Method for detecting cadmium ions and lead ions in water body by using screen-printed electrode electrochemical sensor

Abstract

The application discloses a method for detecting cadmium ions and lead ions in water by using a screen-printed electrode electrochemical sensor, and comprises the following steps: taking a screen-printed electrode with a ZIF-8 / MWCNT nanocomposite modified on the surface of a reaction end as a working electrode to construct a screen-printed electrode electrochemical sensor; detecting the peak current change of a cadmium / lead ion solution to be measured by using the screen-printed electrode electrochemical sensor; and calculating the concentration of cadmium ions and lead ions in the cadmium / lead ion solution to be measured by using a linear regression equation of the cadmium ion concentration, the lead ion concentration and the peak current change. The method has the advantages of simple operation, low cost, high detection efficiency, high detection accuracy and the like, can realize on-site detection of cadmium ions and lead ions in water, is convenient to operate, high in accuracy, strong in anti-interference ability to interference factors, and has very important significance for realizing efficient detection of heavy metal cadmium ions and lead ions in a water environment.

Description

Technical Field

[0001] This invention belongs to the field of heavy metal detection technology, and relates to a method for detecting cadmium ions and lead ions in water, specifically a method for detecting cadmium ions and lead ions in water using a screen-printed electrode electrochemical sensor. Background Technology

[0002] Due to the widespread use of metallic materials, lead and cadmium heavy metal pollutants frequently appear in aquatic environments, along with lead (II, Pb). 2+ Cadmium (II, Cd) can damage the brain, nervous system, and liver. 2+ Heavy metals like lead and cadmium, which can enter the aquatic environment, may cause kidney dysfunction and metabolic disorders, potentially threatening human health. Therefore, it is crucial to monitor cadmium ions (Cd) in water bodies. 2 + ) and lead ions (Pb 2+ Accurate detection of these substances is of great significance for reducing their danger to human health.

[0003] Currently, traditional methods for heavy metal detection include atomic fluorescence spectrometry, atomic absorption spectrophotometry, dithizone spectrophotometry, and oscillometric polarography. Although these methods are relatively mature, they still have some unavoidable drawbacks, such as the need for large equipment and specialized personnel, complex testing procedures, and inconvenience in portability. This limits their application in rapid, portable heavy metal detection. Anodic stripping voltammetry is one of the electrochemical detection methods, characterized by its simplicity and rapid detection, making it very suitable for on-site detection. However, existing electrochemical detection methods based on anodic stripping voltammetry typically use electrochemical sensors constructed with glassy carbon electrodes as the working electrode to detect heavy metals in water. Because these electrochemical sensors are difficult to miniaturize and simplify, the aforementioned detection methods are unable to achieve on-site detection of heavy metals in water. To overcome the aforementioned problems, some researchers have proposed using screen-printed electrodes as working electrodes to construct miniaturized and simplified electrochemical sensors, which would facilitate the on-site detection of heavy metals in water. However, existing electrochemical sensors based on screen-printed electrodes still suffer from drawbacks such as poor thermal stability, poor adsorption capacity, and poor conductivity. These drawbacks result in poor detection sensitivity and narrow detection range, making it difficult for detection methods based on screen-printed electrode electrochemical sensors to obtain accurate detection data and meet the detection limits required by national standards. In other words, it is impossible to determine whether the concentration of heavy metals in water meets the national standards, which greatly limits the widespread application of detection methods based on screen-printed electrode electrochemical sensors. For example, when using a screen-printed electrode modified with reduced graphene oxide (RGO) / molybdenum dioxide (MoS2) composite material and seeded with Hep G2 cells as the working electrode to construct a portable cell electrochemical sensor, its detection limit for cadmium ions is 5 μM, still exhibiting low detection sensitivity. Similarly, using a bismuth-containing screen-printed electrode as the working electrode, the detection limit for cadmium ions is 4.8 μg / L, again showing low sensitivity. Using a polyaniline-modified screen-printed electrode as the working electrode, the detection limit for cadmium ions is 5.41 μg / L, still exhibiting low sensitivity. Furthermore, using a UIO-66-modified screen-printed electrode as the working electrode, the sensor suffers from poor detection sensitivity and a narrow detection range due to the inherent limitations of screen-printed electrodes, such as poor thermal stability, poor adsorption capacity, and poor conductivity. Therefore, obtaining a screen-printed electrode electrochemical sensor with high detection sensitivity and wide detection range is of great significance for the simple and accurate detection of cadmium and lead ions in water. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a simple and accurate method for detecting cadmium and lead ions in water using a screen-printed electrode electrochemical sensor.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for detecting cadmium and lead ions in water using a screen-printed electrode electrochemical sensor includes the following steps:

[0007] S1. A screen-printed electrode electrochemical sensor is constructed by using a screen-printed electrode with a reaction end surface modified with ZIF-8 / MWCNT nanocomposite material as the working electrode; the ZIF-8 / MWCNT nanocomposite material is obtained by combining multi-walled carbon nanotubes and ZIF-8; the multi-walled carbon nanotubes are modified on the surface of ZIF-8 and / or penetrate through the interior of ZIF-8.

[0008] S2. Place the solution containing cadmium ions and / or lead ions to be tested in a screen-printed electrode electrochemical sensor for electrochemical detection to obtain the peak current change of the solution containing cadmium ions and / or lead ions to be tested.

[0009] S3. Based on the peak current change of the solution containing cadmium ions and / or lead ions to be tested, the concentrations of cadmium ions and lead ions in the solution containing cadmium ions and / or lead ions to be tested are calculated using the linear regression equation of cadmium ion concentration and lead ion concentration with peak current change.

[0010] A further improvement to the above method, in step S1, the preparation method of the screen-printed electrode with the reaction end surface modified with ZIF-8 / MWCNT nanocomposite material includes the following steps:

[0011] (1) Carboxylated multi-walled carbon nanotubes, zinc salt and 2-methylimidazole were dissolved in methanol, stirred, sonicated, centrifuged and dried to obtain ZIF-8 / MWCNT nanocomposite material.

