Cerium dioxide modified electrode and preparation method and application thereof

Abstract

The invention discloses a cerium dioxide modified electrode as well as a preparation method and application thereof. The preparation method comprises the steps of preparing dispersion liquid, preparing modification liquid and modifying an electrode. The preparation method comprises the following steps: preparing cerium dioxide, a Nafion dispersing agent and absolute ethyl alcohol into a modification solution, and preparing a cerium dioxide modified electrode by a dispensing method so as to construct the electrochemical sensor. The excellent oxidation-reduction performance of cerium dioxide is utilized, so that the sensitivity of the modified electrode to thallium ions in water can be enhanced. And the Nafion dispersing agent can enhance the bonding strength between the cerium dioxide and the glassy carbon electrode, and in addition, the cerium dioxide is almost insoluble in water and an alkaline solution, so that the problem that the antimony or mercury working electrode possibly indirectly pollutes the environment in the prior art can be effectively solved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical analysis technology, and in particular to a cerium dioxide modified electrode, its preparation method, and its application. Background Technology

[0002] Thallium (Tl) is a silvery-white, soft, and ductile heavy metal with extremely high biotoxicity, far exceeding that of common toxic heavy metals such as mercury (Hg), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn). Although the average abundance of thallium in the Earth's crust is low, only 0.1–1.7 mg / kg, it is abundant in sulfide minerals and is readily distributed as a byproduct of the smelting and processing of non-ferrous metals or precious metals such as lead and zinc, as Tl. + These substances are released into the environment in various forms, posing extremely adverse effects on environmental safety and human health.

[0003] In existing technologies, trace amounts of Tl in water... + There are many detection methods for trace amounts of Tl, such as atomic absorption spectrometry, atomic fluorescence spectrometry, atomic emission spectrometry, colorimetric analysis, mass spectrometry, biosensing, and electrochemical analysis. Among electrochemical analysis methods, anodic stripping voltammetry is highly suitable for the rapid determination of trace Tl in complex matrices due to its excellent properties, including high selectivity, high sensitivity, low detection limit, short analysis time, simple equipment, and ease of miniaturization. In anodic stripping voltammetry, the working electrode is one of the decisive factors in detection sensitivity and selectivity. Therefore, to enhance the electron transfer efficiency, selectivity, and anti-interference ability of the modified electrode system, its surface usually needs to be chemically modified.

[0004] However, in the existing technology, the existing modified electrodes have low sensitivity to the detection of thallium ions in water. Therefore, there is still much room for improvement in the development of more efficient electrochemical detection technology for thallium. Summary of the Invention

[0005] The purpose of this invention is to propose a cerium dioxide modified electrode and its preparation method, thereby solving the problem of low detection sensitivity of existing modified electrodes for thallium ions in water.

[0006] The present invention also aims to propose the application of a cerium dioxide-modified electrode in the electrochemical detection method for thallium ions in water, thereby providing a basis for the detection of thallium ions in water. + This provides another approach for trace detection.

[0007] To achieve this objective, the present invention adopts the following technical solution: This invention provides a method for preparing a cerium dioxide-modified electrode, comprising the following steps: Preparation of dispersion: Mix Nafion dispersant and anhydrous ethanol evenly to obtain a dispersion; Preparation of the modification solution: Cerium dioxide was added to the dispersion and mixed evenly to obtain the modification solution; Modified electrode: The modifying liquid is added dropwise to the glassy carbon surface of the glassy carbon electrode, and after drying, a cerium dioxide modified electrode is obtained.

[0008] In the method for preparing the cerium dioxide-modified electrode, in the step of preparing the modification solution, the crystal structure of the cerium dioxide includes one of cubic, octahedral, or spherical shapes.

[0009] In the method for preparing the cerium dioxide-modified electrode, in the step of preparing the modification solution, the concentration of cerium dioxide in the modification solution is 1-6 mg / mL.

[0010] In the method for preparing the cerium dioxide modified electrode, in the step of preparing the dispersion, the mass ratio of Nafion dispersant to anhydrous ethanol is 2:8.

