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

Abstract

The invention discloses a method for detecting cadmium ions and lead ions in a water body by utilizing a screen-printed electrode electrochemical sensor, which comprises the following steps of: constructing the screen-printed electrode electrochemical sensor by taking a screen-printed electrode of which the surface of a reaction end is modified with a ZIF-8 / MWCNT nano composite material as a working electrode; the method comprises the following steps: detecting the peak current change of a to-be-detected cadmium / lead ion solution by using a screen-printed electrode electrochemical sensor, and calculating the concentrations of cadmium ions and lead ions in the to-be-detected cadmium / lead ion solution by using a linear regression equation of the cadmium ion concentration, the lead ion concentration and the peak current change. The method provided by the invention 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 a water body, and has the advantages of convenient operation, high accuracy, strong anti-interference capability to interference factors, and good application prospect. The method is of great significance to efficient detection of heavy metal cadmium ions and lead ions in the water environment.

Description

Technical Field

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

[0002] Due to the widespread use of metal materials, heavy metal pollutants such as lead and cadmium often appear in water environments. 2+ ) can damage the brain, nervous system and liver, and cadmium (II, Cd 2+ ) may cause renal dysfunction and metabolic disorders, and thus enter the water environment to give you heavy metal lead and cadmium, which may threaten human health. Therefore, it is necessary to control the cadmium ion (Cd 2 + ) and lead ions (Pb 2+ ) is of great significance for reducing their risks to human health.

[0003] At present, traditional heavy metal detection methods include atomic fluorescence spectroscopy, atomic absorption spectrophotometry, dithizone spectrophotometer and oscillographic polarography. Although these methods are relatively mature, they still have some unavoidable shortcomings, such as the need for large equipment and professional equipment, complex testing procedures and inconvenience in carrying, which limits their application in rapid portable detection of heavy metals. Anodic stripping voltammetry is one of the electrochemical detection methods. It has the characteristics of simple operation and rapid detection, and is very suitable for on-site detection. However, in the existing electrochemical detection methods based on anodic stripping voltammetry, electrochemical sensors constructed with glassy carbon electrodes as working electrodes are usually used to detect heavy metals in water. Since the electrochemical sensor is difficult to miniaturize and simplify, the above detection method is difficult to achieve on-site detection of heavy metals in water. In order to overcome the above problems, some researchers have proposed to use screen-printed electrodes as working electrodes to construct miniaturized and simplified electrochemical sensors, which is conducive to the on-site detection of heavy metals in water. However, in the existing electrochemical sensors constructed based on screen-printed electrodes, the screen-printed electrodes still have poor thermal stability, poor adsorption capacity, poor conductivity and other shortcomings, so that the electrochemical sensors constructed by them still have defects such as poor detection sensitivity and narrow detection range, which makes it difficult for the detection method based on screen-printed electrode electrochemical sensors to obtain accurate detection data and meet the detection limit required by the national standard, that is, it is impossible to judge whether the concentration of heavy metals in water can meet the national standard requirements, which greatly limits the wide application of the detection method based on screen-printed electrode electrochemical sensors. For example, the detection method based on screen-printed electrode electrochemical sensors modified with reduced graphene oxide RGO / molybdenum dioxide MoS 2When the composite material and the screen-printed electrode inoculated with Hep G2 cells are used as working electrodes to construct a portable cell electrochemical sensor, the detection limit of cadmium ions is 5μM, and there is still a defect of low detection sensitivity; when the screen-printed electrode containing bismuth is used as the working electrode to construct the electrochemical sensor, the detection limit of cadmium ions is 4.8μg / L, and there is still a defect of low detection sensitivity; when the screen-printed electrode modified with polyaniline is used as the working electrode to construct the electrochemical sensor, the detection limit of cadmium ions is 5.41μg / L, and there is still a defect of low detection sensitivity; when the screen-printed electrode modified with UIO-66 is used as the working electrode to construct the electrochemical sensor, the screen-printed electrode still has the disadvantages of poor thermal stability, poor adsorption capacity, and poor conductivity, which makes the sensor have the defects of poor detection sensitivity and narrow detection range. Therefore, how to obtain 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 ions and lead ions in water. Summary of the invention

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

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

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

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

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

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

[0010] The above method is further improved, in step S1, the method for preparing the screen-printed electrode with the reaction end surface modified with ZIF-8 / MWCNT nanocomposite material comprises the following steps:

