Study On Surface Hydrophilic & Antifouling Design And Oil/Water Separation Characteristics Of Polyethersulfone Membrane

The continuous growth of global energy demand has stimulated the rapid development of petroleum related industries,while also exacerbating the threat of oily wastewater to the ecological environment and human health.Therefore,it is extremely urgent to develop efficient and inexpensive separation materials for oily wastewater.Currently,polymeric membrane separation technology stands out due to its advantages of low energy consumption,high efficiency,and integrated operation.However,due to the inherent lipophilicity of traditional polymers,membrane fouling remains the biggest challenge in real industry.It has been proved that constructing hydrophilic or even super-hydrophilic/underwater super-oleophobic surfaces is an important way to control membrane fouling.Despite the extensive progress made in the existing research results,the preparation of most hydrophilic antifouling membranes faces harsh environments and high costs,and there is a long way to go from conceptual proof testing to real industrial applications.In this dissertation,guided by bionics,using traditional membrane preparation techniques and practical coating strategies,a series of hydrophilic and antifouling oil/water separation membranes were prepared by designing the surface chemical composition and micro/nano rough structure of polyethersulfone（PES）membranes.The main research contents are as follows:1.Blending hydrophilic nanoparticles is the simplest strategy to improve the hydrophilicity of composite membranes in the non-solvent-induced phase separation（NIPS）membrane technology.However,the utilization of nanoparticles on the surface of polymeric membranes is limited,and there are some defects such as poor dispersion and stability.Therefore,an interfacial coordination strategy was proposed to promote forced surface segregation of nanoparticles.The cast solution was prepared by mixing the phenol hydroxy-functionalized halloysite nanotubes（HNTs-DA-TA）with PES to prepare the composite membrane via NIPS technology in the coagulation bath containing Fe³⁺.The effects of Fe³⁺concentration in the coagulation bath and HNTs-DA-TA content in the casting solution on the surface chemical composition,pore structure,micro-morphology,roughness,wettability,separation and antifouling performance of the nanocomposite membrane were studied in detail.The results showed that the coordination reaction between Fe³⁺and phenolic hydroxyl groups can enhance the segregation efficiency of hydrophilic HNTs-DA-TA on the surface of PES membranes,which not only contributes to the formation of asymmetric porous membranes,but also prevents the loss of nanotubes during phase transition.Thanks to these advantages,the hydrophilicity of the composite membranes was enhanced,and the water flux was 3.4 times higher than that of the pristine PES membrane,the rejection rate was>98%.After three cycles of separation,the water flux recovery rate could reach 91%,much higher than 56%of the pristine PES membrane.2.Hydrogel modified super-wetting membrane is an ideal material for oil/water separation.However,the deterioration in mechanical strength and separation efficiency during the swelling process and complicated synthesis procedure limits its industrial application.Therefore,a strategy of using ethanol to dynamically regulate the hydrogen bond crosslinking between polyvinyl alcohol（PVA）and tannic acid（TA）was proposed to prepare a“hydrogel paint”,which could be simply applied on the porous substrate surface by one-step operations（dipping,brushing,spraying,etc.）without additional cross-linking.When the ethanol evaporates,the initially inhibited hydrogen bond cross-link between PVA and TA is re-formed,which leads to the in-situ generation of hydrogel coating.The formation mechanism,preparation scheme,gel properties of the hydrogel coating and the wettability,separation and antifouling properties of the coating modified porous substrate were studied in detail.The results showed that the prepared hydrogel coating exhibited swelling volume stability and ultra-high strength（>10 MPa）.The porous substrate modified by hydrogel showed stable resistance to various types of oil and self-cleaning performance,and showed high separation efficiency for mixed oil and emulsified oil（rejection>99%）.3.The design of hydrogel coating provides a simple and effective way to solve membrane fouling,but it still cannot avoid some defects of coating method.Especially for ultrafiltration grade polymeric membranes,excellent antifouling performance comes at the expense of the original flux of the substrate,and there is a stability risk.Therefore,based on the phase transition differences between polyvinylpyrrolidone（PVP）and TA in different solvents,a solvent-nonsolvent regulated H-bonding crosslinking strategy was proposed to achieve stable in-situ assembly of PVP-TA nanoparticles on the membrane surface during the NIPS process,and prepared a super-wetting membrane with layered nanostructure.By studying the phase transition thermodynamics between PES and PVP-TA systems in different solvents,the formation mechanism of nanostructures was unraveled.In addition,the effects of PVP-TA nanoparticles on the surface chemical composition,roughness,micromorphology,wettability,separation performance,and antifouling performance of the composite membrane were investigated.Benefiting from the antifouling barrier constructed by the nano-layered structure,the prepared membrane exhibited super-hydrophilic/underwater super-oleophobic properties and high efficiency in separating oil-in-water emulsions（flux>2800 L/m²·h,rejection rate>99.5%）and good recyclability.4.The in-situ assembly of hydrophilic additives in the process of NIPS preparation provides a new idea for the preparation of super wetting membranes.However,the construction of surface microstructure relies on the H-bonding cross-linking between PVP and TA,which is destroyed under alkaline conditions,limiting the application of composite membranes.Therefore,an Fe³⁺-induced NIPS strategy was proposed to one-step fabricate antifouling PES based membranes that bear hierarchically spherical structures on the interface and an internalized gel network.More specifically,the hydrogen bonding between hydrophilic additives of PVP and TA,as well as Fe³⁺-TA coordination interaction are orchestrated to modulate their surface segregation behaviors during NIPS,leading to in situ generation of the interfacial assembled nanospheres and embedded gel networks in the PES matrix.The formation conditions of the dual antifouling structure were investigated in detail,and its potential formation mechanism was revealed through thermodynamic analysis.In addition,the effects of dual antifouling structure on the surface chemical composition,microstructure,roughness,wettability,separation and antifouling performance of the composite membrane were discussed in detail.The results showed that,based on the synergistic effect of dual antifouling structures,the ultrafiltration membrane exhibited super-hydrophilic/underwater super-oleophobic properties,and displayed excellent separation efficiency（rejection>99.5%）and long-term stability in emulsified oil separation experiments.In addition,this NIPS strategy could be applied to macroporous substrates in the form of coatings,providing an effective solution for the separation of large volume oil/water mixtures.Stability analysis showed that the prepared membrane or coating still had excellent antifouling and separation performance in a wide range of application environments.