A sensitive electrode for detecting heavy metal ions in water without pre-enrichment, a preparation method and applications thereof

Abstract

The application relates to a sensitive electrode for electrochemically detecting heavy metal ions in water without pre-enrichment, a preparation method and application thereof in detecting heavy metal ions in water, and belongs to the technical field of electrochemical sensing. First, carbon cloth is cleaned, then a mixed solution of sodium tungstate, sodium molybdate, perchloric acid and hydrogen peroxide is used as a deposition solution, the carbon cloth is used as a working electrode, a platinum sheet is used as a counter electrode, and an Ag / AgCl electrode is used as a reference electrode to perform electrochemical deposition, and a molybdenum-doped tungsten oxide sensitive electrode is obtained after cleaning; the molybdenum-doped tungsten oxide sensitive electrode is used as a working electrode, a platinum sheet is used as a counter electrode, and a saturated calomel electrode is used as a reference electrode to detect cadmium ions, lead ions, copper ions and mercury ions. The sensitive electrode prepared by the electrochemical technology has the characteristics of direct high efficiency, good electrochemical detection capability, high sensitivity, wide linear detection range, low detection limit, good stability and good repeatability.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical sensing technology, specifically relating to a sensitive electrode for the electrochemical detection of heavy metal ions in water without pre-enrichment, its preparation method, and its application in the detection of heavy metal ions in water. Background Technology

[0002] There are many pathways to exposure to heavy metal pollution, such as through the atmosphere, soil, food, drinking water, building materials, and daily necessities. While the concentration of heavy metal ions in water is often low, their bioavailability is frequently higher than that in food. This means that even small amounts of heavy metal ions in water can pose a significant health risk. Therefore, achieving rapid, trace-level, accurate, and highly selective on-site detection of heavy metal ions in water is crucial.

[0003] Currently, various techniques are used for the detection of heavy metal ions, such as atomic absorption spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS), and X-ray fluorescence spectrometry (XRF). These techniques are widely used due to their high sensitivity, but they require expensive equipment and complex operation. In contrast, electrochemical detection equipment is simple and easy to operate. Stripping voltammetry is a commonly used and highly sensitive electrochemical analysis method for analyzing trace components. However, traditional stripping voltammetry requires pre-concentration before stripping, i.e., reducing heavy metal ions to zero valence through electrodeposition. While the pre-concentration process improves the sensitivity of detection, it also increases the complexity of the detection process, reduces detection efficiency, and increases power consumption. Furthermore, to ensure successful reduction of heavy metal ions, pre-concentration is usually carried out at low potentials (<-1.0V), which may lead to hydrogen evolution reaction, which is detrimental to the long-term use of the electrode. Summary of the Invention

[0004] The purpose of this invention is to provide a sensitive electrode for the electrochemical detection of heavy metal ions in water without pre-enrichment, its preparation method, and its application in the detection of heavy metal ions in water.

[0005] This invention utilizes an in-situ growth method to grow molybdenum-doped tungsten oxide on a carbon cloth current collector via electrochemical deposition, fabricating a carbon cloth-supported molybdenum-doped tungsten oxide sensitive electrode. This electrode is then used for rapid, direct, and electrochemical detection of heavy metal ions in water without pre-concentration. The electrode offers advantages such as simple fabrication process, good stability, strong detection capability, and environmental friendliness.

[0006] The present invention discloses a method for preparing a sensitive electrode for direct detection of heavy metal ions in water without pre-concentration, comprising the following steps:

[0007] (1) Use carbon cloth as a support electrode and clean the carbon cloth;

[0008] (2) Electrochemical deposition is performed using the carbon cloth obtained in step (1) as the working electrode, the platinum sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode. The deposition solution is a mixture of sodium tungstate aqueous solution, sodium molybdate aqueous solution, perchloric acid aqueous solution and hydrogen peroxide aqueous solution. After deposition, tungsten oxide is obtained on the surface of the carbon cloth. After cleaning, the sensitive electrode for direct detection of heavy metal ions in water without pre-enrichment, as described in this invention, namely the molybdenum-doped tungsten oxide sensitive electrode supported by carbon cloth (Mo-WO3-CC), is obtained.

[0009] Preferably, in step (1) the carbon cloth cleaning process, the reagent used is one or more of toluene, acetone, ethanol, and hydrochloric acid;

[0010] Preferably, in step (1) the cleaning process of carbon cloth, the cleaning time for each reagent is 10 to 15 minutes, and the cleaning process is ended by rinsing with deionized water.

