Underwater Superoleophobicity-underoil Hydrophobic Graphene Microfiltration Membranes Preparation And Oil-water Separation Performance

In recent years,a series of ecological and environmental disasters have been caused due to the increase of oil spills and industrial wastewater.The treatment of oily wastewater has aroused widespread concern.Coventional methods,such as combustion method,biodegradation method,electric flocculation have the disadvantages of low separation efficiency,high cost and high energy consumption,especially the separation of emulsified oil,which has become a difficult problem in the separation field.In order to solve the problems mentioned above,many materials have been designed,especially the pressure driven filter membranes with special wettability.In this paper,graphene（GR）with good water dispersibility and a certain degree of defects was prepared by electrochemical peeling method.Then GR-SiO₂microfiltration membranes were prepared by vacuum filtration and applied to the separation of oil-in-water emulsion.Firstly,GR with good water dispersibility was prepared by electrochemical stripping under the condition of ultrasonic conditions.The GR-SiO₂microfiltration membrane was prepared on the surface of polyethylene terephthalate（PET）nonwoven fabric by by vacuum filtration.The effects of SiO₂content on the structure,wettability and separation efficiency of GR-SiO₂microfiltration membrane were studied.The results showed that with the increased of SiO₂content,the surface roughness and hydrophilicity of GR-SiO₂microfiltration membrane gradually increased,and the underwater oil contact angle（UWOCA）and underoil water contact angle（UOWCA）were also increased.When the SiO₂content increased to 0.05 g,the UWOCA of GR-SiO₂microfiltration membrane was150.0°and the UOWCA was 132.0°,reaching the state of superoleophobicity underwater.The water flux reached 828.06 L/m²·h^-1,the porosity was 82.36%,the separation efficiency of oil-in-water emulsion reached more than 75.22%.In order to further increase the hydrophilicity of the GR-SiO₂microfiltration membrane and the separation efficiency of oil-in-water emulsion,the PVA-GR-SiO₂microfiltration membrane was prepared by introducing polyvinyl alcohol（PVA）on PET support layer.PVA was used to crosslink the SiO₂and GR sheets.The effects of PVA solution with different concentrations on the wettability and the separation efficiency of the microfiltration membranes were studied.The results showed that when the contents of PVA was 3 wt.%,the the UWOCA and UOWCA were 154.3°and 139.0°,respectively.The water flux was 256.41 L/m²·h^-1,the porosity reashed to 84.38%and the separation efficiency of oil-in-water emulsion was 89.9%.The separation efficiency was higher than that of GR-SiO₂microfiltration membrane.Finally,HEC-GR-SiO₂microfiltration membranes were prepared by cross-linking GR and SiO₂with hydroxyethyl cellulose（HEC）.The effects of different concentrations of HEC solutions on the wettability,mechanical properties and separation efficiency of emulsified oil of the HEC-GR-SiO₂microfiltration membranes were studied.It was found that when the HEC content was 1 wt.%,UWOCA and the UOWCA were 155.1°and146.9°,respectively.The water flux was 316.239 L/m²·h^-1and the porosity was 85.55%.The emulsified oil separation efficiency of microfiltration membranes was as high as97.9%,which was obviously higher than that of GR-SiO₂microfiltration membranes and PVA-GR-SiO₂microfiltration membranes.The above method of preparing microfiltration membranes is environmentally,friendly,inexpensive and possesses good oil-in-water separation efficiency,which is of great significance for promoting industrial production in the new era.