Preparation And Characterization Of A Novel Anti-biofouling Polyacrylonitrile Composite Nanofiltration Membrane With Cu²⁺ Immobilization

Nanofiltration （NF） membrane as an important part of the Membrane SeparationTechnology has wide development prospects. Therefore, the preparation of NFmembrane with high permeability, high ion selection performance, high anti-bacterialproperties and chemical stability, has become a hot research topic. In this paper, thepolyacrylonitrile （PAN） porous membrane with good hydrophilicity, high chemicalstability and negative charged is chosen as support membrane. First, the PANmembrane is hydrolyzed in aqueous alkali, due to the large amount of—CN of PANmembrane, which can be transformed into—COO-in the process of alkali treatment,so electro-negativity of membrane surface can be enhanced. Positive polymerpolyelectrolyte—polyethylenimine （PEI） as modified material, PEI can be adsordedonto hydrolytic PAN membrane by electrostatic self-assembly. In the experiment,the PEI adsorb on PAN membrane by static-immersion method anddynamic-electrodeposition method, respectively. Then the PAN composite NFmembrane was prepared by crosslinking of PEI with COO-on the Hydrolyzed PANmembrane. In order to enhance the anti-bacterial properties and anti-biofouling abilityof the NF membrane, Cu²⁺with anti-bacterial property is immobilized onto the NFmembrane, because PEI of PAN composite NF membrane contains a large number of—NH₂and—NH—, which can immobilize Cu²⁺by complexation. Finally, the novelanti-biofouling PAN composite NF membrane with Cu²⁺immobilization is prepared.In this article the preparation of NF membrane with high permeability and highseparation performance is first explored. PAN composite NF membrane is preparedby static-immersion method and dynamic-electrodeposition method, respectively.The effects about concentration, time and tempreture in alkali treatment, theconcentration, time and current in PEI processing; the crosslinking agent, concentration, temperature and time in crosslinking treatment are all investigatedrespectively in preparation of the PAN composite NF membrane. Infrared spectrumanalysis shows that PAN membrane hydrolyzed by NaOH solution treatment,—CNchanges into—COO-. Under the condition: the NaOH concentration2.0mol/L,immersion time40min and immersion temperature50℃. For PEI treatment, in thestatic immersion method, the PEI concentration is2.0g/L, immersion time is4h, inthe dynamic electrodeposition method, PEI concentration is1.0g/L, eletro-depositiontime is10min, eletro-deposition current is5mA; In cross-linking treatment, the GAsolution volume fraction is0.5%, reaction time is15h, reaction temperature is50℃;The PAN composite NF membrane with optimal separation performance can beprepared under the satisfied conditons. By comparing static-immersion method anddynamic-electrodeposition method, it can be concluded that, with the electric fieldforce, dynamic-electrodeposition method can self-assembly much more PEI in shortertime in improved high assembly efficiency.Based on the optimized technological conditions, in order to enhance theanti-bacterial and anti-biofouling properties of the NF membrane, anti-bacterial Cu²⁺is chosen to complex with PEI of PAN composite NF membrane. Finally, the novelanti-biofouling PAN composite NF membrane with Cu²⁺immobilization is prepared.Making use of contact angle test, scanning electron microscopy （SEM）, atomic forcemicroscopy （AFM）, energy dispersive Spectrometer （EDS）, anti-bacterial structureand performance test, anti-biofouling performance test and filtered seawaterexperiment to characterize the membrane performance. The results shows that, thehydrophilic polyelectrolyte PEI improves the hydrophilicity of PAN membrane andthe surface roughness decreases at the same time. When the hydrophobic Cu²⁺immobilized on composite NF membrane surface, the hydrophilicity of the membraneshows a small decrease. The PAN composite NF membrane with Cu²⁺immobilizationshows obvious inhibiting effect on Escherichia coli. The PAN membrane as the blankreference, the inhibitory rate of PAN composite NF membrane without Cu²⁺is only7.1%, but the inhibitory rate of PAN composite NF membrane with Cu²⁺immobilization reaches as high as95.7%. PAN composite NF membrane with Cu²⁺ immobilization shows good inhibitory effect on algae and other microorganisms in sixmonths. Membrane stability test shows that the water flux ranges between20.39-21.46L/（m²·h） and salt rejection between77.71%-83.15%to MgCl2solution.Filtering seawater experiment shows that the water flux stabilizes from20.39L/（m²·h）to21.46L/（m²·h）, the salt rejection ranges between58.26%-62.87%, which isvisualizing a broad practical application prospects. In conclusion, the novel NFmembrane has a good separation performance and an excellent anti-bacterial property,which could open a new avenue for the preparation of bacteriostatic-type NFmembranes and expand the application in water treatments.