Composite sensing electrode and its preparation method and application

Abstract

The present invention discloses a composite sensing electrode, a preparation method thereof, and an application thereof, belonging to the field of environmental detection technology. The preparation method comprises activating CNC, then modifying the activated CNC with a CdS cluster material to obtain a CdS@CNC composite electrode material, and then modifying a GCE electrode with the CdS@CNC composite electrode material to obtain a CdS@CNC-GCE composite sensing electrode. The present invention also discloses the CdS@CNC-GCE composite sensing electrode prepared by the above method and the application of the composite sensing electrode in the detection of heavy metal elements in aqueous solution. The beneficial effects of the present invention are: providing an effective technical method and approach for improving the performance of heavy metal sensor electrodes; the prepared CdS@CNC-GCE composite sensing electrode has strong anti-interference ability and good stability, and can promptly and quickly detect the content of multiple heavy metals, thereby achieving the purpose of dynamically monitoring the changes in heavy metal content during production activities.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental monitoring, in particular to a composite sensing electrode and a preparation method and application thereof. Background Art

[0002] Heavy metal pollution, primarily caused by human factors such as mining, waste gas emissions from industrial activities, wastewater irrigation, and the use of products containing excessive heavy metals, has become a global environmental issue of significant public concern. Toxic heavy metals generally refer to the biotoxic "five toxic elements," led by cadmium, mercury, arsenic, lead, and chromium. Once these heavy metals and other harmful elements enter the human body, they accumulate, causing DNA damage and leading to chronic poisoning.

[0003] To detect trace levels of HMIs in water samples, a variety of conventional techniques have been employed, including atomic absorption spectroscopy, neutron activation analysis, ion chromatography, ultraviolet-visible spectroscopy, and inductively coupled plasma-mass spectrometry. These techniques offer high selectivity and sensitivity, but require complex and expensive instrumentation, are time-consuming, and cannot be performed on-site. Electrochemical detection methods, particularly differential pulse stripping voltammetry (DPSV), stand out for their advantages, including simple sample preparation, low equipment cost, ease of miniaturization, high precision, long-term stability, and fast response speed. Furthermore, DPSV eliminates the need for large-scale instrumentation and enables qualitative and quantitative analysis based on peak changes in the response current curve, making it widely used for rapid heavy metal detection.

[0004] Research on the use of electrochemical detection technology for heavy metal detection has made significant progress in recent years. However, currently proposed heavy metal electrochemical sensors are limited in their detection targets, typically detecting only one or two heavy metals. Simultaneously detecting multiple heavy metal ions with high sensitivity and strong interference resistance remains a major challenge in the development of electrochemical methods. We need to develop an electrochemical sensor electrode with high sensitivity, high selectivity, and high stability for the simultaneous detection of multiple heavy metals. This would enable dynamic monitoring of heavy metal content changes during production activities and provide valuable insights for controlling heavy metal content. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite sensing electrode and its preparation method and application, so as to solve the problem that the existing methods for detecting heavy metals have high requirements for equipment and detection technology, and it is difficult to detect the content of multiple heavy metals in the production process in a timely and rapid manner.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The invention discloses a preparation method of a composite sensing electrode, wherein the preparation method comprises activating CNC, then modifying the activated CNC with a CdS cluster material to obtain a CdS@CNC composite electrode material, and then modifying a GCE electrode with the CdS@CNC composite electrode material to obtain a CdS@CNC-GCE composite sensing electrode.

[0008] Furthermore, CNC activation includes the following steps:

[0009] X1. Add CNC and concentrated nitric acid into a container in sequence, and immerse the CNC in the concentrated nitric acid to prepare a CNC dispersion;

[0010] X2. Seal the container and keep it away from light. After the CNC is activated, separate the activated CNC.

[0011] X3. Use deionized water and anhydrous ethanol to clean the separated CNC, and then dry it for use.

[0012] Furthermore, the CdS cluster material modified activated CNC includes the following steps:

[0013] Y1. Prepare Cd precursor solution and S precursor solution respectively;

[0014] Y2. Take Cd precursor solution, S precursor solution, deionized water and butylamine, mix them evenly to obtain a cluster growth mixed solution;

[0015] Y3, immersing the activated CNC into the cluster growth mixed solution, growing a cluster structure on the surface of the CNC at room temperature, and separating the CdS@CNC cluster material;

[0016] Y4. Use deionized water and anhydrous ethanol to wash the CdS@CNC cluster material in sequence, and then dry it to obtain a CdS@CNC composite electrode material.