[0011] Preferably, the sodium tungstate aqueous solution used in step (2) has a concentration of 0.01–0.04 M, the sodium molybdate aqueous solution has a concentration of 0.001–0.015 M, the perchloric acid aqueous solution has a mass fraction of 70%–72%, the hydrogen peroxide aqueous solution has a mass fraction of 30%, and the volume ratio of the four solutions is 85–105:20–30:1–5:0.5–2;

[0012] Preferably, the electrochemical deposition in step (2) can be pulsed current electrodeposition, with a current of -0.002 to 0.005 A / cm² in one deposition cycle. 2 The current was maintained for 0.1–0.3 s, 0 A / cm. 2 The current was maintained for 0.1 to 0.3 seconds for 4,000 to 6,000 cycles.

[0013] The sensitive electrode for direct detection of heavy metal ions in water without pre-concentration described in this invention is prepared by the above method.

[0014] This invention discloses a sensitive electrode for direct detection of heavy metal ions in water without pre-concentration. This electrode can be applied to the detection of heavy metal ions in water. It utilizes an electrochemical workstation with Mo-WO3-CC as the working electrode, a platinum sheet (1.0cm × 1.0cm) as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. The electrolyte consists of a 0.1–0.3M acetate buffer solution and different concentrations of Cd. 2+ Pb 2+ Cu 2+ Hg 2+The mixed aqueous solution (hereinafter referred to as HMIs solution) was analyzed using differential pulse stripping voltammetry (DPASV) to detect heavy metal ions in the water. The differential pulse voltammetry test curve (DPV) of the sensitive electrode in the HMIs solution and the stripping peak current intensity of the test curve were obtained. A plot of "stripping peak current intensity - Cd" was then generated. 2+ Pb 2 + Cu 2+ or Hg 2+ A linear standard curve for concentration was obtained; further, the sensitive electrode described in this invention was used to test HMIs solutions with unknown metal ion concentrations. Under the same test conditions, the dissolution peak current of the DPV curve could be obtained. Using the above linear standard curve, Cd was calculated. 2+ Pb 2+ Cu 2+ or Hg 2+ The concentration is used to detect heavy metal ions in water.

[0015] Preferably, the pH of the acetate buffer solution is 4 to 6.

[0016] The sensitive electrode prepared by this invention for the direct electrochemical detection of copper ions in water has the following advantages:

[0017] 1) The carbon cloth used in this invention has the advantages of acid and alkali resistance, and can meet the testing requirements of heavy metal ions in solutions under different pH conditions;

[0018] 2) This invention constructs a self-supporting electrode, eliminating the need for spraying / coating sensitive materials, thus giving the electrode better stability;

[0019] 3) This invention introduces oxygen vacancy defects by doping tungsten oxide with molybdenum. Utilizing the valence change characteristics of oxygen vacancies and tungsten, the self-reduction of heavy metal ions on the electrode surface is achieved, thus enabling the detection of heavy metal ions without pre-concentration. This invention successfully prepares a sensitive electrode for the direct detection of heavy metal ions in water without pre-concentration using electrochemical technology. It is direct and efficient, exhibiting excellent electrochemical detection capabilities, high sensitivity, a wide linear detection range, and a low detection limit. Furthermore, it also possesses advantages such as good stability and repeatability. Attached Figure Description

[0020] Figure 1 Scanning electron microscope images; Figure (a) carbon cloth, Figure (c) carbon cloth-supported tungsten oxide (WO3-CC) sensitive electrode prepared in Example 5, Figure (e) carbon cloth-supported molybdenum tungsten oxide (Mo-WO3-CC) sensitive electrode prepared in Example 1; Figures (b, d, f) are magnified views of Figures (a, c, e), respectively.

[0021] Figure 2Differential pulse voltammetry (DPV) curves of the carbon cloth-supported tungsten oxide (WO3-CC) sensitive electrode prepared in Example 5 and the carbon cloth-supported molybdenum tungsten oxide (Mo-WO3-CC) sensitive electrode prepared in Example 1 in 10 μM HMIs solution; the horizontal axis is the dissolution potential and the vertical axis is the response current.

