Electrochemical sensor based on MOF-on-MOF and MWCNTs-COOH cooperative signal amplification effect, preparation method and application

Abstract

The invention provides an electrochemical sensor based on an MOF-on-MOF and MWCNTs-COOH synergistic signal amplification effect as well as a preparation method and application of the electrochemical sensor based on the MOF-on-MOF and MWCNTs-COOH synergistic signal amplification effect. The sensor comprises a silk-screen printing electrode, MWCNTs-COOH modified on the surface of the silk-screen printing electrode, and flower-shaped MIL-88B-NH2-coated UiO-66-NH2, and the MWCNTs-COOH is modified on the surface of the silk-screen printing electrode. Wherein the MIL-88B-NH2 (at) UiO-66-NH2 is synthesized by carrying out in-situ growth on the MIL-88B-NH2 on the surface of a UiO-66-NH2 crystal, so as to obtain the MIL-88B-NH2 (at) UiO-66-NH2 crystal. The sensor can be used for detecting Pb < 2 + >, Cu < 2 + > and / or Hg < 2 + > in a water sample, an MIL-88B-NH2 (at) UiO-66-NH2 / MWCNTs-COOH / SPCE modified electrode is used as a working electrode, an Ag / AgCl electrode is used as a reference electrode, a carbon electrode is used as an auxiliary electrode, differential pulse anodic stripping voltammetry (DPASV) is adopted for detection, a redox peak of heavy metal ions (HMIs) is used as an index signal, and no extra signal label needs to be introduced. The linear range of the sensor is 0.10-25 [mu] M, and the detection limits of the sensor are respectively as low as 5.55 nM, 4.16 nM and 6.38 nM. The sensor prepared by the invention shows excellent selectivity, reproducibility and stability on HMIs in river water and tap water.

Description

Technical Field

[0001] This invention relates to the technical field of electrochemical sensors, specifically to an electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH, its preparation method, and its application. Background Technology

[0002] Rapid industrialization and population explosion have led to a continuous increase in urban and industrial wastewater discharge. This wastewater contaminates water sources originally used for irrigation, drinking, and livestock farming, resulting in the accumulation of heavy metal ions (HMIs) in the human body. Lead ions (Pb) are a typical HMI. 2+ ) and mercury ions (Hg) 2+ Copper (Cu) poses a serious threat to various human organs due to its high toxicity, bioaccumulation, and non-biodegradability. Furthermore, excessive intake of copper (Cu) can lead to adverse effects. 2+ HMIs (Hydrogen-Degenerative Mixtures) may lead to neurodegenerative diseases such as Alzheimer's disease. HMIs have been reported to enter the human body through multiple routes, including the skin, respiratory tract, and digestive tract. Even at trace levels, HMIs can pose significant health risks. To mitigate these health hazards, the World Health Organization has established maximum permissible concentrations of HMIs in drinking water, specifically for Pb. 2+ Cu 2+ and Hg 2+ Limits of 10 µg / L, 2000 µg / L, and 6 µg / L were set. Therefore, systematic monitoring of the environmental concentration of HMIs is of great significance.

[0003] Electrochemical techniques with miniaturized sensing platforms offer advantages such as low cost, rapid response, high sensitivity, and low detection limits. In particular, differential pulsed anodic stripping voltammetry (DPASV) is an effective electrochemical sensing strategy, which can be divided into two main steps: pretreatment and DPV detection. Due to its ability to simultaneously detect multiple analytes, rapid reaction time, and applicability to on-site monitoring, DPASV is an ideal technique for monitoring various HMIs. Furthermore, electrode modification materials are crucial to the DPASV sensing signal, as they can significantly improve pre-enrichment efficiency and promote the electrocatalytic oxidation process of HMIs. To improve electrode stability, sensing materials with high conductivity, large surface area, and abundant active sites need to be rationally designed. Summary of the Invention

[0004] This invention provides an electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH, its preparation method, and its application. This electrochemical sensor uses the redox peaks of HMIs as indicator signals and employs a traditional three-electrode system, with DPASV used to test the sensor's electrochemical performance. Test results show that this sensor has the advantages of high detection sensitivity, fast detection speed, and ease of use.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: An electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH is characterized by comprising a screen-printed electrode, and MWCNTs-COOH and flower-shaped MIL-88B-NH2@UiO-66-NH2 modified on the surface of the screen-printed electrode.

