Iron And Nitrogen Modified Carbon Nanofibers For Enhancing Extracellular Electron Transfer In Shewanella

Microbial fuel cell(MFC)uses electroactive bacteria as a biocatalyst in the anode chamber to generate electricity when decomposing organic matter.Compared with traditional fuel cells,MFC does not require precious metals as catalysts.Biocatalysts are abundant,easily available and renewable.MFC is also widely used in bioenergy and environmental remediationfields due to its mild operating conditions and little impact from environmental changes.The anode is the living place of electroactive bacteria.It provides a carrier for the growth and adhesion of the anode catalyst.At the same time,it also acts as a current collector to collect the electrons generated by the bacteria during the respiration process and transmit them to the cathode through an external circuit.The anode material is one of the important factors affecting the performance of MFC.The slow extracellular electron transfer process between the electroactive microorganisms and the anode electrode interface restricts the catalytic performance of the anode,resulting in slow start-up speed and low maximum output power of MFC,which limits its commercial application.Different anode materials have different physical and chemical properties(such as surface area,biocompatibility,electrical conductivity,and chemical stability),and they have different effects on microbial adhesion,electron transfer,and electrode surface reaction rate.Changing the structure of the anode material and the surface chemistry are important methods to improve the performance of the anode and increase the output power density of the MFC.Fiber-based porous anodes are widely used to improve the performance of MFC,but how the surface chemistry of fiber-based porous anodes can promote the electron transfer process at the interface of MFC anodes is still lacking in in-depth research.Electrospinning can simply and effectively produce polymer nanofiber films.The diameter of polymer fibers ranges from tens of nanometers to several microns.The carbonized electrospun polymer nanofiber film has high porosity and specific surface area,which provides a favorable place for the growth and attachment of microorganisms,promotes the growth of biofilms,and the electron transfer rate between the electroactive bacteria and the anode interface.This paper uses electrospinning technology to prepare carbon nanofibers,and designs and prepares a series of anode materials by modifying the surface of carbon nanofibers with Fe and N.Explore the effect of Fe and N modified carbon nanofibers on the electron transfer process between the typical electricity-producing strain Shewanella putrefaciens CN32 and the electrode.The main research contents and results are as follows:(1)Polyacrylonitrile(PAN),iron(III)acetylacetonate(Fe(Ac Ac)₃),and N,N-dimethylformamide(DMF)are used as spinning precursors.By adjusting the content of Fe(Ac Ac)₃,four carbon nanofibers modified with different Fe content were prepared.Due to excessive Fe(Ac Ac)₃ causing fiber structure deformation,carbon nanofibers Fe@CNF-?,Fe@CNF-?,Fe@CNF-?were finally selected for subsequent electrocatalytic behavior analysis.The experimental results show that iron-modified carbon nanofibers can increase the load of electroactive bacteria on the anode,make it form a continuous electroactive biofilm on the anode,and improve the direct electronic transfer(DET)process of electroactive bacteria.At the same time,because Fe(Ac Ac)₃ increases the specific surface area of carbon nanofibers during the high-temperature carbonization process,it promotes the mediated electron transfer(MET)process.Among them,the Fe@CNF-?electrode with the highest iron content has the most electroactive biofilms attached,and the catalytic current associated with direct electronic transfer is stronger,and it shows better performance in MFC.(2)Using metal organic frame material ZIF-8 as the pore-forming agent,and then through the electrospinning technology and carbonization,the porous carbon nanofiber(PCNF)is prepared.The porous carbon nanofibers are obtained by solvothermal method to obtain nitrogen-modified carbon nanofibers(N-PCNF).XPS results showed that nitrogen was successfully doped on the carbon skeleton after solvothermal reaction.In the electrochemical behavior test of the material,the N-PCNF electrode significantly promoted the redox reaction of the flavin electron mediator at the electrode interface.N-PCN anodes show excellent biocompatibility.A large number of electroactive bacteria are loaded on the anode and a dense electroactive biofilm is formed.Nitrogen modified porous carbon nanofibers mainly promote the mediated electron transfer(MET)process between Shewanella and the electrode interface.(3)On the basis of the first two research works,Fe(Ac Ac)₃(Method 1)and Ferric Chloride(Fe Cl₃·6H₂O)(Method 2)were used as iron sources,and 2,2'-bipyridine was used as nitrogen source to prepare carbon nanofibers modified with higher iron and nitrogen content.After Fe Cl₃·6H₂O and 2,2'-bipyridine form a metal complex,it can better leave a certain content of iron and nitrogen on the fiber.However,by using Fe(Ac Ac)₃ and 2,2'-bipyridine as the iron source and nitrogen source,the content of iron and nitrogen in the polymer fiber is lower after carbonization.Finally,the Fe,N-CNF and Fe-CNF prepared by method two were compared to study the effect of Fe and N modification on the reaction between Shewanella CN32 and the electrode interface.The research results show that the co-modification of iron and nitrogen can significantly promote the extracellular electron transfer process of Shewanella CN32,and the nitrogen modification promotes the redox reaction of flavin molecules on the electrode.The electroactive biofilm load on the anode co-modified with iron and nitrogen also increased significantly.After discharge,XPS test was performed on Fe,N-CNF and Fe-CNF electrodes,and it was found that the valence state of Fe has changed significantly.It is revealed that it may be involved in the process of extracellular electron transfer between the electroactive bacteria and the anode interface.