[0011] In the method for preparing the cerium dioxide modified electrode, in the step of preparing the dispersion, the concentration of Nafion dispersant in the dispersion is 50-600 µL / mL.

[0012] The method for preparing the cerium dioxide-modified electrode includes a glassy carbon electrode pretreatment step before the electrode modification step. The glassy carbon electrode pretreatment step includes: polishing the surface of the glassy carbon electrode once with alumina powder with a particle size of 1 μm; rinsing after the first polishing, followed by ultrasonication in ultrapure water, anhydrous ethanol, and ultrapure water for 30–60 s in sequence; then polishing a second time with alumina powder with a particle size of 0.3 μm, rinsing after the second polishing, followed by ultrasonication in ultrapure water, anhydrous ethanol, and ultrapure water for 30–60 s in sequence; then polishing a third time with alumina powder with a particle size of 0.05 μm, rinsing after the third polishing, followed by ultrasonication in ultrapure water, anhydrous ethanol, and ultrapure water for 30–60 s in sequence, and then drying.

[0013] The present invention also provides a cerium dioxide modified electrode, which is prepared by the above-described method for preparing a cerium dioxide modified electrode.

[0014] The present invention also provides an application of a cerium dioxide modified electrode in an electrochemical detection method for detecting thallium ions in water. The cerium dioxide modified electrode is used as the working electrode, and the square wave stripping voltammetry is used to determine thallium ions in the water.

[0015] In the application of the cerium dioxide modified electrode in the electrochemical detection method for detecting thallium ions in water, the detection parameters of the square wave stripping voltammetry are as follows: the pre-deposition time is 60 to 600 s, the deposition potential is -1.1 to -1.3 V, and the pH value of the acetic acid buffer is 3.5 to 4.5.

[0016] One of the technical solutions in this invention can have the following beneficial effects: This invention first prepares a modification solution using cerium dioxide, Nafion dispersant, and anhydrous ethanol, and then fabricates a cerium dioxide-modified electrode using a drop-coating method to construct an electrochemical sensor. Utilizing the excellent redox properties of cerium dioxide, the sensitivity of the modified electrode to thallium ions in water is enhanced. Furthermore, the Nafion dispersant strengthens the bond between cerium dioxide and the glassy carbon electrode. In addition, cerium dioxide is almost insoluble in water and alkaline solutions, effectively addressing the potential indirect environmental pollution issues associated with antimony or mercury working electrodes in existing technologies. Attached Figure Description

[0017] Figure 1 SWASV curves of the blank control group and the working electrodes prepared in Examples 1-3 in 0.1 mol / L acetate buffer containing Tl are shown. Where a is the blank control group, b is Example 1, c is Example 2, and d is Example 3. Figure 2 The graph shows the relationship between the concentration of cubic cerium dioxide in the modification solution and the electrode response current to Tl. Figure 3 The graph shows the relationship between the concentration of Nafion dispersant in the modified solution and the peak current of the electrode response to Tl. Figure 4 The graph shows the relationship between the pH of the electrolyte solution and the peak current of the electrode response to Tl. Figure 5 The graph shows the enrichment potential versus the peak value of the electrode response current to Tl. Figure 6 The graph shows the enrichment time versus the peak value of the electrode response current to Tl. Detailed Implementation

[0018] The technical solution of the present invention will be further illustrated below through specific embodiments. To facilitate understanding of the present invention, a more comprehensive description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0019] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] This invention provides a method for preparing a cerium dioxide-modified electrode, comprising the following steps: Preparation of dispersion: Mix Nafion dispersant and anhydrous ethanol evenly to obtain a dispersion; Preparation of the modification solution: Cerium dioxide was added to the dispersion and mixed evenly to obtain the modification solution; Modified electrode: The modifying liquid is added dropwise to the glassy carbon surface of the glassy carbon electrode, and after drying, a cerium dioxide modified electrode is obtained.