[0012] (2) The ZIF-8 / MWCNT nanocomposite material was dispersed in a mixture of ethanol and naphthol to prepare a ZIF-8 / MWCNT nanocomposite material dispersion.

[0013] (3) The ZIF-8 / MWCNT nanocomposite dispersion was coated on the reaction end surface of the screen-printed electrode and dried to obtain a screen-printed electrode with the reaction end surface modified with ZIF-8 / MWCNT nanocomposite.

[0014] In a further improvement to the above method, in step (1), the mass ratio of the carboxylated multi-walled carbon nanotubes, zinc salt, and 2-methylimidazole is 1:100:300; the zinc salt is zinc nitrate hexahydrate; the stirring time is ≥4h; the ultrasonication time is 20min~60min; the centrifugation speed is 8000r / min~10000r / min; the centrifugation time is 3min~10min; after centrifugation, the mixture is washed with methanol 3~5 times and distilled water 3~5 times in sequence; the drying is carried out under vacuum conditions; the drying time is 6h~15h; and the mass ratio of multi-walled carbon nanotubes to ZIF-8 in the ZIF-8 / MWCNT nanocomposite material is 1:10~15.

[0015] In a further improvement to the above method, in step (2), the volume ratio of ethanol to naphthol in the ethanol / naphthol mixture is 1:1.

[0016] In a further improvement to the above method, in step (3), 5 μL to 15 μL of ZIF-8 / MWCNT nanocomposite dispersion is coated on the reaction end surface of a single screen-printed electrode; the concentration of the ZIF-8 / MWCNT nanocomposite dispersion is 4 g / L.

[0017] In a further improvement to the above method, in step S1, a screen-printed electrode with a ZIF-8 / MWCNT nanocomposite material modified on the reaction end surface is used as the working electrode, and a three-electrode system is established with a reference electrode and a counter electrode. This system is then connected to an electrochemical workstation to form a screen-printed electrode electrochemical sensor. The reference electrode is a saturated calomel electrode, and the counter electrode is a platinum electrode.

[0018] In a further improvement to the above method, in step S2, differential pulse stripping voltammetry is used to electrochemically detect the solution containing cadmium ions and / or lead ions to be tested; during the electrochemical detection process, the electrodeposition potential is controlled at -0.2V and the electrodeposition time is 150s.

[0019] In a further improvement to the above method, step S2 includes the following treatment before electrochemical detection of the solution containing cadmium and / or lead ions: adjusting the pH of the solution containing cadmium and / or lead ions to 5-6; the pH adjustment agent used is an acetate-sodium acetate buffer solution; the pH of the acetate-sodium acetate buffer solution is 2-5.5; the initial concentration of cadmium ions in the solution containing cadmium and / or lead ions is 5 μg / L-400 μg / L, or 30 μg / L-400 μg / L.

[0020] A further improvement to the above method, in step S3, when the test solution is a cadmium ion solution, the method for constructing the linear regression equation between the cadmium ion concentration and the peak current change includes the following steps:

[0021] (a1) Electrochemical detection of cadmium ion standard solutions of different concentrations was performed using a screen-printed electrode electrochemical sensor to obtain the peak current changes corresponding to cadmium ion standard solutions of different concentrations.

[0022] (a2) Based on the peak current changes corresponding to standard solutions of cadmium ions of different concentrations, a mapping relationship between different concentrations of cadmium ions in the solution and peak current changes was established, and a linear regression equation between cadmium ion concentration and peak current changes was obtained.

[0023] A further improvement to the above method, when the test solution is a lead ion solution, includes the following steps in constructing the linear regression equation between the lead ion concentration and the peak current change:

[0024] (b1) Electrochemical detection of lead ion standard solutions of different concentrations was performed using a screen-printed electrode electrochemical sensor to obtain the peak current changes corresponding to lead ion standard solutions of different concentrations.

[0025] (b2) Based on the peak current changes corresponding to lead ion standard solutions of different concentrations, establish the mapping relationship between lead ion concentrations in the solution and peak current changes, and obtain the linear regression equation between lead ion concentration and peak current changes.

[0026] A further improvement to the above method, when the test solution is a mixed solution containing cadmium and lead ions, includes the following steps in constructing the linear regression equation between the cadmium ion concentration, lead ion concentration, and peak current change:

[0027] (c1) Electrochemical detection of standard solutions containing cadmium ions and lead ions of different concentrations was performed using screen-printed electrode electrochemical sensors to obtain the peak current changes corresponding to standard solutions containing cadmium ions and lead ions of different concentrations.

[0028] (c2) Based on the peak current changes corresponding to standard solutions containing cadmium ions and lead ions of different concentrations, establish the mapping relationship between different concentrations of cadmium ions and peak current changes in the solution, and the mapping relationship between different concentrations of lead ions and peak current changes in the solution, and obtain the linear regression equations of cadmium ion concentration and peak current changes and the linear regression equations of lead ion concentration and peak current changes.

[0029] In a further improvement to the above method, in step (a1), differential pulse stripping voltammetry is used to electrochemically detect cadmium ion standard solutions of different concentrations; during the electrochemical detection process, the electrodeposition potential is controlled at -0.2V and the electrodeposition time is 150s.

[0030] In a further improvement to the above method, step (b1) involves using differential pulse stripping voltammetry to electrochemically detect lead ion standard solutions of different concentrations; during the electrochemical detection process, the electrodeposition potential is controlled at -0.2V and the electrodeposition time is 150s.

[0031] In a further improvement to the above method, in step (c1), differential pulse stripping voltammetry is used to electrochemically detect standard solutions containing cadmium and lead ions of different concentrations; during the electrochemical detection process, the electrodeposition potential is controlled at -0.2V and the electrodeposition time is 150s.