[0011] (1) dissolving carboxylated multi-walled carbon nanotubes, zinc salt and 2-methylimidazole in methanol, stirring, ultrasonicating, centrifuging and drying to obtain a ZIF-8 / MWCNT nanocomposite material;

[0012] (2) dispersing the ZIF-8 / MWCNT nanocomposite material in a mixture of ethanol / naphthol to prepare a ZIF-8 / MWCNT nanocomposite material dispersion;

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

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

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

[0016] The above method is further improved, 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] The above method is further improved. In step S1, a screen-printed electrode with a ZIF-8 / MWCNT nanocomposite material modified on the reaction end surface is used as a working electrode, and a three-electrode system is established with a reference electrode and a counter electrode, which is 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] The above method is further improved, in step S2, differential pulse stripping voltammetry is used to perform electrochemical detection on the solution containing cadmium ions and / or lead ions to be tested; during the electrochemical detection process, the electrodeposition potential is controlled to be -0.2V and the electrodeposition time is 150s.

[0019] The above method is further improved. In step S2, before the solution containing cadmium ions and / or lead ions to be tested is subjected to electrochemical detection, the following treatment is also included: the pH value of the solution containing cadmium ions and / or lead ions to be tested is adjusted to 5-6; the regulator used to adjust the pH value of the solution containing cadmium ions and / or lead ions to be tested is an acetic acid-sodium acetate buffer solution; the pH value of the acetic acid-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 5μg / L-400μg / L, 30μg / L-400μg / L.

[0020] The above method is further improved, in step S3, when the solution to be tested is a cadmium ion solution, the method for constructing the linear regression equation of the cadmium ion concentration and the peak current change comprises the following steps:

[0021] (a1) using a screen-printed electrode electrochemical sensor to perform electrochemical detection on standard cadmium ion solutions of different concentrations, and obtaining peak current changes corresponding to standard cadmium ion solutions of different concentrations;

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

[0023] The above method is further improved, when the solution to be tested is a lead ion solution, the method for constructing the linear regression equation of the lead ion concentration and the peak current change comprises the following steps:

[0024] (b1) using a screen-printed electrode electrochemical sensor to perform electrochemical detection on lead ion standard solutions of different concentrations to obtain peak current changes corresponding to lead ion standard solutions of different concentrations;

[0025] (b2) According to the peak current changes corresponding to the lead ion standard solutions with different concentrations, a mapping relationship between the lead ion concentrations and the peak current changes in the solution is established, and a linear regression equation between the lead ion concentration and the peak current changes is obtained.

[0026] The above method is further improved, when the solution to be tested is a mixed solution containing cadmium ions and lead ions, the method for constructing a linear regression equation of the cadmium ion concentration, lead ion concentration and peak current change comprises the following steps:

[0027] (c1) using a screen-printed electrode electrochemical sensor to perform electrochemical detection on standard solutions containing cadmium ions and lead ions at different concentrations, and obtaining peak current changes corresponding to the standard solutions containing cadmium ions and lead ions at different concentrations;

[0028] (c2) Based on the peak current changes corresponding to standard solutions containing cadmium ions and lead ions at different concentrations, a mapping relationship between different concentrations of cadmium ions in the solution and the peak current changes and a mapping relationship between different concentrations of lead ions and the peak current changes are established, and a linear regression equation between the cadmium ion concentration and the peak current change and a linear regression equation between the lead ion concentration and the peak current change are obtained.

[0029] The above method is further improved in that in step (a1), differential pulse stripping voltammetry is used to perform electrochemical detection on standard solutions of cadmium ions of different concentrations; during the electrochemical detection process, the electrodeposition potential is controlled to be -0.2V and the electrodeposition time is 150s.

[0030] The above method is further improved in that in step (b1), differential pulse stripping voltammetry is used to perform electrochemical detection on standard solutions of lead ions of different concentrations; during the electrochemical detection process, the electrodeposition potential is controlled to be -0.2V and the electrodeposition time is 150s.

