Fabrication Of Superhydrophilic/underwater Superoleophobic PVDF Composite Membrane And Study On Separation Performance Of Oil/water Emulsion

The increasing shortage of clean water resources has become one of the major issues of global concern.With the rapid development of economy,more and more oily wastewater is discharged from human production and life.Emulsified oil,especially surfactant-stabilized oil/water emulsions is difficult to handle,which is a thorny problem in the field of oil/water separation.Membrane separation technology has drawn much attention in wastewater treatment due to its low energy consumption,small area and easy continuous operation.However,oil droplets or particles in oily sewage are intercepted in oil/water separation process,and they are easily adsorbed on the surface or blocked the pore channels of the membrane,resulting in a rapid and continuous decline in flux and a serious reduction in filtration efficiency.Therefore,reducing the affinity between oil droplets and membrane surface is one of the important ways to control membrane fouling.Superhydrophilic/underwater superoleophobic membranes have made some breakthroughs in the field of oil/water emulsion separation.However,the preparation of most special wettable membrane materials still needs special instruments or harsh conditions.The special wettable membrane can not be used for oil/water separation in special environment.The special wettability membrane material prepared has a single function,which is not suitable for the production of oil/water emulsions containing a large number of drug molecules during the pharmaceutical process.These shortages limited its large-scale application.Therefore,it is of great theoretical significance and application value to prepare special wettable membrane by simple method for oil/water separation and even oil/water separation in specific environment.The main contents of this paper are as follows:1.Preparation of inorganic nanomaterials modified PVDF membrane for oil/water emulsion separationIn this study,active sites were provided by pDA surface modified,and the micro-nano structure constructed by simple layer-by-layer,sol-gel and hydrothermal methods,which giving superhydrophilic/underwater superoleophobic properties on the membrane surface to achieve oil/water emulsion separation.?1?Atcitive sites were provided by pDA modified for CaCO₃ growth.The high hydrophilic/underwater superoleophobic?PVDF@PDA@CaCO₃?composiete membrane was prepared by layer-by-layer method.In the process of mineralization,the structure of CaCO₃ could be regulated by the concentration of pecursor showing a high degree of flexibility.The composite membrane could effectively separate various oil/water emulsion under the gravity,the separation efficiency is as high as 99%.However,the particle size of CaCO₃ was large and its distribution is not uniform,which may affect the membrane separation efficiency after long-term circulation.?2?Superhydrophilic/underwater superoleophobic composite membrane?PVDF@pDA@SiO₂?was constructed through the surface modification of SiO₂nanoparticle by sol-gel method.The surface morphology of composite membrane could be controlled by the concentration of tetraethyl orthosilicate?TEOS?.Under the pore-induced capillarity,the permeation flux of surfactant-free and surfactant-stabilized dichloroethane/water emulsion could separately reach 1233 L m^-2h^-1 bar^-1 and 572 L m^-2 h^-1 bar^-1.The total organic carbon?TOC?content in filtrates of the corresponding filtrates is lower than 8.2 ppm and 19 ppm,respectively.The composite membranes displayed 98%of initial separation efficiency after 10 cycles for separation experiments.SiO₂ could evenly distribute the membrane surface and pores due to its small size,which improved the fouling performance and separation efficiency.?3?The grass-like NiCo-LDH/PVDF composite membrane was obtained from growth of nickel cobalt hydroxide?NiCo-LDH?array via hydrothermal method.It was studied the influence of hydrothermal time on the PVDF@pDA@NiCo-LDH composite membrane surface morphology and wetting property.The PVDF@pDA@NiCo-LDH composite membrane had superhydrophilicity/underwater superoleophobicity and low oil-adhesion underwater.The composite membrane could separate surfactant-free and surfactant-stabilized oil/water emulsion by porous capillary force,and the TOC content of the corresponding filtrate was lower than 27ppm and 40 ppm,respectively.Regeneration experiments showed that the separation efficiency of composite membrane was still over 99.5%after 10 cycles,indicating the remarkable recycling performance.The growth of NiCo-LDH array on the surface of PVDF membrane enhanced the fouling resistance and cycling performance of the membrane.The grass-like NiCo-LDH was evenly and intensively distributed on the membrane surface.During the separation process,the thickness of water layer was increased to recuce the contact area between oil drops and the membrane surface,which further improved the antifouling property and separation efficiency.Meanwhile,the separation flux would not be significantly reduced after NiCo-LDH modified due to the needle structure of NiCo-LDH.2.Preparation of acid,alkali,salt resistant PVDF composite membrane by surface grafted hydrophilic modification for oil/water emulsion separationIn the treatment of emulsified wastewater in complex environment?high acid,alkali and salt environments?or industrial oil,membrane separation still faced more challenges.In this paper,through atom transfer radical polymerization?ATRP?and cross-linking polymerization,the surface of anti acid,alkali and salt was constructed in a controllable way to improve the stability of the membrane.It will provide the possibility of oil/water emulsion separation in the complex environment.?1?Poly?vinylidene fluoride?