[0017] Furthermore, the CdS@CNC composite electrode material modified GCE electrode includes the following steps:

[0018] Z1, dispersing the CdS@CNC composite electrode material in deionized water and ultrasonically treating it to obtain a CdS@CNC dispersion;

[0019] Z2. Mix the CdS@CNC dispersion and Nafion solution and ultrasonically treat to obtain a mixed solution. Apply the mixed solution dropwise on the polished GCE electrode surface and dry to obtain a CdS@CNC-GCE composite sensing electrode.

[0020] Furthermore, in step X1, the concentration of the CNC dispersion was controlled to be 2 mg / ml.

[0021] The present invention also provides a composite sensing electrode. The composite sensing electrode is prepared by the above-mentioned composite sensing electrode preparation method to obtain a CdS@CNC-GCE composite sensing electrode.

[0022] The present invention also provides applications of the composite sensing electrode, specifically applications of the CdS@CNC-GCE composite sensing electrode in the detection of heavy metal elements in aqueous solution.

[0023] Furthermore, the heavy metal elements include: Zn, Cd, Pb, Cu and Hg.

[0024] Furthermore, the steps of detecting the heavy metal content in aqueous solution using the CdS@CNC-GCE composite sensing electrode are as follows:

[0025] a. The CdS@CNC-GCE composite sensing electrode was placed in an electrolyte containing ABS buffer and standard solutions of heavy metal ions at different concentrations. The three-electrode DPSV test method was used for testing. During the current-voltage scan, the current value generated by the corresponding heavy metal ions on the electrode surface as the voltage changed was recorded.

[0026] b. Prepare a standard curve and construct a linear equation based on the concentration of the heavy metal ion standard solution and the corresponding current response peak;

[0027] c. Replace the heavy metal ion standard solutions of different concentrations in step a with the aqueous solution to be tested, perform the test according to the test method of step a, obtain the corresponding current response value, and substitute it into the linear equation constructed in step b to calculate the content of heavy metal ions in the aqueous solution to be tested.

[0028] Furthermore, in step b, the linear equation constructed is: Ip=aXmeal+b, wherein Xmetal is the concentration of the heavy metal ion standard solution, and Ip is the current response peak value.

[0029] The present invention has the following advantages:

[0030] 1. By modifying the activated CNC with CdS cluster materials, a CdS@CNC composite electrode material was obtained, which was then used to modify the GCE electrode to obtain a CdS@CNC-GCE composite sensing electrode, providing an effective technical method and approach to improve the performance of heavy metal sensor electrodes.

[0031] 2. The prepared CdS@CNC-GCE composite sensing electrode has strong anti-interference ability and good stability. It can detect the content of various heavy metals in a timely and rapid manner, thereby achieving the purpose of dynamically monitoring the changes in heavy metal content during production activities. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 SEM images of unmodified CNC and CdS@CNC composite electrode materials.

[0033] Figure 2 This is the elemental map of CdS@CNC composite electrode material.

[0034] Figure 3 TEM image and element distribution map of CdS@CNC composite electrode material.

[0035] Figure 4 This is the XRD pattern of CdS@CNC composite electrode material.

[0036] Figure 5 This is the performance test diagram of CdS@CNC-GCE composite sensing electrode.

[0037] Figure 6 This is the standard curve of heavy metal concentration and current response peak of CdS@CNC-GCE composite sensing electrode.

[0038] Figure 7 Verification diagram of the anti-interference (A) and stability (B) of the CdS@CNC-GCE composite sensing electrode. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0040] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0041] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other.

[0042] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0043] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0044] Example 1

[0045] This embodiment provides a method for preparing a composite sensing electrode. The preparation method involves activating CNC (carbon nanocoils with a spatial helical structure), then modifying the activated CNC with a CdS (cadmium sulfide) cluster material to obtain a CdS@CNC composite electrode material. The CdS@CNC composite electrode material is then used to modify a GCE electrode (glassy carbon electrode) to obtain a CdS@CNC-GCE composite sensing electrode.

[0046] Among them, CNC activation includes the following steps:

[0047] X1. Add 100 mg of CNC to a 100 ml clear glass reagent bottle. Then add 50 ml of concentrated nitric acid to the clear glass reagent bottle containing CNC, and immerse the CNC in the concentrated nitric acid to prepare a CNC dispersion with a concentration of 2 mg / ml.

