| Since the 21st century,China and the world have paid great attention to inorganic pollutants,especially to some highly toxic and harmful inorganic pollutants,including heavy metal pollutants,such as mercury,lead,arsenic,zinc,and tin,and inorganic nonmetallic ion contaminants,such as nitrite,sulfides,cyanides and fluorides.Large amount of these toxic and harmful inorganic pollutants will seriously affect the balance of the ecosystem and human health.Therefore,the research on the detection of trace inorganic pollutants is very important.The electrochemical sensor is a detection technology based on ionic conductivity.It has the advantages of fast detection,high sensitivity,easy to operate,low cost and convenient to carry.This technology promotes the development of detection methods for inorganic pollutants.In the experiment,a variety of modified electrodes were prepared for the detection of inorganic pollutants by using dyes and nano-gold particales?AuNPs?based on a glassy carbon electrode?GCE?.The techniques of Cyclic Voltammetry?CV?,Differential pulse voltammetry?DPV?,Linear Sweep Voltammetry?LSV?,Potentiostatic method?Chronoamperometry?,Anodic Stripping Voltammetry?ASV?,and Electrochemical Impedance Spectroscopy?EIS?were used to investigate the electrochemical properties of electrodes.Specific contents are as follows:?1?Preparation of composite electrodes modified with DL-1,4-dithiothreitol?DTT?,AuNPs and methylene blue?PMB?and its application for the detection of mercury ionsMercury ions can bind to sulfhydryl group of DTT because of the strong coordination between them.The concentration of the mercury ion can be determined by measuring the reduction peak current of mercury ions.Methylene blue film?PMB?was prepared by electropolymerization on the bare GCE.Then,AuNPs were deposited by potentiostatic method.Finally,sulfhydryl group was prepared by self-assembly of DTT.The modified electrode was characterized by scanning electron microscopy?SEM?and Energy Dispersive Spectrometer?EDS?.The electrochemical properties of the modified electrode were studied by electrochemical methods such as CV,DPV and EIS.The results showed that the AuNPs exhibited as the morphology of nano-flowers,and uniformly distributed on the surface of the electrode.A small amount of S and O elements were detected by EDS on the surface of the electrode,indicating that thePMB film and DTT film have formed on the electrode surface.Electrochemical studies showed that the capacitive reactance and specific surface area of the modified electrode were increased.Due to the poor conductivity of the DTT film,the electron transferon the electrode surface was slightly reduced,thus verifying the successful preparation of the composite electrode.DPV was used to detect mercury ions with a linear range of 1.0×10-91.0×10-3 mol/L,and the detection limit was 5.4×10-10 mol/L?S/N=3?.Additionally,good specific recognition and reproducibility of the composite electrode for the detection of mercury ions were obtained,indicating that this electrode can be successfully used to detect mercury ions in water environment.?2?Preparation of composite electrodes modified with acidified multi-walled carbon nanotubes?f-MWCNTs?,AuNPs,and PMB and its detection of mercury ionsIn this experiment,the concentration of mercury ions was determined by measuring the peak current resulted from mercury oxidation by using ASV.Similarly,the bare glassy carbon electrode was used as the working electrode,and f-MWCNTs were modified onto the surface of the glassy carbon electrode by a dropwise coating method.Then,PMB was prepared by electropolymerization,and finally,AuNPs were electrodeposited by Chronoamperometry.The modified electrode was characterized by SEM and EDS.The electrochemical properties of the modified electrode were studied by electrochemical methods such as CV,ASV and EIS.The results showed that the layer of PMB combined with f-MWCNTs was porous,and AuNPs evenly distributed on the surface of the electrode.After the modification of f-MWCNTs,the electrode not only was mechanically strong,but also had good electrical conductivity.It could be confirmed by the EDS analysis that the PMB film has been successfully electropolymerized onto the electrode surface.Electrochemical studies have shown that the specific surface area of the modified electrode was greatly increased,providing more active sites for nano-gold deposition and further improving the performance of the modified electrode.ASV was used to detect mercury ions with a linear range of 1.0×10-81.0×10-4 mol/L,and the detection limit was 8.8×10-9 mol/L?S/N=3?.Additionally,good anti-interference and reproducibility of the composite electrode for the detection of mercury ions were obtained,indicating that this electrode can be successfully used to detect mercury ions in water environment.?3?Preparation of composite electrodes modified with f-MWCNTs,AuNPs and methyl red?PMR?and its detection of nitrite ionsIn this experiment,the concentration of nitrite ions was determined by measuring the peak current resulted from mercury oxidation by using CV.The bare GCE was used as the working electrode,on which f-MWCNTs were modified by a dropcoating method,and then PMR was prepared by electropolymerization technique.Finally,AuNPs were electrochemically deposited.The modified electrode was characterized by SEM and EDS.The electrochemical properties of the modified electrode were studied by electrochemical methods such as CV,LSV and EIS.The results showed that the composite of PMR and f-MWCNTs with three-dimentional spatial structure was obtained,and AuNPs uniformly distributed on the surface of the electrode.As demonstrated by EDS analysis,the existence of nitrogen element confirmed that PMR has been successfully modified onto the electrode surface.The electrochemical experiment results indicated that large specific surface area of the modified electrode could help to provide more active sites for nano-gold deposition,thus improving the performance of the modified electrodes.LSV was used to detect nitrite ions with a linear range of 1.0×10-61.0×10-3 mol/L.The detection limit was 7.3×10-7 mol/L?S/N=3?.The repeatability and interference experiment results showed that the prepared composite electrode had relatively high capability of anti-interference and good reproducibility for the detection of nitrite ions,and could be used for the detection of nitrite ions in water environment. |
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