Preparation Of CO₂-driven Switchable Wettability Materials And Study On Their Performance Of Oil/Water Emulsion Separation

In recent years,the frequent occurrence of oil spill accidents and the large amount of industrial oily sewage discharge have caused serious damage to the ecological environment.Toxic substances in oily sewage are harmful to human health because of biological enrichment.Among them,emulsified oil increases the separation difficulty and cleaning cost due to its small and stable particle size.Therefore,the effective treatment of emulsified oil is of great significance to the ecological environment and social development.For the past few years,super-wetting materials have been widely developed and applied in the field of oil-water separation.However,most super-wettability materials can only separate oil-water mixtures or single emulsified oils,and cannot deal with complex emulsion systems.Therefore,it is urgent to develop a material capable of controlling the separation of various emulsified oils on demand.Stimulus responsive materials can change the structure or properties of the polymer on the surface of the material through external stimuli,thus switching the material's own wettability to separate different types of emulsified oils,simplifying the separation process and reducing the cost.Among them,CO₂-responsive materials only involve CO₂ and inert gases in the regulation process,which avoid the generation of by-products and the pollution of the system,and have become the research hotspot of scientists.Nonetheless,CO₂-responsive materials still have problems such as slow response speed and single function,which limit their application in water treatment.In this paper,CO₂-responsive polymer and separation materials were combined to prepare CO₂-responsive nanomaterials and composite membranes.The influence of CO₂-responsive polymer on surface wettability was investigated by adjusting the molecular weight of the CO₂-responsive polymer,studied the surface microstructure and chemical composition of the materials.The oil-water separation performance,catalytic degradation performance,heavy metal ion adsorption performance and regeneration performance of the material were thoroughly investigated.The main research contents are as follows:1.Preparation of CO₂-responsive poly(2-(dimethylamino)ethyl methacrylate)functionalized magnetic halloysite(MHNTs@PDA@PDMAEMA)for efficient,controllable separation of oil-water emulsionIn order to prepare CO₂-responsive material MHNTs@PDA@PDMAEMA with rapid response and efficient separation.Firstly,poly(2-(dimethylamino)ethyl methacrylate)(PDMAEMA)was prepared by RAFT polymerization,and then its main chain end group was reduced to sulfhydryl group by n-butylamine.PDMAEMA was then grafted onto the surface of dopamine-deposited magnetic halloysite(MHNTs@PDA)by Michael addition reaction.The maximum contact angle difference between hydrophilic and hydrophobic of MHNTs@PDA@PDMAEMA(M_n,NMR=24K)is 110°.The material can stably separate oil-in-water emulsions and water-in-oil emulsions under alternating bubble of CO₂/N₂.When CO₂ is bubbled,MHNTs@PDA@PDMAEMA shows super-hydrophilic properties and can be used to separate water-in-oil emulsions containing non-ionic surfactants.When N₂ is bubbled,MHNTs@PDA@PDMAEMA exhibits hydrophobic/lipophilic properties and can be used to separate oil-in-water emulsions containing non-ionic and anionic surfactants.This nanomaterial has outstanding advantages in the separation of emulsified oil.At least 12 kinds of emulsified oil can be separated with a separation efficiency of 99.8%.After 11 cycles,the separation efficiency is still high,and the CO₂ response speed of the material is improved to 10 minutes.This kind of nanomaterial grafted with CO₂-responsive polymer has broad application prospect in the field of oil and water separation.2.Preparation of CO₂-responsive and catalytic multifunctional blend membrane for synergistic oil-water emulsion separation and dye degradation by in-situ reductionIn order to achieve controlled separation of emulsion and catalytic degradation of organic dyes in wastewater,CO₂-responsive block copolymer poly(styrene)-b-poly(2-(diethylamino)ethyl methacrylate)(PS-b-PDEAEMA)was synthesized by RAFT polymerization,and then blended with PVDF-HFP and silver nitrate.PS-b-PDEAEMA-Ag NPs/PVDF-HFP blend membrane were obtained.The surface layer,subsurface layer and cross section of the membrane were studied,and the changes of membrane flux due to chemical composition and CO₂ response were analyzed.The effects of the length of PDEAEMA chain on the wettability and catalytic degradation of block copolymer were investigated.Under the control of CO₂/N₂,the blend membrane can separate both O/W emulsion and W/O emulsion.The longer the chain segment of PDEAEMA in the component,the higher the fluxes of oil-in-water/water-in-oil emulsions.When the membrane was wetting in advance,the fluxes of O/W and W/O emulsion were as high as 6872 and 4216 L·m^-2·h^-1·bar^-1.After 6 cycles,the separation efficiency of the membrane was still higher than 98.0%,and the Ag NPs obtained by in-situ reduction in the membrane were obtained.It can also synergically catalyze the degradation of methylene blue and p-nitrophenol,which has good antifouling and antibacterial properties and renewable properties.The membrane has not only simple preparation method,excellent performance,but also synergistic catalytic degradation performance.3.Mussel biomimetic preparation of CO₂-responsive multi-functional composite membrane for oil-water emulsion separation and adsorption of heavy metal ionsIn order to achieve emulsion separation on demand and improve emulsion separation efficiency as well as the adsorption of heavy metal ions in sewage,the copolymer P(DEAEMA-AM)was obtained by the polymerization of acrylamide(AM)and DEAEMA through RAFT.Inspired by mussels,Si O₂ spheres were uniformly loaded on the surface of PVDF membrane deposited with polydopamine to construct the PVDF@PDA@Si O₂ micro/nano structure.Then,P(DEAEMA-AM)was grafted onto the surface of PVDF@PDA@Si O₂ film by Michael addition reaction to obtain PVDF@PDA@Si O₂@P(DEAEMA-AM).Membrane surface,subsurface and cross section were characterized by SEM,and analyzed the chemical composition of the membrane surface.The influence of Si O₂ micro-nano structure on membrane separation efficiency,and the influence of polymer molecular weight on membrane surface wettability and heavy metal ion adsorption were investigated.The results show that when the molecular weight of the polymer is higher,the contact Angle difference is larger by regulating CO₂/N₂,and the water/oil flux is higher,and the maximum value is 6547 L·m^-2·h^-1·bar^-1.Through CO₂/N₂ regulation,the membrane can separate both O/W emulsion and W/O emulsion,and the separation efficiency is close to 100%.After6 cycles of regulation,the membrane still has a high separation efficiency(99.0%)and chemical stability.In addition,the adsorption on heavy metal ions was studied.The adsorption of copper ions(183.2mg/g)and desorption was carried out by regulating CO₂/N₂.Compared with the traditional adsorption materials,the membrane avoids the use of strong acid to desorb heavy metal ions,which is more green and environmental friendly.