Mechanisms Of Extracellular Electron Transfer In Ferrous-Based Nanomaterials/Shewanella Biohybrid Bacteria

As an emerging bioelectronic technology,microbial fuel cell（MFC）shows great potential in bioremediation,sewage treatment,clean power production and biosensor devices.However,the slowly extracellular electron transfer and poor contacts at biotic-abiotic interfaces limit its practical application.The research of nano materials in improving the performance of MFC mainly focuses on modifying anode materials,the anode biological adhesion can be increased and the electron collection efficiency can be improved by improving the conductivity,biocompatibility and specific surface area of the electrode,one strategy is to construct nano anode materials with layered porous structure,another strategy is chemical modification of anode surface and nano materials modification.Based on this disadvantage,the direct coupling of nano materials with microorganisms can build a close and efficient biological/abiotic interface,which has also become one of the important directions of MFC technology research.S.putrefaciens CN32 studied in this paper is a dissimilatory iron reducing bacteria（DIRB）,it has good biological affinity for iron oxides.Based on the unique physicochemical properties and good biocompatibility of Fe₃O₄/PDA nanocomposites and bimetallic spinel ferrites（manganese ferrite,cobalt ferrite and nickel ferrite）,an efficient and stable biological nano hybrid system was constructed by coupling with S.putrefaciens CN32 and used as MFC anode.The mechanism of iron-based nano materials to enhance the extracellular electron transport of S.putrefaciens CN32 was studied.The main research contents and results are as follows:（1）Fe₃O₄NPs were prepared by coprecipitation and Fe₃O₄/PDA NPs were prepared by self-polymerization of dopamine monomer in alkaline solution.We analyzed the electrochemical activity of S.putrefaciens CN32 modified by different concentrations Fe₃O₄ NPs and different composite proportions Fe₃O₄/PDA NPs and the MFC performance enhancement mechanism.The mechanical contact between Fe₃O₄NPs and bacteria improves the electron collection efficiency.The anode output power density of S.putrefaciens CN32 modified by 3 m M Fe₃O₄ NPs reached 605.4 m W m^-2,which is 4.2 times that of the original bacterial anode(145.3 m W m^-2).Due to the poor conductivity of Fe₃O₄NPs,the combination of conductive polymer PDA and Fe₃O₄ can complement each other.When the concentration of dopamine monomer is 0.6 mg/m L,the composite has the best performance.The output power density of MFC is 986.9m W m^-2,which is 6.8 times that of original bacterial anode.This bioelectric current enhancement mechanism benefits from the good biological affinity and conductivity of Fe₃O₄/PDA NPs and the close affinity contact between materials and bacteria.This makes a multi-channel conductive path formed on the surface of bacterial outer membrane,bacteria and bacteria,bacteria and electrode.In this case,an interconnected"conductive network"is formed in the whole MFC anode chamber,which greatly improves the electron collection efficiency and transfer rate,and finally realizes the superior power generation performance in MFC.（2）Three kinds of bimetallic spinel ferrites（manganese ferrite,cobalt ferrite and nickel ferrite）were synthesized by simple hydrothermal method,and then functional bacteria were constructed by self-assembly.The successful assembly of functional bacteria was confirmed by SEM and TEM.Then the electrochemical behavior of self-assembled bacterial cells was analyzed,it was found that the bacteria modified by manganese ferrite had the highest redox peak current and the lowest electron transfer impedance compared with other self-assembled bacterial cells.The MFC maximum power density of manganese ferrite hybrid bacterial anode reached 1088.6 m W m^-2,which was 7.2 times higher than that of primitive bacterial anode(150.3 m W m^-2).The maximum current density is 2.08 A m^-2,which is 2.8 times higher than that of the original bacterial anode(0.74 A m^-2).This biological current enhancement mechanism is due to the close adhesion of highly conductive manganese ferrite nanoparticles on the surface of bacteria,which leads to build multiple conductive pathways between the bacterial surface and bacteria,and the DET and MET pathways have been enhanced.In addition to enhancing the process of bioelectrocatalysis,manganese ferrite,as spinel photocatalyst,can also excite photoelectrons under light conditions and as supplementary electron source to further improve the output current density.Finally,dual multi-channel energy conversion is realized.