An electrochemical sensor for detecting heavy metal cadmium ions, its construction method and application

Abstract

This invention belongs to the field of electrochemical sensor technology, specifically providing an electrochemical sensor for detecting cadmium ions (Cd(II)) and its construction method. The electrochemical sensor uses a Fe / N-mCS composite material modified on the surface of a screen-printed carbon electrode as the working electrode. It employs a traditional three-electrode system and detects the electrochemical signal of Cd(II) using square-wave anodic stripping voltammetry. The superior properties of the Fe / N-mCS composite material amplify the current signal, improving sensitivity. The electrochemical sensor constructed in this invention exhibits high detection sensitivity, with a detection limit for Cd(II) as low as 0.068 μg / L. ‑1 This invention exhibits strong anti-interference capabilities and can specifically detect cadmium ions in tap water and river water. Furthermore, the electrochemical sensor of this invention demonstrates good repeatability and stability for Cd(II) detection. This invention is of great significance for the rapid detection of heavy metal pollution.

Description

Technical Field

[0001] This invention relates to the field of environmental analysis technology, specifically to an electrochemical sensor for detecting heavy metal cadmium ions, its construction method, and its application. Background Technology

[0002] With industrial development, heavy metal pollution has become increasingly serious. Cadmium, as one of the heavy metal pollutants, is a major cause of "Itai-itai disease" because it cannot be biodegraded. Excessive cadmium in the human body can damage renal tubular function, causing protein loss, and over time, can lead to rickets, spontaneous fractures, and generalized pain. In recent years, cadmium poisoning incidents have occurred frequently, prompting more and more scholars to focus on the research of cadmium pollution and its toxicity. Developing a method with low detection limits and high selectivity is of great practical significance and application value for the trace determination of Cd(II) in actual samples.

[0003] Currently, common methods for detecting cadmium ions include X-ray fluorescence spectroscopy, atomic absorption spectroscopy, and inductively coupled plasma mass spectrometry. These methods are complex to operate and not suitable for on-site detection. Electrochemical analysis, on the other hand, offers advantages such as short analysis time, low cost, high sensitivity, and ease of instrument miniaturization, enabling on-site monitoring of Cd(II) in the environment. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an electrochemical sensor for cadmium ion detection and its construction method. This invention obtains an Fe / N-mCS / SPCE modified electrode by modifying a screen-printed carbon electrode with a high-performance Fe / N-mCS metal composite material. Due to the material's large specific surface area and uniform mesoporous structure, more adsorption binding and catalytic sites are exposed, resulting in excellent performance for Cd(II) detection by the electrochemical sensor. The sensor constructed in this invention also exhibits excellent selectivity, repeatability, and long-term stability, making it valuable for practical applications.

[0005] To achieve the above objectives, the technical method provided by the present invention is as follows:

[0006] An electrochemical sensor for detecting heavy metal cadmium ions uses an electrode with Fe / N-mCS metal composite material modified on the surface of a screen-printed carbon electrode as the working electrode.

[0007] Furthermore, the electrochemical sensor also includes a reference electrode and a counter electrode.

[0008] This invention also provides a method for constructing the above-mentioned electrochemical sensor for detecting heavy metal cadmium ions, comprising the following steps:

[0009] Step S1: Preparation and pretreatment of SPCE;

[0010] Step S2: Preparation of Fe / N-mCS composite material;

[0011] Step S3: The Fe / N-mCS composite material prepared in step (2) is ultrasonically dissolved in ultrapure water, the Fe / N-mCS suspension is dropped onto the pretreated SPCE surface, and dried to obtain the Fe / N-mCS / SPCE modified electrode.

[0012] Preferably, the preparation and pretreatment of SPCE in step S1 specifically includes:

[0013] (1) Preparation of SPCE: Cut the PET substrate to the required size, clean it with water and ethanol and then dry it for later use; then fix the dried PET board on the screen printing machine and print conductive silver paste (thickness of 9μm); after drying, brush on conductive carbon paste (thickness of 5μm) in the same way. After drying, attach insulating stickers to the part where the conductive silver layer and the conductive carbon layer are connected to avoid the influence of the silver layer on the subsequent electrochemical test. After attaching the insulating stickers, the SPCE is obtained. The prepared SPCE is placed in a cool and dry place for later use.

