| Microfiltration membranes（MF）are commonly used to remove impurities and recover biopolymers such as carbohydrates and proteins,and are often used as a pre-treatment step for protein separation and purification.However,non-specific adsorption of biopolymers on the membrane surface can lead to severe membrane fouling,greatly reducing filtration efficiency and lifespan.Therefore,improving the membrane’s anti-fouling ability has become a hot research topic in MF technology.Increasing the hydrophilicity of the membrane surface is widely believed to effectively suppress the adsorption and deposition of bio-pollutants on the membrane surface,thus enhancing the membrane’s anti-fouling ability.Due to their repeating units with oppositely charged groups,polyzwitterions exhibit an overall neutral charge and have strong hydration in ionic solvents,making them excellent interfacial wetting materials and anti-protein adsorption,proved to be a promising type of anti-fouling material.Here,this study used surface grafting technology and layer-by-layer（LBL）self-assembly technology to graft and adsorb polyzwitterions onto the membrane surface.We analyzed the anti-fouling ability of the modified membrane through static protein adsorption experiments and dynamic anti-fouling experiments,as detailed below:（1）The modifiers selected in this study are[3-（methacrylamido）propyl]dimethyl（3-sulfopropyl）ammonium hydroxide inner salt（SPP）,dopamine（DA）,and polyethyleneimine（PEI）.The PDA/PEI intermediate layer is deposited onto the surface of PET film（PET-M）using a mussel-inspired chemical modification method and a three-layer composite membrane is formed by grafting SPP onto PET-M using surface grafting technology for anti-biofouling purposes.A good intermediate layer can be obtained when the deposition time is 12 hours.By optimizing the performance of PET-M-PSPP by changing the content of SPP grafting,the best performance of the PET composite film can be obtained when the SPP concentration is 4.67 mg mL-1.The contact angle（WCA）decreases from 93.3°of pure PET film to 37.4°.The adsorption amounts of bovine serum albumin（BSA）and lysozyme（Lys）are 2.25μg cm-2 and 3.35μg cm-2,respectively,at an adsorption time of 1 hour,which are only 7.1%and 8.3%of that on pure PET film.The recovery rate of the flux before and after filtering the BSA solution of 1 g L-1 is as high as 92.58%.（2）PSPP copolymer was prepared by free radical polymerization,and then a TA/PSPP bilayer multilayer structure was assembled on the PET-M intermediate layer using the layer-by-layer（LBL）self-assembly technique,with the outer layer being the poly-zwitterionic PSPP.The resulting composite membrane was used for surface anti-biofouling.The number-average molecular weight of PSPP was measured to be 2708 Da,with a polydispersity index of 1.1,indicating a relatively uniform molecular weight distribution.By controlling the number of TA/PSPP bilayers,the performance of the composite membrane was optimized.When 8 layers were assembled,the PET membrane showed excellent hydrophilicity,with a water contact angle of only 37.3°.BSA and Lys adsorption experiments showed that the adsorption amounts after 1h were only 2.68μg cm-2 and 5μg cm-2,respectively,representing only 9.9%and 17.3%of that on pure PET membrane.To investigate the applicability of the LBL self-assembly process to other membranes,nylon 6 was selected as the base membrane for modification.When 8 layers were assembled,the membrane achieved a superhydrophilic state with a WCA of 23.2°,and the flux recovery rate in the 1 g L-1 BSA filtration experiment was as high as 92.89%.Compared to grafting-modified composite membranes,LBL self-assembly modified membranes have slightly inferior protein resistance,but they have the advantages of a simpler preparation process,milder preparation conditions,and lower costs.These results indicate that the LBL self-assembly of the TA/PSPP bilayer on the surface of the microfiltration membrane provides a green and simple approach to improve its anti-biofouling ability. |
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