Modified electrode for detecting Ce < 3 + > in water environment and detection method

Abstract

The invention discloses a modified electrode for detecting Ce < 3 + > in a water environment and a detection method, and belongs to the technical field of water quality detection. A traditional three-electrode system is replaced with a laser-induced graphene integrated electrode, Ag / MnO2 at ZnMOF is modified to a working electrode area, then the Ag / MnO2 at ZnMOF / ILIG sensor is prepared, the Ag / MnO2 at ZnMOF / ILIG sensor has higher sensitivity and excellent conductivity, the electrochemical detection cost is remarkably reduced, and the Ag / MnO2 at ZnMOF / ILIG sensor has the advantages of being convenient to carry and good in flexibility and has good application prospects. New possibility and thought are provided for rapid on-site detection of Ce < 3 + > ions; the MnO2 nanoparticles have large specific surface area and catalytic activity, and the response signal of the prepared sensor is amplified; the modification of AgNPs enhances the conductivity of the electrode and accelerates the electron transfer on the surface of the electrode, ZnMOF has high porosity and high specific surface area and can provide more active adsorption sites for a target substance in the reaction process, and after the MnO2 nanoparticles are further modified, the specific surface area and the electrocatalytic activity are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of water body detection, in particular to a method for detecting Ce in water environment. 3+ Modified electrode for detection and detection method. Background Art

[0002] Cerium (Ce) is an important rare earth element and is widely used in modern industry (such as polishing powder, catalyst, phosphor, glass additive), nuclear industry (as a fission product simulant of uranium and plutonium) and medical fields. However, with the increase in its usage, cerium will inevitably enter the water environment through various channels (such as mining, smelting, industrial wastewater, and nuclear facility discharge). Cerium is mainly present in the water environment as trivalent ions (Ce 3+ ) exists in the form of trivalent cerium (Ce 3+ ) itself has relatively low toxicity, but its accumulation in water bodies may have potential impacts on the ecological environment.

[0003] Electrochemical analysis methods, especially the sensing technology based on chemically modified electrodes (CME), have shown great potential in the field of environmental pollutant detection due to their significant advantages such as relatively simple equipment, low cost, fast response speed, easy operation, easy miniaturization and on-site / on-line detection. 3+ The specific and highly sensitive electrochemical detection has the problems of insufficient sensitivity, poor selectivity, and poor stability and reproducibility.

[0004] With the increasing demand for simple, rapid, low-cost, sensitive and selective detection of analytes, ordinary electrochemical sensors can no longer meet people's requirements. High-performance, convenient and flexible electrochemical sensors have become the international frontier research direction. Electrochemical sensors are developing towards integration, portability, miniaturization and so on. At present, there have been many studies on three-electrode integration. Wang YY et al. (Wang YY, Wang Y, Xue Y, et al. Portable and Flexible Hydrogel Sensor for On-Site Atrazine Assay on Agricultural Products [J]. Analytical Chemistry, 2024, 96 (19): 7772-7779.) replaced the traditional three-electrode system with a flexible integrated three-electrode system and developed a portable and flexible hydrogel sensor for simple, rapid and sensitive detection of atrazine. Zuo C et al. (Chen Z, Dong N, Wang Y, et al. All in laser-induced graphene tofabricate the electrochemical biosensor for on-site detection of microcystin-LR[J]. Sensors and Actuators B-Chemical, 2024, 419.) studied the detection of microcystin by a three-electrode integrated electrode modified with gold nanoparticles and verified the on-site detection capability of the sensor, which has good application prospects.

[0005] The application of metal oxides in sensor manufacturing is growing rapidly due to their sensitivity, cost-effectiveness, chemical stability, non-toxicity and rapid response. The advantages of controlled morphology, porous structure, tunable nanopores and ordered mesostructure make nanoporous transition metal oxides ideal photocatalysts in the field of catalysis. Among them, MnO2 is easy to prepare and has good stability, and has been widely used in the field of sensors. MnO2 is an important transition metal oxide. Its nanostructured materials have a larger specific surface area and excellent performance. Manganese oxides have the advantages of low cost and low toxicity. In addition, the electrochemical properties of MnO2 can be easily adjusted by adjusting its morphology and size. Various forms of MnO2 have been developed, such as nanoflowers, nanowires, nanotubes, microspheres, and nanorods, and used for electrochemical sensing. However, the low electrical conductivity of MnO2 limits its application.

