Study On The Construction And Applied Basic Research Of TiO₂-based Surface With Selective Superwettability

The surface with superwettability has widespread application in self-cleaning,anti-fouling and anti-fogging.With the growing demand of practical application,in recent years,the research on super-wettability has been transferred from single-wettability/function to multiple-wettability/function.The selective superwetting surface,which preserves both superlyophobic and superlyophilic property towards water and oil,has been of great theoretical and practical significance for its application in high-efficient and energy-saving oil-water separation.The selective superwetting surface normally fall into four categories:superhydrophobic/superoleophilicsurf ace,superhydrophilic/unde rwatersuperoleophobicsurface,superoleophobic/superhydrophilic surfac e and stimuli-responsive selective superwetting surface.Among them,the superhydroph obic/superoleophilic surface is the ideal surface for the separation of oil-water mixtures.However,according to the classic interface theory,the oil-repellent surface tends to repel water as well,the fabrication of superoleophobic/superhydrophilic surface is challenging.The wettability of stimuli-responsive selective superwetting surface can switch between different selective superwettabilty,this particular property overcomes the drawbacks of surface with single selective superwettability and thus has obvious advantages in application.However,existing stimuli-responsive selective superwetting surface has problems such as poor controllability and low wettability switch efficiency,which lead to the restriction of its application.In order to address the theoretical and practical difficulty in research of superwetting surface,in this study,the mechanism and the separation ability of selective superwetting surface have been intensively studied by considering specific molecular properties of oil and water.The selective wetting equation which based on dispersed and polar components of surface energy was deduced according to surface-interface theory.The relationship between di spersed/polar components of surface energy and oil/water wettability was discovered,the mechanism of selective superwetting surface was explained and the theoretical models of nanoparticle-based selective superwetting surface were established.A photo-responsive superhydrophobic/superoleophilic composite structure was fabricated by attaching fluoride silane on titanium dioxide(TiO₂)nanoparticles.The wettability of the photo-responsive composite structure can switch between superhydrophobicity/superoleop hilicity and superhydrophilicity/underwater superoleophobicity by alternating ultraviolet(UV)irradiation and heating process,respectively.The mass ratio of fluoride silane and T i O₂nanoparticles was optimized by researching the wettability switch efficiency,the wettability switch efficiency and availability were well enhanced after the optimization.By attaching on different substrates,the composite structure can separate various kinds of oil-water mixtures.Moreover,a separation-purification method was proposed by means of the photo-catalysis property of TiO₂,the water-soluble dye was successfully removed by a composite mesh structure during UV irradiation.A fluorinated chains-metal cation chemical structure was constructed by the reaction of perfluoroalkyl acids and metal hydroxide.The dispersed and polar components of surface energy was adjusted by the regulation of perfluoroalkyl acids/metal cation ratio.The fluorinated chain/metal cation ratio was optimized by researching the influence of dispersed and polar components of surface energy on wettability of oil and water.The problem of coexistence of oleophobicity and hydrophilicity was solved by the fabrication of oleophobic/hydrophilic surface.A superoleophobic/superhydrophilic micro-nano composite structure was fabricated by the combination of fluorinated chains-metal cation chemical structure and TiO₂ nanoparticles.By proposing a adhesive-particle superimposed composite structure,the mechanical durability of this kind of superwetting composite structure was well enhanced.A superoleophobic/superhydrophilic composi te structure was fabricated by the combination of fluorinated surfactant and TiO₂ nanoparticles.By attaching on different substrates,the superoleophobic/superhydrophilic composite structure fulfill the high-efficient separation of immiscible oil-water mixtures,oil-in-water emulsions and water-in-oil emulsions.Getting the benefit of the photo-catalysis property of TiO₂,the oil-soluble dye was successfully removed by a composite mesh structure during UV irradiation.In conclusion,focusing on the applica tion of oil-water separation and aiming at the existent common problems in the research of selective superwetting surface,the mechanism and the separation ability of selective superwetting surface have been studied in this work.A dispersed/polar-based theoretical explanation of selective superwettability was proposed,the theoretical explanation provides support for the construction of selective superwetting surface.On this basis,methods for fabricating different types of selective superwetting surface were also proposed,TiO₂ nanoparticle-based superhydrophobic/superoleophilic and superoleophobic/superhydrophilic composite structures were fabricated.By utilizing the selective superwettability of the composite structure and the photo-responsive property of TiO₂,the composite structures fulfilled the separation of different types of oil-water mixtures and purification of polluted oil/water,which provide solution for intricate oil-water separation and waste liquid treatment.