High-efficiency Water Collection Properties On The Functional Materials Inspired By Namib Desert Beetles

To date,water shortage has been a serious issue all over the world.How to effectively and environmentally acquire freshwater is desirably required.It is well known that up to 0.5 g of liquid water is contained in 1 m³ of fog.As a typical example,Namib Desert beetles can capture water from fog to feed themselves attributing to the alternating hydrophobic and hydrophilic regions on their back surfaces.Inspired by this,a great number of water-collecting materials have been fabricated.In the text,we firstly introduce the natural creatures with excellent water capture ability.And then the theoretical studies related to the surface wettabilities were shown。This is followed by presenting the applications of water collection devices or materials in recent years.Firstly,epoxy resins were brush coated on the copper sheets,then different molar ratio（0:1,1:1,2:1,3:1,4:1,5:1,6:1,9:1,12:1,1:0）of Cu and TiO₂（p25）were dip-coated on the above materials,which was followed by immersing the samples in 0.05 M of n-octadecylme（ODT）/hexane solution for 30 min.Because Cu can be modified by ODT to earn a larger WCA while TiO2 can not,Cu acts as hydrophobic site and TiO2 serves as hydrophilic area,which is extremely similar with the back of Namib Desert beetles.With different molar ratio of Cu and TiO₂,the wetting behaviors and water collection rates were varied.As for the hybrid surfaces,the water contact angles grow upon the content of Cu.When molar ratios were larger than 6,the surfaces showed stable superhydrophobicity,however,the water collection efficiency did not vary as surface wettability.The excess concentration ratios of Cu or TiO₂ are disadvantageous for water harvesting in the hybrid surfaces.Thus,at the molar ratio of 9:1,the outstanding water collection efficiency was endowed on the sample with a value of 1309.9 mg h^-1 cm^-2.Moreover,this surface showed excellent mechanical stability and self-cleaning property,contributing to its wide application for future freshwater supply.Then,we use the alkaline oxidation to develop a series of functional copper mesh with different wetting behaviors,i.e.,superhydrphilic copper mesh,superhydrophobic copper mesh,superhydrophobic patterns on the superhydrophilic copper meshes,which can be successfully applied in oil/water separation,self-cleaning and water collection.The superhydrophilic and underwater superoleophobic surface was obtained after the alkaline oxidation,and it could be used for the efficient light oil/water separation.Afterwards,the superhydrophilic mesh film was immersed in the n-octadecylme（ODT）/ethanol solution to earn a lower surface energy and then showed stable superhydrophobicity,which exhibited the ability of the separation of oily wastewater containing heavy oils with high flow flux and separation efficiency.Also,excellent self-cleaning ability can be observed on the superhydrophobic sample.Surprisingly,this functional material could achieve to remove light oils and heavy oils in sequence on a single surface using a rapid and facile approach.What is more,superhydrophobic patterns on the superhydrophilic copper meshes inspired by the Namib Desert beetles manifested good water harvesting property,and the superhyophilic surface with two superhydrophobic circular patterns exhibits a superior water collection rate than uniform superhydrophilic and superhydrophobic copper mesh surfaces with the value of 1316.9 mg h^-1 cm^-2.