Preparation And Antibacterial Properties Of Silver And Zinc Oxide Nanomaterials

In this dissertation, silver and znic oxide nanomaterials with different sizes and shapes weresynthesized by convenient chemical method in liquid phase. The morphology and structure of theas-synthesized samples were characterized by various modern analytical techniques, and their formationmechanisms were proposed. Their antibacterial behaviors of samples were also evaluated. The mainscopes and results of this dissertation are as follows.1. Preparation and Antibacterial Properties of Chitosan Modified Ag NanoparticlesChitosan modified silver nanoparticles (chitosan–Ag NPs) were synthesized through liquid phasereduction with sodium borohydride (NaBH4) as the reductant and chitosan as the surface modificationagent, respectively. The structure and morphology of the as-prepared nanoparticles were investigated bymeasns of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visibleabsorption spectroscopy (UV-Vis), and Fourier transform infrared spectrometry (FTIR). The results showthat the as-synthesized chitosan–Ag NPs have a face-centered cubic (fcc) crystalline structure, and have anaverage size of8～25nm. The surface of Ag nanoparticles is coated by chitosan with the chemical bondsbetween amino, hydroxyl groups and Ag ions, which make the as-synthezied nanoparticles having auniform grain distribution and good dispersibility in water. The antibacterial properties of chitosan–Ag NPsagainst Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were investigated by disc diffusionand broth dilution methods. The results show the as-synthesized chitosan–Ag NPs exhibit goodantibacterial properties against E. coli and S. aureus. The grain sizes of nanoparticles have a remarkableeffect on the antibacterial properties. Generally, under a certain condition, the antibacterial effect is betterwith the size decreasing. Meanwhile, it can be found that the excellent antibacterial property is due tosynergistic effect from Ag and chitosan.2. Preparation and Antibacterial Properties of Triangle Silver NanoplatesIn the presence of seeds, triangle Ag nanoplates and nanospheres were synthesized by liquid chemicalreduction method with L-ascorbic acid as reductant, polyvinyl pyrrolidone (PVP) as surface modificationagent, respectively. Characterizations of the particles were achieved by various techniques such as XRD,TEM, UV-Vis, FTIR, Atomic Force Microscope (AFM) and thermogravimetry and differential thermal analysis (TG&DTA). The antibacterial properties of the samples against Escherichia coli (E. coli) andStaphylococcus aureus (S. aureus) were investigated by disc diffusion and broth dilution methods. Theresults show that the morphology of the as-prepared silver nanoparticles varies with the aging time, theaddition amount of PVP and seeds. Through controlling the aging time, triangle Ag nanoplates andnanospheres with uniform particles sizes and morphologies are obtained, and exhibite a stable dispersibilityin water. Meanwhile, the formation mechanism was proposed, it is suggested that PVP and sodium citrateadsorbing onto a crystal surface of Ag may lead to the formation of triangular nanoplates. The antibacterialresults show that Ag nanospheres exhibit better antibacterial properties than that of nanoplates. It may bedue to the remarkable release effect of Ag ions for spherical Ag nanoparticles.3. Preparation and Antibacterial Activity of ZnO Nanoparticles with Different SizesZnO nanoparticles were prepared by direct precipitation method with Zn(NO3)2and NaOH as rawmaterials, and paticles with different sizes were obtained through changing the water content. Themorphology, structure and optical properties of the particles were charactered by means of XRD, TEM,UV-Vis, and room temperature photoluminescence (PL). The results show that the as-synthesized ZnOnanoparticles have a perfect crystallinity, and exhibit a strong absorption band in the ultraviolet region. Theantibacterial properties of particles against E. coli, S. aureus and Pseudomonas aeruginosa (P. aeruginosa)bacteria were also investigated by the inhibition zone method. It can be found that the particles have theoptimal antibacterial effect on P. aeruginosa. Futhermore, the antibacterial property is improved with thedecreasing of the particles sizes.4. Preparation and Antibacterial Activity of Hexagonal ZnO NanoplatesHexagonal ZnO nanoplates were synthesized by solution direct chemical precipitation method. Themorphology, structure and optical properties of the particles were charactered by means of XRD, TEM, PL,TG&DTA and FTIR. The results show that the as-synthesizd porous single crystal nanoplateswere hexagonal wurtzite structure of ZnO. The formation mechanism of the nanoplates was supposed to bethe oriented attachment process. Antibacterial properties of the as-synthesized nanoplates against E. coli, S.aureus and P. aeruginosa bacteria were also tested through the inhibition zone method. The results showthat the antibacterial property is selective, having the optimal effect on P. aeruginosa. It is also found thatthe antibacterial property is improved with the increasing of ZnO concentration. When the concentration is increased to5mg·mL-1, the inhibition zones diameter grows to the largest value.