Study On Preparation And Antibacterial Property Of PDA Modified Nanofiltration Membrane

Based on the hydrophilicity of polydopamine?PDA?,PDA and polyethyleneimine?PEI?co-deposition and step-deposition were used to coat the polysulfone?PSf?membrane.A suitable method was selected to further load copper and silver to prepare an antibacterial membrane.This simple PDA-based membrane surface modification method did not destroy the original physical and chemical properties of the base membrane,but also improved the separation and antibacterial performance of the membrane.It has important reference significance for the study of PSf membrane modification.The study first determined the optimal modification time by analyzing the changes of the contact angle and desalination performance of the membrane with the modification time of the PDA/PEI co-deposition and PDA-PEI step-deposition.The results showed that as the modification time increased,the rejection of the PDA/PEI co-deposition modified membrane increased first and then decreased,the permeation flux decreased first and then slightly increased,and the contact angle had been increasing.Through analysis,8h was selected as the best modification time.At this time,the membrane PDA/PEI-8 had a highest rejection?83.00%?,the smallest permeation flux?9.78L/?m²·h??,and the contact angle reached 68.55°.In the process of PDA-PEI step-deposition modification,PDA was deposited on the surface of the base membrane first.After modification for 8h,the contact angle and desalination performance of the membrane tended to be stable.8h was the best modification time.Then further PEI deposition on the surface,as time increased,the rejection of the membrane first increased and then decreased,and the permeation flux and contact angle gradually decreased.Through analysis,the best time was 8 h after PEI modification.At this time,the contact angle?49.85°?of the membrane PDA-PEI-8 was much smaller than that of the PSf-based membrane?58.30°?,and the rejection reached 95.20%,but the permeation flux was only 3.60L/?m²·h?.By comparing the changes of surface morphology and element composition before and after membrane modification,both deposition methods could successfully deposit cross-linked coatings of PDA and PEI on PSf membrane.However,the crosslinked polymer on the surface of the membrane PDA/PEI-8 was more uniform,and the Schiff base reaction was more likely to occur.The membrane PDA-PEI-8 had a denser surface and was more prone to Michael addition reaction.Both deposition methods reduced the electronegativity of the membrane surface,but the surface isoelectric point?4.05?of the membrane PDA/PEI-8 was higher than the membrane PDA-PEI-8?4.60?.The metals copper and silver were loaded on the basis of the membrane PDA/PEI8.The fixation of silver were fixed by PDA in-situ reduction of Ag⁺,while copper were loaded onto the membrane surface by the coordination action of Cu²⁺and PEI.The XPS characterization confirmed that silver and copper were fixed on the membrane,the silver content on the membrane surface was 1.60%,and the copper content was 1.36%.The dynamic filtration and static immersion experiments showed that the bond between copper and silver and the membrane was getting stronger and stronger.At the same time,through the bacteriostatic circle and colony counting experiment,the membrane PDA/PEI had a slight bacteriostatic effect.After loading copper,the bacteriostatic rate of the membrane reached 48.20%,and the bacteriostatic rate of the membrane after incorporating silver reached 85.60%.