Synthesis Of Noble Metal Nanoparticles By Typical Dissimilatory Metal Reducing Bacteria And Their Extracellular Polymeric Substances

Due to quantum effects on the properties and structures of the material,nanoparticles always have special physical and chemical properties.They are widely used in many different fields such as optics,catalytic chemistry and electronics.Traditionally,the physical and the chemical methods for synthesis of nanomaterials remain expensive and involve the use of amounts of chemicals,which lead to the generation of secondary wastes.Biological synthesis of nanoparticles eliminates the use of hazardous chemicals and proceeds at ambient temperature and pressure,so it has been proposed as cost-effective and environmentally friendly.This study focused on the green synthesis and application of functional nanomaterials.The biogenic monometallic,bimetallic and magnetically bimetallic nanoparticles were produced by the typical dissmilatory metal reducing bacteria Geobacler sulfurreducens and Shewanello oneidensis MR-1.In addition,the prepared biogenic nanomaterials were studied for treatment of typical recalcitrant pollutants.Moreover,extracellular polymeric substances(EPS)from Shewanella putrefaciens CN-32 were used to reduce metal ions in the presence of iron-bearing mineral.The works more detailed as follows:G.sulfurreducens was studied for the reduction of Pd(II)and the formation of biogenic Pd(0)(bio-Pd).Bio-Pd was characterized by transmission electron microscope,energy dispersive X-ray spectroscopy and X-ray diffraction.Results showed that the bio-Pd nanoparticles located both on the cell surface and inside the periplasm.The increase of cell dry weight to Pd ratio and addition of anthraquinone-2,6-disulfonate(AQDS)not only stimulated Pd(II)reduction,but also resulted in increase of nanoparticle number,decrease of particle diameter and improvement of Cr(VI)reduction efficiency.The relationship between reduction rate and initial Cr(VI)concentration could be described with Michaelis-Menten kinetics.The kinetic constants calculated from experimental data were 891.3 ?mol 1-1 for Km and 3.6 ?mol h-1 mg-1 bio-Pd for Vmax,respectively.Bimetallic nanomaterials possesse higher catalytic activity and stability.S.oneidensis MR-1 was studied for the formation of bio-Pd,biogenic Pt(bio-Pt)and biogenic PdPt(bio-PdPt).The addition of AQDS could stimulate the reduction efficiency of Pd(?)or/and Pt(?)and resulted in the generation of bio-PdQ,bio-PtQ and bio-PdPtQ with smaller particle size.All these six kinds of nanoparticles could catalyze 4-nitrophenol reduction by NaBH4 and their catalytic activities took the following order:bio-PdPtQ?bio-PdPt>bio-PdQ>bio-Pd>bio-PtQ?bio-Pt.Moreover,the bio-PdPtQ nanomaterials could be reused for six cycles with reduction efficiency higher than 92%for catalyzing 4-nitrophenol reduction by NaBH4.Nanomaterials generally are difficult to recycle and reuse.S.oneidensis MR-1 firstly transformed akaganeite into magnetite,which then served as support for the further synthesis of magnetically recoverable Pd/Fe3O4,Au/Fe3O4 and PdAu/Fe3O4 nanocomposites from respective precursor salts.Surface-bound cellular components not only functioned as shape-directing agent to convert some Fe3O4 nanoparticles to nanorods,but also participated in the formation of PdAu alloy nanoparticles on magnetite.All these three kinds of magnetic nanocomposites could catalyze the reduction of 4-nitrophenol by NaBH4.The values of apparent kinetic rate constant(kapp)for Pd/Fe3O4,Au/Fe3O4 and PdAu/Fe3O4 were 0.1671,0.0255 and 0.3282 min-1,respectively.The PdAu/Fe3O4 nanocomposites demonstrated the highest catalytic activity for 4-nitrophenol reduction and could be reused for eight cycles with reduction efficiency higher than 87%.Moreover,nitrobenzene,2-nitrotoluene,3-nitrotolune,4-nitrotoluene,2-nitrophenol,3-nitrophenol and 4-nitrochlorobenzene were also used as substrates to test the catalytic activities of Pd/Fe3O4,Au/Fe3O4 and PdAu/Fe3O4.All the nitroaromatic compounds investigated could be reduced to different extents by NaBH4 in the presence of these three nanocomposites and their catalytic activities took the following order:PdAu/Fe3O4>Pd/Fe3O4>Au/Fe3O4.EPS can reduce many different kinds of metal ions to corresponding metal nanoparticles.Bound-EPS(B-EPS)and loosely-EPS(L-EPS)from S.putrefaciens CN-32 could reduce Ag+to Ag(0)nanoparticles.The sorption kinetics of L-EPS and B-EPS to ?-Fe2O3 nanoparticles could be fitted to the pseudosecond order model.Moreover,?-Fe2O3 nanoparticles sorbed more L-EPS than B-EPS.The existence of ?-Fe2O3 could improve the reduction efficiency of Ag+ by EPS,and Ag(0)nanoparticles bonded to the ?-Fe2O3 with higher content and larger diameter was obtained compared to Ag(0)nanoparticles dispersed in the solution.X-ray photoelectron spectroscopy analyses suggested that the hemiacetal groups of EPS sorbed on the ?-Fe2O3 were responsible for Ag+ reduction.