[0022] This invention first prepares a modification solution using cerium dioxide, Nafion dispersant, and anhydrous ethanol, and then fabricates a cerium dioxide-modified electrode using a drop-coating method to construct an electrochemical sensor. The excellent redox properties of cubic cerium dioxide, along with the abundant active sites provided by its high specific surface area, enhance the detection sensitivity of the modified electrode for thallium ions in water. The Nafion dispersant stabilizes the dispersibility of cerium dioxide through its sulfonic acid groups and enhances its binding strength with the glassy carbon electrode, while simultaneously enriching thallium ions (T). l+ Accelerated mass transfer enhances electrode stability; furthermore, cerium dioxide is almost insoluble in water and alkaline solutions, avoiding the heavy metal pollution risk of existing trivalent bismuth ion systems, while solving the problem of indirect environmental pollution from antimony or mercury electrodes, thus achieving optimization in three aspects: detection sensitivity, electrode stability, and environmental safety.

[0023] Moreover, compared with existing composite modified glassy carbon electrodes, cerium dioxide (304.00 yuan / kg, Maclean) is cheaper than bismuth ions (bismuth nitrate: 4356.00 yuan / kg, Maclean), which can further reduce electrode costs.

[0024] Specifically, in the step of preparing the modification solution, the crystal structure of the cerium dioxide includes one of cubic, octahedral, or spherical shapes.

[0025] In one specific embodiment of the present invention, the method for preparing octahedral cerium dioxide is as follows: 0.814 g Ce(NO3)3·6H2O and 0.700 g hexamethylenetetramine are dissolved in 110 mL of deionized water to obtain Ce. 3+ Mixture; Ce 3+ The mixture was reacted at 75°C for 3 hours to obtain the reaction product; the reaction product was washed three times with deionized water / ethanol and dried at 200°C to obtain octahedral cerium dioxide.

[0026] In one specific embodiment of the present invention, the method for preparing cubic cerium dioxide is as follows: 0.651 g of Ce(NO3)3·6H2O is dissolved in 30 mL of 3 M NaOH solution to obtain Ce 3+ Mixture; then Ce 3+ The mixture was reacted at 180℃ for 24 hours to obtain the reaction product; the reaction product was washed with deionized water / ethanol and dried at 200℃ to obtain cubic cerium dioxide.

[0027] In one specific embodiment of the present invention, the method for preparing spherical cerium dioxide is as follows: 1.3 g Ce(NO3)3·6H2O and 0.3 g NaOH are dissolved sequentially in 96 mL of deionized water to obtain Ce. 3+ Mixture; then add Ce 3+ The mixture was reacted at room temperature for 22 hours to obtain the reaction product; the reaction product was washed with deionized water / ethanol and dried at 200℃ to obtain spherical cerium dioxide.

[0028] CeO2 exists in two oxidation states, +3 and +4, because Ce 4+ The generation or elimination of oxygen cavities can achieve interaction with Ce. 3+ The reversible conversion exhibits excellent redox, oxygen transport, and oxygen storage and release capabilities. Among cerium dioxide of different shapes, cubic cerium dioxide has more oxygen vacancies on its surface, which facilitates the transfer of electrons to the adsorbed thallium, enhancing the enrichment of thallium on the electrode and thus achieving better detection results.

[0029] Specifically, in the step of preparing the modification solution, the concentration of cerium dioxide in the modification solution is 1 to 6 mg / mL.

[0030] When the concentration of cerium dioxide is below 1 mg / mL, the cerium dioxide-modified electrode exhibits low sensitivity to thallium in the electrolyte solution. When the concentration of cerium dioxide is above 6 mg / mL, the thickness of the modification layer on the glassy carbon electrode surface increases, which to some extent slows down the electron transfer rate, and the potential active sites on the cerium dioxide surface tend to saturate, resulting in a significant decrease in the Tl oxidation dissolution peak current value.

[0031] Specifically, in the step of preparing the dispersion, the mass ratio of Nafion dispersant to anhydrous ethanol is 2:8.

[0032] Nafion dispersant acts as both a dispersant and a binder in the dispersion. Therefore, the amount of Nafion dispersant directly affects the dispersion degree of cerium dioxide nanoclusters and the adhesion between the modified solution and the glassy carbon electrode. In a preferred embodiment of the present invention, the mass ratio of Nafion dispersant to anhydrous ethanol is 2:8.

[0033] Specifically, in the step of preparing the dispersion, the concentration of Nafion dispersant in the dispersion is 50–600 µL / mL.