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

[0032] The above method is further improved, in step (a1), before the electrochemical detection of the cadmium ion standard solution of different concentrations, the following treatment is also included: adjusting the pH value of the cadmium ion standard solution to 5-6; the regulator used to adjust the pH value of the cadmium ion standard solution is an acetic acid-sodium acetate buffer solution; the pH value of the acetic acid-sodium acetate buffer solution is 2-5.5; the concentration of the cadmium 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, 11 μg / L, 12 μg / L, 13 μg / L, 14 μg / L, 15 μg / L, 16 μg / L, 17 μg / L, 18 μg / L, 19 μg / L, 20 μg / L, 21 μg / L, 22 μg / L, 23 μg / L, 24 μg / L, 25 μg / L, 26 μg / L, 27 μg / L, 28 μg / L, 29 μg / L, 30 μg / L, 31 μg / L, 32 μg / L, 34 μg / L, 36 μg / L, 37 μg / L, 38 μg / L, 39 μg / L, 40 μg / L, 41 μg / L, 42 μg / L, 43 μg / L, 44 μg / L, 45 μg / L, 46 μg / L, 47 μg / L, 48 μg / L, 49 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 above method is further improved, in step (b1), before the electrochemical detection of the lead ion standard solution of different concentrations, the following treatment is also included: adjusting the pH value of the lead ion standard solution to 5-6; the regulator used to adjust the pH value of the lead ion standard solution is an acetic acid-sodium acetate buffer solution; the pH value of the acetic acid-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 , 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] The above method is further improved, in step (c1), before the electrochemical detection of the standard solution containing cadmium ions and lead ions of different concentrations is performed, the following treatment is also included: the pH value of the standard solution containing cadmium ions and lead ions is adjusted to 5-6; the regulator used to adjust the pH value of the standard solution containing cadmium ions and lead ions is an acetic acid-sodium acetate buffer solution; the pH value of the acetic acid-sodium acetate buffer solution is 2-5.5; the concentration combination of cadmium ions and lead ions in the standard solution containing cadmium ions and lead ions is 100 μg / L (Cd 2+ ) and 100μg / L(Pb 2+ )、120μg / L(Cd 2+ ) and 150μg / L(Pb 2+ )、140μg / L(Cd 2+ ) and 200μg / L(Pb 2+ )、160μg / L(Cd 2+ ) and 250μg / L(Pb 2+ )、180μg / L(Cd 2+ ) and 300μg / L(Pb 2+ )、200μg / L(Cd 2+ ) and 350μg / L(Pb 2+ )、220μg / L(Cd 2+ ) and 400μg / L(Pb 2+ )、240μg / L(Cd 2+ ) and 450μg / L(Pb 2+ )、260μg / L(Cd 2+ ) and 500μg / L(Pb2+ )、280μg / L(Cd 2+ ) and 550μg / L(Pb 2+ )、300μg / L(Cd 2+ ) and 600μg / L(Pb 2+ ).

[0035] The above method is further improved, 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 formula (1);

[0036] y Cd =0.095×x Cd +6.103 (1);

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

[0038] The above method is further improved, 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 formula (2);

[0039] y Pb =0.026×x Pb +1.145 (2);

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

[0041] The above method is further improved, when the solution to be tested 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 as shown in formula (3);

[0042] y Cd =0.094×x Cd +6.696 (3);

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

[0044] The above method is further improved, when the solution to be tested 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 formula (4);

[0045] y Pb =0.026×x Pb +8.838 (4);

