Study On Preparation And Modification Of PDA Crosslinked Film

As people pay more attention to water resources,water treatment technology has also begun to diversify.Among them,nanofiltration membrane,as a new type of water treatment technology,has many advantages such as high treatment efficiency,low treatment cost,and no secondary pollution after treatment.However,the nanofiltration membranes prepared by the mainstream traditional methods have gradually begun to fail to adapt to the current complex and changeable water environment.Therefore,researchers have begun to explore some new methods and materials to prepare new nanofiltration membranes,thereby expanding the use of nanofiltration membranes.Polydopamine,as a kind of polymer polymerization product,has super strong adhesion,can adhere to almost any solid surface without falling off,and the degree of control of the polymerization itself can be controlled to a certain extent during the film preparation process Controlling the pore size and thickness of the active layer on the membrane surface is a very promising membrane modification material.In this paper,a new type of PDA cross-linked film will be prepared,and at the same time,the PDA cross-linked film will be modified to expand its use value,which has certain innovation.(1)PDA cross-linking membranes with different properties were prepared by cross-linking reaction of polydopamine(PDA)with trimesyl chloride at different self-polymerization times.First,the nano-particle size of the aqueous polydopamine solution was measured and found.With the increase of time,the polydopamine particles will gradually become larger,and can reach more than 5000 nm at 25 h.Subsequently,the infrared,contact angle,and scanning electron microscopy tests on the PDA cross-linked films formed at different self-polymerization times confirmed the polymerization.Dopamine was successfully deposited on the membrane surface.The film performance test found that polydopamine with different deposition time had a greater effect on the film performance,and the PDA crosslinked film formed with the PDA self-polymerization time at 1 hour had the best performance.In addition,through the deposition time of the water phase and the organic phase,it can be found that the deposition of the water phase at different times can affect the thickness and compactness of the active layer formed on the surface of the PDA and thus affect the separation accuracy of the active layer.15 min is best.The different deposition time of the organic phase affects the cross-linking reaction between the PDA and TMC,thereby affecting the density of the active layer formed.The optimal organic phase deposition time determined in this experiment is 30 min.(2)After the acidic carbon nanotubes with better dispersibility are introduced into the polydopamine aqueous phase,a modified PDA crosslinked film is prepared by cross-linking and polymerizing the aqueous phase and the organic phase.The modified PDA crosslinked film was characterized by chemical structure,surface morphology and film properties.Among them,FTIR and XPS proved that the surface structure of the membrane changed,and the decrease of the water contact angle indicated that the hydrophilicity of the membrane surface was improved.However,subsequent filtration experiments on the membrane revealed that although the water flux of the modified PDA cross-linked membrane was greatly improved,the retention rate of the modified membrane was reduced from more than 80% to about 50%,and the acidified carbon was changed.The solubility of nanotubes cannot improve the rejection rate of the modified membrane.The reason for this may be that the environment in which the polydopamine aqueous solution is still present is somewhat alkaline.The addition of acidified carbon nanotubes will change the acid-base environment of the aqueous solution to a certain extent,thereby inhibiting the dopamine self-polymerization.The cross-linking reaction has an effect.(3)In order to further improve the biofouling resistance of the PDA crosslinked film,thereby improving the feasibility of commercialization of the PDA crosslinked film,the actual use of the reducibility and stable adhesion of polydopamine in the PDA crosslinked film Nano-silver particles were introduced to modify the PDA cross-linked film,and the existence of nano-silver particles on the surface of the film was confirmed by XPS characterization.The contact angle measurement of the film revealed that the hydrophilic nature of silver would also make the surface of the modified film The hydrophilicity is improved.In order to determine the antibacterial property of the membrane,an adsorption experiment on E.coli was performed on the membrane and it was found that the surface of the modified membrane doped with nano-silver has strong bactericidal performance,but the sterilization of the unmodified membrane is weak.The anti-protein adsorption experiments on the membrane showed that the water flux of the modified membrane decreased more slowly than that of the unmodified membrane,and the water flux of the modified membrane returned to 60% after the membrane was washed with pure water.Above,the water flux of the unmodified membrane is only about 40-50%.