Surface Wettability Of TiO₂ And CuS Nanostructures And Their Applications

Surface wettability is an important property of solid materials.It is mainly controlled by the surface chemical composition and the surface micro/nano structure,and the superwettability,such as superhydrophilicity and superhydrophobicity,can be achieved by modulating the surface chemical composition and structure.The superwetting material has been widely applied in resistant to corrosion,antimicrobial agent,antifreeze,self-cleaning,oil-water separation,sensors,etc.However,due to the more complexity of application environments,the requirements for the controllability and intelligence of the solid surface wettability are becoming more and more stringent,the external excitations,such as light,electric field,heat,magnetism,etc.,induce the changes of surface chemical composition and structure,which in turn stimulates the wetting transition of the solid surface.The result provides a new idea for the precise control and intelligentization of the surface wettability.Metal oxide(sulfide)compounds,such as titanium oxide(TiO₂),copper sulfide(Cu S),etc.,are easy to introduce vacancy defects in their bodies and on their surfaces,and their physical properties are sensitive to external excitations,such as light,electricity,and heat,which are very conducive to the design and development of intelligent wetting surfaces and devices.Sensors based on the electrowetting-on-dielectric(EWOD)responses have huge advantages,such as sensitive response,real-time drive,and controllable micro-droplets,but there still are some problems,such as poor reversibility,complex preparation,and excessive driving voltage.The intelligent on-demand oil-water separation based on the wetting transition requires that the wetting transition of the mesh or porous substrate surface is precisely regulated and stably motivated by external incentives.Therefore,based on the above considerations,we took the topic of"Surface Wettability of TiO₂and Cu S Nanostructures and their Applications"to work from the following aspects and obtained a series of valuable results:(1)Based on the space charge polarization theory,the reduced and bamboo-like layered TiO₂nanotube arrays were designed and prepared by the voltage pulse anodization technique including reduction process of negative voltage.The reduction process synchronously introduces amount of oxygen vacancies,and the bamboo-like layered structure provides a plenty of interfaces to accumulate large amounts of free charges in the TiO₂nanotube arrays,which greatly enhance the space charge polarization in the TiO₂nanotube arrays.Thus,the capacitances of the reduced and layered TiO₂nanotube arrays are clearly increased,which further lead to the obvious enhancement of the electrowetting-on-dielectric(EWOD)responses.Furthermore,the reduced TiO₂nanotube arrays with bamboo-like layered structure are successfully used as the visual sensor to detect the Na Cl and glucose concentration.Especially,it has higher sensitivity for the detection of the Na Cl and glucose solution with low concentration.(2)The simple,fast,large sale preparation of meshy Cu-based materials for the on-demand oil/water separation is still a challenge.Herein,the one-step anodizing process of the Cu mesh to form the tremella-like Cu_xO@Cu_xS nanosheets is reported,and the tremella-like Cu_xO@Cu_xS nanosheets on Cu mesh exhibits excellent mechanical stability and corrosion resistance.The freshly prepared tremella-like Cu_xO@Cu_xS nanosheets without surface modification of organic materials have the superhydrophilicity and underwater superoleophobicity.After storage in atmosphere for about 6 days under room temperature,the wettability is gradually transformed into superhydrophobicity and superlipophilicity.Importantly,the wettability can turn back the superhydrophilicity and underwater superoleophobicity after the annealing process at 200?in air environment.So the stable reversible wetting transition is realized and the mechanism of revisable wetting transition is also detailedly investigated.Lastly,the prepared tremella-like Cu_xO@Cu_xS nanosheets on copper mesh have been successfully applied in on-demand oil/water separation with high separation efficiency.