[0006] The method for fabricating the electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH is characterized by comprising the following steps: S1. Solvothermal preparation of UiO-66-NH2: ZrCl4 and NH2-BDC were dispersed in N,N-dimethylformamide (DMF) at room temperature, stirred and mixed evenly to obtain a suspension, acetic acid was added, and then the above suspension was transferred to an autoclave and heated for hydrothermal reaction; after the reaction was completed, the precipitate was washed in DMF and ethanol, and then vacuum dried to collect UiO-66-NH2 crystals; S2. In-situ growth synthesis of MIL-88B-NH2@UiO-66-NH2: The UiO-66-NH2 prepared in S1 was dispersed in DMF to form a uniform suspension. Then, a mixture of Fe(NO3)3·9H2O, NH2-BDC, DMF and acetonitrile was added to the above suspension and mixed evenly to obtain a mixed solution. The mixed solution was transferred to a three-necked flask and stirred and heated. Using UiO-66-NH2 as seed, an in-situ polymerization reaction was carried out to synthesize MIL-88B-NH2@UiO-66-NH2 through in-situ growth. After the reaction was completed, the precipitate was washed in DMF and then vacuum dried to collect MIL-88B-NH2@UiO-66-NH2. S3. Prepare a suspension of MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH: Add MIL-88B-NH2@UiO-66-NH2 and MWCNTs-COOH powder to DMF and ultrasonically stir until a uniform suspension is formed; S4. The MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH suspension was drop-coated onto the surface of a screen-printed electrode, with a modification amount of 2.0 ~ 10.0 μL; after drying under an infrared lamp, MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH / SPCE was obtained.

[0007] Furthermore, in S1, the molar ratio of ZrCl4 to NH2-BDC is 0.5 to 2.0; the volume of the solvent DMF is 10 to 50 mL; and the volume of acetic acid is 0.9 to 7.2 mL.

[0008] Furthermore, the hydrothermal reaction in S1 has a reaction time of 12 to 48 hours and a reaction temperature of 80 to 160 °C.

[0009] Furthermore, the vacuum drying temperature in S1 is 40 ~ 80 ℃, and the drying time is 2 ~ 24 h.

[0010] Further, the suspension in S2 is prepared by adding 10 to 60 mg of UiO-66-NH2 to 1 to 5 mL of DMF; the molar ratio of Fe(NO3)3·9H2O and NH2-BDC in the mixed solution is 0.5 to 2.0; the volume of DMF is 3 to 30 mL; and the volume of acetonitrile is 3 to 30 mL.

[0011] Furthermore, the reaction time of the in-situ polymerization reaction in S2 is 2 to 10 hours; the reaction temperature is 60 to 120 °C.

[0012] Furthermore, the vacuum drying temperature in S2 is 40 ~ 80℃, and the drying time is 2 ~ 24 h.

[0013] Furthermore, the content of MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH in S3 is 0.25 ~ 4.0 mg / mL.

[0014] The second objective of this invention is to provide an application method for detecting HMIs using an electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH, comprising the following steps: The application method for detecting HMIs using an electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH is characterized by comprising the following steps: (1) Preparation of HAc-Ac - Buffer solution, specifically ABS buffer solution; (2) Prepare ABS solutions containing different concentrations of HMIs, wherein the HMIs are Pb 2+ Cu 2+ and Hg 2+ At least one of them; (3) Using MIL-88B-NH@UiO-66-NH / MWCNTs-COOH / SPCE as the working electrode, carbon electrode as the auxiliary electrode, and Ag / AgCI as the reference electrode, pretreatment was performed by electrodeposition at a potential of -1.6 ~ -0.8V for 60 ~ 240s to reduce HMIs; (4) Adjust the working voltage to the electrochemical window range of -1.2 ~ 0.4 V, test the pretreated electrode by differential pulse voltammetry (DPV), record the voltage-current curve (IV), detect the peak current of the sensor in ABS containing different concentrations of HMIs, establish the linear relationship between the peak current and the concentration of HMIs, and obtain the corresponding linear regression equation. (5) The water sample to be tested is further tested according to the method described in step (4), and the obtained peak current is substituted into the linear regression equation to calculate the concentration of HMIs in the water sample to be tested.

[0015] Further, the pH of the ABS mentioned in step (1) is 3.0 ~ 9.0, and its concentration is 0.05 ~ 0.2 M; the concentration of HMIs in the ABS solution used to prepare HMIs in step (2) is 0.10 ~ 25 μmol / L; in step (5): characterizing Pb 2+ The regression equation for the linear relationship between the concentration and peak current is: I p (μA) = 3.2463 C + 0.1866; Characterizing Cu 2+ The regression equation for the linear relationship between the concentration and peak current is: I p (μA) = 6.7353 C +0.7575; Characterizing Hg 2+ The regression equation for the linear relationship between the concentration and peak current is: I p (μA) = 3.6746 C +0.2742.

