In-situ Preparation Of Nanosheets FeS_X/CC And Its Mechanism For Improving The Performance Of MFC

With the development of the times,industrial and municipal wastewater is increasing.The microbial fuel cell（MFC）is a green bio-energy technology,which can convert organic wastewater into energy.However,due to its low power density and high electrode cost,the MFC can not be applied on a large scale.The transition metal sulfide（FeS_X）as the representative of transition metal compounds can improve the anode surface,it has a greater role in promoting bacterial growth and electricity generation,the above results improve the performance of the MFC device.However,the preparation of FeS_X electrodes with specific morphology has become a key technology because the structure of iron-based sulfides does not have two-dimensional self-plasticity.At the same time,the intrinsic relationship between the change of electron transport mode in MFC and the anode surface morphology and interface adjustment is not intelligible,and the interaction mechanism between FeS_X and microorganisms is not clear.All these need to be studied systematically for understand the synergistic effects between microorganisms and minerals.Therefore,the method of in-situ growth of FeS_X nanosheets was designed in this paper.Furthermore,the interaction mechanism between FeS_X and microorganism at the electrode interface was studied by MFC.The different phases of FeS_X/CC（CC refers to carbon cloth substrate）can be obtained by controlling the hydrothermal time,and the effects of FeS₂/CC and Fe₃S₄/CC on the MFC device were studied.The experimental results show that:（1）FeS₂/CC can be prepared when ferric chloride is used as a iron source and ethanol-water is used as solvent.The Fe₃S₄ is formed on carbon cloth（current collector）when the ripening time is short（<3 h）,and the whole FeS₂ can be formed when the ripening time is sufficient（>10 h）,The results were verified by XRD,XPS and SEM.（2）The effect of different phases of FeS_X on the performance of MFC was compared,and the order of their power densities was FeS₂/CC>Fe₃S₄/CC>CC.FeS₂/CC has good power density(3.16 W·m^-2)and stable cyclicity.After 4cycles,the discharge voltage of MFC device has unobvious decrease.（3）The electrochemical methods（CV,DPV,EIS,etc.）were used to test the elecpathway,and 16s r RNA method was used to test the chaine of microbial community.The existence of FeS_X phase promoted the growth of cells on the electrode surface,which changed the electron transport mode,and it changed the population distribution of bacteria.FeS₂/CC increased the relative abundance of Geobacter from 11%to 22%,which improved the electricity production performance of MFC.Fe₃S₄/CC increased the content of Cloacibacillus from 2.5%to 20.1%.This result shows that different substances of the same species have different effects on microorganisms.The morphology of FeS_X/CC electrode is granular,and the morphology and structure of FeS_X/CC electrode need to be optimized and improved.In order to obtain uniform FeS _X/CC nanosheets,FeS_X/CC nanosheets are uniformly grown on the surface of a current collector by adjusting and controlling parameters such as the type of an iron source,a mineralizer,a solvent and the like.The results showed that:（a）The flaky FeS_X/CC electrode was easier to be obtained by ferric sulfate than by ferric chloride,because the formation of[FeSO₄（SCN₂H₂）]⁺complex improved the adsorption effect of raw materials on carbon fibers.（b）The obtained FeS_X/CC nanosheets are uniformly distributed when ethylene glycol is used as a solvent,and the ethylene glycol has smaller surface tension and larger viscosity.（c）The introduction of Na Cl as a mineralizer not only increases the overall chemical potential,but also can be adsorbed on the surface of the FeS_X nanosheets to reduce the aggregation of FeS_X.Under the synergistic effect of the above factors,FeS_X nanosheets with uniform distribution were finally prepared on the surface of carbon fibers.The phase of the FeS_X/CC electrode can be adjusted by adjusting the ferric salt,the product is Fe_1-XS/CC when the ferric sulfate is used as an iron source,and the product is FeS/CC when the ferrous sulfate is used as an iron source.The effects of Fe_1-XS/CC and FeS/CC on the performance of MFC were further compared,and the highest power density of those MFC was 3.06 W·m^-2.The effects of Fe_1-XS/CC and FeS/CC on the performance of MFC at start-up time and steady state were analyzed.The interaction mechanism between Fe_1-XS/CC and the Geobacterium was explored.The experimental results show that the interaction between the micro-nano particles on the electrode surface and the the Geobacterium is mutual transformation and adaptation.（1）During the start-up period,Fe_1-XS on the surface of Fe_1-XS/CC is decomposed into Fe²⁺and S^2-,an anaerobic and sulfur-containing environment is created to selectively express functional bacteria,and the relative abundance of the Geobacterium on the surface of the electrode increases from 0.5%at the beginning to 66.3%at the end.The electrogenic bacteria metabolize sodium acetate-Fe³⁺to produce biogenic Fe_1-XS and Fe₃O₄ on the surface of bacteria,which also increases the abundance of the Geobacterium population.（2）During the stable operation period of MFC,the biogenic Fe_1-XS and Fe₃O₄ on the surface of bacteria were converted into Fe（Met）Fe（CN）₆.A biological 3D conductive network framework was constructed on the anode,which increased the number of bacteria on the surface of the electrode and enhanced the electron transfer process.Therefore,this part puts forward a synergistic mechanism of microorganisms and minerals.To sum up,the simple method of in-situ preparation of FeS_X/CC nanosheets by MFC anode designed in this paper has reference significance for the development of microbial fuel cells,and the FeS_X electrodes with specific morphology can also be applied to different electrochemical fields.