A manganese dioxide-polypyrrole composite electrode and its preparation method and application in heavy metal detection

Abstract

The present invention provides a manganese dioxide-polypyrrole composite electrode, a preparation method thereof, and an application thereof in heavy metal detection. The present invention adopts an electrochemically in-situ modification method and a three-electrode system to modify a composite electrode composed of metallic nickel, polypyrrole, and manganese dioxide on the surface of the electrode. This electrode combines conductive polypyrrole with manganese oxide having good catalytic activity, greatly improving the ion transport and electron transfer rates during the redox reaction process, increasing the sensitivity of the electrode to the detection of metal ions, and reducing the detection limit. At the same time, the composite structure of the copolymer and the metal on the electrode surface increases the stability of the electrode, enabling the electrode to be reused in a cyclic manner. This composite electrode can be used for the simultaneous detection of trace amounts of Hg<supgt;2+< / supgt>, Pb<supgt;2+< / supgt>, and Cu<supgt;2+< / supgt> ions.

Description

Technical Field

[0001] The invention belongs to the field of electrochemical sensors, in particular to the field of electrochemical detection of heavy metal ions, and relates to a manganese dioxide-polypyrrole composite electrode and a preparation method thereof and application in heavy metal detection. Background Art

[0002] Heavy metals refer to metals with a specific gravity greater than 5, including gold, silver, copper, iron, lead, mercury, etc. With the mining, smelting and processing of heavy metals, a lot of heavy metals have entered the atmosphere, water and soil, causing serious environmental pollution. For example, heavy metals discharged with wastewater, even in low concentrations, can accumulate in algae and sediments, be adsorbed on the surface of fish and shellfish, and concentrate in the food chain, thus causing public hazards. Heavy metals can interact strongly with proteins and various enzymes in the human body, making them inactive, and may also be enriched in certain organs of the human body. If they exceed the limit that the human body can tolerate, they will cause acute poisoning, subacute poisoning, chronic poisoning, etc., which will cause great harm to the human body.

[0003] Activity and persistence indicate the stability of pollutants in the environment. Highly active pollutants are prone to chemical reactions in the environment or during treatment, which reduces their toxicity, but they may also generate pollutants that are more toxic than the original ones, constituting secondary pollution. For example, mercury can be converted into methylmercury, which is more toxic. In contrast to activity, persistence means that some pollutants can maintain their harmfulness for a long time, such as heavy metal lead, which is toxic and difficult to degrade in nature, and can produce bioaccumulation, threatening human health and survival for a long time.

[0004] In natural water bodies, the toxicity of heavy metals generally ranges from 1 to 10 mg / L, while the toxicity of mercury and other substances ranges from 0.01 to 0.001 mg / L. Therefore, the immediate detection of trace amounts of heavy metal ions is extremely important.

[0005] Currently recognized heavy metal analysis methods include: ultraviolet spectrophotometry (UV), atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), inductively coupled plasma (ICP), X-ray fluorescence spectroscopy (XRF), inductively coupled plasma mass spectrometry (ICP-MS), etc. However, these detection methods have high instrument costs, complex operations, long detection times, and the detection accuracy and repeatability cannot be guaranteed. The electrochemical method has a fast detection speed and accurate values, and can be used for emergency detection in on-site environments. Therefore, it is particularly important to develop electrochemical sensing electrodes that can be used for rapid detection of heavy metal ions.

[0006] Polypyrrole is a black solid that is amorphous and insoluble. It has high conductivity, biocompatibility and environmental stability. The monomer is highly active and can be easily oxidized and polymerized. It is non-toxic and environmentally friendly. Polypyrrole has broad application prospects in many fields such as sensors, electronic devices and functional films.

[0007] Therefore, the present invention combines polypyrrole with manganese dioxide having catalytic activity, and the prepared composite electrode has the advantages of high sensitivity, good stability, etc., and realizes the rapid detection of trace heavy metal ions. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a heavy metal ion detection electrode which can detect mercury, lead and copper ions simultaneously, and ensure its reliability and stability.

[0009] The invention provides a manganese dioxide-polypyrrole composite electrode for heavy metal detection and a preparation method thereof.