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

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

[0048] Aiming at the shortcomings of poor detection sensitivity and narrow detection range still existing in the existing detection methods based on screen-printed electrode electrochemical sensors, as well as the defects of difficulty in accurately detecting the concentration of heavy metals in water bodies and poor adaptability caused by the above, the present invention provides a method for detecting cadmium ions and lead ions in water bodies by using screen-printed electrode electrochemical sensors. Firstly, a screen-printed electrode with a reaction end surface modified with a ZIF-8 / MWCNT nanocomposite material is used as a working electrode to construct a screen-printed electrode electrochemical sensor, and then the screen-printed electrode electrochemical sensor is used to perform electrochemical detection on a solution containing cadmium ions and / or lead ions to obtain a peak current change of the solution containing cadmium ions and / or lead ions, and finally, according to the peak current change of the solution containing cadmium ions and / or lead ions, a linear regression equation of cadmium ions, lead ions and peak current change is used to calculate the concentrations of cadmium ions and lead ions in the solution containing cadmium ions and / or lead ions. Compared with conventional screen-printed electrode electrochemical sensors, in the screen-printed electrode electrochemical sensor used in the present invention, the reaction end surface of the screen-printed electrode is modified with a ZIF-8 / MWCNT nanocomposite material, the ZIF-8 / MWCNT nanocomposite material is obtained by compounding multi-walled carbon nanotubes and ZIF-8, and the multi-walled carbon nanotubes are modified on the surface of ZIF-8 and / or penetrate the interior of ZIF-8. On the one hand, the ZIF-8 used has excellent chemical and thermal stability and good adsorption capacity, so it is conducive to adsorbing cadmium ions and lead ions in water bodies, and the multi-walled carbon nanotubes used are a porous nanomaterial with excellent physical properties and adsorption properties, so they can also cooperate with ZIF-8 to make the composite material The material can efficiently adsorb cadmium ions and lead ions in water. On the other hand, multi-walled carbon nanotubes are modified on the surface of ZIF-8 and / or penetrate the interior of ZIF-8, so that the conductivity between ZIF-8 is significantly enhanced. Therefore, the ZIF-8 / MWCNT nanocomposite material is modified on the reaction end surface of the screen-printed electrode, which can respond to the current more quickly and form a larger current intensity, so that the screen-printed electrode electrochemical sensor of the present invention has a wider detection range and higher detection sensitivity. On this basis, when used to detect solutions containing cadmium ions and / or lead ions, the detection can be made more convenient and faster, the operation is simpler, the sensitivity is higher, the detection value is more accurate, and the rapid detection of metal ions lead and cadmium can be achieved. The method of the present invention using a screen-printed electrode electrochemical sensor to detect cadmium ions and lead ions in water has the advantages of simple operation, low cost, high detection efficiency, high detection accuracy, etc. It can realize on-site detection of cadmium ions and lead ions in water, and is convenient to operate, high in accuracy, and has a high detection accuracy for Mn 2+ 、Al 2+ , Fe 2+ , Ca 2+ 、Co 2+It has strong anti-interference ability against interference factors, which is of great significance for the efficient detection of heavy metal cadmium ions and lead ions in water environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

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

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

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

[0053] Figure 4 The figure is a linear regression equation curve diagram of 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 corresponding to the standard solutions containing cadmium ions 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 diagram showing the stability of the screen-printed electrode electrochemical sensor in Example 2 of the present invention under different heavy metal ion interference conditions. DETAILED DESCRIPTION

[0057] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[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 are 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 ions and lead ions in water using a screen-printed electrode electrochemical sensor, specifically using a screen-printed electrode with a reaction end surface modified with a ZIF-8 / MWCNT nanocomposite as a working electrode to construct a screen-printed electrode electrochemical sensor to detect cadmium ions and lead ions in water, comprising 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 the reaction end surface is used as a working electrode, a saturated calomel electrode is used as a reference electrode, and a platinum electrode is used as a counter electrode to establish a three-electrode system, which is connected to an electrochemical workstation to form a screen-printed electrode electrochemical sensor. In this step, the ZIF-8 / MWCNT nanocomposite material is composited with multi-walled carbon nanotubes and ZIF-8 (skeleton material), and the multi-walled carbon nanotubes are modified on the surface of ZIF-8 and / or run through the interior of ZIF-8. In the ZIF-8 / MWCNT nanocomposite material of this embodiment, the mass ratio of multi-walled carbon nanotubes to ZIF-8 is 1:10.

[0063] (2) Select differential pulse stripping voltammetry (DPV) technology, and use the screen-printed electrode electrochemical sensor constructed in step (1) to perform electrochemical detection on water samples containing cadmium ions and water samples containing lead ions, wherein during the electrochemical detection process, the electrodeposition potential is selected to be -0.2v, and the electrodeposition time is selected to be 150s, and the anodic stripping peak current of cadmium ions and lead ions in the water samples to be tested is obtained. In this step, the concentrations of cadmium ions and lead ions in the water samples to be tested are shown in Table 1. Before performing electrochemical detection, the pH value of the water sample is adjusted to 5.0 using acetic acid-sodium acetate buffer solution (initial pH value is 2-3).

[0064] (3) According to 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 are calculated using the linear regression equation of cadmium ions, lead ions and peak current changes, as shown in Table 1.