[0048] X2. Seal the transparent glass reagent bottle and place it away from light for 3 days. After the CNC is activated, separate the activated CNC from the concentrated nitric acid using a vacuum filter.

[0049] X3. Wash the separated CNC with deionized water and anhydrous ethanol for 5-10 times, and then dry the CNC in an oven at 60°C for later use.

[0050] Carbon nanocoils are helical carbon nanotubes. Unlike the line contact between carbon nanotubes and the surface contact between graphene, carbon nanocoils form point contacts, minimizing intermolecular forces. This minimizes intermolecular forces and allows them to be essentially monodispersed in water or other organic solvents, eliminating the problem of carbon nanomaterial agglomeration and maximizing the large specific surface area advantage of carbon nanomaterials. Furthermore, carbon nanocoils inherit the excellent properties of carbon nanotubes, such as good conductivity, excellent mechanical properties, and physicochemical stability. Furthermore, the helicity of carbon nanocoils offers advantages not possessed by carbon nanotubes. First, the spatial porosity created by the helix facilitates the diffusion and adsorption of the HMIs being tested, effectively improving detection sensitivity. Second, the defects introduced by the helical structure give the coil surface a large number of dangling bonds, increasing the surface's chemical activity and facilitating the recombination of nanometals.

[0051] In this embodiment, CNC is acidified with concentrated nitric acid to introduce a large number of oxygen-containing functional groups such as carboxyl, hydroxyl, and nitro groups onto its surface. This not only significantly enhances its hydrophilicity and surface activity, but also effectively improves its dispersion stability in polar solvents and avoids agglomeration. Furthermore, the strong oxidizing property of concentrated nitric acid can be used to remove impurities and amorphous carbon from the CNC surface, thereby improving the purity and structural integrity of the material.

[0052] By controlling the concentration of the CNC dispersion to 2 mg / ml, while ensuring sufficient oxidation, the dispersion uniformity and surface activity of CNC in the reaction system are effectively improved, which helps to introduce functional groups, enhance interfacial bonding ability, and improve the efficiency and controllability of subsequent functional modifications.

[0053] The modification of activated CNC by CdS cluster material includes the following steps:

[0054] Y1. Prepare a Cd precursor solution containing cadmium chloride, 3-mercaptopropionic acid, deionized water, and potassium hydroxide, and a S precursor solution containing thiourea and deionized water, respectively;

[0055] Y2. Take 300 μL of Cd precursor solution, 300 μL of S precursor solution, 6 ml of deionized water and 6 ml of butylamine, and mix them evenly to obtain a cluster growth mixed solution;

[0056] Y3, immersing the activated CNC in a cluster growth mixed solution and letting it stand for 3 days to grow cluster structures on the CNC surface at room temperature, and separating the CdS@CNC cluster material from the solution using a vacuum filtration machine;

[0057] Y4. The separated CdS@CNC cluster material was washed 5-10 times with deionized water and anhydrous ethanol, and then dried in an oven at 60°C to obtain a CdS@CNC composite electrode material.

[0058] SEM characterization Figure 1 As shown, Figure 1 (A) Figure 1 (B) is the unmodified CNC electrode. Figure 1 (C) Figure 1 (D) is CdS@CNC composite electrode material. Elemental spectrum as shown Figure 2 As shown, Figure 2 (B) Figure 2 (C) Figure 2 (D) Elemental spectra of C, S, and Cd, respectively.

[0059] Depend on Figure 1 It can be seen that the CdS@CNC composite electrode material is formed by depositing CdS clusters on the surface of unmodified carbon nanocoil CNC, which proves the effective synthesis of the composite electrode material. Figure 2 (B) Figure 2 (C) Figure 2 (D) It can be seen that the S element and Cd element are evenly distributed on CNC, which once again verifies the successful synthesis of CdS@CNC composite electrode material.

[0060] TEM characterization Figure 3 Shown are TEM images of CdS@CNC composite electrode materials. Figure 3 (C) Figure 3 (D) The distribution of S and Cd elements respectively.

[0061] Depend on Figure 3 It can be observed that S and Cd elements are evenly distributed on CNC, which indicates that the CdS@CNC composite electrode material is successfully synthesized and evenly distributed.