[0006] Based on the above content, the present invention proposes a Ce in water environment 3+Ag / MnO2@ZnMOF modified electrode and detection method for Ce in water environment 3+ detection work. Summary of the Invention

[0007] The purpose of the present invention is to provide a Ce in water environment 3+ Modified electrodes and detection methods for more efficient and accurate detection of Ce in actual water samples 3+ Determination of.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] Ce in a water environment 3+ The modified electrode used for detection is composed of a laser-induced graphene integrated electrode and Ag / MnO2@ZnMOF modified on its surface.

[0010] Preferably, the modified electrode preparation method is as follows:

[0011] A1. Prepare a MnO2@ZnMOF mixed solution for later use;

[0012] A2. Prepare an electrode substrate and use laser-induced graphene integrated electrodes to replace the working electrode, counter electrode, and reference electrode of the traditional three-electrode system, integrating the three electrodes on the electrode substrate;

[0013] A3. Evenly disperse a certain amount of AgNPs into the working electrode area of ​​the integrated electrode and bake them with an infrared lamp to form a uniformly dispersed nanostructure.

[0014] A4. The MnO2@ZnMOF mixed solution prepared in A1 was dropped onto the electrode and dried under an infrared lamp to obtain an Ag / MnO2@ZnMOF modified electrode.

[0015] Preferably, A1 specifically includes the following contents:

[0016] Use an analytical balance to weigh a certain amount of ZnMOF-74 and transfer it into a beaker. Add deionized water and stir until it is initially dissolved, then perform magnetic stirring. Then weigh MnO2 powder and add it to the above mixture and continue magnetic stirring to mix evenly to obtain MnO2@ZnMOF solution.

[0017] Ce in a water environment 3+ The detection method specifically comprises the following steps:

[0018] S1. Use a pipette to measure a certain amount of Na2HPO4 solution and NaH2PO4 solution into a beaker, and ultrasonically treat the mixture to obtain PBS buffer;

[0019] S2, constructing a three-electrode system by laser-induced graphene integrated electrode, and treating the electrode with a mixed solution of AgNPs and MnO2@ZnMOF to prepare an Ag / MnO2@ZnMOF modified electrode;

[0020] S3, using the PBS buffer prepared in S1 as the background electrolyte, based on the Ag / MnO2@ZnMOF modified electrode prepared in S2, the Ce in the water to be tested was completed by adsorption stripping voltammetry. 3+ Detection.

[0021] Preferably, the pH of the PBS buffer in S1 is 6.5.

[0022] Preferably, the Ce in the water to be tested is detected by adsorption stripping voltammetry as described in S3. 3+ For detection, the enrichment voltage range is 0.6~1.1V, the enrichment potential is set to -0.15~-0.2V, and the enrichment time is 100~140s.

[0023] Compared with the prior art, the present invention provides a Ce in water environment 3+ The modified electrode and detection method for detection have the following beneficial effects:

[0024] (1) The present invention replaces the traditional working electrode, counter electrode and reference electrode by laser-induced graphene integrated electrode, and modifies Ag / MnO2@ZnMOF to the working electrode area, thereby preparing Ag / MnO2@ZnMOF / ILIG sensor; compared with the traditional three-electrode system, the integrated composite electrode used in the present invention has higher sensitivity and excellent conductivity, significantly reduces the cost of electrochemical detection, and has the characteristics of portability and good flexibility, which is a good choice for Ce 3+ The rapid on-site detection of ZnMOFs provides new possibilities and ideas. For the modified materials, MnO2 nanoparticles have a large specific surface area and catalytic activity, which amplifies the response signal of the prepared sensor. The modification of AgNPs enhances the conductivity of the electrode and accelerates the electron transfer on the electrode surface. ZnMOFs have high porosity and high specific surface area, which can provide more active adsorption sites for the target substance during the reaction. After further modification of MnO2 nanoparticles, the specific surface area and electrocatalytic activity are improved.

[0025] (2) The prepared electrode was characterized by SEM, XPS, XRD and other characterization methods, proving that the Ag / MnO2@ZnMOF / ILIG was successfully prepared. In addition, the electrochemical properties of the electrode were studied by various electrochemical methods such as CV and EIS. Under the optimal experimental conditions, the sensor prepared by the present invention showed a good linear relationship in the range of 1 to 100 μg / L, with a detection limit as low as 0.12 μg / L, and had excellent repeatability, reproducibility and anti-interference performance. The Ag / MnO2@ZnMOF / ILIG prepared by this method can be successfully applied to the detection of Ce in actual water samples. 3+ Determination of. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart for the preparation of Ag / MnO2@ZnMOF-74 / ILIG mentioned in Example 1 of the present invention;

[0027] Figure 2 (A) and (B) are SEM images of MnO2 and MnO2@ZnMOF-74 / ILIG mentioned in Example 1 of the present invention; (C) and (D) are TEM images of Ag / MnO2@ZnMOF-74;

