Fabrication Of Functionalized PVDF Based Composite Membranes And The Separation Performance For Oil/water Emulsions

The oily wastewater produced from the oil exploitation,oil transportation leakage,industrial production and domestic sewage poses a great threat to the ecological environment and human health.Among them,the oil/water emulsion with oil droplet size less than 20?m is difficult to separate during the oily wastewater.At present,oil skimming,flotation,adsorption,membrane separation and other technologies are commonly applied to separate oil/water emulsion.Membrane separation technology with the advantages of low energy cost,easy operation,eco-friendly and high separation efficiency has been widely used in oil/water emulsions separation.Polyvinylidene fluoride?PVDF?has been recognized as a better oil/water emulsions separation membrane material owning to its outstanding chemical stability,high mechanical strength and well toughness.Nevertheless,during the oil/water emulsions separation,membrans are always be fouled due to hydrophobic C-H group in PVDF.Moreover,when the membrane materials are applied to oil/water emulsion treatment in the actual complex environment,membrane materials are often faced with some problems such as water-soluble dyes in actual water or the actual water environment is acidic and alkaline.The hydraulic method and chemical method are commonly used to wash fouled membrane.But thsed two methods have the disadvantages of incomplete washing and the components of membrane material are easily destroyed.Many studies have found that the superhydrophilic/underwater superoleophobic membrane material has good antifouling performance.Therefore,it is significant to improve the anti-fouling,self-cleaning,acid-alkali resistance and collaborative separation properties of membrane materials.In this paper,superhydrophilic/underwater superoleophobic PVDF based composite membranes were successfully prepared by different preparation methods,which using the polyvinylidene fluoride?PVDF?as substrates by combining polydopamine biomimetic adhesion technology,phase transformation technology,hydrothermal in-situ growth method,sol-gel method,blending method and surface modification method.The specific research contents of this paper are as follows:?1?Preparation of antifouling PVDF/GO@PDA@HNTs composite membranefor oil/water emulsions separationThe PVDF/GO membrane was prepared by blending the prepared grapheme oxide?GO?with polyvinylidene fluoride?PVDF?.And then the PVDF/GO@PDA@HNTs membranewas fabricated based on the halloysite nanotubes?HNTs?with 1D hollow porous structure anchored at PVDF/GO membrane surface via polydopamine?PDA?adhesive.The superhydrophilic/underwater superoleophobic composite membrane was used for oil/water emulsion separation.The experimental results showed that the flux of the composite membrane could reach 550 L m^-2h^-1under gravity-driven as well as high separation efficiency?99.5%?,and the flux recovery ratio could reach 87%.The above results could be concluded that the composite membrane with excellent antifouling performance could efficiently separate oil/water emulsions.?2?Preparation of UV-induced self-cleaning PVDF@PDA@ZnO compositemembrane for oil/water emulsions separationThe hydrophilicity of PVDF membrane was modified by polydopamine?PDA?.After that,a layer of zinc oxide?ZnO?seeds was coated on the PVDF@PDA membrane surface.Finally,the UV-induced self-cleaning PVDF@PDA@ZnO composite membrane was obtained via hydrothermal in-situ growth of the photocatalytic ZnO nanoparticles on the PVDF@PDA composite membrane.The composite membrane had excellent superhydrophilic/underwater superoleophobic,antifouling,stability and self-cleaning properties.According to the separation of different oil/water emulsions,it could be seen that the flux of the composite membrane could reach to 654 L m^-2h-¹under the gravity-driven,and the separation efficiency was higher than 99.1%.After the long time separation/UV-light irradiation,the separation efficiency still could reach 99.27%.?3?Preparation of visible light induced self-cleaning CS@NiFe₂O₄@PVDF composite membrane for oil/water emulsionseparationThe hydrophilic photocatalytic NiFe₂O₄ nanoparticles were prepared by hydrothermal method and secondary calcination method.And then the nanoparticles were dissolved in the mixture of ethanol and water,which was used as the coagulation bath during the phase transformation process.The NiFe₂O₄ nanoparticles were anchored onto the surface of PVDF membrane via this efficient and easy method,and then visible light induced self-cleaning CS@NiFe₂O₄@PVDF composite membrane was successfully prepared via crosslinking with chitosan?CS?by sol-gel method.The separation performance tests of different oil-water emulsions showed that the separation efficiency of the composite membrane could reach more than 99.01%,even under harsh conditions,and the separation efficiency was higher than 98.99%.Moreover,after separation/visible light irradiation,the composite membrane still maintained high separation efficiency with 99.19%,indicating that the excellent self-cleaning and regeneration properties of the as-prepared composite membrane.?4?Preparation of functionalized KGM/PDA/PVDF composite membrane for oil/water emulsions and dye separationThe polymer glucomannan?KGM?with good hydrophilicity,excellent biocompatibility and the ability to effectively combine with various water-soluble pollutants was blended with PDA and PVDF powders,and then the KGM/PDA/PVDF composite membrane was obtained via phase transformation process.The corrosion resistant and multi-functional composite membrane was used for oil/water emulsions and dyes separation.Various performance test results showed that the separation efficiency of the composite membrane reachedup to 99.01%,even underthe strong acid,strong alkali and high salinity environment,the separation efficiency still could reach up to 98.99%.Meanwhile,after the long-time cycle experiments,the separation efficiency of composite membrane could still maintain99.09%?surfactant-free 1,2-chloroethane/water emulsion?.In addition,the dye separation efficiency of the composite membrane could maintain more than 91%under different environments.These results indicated that the composite membrane exhibited outstanding corrosion resistant,regeneration and collaborative separation performances.