[0016] The beneficial effects of this invention are as follows: 1. By constructing the MIL-88B-NH2@UiO-66-NH2 heterostructure, the high specific surface area and abundant active sites of UiO-66-NH2 are combined with the excellent conductivity and electrocatalytic activity of MIL-88B-NH2. This structure not only expands the interfacial reaction region of the material but also promotes the rapid transport of electrons between the frameworks, achieving effective amplification of the electrochemical response signal and laying the material foundation for high-sensitivity detection.

[0017] 2. The sensing process fully utilizes the specific coordination ability of the -NH2 functional group for heavy metal ions, the efficient electron transfer characteristics of MWCNTs-COOH, and the electrostatic attraction between MWCNTs-COOH and positively charged metal ions. These three mechanisms work synergistically at the sensing interface, significantly improving the enrichment efficiency of the target analyte and the interfacial reaction kinetics, thereby enhancing the detection sensitivity and response speed.

[0018] 3. By modifying the surface of a screen-printed carbon electrode with the MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH / SPCE composite material, a stable sensing interface with uniformly distributed active sites is constructed. This interface not only possesses a good electronic conduction network but also prevents material aggregation through the interaction between components, ensuring the reproducibility and long-term stability of the sensor in continuous detection, exhibiting excellent selectivity and reliability. The sensor uses differential pulsed anodic stripping voltammetry (DPASV) for detection, using the redox peaks of heavy metal ions (HMIs) as indicator signals, eliminating the need for additional signal tags. The linear range of this sensor is 0.10 ~ 25 μmol / L, with detection limits as low as 5.55 nmol / L, 4.16 nmol / L, and 6.38 nmol / L, respectively. The sensor prepared in this invention exhibits excellent selectivity, reproducibility, and stability for HMIs in river water and tap water.

[0019] 4. This study clarified and optimized the roles and synergistic pathways of each component in the composite material through interface engineering and component regulation: UiO-66-NH2 mainly provides adsorption and recognition functions, MIL-88B-NH2 enhances electron transfer and catalytic activation, and MWCNTs-COOH serves as a conductive framework and introduces an electrostatic enrichment effect. This innovative multi-component functional design provides new ideas for the development of novel high-performance electrochemical sensing platforms. Attached Figure Description

[0020] Figure 1 This is the preparation process of MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH / SPCE and the flowchart for its use in the detection of various HMIs.

[0021] Figure 2 The images show the morphological characteristics of different modified materials, including: (A) SEM image of UiO-66-NH2; (B) TEM image of UiO-66-NH2; (C) SEM image of MIL-88B-NH2; (D) SEM image of MIL-88B-NH2@UiO-66-NH2; (E) TEM image of MIL-88B-NH2@UiO-66-NH2; and (F) EDS mapping image of MIL-88B-NH2@UiO-66-NH2.

[0022] Figure 3 It contains 25 µmol / L Pb 2+ Cu 2+ , and Hg 2+ DPASV signal diagrams of different modified electrodes in 0.1 mol / L ABS.

[0023] Figure 4 In the presence of different concentrations of Pb 2+ Cu 2+ , and Hg 2+ In 0.1 mol / L ABS, Pb 2+ Cu 2+ , and Hg 2+ The peak current signal.

[0024] Figure 5 Pb 2+ The linear relationship between the concentration and the peak current.

[0025] Figure 6 Cu 2+ The linear relationship between the concentration and the peak current.

[0026] Figure 7 Hg 2+ The linear relationship between the concentration and the peak current. Detailed Implementation

[0027] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific implementation, features and applications of an ultrasensitive electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH proposed according to the present invention are described in detail below. Example 1:

[0028] Figure 1The diagram illustrates the fabrication process of the ultrasensitive electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH, as described in this invention, and its application in the detection of various HMIs. The fabrication method of the ultrasensitive electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH, as described in this invention, includes the following steps: S1. UiO-66-NH2 was prepared by a solvothermal method: 1.0 mmol ZrCl4 and 1.0 mmol NH2-BDC were dispersed in 25 mL DMF at room temperature, stirred and mixed thoroughly to obtain a suspension, and then 3.6 mL acetic acid was added. The suspension was then transferred to an autoclave and heated at 120 °C for 12 h. The precipitate was then washed three times in DMF and ethanol, and then dried under vacuum at 60 °C for 12 h, and UiO-66-NH2 crystals were collected.