[0010] The purpose of the present invention is to provide a manganese dioxide-polypyrrole composite electrode, which takes a metal electrode as a substrate, comprises a working electrode, a reference electrode and an auxiliary electrode, comprises an electrode substrate and an electrode modification layer, wherein the working electrode, the reference electrode and the auxiliary electrode are integrated on the same plane of the electrode, the surface of the metal electrode is modified with a metal nickel layer, and the surface of the working electrode is modified with a manganese dioxide-polypyrrole modification layer.

[0011] Polypyrrole has semiconductor properties, so the quantitative relationship between the change in conductivity of polypyrrole when it is exposed to the detected molecules or ions and the concentration of the detected object can be used to achieve detection and analysis. In addition, polypyrrole also has good conductivity, chemical stability and biocompatibility, and can be compounded with a variety of active materials to enhance its catalytic performance and stability. The compound of polypyrrole and highly catalytically active oxides can significantly improve the conductive environment of the catalyst, maximize its catalytic performance, and obtain a more sensitive chemical sensor.

[0012] The manganese dioxide-polypyrrole modified layer has a three-dimensional bundle structure with a bundle width of 1.5-2.0 μm, wherein manganese dioxide particles are uniformly modified on the surface of polyaniline with a particle size of 5-20 nm.

[0013] The manganese dioxide-polypyrrole composite electrode provided by the present invention combines polypyrrole with excellent conductivity with manganese dioxide with good catalytic performance, and the synergistic effect thereof provides more channels for electron transfer and ion transmission, greatly increases the active area of ​​the electrode, improves the sensing characteristics and response time, and can realize the needs of instant detection and emergency detection at the detection site. At the same time, the three-dimensional skeleton structure of the composite electrode enhances the stability of the electrode, and the repeated recycling of the manganese dioxide-polypyrrole composite electrode can be realized.

[0014] Another object of the present invention is to provide a method for preparing a manganese dioxide-polypyrrole composite electrode.

[0015] The specific steps include:

[0016] S1. Preparation of Ni layer: preparing a Ni buffer layer on the surface of the electrode substrate by electrodeposition to obtain a nickel electrode;

[0017] S2. Preparation of polypyrrole film layer: using nickel electrode as substrate, polypyrrole electrode was prepared by electrodeposition method;

[0018] S3. Preparation of manganese dioxide-polypyrrole composite electrode: Using polypyrrole electrode as a base, manganese dioxide is in situ modified on its surface to obtain a manganese dioxide-polypyrrole composite electrode.

[0019] Further, in step S1, the electrodeposition method is: prepare a nickel plating solution, specifically 200-300 g / L of nickel sulfate, 20-30 g / L of nickel chloride, 20-30 g / L of boric acid, and 0.1-0.2 g / L of sodium dodecyl sulfate, and adjust the solution pH to 3.0-4.0; adopt a double electrode constant current mode, with a titanium mesh electrode as an anode and the electrode substrate as a cathode, set the temperature to 40-50 ° C, and the current density to 1.0-5.0 A / dm 2 , the electrodeposition time is 5 to 10 minutes.

[0020] The synthesis methods of polypyrrole mainly include chemical method and electrochemical polymerization method. The chemical method consumes more oxidants, and the obtained polypyrrole is easy to encapsulate impurities and needs further treatment before use. The electrochemical method is simple to operate, consumes less, and the conditions are easy to control. The obtained polypyrrole has good conductivity and mechanical properties, and can be directly polymerized and modified on the electrode. It is the main method for preparing polypyrrole modified electrodes.

[0021] Further, in step S2, the preparation method of the polypyrrole film layer is: using a nickel electrode as a working electrode, placing it in a polypyrrole solution, Pt as an auxiliary electrode, Ag / AgCl as a reference electrode, applying a potential of 0.3 to 0.8 V, and an electrodeposition time of 10 to 50 seconds, and then placing it in deionized water for ultrasonic cleaning for 3 to 5 minutes.

[0022] The specific composition of the polypyrrole solution is: 30-60 mmol / L pyrrole monomer, 0.1-0.5 mol / L Na2SO4, and 20-50 mmol / L sodium dodecyl sulfate.

[0023] Further, in step S3, the preparation method of the manganese dioxide-polypyrrole composite electrode is: prepare a manganese dioxide solution, the specific composition of which is 0.01~0.05M manganese acetate and 0.01~0.05M potassium chloride solution; adopt a three-electrode system, with a polypyrrole electrode as the working electrode, Pt as the counter electrode, and Ag / AgCl as the reference electrode, and use cyclic voltammetry for scanning deposition, with a potential range of 0.04~1.04V and a scan rate of 30~50mV / s.

