Electrochemical sensor for detecting perfluorooctanoic acid based on molecular imprinting and preparation method and application thereof

Abstract

This invention discloses an electrochemical sensor for detecting perfluorooctanoic acid (PFOA) based on molecular imprinting, its preparation method, and its application, for the analysis and detection of PFOA, an acid mist inhibitor, in pickling solutions. The electrochemical sensor comprises a glassy carbon electrode modified with a composite film of carbon quantum dots and polypyrrole and N-trifluoromethylpyrrolidine-3-amine imprinted with PFOA structures, to prepare a modified electrode CDs / PPy(PFPy)-MIP that selectively recognizes PFOA. (PFOA) / GCE. Using this modified electrode as the working electrode, PFOA in the pickling solution was detected using electrochemical impedance spectroscopy, with a detection limit of 0.064 mg / L. The electrochemical sensor provided by this invention does not require sample separation or other pretreatment; analysis and detection can be performed simply by diluting the sample, offering advantages such as high selectivity and simple operation.

Description

Technical Field

[0001] This invention pertains to the analysis of acid mist inhibitors in rust removal solutions for iron products within the surface treatment industry. Specifically, it relates to a sensor based on molecularly imprinted electrochemical impedance spectroscopy (EMIC) for the specific detection of perfluorooctanoic acid (PFOA) in pickling solutions, and its preparation method. This method utilizes CDs / PPy(PFPy)-MIP... (PFOA) The sensor, consisting of a GCE-modified electrode as the working electrode, a platinum electrode as the auxiliary electrode, and an Ag / AgCl electrode as the reference electrode, uses electrochemical impedance spectroscopy to detect the concentration of PFOA in the pickling solution. Background Technology

[0002] During hot working processes (such as forging and hot rolling), a layer of oxide scale forms on the surface of metals. This oxide scale not only affects the appearance of the metal but also hinders subsequent processing steps. For example, in cold rolling, oxide scale can lead to accelerated wear of the rolls, affecting rolling accuracy and product quality. Pickling can effectively remove this oxide scale, restoring the metal surface to a smooth finish and providing a good foundation for subsequent processing. Similarly, for mechanical parts requiring high-precision surfaces, such as engine blocks and gears, pickling can remove tiny burrs, protrusions, and impurities, making the surface smoother and more even. This improves the assembly accuracy and operational performance of the parts, reduces frictional loss, lowers noise, and increases mechanical efficiency. Therefore, pickling is an indispensable and important process in industrial production.

[0003] The main components of pickling solutions are inorganic acids, primarily hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. Different metals require different pickling solutions, and the main difference lies not only in the type of acid used, but also in the addition of corrosion inhibitors, complexing agents, accelerators, and mist suppressants, all depending on the properties of the metal. Regardless of the type of pickling solution, mist suppressants are essential. Their addition effectively reduces acid mist in the environment, protecting the health of operators and preventing corrosion of equipment in the surrounding environment.

[0004] Anti-fogging agents utilize the unique amphiphilic molecular structure of surfactants, with a hydrophilic group at one end and a hydrophobic group at the other. The hydrophilic group adsorbs water molecules, causing them to distribute evenly on the surface of the pickling solution or metal, while simultaneously reducing the surface tension of the water molecules. This reduced surface tension makes it difficult for the pickling solution to form small droplets and evaporate into the air to form acid mist; instead, it spreads into a thin liquid film on the surface, thus reducing acid mist formation. Furthermore, surfactants also have excellent foaming properties, forming a thick foam layer on the surface of the pickling solution. This foam covers the acid surface, preventing contact between the acid and air, thereby inhibiting acid mist formation. As mentioned above, anti-fogging agents are mostly surfactants. Due to its good stability and excellent surface activity, perfluorooctanoic acid (PFOA) is often used as an anti-fogging agent in pickling solutions. However, due to its environmental toxicity and bioaccumulation, monitoring PFOA in pickling solutions is of great significance for reducing environmental pollution and protecting human health.

