Preparation And Mechanism Of Anti-Biofouling Ultrafiltration Membrane Functionalized By Poly (Ionic Liquid) Brushes

Membrane separation technology is an advanced technology for material separation,concentration and purification based on membrane materials.Recent decades,as one of the high and new technologies in water treatment process,it has developed particularly rapidly and has been widely used in the fields of pollutant removal and water resource recovery.However,in the process of membrane filtration,membrane fouling seriously interferes with the processing efficiency and service life of the membrane,which becomes an inevitable problem in the development of membrane separation technology.Among them,the biofouling formed by bacteria adhering to and multiplying on the membrane surface is complicated and difficult to completely remove,which seriously damages the performance of the membrane.The preparation of functional antibacterial membrane that can inhibit or kill bacteria can effectively alleviate biofouling in the membrane filtration process.Functionalized antibacterial membrane materials can resist the adhesion of bacteria on the membrane surface or kill bacteria at the initial adhesion stage,reduce the formation of biofilm from the source,and effectively alleviate the biofouling phenomenon on the membrane surface.Strategies to achieve antibiofouling through membrane surface modification can be divided into two mechanisms:increasing hydrophilicity to improve the anti-adhesion ability of the membrane and grafting antibacterial agents to improve the antibacterial ability of the membrane.In this study,a series of poly(ionic liquid)(PIL)brushes grafted polyvinylidene fluoride(PVDF)ultrafiltration membranes(PIL-M)with antibacterial effect were developed to directly kill the bacteria adhered to the membrane surface,so as to control the membrane biofouling;On this basis,the di-block PIL brushes with controllable structure was further constructed to improve the hydrophilicity and antibacterial effect of the functionalized membranes.In addition,the antibacterial mechanism of the PIL-M membrane was explored from two aspects of alkyl chain puncture and electrostatic interaction,and the improvement of anti-biofouling ability of the diblock PIL-M membrane was analyzed from the perspectives of the membrane surface energy and the interaction energy between the membrane and the biofouling layer.The research contents and main conclusions are as follows:1.Using atom transfer radical polymerization(ATRP)method functionalized PVDF membrane with PIL brushes to provide them with anti-biofouling properties.Four functionalized membranes with different alkyl chain lengths(C4-M,C8-M,C12-M,and C16-M)were prepared to explore the relationship between surface structure and antibacterial properties.Results showed that all the PIL-M membranes had antibacterial capabilities with the highest efficiency of 84.6%for the C12-M.Moreover,the antibacterial performance was improved by increasing the ATRP reaction temperature and time.Liposome vesicles were used as the bacterial cell membrane model to evaluate the antibacterial membrane damage mechanism.IL and PIL brushes could damage cell membranes through disrupting the lipid bilayer with longer alkyl chain associated with an enhanced effect.Zeta potential measurements showed that the interference of electrostatic interactions with bacteria also played an important role in the bactericidal mechanism.Moreover,filtration experiments in a cross-flow system and the stability test further indicated that PIL-M membranes have favorable anti-biofouling and longterm performances,with a normalized stable flux increase 39.3%larger than that of the pristine PVDF membrane.2.Using ATRP method to introduce cationic and anionic PIL brushes on the surface of PVDF ultrafiltration membrane,and the controllable structure of di-block PIL brushes was constructed,which make founctionalized membrane have more excellent anti-biofouling performance.The characterizations and properties tests of membrtanes proved that the di-block PIL brushes was successfully modified on the membrane surface and the process had no obvious effect on the surface morphology.Cationic PIL brushes made the surface potential of the membrane move to the positive direction and the hydrophilic have fallen slightly,while the introduction of the anionic PIL brushes made the surface potential move to the negative direction,and the hydrophilic improved.Di-block PIL-M membranes have the broad spectrum of antibacterial activity,and the structure of functionalized membrane is different,the antibacterial and antibiofouling effects will be different.When the surface layer was cationic PIL brushes and the bottom layer was anionic PIL brushes,the antibacterial and anti-biofouling effects of di-block functionalized membrane was the best.In addition,through the determination of the membrane surface energy and the interaction energy between the membrane and the biofouling layer to analyze the change of the anti-biofouling property.Cationic PIL brushes increases the surface energy of the membrane and the interaction energy between the membrane and the biofouling layer,while the anionic PIL brushes layer reduces them,which can resist adhesion of bacteria to a certain extent.