[0034] In practical applications, if the concentration of Nafion dispersant is below 50 µL / mL, the cerium dioxide-modified electrode exhibits lower sensitivity to thallium in the electrolyte solution compared to a dispersion with a Nafion dispersant concentration of 50 µL / mL. Furthermore, the increase in Tl peak current value generated by increasing Nafion dispersant dosage from 600 µL / mL to 800 µL / mL shows a significantly slower increase compared to the increase generated by increasing dosage from 400 µL / mL to 600 µL / mL, indicating a significant decrease in marginal benefit.

[0035] Specifically, before the electrode modification step, a glassy carbon electrode pretreatment step is included. The glassy carbon electrode pretreatment step includes: polishing the surface of the glassy carbon electrode once with alumina powder with a particle size of 1 μm; rinsing after the first polishing, and then sonicating in ultrapure water, anhydrous ethanol, and ultrapure water for 30-60 s in sequence; then polishing a second time with alumina powder with a particle size of 0.3 μm, rinsing after the second polishing, and then sonicating in ultrapure water, anhydrous ethanol, and ultrapure water for 30-60 s in sequence; then polishing a third time with alumina powder with a particle size of 0.05 μm, rinsing after the third polishing, and then sonicating in ultrapure water, anhydrous ethanol, and ultrapure water for 30-60 s in sequence, and then drying.

[0036] Using the above steps, the glassy carbon electrode is polished with alumina powder with particle sizes of 1μm, 0.3μm and 0.05μm in sequence to remove the contamination layer of the glassy carbon electrode and form a controllable and regenerable surface morphology, which facilitates the fixation of cerium dioxide on the surface of the glassy carbon electrode.

[0037] The present invention also provides a cerium dioxide modified electrode, which is prepared by the above-described method for preparing a cerium dioxide modified electrode.

[0038] The present invention also provides an application of a cerium dioxide modified electrode in an electrochemical detection method for detecting thallium ions in water. The cerium dioxide modified electrode is used as the working electrode, and the square wave stripping voltammetry is used to determine thallium ions in the water.

[0039] Specifically, the detection parameters of the square wave stripping voltammetry are: the pre-deposition time is 60 to 600 s, the deposition potential is -1.1 to -1.3 V, and the pH value of the acetic acid buffer is 3.5 to 4.5. Example Example

[0040] A method for preparing a cerium dioxide-modified electrode includes the following steps: Preparation of dispersion: Nafion dispersant and anhydrous ethanol were mixed at a mass ratio of 2:8 to obtain a dispersion containing 600 µL / mL Nafion dispersant; the concentration of Nafion dispersant was 5 wt.%. Preparation of the modified solution: Cubic cerium dioxide was added to the dispersion and mixed thoroughly to obtain a modified solution containing 2 mg / mL cerium dioxide. The method for preparing cubic cerium dioxide was as follows: 0.651 g Ce(NO3)3·6H2O was dissolved in 30 mL of 3 M NaOH solution to obtain Ce... 3+ Mixture; then Ce 3+ The mixture was reacted at 180℃ for 24 h to obtain the reaction product; the reaction product was washed with deionized water / ethanol and dried at 200℃ to obtain cubic cerium dioxide; Pretreatment of glassy carbon electrode: The surface of the glassy carbon electrode was polished once with alumina powder with a particle size of 1 μm; after the first polishing, it was rinsed and then sonicated in ultrapure water, anhydrous ethanol and ultrapure water for 60 s in sequence; then, it was polished a second time with alumina powder with a particle size of 0.3 μm, rinsed after the second polishing, and then sonicated in ultrapure water, anhydrous ethanol and ultrapure water for 60 s in sequence; then, it was polished a third time with alumina powder with a particle size of 0.05 μm, rinsed after the third polishing, and then sonicated in ultrapure water, anhydrous ethanol and ultrapure water for 60 s in sequence, and then dried to obtain a clean glassy carbon electrode; Modified electrode: Invert a clean glassy carbon electrode on an electrode holder, use a pipette to transfer 4 µL of the above-mentioned modification solution and drop it onto the glassy carbon surface of the glassy carbon electrode. After drying, a cerium dioxide modified electrode is obtained. Example