[0029] S2. MIL-88B-NH2@UiO-66-NH2 was synthesized using UiO-66-NH2 as a seed material via an in-situ growth strategy: 43 mg of UiO-66-NH2 prepared in S1 was dispersed in 2 mL of DMF and stirred to form a homogeneous suspension. Then, 1.0 mmol Fe(NO3)3·9H2O, 1.0 mmol NH2-BDC, 9 mL of DMF, and 9 mL of acetonitrile were added to the suspension and mixed thoroughly to obtain a homogeneous solution. The mixture was transferred to a 50 mL three-necked flask and stirred and heated to carry out the in-situ polymerization reaction. After the reaction was completed, the product was washed three times in DMF and then dried under vacuum at 60 °C for 12 h. Finally, the product MIL-88B-NH2@UiO-66-NH2 was collected.

[0030] S3. Preparation of MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH suspension: Add 1.0 mg of MIL-88B-NH2@UiO-66-NH2 prepared in S2 and 1.0 mg of MWCNTs-COOH powder to 2 mL of DMF and sonicate until a homogeneous suspension is formed.

[0031] S4. Drop 6 μL of MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH suspension onto the surface of a screen-printed electrode, and dry it under an infrared lamp to obtain MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH / SPCE.

[0032] Application methods of electrochemical sensors based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH: Detection of Pb 2+ and / or Cu 2+ and / or Hg 2+ The working electrode was modified with MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH / SPCE, the reference electrode was Ag / AgCl, and the auxiliary electrode was carbon. DPASV was used for detection. The specific steps are as follows: A1. The pH of the ABS buffer solution is 5.0, and its concentration is 0.1 mol / L.

[0033] A2. Measure a certain amount of Pb respectively. 2+ and / or Cu 2+ and / or Hg 2+ A 100 μmol / L solution was prepared using ABS at pH 5.0. This solution was then diluted layer by layer to obtain a series of Pb solutions with different concentrations. 2+ and / or Cu 2+ and / or Hg 2+ Standard solutions with concentrations ranging from 0.10 to 25 μmol / L.

[0034] A3. Using MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH / SPCE as the working electrode, a carbon electrode as the auxiliary electrode, and Ag / AgCl as the reference electrode, pretreatment was performed by electrodeposition at a potential of -1.2 V for 120 s to reduce HMIs; A4. The pretreated electrode was tested using differential pulse voltammetry (DPV) within an electrochemical window of -1.2 to 0.4 V. Voltage-current curves (IV) were recorded for different concentrations of Pb. 2+ and / or Cu 2+ and / or Hg 2+ In ABS, the peak current of the sensor is detected, and a relationship between the peak current and Pb is established. 2+ and / or Cu 2+ and / or Hg 2+ The linear relationship between concentration and concentration was used to obtain the corresponding linear regression equation.

[0035] Figure 5 For Pb 2+ The linear relationship between concentration and peak current. Regression equation: I p (μA) = 3.2463 C +0.1866, concentration range: 0.10 – 25 μmol / L. R 2 = 0.9933.

[0036] Figure 6 Cu 2+ The linear relationship between concentration and peak current. Regression equation: I p (μA) = 6.7353 C +0.7575, concentration range 0.10 – 25 μmol / L, R 2 = 0.9919.

[0037] Figure 7 For Hg 2+ The linear relationship between concentration and peak current. Regression equation: I p (μA) = 3.6746 C +0.2742, concentration range 0.10 – 25 μmol / L, R 2 = 0.9919.

[0038] According to the formula LOD = 3.3 σ / S Calculate the limits of detection for different HMIs, where σ The standard deviation of the blank measurement is represented by S, and the calibration sensitivity is represented by the sensor's sensitivity to Pb. 2+ Cu 2+ and Hg 2+ The sensitivities were 3.25, 6.74, and 3.67 μA / μM, respectively, and the limits of detection were 5.55, 4.16, and 6.38 nM, respectively.

[0039] A5. Quantitative amounts of HMIs were added to river water and tap water samples to verify the sensor's detection performance. Specifically, the water samples were first allowed to stand, the supernatant was collected, then centrifuged, and filtered through a 0.22 μm filter membrane to remove floating matter. The pH of the water samples was adjusted to 5.0. Then, different concentrations of Pb were added to the treated water samples. 2+ Cu 2+ and Hg 2+ The water sample was used as the test sample. The method described in A4 was used for detection, and the obtained peak current was substituted into the linear regression equation to calculate the concentration of HMIs in the water sample.

