Preparation Of Multistage Rough Super Wetting Nanofiber Membrane For Emulsified Oily Wastewater Purification

Petroleum products have been playing an important role in industrial production.Restricted by the level of social development and economic conditions,spill accidents of oil inevitably occur during its production,transportation,and storage.As a result,the oily sewage and wastewater in water environment are contining to increase.Among them,the emulsified oily sewage with stable dispersion state has great negative impacts on the ecological environment.Therefore,the separation of the emulsified oily sewage is rising rapidly as a tough issue to be resolved.Among numerous separation technologies,membrane separation technology has the advantages of high efficiency,high precision,simple separation process,less pollution.It is an ideal means to separate emulsified oily sewage.Among various separation membrane materials,electrospun nanofibers have the advantages of large specific surface area,high porosity,strong connectivity,good flexibility,adjustable wettability and easy loading of various functional materials,showing great potential in emulsified oily sewage separation applications.Sieving based on selective wettability is the principle of nanofiber membrane emulsified oily wastewater separation,and the separation of different types of emulsified oily wastewater can be achieved by rationally controlling the selective wettability of the fiber membrane surface.This work clarifies the important influence of the surface wettability of nanofibrous materials and the multi-level rough surface of the fiber membrane on the purification of emulsified oily sewage.It aims to combine the surface wettability of separation materials with the ability of electrospinning to prepare multi-stage rough structured nanofibers,regulate the multi-level rough structure and selective oil-water superwetability of the nanofiber membrane synchronously,improving the separation flux,separation efficiency and the antifouling performance of the nanofiber membrane.The following research results were obtained:（1）In this section,the amidated zirconium-based organometallic framework（UiO-66-NH₂）nanoparticles were firstly reacted with diaminomaleonitrile by glutaraldehyde,introducing-C≡N into UiO-66-NH₂.Then the introduced-C≡N were amidoximated with hydroxylamine hydrochloride,obtaining UiO-66-AO nanoparticles.Subsequently,UiO-66-AO was loaded in PAN/DMAC spinning solution,and combined with PVP/（DMAC acetone）solution through a coaxial biphasic spinneret to prepare electrospinning composite nanofiber membranes.The prepared initial AO/PAN/PVP composite nanofiber membrane was treated with a water bath to remove PVP,and a multi-level rough AO/PAN composite nanofiber membrane with a gully structure and UiO-66-AO nanoparticle loading was obtained for oil-water emulsion separation.The prepared 0.5%AO/PAN composite nanofiber membrane has uniform UiO-66-AO nanoparticle loading,and the surface of the nanofiber membrane has a multi-level rough gully structure with good specific surface area,uniform pore size distribution,excellent roughness,surface superhydrophilicity and underwater superoleophobicity.It has a good separation effect on a series of oil-in-water surfactant-stabilized emulsions（O/W SSEs）,especially petroleum ether/water emulsions(J=9686 L·m^-2·h^-1;R～99.4%).（2）To improve the problem of nanoparticle agglomeration and flux decay of nanofiber membranes above,in this section,in-situ polymerization was performed to prepare PVP-UiO-66-NH₂ nanoparticles with good dispersibility in water.Subsequently,PVP-UiO-66-NH₂-loaded PAN composite nanofiber membranes were constructed by continuous electrospinning-electrospraying technique.The dilute solution of PAN loaded with PVP-UiO-66-NH₂ formed a uniform and complete microsphere-fine fiber structure on the surface of PAN electrospun substrate by electrospray.The obtained composite nanofiber membrane obtained superhydrophilicity,underwater superoleophobicity,stable antifouling performance and excellent separation efficiency toward different O/W SSEs（TOC=11.6 mg/L for n-hexane-water SSE,R=99.2%FRR=94.4%）.This work provides a feasible route to design nanofiber membranes with efficiency stability for oil-containing emulsion separation.（3）To explore the effect of surface multi-level roughness on the hydrophilic properties of nanofiber membranes,in this section,PA6-rGO composites were first synthesized via in-situ ring-opening polymerization,and then PA6-rGO nanofiber membrane was constructed combining electrospinning and electrospraying successively.Electrospraying of dilute PA6-rGO solution forms a continuous microsphere/bead-like fibrous structure on the surface of the electrospun substrate,which can effectively enhance the surface hydrophilicity and underwater superoleophobicity.The finally obtained 5%@9%PA6-rGO nanofiber membrane has good antifouling performance（FRR=90.6%）and separation efficiency（R>99%,TOC<50 mg/L）.This work proves that the multi-level rough structure of the surface has an important influence on the surface wetting properties,which enriches the application scenarios for many polymer materials with various excellent properties but not strong hydrophilicity,and expands the selection range of electrospinning materials.（4）In order to explore the effect of hierarchical rough structure on the hydrophobic nanofiber membrane,a superhydrophobic D-H-PTFE nanofiber membrane with a fiber-microsphere structure surface was prepared by electrospinning combined with electrospraying and subsequent heat treatment.Among the D-H-PTFE nanofiber membranes,the 9%D-H-PTFE can reach superhydrophobic status with the WCA of 147.8°.Using 9%D-H-PTFE for gravity-driven separation of oil-water mixture,the oil flux reaches 4909 L·m^-2·h^-1,and the separation efficiency reaches99.99%.In addition,9%D-H-PTFE can not only achieve rapid demulsification of W/O SSEs,(1867.93 L·m^-2·h^-1,98.46%),but also achieve effective demulsification of O/W SSEs(122 L·m^-2·h^-1,98.4%)The above efficiencies remain stable after multiple cycles.Therefore,the 9%D-H-PTFE is expected to be practically applied in a low-pressure driven membrane separation system to achieve preliminary separation of heavy oil wastewater or improve the quality of petroleum products.