| Silver nanoparticles of stable dispersions have been used mostly in areas such asphotography, catalysis, biosensor, photonics, optoelectronics, surface-enhanced Ramanscattering (SERS) detection and antibacterial. Many studies have demonstrated a closerelation between the properties of silver nanoparticles and their sizes, shapes and sizedistributions. Thus, to tailor silver nanoparticles with novel properties, it has been one offocuses that how to control deliberately the nucleation and growth of silver nanoparticles.Nowadays, microbes have a stronger and stronger resistance to traditional antibiotic, so ithas great practical significance to study nano-silver with a strong, broad-spectrumantibacterial activity and difficult to generate resistance. The development of silverantimicrobial materials was reviewed, and the antimicrobial mechanisms of nano-silverand silver ions were introduced, respectively. The antibacterial property of nano-silverdepened on morpholopy, size and size distribution. The smaller for size and moreuniform for size distribution, the stronger the antibacterial activity of silver particles is.Then, it have been explored in detail on how to synthesize the silver nanoparticles withsmall size and uniform size distribution.by an easy, fast and green method. The workmainly includes the following aspects:AgNO3, [Ag(NH3)2]NO3 and [Ag(NH3)2]+ complex ion aqueous solutions withoutNO3- were used as precusors, and the colloidal silver nanoparticles were synthesized byUV irradiation of using poly(N-vinyl-2-pyrrolidone) (PVP) as both reducing andstabilizing agents after a little of additive was added, respectively,. The UV-Vis. spectraand transmission electron microscopy (TEM) showed that the nucleation rate of silvernanoparticles was the fastest, smallest in size and most uniform in size distribution andmost stable when [Ag(NH3)2]+ complex ion aqueous solution without NO3- was used asprecursor; [Ag(NH3)2]NO3, the second; and AgNO3, the worst. In addition, the effects ofconcentration of PVP, temperature and pH value to the as-prepared silver sols were investigated using [Ag(NH3)2]+ complex ion aqueous solutions without NO3- as precusor.The results indicated that the nucleation rate of silver nanoparticles increased withreaction temperature and concentration of PVP, however, the rate is almost unchangeablewhen the PVP/Ag+ (weight ratio) was over 10:1. Therefore, it was the best weightratio 10:1 for PVP/Ag+. The tests about the effects of pH values to the nucleation rate ofsilver nanoparticles showed the most appropriate pH value of the precursor solutions was12.68. The silver particles prepared in the most appropriate PVP/Ag+ and pH value werespheric about 1-3 nm in diameter, and no flocculation or deposition appeared even if theywere placed in dark at room temperature for three months.The colloidal silver nanoparticles were synthesized by microwave irradiationreduction method, and the precusors, reductants and additives were all the same as theabove. The effects of precusors, concentrations of PVP, microwave powers and pHvalues to the as-prepared nano-silver sols have been investigated. The results showed thatthe silver ions had the highest conversion ratio using [Ag(NH3)2]+ complex ion aqueoussolutions without NO3- as precursor, 8:1 for PVP/Ag+ (wt ratio), low middle fire formicrowave power and 12.4 for pH value, and the silver particles were about 1-3 nm insize, monodispersion and fine stability.A highly pure nano-silver sols were prepared by electrolysis method using twohighly pure silver flakes as electrodes and deionized water as electrolytic solution, andPVP served as the supporting electrolyte and stabilizer. The effects of content of PVP,electrolytic time and current density to the colloidal silver nanoparticles were researched.The results indicated that as-synthesized particles were spherical about 1-3 nm in size,monodispersion under the condition of 5 wt % PVP with current density 1-2mA/cm2 for150 min, moreover, the silver sol had such an excellent stability that it had not any changethough it was placed in dark at room temperature for six months.The hydrated sodium ions in Na-montmorillonite (Na-MMT) lamellars wereexchanged at 60℃by AgNO3 and [Ag(NH3)2]+ complex ion aqueous solutions without NO3-, respectively. Then the Ag-MMTs were attained by microwave irradiation usingPVP as both reducing and stabilizing agents. The structures of Na-MMT and Ag-MMTswere characterized by XRD, and the distance between two lamellars decreased indicatedthat the exchange had happened between Ag+ ions or [Ag(NH3)2]+ complex ions andNa+,K+ in the lamellars of MMT. The size and morphology of silver particles loaded onthe surface of Ag-MMT were investigated by field emission scan electron microscope(FE-SEM), and results showed the silver particles were spherical about 20-30 nm in size.The Ag contents of the Na-MMT and the Ag-MMTs were analysed comparatively withX-ray Fluorescent probe. Thermogravimetry analysis showed the Ag-MMT had a morestability from [Ag(NH3)2]+ complex ion aqueous solutions without NO3- than fromAgNO3.The antibacterial properties of nano-silver sols, Na-MMT and Ag-MMTs werestudied using E.coli and S.aureus as representative bacteria. The results showed that theminimal inhibitory concentrations (MIC) of nano-silver sols prepared either by UVphotoreduction, microwave irradiation or electrolysis method were all 1.25 ppm, minimalbactericidal concentrations (MBC) all 2.0 ppm, and bactericidal ratios were beyond 99.9%.The Na-MMT had not and antibacterial activity, and the MICs of Ag-MMTs prepared byAgNO3 were 100 ppm and 150 ppm by [Ag(NH3)2]+ complex ion, respectively. Both ofbactericidal ratios were beyond 99.9%. However, the Ag in the Ag-MMT had a betterslow release proterty from [Ag(NH3)2]+ complex ion than from AgNO3. The pledget,laminate wood flooring and boarding film were dealed with as-prepared nano-silver sols,respectively, and the bactericidal ratios of all the products were beyond 99.9% when theconcentrations of nano-silver sols were up to 20 ppm.
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