Modification Of PVDF Ultrafiltration Membrane By Graphene Oxide (GO) And Zr-Based MOF Materials(UiO-66)and Performance Of Composite Membrane

Polyvinylidene fluoride(PVDF)is a commonly used polymer membrane material,but due to the strong hydrophobicity of PVDF membrane,it is easy to cause membrane fouling in the process of operation,thus becoming the constraints of its expansion in water treatment and other fields.Therefore,it is necessary to improve the hydrophilicity of PVDF membrane in order to improve the pollution resistance of PVDF membrane.In this paper,different hydrophilic materials(GO,UiO-66,GO@UiO-66 composite materials)were used to prepare PVDF composite ultrafiltration membrane,and the influence of the selected materials on the structure and performance of PVDF composite membrane was explored,as follows:(1)The octahedral structure of UiO-66 and"sandwich-like"structure of GO@UiO-66 nanoparticles were prepared by solvothermal method,and the lamellar structure of GO nanoparticles were prepared by the improved Hummers method.The physical and chemical structures of prepared materials were systematically analyzed by XRD and FTIR.The results showed that the three kinds of nano-materials were successfully prepared.(2)PVDF/GO,PVDF/UiO-66 and PVDF/GO@UiO-66 composite ultrafiltration membranes were prepared by immersion precipitated phase conversion method.The crystal structure,molecular structure,microstructure,hydrophilicity,porosity and average pore diameter of PVDF composite ultrafiltration membrane were characterized by XRD,FT-IR,XPS,SEM,AFM and contact angle.The results showed that the nanomaterials were successfully compounded in PVDF membrane,and the porosity and hydrophilicity of PVDF composite ultrafiltration membranes were improved after adding nanomaterials.PVDF showed transformation fromαtoβphase.(3)When GO,UiO-66 and GO@UiO-66 contents were 1.0 wt%,the water flux of PVDF composite ultrafiltration membrane reached 194.1L/m~2/h,182.2L/m~2/h and263.2L/m~2/h,respectively.Compared with pure PVDF membrane,the water flux increased by 35%,28%and 84%,respectively,and the BSA rejection rate increased by19%,20%and 32%.The water contact angle decreased from 78.5°to 64.6°,68.3°and58.3°,respectively.The surface roughness of the membranes increased from 21.5nm to34.5nm,27.2nm and 59.7nm,respectively,due to the floating of the nanomaterials during phase transformation.The flux recovery rate of the membrane reached 71.8%,64.3%and81.8%,respectively,and the anti-fouling ability was greatly improved.The tensile strength increased from 1.8MPa to 2.5MPa,2.2MPa and 3.1MPa.(4)Comparison of PVDF/GO,PVDF/UiO-66 and PVDF/GO@UiO-66 showed that:"Sandwich-like"GO@UiO-66 not only increased the porosity of membrane but also opened the penetration channel of water molecules.And the GO@UiO-66 enhanced the number of hydrophilic functional groups,making the PVDF/GO@UiO-66 had higher hydrophilicity,in the form of hydration layer on the membrane surface,thus,the rejection rate of pollutants of different molecular weight sizes such as bovine serum protein(BSA),humic acid(HA)and rhodamine(Rh B)was improved and the anti-fouling performance was better.In addition,PVDF/GO@UiO-66 composite ultrafiltration membrane had the best mechanical strength and chemical stability.The overall results show that adding"sandwich-like"GO@UiO-66 can significantly improve the performance of the membrane,and has a great possibility for practical application.