[0040] A6. Substitute the peak current data obtained above into the corresponding regression equation to calculate the concentration of HMIs in river water and tap water. The test results are shown in Table 1.

[0041] Table 1. Measurement results of HMIs in river water and tap water Comparative Example 1: A method for preparing and applying an ultrasensitive electrochemical sensor based on MWCNTs-COOH.

[0042] A method for fabricating an ultrasensitive electrochemical sensor based on MWCNTs-COOH / SPCE: S1. Preparation of MWCNTs-COOH suspension: Add 2.0 mg of MWCNTs-COOH powder to 2 mL of DMF and stir ultrasonically until a homogeneous suspension is formed.

[0043] S2. 6 μL of MWCNTs-COOH suspension was drop-coated onto the surface of a screen-printed electrode and dried under an infrared lamp to obtain MWCNTs-COOH / SPCE.

[0044] The prepared ultrasensitive electrochemical sensor based on MWCNTs-COOH / SPCE was used to detect Pb. 2+ and / or Cu 2+ and / or Hg 2+ At that time, the MWCNTs-COOH / SPCE modified electrode was used as the working electrode, the Ag / AgCl electrode was used as the reference electrode, and the carbon electrode was used as the auxiliary electrode. DPASV was used for detection.

[0045] The specific steps are as follows: A1. The pH of the ABS buffer solution is 5.0, and its concentration is 0.1 mol / L.

[0046] A2. Measure a certain amount of Pb respectively. 2+ and / or Cu 2+ and / or Hg 2+ A 25 μmol / L solution was prepared using ABS at pH 5.0.

[0047] A3. Using MWCNTs-COOH / SPCE as the working electrode, a carbon electrode as the auxiliary electrode, and Ag / AgCl as the reference electrode, HMIs were pretreated by electrodeposition at a potential of -1.2 V for 120 s.

[0048] A4. The pretreated electrode was tested using differential pulse voltammetry (DPV) within an electrochemical window of -1.2 to 0.4 V, and the voltage-current curve (IV) was recorded.

[0049] Comparative Example 2: A method for preparing and applying an ultrasensitive electrochemical sensor based on UiO-66-NH2.

[0050] A method for preparing an ultrasensitive electrochemical sensor based on UiO-66-NH2: S1. UiO-66-NH2 was prepared by a solvothermal method: 1.0 mmol ZrCl4 and 1.0 mmol NH2-BDC were dispersed separately in 25 mL DMF at room temperature. The two solutions were stirred and mixed, and then 3.6 mL acetic acid was added. Subsequently, the suspension was transferred to an autoclave and heated at 120 °C for 12 h. The solution was then washed three times in DMF and ethanol, and then dried under vacuum at 60 °C for 12 h to collect UiO-66-NH2 crystals.

[0051] The preparation method of S2. UiO-66-NH2 suspension is as follows: 2.0 mg of UiO-66-NH2 powder is added to 2 mL of DMF and ultrasonically stirred until a uniform suspension is formed.

[0052] S3. 6 μL of UiO-66-NH2 suspension was drop-coated onto the surface of a screen-printed electrode and dried under an infrared lamp to obtain UiO-66-NH2 / SPCE.

[0053] Detection of Pb using an ultrasensitive electrochemical sensor based on UiO-66-NH2 2+ and / or Cu 2+ and / or Hg 2+ At that time, a UiO-66-NH2 / SPCE modified electrode was used as the working electrode, an Ag / AgCl electrode as the reference electrode, and a carbon electrode as the auxiliary electrode. DPASV was used for detection. The specific steps are as follows: A1. The pH of the ABS buffer solution is 5.0, and its concentration is 0.1 mol / L.

[0054] A2. Measure a certain amount of Pb respectively. 2+ and / or Cu 2+ and / or Hg 2+ A 25 μmol / L solution was prepared using ABS at pH 5.0.

[0055] A3. Using UiO-66-NH2 / SPCE as the working electrode, a carbon electrode as the auxiliary electrode, and Ag / AgCl as the reference electrode, pretreatment was performed by electrodeposition at a potential of -1.2 V for 120 s to reduce HMIs.

[0056] A4. The pretreated electrode was tested using differential pulse voltammetry (DPV) within an electrochemical window of -1.2 to 0.4 V, and the voltage-current curve (IV) was recorded.

[0057] Comparative Example 3: A method for preparing and applying an ultrasensitive electrochemical sensor based on MIL-88B-NH2.