[0041] The steps and parameters of Example 2 are the same as those of Example 1, except that spherical cerium dioxide is used in the step of preparing the modification solution. The method for preparing spherical cerium dioxide is as follows: 1.3 g of Ce(NO3)3·6H2O and 0.3 g of NaOH are dissolved sequentially in 96 mL of deionized water to obtain Ce... 3+ Mixture; then add Ce 3+ The mixture was reacted at room temperature for 22 hours to obtain the reaction product; the reaction product was washed with deionized water / ethanol and dried at 200℃ to obtain spherical cerium dioxide. Example

[0042] The steps and parameters of Example 3 are the same as those of Example 1, except that octahedral cerium dioxide is used in the preparation of the modification solution. The preparation method of octahedral cerium dioxide is as follows: 0.814 g Ce(NO3)3·6H2O and 0.700 g hexamethylenetetramine are dissolved in 110 mL of deionized water to obtain Ce... 3+ Mixture; Ce 3+ The mixture was reacted at 75°C for 3 hours to obtain the reaction product; the reaction product was washed three times with deionized water / ethanol and dried at 200°C to obtain octahedral cerium dioxide.

[0043] A glassy carbon electrode pretreated only was used as a blank control group. The blank control group and the cerium dioxide-modified electrodes obtained in Examples 1-3 were used as working electrodes. Thallium was pre-enriched in 0.1 mol / L acetate buffer (pH=4) for 480 s using chronoamperometry. The concentration of thallium in the acetate buffer was 20 µg / L, and the deposition potential was -1.2 V. The current response of the Tl oxidation-dissolution process was then measured using square wave anodic stripping voltammetry. The results are shown in [Figure number missing]. Figure 1 .

[0044] according to Figure 1 It can be seen that the SWASV curve of the unmodified glassy carbon electrode shows almost no peak current signal for thallium, confirming that the bare glassy carbon electrode has poor detection performance for trace concentrations of thallium. The thallium oxidation and dissolution peak current values ​​of cerium dioxide-modified electrodes with different exposed crystal planes follow the order: cubic cerium dioxide > spherical cerium dioxide > octahedral cerium dioxide. This is because oxygen vacancies on the cerium dioxide surface may play an important catalytic role in the redox process of Tl, and to maintain the charge balance of the structure, the formation of oxygen vacancies in cerium dioxide is usually accompanied by the formation of trivalent Ce. The Ce in cubic cerium dioxide... 3+ The relative content of Ce is higher than that of spherical cerium dioxide. 3+ More, and spherical cerium dioxide Ce 3+ The relative content of cerium dioxide is higher than that of octahedral cerium dioxide. Example

[0045] A method for preparing a cerium dioxide-modified electrode includes the following steps: Preparation of dispersion: Nafion dispersant and anhydrous ethanol were mixed at a mass ratio of 2:8 to obtain a dispersion containing 600 µL / mL Nafion dispersant; the concentration of Nafion dispersant was 5 wt.%. Preparation of the modification solution: Cubic cerium dioxide was added to the dispersion and mixed evenly to obtain the modification solution; the content of cerium dioxide in the modification solution is shown in Table 1; Pretreatment of glassy carbon electrode: The surface of the glassy carbon electrode was polished once with alumina powder with a particle size of 1 μm; after the first polishing, it was rinsed and then sonicated in ultrapure water, anhydrous ethanol and ultrapure water for 30 s in sequence; then, it was polished a second time with alumina powder with a particle size of 0.3 μm, rinsed after the second polishing, and then sonicated in ultrapure water, anhydrous ethanol and ultrapure water for 30 s in sequence; then, it was polished a third time with alumina powder with a particle size of 0.05 μm, rinsed after the third polishing, and then sonicated in ultrapure water, anhydrous ethanol and ultrapure water for 30 s in sequence, and then dried to obtain a clean glassy carbon electrode; Modified electrode: Invert a clean glassy carbon electrode on an electrode holder, use a pipette to transfer 4 µL of the above-mentioned modification solution and drop it onto the glassy carbon surface of the glassy carbon electrode. After drying, a cerium dioxide modified electrode is obtained.

