Construction Of Graphene Oxide-based Nacre-inspired Superhydrophilic And Underwater Superoleophobic Mesh And Study On Their Oil/Water Separation Performance

Recently,the oil spills accident frequently occurred and the oily wastewater was arbitrarily discharged,which caused serious pollution to the environment and threatened human health.Therefore,it is of great significance to find an efficient oil-water separation technology for processing oily wastewater.Membrane separation technology exhibits broad perspective in the field of oil-water separation due to its simple operation,high separation efficiency and low energy consumption.Inspired by the lotus leaf and fish scales,many oil-water separation membrane materials have been developed.In particular,superhydrophilic and underwater superoleophobic materials have drawn much attention from researchers.However,there are still some problems to be solved in the research of superhydrophobic and underwater superhydrophobic materials,such as complicated preparation process,poor mechanical performance and chemical stability and short lifetime.The nacre exhibits excellent strong and tough mechanical properties,which is ascribed to its special“brick-and-mortar”structure.The integration of nacre-like structure into the design of superhydrophilic and underwater superoleophobic materials is an effective means to improve its stability and lifetime.Graphene oxide?GO?is one of the ideal building blocks for constructing nacre-like structure due to its unique lamellar structure,good ductility and hydrophilicity and excellent mechanical properties.The purpose of this dissertation is to construct a GO-based nacre-inspired superhydrophilic and underwater superoleophobic mesh system,to characterize their physicochemical properties such as morphology,size,microstructure,surface wettability and roughness,and systematically study their oil-water separation performance.The main research work and results are as follows:?1?The superhydrophilic and underwater superoleophobic GO-Ca²⁺-SA@Fe composite mesh with a GO-Ca²⁺-SA nacre-like structure constructed on the surface of stainless steel mesh by layer-by-layer self-assembly?LBL?method,using GO and sodium alginate?SA?as building blocks,CaCl₂ as chelating agent.The effects of SA,CaCl₂ concentration,assembly times and mesh size on the morphology and wettability of the composite mesh were investigated.Simultaneously,the effects of salt concentration and solution pH on the wettability and oil-water separation performance were also studied.It was found that the(GO-Ca²⁺-SA)₁₅@Fe₃₀₀ composite mesh exhibited superior performance with an underwater oil contact angle 154^o?1,2-dichloroethane?.The mesh exhibits low oil adhesion force in water and can effectively separate a series of oil-water mixture,such as toluene-water,cyclohexane-water,with the oil-water separation efficiency more than 99%and a water flux of 119426 L m^-2 h^-1.The nacre-like structure was constructed through the synergistic self-assembly effect of GO,SA and Ca²⁺,which endowed the composite mesh with good recyclability,salt tolerance,acid and alkali resistance,and excellent mechanical properties?Young's modulus of 35.8±4.9 GPa?.?2?Inspired by the“brick-and-mortar”structure of nacre and mastoid structure of lotus leaf surface,the superhydrophilic and underwater superoleophobic GO-CaCO₃@Fe composite mesh with a GO-CaCO₃ nacre-like structure fabricated on the surface of stainless steel mesh via LBL self-assembly method,utilizing a“bioinspired mineralization”process.The effects of parameters such as GO concentration,dipping numbers and mesh size on the morphology and wettability were studied,and the formation rules of nacre-like structure GO-CaCO₃ was revealed.The effects of salt concentration and pH on the wettability and oil-water separation performance were investigated.The experimental results suggested that?GO-CaCO₃-5?₂₀@Fe₃₀₀composite mesh size exhibited the optimal performance.Its underwater oil contact angle reached 155^o and separation efficiency was more than 99%for a series of oil/water mixtures with high water flux(179640 L m^-2 h^-1)for cyclohexane/water mixture.The bioinspired mesh possessed good self-cleaning?ultralow underwater oil-adhesion force?,excellent mechanical properties?Young's modulus of 25.4±2.6 Gpa?,chemical stability?acid/alkali resistance?and excellent recycle performance.?3?The superhydrophilic and underwater superoleophobic GO-PEI-SH@Fe composite mesh with a GO-PEI-SH multiple component nacre-like structure constructed on the surface of stainless steel mesh by LBL self-assembly method,using GO?polyethylenimine?PEI??silica and halloysite as building blocks.The effects of raw materials type and concentration,dipping numbers and mesh size on the wettability and oil-water separation performance of the composite mesh were studied.Compared with GO-PEI-S@Fe and GO-PEI-H@Fe,GO-PEI-SH@Fe composite mesh possessed a better wettability.The experimental results showed that?GO-PEI-SH-1?₁₅@Fe₃₀₀composite mesh exhibited the best performance with a contact angle of 159^o for 1,2-dichloroethane droplet.?GO-PEI-SH-1?₁₅@Fe₃₀₀ composite mesh possessed low oil adhesion force and small rolling angle,whose oil-water separation efficiency was up to99.8%and the highest water flux reached 195038 L m^-2 h^-1 with Young's modulus of19.7±2.6 GPa.The bioinspired mesh showed excellent recycling,salt tolerance,acid and alkali resistance mechanical performance.