[0058] A method for preparing an ultrasensitive electrochemical sensor based on MIL-88B-NH2: S1. MIL-88B-NH2 was prepared by the following method: 1.0 mmol Fe(NO3)3·9H2O, 1.0 mmol NH2-BDC, 9 mL DMF, and 9 mL acetonitrile were mixed. The mixture was transferred to a 50 mL three-necked flask and stirred and heated. The mixture was washed three times in DMF and then dried under vacuum at 60 °C for 12 h, and MIL-88B-NH2 was collected.

[0059] S2. The method for preparing the MIL-88B-NH2 suspension is as follows: Add 2.0 mg of MIL-88B-NH2 powder to 2 mL of DMF and stir ultrasonically until a uniform suspension is formed.

[0060] S3. 6 μL of MIL-88B-NH2 suspension was drop-coated onto the surface of a screen-printed electrode and dried under an infrared lamp to obtain MIL-88B-NH2 / SPCE.

[0061] Detection of Pb using an ultrasensitive electrochemical sensor based on MIL-88B-NH2 2+ and / or Cu 2+ and / or Hg 2+ At that time, the MIL-88B-NH2 / SPCE modified electrode was used as the working electrode, the Ag / AgCl electrode as the reference electrode, and the carbon electrode as the auxiliary electrode. DPASV was used for detection. The specific steps are as follows: A1. The pH of the ABS buffer solution is 5.0, and its concentration is 0.1 mol / L.

[0062] A2. Measure a certain amount of Pb respectively. 2+ and / or Cu 2+ and / or Hg 2+ A 25 μmol / L solution was prepared using ABS at pH 5.0.

[0063] A3. Using MIL-88B-NH2 / SPCE as the working electrode, a carbon electrode as the auxiliary electrode, and Ag / AgCl as the reference electrode, pretreatment was performed by electrodeposition at a potential of -1.2 V for 120 s to reduce HMIs.

[0064] A4. The pretreated electrode was tested using differential pulse voltammetry (DPV) within an electrochemical window of -1.2 to 0.4 V, and the voltage-current curve (IV) was recorded.

[0065] Comparative Example 4: A method for preparing and applying an ultrasensitive electrochemical sensor based on MIL-88B-NH2@UiO-66-NH2.

[0066] Preparation method of ultrasensitive electrochemical sensor based on MIL-88B-NH2@UiO-66-NH2: S1. UiO-66-NH2 was prepared by a solvothermal method: 1.0 mmol ZrCl4 and 1.0 mmol NH2-BDC were dispersed separately in 25 mL DMF at room temperature. The two solutions were stirred and mixed, and then 3.6 mL acetic acid was added. Subsequently, the suspension was transferred to an autoclave and heated at 120 °C for 12 h. The solution was then washed three times in DMF and ethanol, and then dried under vacuum at 60 °C for 12 h to collect UiO-66-NH2 crystals.

[0067] S2. MIL-88B-NH2@UiO-66-NH2 was synthesized using UiO-66-NH2 as a seed material via an in-situ growth strategy: 43 mg of the prepared UiO-66-NH2 was dispersed in 2 mL of DMF and stirred to form a homogeneous suspension. Then, 1.0 mmol Fe(NO3)3·9H2O, 1.0 mmol NH2-BDC, 9 mL of DMF, and 9 mL of acetonitrile were added to the suspension. The mixture was transferred to a 50 mL three-necked flask and stirred and heated. After washing three times in DMF, it was dried under vacuum at 60 °C for 12 h, and MIL-88B-NH2@UiO-66-NH2 was collected.

[0068] The preparation method for S3. MIL-88B-NH2@UiO-66-NH2 suspension is as follows: 2.0 mg of MIL-88B-NH2@UiO-66-NH2 powder is added to 2 mL of DMF and ultrasonically stirred until a uniform suspension is formed.

[0069] S4. 6 μL of MIL-88B-NH2@UiO-66-NH2 suspension was drop-coated onto the surface of a screen-printed electrode and dried under an infrared lamp to obtain MIL-88B-NH2@UiO-66-NH2 / SPCE.

[0070] Detection of Pb using an ultrasensitive electrochemical sensor based on MIL-88B-NH2@UiO-66-NH2 2+ and / or Cu 2+ and / or Hg 2+ The MIL-88B-NH2@UiO-66-NH2 / SPCE modified electrode was used as the working electrode, the Ag / AgCl electrode as the reference electrode, and the carbon electrode as the auxiliary electrode. DPASV was used for detection. The specific steps are as follows: A1. The pH of the ABS buffer solution is 5.0, and its concentration is 0.1 mol / L.

[0071] A2. Measure a certain amount of Pb respectively. 2+ and / or Cu 2+ and / or Hg 2+ A 25 μmol / L solution was prepared using ABS at pH 5.0.