[0014] (2) Pretreatment of SPCE: in 0.5 mol L -1 The prepared SPCE was activated in H2SO4 solution by cyclic voltammetry. The experimental parameters were as follows: scan range 1.5–2.0 V; scan rate 0.1 V s. -1 .

[0015] Preferably, the preparation of the Fe / N-mCS composite material in step S2 is specifically as follows:

[0016] a. Preparation of precursor PDA-Fe-mel nanospheres: Dopamine hydrochloride (DA·HCl) and melamine were ultrasonically dispersed in ultrapure water at a ratio (mass ratio 1:2) (total solid content 75 mg / mL). -1 The product was added dropwise to a mixed solution containing ultrapure water, ethanol, and ammonia (volume ratio of 45:20:1) under stirring at room temperature. Then, a certain concentration of FeCl3 solution was added dropwise. The reaction solution quickly turned purple-black. After the reaction was completed, the product was washed three times with water, centrifuged, and collected. This product was named PDA-Fe-mel.

[0017] b. Preparation of Fe / N-mCS composite material: The precursor PDA-Fe-mel prepared above was pyrolyzed under an argon atmosphere (preferred pyrolysis conditions were calcination at 800℃ for 3 hours with a heating rate of 2℃ / min). -1 The final product Fe / N-mCS was obtained. Further preferred, the concentration of FeCl3 in step a was 0.05-2.00 mol·L⁻¹. -1 1.00 mol L is preferred.-1 .

[0018] This invention also provides a method for detecting cadmium ions using an electrochemical sensor, comprising the following steps:

[0019] (1) Using the electrochemical sensor for detecting cadmium ions as the working electrode, and forming a three-electrode system with the reference electrode and the counter electrode, the electrochemical signals of different concentrations of Cd(II) were detected by square wave anodic stripping voltammetry (SWASV) in acetic acid-sodium acetate ABS buffer solution, and its standard curve was plotted.

[0020] (2) The concentration of Cd(II) in the sample to be tested can be calculated using the standard curve obtained in step (1).

[0021] Preferably, the concentration of Cd(II) in step (1) is 0.5–300 μg / L. -1 The reference electrode is an Ag / AgCl electrode, and the counter electrode is a platinum wire electrode.

[0022] The electrochemical sensor constructed in this invention exhibits high detection sensitivity, with a detection limit for Cd(II) as low as 0.068 μg / L. -1 This invention exhibits strong anti-interference capabilities and can specifically detect cadmium ions in tap water and river water. Furthermore, the electrochemical sensor of this invention demonstrates good repeatability and stability for Cd(II) detection. This invention is of great significance for the rapid detection of heavy metal pollution.

[0023] With the above structure, the present invention has the following advantages:

[0024] (1) The Fe / N-mCS composite material synthesized in this invention has a loose mesoporous structure, a large specific surface area and a large number of defect sites, which provide adsorption sites and electrocatalytic active centers for Cd(II).

[0025] (2) The sensor constructed in this invention exhibits high sensitivity, high selectivity and excellent stability in the detection of Cd(II).

[0026] (3) The sensor constructed in this invention can be successfully applied to the detection of Cd(II) in various water samples.

[0027] (4) The sensor constructed by this invention has a fast response speed, low detection cost, and wide applicability in the field. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the detection principle of the present invention.

[0029] Figure 2 This is a characterization diagram of the prepared Fe / N-mCS composite material.

[0030] Figure 3 The test conditions for Cd(II) are optimized using Fe / N-mCS / SPCE modified electrodes.

[0031] Figure 4 These are SWASV plots and corresponding linear fitting plots of Cd(II) at different concentrations obtained by the electrochemical sensor.

[0032] Figure 5 This is a bar graph showing the selectivity of an electrochemical sensor for different metal ions.