[0065] Table 1 Test results of different water samples to be tested in Example 1

[0066]

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

[0068] In the present embodiment, in step (3), the method for constructing the linear regression equation of the cadmium ion concentration and the peak current change is: using differential pulse stripping voltammetry, using the screen-printed electrode electrochemical sensor constructed in the above step (1) to respectively 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) L, 25μg / L, 30μg / L, 35μg / L, 40μg / L, 45μg / L, 50μg / L, 60μg / L, 70μg / L, 80μg / L, 90μg / L, 100μg / L, 150μg / L, 200μg / L, 250μg / L, 300μg / L, 350μg / L, and 400μg / L, pH value is 5.0). During the electrochemical detection process, the electrodeposition potential was controlled to be -0.2V and the electrodeposition time was 150s. The peak current change values ​​of the cadmium ion standard solutions with different concentrations were obtained, such as Figure 1 Then, according to the relationship between the standard solution of cadmium ions with different concentrations and the change of peak current, a linear regression equation of cadmium ion concentration and peak current change was constructed, as shown in Figure 2 As shown, specifically as shown in the following formula (1).

[0069] The linear regression equation constructed by cadmium ion concentration and peak current change is:

[0070] y Cd =0.095×x Cd +6.103 (1);

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

[0072] In this embodiment, in step (3), the method for constructing the linear regression equation of lead ion concentration and peak current change is: using differential pulse stripping voltammetry, using the screen-printed electrode electrochemical sensor constructed in the above step (1) to respectively 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) L, 25μg / L, 30μg / L, 35μg / L, 40μg / L, 45μg / L, 50μg / L, 60μg / L, 70μg / L, 80μg / L, 90μg / L, 100μg / L, 150μg / L, 200μg / L, 250μg / L, 300μg / L, 350μg / L, and 400μg / L, pH value is 5.0). During the electrochemical detection process, the electrodeposition potential was controlled to be -0.2V and the electrodeposition time was 150s. The peak current change values ​​of the lead ion standard solutions with different concentrations were obtained, such as Figure 3 Then, according to the relationship between the lead ion standard solution with different concentrations and the peak current change, a linear regression equation between the lead ion concentration and the peak current change was constructed, as shown in Figure 4 As shown, specifically as shown in the following formula (2).

[0073] The linear regression equation constructed by lead ion concentration and peak current change is:

[0074] y Pb =0.026×x Pb +1.145 (2);

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

[0076] In this example, the effect of different pH values ​​on the detection effect was also investigated, specifically: cadmium ion-containing water samples and lead ion-containing water samples with different pH values ​​(the pH values ​​of these water samples are 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, respectively) were detected according to the method in Example 1. The results show that an enhanced peak current can be obtained under slightly acidic or lower pH values ​​(pH=5), while a reduced peak current is obtained under higher or very low pH conditions.

[0077] In this example, the effect of different electrodeposition potentials on the detection effect was also investigated, specifically: according to the method in Example 1, cadmium ion-containing water samples and lead ion-containing water samples with a pH value of 5 were detected 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 platform after -0.2v, and the subsequent peak value fluctuated around the peak value of -0.2v.

[0078] In this example, the effect of different electrodeposition times on the detection effect was also investigated. Specifically, according to the method in Example 1, cadmium ion-containing water samples and lead ion-containing water samples with a pH value 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. At the same time, since a long electrodeposition time is not conducive to POCT instant detection, 150 seconds was selected as the electrodeposition time.

[0079] In the present embodiment, when the solution to be tested is a mixed solution containing cadmium ions and lead ions, the method for constructing the linear regression equation of the corresponding cadmium ion concentration and the peak current change, and the linear regression equation of the lead ion concentration and the peak current change, comprises 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 ions and lead ions of different concentrations to obtain the peak current changes corresponding to the standard solutions containing cadmium ions and lead ions of different concentrations. The results are as follows: Figure 5 As shown. In this step, the standard solutions containing cadmium ions and lead ions of different concentrations are electrochemically detected by differential pulse stripping voltammetry, and during the electrochemical detection process, the electrodeposition potential is controlled to be -0.2V and the electrodeposition time is 150s. In this step, before the electrochemical detection of the standard solutions containing cadmium ions and lead ions of different concentrations is performed, the following treatments are also included: the pH value of the standard solution containing cadmium ions and lead ions is adjusted to 5 using an acetic acid-sodium acetate buffer solution with a pH value of 2 to 3; the concentration combinations of cadmium ions and lead ions in the standard solutions containing cadmium ions and lead ions of different concentrations are 100μg / L (Cd 2+ ) and 100μg / L(Pb 2+ )、120μg / L(Cd 2+ ) and 150μg / L(Pb 2+ )、140μg / L(Cd 2+ ) and 200μg / L(Pb 2+ )、160μg / L(Cd 2+ ) and 250μg / L(Pb 2+ )、180μg / L(Cd2+ ) and 300μg / L(Pb 2+ )、200μg / L(Cd 2+ ) and 350μg / L(Pb 2+ )、220μg / L(Cd 2+ ) and 400μg / L(Pb 2+ )、240μg / L(Cd 2+ ) and 450μg / L(Pb 2+ )、260μg / L(Cd 2+ ) and 500μg / L(Pb 2+ )、280μg / L(Cd 2+ ) and 550μg / L(Pb 2+ )、300μg / L(Cd 2+ ) and 600μg / L(Pb 2+ ).

