Study On Interference Mechanism And Anti-interference Regulation Of Dissolved Organic Matters On Electrochemical Sensing Of Heavy Metals In Aqueous Environment

With the rapid development of industry in China,a large amount of heavy metal-containing industrial wastewater is discharged into surface water and groundwater,which severely harms the environment and human health.Therefore,the accurate,rapid and sensitive detection of heavy metal ions in aqueous environment can help reduce the environment risk of heavy metals from the source.Compared with traditional heavy metal detection methods,electrochemical detection method has the advantages of fast detection speed,low detection cost,and ability of in-situ detection.However,the composition of environmental water is complex,and common dissolved organic matters（DOMs）can interact with heavy metal ions and electrode surfaces,which severely interferes with the accuracy of electrochemical detection and severely restricts the application of electrochemical methods in the field of environmental monitoring.In this thesis,a new bismuth-based electrode was used to build a heavy metal electrochemical sensing platform.The effects of different types of DOMs on the peak current of electrochemical detection of heavy metals were systematically explored.The interference mechanism of DOMs on the electrochemical detection of heavy metals was revealed and the relevant anti-interference pathways were explored to break through the bottleneck of electrochemical method in the application of complex water environment.The main results and conclusions are summarized as follows:（1）The corn flour was used as a precursor,a lotus-shaped porous biocarbon material was successfully prepared by pre-carbonization and KOH activation method,and then porous carbon decorated with bismuth nanaoparticles（Bi/C）were prepared by hydrothermal method and thermal reduction method.The cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）results showed that Bi/C composites possessed a large number of active sites and excellent electron transfer properties.The Bi/C composite materials were used as electrode materials to modify glassy carbon electrodes and 200,300μm microgrid electrodes for electrochemical detection of heavy metal ions.The detection range was up to 10-100 ppb,and the sensitivity was 0.230μA/ppb.The favorable detection performance was attributed to the excellent electrical conductivity of biocarbon and the effective binding sites provided by elemental bismuth.（2）The effects of different concentrations of DOMs on the electrochemical detection of heavy metals were characterized by the change in the stripping peak current.It was found that humus significantly inhibited the peak current,and the effects of surfactants on the peak current were determined by their ionic type.For example,sodium dodecyl sulfate（SDS,an anionic surfactant）of 1000 ppm could increase the peak current of Pb²⁺by 80%,while TX-100（non-ionic surfactant）of 300 ppm could reduce it by 100%.Taking the transmission of heavy metal ions in solutions and at the working electrode surface as the starting point,the internal mechanism of the effects of fulvic acid（FA）,humic acid（HA）,and SDS on electrochemical detection were revealed respectively using a series of characterization methods including density functional theory（DFT）,rotating disk electrode（RDE）,and EIS.The results showed that the interference mechanism of FA and HA was similar,who would combine with heavy metals to inhibit the diffusion of heavy metal ions in the solution to the electrode surface and the electron transfer of heavy metals on the electrode surface（affect the deposition process）.Moreover,the electrode would be passivated（affects the stripping process）.The interference extent of FA and HA was affected by p H,the lower the p H,the weaker the interference.On the one hand,SDS could combine with heavy metal ions by electrostatic interaction to accelerate the diffusion of heavy metal ions between the solution and the electrode surface,which would promote the deposition and stripping process of electrochemical detection.On the other hand,SDS could be adsorbed on the electrode surface,which would lead to electrode passivation and inhibit electron transfer of heavy metal ions on the electron surface.（3）Taking the acceleration of diffusion of heavy metal ions in solutions as the starting point,two anti-interference methods for FA and HA were proposed in this thesis based on the interference mechanism of DOMs on the electrochemical detection of heavy metals:（a）The interference of FA and HA was suppressed by adding high concentration of SDS.The relative peak currents after interference were restored from 10%and 19%to 128%and 45%respectively with addition of 1000 ppm SDS,and SDS was successfully applied as an anti-interference agent for electrochemical detection of heavy metals in actual water samples including Yujia Lake water,Tangxun Lake wastewater and leachate.It was found the lower the DOMs contents in water samples,the better the anti-interference effects.The anti-interference mechanism of SDS was studied by RDE and adding high concentration SDS as an interfering agent before the deposition or stripping process.The results showed that high concentration of SDS could easily complex with Pb²⁺in contrast to FA or HA,thereby accelerating the diffusion of Pb²⁺between the solution and the electrode surface.（b）The microelectrode systems were used as a heavy metal sensing platform to suppress the interference of FA and HA.The results showed that the microgrid electrode can completely eliminate the interference of FA and HA at concentrations of 40 ppm and below.And the smaller the electrode size,the better the anti-interference effects on FA and HA by comparing the effects of different concentrations of FA and HA on the stripping peak current of the glassy carbon electrode,300μm and 200μm microgrid electrode systems.The anti-interference mechanism of microgrid electrode was speculated based on the unique electrochemical properties of the microelectrode:the hemispherical diffusion mode provided by the microelectrode could greatly accelerate the diffusion process of heavy metal ions from the solution to the electrode surface.