[0072] A3. Using MIL-88B-NH2@UiO-66-NH2 / SPCE as the working electrode, a carbon electrode as the auxiliary electrode, and Ag / AgCl as the reference electrode, pretreatment was performed by electrodeposition at a potential of -1.2 V for 120 s to reduce HMIs.

[0073] A4. The pretreated electrode was tested using differential pulse voltammetry (DPV) within an electrochemical window of -1.2 to 0.4 V, and the voltage-current curve (IV) was recorded.

[0074] Figure 2 The morphology of the different modified materials prepared in Example 1 and Comparative Examples 1 to 4 is characterized, where (A) is a SEM image of UiO-66-NH2; (B) is a TEM image of UiO-66-NH2; (C) is a SEM image of MIL-88B-NH2; (D) is a SEM image of MIL-88B-NH2@UiO-66-NH2; (E) is a TEM image of MIL-88B-NH2@UiO-66-NH2; and (F) is an EDS mapping image of MIL-88B-NH2@UiO-66-NH2. The SEM and TEM images of UiO-66-NH2 show a smooth surface and a regular octahedral structure with an average particle size of 40 nm. MIL-88B-NH2 exhibits a rod-like morphology with a length of approximately 400 nm and a width of approximately 30 nm. SEM and TEM images of MIL-88B-NH2@UiO-66-NH2 show a flower-like morphology composed of octahedral MIL-88B-NH2 and rod-shaped UiO-66-NH2 particles, with a total particle size of approximately 500 nm. C, N, and O elements are distributed throughout the particles, while Fe and Zr are distributed in the rod-shaped and octahedral portions, respectively. These results indicate that MIL-88B-NH2 epitaxially grown on each facet of UiO-66-NH2 forms a flower-like MOF on the MOF hybrid.

[0075] Figure 3 To contain 25 µmol / L Pb 2+ Cu 2+ and Hg 2+DPASV signal diagrams of different modified electrodes in 0.1 mol / L ABS. The current response of SPCE to blank ABS is negligible. However, in 0.1 M ABS containing HMIs, SPCE has a significant effect on Pb. 2+ Cu 2+ and Hg 2+ The MIL-88B-NH2@UiO-66-NH2 / SPCE exhibited a weak oxidation peak current. Three distinct exfoliation peaks were observed at -0.78, -0.28, and 0.04 V, attributed to its excellent electrocatalytic activity and abundant binding sites. Due to the effective surface area and abundant electron transport channels of MWCNTs-COOH, MWCNTs-COOH / SPCE showed a significant oxidation peak current for HMIs. MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH / SPCE exhibited the strongest current response to HMIs, confirming its superior electrochemical activity.

[0076] Figure 4 In the presence of different concentrations of Pb 2+ Cu 2+ and Hg 2+ In 0.1 mol / L ABS, Pb 2+ Cu 2+ and Hg 2+ The peak current signal of HMI. As the concentration of HMI decreases, the oxidation peak current of HMI shows a linear decreasing trend.

[0077] According to the formula LOD = 3.3 σ / S The detection limits of the sensor prepared in Example 1 of this invention for different HMIs were calculated respectively. σ The standard deviation of the blank measurement is represented by S, and the calibration sensitivity is represented by the sensor's sensitivity to Pb. 2+ Cu 2+ and Hg 2+ The sensitivities were 3.25, 6.74, and 3.67 μA / μmol / L, respectively, and the limits of detection were 5.55, 4.16, and 6.38 nmol / L, respectively.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An electrochemical sensor based on MOF-on-MOF and MWCNTs-COOH synergistic signal amplification effect, characterized in that: It includes screen-printed electrodes, MWCNTs-COOH and flower-shaped MIL-88B-NH2@UiO-66-NH2 modified on the surface of the screen-printed electrodes.