[0028] Figure 3 This is the EDS mapping image of the Ag / MnO2@ZnMOF-74 / ILIG electrode mentioned in Example 1 of the present invention;

[0029] Figure 4 (A) is the overall spectrum of the Ag / MnO2@ZnMOF-74 / ILIG electrode mentioned in Example 1 of the present invention; (B) and (C) are the narrow spectra of C and Mn elements, respectively;

[0030] Figure 5 The Raman spectra of the electrode before and after modification mentioned in Example 1 of the present invention are shown;

[0031] Figure 6 The contact angle characterization diagrams mentioned in Example 1 of the present invention, wherein (A) and (B) are the contact angle characterization diagrams of LIG and Ag / MnO2@ZnMOF-74 / ILIG electrodes, respectively;

[0032] Figure 7 (A) and (B) are the CV and EIS graphs of different electrodes mentioned in Example 1 of the present invention in a mixed solution of 5mM K3[Fe(CN)6] and 0.1MKCl; (C) is the CV graph of the mixed solution of 0.1mg / LCe 3+ Response signals detected by different electrodes;

[0033] Figure 8(A), (B), and (C) are CV images of LIG, Ag / ZnMOF-74 / ILIG, and Ag / MnO2@ZnMOF-74 / ILIG electrodes mentioned in Example 1 of the present invention at different scan rates in 1 M KOH solution; (D) is the relationship between scan rate and current density;

[0034] Figure 9 (A) CV images of Ag / MnO2@ZnMOF-74 / ILIG in 5M K[Fe(CN)] solution at different scan rates mentioned in Example 1 of the present invention; (B) linear relationship between peak current and scan rate;

[0035] Figure 10 DPSV response of the Ag / MnO2@ZnMOF-74 / ILIG electrode mentioned in Example 1 of the present invention in PBS buffer solutions with different pH values;

[0036] Figure 11 (A) and (B) are Ag / ZnMOF-74 / LIG prepared with different AgNPs drop coating amounts in Example 1 of the present invention on Ce 3+ DPSV response in solution; (C), (D) and (E), (F) are Ag / ZnMOF-74 / LIG prepared with different MnO2 and ZnMOF-74 mixing ratios and drop coating amounts on Ce 3+ DPSV response in solution;

[0037] Figure 12 (A), (B), (C), and (D) are the results of Ag / MnO2@ZnMOF-74 / ILIG in Ce at different enrichment potentials and enrichment times mentioned in Example 1 of the present invention. 3+ DPSV response in solution;

[0038] Figure 13 The Ag / MnO2@ZnMOF-74 / ILIG mentioned in Example 1 of the present invention was used to detect different concentrations of Ce. 3+ DPSV response of the solution and linear relationship diagram;

[0039] Figure 14 (A) is the modified electrode detection of Ce mentioned in Example 1 of the present invention, which is prepared by five identical preparation methods. 3+ Solution; (B) Ag / MnO2@ZnMOF-74 / LIG electrode in Ce containing different interfering ions 3+ Peak current signal value in solution. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are merely exemplary and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solutions of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, and such modifications and replacements fall within the scope of protection of the present invention.

[0041] It should be emphasized that 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 the present invention belongs. Although any methods, devices, and materials similar or equivalent to those herein can be used in the practice or testing of the present invention, the preferred methods, devices, and materials are now described.

[0042] The present invention proposes a Ce in water environment 3+ A modified electrode for detection, namely an Ag / MnO2@ZnMOF / ILIG, was proposed. 3+ The detection method and specific embodiments are as follows.

[0043] Example 1:

[0044] Ce in a water environment 3+ The detection method specifically comprises the following steps:

[0045] (1) Solution preparation:

[0046] 1.1) Preparation of PBS buffer at pH 6.5

[0047] Use a pipette to measure 31.5 mL of the prepared 0.2 mol / L Na2HPO4 solution and 68.5 mL of the 0.3 mol / L NaH2PO4 solution into a beaker, and sonicate the mixture for 10 minutes to obtain a PBS buffer solution with a pH of 6.5.

[0048] 1.2) Preparation of MnO2@ZnMOF-74 solution

[0049] Use an analytical balance to weigh 1.25g of ZnMOF-74 and transfer it to a beaker. Add 50mL of deionized water and stir until it is initially dissolved. Then, magnetically stir for 10 minutes. Next, weigh 1.25g of MnO2 powder and add it to the above mixture and continue magnetic stirring for 30 minutes to mix the two evenly to obtain a MnO2 and ZnMOF-74 mixed solution with a concentration of 2.5g / L for use.

