Removal Of Refractory Pollutants By Photoelectrocatalysis Coupled With Microbial Fuel Cell

By studying the phenomenon of extracellular reduction of iron and manganese minerals by bacteria in nature,people have developed the technology of microbial fuel cells(Microbial Fuel Cells,MFCs).While degrading pollutants,MFC directly converts chemical energy in pollutants into electrical energy,which helps solve the above problems at the same time.However,recent research results show that MFCs have limited electrons and are difficult to distribute to the degradation process of refractory pollutants,thus limiting their application prospects.In order to solve this problem,the basic idea of this article lies in:To explore ways to increase the rate of extracellular electron transfer(EET)from the aspects of selecting and preparing MFC high-performance electrodes,and regulating the conformation of the outer membrane electron transfer proteins of electroproducing bacteria;improve the efficiency of the current generated by MFC for the degradation of refractory organics to promote its degradation of pollutants.In the experiment,the method of electrochemical modification using metal as the electrode substrate to prepare a high-performance electrode was first studied.The prepared metal electrode was applied to the MFC anode,and then photocatalysis was coupled with the MFC,and the photocatalysis was achieved by the bias voltage output by the MFC.In order to promote the degradation of azo dyes,the effect of the conformation of the outer membrane heme protein on the current output was studied in situ by circular dichroism.The adjustment of the conformation of the outer membrane protein through low-temperature culture promoted the current density(unit heme protein).)Improving.The specific conclusions are as follows:1)Electrochemical modification of metal materials to increase the current of MFC anodes.A method for growing acicular Fe₃O₄/Fe₂O₃ nanorod anodes with stainless steel as the substrate was studied to promote the adhesion of electrogenic bacteria to the anode of MFC and increase the interface electron transfer rate.Fe₂O₃ nanostructures were grown on the stainless steel after anodizing,and then further modified by cyclic voltammetry,Fe₂O₃ was oxidized and fragmented to produce needle-shaped Fe₃O₄.The surface roughness of the modified material was greatly improved,and the hydrophilicity of the nanostructure promoted the adhesion of the electro-producing bacteria biofilm,and has better capacitance characteristics and promotes electron transfer.The electron-transporting ability of TiO₂ nanotube array(TNA)structure grown on titanium as the anode was studied.Under the control of different anodizing temperatures,titanium wafers grow nanotube structures with different lengths and surface roughness.When the anodizing temperature was increased from 30°C to 75°C,the length of the TNA increases from 1.459?m to 4.183?m.The nanotubes grown at high temperature had greater resistance and were not conducive to interfacial electron transfer;on the other hand,the roughness of the prepared nanotube tip was significantly improved at higher temperatures,and the greater roughness was conducive to the adhesion of the electro-producing bacteria biofilm.The experiment found that the TNA electrode prepared under the condition of 45°C anodizing balances the two factors of resistance and roughness,and had a higher electron transfer rate.A blue TiO₂ nanotube array(BTNA)was prepared by electrochemical cathodic reduction to improve its performance as an MFC anode.Electrochemical cathodic reduction of BTNA significantly increased the carrier concentration of the material,reduced the interface resistance of TiO₂,thereby increasing the electron transfer rate at the interface side,and the increase in the conductivity of the material also provided a better condition for the enrichment of electro-producing bacteria biofilm.2)MFC and photocatalytic coupling promote degradation of pollutantsA photocatalytic cathode MFC was constructed with BTNA as the cathode and coupled with the MFC anode,and its degradation of the azo dye ABRX3 was studied.The photoelectron produced by BTNA reduces oxygen to form free radicals under light conditions,and the photoelectrocatalytic degradation kinetic constant of the material reached 0.2763/h,which was double the rate of electrocatalytic reduction.The photocatalytic cathode promoted the degradation of dyes.A microbial fuel cell-photocatalytic cell(MFC-PEC)coupling system was established.The degradation of azo dye ABRX3 by PEC using a small current generated by MFC was studied.On one hand,by connecting the two in parallel,the bias generated by the MFC was applied to the PEC,which generated photoelectrocatalysis to facilitate the degradation of the dye;on the other hand,by using the MFC as a preprocessing unit of the PEC,the ABRX3 sequence degradation in the MFC and the PEC was realized.The dye was first degraded in the MFC anode,and its chemical oxygen demand(COD)was reduced by 56%,and the decolorization rate reached 85%.After further degradation by PEC,the COD and decolorization rate of the dye were reduced by 25%and 12%again.This system achieved deep decolorization of high-concentration azo dyes.The combination of photocatalytic WO₃/TiO₂ material and carbon felt was used to construct a biophotoanode,and the rapid removal of aniline,a toxic intermediate of azo dye,was achieved directly at the MFC anode.Tungsten trioxide WO₃ was modified on the surface of TNA by electrochemical deposition to build a heterojunction structure,so that the material's absorption of light was extended to the visible light region.The study found that the aniline concentration decreased from 63.3±6.2 mg/L to 9.3±5.5 mg/L in a sequential batch test.Moreover,bioelectricity and photocatalysis have a synergistic effect.Photocatalysis enhanced the extracellular electron transfer of microorganisms,the maximum current of MFC increases by 28.5%,and the resistance at the anode interface decreased from 136.9?to 69.9?.Analysis of the microbial community of the biological photoanode revealed that no typical aniline-degrading bacteria were found in the MFC anode,and photocatalytic degradation of aniline was mainly driven by the system.However,the biophotoelectrode increased the relative abundance of the typical electric-producing bacterium Geobacter in the biofilm and promoted the increase of MFC current.The construction of biological photoelectrode provided a new method to overcome the problem of low anaerobic degradation rate of toxic azo intermediates in MFC.3)Regulate the conformation of heme protein and promote extracellular electron transfer of electric-producing bacteriaThe in situ optical method based on circular dichroism(CD)was used to characterize the conformation of protein Mtr C on the surface of engineered E.coli.It was found that the expression of Mtr C increased from 5×10^-9 M to 22×10^-9 M,and the molar ellipticity??(the ellipticity of 1molar Mtr C)decreased from 12×10³ to 2.5×10³/M/cm.This indicates that when the expression of Mtr C is enhanced,the intensity of the exciton coupling between the heme centers is significantly weakened.It is found through fitting data that the molar ellipticity(??)of Mtr C and the current density show a certain linear relationship.The current density increases with the increase of the molar ellipticity of CD,which strongly indicates that the heme interaction of Mtr C,that is,the spatial distance between the heme centers affects the EET rate.The construction of this living cell in situ CD method provides a better method for optimizing the structure of the outer membrane heme protein of the electroproducing bacteria and promoting the improvement of the electron transfer of the electroproducing bacteriaThe method of adjusting the outer membrane fatty acid composition of electroproducing bacteria through low temperature culture to change the conformation of the outer membrane heme protein and promote the electron transfer was studied.The experiment found that the current output density of MR-1 unit Mtr C increased significantly after low temperature cultivation,and the current density of Mtr C at 4°C was 5.5 times that of 30°C.The in situ CD method was used to measure the conformation of Mtr C and Mtr A.The experimental results showed that the low temperature conditions did increase the molar ellipticity of Mtr C and Mtr A,thereby making the heme center responsible for electron transfer more compact and conducive to electron transfer.