[0005] For the detection of PFOA in pickling solutions, chromatography-mass spectrometry (GC-MS) is often used. However, due to the presence of numerous other metal ions and organic additive molecules in the pickling solution, pretreatment for separation is often necessary. To address these challenges, this invention develops a modified electrode, CDs / PPy(PFPy)-MIP, with an extremely low detection limit (lowest detection limit of 0.064 mg / L). (PFOA) / GCE sensor. Because this invention eliminates the need for pretreatment such as separation of the pickling solution sample when analyzing PFOA, and other metal ions coexisting in the pickling solution do not cause interference, the modified electrode constructed in this invention for the analysis of PFOA in pickling solutions not only has advantages such as high sensitivity, strong specificity, and simple instrumentation, but more importantly, it eliminates the need for sample pretreatment, which has significant practical implications for the rapid analysis of PFOA. Summary of the Invention

[0006] The purpose of this invention is to address the cumbersome nature of PFOA analysis in pickling solutions, which requires extensive sample pretreatment. This invention provides an electrochemical sensor based on molecular imprinting for the detection of perfluorooctanoic acid (PFOA), its preparation method, and an electrochemical impedance spectroscopy (EIS) analysis method for the specific detection of PFOA in pickling solutions.

[0007] This invention first provides an electrochemical AC impedance sensor for detecting PFOA based on molecular imprinting, comprising a modified electrode constructed on the surface of a conductive substrate by co-modification of carbon quantum dots and a molecularly imprinted polymer with PFOA molecular structure, wherein the molecularly imprinted polymer is obtained by electropolymerization of pyrrole and N-trifluoromethylpyrrolidine-3-amine.

[0008] The electrochemical impedance sensor of the present invention is based on the fact that the hydrophobicity of the polypyrrole (PPy) and polytrifluoropyrrole (PFPy) composite film (PPy(PFPy)) formed on the electrode during the electropolymerization of pyrrole (Py) and N-trifluoromethylpyrrole-3-amine (FPy, CAS 1420963-61-6) is stronger than that of the PPy film, thereby improving the interaction between the electropolymerized composite film (PPy(PFPy)) and the hydrophobic PFOA.

[0009] Furthermore, this invention uses PFOA as the imprinted molecule. Since the pH of the electropolymerization solution is approximately 7.4, under these pH conditions, PFOA exists entirely in anionic form. Therefore, during the electropolymerization of Py and FPy, PFOA is readily incorporated into the composite membrane (PPy(PFPy)), forming the electropolymerized composite membrane PPy(PFPy)-MIP(PFOA) / GCE. As PFOA is removed from the polymer composite membrane, the modified electrode PPy(PFPy)-MIP... (PFOA) The polymer composite film of / GCE retains the spatial structure of the imprinted PFOA molecule. Similarly, due to the hydrophobicity of the imprinted PFOA molecule, the electropolymerized electrode PPy (PFPy)-MIP... (PFOA) The hydrophobicity of the GCE composite film is stronger than that of composite films doped with other non-hydrophobic anions. Based on this, the modified electrode PPy(PFPy)-MIP (PFOA) The interaction between the polymer film of / GCE and PFOA is further enhanced.

[0010] Because the electrodeposited polymer film has high resistance, it severely hinders electron transport on the electrode. To effectively improve the electron transport capability of the modified composite film electrode, this invention cleverly utilizes carbon quantum dots (CDs) to enhance the electron transport performance of the PPy (PFPy) composite film. The use of CDs is primarily based on the following considerations: (1) Carbon quantum dots typically contain abundant oxygen-containing functional groups such as hydroxyl and carboxyl groups on their surface. The nitrogen atoms on the polypyrrole molecular chain have lone pairs of electrons, which can form hydrogen bonds with the hydroxyl and carboxyl groups on the carbon quantum dot surface. The formation of hydrogen bonds can enhance the interaction between the two, allowing them to be better bonded together in the composite material and improving the performance of the CDs / PPy(PFPy)-MIP material. (PFOA) Stability and uniformity.

