Preparation And Performance Characterization Of High Performance With Antifouling PVDF Ultrafiltration Membranes

Membrane separation technology is an emerging technology which takes separation membrane as the core to separate,concentrate and purify substances.It is an economic,environmental and efficient separation method.At present,polyvinylidene fluoride(PVDF)has become one of the most popular membrane separation materials due to its advantages of chemical stability,mechanical strength and membrane formation properties.However,its high hydrophobicity and susceptibility to protein pollution of PVDF membrane,its lifetime is reduced and replacement cost is increased,which limits the further application in the field of water treatment.Therefore,how to reduce membrane fouling has become a hot spot in membrane technology.The introduction of hydrophilic materials and inorganic nanomaterials can significantly improve membrane performance.The surface of the graphene oxide(GO)carbon layer has abundant hydrophilic oxygen-containing functional groups,large specific surface area and strong surface modifiability,which can be used as an ideal hydrophilic inorganic additive to improve membrane performance.Perfluorosulfonic acid(PFSA)has excellent chemical resistance,thermal stability,mechanical properties and oxidation resistance,which is widely used in fuel cells,chlor-alkali,catalysis,etc.PFSA has hydrophilic terminal sulfonate groups,which can improve the hydrophilicity of PVDF membranes.In this thesis,GO was prepared using the modified Hummers method.PFSA-g-GO nanocomposites were firstly prepared by PFSA grafted on GO in various mass ratios through esterification reaction.Then a series of PVDF/PFSA-g-GO ultrafiltration(UF)membranes was constructed by a non-solvent induced phase separation(NIPS)method using PVDF as polymer,the obtained diverse PFSA-g-GO nanocomposites as additives in different dosages,polyvinylpyrrolidone(PVPK30)as a porogen and N,N-dimethylacetamide(DMAc)as solvent.PFSA-g-GO nanocomposites and PVDF/PFSA-g-GO membranes were characterized by X-ray diffraction(XRD),Thermogravimetric analysis(TGA),Fourier transform infrared spectroscopy(FT-IR),atomic force microscope(AFM),scanning electron microscope(SEM)and water contact angle,etc.The bovine serum albumin(BSA)and humic acid(HA)were chosen as model system to examined UF membranes performance.The results indicated that compared with PVDF membrane,the permeability and the antifouling performance of proposed PVDF/PFSA-g-GO membranes were enhanced.For example,the pure water flux of M4membrane was up to 587.4 L/m~2·h(PFSA/GO mass ratio of 2.5:1,fraction of PFSA-g-GO in dope solution of 0.5wt%),which was 1.5 times that of PVDF membrane,the rejection of BSA and HA was up to 93.9%and 79.6%,respectively.Compared with PVDF membrane,after membrane fouling and simple surface cleaning,the flux recovery(FRR)of M4membrane was still quite high after two cycles,up to 82.3%,which was 17.7%higher than PVDF membrane.Secondly,in order to improve the structure and performance of the membrane and make the added hydrophilic nanocomposites not easy to fall off in the membrane,in this thesis,PEG was grafted on GO to obtain hydrophilic PEG-g-GO nanocomposites.PVDF-OH was obtained by Fenton reaction of PVDF powder,and the obtained PEG-g-GO nanocomposites were grafted on PVDF-OH through the hydrogen bond to obtain hydrophilic PVDF-OH-PEG-g-GO membrane.The obtained membrane was characterized by FT-IR.The porosity,pore size,surface hydrophilicity and permeability of the constructed PVDF-OH-PEG-g-GO membranes with different contents of PEG-g-GO nanocomposites were investigated.The separation and antifouling performance of membrane were examined using BSA as a model system.The results showed that the hydrophilicity,permeability and antifouling performance of the membrane were improved to some extent.For example,when the content of PEG-g-GO nanocomposite was 0.1wt%,the contact angle of PVDF-OH-PEG-g-GO membrane was smaller than that of PVDF,the membrane hydrophilicity was improved.The water flux was up to 113.8 L/m~2·h,which was 2.35 times of PVDF membrane.The FRR of pure PVDF membrane was 84.7%.The FRR of PVDF-OH-PEG-g-GO membrane with 0.1wt%PEG-g-GO composites was 9.4%higher than that of PVDF membrane.