[0032] The above method is further improved in step (a1) by including the following treatment before electrochemical detection of cadmium ion standard solutions of different concentrations: adjusting the pH of the cadmium ion standard solutions to 5-6; the pH adjustment agent used is an acetate-sodium acetate buffer solution; the pH of the acetate-sodium acetate buffer solution is 2-5.5; and the concentrations of the cadmium ion standard solutions are successively 0 μg / L, 0.5 μg / L, 1 μg / L, 2 μg / L, 3 μg / L, and 4 μg / L. L, 5μg / L, 6μg / L, 7μg / L, 8μg / L, 9μg / L, 10μg / L, 15μg / L, 20μg / L, 25μg / L, 30μg / L, 35μg / L, 40μg / L, 45μg / L, 50 μg / L, 60 μg / L, 70 μg / L, 80 μg / L, 90 μg / L, 100 μg / L, 150 μg / L, 200 μg / L, 250 μg / L, 300 μg / L, 350 μg / L, and 400 μg / L.

[0033] The method described above is further improved in step (b1) by including the following treatment before electrochemical detection of lead ion standard solutions of different concentrations: adjusting the pH of the lead ion standard solution to 5-6; the pH adjustment agent used is an acetate-sodium acetate buffer solution; the pH of the acetate-sodium acetate buffer solution is 2-5.5; and the concentration of the lead ion standard solution is 0 μg / L, 0.5 μg / L, 1 μg / L, 2 μg / L, 3 μg / L, or 4 μg / L. , 5μg / L, 6μg / L, 7μg / L, 8μg / L, 9μg / L, 10μg / L, 15μg / L, 20μg / L, 25μg / L, 30μg / L, 35μg / L, 40μg / L, 45μg / L, 50 μg / L, 60 μg / L, 70 μg / L, 80 μg / L, 90 μg / L, 100 μg / L, 150 μg / L, 200 μg / L, 250 μg / L, 300 μg / L, 350 μg / L, and 400 μg / L.

[0034] In a further improvement to the above method, step (c1) includes the following treatment before electrochemical detection of standard solutions containing cadmium and lead ions of different concentrations: adjusting the pH of the standard solutions containing cadmium and lead ions to 5-6; using an acetate-sodium acetate buffer solution as the pH adjuster; the pH of the acetate-sodium acetate buffer solution being 2-5.5; and the concentration combination of cadmium and lead ions in the standard solutions containing cadmium and lead ions being 100 μg / L (Cd). 2+ ) and 100 μg / L (Pb 2+ ), 120 μg / L (Cd 2+ ) and 150 μg / L (Pb 2+ ), 140 μg / L (Cd 2+ ) and 200 μg / L (Pb 2+ ), 160 μg / L (Cd 2+ ) and 250 μg / L (Pb 2+ ), 180 μg / L (Cd 2+ ) and 300 μg / L (Pb 2+ ), 200 μg / L (Cd 2+ ) and 350 μg / L (Pb 2+ ), 220 μg / L (Cd 2+ ) and 400 μg / L (Pb 2+ ), 240 μg / L (Cd 2+ ) and 450 μg / L (Pb 2+ ), 260 μg / L (Cd 2+ ) and 500 μg / L (Pb 2+ ), 280 μg / L (Cd 2+ ) and 550 μg / L (Pb 2+ ), 300 μg / L (Cd 2+ ) and 600 μg / L (Pb 2+ ).

[0035] The above method is further improved in step S3, when the test solution is a cadmium ion solution, the linear regression equation of the cadmium ion concentration and the peak current change is shown in equation (1).

[0036] y Cd =0.095×x Cd +6.103 (1);

[0037] In equation (1), y Cd x represents the peak current value of cadmium ions. Cd For cadmium ion solubility, the correlation coefficient R 2=0.995, detection range is 0.5μg / L~400μg / L, and detection limit is 0.5μg / L.

[0038] The above method is further improved. When the test solution is a lead ion solution, the linear regression equation of the lead ion concentration and the peak current change is shown in equation (2).

[0039] y Pb =0.026×x Pb +1.145 (2);

[0040] In equation (2), y Pb x represents the peak current value of lead ions. Pb For lead ion solubility, the correlation coefficient R 2 =0.994, detection range is 5μg / L~400μg / L, and detection limit is 5μg / L.

[0041] The above method is further improved. When the test solution is a mixed solution containing cadmium ions and lead ions, the linear regression equation of the cadmium ion concentration and the peak current change is shown in equation (3).

[0042] y Cd =0.094×x Cd +6.696 (3);

[0043] In equation (3), y Cd x represents the peak current value of cadmium ions. Cd For cadmium ion solubility, the correlation coefficient R 2 =0.996, detection range is 0.5μg / L~400μg / L, and detection limit is 0.5μg / L.

[0044] The above method is further improved. When the test solution is a mixed solution containing cadmium ions and lead ions, the linear regression equation of the lead ion concentration and the peak current change is shown in equation (4).

[0045] y Pb =0.026×x Pb +8.838 (4);

[0046] In equation (4), y Pb x represents the peak current value of lead ions. Pb For lead ion solubility, the correlation coefficient R 2 =0.995, detection range is 5μg / L~400μg / L, and detection limit is 5μg / L.