[0024] The manganese dioxide-polypyrrole composite electrode prepared by the present invention was observed by scanning electron microscope (SEM).

[0025] Figure 1 is a SEM morphology image of the manganese dioxide-polypyrrole composite electrode prepared by the present invention, wherein Figure 1 (a) and Figure 1 (b) is the SEM image of the polypyrrole electrode. Figure 1 (c) and Figure 1 (d) is a SEM image of a manganese dioxide-polypyrrole composite electrode prepared after in-situ modification of manganese dioxide on the surface of a polypyrrole electrode. As can be seen from the figure, the polypyrrole electrode is regularly distributed in bundles. After in-situ modification by electrochemical methods, a layer of manganese dioxide film is evenly covered on the surface of the polypyrrole, which greatly increases the roughness of the composite electrode and effectively increases the specific surface area of ​​the modified electrode. Such a three-dimensional structure is conducive to the improvement of sensing performance.

[0026] Another object of the present invention is to provide an application of a manganese dioxide-polypyrrole composite electrode in heavy metal ion detection.

[0027] The manganese dioxide-polypyrrole composite electrode provided by the present invention can simultaneously detect trace heavy metals in a liquid environment, wherein the liquid environment includes water, sweat, urine, blood, beverages, food, soil and other environments.

[0028] The manganese dioxide-polypyrrole composite electrode provided by the invention can simultaneously monitor trace heavy metals including mercury, lead and copper ions.

[0029] The manganese dioxide-polypyrrole composite electrode prepared by the present invention can be directly connected to an electrochemical detection device to realize instant detection of heavy metal ions at the sampling site without complicated pre-treatment procedures, and can be specifically used for a portable rapid detection sensor.

[0030] The response performance of the manganese dioxide-polypyrrole composite electrode prepared by the present invention is tested by cyclic voltammetry scanning, chronoamperometric detection and other methods.

[0031] Attached Figure 2The square wave voltammetry curves of the manganese dioxide-polypyrrole composite electrode prepared by the present invention for detecting mercury ions of different concentrations. As can be seen from the figure, as the concentration of mercury ions increases, its characteristic peak current gradually increases, indicating that the manganese dioxide-polypyrrole composite electrode prepared by the present invention can achieve the single detection of mercury ions.

[0032] Attached Figure 3 The figure is a performance test curve of the manganese dioxide-polypyrrole composite electrode prepared by the present invention to lead ions at different scanning speeds, wherein the scanning speed is 60mV / s, 80mV / s, 100mV / s, 120mV / s, and 140mV / s. It can be seen from the figure that as the scanning speed increases, the lead ion peak current gradually increases, indicating that the manganese dioxide-polypyrrole composite electrode prepared by the present invention has excellent response performance to lead ions.

[0033] Attached Figure 4 The present invention is a manganese dioxide-polypyrrole composite electrode prepared by the present invention for detecting different concentrations of mercury ions, lead ions and copper ions (a) cyclic voltammetry curves and (b) linear fitting curves of peak current and ion concentration. As can be seen from the figure, as the concentration of the three heavy metal ions gradually increases, the corresponding peak current also gradually increases, and the fitting curves of ion concentration and peak current show a good linear relationship, indicating that the manganese dioxide-polypyrrole composite electrode prepared by the present invention has good response performance to the three heavy metal ions. At the same time, it can be seen from the figure that the three peaks representing mercury ions, lead ions and copper ions can be clearly distinguished, indicating that the manganese dioxide-polypyrrole composite electrode prepared by the present invention can realize the simultaneous detection of three heavy metal ions, mercury ions, lead ions and copper ions.

[0034] The above shows that the mercury ion, lead ion and copper ion composite electrode prepared by the present invention has high sensitivity and low detection limit for the detection of heavy metal ions mercury, lead and copper, and can realize simultaneous detection and separate instant detection of mercury ions, lead ions and copper ions.

[0035] The present invention adopts an electrochemical in-situ modification method and a three-electrode system to modify metal nickel, polypyrrole, and manganese dioxide on the electrode surface to form a composite electrode. The electrode combines conductive polypyrrole with manganese oxide with good catalytic activity, which greatly improves the speed of ion transmission and electron transfer during the redox reaction, increases the sensitivity of the electrode to metal ion detection, and reduces the detection limit. At the same time, the composite structure of the copolymer and the metal on the electrode surface increases the stability of the electrode, allowing the electrode to be reused. The composite electrode can be used to simultaneously detect trace amounts of Hg 2+ , Pb 2+ and Cu 2+ ion.

