| Microbial fuel cell(MFC)uses microbies as the catalyst,waste biomass,organic wastewater and other organic substances as fuel to produce electricity by biological oxidation.So far,carbon materials have been extensively used as the anode of MFC,such as graphite block,carbon paper,carbon cloth and carbon felt.Although carbon materials are light and good corrosion resistance,they are brittle and rather difficult for secondary machining,and neither easy to adhere microbies.By conductive polymer coated on the surface of the common substrate,electrodes of MFC can change the characteristics of the electrode easily and quickly.It has becoming a new direction to enhance MFC.Compared with other conductive polymers,the conductive polymer poly 3,4-ethylenedioxythiophene(PEDOT)has excellent chemical stability,high conductivity and good biocompatibility,so it is suitable to be used as an electrode coating for MFC.In this study,marine Shewanella sp.S2 was used as an exoelectrogenic strainto investigate the effects of PEDOT on the current generation and decolorization in MFC and the main results as follow:(1)A layer of PEDOT film was successfully plated on the surface of high purity graphite by cyclic voltammetry(CV)polymerization.The PEDOT film on the surface of graphite electrode was characterized by scanning electron microscope(SEM).The results showed that PEDOT was uniformly covered with 200-400 nm dot-like form on the electrode surface.The CV test results of the potassium ferricyanide solution showed that the peak potential and the redox current had little effect compared with unmodified graphite electrodes,but the area of the CV curve was much larger than that of the unmodified graphite electrode,indicated that the PEDOT modified improved the electrical conductivity of the electrode.EIS test results showed that the ohm resistance and transfer resistance of the unmodified graphite electrode were 17.1Ω and 163.6 Ω,and PEDOT modified electrode were 11 Ω and 2.4 Ω,respectively,which further indicated that PEDOT modified could significantly increase the catalytic activity of the electrode and reduce the electron transfer resistance.(2)The effects of PEDOT modified on the decolorization of XP2R was studied by using H-MFC.Three kinds of decolorization methods were set up,(a)MFC decolorization of PEDOT modified anode with disconnected external circuit(i.e.,anaerobic decolorization),(b)MFC decolorization of graphite anode,(c)MFC decolorization of PEDOT modified anode.The decolorization and electricity generation of MFC after the first decolorization and electricity generation showed that the decolorization speed was the fastest of PEDOT modified anode,followed by anaerobic decolorization,and the worst was graphite anode decolorization.The decolorization rate of unit bacteria density,time and volume of three decolorization modes of a,b and c were 6.82,6.27,and 8.02 mg·L-1·h-1·ODU-1.The reason was that when the anode solution was changed,the bacteria in the liquid was removed,and the quantity of bacteria adsorbed on the electrode determined the decolorization speed.Both a and c were PEDOT anodes.The number of adsorbed microorganisms was high,so the two decolorization rate was fast.At the same time,c decolorization was better than a decolorization,indicated that MFC power generation was conducive to decolorization.In the case of b,decolorization was slow due to a small number of bacteria adsorbed by graphite.From the results of electricity generation,the PEDOT modified anode can significantly increase the power generation,and the MFC current density of modified and unmodified PEDOT were 184 and 90 mA/m2 respectively.Comparing decolorization rate and electricity generation rate,it was found that three decolorization had been completed within 74-119 h,but the maximum output current density needed to reach 160 h.(3)The effects of PEDOT modified on the decolorization of RB19 was studied by using H-MFC.Three decolorization methods were set up to decolorization with XP2R and consistent results were obtained.The fastest decolorization speed is PEDOT modified electrode,followed by anaerobic decolorization,and the worst was graphite anode decolorization.The decolorization rate of unit bacteria density,time and volume of three decolorization methods of a,b and c were 4.52,4.21 and 5.30 mg·L-1·h-1·ODU-1,respectively.The reason was the same with(2).From the results of electricity generation,the PEDOT modified anode can significantly increase the power generation,and the MFC current density of modified and unmodified PEDOT were 192 and 110 mA/m2.Comparing decolorization rate and power generation rate,it was found that three decolorization had been completed within 160 h,but the maximum output current density needed to reach 190 h.(4)The mechanism of decolorization and electricity generation by PEDOT was preliminarily discussed.Scanning electron microscopy(SEM)results showed that PEDOT modified significantly increased the adsorption capacity of electric generation bacteria on the anode surface.Because the roughness of the electrode surface was far less than the size of the bacteria,it was speculated that the increase of MFC decolorization and electricity generation capacity were mainly due to the effect of PEDOT rather than the surface roughness of the anode.From the decolorization and electricity generation experiment results of MFC,electricity generation was related to cell growth,and these new growth cells entered the anode solution.Therefore,comprehensive analysis,under the conditions of this experiment,Shewanella sp.S2 would use the method of secreting soluble electron medium and cytochrome on the extracellular membrane to carry out extracellular electron transfer.Dyes are one of the largest categories of organic compounds produced by human production and have significant environmental impact.At present,there is no report about decolorization and electricity generation based on PEDOT modified MFC anode.Our research results indicated that the anode modification by PEDOT coating cloud enhance decolorization and electricity generation in MFC. |
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