Amino Functionalized Carbon Nanotubes Improve The Surface Properties Of Cathode And Enhance The Chromium Removal Efficiency Of Autotrophic Electroactive Bacteria

Cr(?)-reducing microbial fuel cells(MFCs)is an emerging biotechnology in the field of Cr(?)restoration.This technology uses electrochemically active microorganisms on the anode and cathode as a"catalyst"to reduce Cr(?)to Cr(III).Electrons produced by the electrochemically active bacteria on the anode surface oxidizing inorganic or organic matter are transferred to the cathode through an external circuit.The metal-reducing bacteria on the surface of the cathode further transfer electrons to the electron acceptor(Cr(?))to complete the reduction of Cr(?).At present,due to the limitation of cathode materials,the attachment speed of electrotrophic bacteria on the surface of the MFC cathode and its relatively small proportion in the biofilm greatly limit the efficiency of MFC's electricity generation and Cr(?)removal.In this paper,firstly,the amino surface electrode with high chromium removal potential was selected from the electrodes with different surface characteristics.Then,the effect of amino surface electrode on the formation of anode biofilm of microbial fuel cell was further studied.Finally,the mechanism of amino surface electrode promoting the cathodic biological chromium removal efficiency of sediment fuel cell was clarified.The specific research contents are as follows:(1)Selection of high efficiency chromium removal electrode based on surface characteristic testFirstly,NH₂-CNT/CC electrode with high chromium removal efficiency was selected based on the surface characteristics.In this study,we prepared three kinds of electrodes with different surface properties by using CNT(CC,COOH-CNT/CC and NH₂-CNT/CC).Specifically,CNT were functionalized by acidification and amination,and then the surface of carbon cloth was modified by layer by layer assembly technology to prepare COOH-CNT/CC and NH₂-CNT/CC electrodes(CC was blank electrode).Then,the modified electrode was selected based on its conductivity,mainly including the tests of the surface morphology,functional group composition,specific surface area and electrochemical catalytic ability.Finally,based on the chromium adsorption performance of the electrode,we compared the chromium adsorption capacity of the electrode in the chromium solution,and further screened the high-efficiency chromium removal electrode.(2)The effect of amino surface on the formation of biofilm of NH₂-CNT/CC electrodeThen we proved that the affinity amino surface can promote the formation of biofilm on the surface of the NH₂-CNT/CC electrode.After clarifying the properties of the NH₂-CNT/CC electrode,it is necessary to further study the influence of the NH₂-CNT/CC carbon cloth electrode on the formation of biofilms.Firstly,NH₂-CNT/CC was used as the anode of the dual-chamber MFC,and the enrichment rate of the biofilm on the electrode surface was verified by the voltage change of the MFC during multiple rounds of operation.The highest voltage reached by NH₂-CNT/CC was 643 m V.,The maximum power density was 1685 m W/m²,which is 1.3 times that of CC(1296m W/m²).After the operation,the electrochemical performance of the NH₂-CNT/CC electrode is tested to further characterize the electrode performance of the NH₂-CNT/CC in the MFC.Finally,the influence of the amino carbon nanotubes on the surface biomass formation of the NH₂-CNT/CC electrode was compared by observing the surface morphology of the electrode.(3)Study on the mechanism of high efficiency chromium removal of NH₂-CNT/CCWe further studied the high-efficiency chromium removal mechanism of the NH₂-CNT/CC bio-cathode deposit fuel cell.In this study,NH₂-CNT/CC was first used as the cathode of a sediment microbial fuel cell to perform a long-term chromium removal experiment to test the electricity generation and biological chromium removal efficiency of the NH₂-CNT/CC electrode.The highest voltage of NH₂-CNT/CC reached 241 m V,which was 1.76 times that of CC MFC(137 m V).On the 40th day,the removal rate of Cr(?)by CC reached a maximum of 0.99 mg/L·d,while the removal rate of Cr(?)by NH₂-CNT/CC SMFC was faster,reaching a maximum of2.04 on the 36th day.mg/L·d.Then after the experiment,the mechanism of NH₂-CNT/CC electrode to achieve high-efficiency biological chromium removal was clarified by means of electron microscopy,EDS,EPS,and electrochemical performance testing.Finally,16S r RNA sequencing technology was used to analyze the changes of the bacteria on the surface of the electrode to determine the chromium-reducing bacteria that can remove chromium in this experiment.