| In this paper,two strains Shewanella oneidensis MR-1 and Shewanella putrefaciens were used on reducing Se(Ⅳ)into Se(0)nanoparticles,and its influencing factors of Se(Ⅳ)reduction to find out the mechanism of Se(Ⅳ)reduction.The products were synthesized by microorganisms which characterized by X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS),dynamic light scattering(DLS)and fourier transform infrared(FTIR)spectroscopy to provide a basis for the application of Se(0)nanoparticles.Finally,in order to decrease the toxicity of the Se(Ⅳ)and provide theoretical basis for repair of Hg pollution,the Se(0)nanoparticles were used for Hg remediation.The main results are as follows:Laboratory culture condition,the study of S.oneidensis MR-1 and S.putrefaciens Se(Ⅳ)reduction and its impacts.The results showed that the concentration of Se(Ⅳ)S.oneidensis MR-1 and S.putrefaciens growth has certain inhibitory effect.A high concentration of Se(Ⅳ)significantly reduced S.oneidensis MR-1 and S.putrefaciens reduction rate of Se(Ⅳ).With the increase of concentration of Se(Ⅳ),Se(Ⅳ)reduction rate significantly decreased,Se(Ⅳ)can inhibit the strain growth and activity(Ⅳ)reduction.And S.oneidensis MR-1 and S.putrefaciens reduction of Se(Ⅳ)increased with the increase of bacteria suspension inoculation enhanced.The optimal growth p H value is neutral and weak alkaline environment than weak acid environment more conducive to strains on the reduction of Se(Ⅳ).By SEM-EDS analysis,it was confirmed that the red reduction products synthesized around the two strains were Se(0)nanoparticles.Adding different exogenous electron shuttle substance to explore electronic shuttle to S.oneidensis MR-1 and S.putrefaciens influence on Se(Ⅳ)reduction,adding riboflavin,rotenone and N-acetyl-L-methionine(Ac Met)method,to study the electron donor effects on microbial reduction of Se(Ⅳ).Exogenous add electronic shuttle body riboflavin can enhance Se(Ⅳ)reduction,exogenous add low concentration riboflavin on Se(Ⅳ)reduction is small,when the concentration of exogenous add riboflavin over 4 μmol/L will speed up the microbial reduction of Se(Ⅳ).Two kinds of electron transfer inhibitors:rotenone and Ac Met had negative impacts on Se(Ⅳ)reduction.With the increase of concentration of exogenous rotenone and Ac Met,Se(Ⅳ)is suppressed in the reduction of gradually,rotenone inhibition effect of Se(Ⅳ)reduction than Ac Met.Se(0)nanoparticles were purified and synthesized by S.oneidensis MR-1 and S.putrefaciens at the same time.By XPS spectroscopy analysis showed that two strains were able to Se(Ⅳ)reduction in red Se(0)particles.SEM and TEM analysis confirmed that the biological Se(0)nanoparticles produced in the experiment were spherical particles.The Se(0)nanoparticles synthesized by S.oneidensis MR-1 were uniformly spherical with small diameter and relatively pure nanoparticles.The Se(0)nanoparticles synthesized by S.putrefaciens showed inhomogeneity and aggregation,and there were many impurities.DLS results showed that the Se(0)nanoparticles synthesized by S.oneidensis MR-1 ranged from 265 nm to 530 nm with an average particle size of 375±31 nm.The size distribution of Se(0)nanoparticles synthesized by S.putrefaciens ranged from 578 nm to 972 nm,with an average size of 578±48 nm.The FTIR analysis showed that the Se(0)nanoparticles synthesized by S.oneidensis MR-1 and S.putrefaciens had the presence of carbohydrate,polysaccharide and protein,which are related to extracellular polymer.The biological Se(0)nanoparticles generated by Raman spectroscopic analysis did not appear characteristic peaks,indicating that no single crystal structure was formed.In this case,Se(0)nanoparticles were adsorbed on the surface of the extracellular polymer in amorphous form.By simulating the reduction rate of Se(Ⅳ)and removal rate of Hg(Ⅱ)of microorganisms in the presence of Se(Ⅳ)and Hg(Ⅱ),the experiment explores the role of microorganisms in the complex fixation of Hg(Ⅱ)in the process of reducing Se(Ⅳ)in the environment containing mercury.The results showed that both S.oneidensis MR-1 and S.putrefaciens could effectively reduce Se(Ⅳ)and remove Hg(Ⅱ)in the culture medium.XPS energy spectrum analysis showed that the immobilization of Hg(Ⅱ)was mainly formed by the combination of Hg(Ⅱ)and Se(Ⅱ).The black particles generated under the action of S.oneidensis MR-1 and S.putrefaciens were confirmed to be Hg Se by SEM-EDS.TEM analysis showed that the Hg Se nanoparticles under the action of S.oneidensis MR-1were uniformly spherical with an average surface diameter of about 150±50 nm.The average surface diameter of Hg Se nanoparticles generated by S.putrefaciens was about200±50 nm. |
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