[0022] Figure 3 Scanning electron microscope (SEM) images of carbon cloth-supported molybdenum-doped tungsten oxide (Mo-WO3-CC) sensitive electrodes prepared in Examples 1, 2, 3, and 4: Figure (a) shows the Mo-WO3-CC sensitive electrode prepared with a molar ratio of sodium molybdate to sodium tungstate of 0.02:1; Figure (b) shows the Mo-WO3-CC sensitive electrode prepared with a molar ratio of sodium molybdate to sodium tungstate of 0.01:1; Figure (c) shows the Mo-WO3-CC sensitive electrode prepared with a molar ratio of sodium molybdate to sodium tungstate of 0.05:1; Figure (d) shows the Mo-WO3-CC sensitive electrode prepared with a molar ratio of sodium molybdate to sodium tungstate of 0.1:1; Figures (a2, b2, c2, d2) are magnified views of Figures (a1, b1, c1, d1), respectively.

[0023] Figure 4 Differential pulse voltammetry (DPV) curves of the Mo-WO3-CC electrodes prepared in Examples 1, 2, 3 and 4 in 10 μM HMIs solution; the horizontal axis is the dissolution potential and the vertical axis is the response current.

[0024] Figure 5 (a) Differential pulse voltammetry (DPV) curves of the Mo-WO3-CC sensitive electrode prepared in Example 1 in HMIs solutions of different concentrations (specific values ​​of the concentration coordinates are 100 nM, 200 nM, 500 nM, 1 μM, 2 μM, 5 μM, 10 μM, 20 μM, 50 μM, and 100 μM, respectively); Figure 5 (b), (c), (d), and (e) show the test curves (DPV) showing the dissolution peak current as a function of Cd. 2+ Pb 2+ Cu 2 + Hg 2+ Standard curve of two linear relationships of concentration change (Cd) 2+ : 100nM~10μM and 10μM~100μM; Pb 2+ : 100nM~20μM and 20μM~100μM; Cu 2+ : 100nM~10μM and 10μM~100μM; Hg 2+ (100nM~20μM and 20μM~100μM).

[0025] Figure 6 (a) is an anti-interference test diagram of the Mo-WO3-CC sensitive electrode prepared in Example 1; Figure 6 (b) Comparison of results of 8 consecutive DPASV tests on the same Mo-WO3-CC sensitive electrode in 10 μM HMIs solution; Figure 6 (c) Comparison of DPASV test results for 8 Mo-WO3-CC sensitive electrodes in 10 μM HMIs solution; Figure 6 (d) is a comparison of the DPASV test results of the same Mo-WO3-CC sensitive electrode on different days within 30 days in 10 μM HMIs solution. The vertical axis represents the dissolution peak current.

[0026] like Figure 1 As shown, the carbon cloth has a relatively smooth surface (Fig. ab); after pulsed current deposition, a dense tungsten oxide layer grows on the CC surface (Fig. cd); after adding sodium molybdate to the deposition solution, the surface morphology of the Mo-WO3-CC sensitive electrode prepared by pulsed current deposition (Fig. ef) is the same as that of the electrode prepared in Example 5.

[0027] like Figure 2 As shown, the WO3-CC sensing electrode and the Mo-WO3-CC sensing electrode prepared in Example 1 are sensitive to 10 μM Cd. 2+ Pb 2+ Cu 2+ Hg 2+ All showed a response, with the molybdenum-doped Mo-WO3-CC showing the best response (Example 1).

[0028] like Figure 3 As shown, it can be seen that the change in molybdenum doping amount does not have a significant impact on the morphology of the Mo-WO3-CC sensitive electrode, and the electrode surface is a dense nanolayer.

[0029] like Figure 4 As shown, the Mo-WO3-CC electrodes prepared in Examples 1, 2, 3, and 4 are effective against 10 μM Cd. 2+ Pb 2+ Cu 2+ Hg 2+ All samples showed a response, with the Mo-WO3-CC sensitive electrode prepared with a molar ratio of sodium molybdate to sodium tungstate of 0.02:1 in the deposition solution showing the best response (Example 1). The responses of Examples 1, 2, 3, and 4 were all better than those of the WO3-CC sensitive electrode.

[0030] like Figure 5As shown in the DPV curve, the dissolution peak current between -1.0V and 0.45V varies with Cd. 2+ Pb 2+ Cu 2+ Hg 2+ The dissolution peak current increases with increasing concentration (Figure a, concentration range 100 nM–100 μM); the dissolution peak current of the DPV curve increases with increasing Cd. 2 + Pb 2+ Cu 2+ Hg 2+ The concentration increases exhibit a two-segment linear relationship (Figures b, c, d, and e). When testing HMIs solutions of unknown concentration using the sensitive electrode described in this invention, the dissolution peak current of the DPV curve can be obtained under the same testing conditions. Using this linear relationship, Cd can be calculated. 2+ Pb 2+ Cu 2+ Hg 2+ concentration.

