Controllable Preparation Of Silver Nanoparticles And Its Antibacterial Property

Silver nanoparticles (Ag NPs) have the advantages of the broad-spectrum antibiosis and high security. The properties and function of Ag NPs mainly depend on their shape and size, so the controllable preparation of Ag NPs has become one of the focuses of research recently. In this paper, the chemical reduction method in aqueous solution was used, with glucose as the reducing agent, chitosan as the stabilizing agent and silver nitrate as silver source. The influence factors of the reaction were investigated and the controllable synthesis of Ag NPs was proposed. Finally the antibiotic properties of Ag NPs was studied.In this work, based on the one-factor experiments the effects of the reaction conditions of the solution chemical reduction had been investigated by the ultraviolet-visible spectrophotometry, X-ray diffraction and transmission electron microscopy (TEM). A temperature of ca.60℃ and a reaction solution of pH=7.30-8.30 were effective to obtain stable Ag NPs colloid with smaller size. TEM micrographs confirmed that the Ag NPs were all spherical with a very narrow size distribution. The results of Fourier transform infrared spectroscopy (FTIR) indicated that the chitosan protected the Ag NPs from agglomeration and growth by coordinating N with the silver. When the weight ratio of chitosan to AgNO3 is 980, a good stability of the Cts-Ag NPs colloids was obtained,The second part of the thesis explored a simple method of controllable preparation of Ag NPs in water phase. Through adding Ag NPs with different size as Ag0 seed in the solution chemical reduction system, a series of spherical Ag NPs with different size had been obtained. With the increasement of the seed size, the size of Ag NPs raised correspondingly from 6 nm,9 nm, up to 25 nm steadily. Keeping Ag at lower concentration through the grow process of Ag NPs had been considered of the key in the controllable synthesis of Ag NPs.The third part of this thesis studied the antibacterial activity of Ag NPs by Optical Density 600 and explored the antibacterial mechanism. Antimicrobial test results showed that Ag NPs were found to exhibit good antibacterial activity against S.aureus, especialy to E.coli. At the same concentration, the antibacterial property of Ag NPs decreased sharply with the increasement of their particle size, due to that smaller Ag NPs had more surface area and ratio of surface atoms which was beneficial to the adsorption of Ag NPs in the surface of the cell wall to destroy. Antibacterial activity to the same bacteria of Ag NPs with the same size increased continuously with the increasement of the silver content. Compared with PVP-Ag NPs, AgNO3 and chitosan, the Cts-Ag NPs had the best antibacterial property.