[0036] The beneficial effects of the present invention are:

[0037] (1) The present invention combines highly conductive polypyrrole with catalytically active manganese dioxide to form a multilayer skeleton structure of polymer / metal oxide. The synergistic effect between the structures greatly improves the response characteristics of the electrode to heavy metal ions, while increasing the stability of the electrode and improving the reliability and accuracy of detection.

[0038] (2) The electrode preparation process of the present invention is simple, and the in-situ modified electrochemical method can effectively avoid the agglomeration and inactivation of particles. It has low cost and is suitable for industrial application.

[0039] (3) The electrode of the present invention can realize the individual detection and simultaneous detection of heavy metal ion mercury, lead and copper pollutants in water, food and atmospheric environment, and promote the popularization and application of environmental rapid detection sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The invention is further described using the accompanying drawings, but the embodiments in the accompanying drawings do not constitute any limitation to the invention. A person skilled in the art can obtain other drawings based on the following drawings without creative work.

[0041] Figure 1 is a SEM morphology image of the manganese dioxide-polypyrrole composite electrode prepared by the present invention;

[0042] Figure 2 The square wave voltammetric curve of the manganese dioxide-polypyrrole composite electrode prepared by the present invention for detecting mercury ions of different concentrations;

[0043] Figure 3 This is a performance test curve of the manganese dioxide-polypyrrole composite electrode prepared by the present invention for lead ions at different scanning speeds;

[0044] Figure 4 The present invention discloses (a) a cyclic voltammetry curve and (b) a linear fitting curve of peak current and ion concentration of the manganese dioxide-polypyrrole composite electrode prepared by the present invention for detecting mercury ions, lead ions and copper ions of different concentrations. DETAILED DESCRIPTION

[0045] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail in conjunction with the following specific embodiments and with reference to the accompanying drawings.

[0046] Example 1

[0047] Preparation of manganese dioxide-polypyrrole composite electrode:

[0048] S1. Electrode pretreatment: PI was selected as the substrate material and the substrate PI was pretreated. Specifically, PI was placed in acetone, ultrasonically treated for 5 minutes, washed with deionized water and then immersed in a 2.0 M hydrochloric acid solution for 10 minutes.

[0049] S2. Preparation of Ni layer: Prepare an electroplated nickel solution with the following composition: 200 g / L nickel sulfate; 20 g / L nickel chloride; 20 g / L boric acid; 0.1 g / L sodium dodecyl sulfate; adjust the solution pH to 3.0. Use a dual-electrode constant current mode, with a titanium mesh electrode as the anode and PI as the cathode, set the temperature to 40°C, and the current density to 1.0 A / dm 2 , electroplating treatment for 5 minutes to obtain a Ni buffer layer.

[0050] S3. Preparation of polypyrrole film layer: prepare polypyrrole solution, the specific composition is: 30mmol / L pyrrole monomer, 0.1mol / L Na2SO4, 20mmol / L sodium dodecyl sulfate. Place Ni / PI electrode into the prepared polypyrrole solution, adopt a three-electrode system, use the above electrode as the working electrode, Pt as the counter electrode, Ag / AgCl as the reference electrode, apply 0.3V potential, electrodeposition time 50s, and then place in deionized water for ultrasonic cleaning for 3min to obtain PPy / Ni electrode.

[0051] S4. Preparation of composite electrode: Using PPy / Ni electrode as substrate, in-situ modify manganese dioxide on its surface. Prepare 0.01M manganese acetate and 0.01M potassium chloride solution. Use a three-electrode system, with PPy / Ni electrode as working electrode, Pt as counter electrode, and Ag / AgCl as reference electrode. Use cyclic voltammetry for scanning deposition, with a potential range of 0.04V and a scanning speed of 30mV / s to obtain a manganese dioxide-polypyrrole composite electrode.

[0052] Example 2

[0053] Preparation of manganese dioxide-polypyrrole composite electrode:

[0054] S1. Electrode pretreatment: ceramics were selected as the base material, and the base ceramics were pretreated. Specifically, the ceramic base was placed in acetone, ultrasonically treated for 10 minutes to remove surface stains, washed with deionized water, and then immersed in a 4.0 M hydrochloric acid solution for 15 minutes to remove the oxide layer and roughen the surface.