[0031] like Figure 6 As shown, common cation pairs with Cd 2+ Pb 2+ Cu 2+ Hg 2+ The current has a relatively small impact during the detection process (other cations with a concentration of 100 μM were added to a 10 μM HMIs solution, namely Zn). 2+ Ni 2+ Mg 2+ K + NH 4+ SO4 2+ HCO3 - CO3 2- The dissolution peak current remained within 90%–108% of that in the blank group (Figure a); the same Mo-WO3-CC sensitive electrode was repeatedly tested 8 times for Cd. 2+ Pb 2+ Cu 2+ Hg 2+ The relative standard deviations (RSDs) of the dissolution peak currents (the RSD is obtained by dividing the standard deviation by the corresponding average value and multiplying by 100%, which can be used to analyze the precision of the results in the detection process) were 1.86%, 2.77%, 0.99%, and 0.99% (Figure b); DPASV tests were performed on eight Mo-WO3-CC sensitive electrodes in 10 μM HMIs solution for Cd. 2+ Pb 2+ Cu 2+ Hg 2+The relative standard deviations of the dissolution peak currents were 2.60%, 2.20%, 1.82%, and 1.34%, respectively (Figure c); the test results of the same Mo-WO3-CC sensitive electrode placed in deionized water at room temperature for 30 days at different times, for Cd 2+ Pb 2+ Cu 2+ Hg 2+ The relative standard deviations of the dissolution peak currents were 2.04%, 1.61%, 3.45%, and 3.30%, respectively (Figure d). Figure 6 a and Figure 6 In d, the four bars in the same group from left to right correspond to Cd respectively. 2+ Pb 2+ Cu 2 + Hg 2+ . Detailed Implementation

[0032] Example 1

[0033] The preparation method of the sensitive electrode suitable for electrochemical copper ion detection is as follows:

[0034] a) Cut the carbon cloth (CC) to a size of 1.0cm × 1.0cm, and ultrasonically clean it with toluene, acetone, and ethanol respectively, followed by ultrasonic cleaning with deionized water. Each ultrasonic cleaning session lasts 10 minutes.

[0035] b) Add 25 mL of 0.0025 M sodium molybdate aqueous solution, 2 mL of 70% perchloric acid aqueous solution, and 0.7 mL of 30% hydrogen peroxide aqueous solution to 100 mL of 0.0315 M sodium tungstate aqueous solution to prepare the precipitation solution.

[0036] c) A three-electrode system was used, with the carbon cloth treated in step a) as the working electrode, a platinum sheet (1.0 cm × 1.0 cm) as the counter electrode, and an Ag / AgCl electrode as the reference electrode; tungsten oxide was deposited using pulsed electrodeposition, with an A / cm² voltage of -0.0025 A / cm² in one deposition cycle. 2 The current is maintained for 0.1s, 0A / cm 2 The current was maintained at 0.1 s for 5000 cycles; the total deposition time was 1000 s. The resulting carbon cloth-supported molybdenum-doped tungsten oxide (Mo-WO3-CC) sensing electrode was rinsed with deionized water and then used for later use.

[0037] d) Electrochemical heavy metal ion detection was performed using a Mo-WO3-CC sensitive electrode, employing a three-electrode system: Mo-WO3-CC as the working electrode, a platinum sheet (1.0 cm × 1.0 cm) as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. Electrochemical tests were conducted using electrodes containing different concentrations of Cd. 2+ Pb 2+ Cu 2+ Hg 2+ A 0.1M acetate buffer solution with a pH of 5.0 was used as the electrolyte (soluble heavy metal salts were dissolved in the acetate buffer solution, namely cadmium nitrate, lead nitrate, copper chloride, and mercuric nitrate, Cd). 2+ Pb 2+ Cu 2+ Hg 2+ Four heavy metal ions were simultaneously dissolved in the same acetate buffer solution for DPASV testing using differential pulse voltammetry (DPASV). The potential range was -1.0 V to 0.45 V (vs. SCE). Before DPV testing, the sensitive electrode was activated using cyclic voltammetry in a 0.1 M acetate buffer solution with a pH of 5.5. The potential range was -1.0 V to 0.45 V (vs. SCE); the number of cycles was 30, and the scan rate was 50 mV / s. -1 .