[0047] Compared with the prior art, the advantages of the present invention are as follows:

[0048] To address the shortcomings of existing detection methods based on screen-printed electrode electrochemical sensors, such as poor detection sensitivity and narrow detection range, which lead to difficulties in accurately detecting heavy metal concentrations in water and poor applicability, this invention provides a method for detecting cadmium and lead ions in water using a screen-printed electrode electrochemical sensor. First, a screen-printed electrode with a reaction end surface modified with ZIF-8 / MWCNT nanocomposite material is used as the working electrode to construct a screen-printed electrode electrochemical sensor. Then, the screen-printed electrode electrochemical sensor is used to electrochemically detect solutions containing cadmium and / or lead ions, obtaining the peak current changes of the solution containing cadmium and / or lead ions. Finally, based on the peak current changes of the solution containing cadmium and / or lead ions, the concentrations of cadmium and lead ions in the solution are calculated using a linear regression equation between cadmium and lead ions and the peak current changes. Compared to conventional screen-printed electrode electrochemical sensors, the screen-printed electrode electrochemical sensor used in this invention modifies the reaction end surface of the screen-printed electrode with a ZIF-8 / MWCNT nanocomposite material. This ZIF-8 / MWCNT nanocomposite material is obtained by combining multi-walled carbon nanotubes and ZIF-8, with the multi-walled carbon nanotubes modifying the surface of ZIF-8 and / or penetrating through the interior of ZIF-8. On the one hand, the ZIF-8 used has excellent chemical and thermal stability and good adsorption capacity, thus facilitating the adsorption of cadmium and lead ions in water. On the other hand, the multi-walled carbon nanotubes used are porous nanomaterials with excellent physical and adsorption properties, thus also working in conjunction with ZIF-8 to enhance the composite material. The material can efficiently adsorb cadmium and lead ions in water. Furthermore, multi-walled carbon nanotubes (MWCNTs) modify the surface of ZIF-8 and / or penetrate its interior, significantly enhancing the conductivity between ZIF-8 molecules. Therefore, modifying this ZIF-8 / MWCNT nanocomposite material onto the reaction end surface of the screen-printed electrode results in a faster current response and a larger current intensity. This gives the screen-printed electrode electrochemical sensor of this invention a wider detection range and higher detection sensitivity. Based on this, when used to detect solutions containing cadmium and / or lead ions, detection becomes more convenient, faster, simpler, more sensitive, and more accurate, and it can achieve rapid simultaneous detection of both lead and cadmium ions. This invention's method for detecting cadmium and lead ions in water using a screen-printed electrode electrochemical sensor has advantages such as simple operation, low cost, high detection efficiency, and high detection accuracy. It enables on-site detection of cadmium and lead ions in water, and is convenient and accurate. 2+ Al 2+ Fe 2+ Ca 2+ Co 2+It has strong anti-interference ability against interference factors, which is of great significance for achieving efficient detection of heavy metal cadmium and lead ions in the water environment. Attached Figure Description

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0050] Figure 1 This is a graph showing the peak current changes corresponding to standard solutions of cadmium ions at different concentrations in Example 1 of the present invention.

[0051] Figure 2 This is a linear regression curve of the cadmium ion concentration and peak current change in Example 1 of the present invention.

[0052] Figure 3 This is a graph showing the peak current changes corresponding to different concentrations of lead ion standard solutions in Example 1 of the present invention.

[0053] Figure 4 This is a linear regression curve of the lead ion concentration and peak current change in Example 1 of the present invention.

[0054] Figure 5 This is a graph showing the peak current changes of standard solutions containing cadmium and lead ions at different concentrations in Example 1 of the present invention.

[0055] Figure 6 This is a SEM image of the ZIF-8 / MWCNT nanocomposite material modified on the surface of the screen-printed electrode reaction end in Example 1 of the present invention.

[0056] Figure 7 This is a stability diagram of the screen-printed electrode electrochemical sensor in Embodiment 2 of the present invention under different heavy metal ion interference conditions. Detailed Implementation

[0057] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0058] In the following examples, unless otherwise specified, the raw materials and instruments used are commercially available, the processes used are conventional processes, the equipment used is conventional equipment, and the data obtained are the average values ​​of more than three repeated experiments.

[0059] Example 1

[0060] A method for detecting cadmium and lead ions in water using a screen-printed electrode electrochemical sensor, specifically employing a screen-printed electrode with a reaction end surface modified with ZIF-8 / MWCNT nanocomposite material as the working electrode to detect cadmium and lead ions in water, includes the following steps:

[0061] (1) Construction of screen-printed electrode electrochemical sensor:

[0062] A screen-printed electrode with a ZIF-8 / MWCNT nanocomposite material modified on its reaction end surface was used as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum electrode as the counter electrode to establish a three-electrode system. This system was then connected to an electrochemical workstation to form a screen-printed electrode electrochemical sensor. In this step, the ZIF-8 / MWCNT nanocomposite material was obtained by combining multi-walled carbon nanotubes and ZIF-8 (the framework material), with the multi-walled carbon nanotubes modifying the surface of ZIF-8 and / or penetrating the interior of ZIF-8. In this embodiment, the mass ratio of multi-walled carbon nanotubes to ZIF-8 in the ZIF-8 / MWCNT nanocomposite material was 1:10.

[0063] (2) Differential pulse stripping voltammetry (DPV) was selected, and the screen-printed electrode electrochemical sensor constructed in step (1) was used to perform electrochemical detection on water samples containing cadmium ions and lead ions. During the electrochemical detection process, the electrodeposition potential was set to -0.2V and the electrodeposition time was set to 150s to obtain the anodic stripping peak currents of cadmium ions and lead ions in the water samples to be tested. The concentrations of cadmium ions and lead ions in the water samples to be tested in this step are shown in Table 1. Before performing electrochemical detection, the pH of the water samples was adjusted to 5.0 using an acetate-sodium acetate buffer solution (initial pH value of 2-3).

[0064] (3) Based on the anodic dissolution peak current of cadmium ions and lead ions in the water sample to be tested, the concentrations of cadmium ions and lead ions in the water sample to be tested were calculated using the linear regression equation of cadmium ions, lead ions and peak current changes, as shown in Table 1.

[0065] Table 1. Detection results of different water samples in Example 1.

[0066]

[0067] As shown in Table 1, compared with ICP-MS, the recovery rate of the method of the present invention is 98% to 117%, which indicates that the method of the present invention has good accuracy. Therefore, the detection method of the present invention based on screen-printed electrode electrochemical sensor can achieve accurate detection of cadmium ions and lead ions in water.