/graphene oxide?PVDF/GO?blend membrane was used as base membrane,3-aminopropyltriethoxysilane?APTES?was modified to introduce the active site.The acid,alkali and salt resistant composite membrane was prepared by grafting acrylamide polymer onto the surface of PVDF/GO blend membrane via controlled ATRP method.The prepared composite membrane showed superhydrophilicity/underwater superoleophobicity due to the irregular rod-like structure on the surface and pore-induced capillarity.The composite membrane also displayed excellent stability in acidic,alkaline and high salty environments.In addition,the composite membrane showed high fluxes(1000±44 L m^-2 h^-1 bar^-1)and notable separation efficiency?98%?for various oil/water emulsion separation.?2?To further study the application of emulsion separation in complex environments,the PVDF/GO blend membrane was used as base substratea and?-methacryloxypropyltrimethoxysilane?KH-570?was modified to introduc double bond.A stable cross-linked PVDF/GO composite membrane was prepared by initiation polymerization between acrylic acid and ethyleneglycol dimethacrylate?EGEMA?.The cross-linked composite membrane could effectively separate various stable oil/water emulsion under solely gravity-driven with high separation efficiency of above 99%.In addition,because of the formation of covalent bond bridged multiple crosslinked network during the crosslinking,the composite membrane showed underwater superoleophobicity in complex environments such as acid,alkali and salty environments.The composite membrane could effectively separate oil/water emulsion in complex environment.The regeneration experiments showed that the composite membrane has remarkable recycling performance.3.Preparation of underwater superoleophobic PVDF imprinted composite membrane for synergistic oil/water emulsion and antibiotic selective separationThe addition of organic extractant can easily produce oil/water emulsion containing a large number of pharmaceutical molecules during pharmaceutical process.It is difficult to achieve synchronous emulsion and selective drug molecules separation.In this study,the wettability and molecular imprinted membrane was combined for oil/water emulsion and selective tetracycline?TC?separate by capillary force and imprinting effect,which provides new idea for application of oil/water separation.?1?UiO-66-NH₂ was adhered by one-step on the surface of PVDF membrane via delayed phase inversion to prepare PVDF/UiO-66-NH₂ hybrid membrane?PU membrane?.Active sites were provided by pDA surface modification,the PVDF/UiO-66-NH₂ imprinted composite membrane?PUIM?was prepared by sol-gel method with etracycline hydrochloride?TC?as target,APTES as functional monomer and TEOS as crosslinking agent.The thickness of imprinting layer could be controlled by imprinting reaction time.The superhydrophilic/underwater superoleophobic PUIM was used for the synergistic oil/water emulsion and TC selective separation.In the process of emulsion separation,PUIM showed high flux(2230 L m^-2 h^-1 bar^-1)and significant separation efficiency?99%?,and TC separation efficiency could reach89.1%.In addition,PUIM had outstanding anti-fouling performance and stability separation performance in the process of cyclic experiments.?2?In order to further improve the antifouling performance of imprinted membrane,by adding amphoteric thiobetaine?SBT?in the PVDF phase separation process for segregation,the hydrophobic chain segment was anchored in the main body of the membrane,while the hydrophilic chain segment was exposed on the surface or pore channel of the membrane,which realized the simultaneous modification of the surface and internal pore channel of the PVDF membrane.The as-prepared hybrid?SBT/PVDF?membrane had remarkable anti-fouling property.Additionally,-NH₂was introduced by APTES hydrolytic polymerization to provide adsorption sites for TC.In the imprinting process,dopamine was used as functional monomer and crosslinking agent.The morphology and properties of SPICM membrane was controlled by reaction temperature.The SPICM membrane could be used for synergistic oil/water emulsion and TC selective separation under gravity-driven due to the capillary force and imprinting effect.In the process of emulsion separation,SPICM showed high flux(626 L m^-2 h^-1)and separation efficiency?99%?.The separation efficiency of TC was also reached 88.3%.