Preparation And Antibacterial Properties Of Water-soluble Sliver Nanomaterials

In this dissertation, water-soluble silver nanomaterials were synthesized by chemical reduction method in liquid phase, and the oxide loaded Ag nanomaterials with hybrid structure were also prepared. The morphology and structure of the as-synthesized samples were characterized using with various modern analytical techniques. Their antibacterial behaviors were also evaluated. The main scopes and results of this dissertation are as follows.1. Preparation and Antibacterial Properties of Water-soluble Ag NanoparticlesWater-soluble surface modified silver nanoparticles were synthesized by liquid phase reduction with tannic acid as the reductant and polyvinyl pyrrolidone (PVP) as the surface modification agent. The structure and morphology of the as-synthesized powders were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible absorption spectroscopy (UV-vis), and Fourier-transform infrared spectrometry (FT-IR). The antibacterial activity of the water-soluble Ag nanoparticles against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was investigated by broth dilution. The stable dispersion duration of the as-synthesized Ag nanoparticles in water was also determined. A mechanism for PVP modified Ag nanoparticle formation is proposed. The results show that the as-synthesized PVP modified Ag nanoparticles have a face-centered cubic crystalline structure. The average diameter of the Ag nanoparticles ranges from 15–17 nm. The as-synthesized powders have good solubility in water over a long period of time. PVP modified Ag nanoparticles exhibit good antibacterial properties against E. coli and S. aureus. This simple and mild preparation method can be easily increased to an industrial scale process and, therefore, PVP modified Ag nanoparticles are potentially a new type of antibacterial.2. Synthesis and Antibacterial Properties of Silver NanodendritesA simple, green method was developed for the synthesis of silver nanodendrites by an aqueous chemical route. This method involves the reduction of silver nitrate with absolute alcohol using PVP as the surfactant. UV–vis absorption spectra, XRD and Energy dispersive spectrometry (EDS) suggest the formation of Ag nanoparticles. TEM images show the shape and sizes of the nanoparticles. During the synthesis, it was found that the morphology and size distribution of the as-prepared silver nanoparticles varied with the concentration of the precursor metal salts, reaction time and surfactant ratios. The formation mechanism of Ag nanodendrites was determined based on the investigation of the above reaction parameters. Simple methods, nontoxic chemicals and environmentally benign solvents make this synthesis ideally suited for industrial production. The minimum inhibitory concentration (MIC) values of the as-synthesized powders against E. coli and S. aureus were also tested.3. Preparation and Antibacterial Activity of SiO₂@Ag Hybrid NanoparticlesSilica particles were deposited with Ag nanoparticles to achieve hybrid structure by a simple in situ chemical reduction method. Firstly, silica nanoparticles using 3-mercaptopropyltrimethoxysilane (MPS) as the sole silica source were synthesized successfully by a St(?)ber method at room temperature,The average diameter of the silica nanoparticles prepared was about 190.2 nm. Secondly, organic silica nanoparticles deposited with silver (SiO₂@Ag) were synthesized by the in situ reduction of AgNO3 on the surface of SiO₂ at the present of reducing agent. The structure and morphologies of SiO₂@Ag hybrid nanoparticles were investigated through UV-vis, TEM, XRD and X-ray Photoelectron Spectroscopy (XPS), etc. Antimicrobial activity studies were carried out on both Gram negative (E. coli) and Gram positive (S. aureus) bacterial strains. The results show that the as-synthesized SiO₂@Ag hybrid nanoparticles exhibite better antibacterial properties against E. coli and S. aureus bacteria than that of the commercially available drug, namely Benzylpenicillin sodium powder.4. Preparation and Antibacterial Activity of Fe₃O₄@Ag hybrid nanoparticlesFe₃O₄@Ag hybrid nanoparticles were synthesized by an in situ chemical reduction method. Firstly, Fe₃O₄ nanoparticles were synthesized successfully in water by hydrolyzation of iron salts. This method was very simple, and had advantages of being processed without high temperature and the protection of inert gases, and all the chemical agents used were inexpensive, environmentally benign and nontoxic. Secondly, Fe₃O₄ nanoparticles were surface modified by reaction with polyacrylic acid (PAA). Thirdly, Fe₃O₄@Ag hybrid nanoparticles were synthesized by the reduction of AgNO3 on the surface of Fe₃O₄ at the present of reducing agent. The structure and morphology of the as synthesized hybrid nanoparticles were investigated by Uv-vis, TEM and XRD, etc. The formation mechanism of Fe₃O₄@Ag hybrid nanoparticles was analysed. Antibacterial properties of the as synthesized Fe₃O₄@Ag hybrid nanomaterials against E. coli and S. aureus bacteria were also tested. The results showe that the average diameter of the Fe₃O₄ nanoparticles prepared is about 100 nm, the sizes of Fe₃O₄ nanoparticles were homogeneous, and the particles disperse well without aggregation. The as synthesized Fe₃O₄@Ag hybrid nanoparticles exhibite good antibacterial properties against E. coli and S. aureus.