A quadruple biomimetic hydrophilic/hydrophobic Janus composite material integrating Cu(OH)2 micro-needles and embedded bead-on-string nanofiber membrane for efficient fog harvesting

Abstract

Fog harvesting is one of the effective ways to solve the water shortage, especially in poor arid and semi-arid areas. Over the last decade, various fog harvesting materials have been reported continuously, but most of the materials have problems such as the inability to obtain fog from the fog-harvesting surface instantly and the existence of secondary evaporation of the captured fog. Inspired by the asymmetric microgeometry of cactus spines, the alternate hydrophobic/hydrophilic micropattern on the desert beetle back, the spindle-knot of spider silk and the asymmetric wettability of lotus leaf, we successfully designed a quadruple biomimetic Janus composite material with asymmetric microtopology and anisotropic wettability by chemical etching and electrospinning. The material achieves an excellent fog harvesting efficiency with 80.57 mg·min−1·cm−2 through the efficient fog capture and unidirectional droplets transport. Besides, the secondary evaporation of captured water is greatly reduced by the material, and the water retention rate can reach 92.97 % at 25 °C and 72.57 % at 50 °C, which is 8.57 % and 41.49 % higher than the original samples, respectively. We believe it is greatly promising for relieving societal water scarcity.