[0011] (2) Carbon quantum dots have a large number of functional groups and active sites on their surface, while polypyrrole is a conductive polymer with a conjugated structure. When the two come into contact, due to the energy level difference between carbon quantum dots and polypyrrole, electrons can be transferred from carbon quantum dots to the conjugated system of polypyrrole, or from polypyrrole to carbon quantum dots, thereby changing the electron cloud distribution and electrical properties of both, and thus improving the modified electrode CDs / PPy(PFPy)-MIP. (PFOA) Electron transport capability of / GCE composite membrane.

[0012] This invention further provides a method for preparing the above-mentioned electrochemical impedance spectroscopy sensor based on molecular imprinting for PFOA detection, comprising the following specific steps: (1) A clean GCE electrode was used as the working electrode, an Ag / AgCl electrode as the reference electrode, and a platinum electrode as the auxiliary electrode. Electropolymerization was carried out in PBS buffer containing functional monomers Py and FPy, as well as the template-imprinted molecule PFOA. The polymerization conditions were: cyclic voltammetry scans in the range of 0–0.8 V, scans of 10–30 cycles, a scan rate of 100 mV / s, and electropolymerization at room temperature. The number of scan cycles affects the film thickness of the modified electrode, with the optimal number of cycles being 20 cycles. After thorough washing with deionized water, the modified electrode was immersed in a mixture of ethanol and DMF (v / v, 9:1), and then thoroughly washed with deionized water to obtain the modified electrode PPy(PFPy)-MIP. (PFOA) / GCE.

[0013] In the electropolymerization solution, the molar ratio of Py, FPy and PFOA is 10:1:1; and the concentration of Py in the electropolymerization solution is 1 mmol / L.

[0014] (2) Take 2-5 μL of CDs dispersion and drop it onto PPy(PFPy)-MIP (PFOA) On the / GCE electrode, drying at room temperature yields CDs / PPy(PFPy)-MIP. (PFOA) / GCE modified electrode. The amount of CDs dropped onto the electrode has a significant impact on its resistance; the optimal amount is 3 μL.

[0015] The CDs dispersion was prepared as follows: a mixed solution of citric acid and ethylenediamine was prepared with deionized water and placed in a high-pressure autoclave lined with polytetrafluoroethylene and reacted at 200 °C for 5 h. After the reaction was completed, the mixture was cooled to room temperature, and the liquid in the autoclave was transferred to a dialysis membrane and dialyzed in ultrapure water. The liquid in the membrane was centrifuged and freeze-dried to obtain carbon quantum dot powder. 1 mg of CDs was dispersed in 1 ml of N,N-dimethylformamide (DMF) solvent to obtain a CDs dispersion with a concentration of 1 mg / mL.

[0016] This invention also provides the application of the aforementioned electrochemical impedance spectroscopy sensor based on molecular imprinting for PFOA detection in PFOA detection. In a specific embodiment of this invention, the sensor is used to detect the concentration of PFOA in pickling solution. The detection method specifically includes: (1) Plotting the PFOA standard curve A series of solutions with different PFOA concentrations were prepared using PBS buffer solution at pH 7.4 and a concentration of 0.1 mol / L. The modified electrode CDs / PPy(PFPy)-MIP was then applied. (PFOA) / GCE was placed in the above solution and enriched for 10 min at room temperature with stirring. After enrichment, the modified electrode was washed with deionized water and used as the working electrode. A three-electrode system was formed with Ag / AgCl as the reference electrode and a platinum wire electrode as the counter electrode, and placed in a solution containing Fe(CN)6. 3- / 4- AC impedance was measured in a 0.1 mol / L KCl solution with a concentration of 5 mmol / L. The test parameters were: potential 0.2 V, applied sinusoidal potential amplitude 10 mV, frequency range 1–1 x 10⁻⁶ mV. 5 Hz. Establishment of AC impedance sensor modified electrode CDs / PPy(PFPy)-MIP (PFOA) By combining the change in the charge transfer resistance (Rct) of PFOA (ΔRct) with the concentration of PFOA in the standard solution, the corresponding linear regression equation was obtained.

