Preparation Of GO/PVP/PVDF Composite Ultrafiltration Membrane And Its Antifouling Properties

Poly(vinylidene fluoride)(PVDF)has been widely used as the main ultrafiltration membrane materials in the field of water treatment.However,the main limitation in the popularization and application of it is the membrane fouling by its poor hydrophilicity.Graphene oxide is strongly hydrophilic because it has a large specific surface area and contains a large number of hydrophilic functional groups,and so make it a good material of hydrophilic inorganic addition.In this paper,GO/PVP/PVDF composite ultrafiltration(UF)membrane were prepared with polyvinylidene fluoride(PVDF),polyvinylpyrrolidone(PVP),graphene(GO)by general phase inversion method,and so improving the hydrophilicity and anti-fouling properties of PVDF membranes.The main conclusions are as follows.(1)The graphene oxide(GO)was prepared through a modified Hummers’ method,and its microstructure,chemical structure and dispersion properties were systematically analyzed.Results show that GO is a monolithic structure or a stack of several monolithic layers,and the thickness of GO monolithic layer prepared in this study is about 1.5 nm.The graphene is strongly hydrophilic because there are a large number of hydrophilic functional groups including C=O,-COOH,C-OH,etc on the surface and edge,and this also increased layer spacing.The graphene oxide has a good dispersibility in water,DMAc and PVP,the above properties have laid a foundation for the preparation of GO / PVP / PVDF composite ultrafiltration membranes.(2)Used the graphene nanoparticles to modify the hydrophilic of PVDF membrane.The effect on the membrane chemical structure,contact angle,membrane surface zeta potential,mechanical strength,porosity,average pore size and permeability were investigated when the GO additions are 0,0.1,0.3,0.5,0.7 wt%respectively.The results show:The mechanical strength of the composite membrane is largest when the addition amount of GO is 0.3 wt%,indicating that the proper amount of GO nanoparticles can improve the mechanical strength of the membrane effectively;The results of infrared spectroscopy show that the content of hydrophilic groups in the composite membrane increased effectively,the contact angle decreased from 74.61?(M0)to 66.39?(M2),so the membrane hydrophilicity was enhanced;The Zeta potential of the membrane show that the charge of the composite membrane increased so the electrostatic repulsion of the membrane increased,which improved the ability of anti-pollution.The addition of GO can effectively improve the porosity and average pore size of the composite membrane,and enhance the permeability of the composite membrane in a degree.(3)The membrane cross-sectional structure,surface morphology,and roughness were observed by scanning electron microscopy(SEM)and atomic force microscopy(AFM).SEM results show that the membrane structure became composite asymmetric,composed of cortex and finger holes,the structure of finger holes were lengthened and wided,and the pure water flux increased by 10-33%;At the same time,results of the two-dimensional,three-dimensional image analysis of AFM show that the composite membrane roughness decreased,reducing the accumulation of contaminants at the depressions of the membrane surface,slowing the membrane pollution.(4)Bovine serum albumin(BSA),sodium alginate(SA)and humic acid(HA)were selected for the three typical contaminants for filtration experiments.The adhesion force between different composite membranes and typical contaminants was quantitatively determined by atomic force microscopy(AFM)which combined with laboratory homemade colloidal probes.The effects of different additions of GO on the membrane fouling were analyzed by combining the macroscopic filtration experiment with the microscopic force analysis.According to the results:GO/PVP/PVDF composite ultrafiltration membrane was used to filter the three typical pollutants.Compared with pure PVDF membrane,the flux reduction of GO/PVP/PVDF composite ultrafiltration membrane was improved and the flux recovery rate increased after cleaning,when the addition amount of GO is 0.3 wt%,the flux reduction rate of the composite membrane was the smallest and the flux recovery rate was the highest,indicating that the addition of GO can improve the anti-pollution ability of the composite membrane effectively.The forces between GO/PVP/PVDF-contaminants were smaller than that between PVDF-contaminants because the addition of graphene oxide not only enhanced the membrane’s hydrophilicity but also increased the charge of membrane,therefore,the hydration and electrostatic repulsion of the composite membrane were enhanced,which improved the composite membrane anti-pollution ability effectively.Compared the results of macroscopic filtration test and microscopic force test,the change of forces between membrane and pollutants were consistent with that of macroscopic filtration experiment,it is shown that GO/PVP/PVDF composite UF membrane has a superior anti-fouling propensities compared to traditional PVDF UF membrane.(5)Comprehensive analysis in the pore structure,membrane physical and chemical properties of GO/PVP/PVDF composite ultrafiltration membrane,macroscopic and microscopic anti-pollution behavior of typical pollutants show: although the performance of the composite membrane is better than that of the pure PVDF membrane,the addition of the GO nanoparticles in the composite membrane is not the more the better,but the amount of the addition of the GO nanoparticles should be controlled within the appropriate range.In this study,when the addition amount of GO is 0.3 wt%,the pore structure,physical and chemical properties and anti-pollution ability of GO/PVP/PVDF composite ultrafiltration membrane are the best,and when the addition amount exceeds 0.3 wt%,the membrane performance decline.