[0068] In this embodiment, the method for constructing the linear regression equation between cadmium ion concentration and peak current change in step (3) is as follows: using differential pulse stripping voltammetry, the screen-printed electrode electrochemical sensor constructed in step (1) is used to detect cadmium ion standard solutions of different concentrations (the gradients of these cadmium ion standard solutions are 0 μg / L, 0.5 μg / L, 1 μg / L, 2 μg / L, 3 μg / L, 4 μg / L, 5 μg / L, 6 μg / L, 7 μg / L, 8 μg / L, 9 μg / L, 10 μg / L, 15 μg / L, 20 μg / L, etc.). The concentrations of cadmium ions were set at 25 μg / L, 30 μg / L, 35 μg / L, 40 μg / L, 45 μg / L, 50 μg / L, 60 μg / L, 70 μg / L, 80 μg / L, 90 μg / L, 100 μg / L, 150 μg / L, 200 μg / L, 250 μg / L, 300 μg / L, 350 μg / L, and 400 μg / L (pH 5.0). During electrochemical detection, the electrodeposition potential was controlled at -0.2 V and the electrodeposition time at 150 s. The peak current changes of standard solutions with different concentrations of cadmium ions were obtained. Figure 1 As shown. Then, based on the relationship between cadmium ion standard solutions of different concentrations and peak current changes, a linear regression equation between cadmium ion concentration and peak current changes was constructed, as shown. Figure 2 As shown in the figure, specifically as shown in equation (1).

[0069] The linear regression equation constructed from the changes in cadmium ion concentration and peak current is as follows:

[0070] y Cd =0.095×x Cd +6.103 (1);

[0071] In equation (1), y Cd x represents the peak current value of cadmium ions. Cd For cadmium ion solubility, the correlation coefficient R 2 =0.995, detection range is 0.5μg / L~400μg / L, and detection limit is 0.5μg / L.

[0072] In this embodiment, the method for constructing the linear regression equation between lead ion concentration and peak current change in step (3) is as follows: Differential pulse stripping voltammetry is used, and the screen-printed electrode electrochemical sensor constructed in step (1) is used to detect lead ion standard solutions of different concentrations (the gradients of these lead ion standard solutions are 0 μg / L, 0.5 μg / L, 1 μg / L, 2 μg / L, 3 μg / L, 4 μg / L, 5 μg / L, 6 μg / L, 7 μg / L, 8 μg / L, 9 μg / L, 10 μg / L, 15 μg / L, 20 μg / L, etc.). L, 25 μg / L, 30 μg / L, 35 μg / L, 40 μg / L, 45 μg / L, 50 μg / L, 60 μg / L, 70 μg / L, 80 μg / L, 90 μg / L, 100 μg / L, 150 μg / L, 200 μg / L, 250 μg / L, 300 μg / L, 350 μg / L, and 400 μg / L (pH 5.0 all), during electrochemical detection, the electrodeposition potential was controlled at -0.2 V and the electrodeposition time at 150 s. The peak current changes of lead ion standard solutions of different concentrations were obtained, such as... Figure 3 As shown. Then, based on the relationship between lead ion standard solutions of different concentrations and peak current changes, a linear regression equation between lead ion concentration and peak current changes was constructed, as shown. Figure 4 As shown in the figure, specifically as shown in equation (2).

[0073] The linear regression equation constructed from the changes in lead ion concentration and peak current is as follows:

[0074] y Pb =0.026×x Pb +1.145 (2);

[0075] In equation (2), y Pb x represents the peak current value of lead ions. Pb For lead ion solubility, the correlation coefficient R 2 =0.994, detection range is 5μg / L~400μg / L, and detection limit is 5μg / L.

[0076] In this embodiment, the effect of different pH values ​​on the detection results was also investigated. Specifically, cadmium-containing and lead-containing water samples with different pH values ​​(pH values ​​of 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, and 7.0, respectively) were tested according to the method in Example 1. The results showed that enhanced peak current was obtained at slightly acidic or lower pH values ​​(pH=5), while reduced peak current was obtained under higher or very low pH conditions.

[0077] In this embodiment, the effect of different electrodeposition potentials on the detection effect was also investigated. Specifically, following the method in Example 1, cadmium-containing and lead-containing water samples with a pH of 5 were tested under different potential conditions (-0.5V, -0.4V, -0.3V, -0.2V, -0.1V, 0V, 0.1V). The results showed that in the DPV measurement, the oxidation current of all detected metal ions reached a plateau after -0.2V, and the subsequent peak values ​​fluctuated around the peak value at -0.2V.

[0078] In this embodiment, the effect of different electrodeposition times on the detection effect was also investigated. Specifically, following the method in Example 1, cadmium-containing and lead-containing water samples with a pH of 5 were tested under different electrodeposition time conditions (50s-225s). The results showed that the oxidation current increased rapidly and continuously with the extension of the electrodeposition time. However, since excessively long electrodeposition times are not conducive to real-time POCT detection, 150 seconds was selected as the electrodeposition time.

[0079] In this embodiment, when the test solution is a mixed solution containing cadmium ions and lead ions, the method for constructing the corresponding linear regression equations for the changes in cadmium ion concentration and peak current, and the linear regression equations for the changes in lead ion concentration and peak current, includes the following steps:

[0080] (c1) The screen-printed electrode electrochemical sensor constructed in Example 1 was used to perform electrochemical detection on standard solutions containing cadmium and lead ions of different concentrations. The peak current changes corresponding to the standard solutions containing cadmium and lead ions of different concentrations were obtained, and the results are as follows: Figure 5 As shown. In this step, differential pulse stripping voltammetry is used to electrochemically detect standard solutions containing cadmium and lead ions of different concentrations. During the electrochemical detection process, the electrodeposition potential is controlled at -0.2V and the electrodeposition time is 150s. Before electrochemical detection of the standard solutions containing cadmium and lead ions of different concentrations, the following treatment is also included: adjusting the pH of the standard solutions containing cadmium and lead ions to 5 using an acetate-sodium acetate buffer solution with a pH of 2-3; the concentration combinations of cadmium and lead ions in the different concentrations of standard solutions containing cadmium and lead ions are successively 100μg / L (Cd). 2+ ) and 100 μg / L (Pb 2+ ), 120 μg / L (Cd 2+ ) and 150 μg / L (Pb 2+ ), 140 μg / L (Cd 2+ ) and 200 μg / L (Pb 2+ ), 160 μg / L (Cd 2+ ) and 250 μg / L (Pb 2+ ), 180 μg / L (Cd2+ ) and 300 μg / L (Pb 2+ ), 200 μg / L (Cd 2+ ) and 350 μg / L (Pb 2+ ), 220 μg / L (Cd 2+ ) and 400 μg / L (Pb 2+ ), 240 μg / L (Cd 2+ ) and 450 μg / L (Pb 2+ ), 260 μg / L (Cd 2+ ) and 500 μg / L (Pb 2+ ), 280 μg / L (Cd 2+ ) and 550 μg / L (Pb 2+ ), 300 μg / L (Cd 2+ ) and 600 μg / L (Pb 2+ ).

[0081] (c2) Based on the peak current changes corresponding to standard solutions containing cadmium ions and lead ions of different concentrations, establish the mapping relationship between different concentrations of cadmium ions and peak current changes in the solution and the mapping relationship between different concentrations of lead ions and peak current changes in the solution. The linear regression equations of cadmium ion concentration and peak current change and the linear regression equations of lead ion concentration and peak current change are obtained, as shown in equation (3) and equation (4), respectively.

[0082] When the test solution is a mixed solution containing cadmium ions and lead ions, the linear regression equation of cadmium ion concentration and peak current change is shown in equation (3).

[0083] y Cd =0.094×x Cd +6.696 (3);

[0084] In equation (3), y Cd x represents the peak current value of cadmium ions. Cd For cadmium ion solubility, the correlation coefficient R 2 =0.996, detection range is 0.5μg / L~400μg / L, and detection limit is 0.5μg / L;

[0085] When the test solution is a mixed solution containing cadmium ions and lead ions, the linear regression equation of lead ion concentration and peak current change is shown in equation (4).

[0086] y Pb =0.026×x Pb +8.838 (4);

[0087] In equation (4), y Pb x represents the peak current value of lead ions. PbFor lead ion solubility, the correlation coefficient R 2 =0.995, detection range is 5μg / L~400μg / L, and detection limit is 5μg / L.

[0088] In Example 1, the method for preparing the screen-printed electrode with the reaction end surface modified with ZIF-8 / MWCNT nanocomposite material includes the following steps:

[0089] (1) According to the mass ratio of carboxylated multi-walled carbon nanotubes, zinc salt and 2-methylimidazole of 1:100:300, carboxylated multi-walled carbon nanotubes, zinc salt (specifically zinc nitrate hexahydrate) and 2-methylimidazole were dissolved in methanol, stirred for 4 hours, sonicated for 30 minutes, centrifuged at 8000 r / min for 5 minutes, and after centrifugation, the mixture was washed with methanol 3 times and distilled water 3 times in sequence, and then placed in a vacuum drying oven for vacuum drying for 12 hours to obtain ZIF-8 / MWCNT nanocomposite material;

[0090] (2) The ZIF-8 / MWCNT nanocomposite material was dispersed in a mixture of ethanol and naphthol (the volume ratio of ethanol to naphthol in the mixture was 1:1) to prepare a ZIF-8 / MWCNT nanocomposite material dispersion with a concentration of 4 g / L.

[0091] (3) 10 μL of ZIF-8 / MWCNT nanocomposite dispersion was coated on the reaction end surface of a single screen-printed electrode and dried at room temperature to obtain a screen-printed electrode with the reaction end surface modified with ZIF-8 / MWCNT nanocomposite.

[0092] Figure 6 This is a SEM image of the ZIF-8 / MWCNT nanocomposite material modified on the surface of the screen-printed electrode reaction end in Example 1 of this invention. Figure 6 As can be seen, the ZIF-8 nanocrystals in the ZIF-8 / MWCNT nanocomposite material prepared in this invention exhibit a typical rhombic dodecahedral morphology with similar particle sizes, indicating that the composite material does not alter the material morphology and will not affect its properties. Furthermore, the ZIF-8 / MWCNT nanocomposite material contains MWCNTs, which are elongated strips in shape. Similarly, TEM images show that some multi-walled carbon nanotubes modify the ZIF-8 surface, while others penetrate the interior of the ZIF-8. Therefore, by combining ZIF-8 and MWCNTs, not only is electrical conductivity improved, but the structural characteristics and chemical properties of the metal-organic framework are also preserved.

[0093] Example 2

[0094] The anti-interference capability of the screen-printed electrode electrochemical sensor was investigated. Specifically, the screen-printed electrode electrochemical sensor constructed in Example 1 was used to detect cadmium ion solutions and lead ion solutions containing different interfering substances. The steps included: adding ten times the amount of Mn to cadmium ion solutions (100 μg / L) and lead ion solutions (100 μg / L) with a pH of 5. 2+ Al 2 + Fe 2+ Ca 2+ Co 2+ The concentrations of various heavy metal ions in the above samples (test solutions) were detected according to the method in Example 1. Figure 7 As shown.

[0095] The results showed that five interfering ions (Mn) 2+ Al 2+ Fe 2+ Ca 2+ Co 2+ The influence of the differential pulse stripping voltammetry stripping peak current variation on the cadmium and lead ions under test is within ±10%, which shows that the screen-printed electrode electrochemical sensor of the present invention has excellent anti-interference ability when detecting cadmium and lead ions.

[0096] The above results show that the method for detecting cadmium and lead ions in water using a screen-printed electrode electrochemical sensor has the advantages of simple operation, low cost, high detection efficiency, and high detection accuracy. It can achieve on-site detection of cadmium and lead ions in water, and is convenient and accurate. 2+ Al 2+ Fe 2+ Ca 2+ Co 2+ It has strong anti-interference ability against interference factors, which is of great significance for achieving efficient detection of heavy metal cadmium and lead ions in the water environment.

