Underwater Superoleophobic Composite Membrane Material For Oil-Water Separation

Frequent oil spill accidents and many chemical industries that use oil as raw materials inevitably discharge a large amount of oil wastewater during processing and production,which will cause serious damage to human living environment and ecological environment system.Therefore,it is urgent to develop a new technology for efficient treatment of oily wastewater based on new materials.In recent years,based on the study of surface wettability of materials,materials for treating oily wastewater are mainly divided into two categories:membrane separation materials with special wettability and adsorption materials.In this paper,aiming at common oil slick wastewater and emulsified oil wastewater which is difficult to treat,a novel nano-polymer coating material with special structure and properties was prepared by using polyethyleneimine with high reactivity and natural polyphenol tannic acid as raw materials.Through simple immersion deposition or controllable in-situ growth strategy,the composite membrane material with special wettability was prepared by constructing micro-nano size structure on the surface and regulating surface energy,which realized efficient and stable separation of different types of oil wastewater.The main contents are as follows:（1）Optimized preparation of PEI-TA@SiO₂ hydrogel coated composite reticulated membrane and oil-water separation performance test.Based on stainless steel mesh,gellable polyethyleneimine and natural polyphenol tannic acid were selected as raw materials,and silica nanoparticles were doped at the same time.The flowable coating material was obtained by two-step sol-gel method,and then a super hydrophilic/underwater super oleophobic coating composite mesh membrane was prepared by dipping and depositing on the stainless steel mesh film.The contact angles between water in air and oil in water are 2°±1.5°and 156.5°±1.0°,respectively.The surface of the reticulated mesh membrane compounded by coating materials is covered by a layer of micro-nano polymer,which changes the micro-morphology and roughness of the surface.After the separation test of simulated oil-water mixture,it is found that the coated composite mesh membrane can separate oil and water efficiently.The separation efficiency of various types of oil-water mixtures is higher than 99.28%,and the permeate flux is always higher than 14590 L·m^-2·h^-1.After 30 cycles of recycling,the separation efficiency is still higher than 98.05%.（2）Optimization of preparation process and performance test of 2D-ZIF@ZIF-8 layered structure coating composite mesh.In order to improve the stability and durability of the composite mesh,the in-situ growth of 2D-ZIF composite mesh with 2D-ZIF@ZIF-8 composite layered rough structure coating was obtained by using the limiting effect of crystal seeds layer on the secondary growth and crystallization process of 2D-ZIF.The contact angles of water in the air and oil in the water on the surface of the composite mesh are 0°and 160°±1.0°respectively.It was found that the composite reticulated membrane was suitable for the efficient separation of various types of oil-water mixtures when it was used to simulate the separation of different oils.After 30 cycles of oil-water separation test,the high-efficiency oil-water separation efficiency of 96.8%is still maintained.At the same time,the separation of oil-water mixture of composite mesh membrane in different harsh environments is also tested,and its environmental adaptability is good.（3）Optimization and control of the preparation process and performance test of coated composite filter membrane modified by in-situ growth of ZIF-8@TA particles.In order to improve the hydrophilicity of the filter membrane and the separation performance of oil-water emulsion,the metal cation Zn²⁺was anchored on the surface of PVDF membrane by using the ability of plant-based polyphenol tannic acid,and then a new composite filter membrane of ZIF-8@TA nanoparticles with core-shell structure combined with commercial PVDF filter membrane was obtained.The wettability of the filter membrane surface was improved,and the coating morphology with micro-nano rough structure was constructed.Superhydrophilicity in air was obtained by optimizing the preparation process.The water contact angle of the prepared composite filter membrane can reach 0°within 0.2s in air,and the separation efficiency of various types of oil-water emulsions is higher than 99.02%.After 14 cycles of emulsion separation,its separation efficiency is still close to 99%,which proves that it can separate oil-water emulsion stably and efficiently.