[0050] 1.3) Preparation and testing of Ag / MnO2@ZnMOF-7 / ILIG electrode

[0051] The preparation process of Ag / MnO2@ZnMOF-74 / ILIG electrode is as follows Figure 1 As shown, first prepare a MnO2@ZnMOF-74 mixed solution; then start preparing the electrode substrate, use CAD software to draw the desired integrated electrode pattern, and set the laser power to 60 and depth to 25 in the program. Then, the prepared electrode substrate is flat and tightly attached to a high-temperature resistant thick cardboard and placed in the instrument for laser etching. This method can be used to prepare multiple electrodes at a time. The entire plate electrode is cut into the desired single electrode shape, and a certain amount of AgNPs is evenly dispersed in the working electrode area. It is then dried with an infrared lamp to form a uniformly dispersed nanostructure. Finally, the prepared MnO2@ZnMOF-74 mixed solution is drop-coated on the electrode, dried with an infrared lamp, and then the electrode is treated with a blue film to enhance its waterproof function.

[0052] (2) Ce 3+ Electrochemical detection

[0053] PBS buffer (pH = 6.5) prepared from sodium dihydrogen phosphate-disodium hydrogen phosphate solution was selected as the background electrolyte, and adsorption stripping voltammetry was used to detect Ce. 3+ The collection voltage range was 0.6 V to 1.1 V, the collection potential was set at -0.2 V, and the collection time was 120 s. CV experiments to measure the electrode active area were conducted in 1 M KOH solution with a potential range of -0.25 V to -0.15 V and a scan rate of 20 mV / s to 100 mV / s. EIS experiments were conducted in a mixed solution of 5 mM K3[Fe(CN)6] and 0.1 M KCl.

[0054] (3) Material characterization

[0055] 3.1) SEM, TEM, and EDS characterization

[0056] In order to analyze the microstructure of Ag / MnO2@ZnMOF-74 / ILIG, SEM and TEM were used to characterize it. EDS mapping was also used to analyze the element content on the electrode surface.

[0057] See also Figure 2 , Figure 2 (A) is the SEM image of MnO2 / ILIG, where nano-MnO2 structures with a diameter of 100 nm can be clearly seen dispersed on the electrode surface. Figure 2 (B) is the SEM characterization of the prepared MnO2@ZnMOF-74 / ILIG. It can be seen that nano-MnO2 is successfully loaded on the lamellar ZnMOF-74 structure, further increasing the specific surface area of ​​the electrode. Figure 2(C) is the TEM diffraction image of the prepared Ag / MnO2@ZnMOF material. It can be seen that AgNPs are evenly distributed on the ZnMOF-74 sheet structure. Figure 2 (D) Zooming in on a specific area of ​​the final modified electrode reveals AgNPs and MnO2 distributed on the ZnMOF-74 surface. The AgNPs compensate for the ZnMOF-74's strong adsorption properties but weak conductivity. The modified nano-MnO2 further increases the electrode's surface area, synergizing with the porous effect of ZnMOF-74 to significantly enhance the selective adsorption of target compounds. The synergistic effect of these three materials enhances the sensor's response signal.

[0058] EDS mapping was used to systematically characterize the surface element distribution and composition of Ag / MnO2@ZnMOF-74 / ILIG. Figure 3 , confirming the successful loading of C (18.7%), N (9.4%), O (22.5%), Zn (12.5%), and Mn (46.6%) species onto the ILIG substrate. A trace amount of 1.8% Ag was dispersed on the functionalized electrode surface. The similar distribution of Zn and Mn elements on the modified ILIG electrode further demonstrates the successful surface modification of the material, resulting in the electrode's excellent catalytic properties.

[0059] 3.2) XPS analysis

[0060] XPS characterization is used to study the chemical state and elemental composition of the material. The XPS characterization of Ag / MnO2@ZnMOF-74 / ILIG is as follows: Figure 4 As shown. Figure 4 (A) It can be seen that Zn, Mn, C, Ag, and O elements are successfully modified on the electrode surface, which is consistent with the EDS experimental results. Figure 4 (B) shows the high-resolution XPS analysis results of C1s. It can be clearly seen from the figure that it has three binding energy peaks, located at 284.8eV, 286.3eV and 289.3eV, which correspond to CC / C=C, CO, and OC=O. Figure 4 (C) shows the high-resolution XPS analysis results of Mn 2p. 1 / 2 、Mn 2p 3 / 2 and Mn 2p 3 / 2 The peaks are located at 640.69eV, 641.90eV, 652.91eV and , respectively, indicating the presence of Mn 4+ and Mn 3+ This is because there may be oxygen vacancies or structural defects in the manganese dioxide crystal. The formation of oxygen vacancies in the crystal will lead to local charge imbalance, and some Mn 4+ Reduced to Mn3+ To maintain electrical neutrality.

