Antibacterial Study Of Ag/graphened Nanocomposites Synthesized With Grape Seed Extract

Conventional organic antibiotics are not able to inhibit the propagation of bacteria cells completely due to bacteria resistance.Thus,some functional nanomaterials have been intensively attracted more and more attention which has wonderful antibacterial activity.Ag nanoparticles（Ag NPs）have been studied for more than 100 years as an antibacterial material.It is well known that Ag NPs can act on microorganisms,disrupt the cellular membranes of them and inhibit the DNA reproduction.Then the propagating number of microorganism can be controlled which results in cell death.However with the development of study,the researchers found that Ag NPs are oxidized easily and can aggregate in the liquid environment.Further more,lots of byproducts and wastes are produced during the process of chemical synthesis,which may leave a certain effects on the environment.These defects have become the most restricted factor for the study on antibacterial application.As a new type of nano material,graphene oxide（GO）has a large number of reactive oxygen-containing groups（–OH,–COOH）on its basal plane,which has good stability and excellent biocompatibility.At the same time,GO has the characteristics of large specific surface area and significantly broad antimicrobial activity,which can be complexed with Ag NPs to improve the stability and antibacterial properties of Ag NPs.In this paper,we synthesized Ag NPs by a green and simple method and the rape seeds extract was used as synergistic reducing agent.Then the product was complexed with two-dimensional（2D）sheet of graphite nanocomposites.The antibacterial properties of the composites were also studied.（1）The GO/Ag composites with excellent antibacterial properties were prepared by “one pot” green method.AgNO3 was used as the source of Ag in the synthesis of Ag NPs and grape seed extract was used as reducing agent and stabilizer.The GO/Ag composites were characterized by UV-vis,XRD,TEM,FT-IR and Zeta-potential,its antibacterial properties were also studied.The results showed that the silver ions were reduced to Ag NPs by grape seed extract,and the Ag NPs was loaded on the surface of GO nanosheets successfully,the average particle size of Ag NPs was 40-50 nm.The antibacterial properties of GO/Ag changed significantly with the concentration of AgNO3.The data showed that GO/Ag had better antibacterial activity when the concentration of silver nitrate was 2 mM.Moreover,the minimum inhibitory concentration of GO/Ag could reach 23.8 g/m L,lower than Ag NPs of 25.5 g/m L which reflected the excellent antibacterial properties of GO/Ag and the synergistic antibacterial effect of two kinds of materials.（2）As with GO,graphitic-phase C₃N₄（g-C₃N₄）has two dimensional（2D）nano sheet structure.In this paper,g-C₃N₄/Ag nanocomposites were prepared via economical and green method by using grape seed extract as the reducing agent and stabilizer,the antibacterial activity against four kinds of clinical pathogenic bacteria were also investigated.The prepared g-C₃N₄/Ag nanocomposites have better antibacterial properties than Ag NPs and its germicidal effect on gram-negative was better than that on gram-positive.Bacterial angular leaf spot caused by Pseudomonas syringae is an important reason for the reduction of cucumber output.In this study,g-C₃N₄/Ag was used as an active substance,its antibacterial activity against Pseudomonas syringae was studied.Then the integrity of cell membrane was observed by optical microscope and TEM,the antibacterial mechanism was also demonstrated.Studies have shown that when g-C₃N₄/Ag entered into the bacterial membrane,the activated oxygen was formed and destroied the integrity of the cell,then the bacteria was killed.In addition,g-C₃N₄/Ag was used as the active substance and physiological saline was used as control,and then applied them to the cucumber leaves respectively.The results showed that there were no spots on the leaves of cucumber with g-C₃N₄/Ag,while the cucumber leaves with normal saline showed yellow spots,which indicated that g-C₃N₄/Ag could inhibit the occurrence of bacterial angular leaf spot.That is to say,g-C₃N₄/Ag nanocomposites have good potential application in the treatment of plant bacterial diseases.（3）In this study,Ag/Ti O₂ nanocomposites were prepared by grape seed extract with a two-step synthetic method.Grape seed extract was used as the reducing agent and stabilizer.The Ag/TiO₂ composites were characterized by UV-vis,XRD,TEM,FT-IR and Zeta-potential,the antibacterial properties were also studied.The results showed that the AgNO3 was reduced to Ag NPs and loaded on TiO₂ nanosheets.The effective functional groups of grape seed extract were modified on Ag/TiO₂ nanocomposites successfully.When the concentration of silver nitrate was 3 mM,the bacteriostatic effect of Ag/TiO₂ was the best,and the minimum inhibitory concentration（MIC）and the minimum bactericidal concentration（MBL）were 1.2478 μg/m L and 4.9915 μg/m L respectively.Compared with merely Ag NPs,the Ag/TiO₂ nanocomposites have better antibacterial properties.In addition,the antibacterial activity of Ag/TiO₂ under light and dark conditions was also studied.The data showed that the Ag/TiO₂ had better antibacterial activity.