[0055] S2. Preparation of Ni layer: Prepare an electroplated nickel solution with the following composition: 300 g / L nickel sulfate; 30 g / L nickel chloride; 30 g / L boric acid; 0.2 g / L sodium dodecyl sulfate; adjust the solution pH to 4.0. Use a dual-electrode constant current mode, with a titanium mesh electrode as the anode and a ceramic substrate as the cathode, set the temperature to 50°C, and the current density to 5.0 A / dm2 , electroplating treatment for 10 min to obtain a Ni buffer layer.

[0056] S3. Preparation of polypyrrole film layer: prepare polypyrrole solution, the specific composition is: 60mmol / L pyrrole monomer, 0.5mol / L Na2SO4, 50mmol / L sodium dodecyl sulfate. Place the above electrode into the prepared polypyrrole solution, adopt a three-electrode system, use the above electrode as the working electrode, Pt as the counter electrode, Ag / AgCl as the reference electrode, apply a potential of 0.8V, electrodeposition time 10s, and then place in deionized water for ultrasonic cleaning for 5min to obtain a PPy / Ni electrode.

[0057] S4. Preparation of composite electrode: Using PPy / Ni electrode as substrate, in-situ modify manganese dioxide on its surface. Prepare 0.05M manganese acetate and 0.05M potassium chloride solution. Use a three-electrode system, with PPy / Ni electrode as working electrode, Pt as counter electrode, and Ag / AgCl as reference electrode. Use cyclic voltammetry for scanning deposition, with a potential range of 1.04V and a scanning speed of 50mV / s to obtain a manganese dioxide-polypyrrole composite electrode.

[0058] Example 3

[0059] Preparation of manganese dioxide-polypyrrole composite electrode:

[0060] S1. Electrode pretreatment: Silicon base was selected as the base material, and the base silicon base was pretreated. Specifically, the silicon base was placed in acetone, ultrasonically treated for 8 minutes to remove surface stains, washed with deionized water, and then immersed in a 3.0 M hydrochloric acid solution for 12 minutes to remove the oxide layer and roughen the surface.

[0061] S2. Preparation of Ni layer: Prepare the electroplated nickel solution, the specific composition is: nickel sulfate 250g / L; nickel chloride 25g / L; boric acid 25g / L; sodium dodecyl sulfate 0.15g / L; adjust the solution pH to 3.5. Use the double electrode constant current mode, with the titanium mesh electrode as the anode and the silicon-based electrode as the cathode, set the temperature to 45°C, and the current density to 3.0A / dm 2 , electroplating treatment for 8 minutes to obtain a Ni buffer layer.

[0062] S3. Preparation of polypyrrole film layer: prepare polypyrrole solution, the specific composition is: 50mmol / L pyrrole monomer, 0.3mol / L Na2SO4, 35mmol / L sodium dodecyl sulfate. Place the above electrode into the prepared polypyrrole solution, adopt a three-electrode system, use the above electrode as the working electrode, Pt as the counter electrode, Ag / AgCl as the reference electrode, apply a potential of 0.5V, electrodeposition time 30s, and then place in deionized water for ultrasonic cleaning for 4min to obtain a PPy / Ni electrode.

[0063] S4. Preparation of composite electrode: Using PPy / Ni electrode as substrate, in-situ modify manganese dioxide on its surface. Prepare 0.03M manganese acetate and 0.03M potassium chloride solution. Use a three-electrode system, with PPy / Ni electrode as working electrode, Pt as counter electrode, and Ag / AgCl as reference electrode. Use cyclic voltammetry for scanning deposition, with a potential range of 0.08V and a scanning speed of 40mV / s to obtain a manganese dioxide-polypyrrole composite electrode.

[0064] Example 4

[0065] Preparation of manganese dioxide-polypyrrole composite electrode:

[0066] S1. Electrode pretreatment: FR-4 was selected as the substrate material, and the substrate FR-4 was pretreated. Specifically, FR-4 was placed in acetone, ultrasonically treated for 6 minutes to remove surface stains, washed with deionized water, and then immersed in a 4.0M hydrochloric acid solution for 11 minutes to remove the oxide layer and roughen the surface.

