| Microfiltration membranes are often used to remove microorganisms in the fields of food processing,medicine and biochemical pharmaceuticals,etc.However,microbial fouling is still a major problem in their applications.In this paper,by using modern dopamine biomimetic adhesion chemistry and controlled/"living"RAFT radical polymerization reaction,the surface of the microfiltration membrane with dual functions of active anti-bacterial and passive anti-adhesion was constructed to alleviate biofouling during membrane operation.（1）Firstly,a highly effective,stable and non-toxic polydimethylaminoethyl methacrylate-butylammonium bromide PDB was used as active an-tibacterial agents,and polysulfobetaine zwitterionic polymer PSB with excellent hydration ability as passive anti-adhesive component,by two-step RAFT polymerization,PSB-b-PDB block polymer was prepared.Using polydopamine as a secondary reaction platform and grafting PSB-b-PDB to the commercial PVDF membrane by Michael addition reaction under the action of Na BH4 to construct a membrane surface with the layered polymer brush,the lower layer of the polymer brush was an anti-adhesion zwitterionic polymer brush,and the upper layer was an antibacterial quaternary ammonium polymer brush.The functional polymer brush was constructed to endow the membrane active anti-bacterial and passive anti-adhesion properties.It was found that the hydrophilicity of the modified membrane was significantly improved,the initial water contact angle changed from 128°for pure membrane to 44.6°,and dropped to0°in 10 s,the isoelectric point of the modified membrane was p H=6.9,and the water flux measured at 0.02 MPa was 1.61 times larger than that of the pure membrane.At the same time,the modified membrane antibacterial rate of E.coli and S.aureus was 98.3%and 98.7%,respectively.During the bacterial solution separation experiment,the E.coli solution flux of modified membrane was 1.61 times that of pure membrane,and the water flux recovery was 73.2%,while the recovery of the pure membrane was only 42.0%.（2）The positive charge density of the quaternary ammonium salt on the membrane surface will affect the anti-bacterial and anti-adhesion properties of the membrane.The higher the positive charge density,the stronger the bacteria with negative charge will adhere to the membrane surface.In order to balance the relationship between anti-bacterial and anti-adhesion,and further improve the anti-biofouling ability of the membrane,the synthetic hyperbranched polyacrylmorpholine（HPA）was used as a hydrophilic modifier,and the quaternary ammonium dimethylaminoethyl acrylate-dodecylammonium bromide（DMAEA-DB）as an active bactericide.Using dopamine biomimetic adhesion-mediated Michael addition reaction,the HPA coating was grafted to the microfiltration membrane,and then the efficient click chemistry reaction of thiol-ene was used to bond the antibacterial quaternary ammonium DMAEA-DB to the membrane surface to prepare a modified membrane with low positive charge density,high efficiency active anti-bacterial/passive anti-adhesion properties.It was found that the hydrophilicity and permeability of the modified membrane were significantly improved compared with the pure membrane,and the isoelectric point of modified membrane was p H=5.8.At the same time,the modified membrane exhibits excellent antibacterial properties,the antibacterial rate against E.coli was 90.2%,and the antibacterial rate against S.aureus was 96.1%.In the bacterial solution filtration experiment,the modified membrane has a lower flux attenuation,and the water flux recovery was82.0%,showing excellent anti-bacterial and anti-adhesion properties. |