[0097] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for detecting cadmium and lead ions in water using a screen-printed electrode electrochemical sensor, characterized in that, Includes the following steps: S1. A screen-printed electrode electrochemical sensor is constructed using a screen-printed electrode with a reaction end surface modified with ZIF-8 / MWCNT nanocomposite material as the working electrode; the ZIF-8 / MWCNT nanocomposite material is obtained by combining multi-walled carbon nanotubes and ZIF-8; the multi-walled carbon nanotubes are modified on the surface of ZIF-8 and penetrate through the interior of ZIF-8; the mass ratio of multi-walled carbon nanotubes to ZIF-8 in the ZIF-8 / MWCNT nanocomposite material is 1:10-15; the preparation method of the screen-printed electrode with the reaction end surface modified with ZIF-8 / MWCNT nanocomposite material includes the following steps: (1) Carboxylated multi-walled carbon nanotubes, zinc salt and 2-methylimidazole were dissolved in methanol, stirred, sonicated, centrifuged and dried to obtain ZIF-8 / MWCNT nanocomposite material. (2) The ZIF-8 / MWCNT nanocomposite material was dispersed in a mixture of ethanol and naphthol to prepare a ZIF-8 / MWCNT nanocomposite material dispersion; (3) The ZIF-8 / MWCNT nanocomposite dispersion was coated on the reaction end surface of the screen-printed electrode and dried to obtain a screen-printed electrode with the reaction end surface modified with ZIF-8 / MWCNT nanocomposite. S2. Place the solution containing cadmium ions and / or lead ions to be tested in a screen-printed electrode electrochemical sensor for electrochemical detection to obtain the peak current change of the solution containing cadmium ions and / or lead ions to be tested. S3. Based on the peak current change of the solution containing cadmium ions and / or lead ions to be tested, the concentrations of cadmium ions and lead ions in the solution containing cadmium ions and / or lead ions to be tested are calculated using the linear regression equation of cadmium ion concentration and lead ion concentration with peak current change.

2. The method according to claim 1, characterized in that, In step (1), the mass ratio of the carboxylated multi-walled carbon nanotubes, zinc salt, and 2-methylimidazole is 1:100:300; the zinc salt is zinc nitrate hexahydrate; the stirring time is ≥4h; the ultrasonication time is 20min~60min; the centrifugation speed is 8000r / min~10000r / min; the centrifugation time is 3min~10min; after centrifugation, the mixture is washed with methanol 3~5 times and distilled water 3~5 times in sequence; the drying is carried out under vacuum conditions; the drying time is 6h~15h. In step (2), the volume ratio of ethanol to naphthol in the ethanol / naphthol mixture is 1:1; In step (3), 5 μL to 15 μL of ZIF-8 / MWCNT nanocomposite dispersion is coated on the reaction end surface of a single screen-printed electrode; the concentration of the ZIF-8 / MWCNT nanocomposite dispersion is 4 g / L.

3. The method according to claim 1 or 2, characterized in that, In step S1, a screen-printed electrode with ZIF-8 / MWCNT nanocomposite material modified on the reaction end surface is used as the working electrode. Together with the reference electrode and the counter electrode, a three-electrode system is established and connected to an electrochemical workstation to form a screen-printed electrode electrochemical sensor. The reference electrode is a saturated calomel electrode, and the counter electrode is a platinum electrode.

4. The method according to claim 1 or 2, characterized in that, In step S2, differential pulse stripping voltammetry is used to electrochemically detect the solution containing cadmium ions and / or lead ions to be tested; during the electrochemical detection process, the electrodeposition potential is controlled at -0.2V and the electrodeposition time is 150s.

5. The method according to claim 4, characterized in that, In step S2, before electrochemical detection of the solution containing cadmium ions and / or lead ions to be tested, the following treatment is also included: adjusting the pH value of the solution containing cadmium ions and / or lead ions to be tested to 5-6; the pH value of the solution containing cadmium ions and / or lead ions to be tested is adjusted by an acetate-sodium acetate buffer solution; the pH value of the acetate-sodium acetate buffer solution is 2-5.5; the initial concentration of cadmium ions in the solution containing cadmium ions and / or lead ions to be tested is 5 μg / L-400 μg / L, or 30 μg / L-400 μg / L.

6. The method according to claim 1 or 2, characterized in that, In step S3, when the test solution is a cadmium ion solution, the method for constructing the linear regression equation of cadmium ion concentration and peak current change includes the following steps: (a1) Electrochemical detection of cadmium ion standard solutions of different concentrations was performed using a screen-printed electrode electrochemical sensor to obtain the peak current changes corresponding to cadmium ion standard solutions of different concentrations. (a2) Based on the peak current changes corresponding to standard solutions of cadmium ions of different concentrations, establish the mapping relationship between different concentrations of cadmium ions in the solution and the peak current changes, and obtain the linear regression equation between cadmium ion concentration and peak current changes. When the test solution is a lead ion solution, the method for constructing the linear regression equation of lead ion concentration and peak current change includes the following steps: (b1) Electrochemical detection of lead ion standard solutions of different concentrations was performed using a screen-printed electrode electrochemical sensor to obtain the peak current changes corresponding to lead ion standard solutions of different concentrations. (b2) Based on the peak current changes corresponding to lead ion standard solutions of different concentrations, establish the mapping relationship between lead ion concentrations in the solution and peak current changes, and obtain the linear regression equation between lead ion concentration and peak current changes. When the test solution is a mixed solution containing cadmium ions and lead ions, the method for constructing the linear regression equation of the cadmium ion concentration, lead ion concentration and peak current change includes the following steps: (c1) Electrochemical detection of standard solutions containing cadmium ions and lead ions of different concentrations was performed using a screen-printed electrode electrochemical sensor to obtain the peak current changes corresponding to the standard solutions containing cadmium ions and lead ions of different concentrations. (c2) Based on the peak current changes corresponding to standard solutions containing cadmium ions and lead ions of different concentrations, establish the mapping relationship between different concentrations of cadmium ions and peak current changes in the solution, and the mapping relationship between different concentrations of lead ions and peak current changes in the solution, and obtain the linear regression equations of cadmium ion concentration and peak current changes and the linear regression equations of lead ion concentration and peak current changes.