[0067] S2. Preparation of Ni layer: Prepare an electroplated nickel solution with the following composition: 280 g / L nickel sulfate; 28 g / L nickel chloride; 28 g / L boric acid; 0.18 g / L sodium dodecyl sulfate; adjust the solution pH to 3.0. Use a dual-electrode constant current mode, with the titanium mesh electrode as the anode and the silicon-based electrode as the cathode, set the temperature to 50°C, and the current density to 2.0 A / dm 2 , electroplating treatment for 9 minutes to obtain a Ni buffer layer.

[0068] S3. Preparation of polypyrrole film layer: prepare polypyrrole solution, the specific composition is: 40mmol / L pyrrole monomer, 0.4mol / L Na2SO4, 25mmol / L sodium dodecyl sulfate. Place Ni electrode in the prepared polypyrrole solution, adopt three-electrode system, use the above electrode as working electrode, Pt as counter electrode, Ag / AgCl as reference electrode, apply 0.7V potential, electrodeposition time 40s, and then place in deionized water for ultrasonic cleaning for 5min to obtain PPy / Ni electrode.

[0069] S4. Preparation of composite electrode: Using PPy / Ni electrode as substrate, in-situ modify manganese dioxide on its surface. Prepare 0.04M manganese acetate and 0.04M potassium chloride solution. Use a three-electrode system, with PPy / Ni electrode as working electrode, Pt as counter electrode, and Ag / AgCl as reference electrode. Use cyclic voltammetry for scanning deposition, with a potential range of 0.06V and a scanning speed of 35mV / s to obtain a manganese dioxide-polypyrrole composite electrode.

[0070] Example 5

[0071] Detection of heavy metal ions Hg by manganese dioxide-polypyrrole composite electrode 2+ :

[0072] The manganese dioxide-polypyrrole composite electrode prepared in Example 1 was used as the working electrode, the reference electrode was the Ag / AgCl electrode, and the platinum electrode was used as the counter electrode. The deposition potential was 0.2 V, the deposition time was 60 s, the amplitude was 0.05 V, the test concentration gradient was 0.8-1.3 mg / L (0.1 mg / L gradient), and the square wave voltammetry curve of the composite electrode for mercury ion detection was obtained. Figure 2 .

[0073] Attached Figure 2 It shows that the peak current density increases with Hg 2+ The concentration increases, so the manganese dioxide-polypyrrole composite electrode prepared in Example 1 has excellent response characteristics to trace mercury ions and can be used for the separate detection of trace mercury ions.

[0074] Example 6

[0075] Detection of heavy metal ion Pb by manganese dioxide-polypyrrole composite electrode 2+ :

[0076] Take the manganese dioxide-polypyrrole composite electrode prepared in Example 2, use acetic acid-sodium acetate buffer solution with pH 3.5 as the test solution, and test at scanning speeds of 60mV / s, 80mV / s, 100mV / s, 120mV / s, and 140mV / s. Scan 10 times, take the last time as the result display, and get the attached Figure 3 .

[0077] Attached Figure 3 It shows that the peak current density increases with the increase of scanning speed. Therefore, the manganese dioxide-polypyrrole composite electrode prepared in Example 2 has excellent response characteristics to lead ions and can be used for the separate detection of trace lead ions.

[0078] Example 7

[0079] Manganese dioxide-polypyrrole composite electrode simultaneously three heavy metal ions:

[0080] The manganese dioxide-polypyrrole composite electrode prepared in Example 3 was used as the working electrode, and was placed in a 0.1 mol / L acetic acid-sodium acetate buffer solution (pH 4.5), and Pb was gradually added. 2+ , Hg 2+ and Cu 2+ The mixed solution was prepared with platinum as the counter electrode, silver-silver chloride as the reference electrode, the deposition potential was -1.3V, the deposition time was 180s, the test concentration was 1.40-2.40mg / L, and the peak current change curve was measured to obtain the attached Figure 4 .

[0081] Attached Figure 4 It shows that the peak current density increases with the concentration of the mixed solution, and three completely different oxidation peaks appear, corresponding to Pb 2+ , Hg 2+ and Cu 2+ Three heavy metal elements, therefore, the manganese dioxide-polypyrrole composite electrode prepared in Example 3 can simultaneously detect trace heavy metal elements lead ions, mercury ions and copper ions.