[0062] XRD characterization Figure 4 As shown in the figure, the XRD spectrum of the CdS@CNC composite electrode material is characterized, the abscissa is the diffraction angle, and the ordinate is the diffraction intensity.

[0063] Depend on Figure 4 The XRD peaks of the CdS@CNC composite electrode material are basically consistent with the peaks of the CdS standard card (PDF#89-0440), further proving the effective synthesis of the CdS@CNC composite electrode material.

[0064] When constructing electrochemical sensors for heavy metal ions, introducing CdS clusters as modification materials has significant advantages. First, CdS clusters are composed of nanoparticles with a high specific surface area and abundant surface active sites, which are conducive to the adsorption and enrichment of heavy metal ions. Secondly, CdS is a typical II-VI semiconductor material with good electron transport properties, which can effectively promote the charge transfer process at the electrode interface. In addition, the sulfur ions (S²⁻) on the surface of CdS can form a stable complex structure with heavy metal ions such as Pb²⁺ and Hg²⁺, thereby enhancing the selective recognition ability of the material. Modifying CdS clusters on carbon nanocoils CNC with good conductivity not only improves the electrochemical activity of the electrode, but also realizes the interfacial synergistic effect, which helps to build a sensitive, stable and highly selective heavy metal detection platform.

[0065] The combination of CdS clusters and CNC not only creates a fast electron channel through the CNC, improving overall conductivity, but also utilizes CdS to enrich and identify target ions, significantly enhancing the electrode's response current and selective detection capabilities. This configuration combines structural innovation with functional synergy, breaking through the performance bottleneck of traditional electrode materials and possessing great application potential.

[0066] The modification of GCE electrode with CdS@CNC composite electrode material includes the following steps:

[0067] Z1. Disperse 1 mg of CdS@CNC composite electrode material in 1 ml of deionized water and ultrasonicate for 10 min to obtain a CdS@CNC dispersion.

[0068] Z2. Take 180 μL of CdS@CNC dispersion and 20 μL of Nafion solution, mix them and ultrasonicate them for 10 minutes to obtain a mixed solution. Take 5 μL of the mixed solution and drop it on the polished surface of the GCE electrode to prepare a CdS cluster-modified N-CNT / CC composite electrode (CdS@CNT / CC). Then dry it in an oven at 60°C for 10 minutes to obtain a CdS@CNC-GCE composite sensing electrode.

[0069] The GCE electrode polishing method involves sprinkling a small amount of aluminum oxide polishing powder onto the chamois leather. Holding the electrode vertically, grind it in a figure-8 pattern. Polishing is performed using two different aluminum oxide polishing powders, 0.3μm and 0.05μm, until the surface is mirror-smooth. Ultrasonic cleaning is then performed with deionized water and then anhydrous ethanol for three minutes each. The electrode is then dried in a 60°C oven and set aside.

[0070] Example 2

[0071] This embodiment provides a CdS@CNC-GCE composite sensing electrode prepared by the method described in Example 1.

[0072] Example 3

[0073] This embodiment also provides applications of the CdS@CNC-GCE composite sensing electrode of Example 2, specifically applications of the CdS@CNC-GCE composite sensing electrode in the detection of heavy metal elements in aqueous solution.

[0074] Among them, heavy metal elements include: Zn, Cd, Pb, Cu and Hg.

[0075] The specific steps for using the CdS@CNC-GCE composite sensing electrode to quickly detect the heavy metal content in aqueous solution are as follows:

[0076] a. To 100 ml of electrolyte (ABS acetate buffer: 1 mol / L acetic acid, 1 mol / L sodium acetate, adjusted to pH 6), add 0 μL, 20 μL, 40 μL, 100 μL, 200 μL, 300 μL, 400 μL, 500 μL, 600 μL, 700 μL, and 800 μL of heavy metal ion standard solution, respectively, so that the heavy metal concentration range in the detection system is 0-8 μg / mL. Using the three-electrode DPSV test method, the CdS@CNC-GCE composite sensing electrode is placed in the above standard solutions of different concentrations and a current-voltage scan is performed. The current value generated by the corresponding heavy metal ion on the electrode surface as the voltage changes during the entire scan process is recorded;

