| In recent decades,with the progress of society,the development of industry and the improvement of human living standards,a large amount of industrial wastewater and domestic sewage discharge and frequent oil leakage,and these sewage often contains stable and small particle sizes oil/water emulsions(typically less than 20 ?m),so emulsified oily sewage is the most difficult wastewater problem.Meanwhile,the emulsified oily sewage was discharged into rivers or penetrated underground,which will not only cause serious damage to the ecological environment and groundwater,but also threaten the life and health of marine life and humans,and also endanger the growth of crops.The problem of oily wastewater has been a global challenge.Membrane separation technology can distinguish molecules based on the molecular size,shape,and physical-chemical interaction parameters to minimize energy output.At the same time,membrane separation technology has the following advantages:clean and environmentally friendly,efficient and economical,and can be recycled.At present,membrane materials have been modified by super-wettability and pore size adjustment to make them have the advantages of high separation efficiency and simple operation,which has become a research hotspot for treating oily sewage in the world.However,there are still some problems in a large number of research reports:1.how to achieve the versatility of membrane materials(such as demulsification and separation performance);2.how to achieve intelligent separation(such as pH-controlled hydrophilic/hydrophobic mutual conversion);3.how to improve the durability of the functional layer of the membrane;4 how to improve the mechanical properties and tensile resistance of the membrane;5.how to avoid the problem of flux reduction of the membrane;6.how to solve the problem of the membrane surface was susceptible to contamination by organic solvents and oil,it is extremely important to prepare multifunctional membranes with high stability,excellent separation performance and resistance to oil pollution for the treatment of oily sewage.Based on the above problems,the porous base material was modified by a simple and feasible method to prepare a composite membrane with excellent separation,performance and multifunctionality for stable emulsified oily wastewater treatment.That is,the porous material stencil,electrostatic spinning membrane,alumina membrane,non-woven fabric and mixed cellulose membrane as substrate,and then modify the surface with polymers(such as PDVB,PS-b-P4VP,PMDAEMA,and b-PEI/PAA),small molecules(FAS/Zonyl(?)321 and POTS),and inorganic and organic(such as ZIF-8,ZIF-90,SiO2,GO,PG and g-CN@BOC)make it super-wettable and suitable pore diameter,so as to achieve separation of stable oily wastewater.The modification not only makes the prepared composite membranes have special wettability,but also improves the durability and repeatability.It is more important to give it special functions such as self-repairing function and self-cleaning performance,so that the prepared functional membranes have great potential and advantages in the treatment of oily wastewater.The thesis focuses on the following work:(1)We prepared PDVB-modified steel mesh and PDMAEMA-modified steel mesh by surface polymerization,and combined them to obtain dual-functional membranes with demulsification and separation functions for stable water-in-oil emulsion separation.Modification of PDVB on the steel mesh by a simple surface polymerization method to obtain superhydrophobic properties,modification of PDMAEMA on the steel mesh to obtain the function of demulsification,and the formation of microscopic rough surface further enhances its wettability,and then two steel meshes with different functions are combined to prepare a composite membrane with both demulsification and separation functions.The prepared bifunctional membrane exhibits excellent separation performance for emulsifier-stabilized water-in-oil emulsions,and the separation efficiency for various water-in-oil emulsions is above 99%.More importantly,it still has good separation performance(reach to 99%)after multiple separation cycles.(2)In order to be used for the rapid separation of oil-in-water emulsions and the demulsification and separation functions on the same membrane,we prepared a bifunctional bionic Janus membrane by steam diffusion method and surface polymerization method for separation of oil-in-water emulsions.We first modified POTS on one side of the non-woven fabric by steam diffusion,and then modified PDMAEMA by surface polymerization on the other side of the membrane to obtain a bifunctional Janus membrane.The prepared biomimetic Janus membrane has excellent separation performance,and the separation efficiency for different emulsifier-stabilized oil-in-water emulsions is above 99.98%,and it has a high flux of up to 1.53 × 103Lm-2h-1.