Biosynthesis And Catalytic Performance Research Of Ag And Ag₂S Nanocomposites

The nanocomposites synthesized by microorganisms as an environmentally friendly green synthesis method.Microbial synthesis possesses outstanding features,such as reaction with a mild condition wide range of microbial sources and the obtained sample with good biocompatibility.Bacteria,fungi and yeasts have been widely used to research on the biosynthesized nanocomposites.However,it was mostly used in the synthesis of monomeric nanomaterials,and the research has rarely been reported that the nanocomposites was obtained by microbial.The manuscript is aim to a Gram-negative bacteria--Shewanella oneidensis MR-1(S.oneidensis MR-1)as a biological reducing agent for in-situ synthesis of Ag and Ag2S nanocomposites on the surface of the supports,and its application to the catalytic degradation of environmental organic contaminant was investigated.The main contents and results of the research are as follows:(1)Research on the biosynthesis of Ag/Fe3O4 magnetic composite material and its photocatalytic capabilityS.oneidensis MR-1 synthesize Ag/Fe3O4 composites in situ on the surface of Fe3O4 with the Ag iron as an electron acceptor.The structure and property of Ag/Fe3O4 were characterized by TEM,EDX,VSM and XPS,respectively.The results showed that Ag NPs with the size of about 15 nm,were relatively distributed homogeneously on the surface of Fe3O4 microspheres.The Ag/Fe3O4 composite exhibit the high photocatalytic activity,which can degrade 96.3%methylene blue(MB)within 50 min.The composite possesses highest catalytic performance when the pH 7 and the concentration is 0.3 g/L.The Ag/Fe3O4 composite can be separated from solution by the external magnetic field,due to it have the superparamagnetism just like Fe3O4,which beneficial to recycle and re-use.After six cycles,the catalytic activity can be maintained at about 90%.(2)Research on the biosynthesis and catalytic degradation performance of Ag2S/TNTs nanocompositesS.oneidensis MR-1 synthesis of Ag2S/TNTs nanocomposites in site on the outer wall of TiO2 nanotubes(TNTs)with Na2S2O3 as electron acceptor.The prepared Ag2S/TNTs nanocomposites were characterized by TEM.XRD,XPS and DRS.The results show that the Ag2S nanoparticles with an average particle size of 4.87±1.66 nm are evenly distributed on the outer wall of TNTs.It can be regulating the loading of Ag2S NPs on the surface of TNTs by adjust the Ag/Ti molar ratio in the precursor.The Ag=S/TNTs nanocomposites synthesized with a precursor Ag/Ti molar ratio of 1/1 0 had highest catalytic reduction efficiency for 4-Nitrophenol(4-NP).The catalytic eff-iciency reached 98.3%within 50 min in the presence ofNaBH4.and the reaction accorded with the first-order kinetic model with the reaction kinetic constant of 0.07992 min'1.Meanwhile,the nanocomposites exhibit high cycle stability,and the catalytic activity still remain at 87%even after eight cycles.The Ag2S/TNTs nanocomposites have strong light absorption properties in the visible region,due to the loading of Ag2S NPs with narrow band gap,it can effectively photocatalytic degradation of 4-NP under visible light irradiation.Moreover,the reaction followed the the first-order kinetic model with a rate of 0.69 h-1Ag and Ag2S nanocomposites were successfully synthesized using S.oneidensis KMR-1 as reducing agent,which possess outstanding catalytic properties and cyclic stability for degradation environmental organic pollutants.It provides an effective way for green synthetic nanocomposites.