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

[0082] When the solution to be tested 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 as shown in formula (3);

[0083] y Cd =0.094×x Cd +6.696 (3);

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

[0085] When the solution to be tested 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 formula (4);

[0086] y Pb =0.026×x Pb +8.838 (4);

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

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

[0089] (1) dissolving carboxylated multi-walled carbon nanotubes, zinc salt (specifically zinc nitrate hexahydrate) and 2-methylimidazole in methanol at a mass ratio of 1:100:300, stirring for 4 hours, ultrasonicating for 30 minutes, centrifuging at a speed of 8000 r / min for 5 minutes, and after centrifugation, washing with methanol 3 times and distilled water 3 times in sequence, placing in a vacuum drying oven for vacuum drying for 12 hours to obtain a ZIF-8 / MWCNT nanocomposite material;

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

[0091] (3) 10 μL of the 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 the 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 the present invention. Figure 6 It can be known that ZIF-8 nanocrystals demonstrate typical rhombic dodecahedron morphology in the ZIF-8 / MWCNT nanocomposite prepared by the present invention, and particle diameter is close, indicating that the composite material does not change the material morphology and can not affect material properties. In addition, there is MWCNT in the ZIF-8 / MWCNT nanocomposite, and the shape presents elongated strip. Similarly, TEM images show that some multi-walled carbon nanotubes are modified on the ZIF-8 surface, and others run through the inside of ZIF-8, thereby by combining ZIF-8 and MWCNT together, not only improve electrical conductivity, but also can keep the structural characteristics and chemical properties of metal organic framework simultaneously.

[0093] Example 2

[0094] The anti-interference ability 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, comprising the following steps: adding ten times the amount of Mn 2+ 、Al 2 + , Fe 2+ , Ca 2+ 、Co 2+ The above samples were tested for various heavy metal ion concentrations in the above samples (test solutions) by referring to the method of Example 1. Figure 7 shown.

[0095] The results showed that five interfering ions (Mn 2+ 、Al 2+ , Fe 2+ , Ca 2+ 、Co 2+ ) on the change of the differential pulse stripping voltammetry stripping peak current of the cadmium ions and lead ions to be measured is within ±10%. It can be seen that the screen-printed electrode electrochemical sensor of the present invention has excellent anti-interference ability when detecting cadmium ions and lead ions.

[0096] From the above results, it can be seen that the method of detecting cadmium ions and lead ions in water using screen-printed electrode electrochemical sensors has the advantages of simple operation, low cost, high detection efficiency, high detection accuracy, etc., and can realize on-site detection of cadmium ions and lead ions in water, and is convenient to operate, high in accuracy, and has a good detection accuracy. 2+ 、Al 2+ , Fe 2+ , Ca 2+ 、Co 2+ It has strong anti-interference ability against interference factors, which is of great significance for the efficient detection of heavy metal cadmium ions and lead ions in water environment.