(3)The above functional membrane materials can only separate water-in-oil emulsions or oil-in-water emulsions.In order to obtain functional membrane materials that can be used to separate both oil-in-water emulsions and water-in-oil emulsions.The PAN@ZIF-8 composite membrane was prepared by mixing PAN and hydrophobic ZIF-8 by electrospinning technology with special wetting super-oleophobicity underwater and super-hydrophobicity underoil.Because the PAN film alone still has a certain degree of adhesion to oil under water,the same oil also has a certain degree of adhesion to water under water,so it cannot separate oil/water emulsion.The addition of hydrophobic ZIF-8 can not only improve its wettability(super-oleophobicity underwater and super-hydrophobicity underoil),but also because of the presence of ZIF-8,the prepared composite membrane has a microscopic rough structure,which can further improves its wettability,thus exhibiting excellent separation performance for stable oil-in-water emulsion or a water-in-oil emulsion.The separation efficiency of the two types of emulsions is above 99.95%,and the same has a high flux above 900 L/m2 h.More importantly,it has excellent reusability,and the separation efficiency is still above 99.9%after multiple cycles.(4)In order to make membrane separation materials intelligent,pH-controllable water wettability(hydrophilic/hydrophobic interchangeable)intelligent composite membranes was prepared for the separation of oil-water emulsions.It is well known that membrane surface pollution has always been an important reason hindering its development,and by changing the hydrophilicity and hydrophobicity of the membrane,the membrane surface pollution can be reduced to a certain extent.In view of this,we prepared a PS-b-P4VP modified alumina film with pH response,which exhibited hydrophobicity when the pH was greater than 7,and exhibited hydrophilicity when the pH was less than 7.At the same time,the roughness of the film surface can be increased due to the deposition of nano-silica.Combining the hydrophilic or hydrophobic and rough structure of the membrane can effectively separate oil-in-water emulsions or water-in-oil emulsions.The separation efficiency is as high as 99.98%,and at the same time,it has good reusability,and maintains excellent separation performance after multiple cycles.Therefore,the preparation of intelligent membranes provides new ideas for sewage treatment and environmental restoration.(5)In order to improve the durability and mechanical properties of the film and make it more advantageous in practical applications,a multifunctional membrane material with self-repairing properties is considered to be the best way to solve this problem.According to their self-healing mechanism,we prepared two different self-healing composite membranes(namely the self-healing of the functional layer and the self-healing at the rupture),which are classified according to their destruction methods,one is chemical destruction and the other is physical destruction.For chemical damage,we prepared FAS and Zonyl(?)321 modified ZIF-90 composite membrane.When the surface functional layer(superhydrophobic property)is destroyed by oxygen plasma,it can obtain its superhydrophobic property after heat treatment.After 100 cycles of oxygen plasma destruction/heat treatment and 200 washings,the contact angle of the water is still higher than 160°,and the surface is unchanged.Aiming at the physical damage,we prepared b-PEI/PAA modified PAN membrane.When the prepared composite membrane is broken or has deep scratches,the damaged parts can be quickly rejoined together in the presence of water,and the separation efficiency of different oil-water emulsions is still above 99.9%.Therefore,the composite membrane with self-repairing function can not only improve its durability and mechanical properties for water treatment,but also provide new ideas for wastewater treatment.(6)Membrane materials for oily sewage treatment,especially for membrane materials with high,they are extremely susceptible to pollution by oil or organic solvents,and the separation performance(separation efficiency and flux)of the membrane will be affected.So this greatly limits the long-term use of the membrane;In order to solve this problem,we prepared a 2D heterojunction GO/PG/CN@BOC membrane with self-cleaning performance driven by visible light for stable oil-in-water Emulsion separation;The separation efficiency of different oil/water emulsions is more than 99.95%,and the excellent flux recovery rate reaches 99.8%.the GO/PG/CN@BOC composite membrane is prepared by vacuum self-assembly method.The addition of palygorskite and heterojunction structure can effectively improve GO and CN@BOC layer spacing,and which could increase the flux;meanwhile,the presence of palygorskite can avoid the decrease of the layer spacing due to the pressure during the using,so that the flux can be kept constant.Therefore,the prepared 2D heterojunction membrane provides new ideas for the further development of water treatment membranes. |
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