[0077] like Figure 5 As shown in the figure, the sub-figures are, in order, the DPSV curves of the joint detection of heavy metal ions Zn(Ⅱ), Cd(Ⅱ), Pb(Ⅱ), Cu(Ⅱ) and Hg(Ⅱ), the DPSV curve of the gradient detection of Zn(Ⅱ), the DPSV curve of the gradient detection of Cd(Ⅱ), the DPSV curve of the gradient detection of Pb(Ⅱ), the DPSV curve of the gradient detection of Cu(Ⅱ) and the DPSV curve of the gradient detection of Hg(Ⅱ), reflecting the current value generated by the heavy metal ions on the electrode surface as the voltage changes. Figure 5 (A) It shows that the CdS@CNC-GCE composite sensing electrode can simultaneously detect heavy metal ions Zn(Ⅱ), Cd(Ⅱ), Pb(Ⅱ), Cu(Ⅱ) and Hg(Ⅱ) without interfering with each other. Figure 5 (B) Figure 5 (C) Figure 5 (D) Figure 5 (E) Figure 5 (F) It shows that the CdS@CNC-GCE composite sensing electrode can detect heavy metal ions Zn(Ⅱ), Cd(Ⅱ), Pb(Ⅱ), Cu(Ⅱ) and Hg(Ⅱ) individually, and the response value of individual detection increases with the increase of the concentration of heavy metal ions.

[0078] b. According to the concentration of the heavy metal ion standard solution and the corresponding current response peak, the heavy metal concentration and the current response peak are matched, and the linear equation is fitted using Origin software to make a standard curve. The linear equation is constructed: Ip=aXmeal+b, where Xmetal is the concentration of the heavy metal ion standard solution and Ip is the current response peak. The following is obtained: Figure 6 The standard curves of heavy metal concentration and current response peak of CdS@CNC-GCE composite sensing electrode are shown;

[0079] like Figure 6 As shown in the figure, the sub-figures are the linear relationships between the concentration and the current peak when the heavy metal ions Zn (Ⅱ), Pb (Ⅱ), Cd (Ⅱ), Cu (Ⅱ) and Hg (Ⅱ) are detected separately, respectively. Among them, the regression equation of the current response change value for detecting Zn (Ⅱ) is Ⅰ=0.697665XZn+2.71, and the correlation coefficient is 0.9942; the regression equation of the current response change value for detecting Pb (Ⅱ) is Ⅰ=1.85XPb +2.36, and the correlation coefficient is 0.99252; the regression equation of the current response change value for detecting Cd (Ⅱ) is Ⅰ=3.43XCd +1.01, and the correlation coefficient is 0.99367; the regression equation of the current response change value for detecting Cu (Ⅱ) is Ⅰ=0.53045XCu+3.06, and the correlation coefficient is 0.99239; The regression equation for the current response change of (Ⅱ) is Ⅰ = 0.905369XHg + 1.53, with a correlation coefficient of 0.99383. This regression equation demonstrates that the CdS@CNC-GCE composite sensing electrode has excellent detection performance for the heavy metal ions Zn(Ⅱ), Cd(Ⅱ), Pb(Ⅱ), Cu(Ⅱ), and Hg(Ⅱ).

[0080] c. Detection of heavy metals in samples: Replace the heavy metal ion standard solutions of different concentrations in step a with the aqueous solution to be tested, perform the test according to the test method in step a, obtain the corresponding current response value, and substitute it into the linear equation constructed in step b to calculate the content of heavy metal ions in the aqueous solution to be tested.

[0081] Anti-interference test of CdS@CNC-GCE composite sensing electrode:

[0082] The CdS@CNC-GCE composite sensing electrode was placed in 100 mL of electrolyte, to which 400 μl of standard solutions of heavy metal ions Zn(Ⅱ), Cd(Ⅱ), Pb(Ⅱ), Cu(Ⅱ), and Hg(Ⅱ) were pre-added. Interfering ions Al(Ⅲ), As(Ⅱ), Bi(Ⅱ), Ca(Ⅱ), Co(Ⅱ), Cr(Ⅱ), Fe(Ⅲ), Mg(Ⅱ), Mn(Ⅱ), Na(Ⅰ), and Ni(Ⅱ) were then added to the electrolyte in sequence. Two DPSV tests were performed for each addition of a heavy metal ion to obtain the detection curve under interference conditions, as shown in Figure 2. Figure 7 From the relationship between different interfering ions and the current response peak of the CdS@CNC-GCE composite sensing electrode shown in (A), it can be seen that the composite sensing electrode of the present application has good anti-interference ability.