[0061] 3.3) Raman spectroscopy analysis

[0062] For LIG electrodes, Raman spectroscopy can effectively evaluate their graphitization degree, defect density, and the effects of chemical modification. In the Raman spectrum of LIG, two characteristic peaks, D peak and G peak, are usually observed. By analyzing the Raman spectrum of LIG electrodes, its defect structure can be evaluated. D / I G The ratio is a key parameter for analyzing the defect density of materials. The larger the ratio, the more defects there are in the material. Figure 5 Figure 2 is the Raman spectrum analysis of bare ILIG electrode and Ag / MnO2@ZnMOF-74 / ILIG. Figure 5 It can be seen that the bare electrode I D / I G The value is 1.09, while the electrode modified with AgNPs and MnO2@ZnMOF-74 has an I D / I G The value increased to 1.28. This indicates that the degree of defect in the modified electrode has increased, thus providing more active adsorption sites for the electrode.

[0063] 3.4) Contact angle analysis

[0064] In order to verify the wettability of the integrated electrode, deionized water was dropped on the ILIG electrode before and after modification to measure its contact angle. The smaller the contact angle, the better the hydrophilicity of the material. Figure 6 It can be seen that compared with the bare electrode, the Ag / MnO2@ZnMOF-74 / ILIG electrode has a smaller contact angle, θ of 32°. This may be because the introduction of nanoparticles increases the surface energy of the sensor surface, making it easier for the liquid to spread on the electrode surface, and the pore structure of the MOF material can capture liquid molecules and increase the contact area between the liquid and the surface, thereby reducing the electrode contact angle and improving the hydrophilicity of the electrode surface.

[0065] (4) Electrochemical behavior of different electrodes

[0066] In order to further study the electrochemical performance of different electrodes, CV and EIS tests were performed. Figure 7 , Figure 7(A) The figure shows the CV test results of Ag / ZnMOF-74 / ILIG, Ag / MnO2@ZnMOF-74 / LIG, and Ag / MnO2@ZnMO F-74 / ILIG. All three electrodes exhibit a pair of reversible redox peaks during the CV experiment. Compared to the single electrode, the peak potential difference of Ag / MnO2@ZnMOF-74 / ILIG is reduced, while the peak current is increased. Its peak potential difference is 290 mV, and its peak current is 226 μA. Similarly, tests using an integrated electrode show that the peak potential difference of the Ag / ZnMOF-74MnO2 / LIG electrode is reduced, while the peak current is increased, compared to Ag / ZnMOF-74 / LIG. Figure 7 (B) is the impedance test diagram of different electrodes in 5mM K3[Fe(CN)6] and 0.1M KCl solution. The integrated electrode has lower impedance than the single electrode. Continuing to modify the electrode surface with nano-MnO2 can effectively reduce the resistance of the integrated electrode. The EIS results show that the resistance of the integrated electrode is consistent with the CV Figure 1 To.

[0067] The present invention upgrades the traditional three-electrode system and uses a three-electrode integrated electrode to replace the traditional three electrodes for experiments and evaluate their electrochemical behavior. Figure 7 (C) shows the different electrodes at 0.1 mg / L Ce. 3+ DPSV response in solution. The black curve shows the test results for Ag / ZnMOF-74 / LIG, with a peak current of 10μA. The blue curve shows the test curve for Ag / MnO2@ZnMOF-74 / ILIG, with a peak current of approximately 16μA, a 6μA increase compared to the traditional three-electrode structure. Furthermore, this chapter also introduces material upgrades, adding nano-MnO2 to the Ag / ZnMOF-74 / LIG structure. As shown in the figure, the addition of nano-MnO2 increases the sensor's oxidation peak current by 4μA, which is attributed to the synergistic adsorption and coordination between MnO2 and ZnMOF-74, which increases the specific surface area of ​​the electrode.