[0033] Figure 6 It shows the repeatability and long-term stability of the electrochemical sensor. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0035] This invention provides an electrochemical sensor for detecting heavy metal cadmium ions and its construction method, the principle of which is as follows: Figure 1 As shown, a Fe-doped nitrogen-rich mesoporous carbon nanosphere (Fe / N-mCS) composite material was prepared through a self-assembly polymerization and pyrolysis strategy. The Fe / N-mCS composite material, due to its loose mesoporous structure, large specific surface area, and numerous defect sites, provides adsorption sites and electrocatalytic active centers for Cd(II). A traditional three-electrode system was employed: an electrode with Fe / N-mCS metal composite material modified on the surface of a screen-printed carbon electrode served as the working electrode; a reference electrode and a counter electrode were also included. The electrochemical signal was detected by square wave anodic stripping voltammetry (SWASV), and quantitative detection was achieved based on the correlation between the current signal magnitude and the Cd(II) concentration.

[0036] A method for constructing an electrochemical sensor for detecting heavy metal cadmium ions includes the following steps:

[0037] Step S1: Preparation and pretreatment of SPCE;

[0038] Step S2: Preparation of Fe / N-mCS composite material;

[0039] Step S3: The Fe / N-mCS composite material prepared in step (2) is ultrasonically dissolved in ultrapure water, the Fe / N-mCS suspension is dropped onto the pretreated SPCE surface, and dried to obtain the Fe / N-mCS / SPCE modified electrode.

[0040] A method for detecting cadmium ions using an electrochemical sensor, characterized by comprising the following steps:

[0041] (1) Using the electrochemical sensor for detecting cadmium ions as the working electrode, and forming a three-electrode system with the reference electrode and the counter electrode, the electrochemical signals of different concentrations of Cd(II) were detected in ABS buffer solution by square wave anodic stripping voltammetry (SWASV), and its standard curve was plotted.

[0042] (2) The concentration of Cd(II) in the sample to be tested can be calculated using the standard curve obtained in step (1).

[0043] The concentration of Cd(II) in step (1) is 0.5–300 μg / L. -1 The reference electrode is an Ag / AgCl electrode, and the counter electrode is a platinum wire electrode.

[0044] To illustrate the technical solution described in this invention, specific embodiments are provided below:

[0045] Preparation and pretreatment of SPCE: (1) Preparation of SPCE: Cut the PET substrate into the required size, clean it with water and ethanol and then dry it for later use; then fix the dried PET board on the screen printing machine and print conductive silver paste (thickness of 9μm); after drying, brush on conductive carbon paste (thickness of 5μm) in the same way. After drying, attach insulating stickers to the part where the conductive silver layer and the conductive carbon layer are connected to avoid the influence of the silver layer on the subsequent electrochemical test. After attaching the insulating stickers, the SPCE is obtained. The prepared SPCE is placed in a cool and dry place for later use.

[0046] (2) Pretreatment of SPCE: in 0.5 mol L -1 The prepared SPCE was activated in H2SO4 solution by cyclic voltammetry. The experimental parameters were as follows: scan range 1.5–2.0 V; scan rate 0.1 V s. -1 .

[0047] Example 1: Preparation and characterization of Fe / N-mCS composite material

[0048] (1) Preparation of precursor PDA-Fe-mel nanospheres

[0049] PDA-Fe-mel nanospheres were prepared via an aqueous polymerization process. First, 50 mg of DA-HCl and 100 mg of melamine were added to 2 mL of ultrapure water and ultrasonically dispersed for 10 min. Then, under stirring at room temperature, the mixture was added dropwise to a mixed solution containing 9 mL of ultrapure water, 4 mL of ethanol, and 0.2 mL of ammonia. The polymerization reaction turned the solution yellowish-brown. Subsequently, 0.284 mL of FeCl3 (0.1 mol / L) was added dropwise. -1The solution was stirred continuously for 30 hours until it turned purple-black. After the reaction was completed, the mixture was washed three times with ultrapure water, centrifuged, collected, and freeze-dried to obtain a black powder, which was designated as PDA-Fe-mel.

[0050] (2) Preparation of Fe / N-mCS

[0051] The precursor PDA-Fe-mel prepared above was pyrolyzed under an argon atmosphere and calcined at 800℃ for 3 hours with a heating rate of 2℃ / min. -1 The final product Fe / N-mCS was obtained.

[0052] (3) Characterization of Fe / N-mCS composite materials

[0053] The synthesized materials were characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, and nitrogen adsorption-desorption experiments.