[0038] Experimental results show that the sensitive electrode prepared by the method of this invention is effective against Cd ions ranging from 100 nM to 10 μM. 2+ Detection sensitivity (sensitivity is based on Cd) 2+ The linearity of the standard curve plotted from the concentration and corresponding peak current intensity was 16.01 μA μM. -1 cm -2 For Cd in the range of 10 μM to 100 μM 2+ The detection sensitivity is 9.18 μA / μM. -1 cm -2 When the signal / noise ratio is 3 (S / N = 3), the detection limit (LOD = 3σ / S, where σ is the standard deviation and S is the sensitivity) is 14.7 nM (e.g., Figure 5 (as shown); for Pb in the range of 100 nM to 20 μM 2+ The detection sensitivity is 22.73 μA / μM. -1 cm -2 For Pb in the range of 20 μM to 100 μM 2+ The detection sensitivity is 11.21 μA μM. -1 cm -2 The detection limit is 17.1 nM (e.g., Figure 5 (as shown); for Cu in the range of 100 nM to 10 μM 2+The detection sensitivity is 20.99 μA μM. -1 cm -2 For Cu in the range of 10 μM to 100 μM 2+ The detection sensitivity is 9.38 μA μM. -1 cm -2 The detection limit is 11.2 nM (e.g., Figure 5 (as shown); for Hg in the range of 100 nM to 20 μM 2+ The detection sensitivity is 42.72 μA μM. -1 cm -2 For Hg in the range of 20 μM to 100 μM 2+ The detection sensitivity is 9.57 μA μM. -1 cm -2 The detection limit is 13.1 nM (e.g., Figure 5 (As shown). In addition, the sensitive electrode prepared in this embodiment exhibits good selectivity, repeatability, and stability (e.g., Figure 6 (As shown). The dissolution peak values ​​of the DPV curves of the sensitive electrode prepared in this embodiment for the detection of 10 μM cadmium, lead, copper, and mercury ions were 377.71, 470.91, 314.15, and 1177.71 μA cm⁻¹, respectively. -2 (like Figure 2 (As shown).

[0039] Example 2

[0040] a) The cleaning process for the carbon cloth is as described in Example 1;

[0041] b) Add 25 mL of 0.00125 M sodium molybdate aqueous solution, 2 mL of 70% perchloric acid aqueous solution, and 0.7 mL of 30% hydrogen peroxide aqueous solution to 100 mL of 0.0315 M sodium tungstate aqueous solution to prepare the precipitation solution.

[0042] c) The electrode preparation process is as described in Example 1;

[0043] d) The testing process was the same as in Example 1. The experimental results showed that the dissolution peak values ​​of the DPV curves of the Mo-WO3-CC sensitive electrode prepared in this example for the detection of 10μM cadmium, lead, copper, and mercury ions were 195.72, 421.60, 303.08, and 637.6 μA cm⁻¹, respectively. -2 (like Figure 4 (As shown).

[0044] Example 3

[0045] a) The cleaning process for the carbon cloth is as described in Example 1;

[0046] b) Add 25 mL of 0.00625 M sodium molybdate aqueous solution, 2 mL of 70% perchloric acid aqueous solution, and 0.7 mL of 30% hydrogen peroxide aqueous solution to 100 mL of 0.0315 M sodium tungstate aqueous solution to prepare the precipitation solution.

[0047] c) The electrode preparation process is as described in Example 1;

[0048] d) The testing process was the same as in Example 1. The experimental results showed that the dissolution peak values ​​of the DPV curves of the Mo-WO3-CC sensitive electrode prepared in this example for the detection of 10μM cadmium, lead, copper, and mercury ions were 122.84, 271.68, 223.48, and 383.6 μA cm⁻¹, respectively. -2 (like Figure 4 (As shown).

[0049] Example 4

[0050] a) The cleaning process for the carbon cloth is as described in Example 1;

[0051] b) Add 25 mL of 0.0125 M sodium molybdate aqueous solution, 2 mL of 70% perchloric acid aqueous solution, and 0.7 mL of 30% hydrogen peroxide aqueous solution to 100 mL of 0.0315 M sodium tungstate aqueous solution to prepare the precipitation solution.

