water Transport and Efficient Fog Harvesting

Abstract

Water shortages have become a serious issue that threatens the survival of humans, particularly in arid regions. Collecting fog from the air environment is an effective approach to obtaining freshwater resources. Herein, inspired by cactus spines, we fabricated a superhydrophilic conical copper needle by the combination of electrochemical etching and the SiO2 colloidal self-assembly method for water transportation and fog collection. It was found that a water film would be formed on the surface of the as-prepared copper needle once a water droplet was transported from the tip to the base, which acted as a lubricating film to reduce the frictional resistance between the following water droplets and the copper needle and promote the self-propelled movement of the droplets. As a result, the transport velocity and the longest transport distance of a single water droplet on the as-prepared copper needle were high up to 142 mm/s and 42 mm, respectively. Besides, the results reveal that the droplet transport distance decreased with the increase of apex angles, whereas it increased with the increase of droplet volume and tilt angles. Additionally, the as-prepared copper needle exhibited an outstanding water collection rate of ∼1700 mg/h for a single copper needle, which is five times that of the original copper needle. This work provides a facile and low-cost method to fabricate conical copper needles for water droplet manipulation and efficient fog collection, showing great application potential in the fields of microfluid, desalination, and freshwater collection.