[0017] (2) Detection of PFOA in pickled samples Dilute the acid wash solution 1000 times with PBS buffer and bring the volume to 50 mL in a volumetric flask. Place the diluted sample solution in a 100 mL beaker and add the modified electrode CDs / PPy(PFPy)-MIP. (PFOA) / GCE was placed in the above sample solution and stirred for 10 min at room temperature. The AC impedance was tested according to the method in step (1) above. The measured ΔRct was substituted into the regression equation of the standard curve to calculate the concentration of PFOA in the pickling solution sample.

[0018] The electrochemical impedance sensor prepared in this invention is based on the composite membrane CDs / PPy(PFPy)-MIP. (PFOA) The strong interaction with PFOA occurs when the modified electrode CDs / PPy(PFPy)-MIP (PFOA)When GCD encounters PFOA in solution, due to the spatial structure of PFOA in the modified electrode composite film and its similar hydrophobicity, PFOA in the aqueous solution is quickly enriched by the modified electrode film and enters the modified electrode, forming a CDs / PPy(PFPy)-MIP(PFOA) / GCD electrode. At this point, the electrode is placed in a probe containing Fe(CN)6, which readily undergoes redox reactions. 3- / 4- In a potassium chloride solution, CDs / PPy(PFPy)-MIP can be determined. (PFOA) Charge transfer resistance of the / GCD modified electrode. The charge transfer resistance of the modified electrode is related to the charge transfer resistance of the modified electrode composite film CDs / PPy(PFPy)-MIP. (PFOA) The amount of PFOA entering the composite membrane is related to the amount of CDs / PPy(PFPy)-MIP. The more PFOA enters the composite membrane, the better the performance. (PFOA) The larger the charge transfer resistance of / GCD ( Figure 2 The charge transfer resistance is linearly related to the concentration of PFOA in the solution, thus realizing CDs / PPy(PFPy)-MIP. (PFOA) Selectivity determination of PFOA using a / GCD modified electrode.

[0019] A significant advantage of this invention is the development of a method for detecting PFOA in pickling solutions. When using this invention for PFOA detection, only the pickling solution needs to be diluted; no pretreatment of the pickling sample before separation is required. This is due to the modified electrode CDs / PPy(PFPy)-MIP. (PFOA) / GCE has high sensitivity; even when the pickling solution is diluted 1000 times, it can still analyze and detect PFOA in the pickling solution. At the same time, due to the high selectivity of the modified electrode composite film for PFOA, even if other metal ions and organic substances coexist in the pickling solution, they will not interfere with the determination of PFOA. Attached Figure Description

[0020] Figure 1 The following are the infrared spectra of polymers: (a) PPy, (b) PPy(PFPy), and (c) PPy(PFPy)-MIP(PFOA).

[0021] Figure 2 The AC impedance response diagram is shown in Fe(CN)6. 3- / 4- The concentration of PFOA was 5 mmol / L in a 0.1 mol / L KCl solution. The concentrations of PFOA enriched were 0.1 mg / L, 0.75 mg / L, 1.0 mg / L, 3.0 mg / L, 4.0 mg / L, 8.0 mg / L and 10 mg / L.

[0022] Figure 3This is a standard curve plotted based on the AC impedance response diagram. Detailed Implementation

[0023] To further illustrate the effectiveness of the technical method used in this invention for detecting PFOA in pickling solutions, detailed examples are provided. Example

[0024] (1) Preparation of CDs dispersion 1.05 g of citric acid monohydrate (0.5 mol / L) and 0.3 g of ethylenediamine (0.5 mol / L) were dissolved in 10 mL of ultrapure water. After stirring for 10 minutes, the resulting mixture was transferred to a 50 mL PTFE autoclave and heated at 200 °C for 5 hours. After the reaction liquid cooled to room temperature, the CDs solution was dialyzed against ultrapure water using a dialysis membrane. Finally, the CDs solution was centrifuged and freeze-dried to obtain a brown CDs powder. 1 mg of CDs was dispersed in 1 mL of N,N-dimethylformamide (DMF) solvent to obtain a CDs dispersion with a concentration of 1 mg / mL.