[0068] The electrochemically active area and the effective area involved in the electrochemical reaction are important parameters for determining the sensitivity of the sensor. According to the electrochemically active area calculation principle: ECSA = Cdl / Cs, because the specific capacitance (Cs) is generally a fixed value, the double-layer capacitance of the electrode surface is positively correlated with the electrochemically active area, so we can effectively evaluate the difference in the change of the electrochemically active area by comparing the double-layer capacitance Cdl value. Figure 8 As shown, Figure 8 (A), (B), and (C) are CV images of ILIG, Ag / ZnMOF-74 / ILIG, and Ag / MnO2@ZnMOF-74 / ILIG electrodes at different scan rates in 1 M KOH solution, respectively. Figure 8(D) Fitting was performed to determine the correlation between the scan rate and the current density difference at a potential of -0.2 V. The capacitance of the modified material can be determined by the slope of the linear equation. Calculations show that the double-layer capacitances of the ILIG, Ag / ZnMOF-74 / ILIG, and Ag / MnO2@ZnMOF-74 / ILIG electrodes are 2.58 mF cm-3, respectively. -2 、2.72mF cm -2 、3.63mF cm -2 With the modification of AgNPs and MnO2@ZnMOF-74, the electrochemical active area of ​​the electrode increases, indicating that ZnMOF-74 and MnO2 can provide more adsorption active sites for the electrode, which is beneficial to Ce 3+ enrichment, thus improving the detection signal of the sensor.

[0069] In the CV experiment, the same electrode under different scan rates, [Fe(CN)6] 3- / 4- The redox peak current values ​​are also different. At different scan rates, the CV curves of the Ag / MnO2@ZnMOF-74 / ILIG electrode are as follows: Figure 9 As shown, Figure 9 (A) CV images of Ag / MnO2@ZnMOF-74 / ILIG in 5M K[Fe(CN)] solution at different scan rates. Figure 9 (B) is the linear relationship between the oxidation peak current and the scan rate. As the scan rate increases (20-200mV / s), the oxidation peak current and the scan rate also increase. The oxidation peak current is related to the scan rate (v) and the square root of the scan rate (v 1 / 2 ) showed a good linear relationship. When the linear relationship between the peak oxidation current and v is better, it indicates that the redox reaction on the electrode surface is mainly controlled by adsorption; with v 1 / 2 A better linear relationship indicates that diffusion control is dominant. Therefore, the size of the regression coefficient (R 2 ) can be used to determine the control mechanism of the reaction. The fitting calculation found that the Ag / MnO2@ZnMOF-74 / ILIG electrode detected Ce 3+ The linear relationship between the peak current of the oxidation of the probe and v is better, which indicates that the oxidation reaction of the probe on the electrode surface is mainly controlled by adsorption.

[0070] (5) Optimization of experimental conditions of the present invention

[0071] 5.1) Optimization of buffer

[0072] In order to realize the detection of Ce by the prepared sensor 3+To achieve the best performance, the experimental conditions such as buffer solution, AgNPs drop coating amount, ratio of ZnMOF-74 and MnO2, enrichment potential and enrichment time were optimized. The buffer pH has a great influence on the detection performance of the electrochemical sensor, so it was optimized first. Figure 10 As shown, Figure 10 (A) shows the current response signal of the sensor at different pH values. It can be seen that the peak position of the electrode gradually decreases with the increase of pH. When the pH value increases from 6 to 6.5, the sensor reaches the maximum peak current signal. Then, the current begins to decrease with the increase of pH value. Considering all factors, pH=6.5 is selected as the best electrode for detecting Ce. 3+ The optimal pH value.

[0073] 5.2) Modification materials

[0074] like Figure 11 As shown, Figure 11 (A) To optimize the amount of AgNPs applied, keeping other conditions the same, the Ag / MnO2@ZnMOF-74 / ILIG electrode was used to react with 0.1 mg / L Ce when the amount of AgNPs applied was 2, 4, 6, 8, and 10 μL. 3+ The solution was tested, such as Figure 11 As shown in Figure (B), experimental data indicate that the peak current signal response reaches its maximum when the AgNPs application volume is 4 μL. As the AgNPs application volume continues to increase, the peak current signal response begins to gradually decrease. An appropriate amount of metal nanoparticles can evenly cover the electrode surface, providing sufficient active sites, enhancing electron transfer and catalytic reactions. However, excessive application volume can cause nanoparticle aggregation, reducing electrode sensitivity. Taking all factors into consideration, the optimal AgNPs application volume is 4 μL.