[0046] Table 1 - Cerium Dioxide Content Example Group B Example 4 Example 5 Example 6 Example 7 Example 8 Cerium dioxide content (mg / mL) 1 2.5 4 6 8 Using the cerium dioxide-modified electrodes obtained in Examples 4-8 as working electrodes, thallium was pre-concentrated in 0.1 mol / L acetate buffer (pH = 4) for 480 s using chronoamperometry. The concentration of thallium in the acetate buffer was 20 µg / L, and the deposition potential was -1.2 V. The current response of the Tl oxidation-dissolution process was then measured using square wave anodic stripping voltammetry. The results are shown in […]. Figure 2 .

[0047] according to Figure 2 It was observed that as the content of cubic cerium dioxide increased from 1 mg / mL to 6 mg / mL, the electrochemical signal of thallium detected by the electrochemical sensor using the aforementioned cerium dioxide-modified electrode gradually increased. This is because the increased content of cubic cerium dioxide provides a larger contact area and more active sites for the thallium pre-enrichment process. However, when the content of cubic cerium dioxide continued to increase to 8 mg / mL, the thickness of the modification layer on the glassy carbon electrode surface increased, slowing down the electron transfer rate, and the potential active sites on the surface of cubic cerium dioxide tended to saturate, resulting in a significant decrease in the peak current value of thallium oxidation dissolution. Example

[0048] A method for preparing a cerium dioxide-modified electrode includes the following steps: Preparation of dispersion: Nafion dispersant and anhydrous ethanol were mixed at a mass ratio of 2:8 to obtain a dispersion; the concentration of Nafion dispersant was 5 wt.%; the content of Nafion dispersant in the dispersion is shown in Table 2; Preparation of the modification solution: The steps are the same as in Example 1, except that the content of cerium dioxide in the modification solution is 6 mg / mL; Pretreatment of glassy carbon electrode: The steps for pretreatment of glassy carbon electrode are the same as in Example 1; Modified electrode: Invert a clean glassy carbon electrode on an electrode holder, use a pipette to transfer 4 µL of the above-mentioned modification solution and drop it onto the glassy carbon surface of the glassy carbon electrode. After drying, a cerium dioxide modified electrode is obtained.

[0049] Table 2 - Content of Nafion dispersant Example Group C Example 9 Example 10 Example 11 Example 12 Example 13 Example 14 Example 15 Nafion dispersant concentration (mg / mL) 0 50 100 200 400 600 800 Using the cerium dioxide-modified electrodes obtained in Examples 9-15 as working electrodes, thallium was pre-concentrated in 0.1 mol / L acetate buffer (pH = 4) for 480 s using chronoamperometry. The concentration of thallium in the acetate buffer was 20 µg / L, and the deposition potential was -1.2 V. The current response of the Tl oxidation-dissolution process was then measured using square wave anodic stripping voltammetry. The results are shown in […]. Figure 3 .

[0050] according to Figure 3 It was found that before the addition of Nafion dispersant, the cerium dioxide-modified electrode was very insensitive to the electrochemical detection of thallium in the electrolyte solution, with the thallium oxidation dissolution peak current value being less than 1 µA. When 50 µL / mL Nafion dispersant was added to the dispersion, the peak thallium current obtained by SWASV testing increased by at least 5 times compared to the response value of Example 9 without Nafion dispersant. With increasing Nafion dispersant dosage, the electrochemical sensor using the cerium dioxide-modified electrode showed increasingly better thallium detection performance. This is because Nafion dispersant has good dispersibility, film-forming properties, and a large surface area, allowing cubic cerium dioxide nanoparticles to be well dispersed and strongly adhered to the glassy carbon electrode surface, thus facilitating the redox reaction of thallium. When the amount of Nafion dispersant is 600 µL / mL, the electrochemical sensor using cerium dioxide-modified electrodes can achieve high detection performance. However, when the amount of Nafion dispersant increases from 600 µL / mL to 800 µL / mL, the growth of the peak thallium current slows down significantly, and the marginal benefit decreases significantly. Example