[0054] From the TEM of the material Figure 2 A and Figure 2 B) It can be seen that the Fe / N-mC synthesized by pyrolysis under an argon atmosphere exhibits a distinct loose porous structure and dark irregular particles, indicating the formation of mesoporous carbon materials and iron compounds. Figure 2 C is a FESEM image of Fe / N-mCS, which can more clearly show that the spherical structure of Fe / N-mCS is stacked to form a porous structure of varying degrees and has many defects. Figure 2 D represents the EDS characterization of Fe / N-mCS, with elemental contents of C, N, O, and Fe of 72.27%, 7.11%, 16.02%, and 4.6% (wt%), respectively. To further explore the potential of the prepared composite material in electrochemical applications, its graphitization and defect levels were characterized by Raman spectroscopy. Figure 2 As shown in E, where 1356cm -1 and 1596cm -1 The peaks at that point are the D and G bands, caused by the irregular and low-symmetry structure of carbon and the vibrations of conjugated carbon-carbon double bonds in the graphite crystal structure, respectively. The intensity ratio of the D and G bands (I) D / I G This is often used to quantify the defect degree of carbon materials. The IF of Fe / N-mCS and N-mCS is calculated by fitting the peak area. D / I GThe values ​​of 1.958 and 1.964, respectively, indicate that the N-mCS-based material has a high degree of defect, and that Fe3O4 doping did not destroy its defect structure. This is attributed to the porosity of the carbon nanospheres and the defect structure formed by irregular stacking during pyrolysis. Therefore, Fe / N-mCS with abundant defect sites is expected to provide a large number of catalytic active centers and accelerate electron transfer in the electrocatalytic process. The porous structure of the material was analyzed in detail through nitrogen adsorption-desorption experiments, and its nitrogen adsorption-desorption isotherm is shown below. Figure 2 As shown in Figure F, the BET specific surface area and pore volume of Fe / N-mCS were calculated to be 388.31 m². 2 g -1 and 0.64cm 3 g -1 The pore size distribution curve (inset) based on density functional theory (DFT) shows that the pore distribution of Fe / N-mCS is relatively concentrated and within the mesoporous range, with an average pore size of 4.38 nm. This indicates that Fe / N-mCS has a large specific surface area and a uniform mesoporous structure, which is conducive to exposing more adsorption binding and catalytic sites and promoting the electrocatalytic redox process of Cd(II).

[0055] Example 2: Sensor Construction and Performance Testing

[0056] (1) Construction of electrochemical sensors:

[0057] First, in 0.5 mol L -1 The prepared SPCE was activated in H2SO4 solution by cyclic voltammetry. The experimental parameters were as follows: scan range 1.5–2.0 V; scan rate 0.1 V s. -1 Next, 1 mg of Fe / N-mCS was ultrasonically dispersed in 1 mL of ultrapure water, and 10 μL was dropped onto a pre-wetted SPCE surface and dried at room temperature to obtain the Fe / N-mCS / SPCE modified electrode.

[0058] (2) Optimization of test conditions for Cd(II)

[0059] In electrochemical detection, different testing environments and electrochemical technique parameters have a significant impact on the detection results. Therefore, the experiment was conducted in a solution containing 50 μg L... -1 The pH values ​​of the buffer solution were respectively affected by the Cd(II) solution. Figure 3 A) SWASV deposition potential ( Figure 3 B) and deposition time ( Figure 3C) Three parameters were optimized to determine the optimal testing conditions for Cd(II) using the Fe / N-mCS / SPCE-based electrochemical sensor. All electrochemical test results for Cd(II) were based on three independent tests using Fe / N-mCS / SPCE from the same preparation process to ensure the reliability of the results. The optimal testing conditions, determined from the experimental results, were: 0.1 mol L at pH 4.5. -1 In ABS buffer solution, the deposition potential of SWASV was used as the deposition time for quantitative determination of Cd(II) at -1.5V and 300s.