7. The method according to claim 6, characterized in that, In step (a1), differential pulse stripping voltammetry is used to electrochemically detect cadmium ion standard solutions of different concentrations; during the electrochemical detection process, the electrodeposition potential is controlled at -0.2V and the electrodeposition time is 150s. In step (b1), differential pulse stripping voltammetry is used to electrochemically detect lead ion standard solutions of different concentrations; during the electrochemical detection process, the electrodeposition potential is controlled at -0.2V and the electrodeposition time is 150s. In step (c1), differential pulse stripping voltammetry is used to electrochemically detect standard solutions containing cadmium and lead ions of different concentrations; during the electrochemical detection process, the electrodeposition potential is controlled at -0.2V and the electrodeposition time is 150s.

8. The method according to claim 7, characterized in that, In step (a1), before electrochemical detection of cadmium ion standard solutions of different concentrations, the following treatment is also included: adjusting the pH of the cadmium ion standard solutions to 5-6; the pH adjustment agent used to adjust the pH of the cadmium ion standard solutions is an acetate-sodium acetate buffer solution; the pH of the acetate-sodium acetate buffer solution is 2-5.5; the concentrations of the cadmium ion standard solutions are successively 0 μg / L, 0.5 μg / L, 1 μg / L, 2 μg / L, 3 μg / L, 4 μg / L, 5 μg / L, 6 μg / L, 7 μg / L, 8 μg / L, 9 μg / L, 10 μg / L, 15 μg / L, 20 μg / L, 25 μg / L, 30 μg / L, 35 μg / L, 40 μg / L, 45 μg / L, 50 μg / L, and 60 μg / L. 70μg / L, 80μg / L, 90μg / L, 100μg / L, 150μg / L, 200μg / L, 250μg / L, 300μg / L, 350μg / L, and 400μg / L; In step (b1), before electrochemical detection of lead ion standard solutions of different concentrations, the following treatment is also included: adjusting the pH of the lead ion standard solution to 5-6; the pH adjustment agent used to adjust the pH of the lead ion standard solution is an acetate-sodium acetate buffer solution; the pH of the acetate-sodium acetate buffer solution is 2-5.5; the concentration of the lead ion standard solution is 0 μg / L, 0.5 μg / L, 1 μg / L, 2 μg / L, 3 μg / L, 4 μg / L, 5 μg / L, 6 μg / L, 7 μg / L, 8 μg / L, 9 μg / L, 10 μg / L, 15 μg / L, 20 μg / L, 25 μg / L, 30 μg / L, 35 μg / L, 40 μg / L, 45 μg / L, 50 μg / L, 60 μg / L. 70μg / L, 80μg / L, 90μg / L, 100μg / L, 150μg / L, 200μg / L, 250μg / L, 300μg / L, 350μg / L, and 400μg / L; In step (c1), before electrochemical detection of standard solutions containing cadmium and lead ions of different concentrations, the following treatment is also included: adjusting the pH of the standard solutions containing cadmium and lead ions to 5-6; the pH adjustment agent used for the standard solutions containing cadmium and lead ions is an acetate-sodium acetate buffer solution; the pH of the acetate-sodium acetate buffer solution is 2-5.5; the concentration combination of cadmium and lead ions in the standard solutions containing cadmium and lead ions is 100 μL. g / L and 100 μg / L, 120 μg / L and 150 μg / L, 140 μg / L and 200 μg / L, 160 μg / L and 250 μg / L, 180 μg / L and 300 μg / L, 200 μg / L and 350 μg / L, 220 μg / L and 400 μg / L, 240 μg / L and 450 μg / L, 260 μg / L and 500 μg / L, 280 μg / L and 550 μg / L, 300 μg / L and 600 μg / L.

9. The method according to claim 8, characterized in that, In step S3, when the solution to be tested is a cadmium ion solution, the linear regression equation of the cadmium ion concentration and the peak current change is shown in equation (1). and Cd =0.095×x Cd +6.103(1); In equation (1), y Cd x represents the peak current value of cadmium ions. Cd For cadmium ion solubility, the correlation coefficient R 2 =0.995, detection range is 0.5 μg / L to 400 μg / L, and detection limit is 0.5 μg / L; When the solution to be tested is a lead ion solution, the linear regression equation of the lead ion concentration and the peak current change is shown in equation (2); and Pb =0.026×x Pb +1.145(2); In equation (2), y Pb x represents the peak current value of lead ions. Pb For lead ion solubility, the correlation coefficient R 2 =0.994, detection range is 5μg / L~400μg / L, and detection limit is 5μg / L; When the test solution is a mixed solution containing cadmium ions and lead ions, the linear regression equation of the cadmium ion concentration and the peak current change is shown in equation (3). and Cd =0.094×x Cd +6.696(3); In equation (3), y Cd x represents the peak current value of cadmium ions. Cd For cadmium ion solubility, the correlation coefficient R 2 =0.996, detection range is 0.5μg / L~400μg / L, and detection limit is 0.5μg / L; When the test solution is a mixed solution containing cadmium ions and lead ions, the linear regression equation of the lead ion concentration and the peak current change is shown in equation (4). and Pb =0.026×x Pb +8.838(4); In equation (4), y Pb x represents the peak current value of lead ions. Pb For lead ion solubility, the correlation coefficient R 2 =0.995, detection range is 5 μg / L to 400 μg / L, and detection limit is 5 μg / L.

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