[0083] Stability test of CdS@CNC-GCE composite sensing electrode:

[0084] Fifteen CdS@CNC-GCE composite sensing electrodes were prepared and DPSV detection was performed separately. 400 μl of heavy metal ion standard solutions of Zn (Ⅱ), Cd (Ⅱ), Pb (Ⅱ), Cu (Ⅱ) and Hg (Ⅱ) were added to 100 mL of electrolyte, as shown in Figure 2. Figure 7 (B) The current response peaks of multiple CdS@CNC-GCE composite sensing electrodes tested in standard solutions indicate that the composite sensing electrodes prepared by this method have good stability.

[0085] In the anti-interference and stability verification, the electrolyte was ABS acetate buffer; the heavy metal ion concentration was 0.4 μg / mL.

[0086] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a composite sensing electrode, characterized in that: The preparation method activates CNC, then uses CdS cluster material to modify the activated CNC to obtain a CdS@CNC composite electrode material, and then uses the CdS@CNC composite electrode material to modify a GCE electrode to prepare a CdS@CNC-GCE composite sensing electrode; The CNC is a carbon nanocoil; The CdS cluster material modification of the activated CNC comprises the following steps: Y1. Prepare Cd precursor solution and S precursor solution respectively; Y2. Take Cd precursor solution, S precursor solution, deionized water and butylamine, mix them evenly to obtain a cluster growth mixed solution; Y3, immersing the activated CNC into the cluster growth mixed solution, growing a cluster structure on the surface of the CNC at room temperature, and separating the CdS@CNC cluster material; Y4. The CdS@CNC material was washed with deionized water and anhydrous ethanol in sequence, and then dried to obtain a CdS@CNC composite electrode material.

2. The method for preparing the composite sensing electrode according to claim 1, wherein: The CNC activation comprises the following steps: X1. Add CNC and concentrated nitric acid into a container in sequence, and immerse the CNC in the concentrated nitric acid to prepare a CNC dispersion; X2. Seal the container and keep it away from light. After the CNC is activated, separate the activated CNC. X3. Use deionized water and anhydrous ethanol to clean the separated CNC, and then dry it for use.

3. The method for preparing the composite sensing electrode according to claim 1, wherein: The CdS@CNC composite electrode material modified GCE electrode comprises the following steps: Z1, dispersing the CdS@CNC composite electrode material in deionized water and ultrasonically treating it to obtain a CdS@CNC dispersion; Z2. Mix the CdS@CNC dispersion and Nafion solution and ultrasonically treat to obtain a mixed solution. Apply the mixed solution dropwise on the polished GCE electrode surface and dry to obtain a CdS@CNC-GCE composite sensing electrode.

4. The method for preparing the composite sensing electrode according to claim 2, wherein: In the X1 step, the concentration of the CNC dispersion was controlled to be 2 mg / mL.

5. Composite sensing electrode, characterized by: The CdS@CNC-GCE composite sensing electrode is prepared by the preparation method of the composite sensing electrode according to any one of claims 1 to 4.

6. Application of composite sensing electrode, characterized by: Use of the CdS@CNC-GCE composite sensing electrode as claimed in claim 5 in the detection of heavy metal elements in aqueous solution.

7. The use of the composite sensing electrode according to claim 6, characterized in that: The heavy metal elements include: Zn, Cd, Pb, Cu and Hg.

8. The use of the composite sensing electrode according to claim 7, characterized in that: The steps of detecting the heavy metal content in the aqueous solution using the CdS@CNC-GCE composite sensing electrode are as follows: a. The CdS@CNC-GCE composite sensing electrode was placed in an electrolyte containing ABS buffer and standard solutions of heavy metal ions at different concentrations. The three-electrode DPSV test method was used for testing. During the current-voltage scan, the current value generated by the corresponding heavy metal ions on the electrode surface as the voltage changed was recorded. b. Prepare a standard curve and construct a linear equation based on the concentration of the heavy metal ion standard solution and the corresponding current response peak; c. Replace the heavy metal ion standard solutions of different concentrations in step a with the aqueous solution to be tested, perform the test according to the test method of step a, obtain the corresponding current response value, and substitute it into the linear equation constructed in step b to calculate the content of heavy metal ions in the aqueous solution to be tested.

9. The use of the composite sensing electrode according to claim 8, characterized in that: In the step b, the linear equation constructed is: Ip=aXmeal+b, wherein Xmetal is the concentration of the heavy metal ion standard solution, and Ip is the current response peak.

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