[0060] (3) Evaluation of the detection performance of Cd(II)

[0061] Under the above optimal test conditions, the SWASV current response of Fe / N-mCS / SPCE to different concentrations of Cd(II) was studied, such as... Figure 4 As shown in Figure A, the dissolution current signal increases continuously with increasing Cd(II) concentration. This occurs in the range of 0.5–300 μg / L. -1 Within the concentration range, the two show a good linear relationship, such as... Figure 4 As shown in B, the corresponding linear regression equation is I(μA)=0.4445C(μg L). -1 )+1.4267,(R 2 =0.993). The limit of detection (LOD) was 0.068 μg / L. -1 (S / N = 3), sensitivity is 0.4445 μA / μg -1 Both my country's national standard (GB 5749-2022) and the U.S. Environmental Protection Agency (EPA) stipulate that the threshold level for Cd(II) in drinking water is 5 μg / L. -1 The World Health Organization (WHO) guidelines for drinking water quality stipulate that the Cd content in safe drinking water should not exceed 3 μg / L. -1 Therefore, the Cd(II) electrochemical sensor based on Fe / N-mCS / SPCE provided by this invention can fully meet the relevant detection requirements and has the potential for practical application.

[0062] (4) Selectivity evaluation of sensors

[0063] Since actual sample testing often involves complex mixed systems containing different types of metal cations, selectivity is a crucial indicator for evaluating the electrochemical detection performance of heavy metal ions. Therefore, seven common interfering ions—Pb(II), Hg(II), As(III), Mn(II), Ni(II), Co(II), and Cr(VI)—were selected to investigate the selectivity of a Cd(II) electrochemical sensor based on Fe / N-mCS / SPCE. Figure 5 In A, the effects of Fe / N-mCS / SPCE on 50 μg L were compared. - 1 The current response of Cd(II) and 10 times the concentration of interfering ions was measured. It was found that the sensor did not respond to any interfering ions, and the relative standard deviation of the current response was only -2.91% for a mixed system containing various ions. Figure 5 B investigated the effect of Fe / N-mCS / SPCE on 50 μg L in systems containing different interfering substances. -1 The signal response of Cd(II) shows that the current signal remains stable, and the absolute value of the error is less than 2.35%. This demonstrates that the Cd(II) sensor based on Fe / N-mCS / SPCE exhibits good selectivity and can meet the anti-interference requirements for detecting complex systems.

[0064] (5) Sensor reproducibility and long-term stability assessment

[0065] Reproducibility is another important factor in evaluating electrochemical sensors. Ten Fe / N-mCS / SPCE modified electrodes fabricated in the same batch were selected, and their performance in 0.1 mol L⁻¹ was tested. -1 In ABS (pH=4.5), 50 μg L -1 The reproducibility of the sensor was investigated by analyzing the current response of Cd(II). The results are as follows: Figure 6 As shown in Figure A, similar test results were obtained on 10 modified electrodes, with a relative standard deviation of 2.3%, indicating that the Cd(II) electrochemical sensor based on Fe / N-mCS / SPCE constructed by this preparation process has good reproducibility.

[0066] Practical applications also require the sensor to maintain stability over long periods. A batch of Fe / N-mCS / SPCE was prepared under the same conditions and stored at room temperature, with tests performed every three days. The results are as follows: Figure 6 As shown in Figure B, it can be observed that within one month, the Fe / N-mCS / SPCE-based Cd(II) electrochemical sensor effectively controlled 50 μg L⁻¹ of cadmium chloride. -1 The Cd(II) sensor exhibits a relatively stable electrochemical signal with relatively small error, demonstrating that it has good long-term stability and can meet the requirements for long-term storage in practical applications.

[0067] Example 3: Detection of Cd(II) in real samples

[0068] Various water bodies are key targets for heavy metal detection. This experiment selected actual samples of tap water and river water for spiked recovery experiments to evaluate the practical application capability of the Fe / N-mCS / SPCE-based Cd(II) electrochemical sensor. The treatment methods for tap water and river water are as follows:

[0069] Tap water samples: Prepare ABS (pH=4.5) buffer solution using laboratory tap water instead of ultrapure water.

[0070] Actual river water sample: The river water sample was taken from the Youth River at the Xuhui Campus of East China University of Science and Technology. After sampling, the sample was left to stand for three days. The supernatant was then filtered using filter paper and a 0.22μm aqueous filter membrane. The filtrate was used to prepare ABS buffer solution.