[0082] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0083] In addition, it should be understood that although this specification is described in accordance with the implementation methods, not every implementation method contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should take the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art. The technical details not described in detail in the present invention can be implemented by any prior art in the art. In particular, all technical features not described in detail in the present invention can be implemented by any prior art.

Claims

1. A manganese dioxide-polypyrrole composite electrode, with a metal electrode as a substrate, including a working electrode, a reference electrode and an auxiliary electrode, including an electrode substrate and an electrode modification layer, characterized in that: The working electrode, the reference electrode and the auxiliary electrode are integrated on the same plane of the electrodes, the metal electrode surface is modified with a metal nickel layer, and the working electrode surface is modified with a manganese dioxide-polypyrrole modification layer; an electrochemical in-situ modification method is adopted, and the manganese dioxide-polypyrrole modification layer has a three-dimensional bundle structure, and the bundle width is 1.5 to 2.0 μm, wherein manganese dioxide particles are uniformly modified on the polypyrrole surface, and the particle size is 5 to 20 nm; The manganese dioxide-polypyrrole composite electrode can simultaneously detect trace heavy metals in a liquid environment; The trace heavy metals include mercury, lead and copper ions.

2. The method for preparing a manganese dioxide-polypyrrole composite electrode according to claim 1, characterized in that: The following steps are involved: S1. Preparation of Ni layer: preparing a Ni buffer layer on the surface of the electrode substrate by electrodeposition to obtain a nickel electrode; S2. Preparation of polypyrrole film layer: using nickel electrode as substrate, polypyrrole electrode was prepared by electrodeposition method; S3. Preparation of manganese dioxide-polypyrrole composite electrode: Using polypyrrole electrode as substrate, manganese dioxide is in situ modified on its surface to obtain manganese dioxide-polypyrrole composite electrode.

3. The method for preparing the manganese dioxide-polypyrrole composite electrode according to claim 2, characterized in that: In step S1, the electrodeposition method is as follows: prepare a nickel plating solution, specifically 200-300 g / L nickel sulfate, 20-30 g / L nickel chloride, 20-30 g / L boric acid, and 0.1-0.2 g / L sodium dodecyl sulfate, and adjust the solution pH to 3.0-4.0; adopt a double-electrode constant current mode, with a titanium mesh electrode as an anode and the electrode substrate as a cathode, set the temperature to 40-50°C, and the current density to 1.0-5.0 A / dm 2 , the electrodeposition time is 5 to 10 minutes.

4. The method for preparing the manganese dioxide-polypyrrole composite electrode according to claim 2, characterized in that: In step S2, the preparation method of the polypyrrole film layer is: using the nickel electrode as the working electrode, placing it in a polypyrrole solution, using Pt as the auxiliary electrode, and using Ag / AgCl as the reference electrode, applying a potential of 0.3 to 0.8 V, and the electrodeposition time is 10 to 50 seconds, and then placing it in deionized water for ultrasonic cleaning for 3 to 5 minutes.

5. The method for preparing the manganese dioxide-polypyrrole composite electrode according to claim 4, characterized in that: The specific composition of the polypyrrole solution is: 30-60 mmol / L pyrrole monomer, 0.1-0.5 mol / L Na2SO4, and 20-50 mmol / L sodium dodecyl sulfate.

6. The method for preparing the manganese dioxide-polypyrrole composite electrode according to claim 2, characterized in that: In step S3, the preparation method of the manganese dioxide-polypyrrole composite electrode is: preparing a manganese dioxide solution, specifically composed of 0.01-0.05M manganese acetate and 0.01-0.05M potassium chloride solution; A three-electrode system is adopted, with the polypyrrole electrode as the working electrode, Pt as the counter electrode, and Ag / AgCl as the reference electrode, and cyclic voltammetry is used for scanning deposition, with a potential range of 0.04 to 1.04 V and a scanning rate of 30 to 50 mV / s.

7. Use of the manganese dioxide-polypyrrole composite electrode as claimed in claim 1 in the detection of heavy metal ions.

8. Use of the manganese dioxide-polypyrrole composite electrode in heavy metal ion detection according to claim 7, characterized in that: The manganese dioxide-polypyrrole composite electrode can simultaneously detect trace heavy metals in a liquid environment, and the liquid environment includes water, sweat, urine, blood, beverages, food and soil environments.

9. Use of the manganese dioxide-polypyrrole composite electrode in heavy metal ion detection according to claim 8, characterized in that: The trace heavy metals include mercury, lead and copper ions.

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