[0097] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for detecting cadmium ions and lead ions in water using a screen-printed electrode electrochemical sensor, characterized in that: The following steps are involved: S1. Using a screen-printed electrode with a ZIF-8 / MWCNT nanocomposite material modified on the reaction end surface as a working electrode, a screen-printed electrode electrochemical sensor is constructed; the ZIF-8 / MWCNT nanocomposite material is obtained by compounding multi-walled carbon nanotubes and ZIF-8; the multi-walled carbon nanotubes are modified on the surface of ZIF-8 and / or penetrate the interior of ZIF-8; S2, placing the solution containing cadmium ions and / or lead ions to be tested in a screen-printed electrode electrochemical sensor for electrochemical detection, and obtaining a peak current change of the solution containing cadmium ions and / or lead ions to be tested; S3. According to the peak current change of the solution containing cadmium ions and / or lead ions to be measured, the concentrations of cadmium ions and lead ions in the solution containing cadmium ions and / or lead ions to be measured are calculated using a linear regression equation of cadmium ion concentration, lead ion concentration and peak current change.

2. The method according to claim 1, characterized in that In step S1, the method for preparing the screen-printed electrode with the reaction end surface modified with ZIF-8 / MWCNT nanocomposite material comprises the following steps: (1) dissolving carboxylated multi-walled carbon nanotubes, zinc salt and 2-methylimidazole in methanol, stirring, ultrasonicating, centrifuging and drying to obtain a ZIF-8 / MWCNT nanocomposite material; (2) dispersing the ZIF-8 / MWCNT nanocomposite material in a mixture of ethanol / naphthol to prepare a ZIF-8 / MWCNT nanocomposite material dispersion; (3) coating the ZIF-8 / MWCNT nanocomposite dispersion on the reaction end surface of the screen-printed electrode and drying the dispersion to obtain a screen-printed electrode with the reaction end surface modified with the ZIF-8 / MWCNT nanocomposite.

3. The method according to claim 2, characterized in that In step (1), the mass ratio of the carboxylated multi-walled carbon nanotubes, the zinc salt and the 2-methylimidazole is 1:100:300; the zinc salt is zinc nitrate hexahydrate; the stirring time is ≥4h; the ultrasonic time is 20min-60min; the centrifugal speed is 8000r / min-10000r / min; the centrifugal time is 3min-10min; after the centrifugation is completed, it also includes washing with methanol 3 times-5 times and distilled water 3 times-5 times in sequence; the drying is carried out under vacuum conditions; the drying time is 6h-15h; the mass ratio of multi-walled carbon nanotubes to ZIF-8 in the ZIF-8 / MWCNT nanocomposite material is 1:10-15; 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.

4. The method according to any one of claims 1 to 3, characterized in that In step S1, a screen-printed electrode with a ZIF-8 / MWCNT nanocomposite material modified on the reaction end surface is used as a working electrode, and a three-electrode system is established with a reference electrode and a counter electrode, 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.

5. The method according to any one of claims 1 to 3, characterized in that: In step S2, differential pulse stripping voltammetry is used to perform electrochemical detection on the solution containing cadmium ions and / or lead ions to be detected; during the electrochemical detection process, the electrodeposition potential is controlled to be -0.2V and the electrodeposition time is controlled to be 150s.

6. The method according to claim 5, characterized in that In step S2, before the solution containing cadmium ions and / or lead ions to be tested is subjected to electrochemical detection, the following treatment is also included: the pH value of the solution containing cadmium ions and / or lead ions to be tested is adjusted to 5-6; the regulator used to adjust the pH value of the solution containing cadmium ions and / or lead ions to be tested is an acetic acid-sodium acetate buffer solution; the pH value of the acetic acid-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 5μg / L-400μg / L, 30μg / L-400μg / L.