[0075] 5.3) Testing conditions

[0076] In order to obtain better sensing performance, the mixing ratio of ZnMOF-74 and MnO2 was optimized, such as Figure 11 As shown in (C), when the mass ratio of ZnMOF-74 and MnO2 increases from 1:4 to 4:1, the peak current in the electrochemical reaction process first increases and then decreases. This is because when the ratio is 1:1, MnO2 is evenly distributed on the surface of ZnMOF-74, which can promote the redox reaction and the peak current reaches the maximum. When the excess metal oxide on the electrode surface reduces the conductivity of the electrode (such as Figure 11 (D) As shown). Therefore, the preparation of the drop coating material is to mix in a ratio of 1:1, at which time the concentration of ZnMOF and MnO2 is 2.5g / L. The drop coating amount of the MnO2@ZnMOF mixed material is further optimized. Figure 11(E) As can be seen, the peak current gradually increases as the drop amount increases from 2 μL to 6 μL. This is because initially, as the drop amount of MnO2@ZnMOF increases, the specific surface area of ​​the electrode is increased, the adsorption capacity is enhanced, and more Ce in the solution is absorbed. 3+ Participate in oxidation reactions, see Figure 11 (F) When the drop volume exceeds 6 μL, the current response decays significantly. This may be because the material accumulates too thickly on the electrode surface, the conductivity deteriorates, and the electron transfer is hindered.

[0077] The accumulation potential is a key parameter affecting the sensitivity of electrochemical sensors. It determines the adsorption or accumulation efficiency of the target substance on the electrode surface. The accumulation time determines the total amount of the target substance adsorbed or accumulated on the electrode surface, which directly affects the sensitivity of the sensor. 3+ The enrichment potential and enrichment time were optimized.

[0078] See also Figure 12 , Figure 12 (A) is the optimization result of the enrichment time. When the enrichment time increases from 60s to 120s, the Ag / MnO2@ZnMOF-74 / ILIG electrode detects Ce. 3+ The response signal gradually increases. Generally speaking, the longer the enrichment time, the more the target substance is adsorbed or enriched on the electrode surface, and the stronger the sensor signal response. Figure 12 (B) When the accumulation time continues to increase, the current response decreases. This may be because the electrode has been in water for too long and has become wet, affecting the conductivity of the electrode. Therefore, the optimal accumulation time of the sensor is selected as 120s. Then the electrode accumulation potential is optimized, as shown in the following example. Figure 12 As shown in (C) and (D), the current response signal reaches an inflection point when the enrichment potential is -0.2 V. 3+ The adsorption efficiency is highest on the electrode surface, and -0.2 V is selected as the optimal enrichment potential.

[0079] (6) Linear range and detection limit

[0080] Through the optimization of the above experimental conditions, the optimal experimental conditions were determined: the buffer solution was PBS buffer with pH = 6.5, the drop amount of AgNPs was 4μL, the concentration ratio of ZnMOF-74 and MnO2 was 1:1, the enrichment potential was -0.2V, and the enrichment time was 120s. 3+ The stock solution was prepared into solutions of different concentrations. Experiments were carried out using DPSV under the optimal modification and detection conditions. The results are shown in Figure 2. Figure 13 As shown, with Ce 3+As the concentration increases, the peak current value of the dissolution also increases. In the concentration range of 1-100μg / L, the sensor response current is similar to Ce 3+ The concentration showed a good linear relationship, and the linear regression equation was obtained after analysis:

[0081] y=0.126x+3.020

[0082] R 2 =0.991

[0083] Use LOD = k·S b / M calculates the detection limit, where k is the confidence factor (taken as 3); S b is the standard deviation of the blank sample; M is the slope of the standard curve in the low concentration range. The detection limit of the sensor is calculated to be 0.12μg / L; the experimental results show that the prepared Ag / MnO2@ZnMOF-74 / ILIG sensor can successfully detect Ce 3+ Compared with similar works, as shown in Table 1, the sensor detects Ce 3+ It has certain advantages in detection limit and linear range.

[0084] Table 1 Comparison of similar work

[0085]

[0086] (7) Anti-interference and reproducibility of electrodes

[0087] Reproducibility is an important parameter for evaluating electrode performance. Under the optimal experimental conditions, 0.1 mg / LCe 3+ The reproducibility of the electrode is tested using the test solution. Five electrodes prepared in the same way are used to detect the target substance. The results are as follows Figure 14 As shown in the figure, the peak current calibration deviation is 6.0%, indicating that the sensor constructed in this study is sensitive to the target substance Ce. 3+ The detection has good reproducibility.

[0088] Environmental water contains a variety of substances, and a variety of anions and cations coexist. These ions may interfere with the performance of the sensor. 3+ Interfering ions that may exist in practice were introduced into the solution to explore the anti-interference ability of the Ag / MnO2@ZnMOF-74 / ILIG sensor. Figure 14 As shown in (B), 100 times of Ce was added 3+ Concentration of K + 、Na + 、Mn 2+ 、Zn 2+ 、Nd 2+ 、NO3 -、SO4 2- The experimental results show that the added ions do not have much effect on the response signal detected by the electrode, which proves that the sensor has good anti-interference ability.