[0051] A method for preparing a cerium dioxide-modified electrode includes the following steps: Preparation of dispersion: Nafion dispersant and anhydrous ethanol were mixed at a mass ratio of 2:8 to obtain a dispersion containing 600 µL / mL Nafion dispersant; the concentration of Nafion dispersant was 5 wt.%. Preparation of the modified solution: Cubic cerium dioxide was added to the dispersion and mixed evenly to obtain a modified solution containing 2 mg / mL cerium dioxide; Pretreatment of glassy carbon electrode: The steps for pretreatment of glassy carbon electrode are the same as in Example 1; Modified electrode: Invert a clean glassy carbon electrode on an electrode holder, use a pipette to transfer 4 µL of the above-mentioned modification solution and drop it onto the glassy carbon surface of the glassy carbon electrode. After drying, a cerium dioxide modified electrode is obtained.

[0052] Using the cerium dioxide-modified electrode obtained above as the working electrode, thallium in 0.1 mol / L acetate buffer solution was pre-concentrated for 480 s using chronoamperometry. The concentration of thallium in the acetate buffer solution was 20 µg / L, the pH value of the acetate buffer solution is shown in Table 3, and the deposition potential was -1.2 V. The current response of the Tl oxidation and dissolution process was then measured by square wave anodic stripping voltammetry. The results are shown in Table 3. Figure 4 .

[0053] Table 3 - pH of Acetic Acid Buffer Solution Example Group D Example 16 Example 17 Example 18 Example 19 Example 20 Example 21 pH value 3 3.5 4 4.5 5 5.5 according to Figure 4 It can be seen that when the pH value increases from 3 to 3.5, the peak value of Tl current increases significantly. This is because at pH = 3, the higher concentration of H+... + It exhibits strong competition with thallium ions, H + The cerium dioxide-modified electrode surface gains electrons and undergoes a reduction reaction to produce hydrogen gas, i.e., the hydrogen evolution reaction. This reaction, to some extent, inhibits thallium deposition, thus affecting the detection efficiency of thallium. When pH=4.5, the Tl peak current value increases slowly, indicating that the effect of hydrogen evolution gradually weakens. As shown in Examples 19-21, as the pH value continues to increase, the hydrolysis of thallium begins to intensify, and therefore the thallium peak value begins to decrease significantly again. Therefore, an acetate buffer solution with a pH of 4.5 is most suitable for the detection of thallium ions in water. Example

[0054] A method for preparing a cerium dioxide-modified electrode, wherein the steps are the same as in Example 19.

[0055] Using the cerium dioxide-modified electrode obtained above as the working electrode, thallium in 0.1 mol / L acetate buffer (pH = 4.5) was pre-concentrated for 480 s using chronoamperometry. The concentration of thallium in the acetate buffer was 20 µg / L, and the deposition potential is shown in Table 4. The current response during the thallium oxidation and dissolution process was then measured using square wave anodic stripping voltammetry. The results are shown in Table 4. Figure 5 .

[0056] Table 4 - Deposition Potential Example Group E Example 22 Example 23 Example 24 Example 25 Deposition potential (V) -1.4 -1.3 -1.2 -1.1 The deposition potential largely determines the sensitivity of SWASV in detecting heavy metal ions; therefore, optimizing the deposition potential is crucial for the detection results. When the deposition potential is too low, the potential difference generated by the electrode system is too small, making it difficult to attract or only attracting a small number of heavy metal ions to deposit on the cerium dioxide-modified electrode surface. This results in the SWASV test failing to obtain a significant thallium peak signal or producing incomplete peaks. Conversely, if the set deposition potential is too high, the H+ in the acidic electrolyte solution will be affected. + The thallium will accumulate on the surface of the cerium dioxide-modified electrode and capture electrons to undergo a hydrogen evolution reaction. The generated hydrogen gas will occupy the active sites of thallium on the cerium dioxide surface, further leading to a decrease in the electrochemical dissolution signal of thallium.

[0057] according to Figure 5 It can be seen that the deposition potential in Example 23 was -1.3 V, at which the peak value of thallium in the current dissolution curve was the highest. When the deposition potential was set to -1.4 V, the deposition potential began to have an adverse effect on the redox process of thallium, resulting in a decrease in its dissolution current peak value. Example

[0058] A method for preparing a cerium dioxide-modified electrode, wherein the steps are the same as in Example 19.

