Synthesis And Antimicrobial Activity Of Polyethyleneimine Modified Silver-based Nanocomposite

The antibiotics resistance of bacteria represents one of the most serious threats to public health in the 21^st century,urging scientists to develop a new type of green and effective antibacterial material.Two-dimensional nanocomposite decorated with various silver nanoparticles(Ag NPs)have received tremendous attention due to their antibacterial activity and biocompatibility.However,they tend easily to aggregate in the solution and the antibacterial performance only depends on the release of Ag ions(Ag⁺).Therefore,in this dissertation,two-dimensional nanomaterials including graphene oxide(GO),reduced graphene oxide(r GO)and graphite phase carbon nitride(CN)were used as carriers,and polyethyleneimine(PEI)with antibacterial activity was used as a surfactant.Then Ag NPs were loaded to further enhance the antibacterial properties of the two-dimensional nanomaterials.We focus on the preparation of different materials including Ag/PEI/GO antibacterial,Ag/PEI/r GO antibacterial and Ag/PEI/CN photocatalytic antibacterial,the investigation of the antibacterial performance(minimum inhibitory concentration,minimum bactericidal concentration,etc.),the study of the effect of PEI as a surfactant on the antibacterial properties of the material,as well as the proposal of the antibacterial mechanism.The main contents of this research are as follows:(1)GO matrix was successfully prepared with flake graphite as raw material using the modified Hummers'method.In order to further enhance the antibacterial activity of GO,PEI with antibacterial activity was chosen as the surfactant and N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride(EDC·HCl)as the activator to prepare the PEI/GO matrix nanomaterial.Then silver nitrate(Ag NO₃)was used as silver source and sodium borohydride(Na BH₄)was used as a reducing agent to prepare Ag/PEI/GO antibacterial nanomaterial by a simple in-situ reduction method.The Ag NPs with an average particle size of 18.1 nm were uniformly deposited onto the PEI/GO nanosheets.Through the antibacterial performance test,it was concluded that the Ag/PEI/GO nanomaterial showed good antibacterial performance.When Ag/PEI/GO acted on E.coli,the minimum values of the inhibitory concentration(MIC)and bactericidal concentration(MBC)were 120 ppm and 70 ppm,respectively.(2)In order to simplify the reaction and reduce the size of Ag NPs particles to further improve the antibacterial activity of the material,a simpler hydrothermal method was used to successfully couple PEI on the surface of r GO,and a water-soluble PEI/r GO matrix nanomaterial was prepared.Then Ag NO₃ was used as silver source and Na BH₄ was used as a reducing agent,and the Ag/PEI/r GO antibacterial nanomaterial was prepared by a simple in-situ reduction method in an ice bath.The Ag NPs with an average particle size of 9.8 nm were uniformly deposited onto the PEI/r GO nanosheets,which was beneficial to improve the antibacterial performance.Through the antibacterial performance test,it was found that the antibacterial activity of Ag/PEI/r GO was significantly higher than that of Ag/r GO antibacterial nanomaterials,which proved that PEI can effectively enhance the antibacterial activity of nanomaterials.When Ag/PEI/r GO acted on E.coli,the MIC value was 30 ppm,while the MBC value was 20 ppm.When S.aureus was used,the MIC and MBC values were recorded to be 50 ppm and 40 ppm,respectively.Under the action of PEI,the antibacterial nanomaterials also showed good stability.(3)Compared with GO,CN demonstrates good photocatalytic and antibacterial activity.CN was employed as the matrix material to further improve the antibacterial properties.As a surfactant,PEI can be successfully grafted onto CN by electrostatic adsorption.Then Ag NO₃was used as silver source and Na BH₄ was used as the reducing agent,and the Ag/PEI/CN antibacterial nanomaterial was prepared by a simple in-situ reduction method in an ice bath.The Ag NPs with an average particle size of 10.8 nm were uniformly deposited onto the PEI/CN nanosheets,which is favorable for improving the antibacterial effect of CN.It was also found that Ag/PEI/CN composites exhibited better antibacterial activity under light conditions with MIC and MBC values of less than 30 ppm and 10 ppm,respectively.Compared with CN,Ag/CN and Ag/PEI,Ag/PEI/CN showed better photocatalytic degradation performance.It is supposed that loading Ag onto PEI/CN can enhance the light adsorption and inhibit the recombination of photogenerated carriers.Therefore,under light conditions,together with the synergistic effect of Ag⁺produced by Ag NPs,the reactive oxygen-containing species(ROS)generated by CN and PEI contributed to the antibacterial performanmce.