Researches On Preparation And Oil-water Separation Properties Of Films With Special Wettability

With the process of urbanization and industrialization gradually accelerating,the direct discharge of oily wastewater has caused great harm to the water environment,and ultimately jeopardized human health and life.Therefore,effective separation of oily wastewater is imminent.In recent years,inspired by nature,it has been discovered that oil-water separation materials prepared with special wetting films have become a new idea for solving this problem.In addition to the oil-water separation,the superhydrophobic film layer can utilize the surface air film to improve the corrosion resistance of the metallic matrix effectively.Therefore,the special wetting films can not only be used for oil-water separation,but also applied in the fields of self-cleaning,anti-fouling and anti-corrosion.At the same time,the preparation and research of the films with switchable wettability can promote the development of smart materials.In this paper,foamed copper and brass meshes were used as the substrates.Chemical deposition,alternating current deposition and chemical spraying techniques were used to prepare special wetting films with controlled wettability on copper and its alloys.A series of characterizations were conducted.The preparation method of the film layer is gradually improved,from the one-step method to construct the micro/nano rough structure by the natural hydrophobic materials to prepare a superhydrophobic film,and to explore the corresponding wettability conversion mechanism,which is simple and easy.At the same time,the use of special wetting films and separation devices has gradually improved its application in the field of oil-water separation.（1）The superhydrophobic Cu₂S film was prepared on copper foam by chemical deposition technique.The relationship between the deposition parameters and its microscopic morphology and wettability of the surface was studied.It was found that the film was uniformly covered with micronodules aggregated by nanoparticles.The chemical composition of film is Cu₂S and Cu[CH₃（CH₂）₁₂COO]₂,and then we put forward the reaction mechanism.With the thermal oxidation and the modification by tetradecanoic acid,a rapid wettability conversion of the copper foam surface is achieved,so that we can control over the surface wettability.And then a mechanism for intrinsic sparse conversion is introduced.The superhydrophobic film was repeatedly soaked in muddy water for 20 times,and it remained silt-free and had good self-cleaning antifouling properties.The surface scratch test showed that the copper foam dragged 600 mm on a sandpaper still has superhydrophobicity,indicating that the superhydrophobic foam copper has a certain wear resistance.In addition,the superhydrophobic film also has excellent chemical stability and weather resistance.The superhydrophobic copper foam can be used as a boat to carry out the oil-water separation performance test.It is simple and easy to use.After 5 times of recycling,the oil-water separation efficiency is still above 94%.（2）In order to seek the participation of free low surface energy agents in the preparation of superhydrophobic films,the superhydrophobic Cu₂S films were prepared on the copper meshes by alternating current deposition method.It was proved that Cu₂S is a natural hydrophobic material similar to Cu₂O.Under the optimum deposition parameters,the surface of the mesh is uniformly covered with 3D cauliflower-like micro-scale rough structures composed of nano-pectoid particles.The contact angle is as high as 158.9°and the roll angle is as low as about 1°.By controlling the temperature and time,the surface materials of the film were converted between Cu₂S and Cu_2-xS,and then the wettability transition can be achieved.The chemical composition of the special wetting film was analyzed and the reaction mechanism was explored.Using the special wetting films and a self-made gravity separation device for oil-water separation experiments,it was found that both the superhydrophobic and superhydrophilic films have good oil-water separation characteristics,and the oil-water separation efficiency of the films to various organic substances are above 96%.At the same time,the superhydrophobic film also has good wear resistance.（3）Based on the above studies,in order to expand the development of superhydrophobic films prepared by natural hydrophobic materials,a method for preparing superhydrophobic Cu₂O films by chemical spraying was studied,which is highly applicable.Through the control of the temperature of the special wetting film,the mutual transformation of Cu₂O/CuO on the surface of the film is realized,and the special wettability of the surface is changed.The composition of the film under different processing conditions was analyzed,and the film formation mechanism and wettability conversion mechanism were proposed.The potentiodynamic polarization curves in 3.5 wt.%NaCl aqueous solution show that the corrosion potential of the superhydrophobic film relative to brass increases from-0.188 V to-0.131 V,and the corrosion current density also varies from 1.07×10^-5 A/cm² to 7.13×10^-7A/cm²,it is reduced by nearly two orders of magnitude,indicating that the superhydrophobic Cu₂O film significantly improves the corrosion resistance of brass.Special wetting films under different treatment conditions can efficiently separate different kinds of oils regardless of the light oil or heavy oil in the mixture with the aid of a peristaltic pump.This simple,environmental friendly,low-cost and high-efficiency method and the wetting transition technology can provide effective methods and ideas for the large-scale preparation of special wetting films with corrosion resistance and the separation of oily waste water.Furthermore,it can be easily extended to other material surfaces.