[0071] The experiment selected 10 μg L -1 50 μg L -1 and 100 μg L -1 Three concentrations were used as standard addition concentrations for Cd(II), and the test results are shown in Table 1. Each test result was based on three parallel experiments. The calculated recoveries of tap water and river water samples at the three different concentrations were 98.94%, 102.66%, and 99.12%, and 101.63%, 97.12%, and 99.17%, respectively. Furthermore, the Cd(II) content of each spiked recovery sample was compared using inductively coupled plasma atomic absorption spectrometry (ICP-AES). The test results were very close to those of the prepared electrochemical sensor, with a maximum relative deviation of 6.01%. These results confirm the ability of the Fe / N-mCS / SPCE-based electrochemical sensor to detect Cd(II) in actual water samples, demonstrating its practical application value.

[0072] Table 1 Comparison of Cd(II) spiked recovery experiments and ICP-AES tests in tap water and river water

[0073]

[0074] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An electrochemical sensor for detecting heavy metal cadmium ions, characterized in that, An electrode with a Fe / N-mCS nitrogen-doped mesoporous carbon sphere composite material modified on the surface of a screen-printed carbon electrode is used as a working electrode; the Fe / N-mCS composite material is prepared by the following method: (1) Preparation of precursor PDA-Fe-mel nanospheres: Dopamine hydrochloride and melamine were dispersed in ultrapure water, and then added dropwise into a mixed solution containing ultrapure water, ethanol and ammonia water under stirring at room temperature; then, a FeCl3 solution with a concentration of 0.05-2.00 mol·L -1 was added, and the reaction solution quickly turned purple black. After the reaction was completed, the product was collected by centrifugation after washing with water three times, and was denoted as PDA-Fe-mel; (2) Preparation of Fe / N-mCS: pyrolysis of the above-prepared precursor PDA-Fe-mel under an argon atmosphere to obtain the final product Fe / N-mCS.

2. The electrochemical sensor for detecting heavy metal cadmium ions according to claim 1, characterized in that, The electrochemical sensor further comprises a reference electrode and a counter electrode.

3. A method of constructing an electrochemical sensor for detecting heavy metal cadmium ions as claimed in claim 1, wherein, The method comprises the following steps: Step S1: Preparation and pretreatment of the SPCE; Step S2: Preparation of the Fe / N-mCS composite material; Step S3: ultrasonic dissolution of the Fe / N-mCS composite material prepared in step S2 in ultrapure water, dropwise addition of the Fe / N-mCS suspension to the surface of the pretreated SPCE, drying, and obtaining the Fe / N-mCS / SPCE electrode.

4. The method for constructing an electrochemical sensor for detecting heavy metal cadmium ions according to claim 3, characterized in that, The SPCE is prepared and pretreated according to the following method: (1) Preparation of the SPCE: cut the PET plate into the required size, clean it with water and ethanol, and dry it for standby; then, fix the dried PET plate on a screen printing machine, print conductive silver paste; after drying, brush conductive carbon paste on the same way, dry, and then paste insulating tape on the connecting part of the conductive silver layer and the conductive carbon layer; after pasting the insulating tape, the SPCE is obtained, and the prepared SPCE is placed in a cool and dry place for standby; (2) Pretreatment of the SPCE: activate the prepared SPCE in an H2SO4 solution by cyclic voltammetry.

5. The method of detecting cadmium ions by the electrochemical sensor of claim 1, wherein, The method comprises the following steps: (1) The electrochemical sensor for detecting cadmium ions is used as a working electrode, and a reference electrode and a counter electrode form a three-electrode system; the electrochemical signals of different concentrations of Cd(II) are detected by square wave anodic stripping voltammetry in an acetic acid-sodium acetate buffer solution, and a standard curve is drawn; (2) the concentration of Cd(II) in the sample to be measured can be calculated by using the standard curve obtained in step (1).

6. The method of detecting cadmium ions according to claim 5, wherein The Cd (II) concentration in the step (1) is 0.5-300 μg / L -1 The reference electrode is Ag / AgCl electrode, and the counter electrode is platinum wire electrode.

Images