[0089] (8) Testing of actual water samples

[0090] Under optimized experimental conditions, the prepared sensor was applied to Ce in tap water and groundwater. 3+ Preparation of 50 and 100 μg / L Ce 3+ The results are shown in Table 2. The spiked recoveries of the constructed electrochemical sensor are between 95.36% and 97.91%, and the RSDs are between 1.89% and 4.62%. The results show that the Ag / MnO2@ZnMOF-74 / ILIG sensor can be used for the detection of actual water samples.

[0091] Table 2 Detection of actual water samples by Ag / MnO2@ZnMOF-74 / ILIG electrode

[0092]

[0093] In summary, the present invention replaces the traditional LIG working electrode, platinum wire and reference electrode with an integrated electrode, which has the advantages of low cost and greater portability. At the same time, MnO2 nanoparticles are introduced into the material and mixed with ZnMOF-74 by a simple magnetic stirring method. MnO2 nanoparticles have a large specific surface area and catalytic activity, which amplifies the response signal of the prepared sensor. The prepared electrode was characterized by SEM, XPS, XRD and other characterization methods, proving that the Ag / MnO2@ZnMOF-74 / ILIG electrode was successfully prepared. The following conclusions can be drawn: (1) The modification of AgNPs enhances the conductivity of the electrode and accelerates the electron transfer on the electrode surface. ZnMOF-74 has high porosity and high specific surface area, which can provide more active adsorption sites for the target substance during the reaction process. After further modification of MnO2 nanoparticles, the specific surface area and electrocatalytic activity are improved. (2) The optimal detection conditions of the sensor were explored by controlling the variable method: PBS buffer with a pH of 6.5 was selected, the optimal drop amount of AgNPs was 4 μL, the optimized ratio of ZnMOF-74 and MnO2 was 1:1, the drop amount was 6 μL, and the optimal enrichment potential and enrichment time were -0.2 V and 180 s. (3) The prepared sensor detected Ce 3+ The detection limit is 0.12 μg / L, and it shows good linearity in the range of 1-100 μg / L. The prepared sensor has good repeatability, reproducibility and anti-interference performance, and can be used for detection of actual water samples.

[0094] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A Ce in a water environment 3+ The modified electrode for detection is characterized in that It consists of a laser-induced graphene integrated electrode and Ag / MnO2@ZnMOF modified on its surface.

2. Ce in a water environment according to claim 1 3+ The modified electrode for detection is characterized in that The modified electrode preparation method is as follows: A1. Prepare a MnO2@ZnMOF mixed solution for later use; A2. Prepare an electrode substrate and use laser-induced graphene integrated electrodes to replace the working electrode, counter electrode, and reference electrode of the traditional three-electrode system, integrating the three electrodes on the electrode substrate; A3. Evenly disperse a certain amount of AgNPs into the working electrode area of ​​the integrated electrode and bake them with an infrared lamp to form a uniformly dispersed nanostructure. A4. The MnO2@ZnMOF mixed solution prepared in A1 was dropped onto the electrode and dried under an infrared lamp to obtain an Ag / MnO2@ZnMOF modified electrode.

3. Ce in a water environment according to claim 1 3+ The modified electrode for detection is characterized in that A1 specifically includes the following: Use an analytical balance to weigh a certain amount of ZnMOF-74 and transfer it into a beaker. Add deionized water and stir until it is initially dissolved, then perform magnetic stirring. Then weigh MnO2 powder and add it to the above mixture and continue magnetic stirring to mix evenly to obtain MnO2@ZnMOF solution.

4. Ce in an aqueous environment using the modified electrode as described in any one of claims 1 to 3 3+ The detection method is characterized in that The specific steps include: S1. Use a pipette to measure a certain amount of Na2HPO4 solution and NaH2PO4 solution into a beaker, and ultrasonically treat the mixture to obtain PBS buffer; S2, constructing a three-electrode system by laser-induced graphene integrated electrode, and treating the electrode with a mixed solution of AgNPs and MnO2@ZnMOF to prepare an Ag / MnO2@ZnMOF modified electrode; S3, using the PBS buffer prepared in S1 as the background electrolyte, based on the Ag / MnO2@ZnMOF modified electrode prepared in S2, the Ce in the water to be tested was completed by adsorption stripping voltammetry. 3+ Detection.

5. Ce in a water environment according to claim 4. 3+ The detection method is characterized in that The pH of the PBS buffer in S1 is 6.

5.

6. Ce in a water environment according to claim 4. 3+ The detection method is characterized in that As described in S3, Ce in the water to be tested was determined by adsorption stripping voltammetry. 3+ For detection, the enrichment voltage range is 0.6~1.1V, the enrichment potential is set to -0.15~-0.2V, and the enrichment time is 100~140s.

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