[0052] c) The electrode preparation process is as described in Example 1;

[0053] d) The testing process was the same as in Example 1. The experimental results showed that the dissolution peak values ​​of the DPV curves of the Mo-WO3-CC sensitive electrode prepared in this example for the detection of 10μM cadmium, lead, copper, and mercury ions were 155.20, 321.52, 266.36, and 462 μA cm⁻¹, respectively. -2 (like Figure 4 (As shown).

[0054] Example 5

[0055] a) The cleaning process for the carbon cloth is as described in Example 1;

[0056] b) Add 2 mL of 70% perchloric acid aqueous solution and 0.7 mL of 30% hydrogen peroxide aqueous solution to 100 mL of 0.0315 M sodium tungstate aqueous solution to prepare the precipitation solution.

[0057] c) The electrode preparation process is as described in Example 1. The carbon cloth-supported tungsten oxide (WO3-CC) sensitive electrode is rinsed with deionized water and then used for later use.

Claims

1. A method for preparing a sensitive electrode for direct detection of heavy metal ions in water without pre-concentration, comprising the following steps: (1) Use carbon cloth as a support electrode and clean the carbon cloth; (2) Electrochemical deposition was performed using the carbon cloth obtained in step (1) as the working electrode, the platinum sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode; the deposition solution was a mixture of sodium tungstate aqueous solution, sodium molybdate aqueous solution, perchloric acid aqueous solution and hydrogen peroxide aqueous solution; After deposition, molybdenum-doped tungsten oxide is obtained on the surface of carbon cloth. After cleaning, a molybdenum-doped tungsten oxide sensitive electrode for direct detection of heavy metal ions in water without pre-enrichment is obtained. The sodium tungstate aqueous solution used in the precipitation solution has a concentration of 0.01~0.04M, the sodium molybdate aqueous solution has a concentration of 0.001~0.015M, the perchloric acid aqueous solution has a mass fraction of 70%~72%, and the hydrogen peroxide aqueous solution has a mass fraction of 30%; the volume ratio of the four solutions is 85~105:20~30:1~5:0.5~2.

2. The method for preparing a sensitive electrode for direct detection of heavy metal ions in water without pre-concentration as described in claim 1, characterized in that: In step (1) the cleaning process of carbon cloth, one or more of the following reagents are used: toluene, acetone, ethanol, and hydrochloric acid; the cleaning time for each reagent is 10-15 minutes, and the cleaning process is ended by rinsing with deionized water.

3. The method for preparing a sensitive electrode for direct detection of heavy metal ions in water without pre-concentration as described in claim 1, characterized in that: In step (2), the electrochemical deposition is pulsed current electrodeposition, with a current of -0.002 to 0.005 A / cm² in one deposition cycle. 2 The current was maintained for 0.1~0.3s, 0A / cm. 2 The current was maintained for 0.1 to 0.3 seconds for 4,000 to 6,000 cycles.

4. A sensitive electrode for direct detection of heavy metal ions in water without pre-concentration, characterized in that: It is prepared by the method described in any one of claims 1 to 3.

5. The application of the sensitive electrode for direct detection of heavy metal ions in water without pre-concentration as described in claim 4 in the detection of heavy metal ions in water, characterized in that: It utilizes an electrochemical workstation, with a sensitive electrode as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. The electrolyte consists of a 0.1–0.3 M acetate buffer solution and Cd solutions of varying concentrations. 2+ Pb 2 + Cu 2+ Hg 2+ Mixing of aqueous solutions; Differential pulse stripping voltammetry was used to detect heavy metal ions in water. The differential pulse voltammetry test curve of the sensitive electrode in the electrolyte and the stripping peak current intensity of the test curve were obtained. A "stripping peak current intensity - Cd" plot was then generated. 2+ Pb 2+ Cu 2+ or Hg 2+ A linear standard curve for the concentration was obtained; then, an electrolyte with an unknown heavy metal ion concentration was tested using a sensitive electrode, and the dissolution peak current of the differential pulse voltammetry test curve was obtained under the same test conditions; then, the Cd was calculated using the linear standard curve. 2+ Pb 2+ Cu 2+ or Hg 2+ The concentration is used to detect heavy metal ions in water.

6. The application of the sensitive electrode for direct detection of heavy metal ions in water without pre-concentration as described in claim 5 in the detection of heavy metal ions in water, characterized in that: The pH value of acetate buffer solution is 4~6.

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