2. The method for preparing the electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH as described in claim 1, characterized in that, Includes the following steps: S1. Solvothermal preparation of UiO-66-NH2: ZrCl4 and NH2-BDC were dispersed in N,N-dimethylformamide (DMF) at room temperature, stirred and mixed evenly to obtain a suspension, acetic acid was added, and then the above suspension was transferred to an autoclave and heated for hydrothermal reaction; after the reaction was completed, the precipitate was washed in DMF and ethanol, and then vacuum dried to collect UiO-66-NH2 crystals; S2. In-situ growth synthesis of MIL-88B-NH2@UiO-66-NH2: The UiO-66-NH2 prepared in S1 was dispersed in DMF to form a uniform suspension. Then, a mixture of Fe(NO3)3·9H2O, NH2-BDC, DMF and acetonitrile was added to the above suspension and mixed evenly to obtain a mixed solution. The mixed solution was transferred to a three-necked flask and stirred and heated. Using UiO-66-NH2 as seed, an in-situ polymerization reaction was carried out to synthesize MIL-88B-NH2@UiO-66-NH2 through in-situ growth. After the reaction was completed, the precipitate was washed in DMF and then vacuum dried to collect MIL-88B-NH2@UiO-66-NH2. S3. Prepare a suspension of MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH: Add MIL-88B-NH2@UiO-66-NH2 and MWCNTs-COOH powder to DMF and ultrasonically stir until a uniform suspension is formed; S4. The MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH suspension was drop-coated onto the surface of a screen-printed electrode, with a modification amount of 2.0 ~ 10.0 μL; after drying under an infrared lamp, MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH / SPCE was obtained.

3. The method for fabricating the electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH according to claim 2, characterized in that, The molar ratio of ZrCl4 to NH2-BDC in S1 is 0.5 to 2.0; the volume of DMF solvent is 10 to 50 mL; and the volume of acetic acid is 0.9 to 7.2 mL.

4. The method for fabricating the electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH according to claim 2, characterized in that, The hydrothermal reaction in S1 has a reaction time of 12 to 48 hours and a reaction temperature of 80 to 160 °C.

5. The method for fabricating the electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH according to claim 2, characterized in that, The vacuum drying temperature in S1 is 40 ~ 80 ℃, and the drying time is 2 ~ 24 h.

6. The method for fabricating the electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH according to claim 2, characterized in that, The suspension described in S2 is prepared by adding 10 to 60 mg of UiO-66-NH2 to 1 to 5 mL of DMF; the molar ratio of Fe(NO3)3·9H2O and NH2-BDC in the mixed solution is 0.5 to 2.0; the volume of DMF is 3 to 30 mL; and the volume of acetonitrile is 3 to 30 mL.

7. The method for fabricating the electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH according to claim 2, characterized in that, The reaction time of the in-situ polymerization reaction in S2 is 2 to 10 h; the reaction temperature is 60 to 120 ℃; the vacuum drying temperature is 40 to 80 ℃; and the drying time is 2 to 24 h.

8. The method for fabricating the electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH according to claim 2, characterized in that, The content of MIL-88B-NH2@UiO-66-NH2 / MWCNTs-COOH in S3 is 0.25 ~ 4.0 mg / mL.

9. The application method of the electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH for detecting HMIs according to claim 1, characterized in that, Includes the following steps: (1) Preparation of HAc-Ac - buffer solution, i.e. ABS buffer solution; (2) preparing ABS solutions containing different concentrations of HMIs, the HMIs being at least one of Pb 2+ , Cu 2+ , and Hg 2+ ; (3) Using MIL-88B-NH@UiO-66-NH / MWCNTs-COOH / SPCE as the working electrode, carbon electrode as the auxiliary electrode, and Ag / AgCI as the reference electrode, pretreatment was performed by electrodeposition at a potential of -1.6 ~ -0.8V for 60 ~ 240s to reduce HMIs; (4) Adjust the working voltage to the electrochemical window range of -1.2 ~ 0.4 V, test the pretreated electrode by differential pulse voltammetry (DPV), record the voltage-current curve (IV), detect the peak current of the sensor in ABS containing different concentrations of HMIs, establish the linear relationship between the peak current and the concentration of HMIs, and obtain the corresponding linear regression equation. (5) The water sample to be tested is tested according to the method described in step (4), and the obtained peak current is substituted into the linear regression equation to calculate the concentration of HMIs in the water sample to be tested.

10. The application method of the electrochemical sensor based on the synergistic signal amplification effect of MOF-on-MOF and MWCNTs-COOH according to claim 9, characterized in that, The pH of the ABS mentioned in step (1) is 3.0 ~ 9.0, and its concentration is 0.05 ~ 0.2 mol / L; In step (5): Characterizing Pb 2+ The regression equation for the linear relationship between the concentration and peak current is: I p (μA) = 3.2463 C +0.1866; Characterizing Cu 2+ The regression equation for the linear relationship between the concentration and peak current is: I p (μA) = 6.7353 C +0.7575; Characterizing Hg 2+ The regression equation for the linear relationship between the concentration and peak current is: I p (μA) = 3.6746 C +0.2742; In step (2), the concentration of HMIs in the ABS solution used to prepare HMIs is 0.10 ~ 25 μmol / L.

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