7. The method according to any one of claims 1 to 3, characterized in that: In step S3, when the solution to be tested is a cadmium ion solution, the method for constructing a linear regression equation of the cadmium ion concentration and the peak current change comprises the following steps: (a1) using a screen-printed electrode electrochemical sensor to perform electrochemical detection on standard cadmium ion solutions of different concentrations, and obtaining peak current changes corresponding to standard cadmium ion solutions of different concentrations; (a2) establishing a mapping relationship between different concentrations of cadmium ions in the solution and the change in peak current according to the change in peak current corresponding to the standard solutions of cadmium ions with different concentrations, and obtaining a linear regression equation between the cadmium ion concentration and the change in peak current; When the solution to be tested is a lead ion solution, the method for constructing a linear regression equation of the lead ion concentration and the peak current change comprises the following steps: (b1) using a screen-printed electrode electrochemical sensor to perform electrochemical detection on lead ion standard solutions of different concentrations to obtain peak current changes corresponding to lead ion standard solutions of different concentrations; (b2) establishing a mapping relationship between different concentrations of lead ions in the solution and the change in peak current according to the change in peak current corresponding to the lead ion standard solutions with different concentrations, and obtaining a linear regression equation between the lead ion concentration and the change in peak current; When the solution to be tested is a mixed solution containing cadmium ions and lead ions, the method for constructing a linear regression equation of the cadmium ion concentration, the lead ion concentration and the peak current change comprises the following steps: (c1) using a screen-printed electrode electrochemical sensor to perform electrochemical detection on standard solutions containing cadmium ions and lead ions at different concentrations, and obtaining peak current changes corresponding to the standard solutions containing cadmium ions and lead ions at different concentrations; (c2) Based on the peak current changes corresponding to standard solutions containing cadmium ions and lead ions at different concentrations, a mapping relationship between different concentrations of cadmium ions in the solution and the peak current changes and a mapping relationship between different concentrations of lead ions and the peak current changes are established, and a linear regression equation between the cadmium ion concentration and the peak current change and a linear regression equation between the lead ion concentration and the peak current change are obtained.

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

9. The method according to claim 8, 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 value of the cadmium ion standard solution to 5-6; the regulator used to adjust the pH value of the cadmium ion standard solution is an acetic acid-sodium acetate buffer solution; the pH value of the acetic acid-sodium acetate buffer solution is 2-5.5; the concentration of the cadmium 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 , 6μg / L, 7μg / L, 8μg / L, 9μg / L, 10μg / L, 15μg / L, 20μg / L, 25μg / L, 30μg / L, 35μg / L, 40μg / L, 45μg / L, 50μg / 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; In step (b1), before the electrochemical detection of lead ion standard solutions of different concentrations, the following treatment is also included: adjusting the pH value of the lead ion standard solution to 5-6; the regulator used to adjust the pH value of the lead ion standard solution is an acetic acid-sodium acetate buffer solution; the pH value of the acetic acid-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, 6μg / L, 7μg / L, 8μg / L, 9μg / L, 10μg / L, 15μg / L, 20μg / L, 25μg / L, 30μg / L, 35μg / L, 40μg / L, 45μg / L, 50μg / L , 60μg / 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 the electrochemical detection of the standard solutions containing cadmium ions and lead ions of different concentrations, the following treatment is also included: the pH value of the standard solution containing cadmium ions and lead ions is adjusted to 5-6; the pH value of the standard solution containing cadmium ions and lead ions is adjusted using an acetic acid-sodium acetate buffer solution; the pH value of the acetic acid-sodium acetate buffer solution is 2-5.5; the concentration combination of cadmium ions and lead ions in the standard solution containing cadmium ions and lead ions is 100 μ g / L and 100μg / L, 120μg / L and 150μg / L, 140μg / L and 200μg / L, 160μg / L and 250μg / L, 180μg / L and 300μg / L, 200μg / L and 350μg / L, 220μg / L and 400μg / L, 240μg / L and 450μg / L, 260μg / L and 500μg / L, 280μg / L and 550μg / L, 300μg / L and 600μg / L.

10. The method according to claim 9, 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 formula (1); and Cd =0.095×x Cd +6.103 (1); In formula (1), y Cd is the peak current value of cadmium ions, x Cd is the cadmium ion solubility, and the correlation coefficient R 2 =0.995, detection range is 0.5μg / L~400μg / L, detection limit is 0.5μg / 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 formula (2); and Pb =0.026×x Pb +1.145 (2); In formula (2), y Pb is the peak current value of lead ions, x Pb is the lead ion solubility, and the correlation coefficient R 2 =0.994, the detection range is 5μg / L~400μg / L, and the detection limit is 5μg / L; When the solution to be tested 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 as shown in formula (3); and Cd =0.094×x Cd +6.696 (3); In formula (3), y Cd is the peak current value of cadmium ions, x Cd is the cadmium ion solubility, and the correlation coefficient R 2 =0.996, detection range is 0.5μg / L~400μg / L, detection limit is 0.5μg / L; When the solution to be tested 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 formula (4); and Pb =0.026×x Pb +8.838 (4); In formula (4), y Pb is the peak current value of lead ions, x Pb is the lead ion solubility, and the correlation coefficient R 2 =0.995, the detection range is 5μg / L~400μg / L, and the detection limit is 5μg / L.

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