Superhydrophilic And Underwater Superoleophobic Chitosan/silica Coated Membrane For Oily Wastewater Treatment

With the development of modern science and technology and the improvement of people’s quality of life,people have paied more attention to environmental protection.Oil pollution,as a common pollution,has greatly endangered the environmental protection and ecological balance.Among the many methods for treating oily wastewater,the membrane separation method is widely used because of its advantages of simple operation,high efficiency,low energy consumption,fast reaction rate and no secondary pollution.The membrane materials with high flux,low cost and stable properties are the focus of membrane separation technology.In this paper,membrane separation technology was used to treat the oil and emulsified oil in oily wastewater,and a chitosan/silica nanoparticles composite coating material with superhydrophilicity and underwater superoleophobicity was prepared.The composite coating materials were characterized by means of contact angles(CAs)and Fourier transform infrared(FTIR).The coating material was then coated onto the surface of stainless steel mesh and PVDF microporous membrane.The stainless steel mesh and PVDF microporous membrane were characterized by scanning electron microscopy(SEM)and contact angles.The oil-water separation experiments were carried out to study the treatment effect of the oil slick wastewater and emulsified oil wastewater respectively,and the mechanism was discussed.Conclusion as below:1.The chitosan/silica nanoparticles composite coating material with superhydrophilicity and underwater superoleophobicity was prepared.The experimental results show that chitosan,silica nanoparticles and glutaraldehyde three solutions can be mixed reaction.The reaction of chitosan and glutaraldehyde can improve the film-forming and stability of chitosan.Chitosan can react with silica nanoparticles to improve the hydrophilicity of chitosan.The optimum volume ratio of the chitosan,silica and glutaraldehyde solution was 50 mL: 50 m L: 0.05 mL.The resulting mixed solution has better film-forming properties,stability,hydrophilicity in the air and underwater oil-repellency.2.The superhydrophilic and underwater superoleophobic modified stainless steel mesh membrane material was prepared.After scanning electron microscope and contact angle test,it was found that the purpose of the modified stainless steel wire mesh was successfully achieved by spraying the chitosan/silica nanoparticles composite coating material onto the surface of the etched stainless steel mesh,which made stainless steel wire mesh possess the superhydrophilicity and underwater superoleophobicity,and 350 mesh stainless steel mesh material for the best specifications.By simulating the oil-water separation experiment,it was found that the oil-water separation effect could reach more than 99 %.The oil-water separation effect is good,which can provide reference for the treatment of oil-bearing wastewater.At the same time,oil-water separation experiments were carried out using oily wastewater with different pH values.The results show that the coated stainless steel wire mesh has good stability and can be applied in different environments.Most importantly,after cleaned by the low concentration of sodium hydroxide solution and repeated the above experiment 10 times,the modified stainless steel mesh material remains the good separation efficiency,indicating that it has a good repeatability.3.The modified PVDF microporous membrane material with superhydrophibicity and underwater superoleophobicity was prepared.After scanning electron microscope and contact angle test,it was found that the purpose of the modified PVDF microporous membrane was successfully achieved by spraying the chitosan/silica nanoparticles composite coating material onto the surface of the etched PVDF microporous membrane,which made the etched PVDF microporous membrane possess the superhydrophilicity and underwater superoleophobicity.By simulating the emulsified oil-water separation experiment,the total organic carbon content of oily wastewater was decreased,and the emulsified oil-water separation efficiency was over 99 %.It has good demulsification effect and can provide reference for the treatment of emulsified oily wastewater.After the membrane flux test,we found that compared with the original PVDF microporous membrane,the modified PVDF microporous membrane for pure water and oil water flux have been greatly improved.In addition,after cleaned by the low concentration of sodium hydroxide solution and repeated the above experiment 10 times,the modified PVDF membrane material remains the good separation efficiency,indicating that it has a good repeatability.