[0059] Using the cerium dioxide-modified electrode obtained above as the working electrode, thallium was pre-enriched in 0.1 mol / L acetate buffer (pH = 4.5) using chronoamperometry. The concentration of thallium in the acetate buffer was 20 µg / L. The enrichment time is shown in Table 5, and the deposition potential was -1.3 V. The current response of the Tl oxidation-dissolution process was then measured using square wave anodic stripping voltammetry. The results are shown in Table 5. Figure 6 .

[0060] Table 5 - Enrichment Time Example group F Example 16 Example 17 Example 18 Example 19 Example 20 Example 21 Enrichment time (s) 60 120 240 360 480 600 As the enrichment time gradually increases, the peak signal of thallium also increases, and it continues to rise even at 600 s. This is because the thallium in the electrolyte solution is not completely reduced to the surface of the modified electrode, thus failing to achieve optimal detection results. However, if the deposition time is too long, the detection efficiency will decrease, which is not conducive to rapid detection.

[0061] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these equivalent variations or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A method for preparing a cerium dioxide-modified electrode, characterized in that, Includes the following steps: Preparation of dispersion: Mix Nafion dispersant and anhydrous ethanol evenly to obtain a dispersion; Preparation of the modification solution: Cerium dioxide was added to the dispersion and mixed evenly to obtain the modification solution; Modified electrode: The modifying liquid is added dropwise to the glassy carbon surface of the glassy carbon electrode, and after drying, a cerium dioxide modified electrode is obtained.

2. The method for preparing a cerium dioxide-modified electrode according to claim 1, characterized in that, In the step of preparing the modification solution, the crystal structure of the cerium dioxide includes one of cubic, octahedral, or spherical shapes.

3. The method for preparing a cerium dioxide-modified electrode according to claim 1, characterized in that, In the step of preparing the modification solution, the concentration of cerium dioxide in the modification solution is 1 to 6 mg / mL.

4. The method for preparing a cerium dioxide-modified electrode according to claim 1, characterized in that, In the step of preparing the dispersion, the mass ratio of Nafion dispersant to anhydrous ethanol is 2:

8.

5. The method for preparing a cerium dioxide-modified electrode according to claim 1, characterized in that, In the step of preparing the dispersion, the concentration of Nafion dispersant in the dispersion is 50–600 µL / mL.

6. The method for preparing a cerium dioxide-modified electrode according to claim 1, characterized in that, Before the electrode modification step, a glassy carbon electrode pretreatment step is included, which includes: polishing the glassy carbon electrode surface once with alumina powder with a particle size of 1 μm; rinsing after the first polishing, and then sonicating in ultrapure water, anhydrous ethanol, and ultrapure water for 30-60 s in sequence; then polishing a second time with alumina powder with a particle size of 0.3 μm, rinsing after the second polishing, and then sonicating in ultrapure water, anhydrous ethanol, and ultrapure water for 30-60 s in sequence; then polishing a third time with alumina powder with a particle size of 0.05 μm, rinsing after the third polishing, and then sonicating in ultrapure water, anhydrous ethanol, and ultrapure water for 30-60 s in sequence, and then drying.

7. A cerium dioxide-modified electrode, characterized in that, The cerium dioxide-modified electrode is prepared by the method for preparing cerium dioxide-modified electrodes according to any one of claims 1 to 6.

8. The application of a cerium dioxide-modified electrode in an electrochemical detection method for thallium ions in water, characterized in that, Using the cerium dioxide-modified electrode as described in claim 7 as the working electrode, thallium ions in water were determined by square wave stripping voltammetry.

9. The application of the cerium dioxide-modified electrode according to claim 8 in the electrochemical detection method for thallium ions in water, characterized in that, The detection parameters of the square wave stripping voltammetry are as follows: the pre-deposition time is 60 to 600 s, the deposition potential is -1.1 to -1.3 V, and the pH value of the acetic acid buffer is 3.5 to 4.5.

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