Preparation And Antibacterial Properties Of Silver-based Nanometric Antibacterial Materials

With development of modern science and technology and progress of the society, the demands of people to antibacterial materials will enhance rapidly. It has become an important study topic and attracted a lot of attention in the past years to explore and develop new-type anti-bacterium materials with high efficiency, innocuity and lasting anti-bacterium capacity to control and restrain the growth and reproduction of deleterious bacteria. Due to some notable advantages such as high efficiency, broad-spectrum, low toxin , tastelessness and non-pollution, the silver-based antimicrobial agents has become a preferred field in antibacterial research.The preparations of nanometric silver sols and silver-loaded antimicrobials and their antibacterial activities were studied in this thesis. The morphologies of the antimicrobials were characterized by transmission electron microscope(TEM), scanning electron microscope(SEM) and atomic force microscope (AFM), the optical characteristics were analyzed by ultraviolet-visible spectroscopy(UV-Vis spectra) and Fourier transform infrared spectroscopy(FT-IRs), the structures were evaluated by X-ray diffraction (XRD) and the chemical states of silver in matrix antimicrobials were investigated by X-ray photoelectron spectrum (XPS). The antibacterial activities of the antimicrobials and antibacterial products were characterized by inhibition zone, dilution and immersion. Escherichia coli (E.coli, ATCC25922), Peudomonas eruginosa (P. eruginosa, ATCC27853), Staphylococcus aureus (S. aureus, ATCC25923) and Candida albicans (C. albicans) are employed as models. These as-prepared materrials are proved to have good and long-lived antiseptic property to Gram-positive, Gam-negative bacteria and mildew.The dissertation consists of seven parts:In Chapter 1, a review on an investigation progress of the silver-based anti-bacterial materials has been described.In chapter 2, Ag colloids were prepared by reduction method, in which the silver nitrate, sodium borohydride and tri-sodium citrate, and PVP served as precursor, reductant and stabilizer, respectively. The synthesized colloids have potent antibacterial activity toward both gram-positive and gram-negative bacteria. Further studies demonstrated that the Ag nanoparticle distribution was uniform by UV-Vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and atom force microscopy (AFM).In chapter 3, Ag/PVA nanocomposites were prepared by in situ reduction method, in which the silver nitrate, sodium borohydride and poly (vinyl alcohol) (PVA) acted as precursor, reductant and stabilizer, respectively. The synthesized composites have a high antibacterial activity toward both gram-positive and gram-negative bacteria. PVA molecules effectively protected silver nanoparticles to avoid aggregation of the particles so that prepared silver nanopartilces were of small grain size, well-dispersive and stable in aqueous solution.In chapter 4, stable Ag colloids were prepared by a simple process with polyethylene glycol (PEG) as an environmentally benign reducing agent and stabilizer, with water as green solvent. The structural and spectral analyses have showed a uniform size distribution with an average grain size less than 10 nm. The PEG-stablized colloids showed a high antibacterial activity toward gram-positive, gram-negative bacteria and fungi.In chapter 5, the stable Ag/SiO₂ nanocomposites were prepared simply by an immersion method. The Ag/SiO₂ nanocomposites were characterized by UV–vis spectra, transmission electron microscopy (TEM) and atom force microscopy (AFM). The antibacterial experiments demonstrated the nanoparticles had a high and long-lived antibacterial activity toward gram-positive and gram-negative bacteria.In chapter 6, the mesoporous nanocomposites Ag/MCM-41 were prepared respectively by a one-route procedure and a two-route one. Structural analyses have showed that nanoscale silver particles uniformly distributed inner the holes and on the surface of MCM-41 matrix. High antibacterial activities toward gram-positive and gram-negative bacteria attributed to conjunct actions of Ag+ ion and silver nanoparticles.In chapter 7, the mesoporous Ag/SBA-15 nanocomposites were prepared by a two-step procedure. The Ag/SBA-15 nanocomposites were systemically characterized by UV–vis spectra, transmission electron microscopy (TEM), atom force microscopy (AFM) and so on. The antibacterial activity of the Ag/SBA-15 nanocomposites was also studied. The results showed that the sample has high antibacterial activity toward gram-positive and gram-negative.