Preparation Of Biomimetic Superwetting Surfaces And Its Fog Harvesting Performance

Refreshing drinking water is the essential demand of mankind.Although advanced technique has significantly increased the efficiency of drinking water supply,the water crisis still endangers the survival of human beings all over the word,especially in poverty-stricken regions.Fog harvesting is potential in accessing fresh water in those arid areas where fog water is richer than the rain.And it is of great significance for the people living there.The fog harvesting ability of desert beetles,spider silks and cactus thorns has greatly inspired the development of biomimetic fog harvesting,but the fog harvesting performance of individual creature is far from optimal.Studies have shown that the cooperation among different mechanisms of many organisms is more effective in fog harvesting performance.For example,the integrations of Namib desert beetles,cactus thorns,pitcher plants and wet spider silks or micro/nanostructured conical spine and Janus membrane have been proved effective in enhancing the fog harvesting ability.The desert beetle-inspired(super)hydrophobic-(super)hydrophilic alternating chemistry patterns and JMs with asymmetric wettability on two sides of membrane have both shown great potential in fog harvesting.In this paper,we integrated(super)hydrophobic-(super)hydrophilic alternating chemistry pattern induced by desert beetles and the asymmetric wettability of Janus by a simple liquidus surface modification.The nanoscale(super)hydrophilic-(super)hydrophobic alternating chemistry pattern enhanced the fog capture,the asymmetric wettability of the two sides of sample introduced the special unidirectionally two stage-water transport.Especially,their cooperation induced a newly enhanced fog harvesting mechanism,which enhanced the fog capture,water supply and water removal and made the Janus copper mesh more effective during fog harvesting compared with the corresponding superhydrophilic membranes,the JM showed an 800%enhancement in fog harvesting.After we have a certain understanding of the fog harvesting mechanism,we will focus on the simple preparation and large-scale manufacturing of the fog harvesting collectors,which are current challenges and difficulties in preparation of biomimetic superwetting surface.Inspired by the alternating hydrophilic-hydrophobic micropattern on the backs of desert beetles,using a simple spraying method and selective modification of mercaptan,we successfully fabricated the biomimetic hybrid superhydrophilic-superhydrophobic surface.This surface consists of a hydrophobic micro-particle/hydrophilic nano-particle hierarchical structure.Hydrophobic microparticles were composed of Cu₂O microparticles that were easily modified by ODT,and hydrophilic nanoparticles consisted of Zr O₂ nanoparticles that were not easily modified by ODT.When the mass ratio of Cu₂O microparticles to Zr O₂nanoparticles in the spraying suspension was 8:1,the as-prepared hybrid sample had the highest fog collection efficiency of approximately 1707.25 mg/cm²h^-1,which was two times higher than that of the superhydrophilic sample,showing a prominent enhancement of the fog harvesting capability.The special hierarchical structure can facilitate the water harvesting behavior.In addition,the fabrication method has a low production cost and is facile,making the large-scale manufacture of fog harvesting collectors possible.