Preparation And Properties Of Orientated CNT/Poly(Vinylidene Fluoride) Composite Ultrafiltration Membranes

Polyvinylidene fluoride(PVDF)polymeric material has stable physical and chemical properties and has an excellent potential application in the water treatment field.However,because of its high hydrophobicity and low surface energy,the PVDF membrane can be polluted by organic matters during the membrane process.Thus,a sharp drop in water flux and a decrease in membrane life-time often happened and restricted its widespread application.The limitation of the ultrafiltration membrane performance includes the hydrophobicity of PVDF and the lack of fast water molecular channels in the bulk membrane.Therefore,improving the hydrophilicity of PVDF water treatment membrane and constructing nano-water molecular channels has become a research hotspot in this field.Carbon nanotubes(CNTs)have a channel structure through which water molecules are transported in the form of high-speed single chains,and CNTs also have excellent mechanical and electrical properties.The study of surface hydrophilized carbon nanotubes is of great significance for constructing PVDF ultrafiltration membrane nano-water channels and anti-fouling properties.In this paper,magnetic nanoparticles(Fe₃O₄)prepared by chemical co-precipitation method were coated on the surface of carbon nanotubes by electrostatic adsorption to prepare magnetic carbon nanotubes.Then,functional end-azide poly(methyl methacrylate)(PMMA-N₃)and end-acetylated poly(polyethylene glycol methacrylate)block PMMA(P(PEGMA)-b-PMMA-alkynyl)were prepared by reversible addition-fragmentation chain transfer(RAFT)polymerization.Finally,magnetic carbon nanotubes'surface was modified by combining copper-catalyzed alkynyl-azide and UV-induced mercapto-alkynyl click-chemistry.mCNTs-g-PMMA and mCNTs-g-b-P(PEGMA)were added to the PVDF dope solution.Orientated CNTs/PVDF composite ultrafiltration membranes were prepared by stable magnetic field environment(?0.65T)and non-solvent-induced phase separation(NIPS)method.The structure and properties of the composite ultrafiltration membranes were characterized.(1)The chemical co-precipitation method and electrostatic adsorption method were combined to establish an effective preparation method for magnetic carbon nanotubes.By combining RAFT polymerization with click chemistry,the compatible PMMA chain can be controllably grafted onto the surface of magnetic carbon nanotubes.XRD,TEM,and VSM showed that the particle size of Fe₃O₄ decreased with the increase of Na OH concentration,and when the concentration of Na OH was 0.05g·m L^-1,the particle size of magnetic particles was the minimum 5nm.The saturation magnetic induction intensity was 20.5 emu/g.FTIR,TGA,and GPC tests showed that PMMA was successfully grafted onto the surface of magnetic carbon nanotubes.When the molecular weight of PMMA was 12457 g·mol^-1,the grafting rate was 26.78%,and the saturation magnetic induction intensity of mCNTs-g-PMMA was 14.6emu/g.(2)P(PEGMA)-b-PMMA-alkynyl was synthesized by RAFT polymerization.The copolymer P(PEGMA)-b-PMMA-alkynyl was grafted onto the surface of magnetic mercapto carbon nanotubes(mCNTs-SH)by a mercapto-alkynyl click reaction initiated by ultraviolet light.The dispersion of CNTs in solvent and polymer matrix could be greatly improved.RAFT reagent structures,PMMA-alkynyl,and P(PEGMA)-b-PMMA-alkynyl were verified by FTIR,gas chromatography,¹HNMR.GPC,VSM,TGA,and TEM analyzed the magnetic response state of mCNTs,the effect of the copolymer with different block content on the graft ratio and the surface morphology of mCNTs.When the molecular weight of P(PEGMA)-b-PMMA grafted onto the surface of magnetic carbon nanotubes reached 17099 g·mol^-1,the maximum grafting rate was 40.2%.Moreover,the surface grafted magnetic carbon nanotubes also showed superparamagnetism,and the saturation magnetic response strength was 10.1 emu/g.(3)mCNTs/PVDF composite ultrafiltration membrane was prepared by NIPS method combining with a magnetic field(?0.65T).The effect of mCNTs additoin on the performance of PVDF composite ultrafiltration membrane was studied.The experimental results show that the performance of the composite membrane by adding mCNTS-g-PMMA-b-P(PEGMA)(a double-layer interface)is better than by adding mCNTS-g-PMMA(a single-layer interface).Compared with mCNTs-g-PMMA/PVDF composite membrane,the mCNTS-g-PMMA-b-P(PEGMA)/PVDF composite membrane,the maximum value of pure water flux increased from 5.37 LMH to 14.78LMH,and the maximum value of BSA protein adsorption decreased from 81.1?g/cm² to 25.7?g/cm²,which is due to the excellent hydrophilicity and anti-protein adsorption performance of PEGMA segments.TEM and XRD shows that the magnetic carbon nanotubes can be arranged in order at a low magnetic field(?0.65T).