The Studies On Valence Regulation Of U(?) By Electron Shuttle-mediated Photoelectron And Two Strains Of Reducing Bacteria

With the rapid development of nuclear energy,the environmental pollution of uranium is becoming increasingly serious.Biogeochemical interactions play an important role in controlling the morphology and migration of uranium and other redox-sensitive radionuclides.Semiconductor mineral photoelectrons can promote the growth of microorganisms and regulate the transformation of uranium.Therefore,the study of uranium valence transition has important guiding significance for the treatment of uranium pollution.The anatase and hematite composite minerals,electron shuttle riboflavin?RF?and sodium sulfonate-2-sulfonate?AQS?,Gram-negative bacteria Shewanella putrefaciens and Kocuria rosea were selected as a research object.Based on the combination of electrochemistry,interface chemistry and spectroscopy,the influence of electron shuttle on migration and transformation mechanism between U?VI?and two reducing bacteria was inveligated.The completed results as following:1.In this study,anatase,hematite and?-Fe₂O₃/TiO₂ composite mineral electrodes were prepared by hydrothermal synthesis.The structure,morphology and light absorption properties of the mineral electrode were characterized by XRD,SEM,FTIR and DRS.The electrochemical performance of the mineral electrode was analyzed by electrochemical workstation.The photocatalytic reduction of Cr?VI?was investigated.The results show that the diffraction peaks of?-Fe₂O₃/TiO₂ composite electrode are consistent with anatase,and there are no new diffraction peaks in different proportions of composite mineral electrodes.The electrode morphology is granular and short columnar.The content of Fe is too high,and particle agglomeration occurs on the surface.The composite?-Fe₂O₃/TiO₂ electrodes showed an enhanced absorbance in visible light region and had good stability to photoelectrochemical reduction of Cr?VI?.The pH value has a great influence on the form and photocatalytic efficiency of Cr?VI?.When pH=5.0,the reduction rate of Cr?VI?is the highest.Under visible light irradiation,100%removal efficiency of Cr?VI?was obtained after 40 min treatment.2.Based on electrochemical and interfacial chemistry,the redox process of U?VI?was studied.The effects of organic small molecules?citric acid,oxalic acid?,photoelectrocatalysis,pH and dissolved oxygen on the photocatalytic removal of U?VI?by?-Fe₂O₃/TiO₂ composite minerals were investigated.The results show that U?VI?is mainly converted into U?IV?by a two-step single electron reduction process,while the oxidation process is U?IV?directly oxidized to U?VI?.The pH value has an effect on the presence of U?VI?in aqueous solution and the photoelectric properties of the electrode.After adding citric acid and oxalic acid,the EIS analysis system becomes smaller,the electrolyte resistance Rs and the electron transfer resistance Rct are both reduced,and the electron transfer speed is accelerated.The synergistic rate of photocatalytic removal of U?VI?reached 179.4%on E_bias=1.0 V vs.SCE.The removal rates of U?VI?were 72.6%and 53%with adding citric acid and oxalic acid,which were 2.09 times and 1.3 times higher than the control.3.The redox activity of RF and AQS and its effect on U?VI?redox activity were investigated by electrochemical means.The effects of RF and AQS on photoelectron reduction U?VI?,electron transfer kinetics and reduction products were investigated.The results show that both the RF and AQS redox reactions are quasi-reversible reactions,and the electrochemical conversion of RF and AQS belongs to diffusion control.The electrical resistance of the U?VI?aqueous solution was reduced with adding RF and AQS.SEM analysis showed that the reduced product formed a flaky,needle-like crystalline mineral on the counter electrode,and EDS analysis indicated that it contained U mineral.After adding RF and AQS,the flaky and needle-shaped productswere deposited on the counter electrode,which were?UO₂?₈O₂?OH?₁₂.12H₂O and UO₂.4.The cyclic voltammetric properties of the cells and supernatants of S.putrefaciens and K.rosea were investigated by bioelectrochemical methods.The redox activities of the two strains were studied.Three-dimensional fluorescence analysis of the characteristics of secreted substances during the interaction between S.putrefaciens,K.rosea and U?VI?.The results showed that there were obvious redox peaks of the supernatant and bacterial liquid with S.putrefaciens and K.rosea.The redox peak was flavin substance.S.putrefaciens,K.rosea and U?VI?produced redox and humus-like substances with redox activity,and the quality of flavin and humus-like substances increased with the increase of reaction time.5.Electron transfer between S.putrefaciens,K.rosea and U?VI?mediated RF and AQS was studied.The reduction products were analyzed by SEM,EDS,FTIR,XPS and XRD.The results showed that both RF and AQS promoted the removal of U?VI?by S.putrefaciens and K.rosea.A large amount of flaky crystals were formed by S.putrefaciens reacts with U?VI?.The product is a crystal of uranium hydrogen phosphate?H₂?UO₂?₂?PO₄?₂·8H₂O?,which is formed by U?VI?minerals.Adding RF and AQS,amorphous U?VI?and U?IV?minerals were formed by S.putrefaciens interacts with uranium.Uranium oxides of U?VI?and U?IV?was formed by K.rosea interacts with uranium.After the addition of the electron shuttle AQS and RF,the interaction product between K.rosea and uranium still exists in both U?VI?and U?IV?valence states,but the proportion of U?IV?increases by 3.7%and 5.9%.