| An anaerobic bacterium resistant to silver was isolated from petroleum wastewater of Daqing oil field using the method of silver nitrate concentration gradient. The strain was identified by morphological observation and molecular biology method and it was used as a biological material to synthesis Ag/AgCl composite nanoparticles. The nanoparticles were characterized by UV-vis spectrum, X-ray diffraction (XRD), Transmission electron microscopy (TEM), high-resolution transmission electron microscope (HRTEM), Fourier transform infrared spectroscopy (FTIR), etc. In this work, both the reaction conditions and catalytic properties of Ag/AgCl composite nanoparticles are studied.This study open a new route for biosynthesis of metal nanocomposites.The main experimental contents are as follows:(1) Screening an anaerobic bacterium resistant to silverAn anaerobic bacterium resistant to silver was isolated from petroleum wastewater of water treatment stations in Daqing oil field using the method of silver nitrate concentration gradient. The result of morphological observation showed that most of its colonies present oval, black, translucent, neat, smooth surface appearance. The result of microscope observation showed that it was a Gram-negative bacteria, a short rod, about 1.0～1.6 μm×0.2～0.8 μm in length, motive, no spores.Results of physiological and biochemical test showed that the optimum growth temperature and pH values for strain were 37℃ and 8.0,respectively.The strain could use L-linalyl acetate, peptone, glucose, saccharose and Sodium (S)-lactate as carbon resource and nitrate as nitrogen resource.Molecular biology identification results indicated that the strain was closely related to the strain Garciella sp.EMZY-1 (99% sequence similarity).The strain was identified as Garciella sp.wxz01 by the morphological, physiological, biochemical characteristics and the comparative analysis of 16S rDNA sequence.(2) Biosynthesis of Ag/AgCl composite nanoparticles and the study of synthesis conditionsThis study reported on synthesis of Ag/AgCl composite nanoparticles using the isolated anaerobic bacteria as biological material mixed with silver nitrate solution. The products was characterized by UV-vis, XRD, TEM, HRTEM, FTIR, etc. UV-vis spectrum showed that a wide and strong absorption peak between 350～700 nm;The XRD pattern of the products exhibited diffraction peaks at 2θ=38.116°,44.277°,64.426° and 77.472°,which are indexed to the metal silver(JCPDSfile:65-2871).However,20=27.831°,32.243°,46.233°,54.478°,57.478°, 67.471°,74.471° and 76.734°,which can be indexed to the AgCl respectively (JCPDS file:31-1238). It proves that Ag/AgCl composite nanoparticles were successfully synthesized. TEM micrograph showed Ag/AgCl composite nanoparticles were spherical or nearly spherical shape, most of these nanoparticles was monodisperse, in the range of 10～50 nm. The lattice fringes corresponding to (111) of Ag and the lattice fringes corresponding to (200) crystallographic planes of AgCl could be observed from HRTEM image. Based on TEM micrograph, the average particle size of Ag/AgCl composite nanoparticles was 27 nm. Analysis of FTIR results suggests biological synthesis can improve the stability and dispersion of the nanoparticles. The study of synthesis conditions showed that temperature and pH is the important condition of Ag/AgCl composite nanoparticles preparation. The synthesis reaction can occur at suitable temperature of 15～37℃ and suitable initial pH of 6-9. The result of atomic absorption spectrometer showed that Ag/AgCl composite nanoparticles conversion rate was 79.68%.It was close to the conversion rate of Ag/AgCl composite nanoparticles which synthesized by chemical methods.(3)Research on mechanism for the synthesis of Ag/AgCl composite nanoparticles and photocatalytic activityThis study preliminarily explores the mechanism of the synthesis of Ag/AgCl composite nanoparticles by SDS-PAGE technology. The result of SDS-PAGE showed that the bacteria fermentation liquor produced two new proteins with molecular weight c.a.80 kDa and 140 kDa after reaction with silver nitrate solution. Spectrum of proteins attached to Ag/AgCl composite nanoparticles indicated that after treated with SDS and urea, protein with molecular weight c.a.80 kDa was separated from Ag/AgCl composite nanoparticles while treated with distilled water were not, which suggested that protein with molecular weight c.a.80 kDa had a significant effect on the stability of Ag/AgCl composite nanoparticles. The result of determination of nitrate reductase activity showed that nitrate reductase was induced by a certain concentration of silver nitrate solution and NRA increased gradually with the increase of silver nitrate solution induction time. But when the NO3- concentration reaches a certain value, the nitrate reducase activity falling due to the inhibitory effect of heavy metal ions in culture.The photocatalytic properties of Ag/AgCl composite nanoparticles were investigated by evaluating on degradation experiment of methyl orange (MO). The result shows that when under the condition of visible light irradiation and adds the Ag/AgCl composite nanoparticles, the degradation rate of methyl orange solution was up to 96% after 70 min.Therefore, Ag/AgCl composite nanoparticles can be used as an efficient photocatalyst and applied to photocatalytic degradation field. |
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