[0025] (2) CDs / PPy(PFPy)-MIP (PFOA) / GCD modified electrode preparation A clean GCE electrode (3 mm in diameter) was used as the working electrode, an Ag / AgCl electrode as the reference electrode, and a platinum electrode as the auxiliary electrode. Electropolymerization was performed in PBS buffer containing 1 mmol / L Py, 0.1 mmol / L FPy, and 0.1 mmol / L PFOA. The polymerization conditions were cyclic voltammetry scans of 20 cycles within the range of 0–0.8 V at a scan rate of 100 mV / s, at room temperature. After electropolymerization, the modified electrode was thoroughly washed with deionized water, immersed in a mixture of ethanol and DMF (v / v, 9:1), and then thoroughly washed with deionized water to obtain the modified electrode PPy(PFPy)-MIP. (PFOA) / GCE.

[0026] Take 3 μL of a 1 mg / mL CD dispersion and drop it onto PPy(PFPy)-MIP. (PFOA) On the / GCE electrode, drying at room temperature yields CDs / PPy(PFPy)-MIP. (PFOA) / GCE modified electrode.

[0027] (3) Plotting the PFOA standard curve A series of PFOA concentrations of 0.1 mg / L, 0.75 mg / L, 1.0 mg / L, 3.0 mg / L, 4.0 mg / L, 8.0 mg / L, and 10 mg / L were prepared using 0.1 mol / L PBS buffer solution (pH 7.4) to create standard curves. The modified electrode CDs / PPy(PFPy)-MIP was then used. (PFOA) / GCE was placed in the above solution and enriched for 10 min at room temperature with stirring. The modified electrode after enrichment was washed with deionized water and used as the working electrode. A three-electrode system was formed with Ag / AgCl as the reference electrode and a platinum wire electrode as the counter electrode, and placed in a solution containing Fe(CN)6. 3- / 4- AC impedance was measured in a 0.1 mol / L KCl solution with a concentration of 5 mmol / L. The test parameters were: potential 0.2 V, applied sinusoidal potential amplitude 10 mV, frequency range 1–1 x 10⁻⁶. 5 Hz. Establishment of modified electrode CDs / PPy(PFPy)-MIP (PFOA) By combining the changes in charge transfer resistance (Rct) before and after PFOA treatment (ΔRct) with the PFOA concentration in the standard solution, the corresponding linear regression equation was obtained as: ΔRct = 1.2C + 2.27, with a linear range of 0.1 mg / L to 10 mg / L, and a correlation coefficient R. 2 = 0.9960 The limit of detection is 0.064 mg / L.

[0028] (4) Detection of PFOA in pickled samples Pickling solutions have various compositions. To illustrate the effectiveness of this invention, the pickling process described in the literature published by Chen Jianqiu et al., "Development of Pickling Solution Formula for Steel Oxide Layer," Surface Technology, 2005(34), 69-70, is slightly modified. The composition of the pickling solution is shown in Table 1. The concentration of the acid mist inhibitor PFOA in the pickling solution is typically 0.2 g / L to 1.0 g / L, but in Table 1 of this invention, it is set to 1 g / L.

[0029] Table 1 Composition of pickling solution

[0030] Dilute the washing solution in Table 1 1000 times with PBS buffer. Accurately transfer 50 mL of the diluent into a 100 mL beaker. Add the modified electrode CDs / PPy(PFPy)-MIP (PFOA) / GCE was placed in the diluent and stirred for 10 min at room temperature. The AC impedance was tested according to the method in step (3) above. The measured ΔRct was substituted into the regression equation of the standard curve to calculate the concentration of PFOA in the pickling solution sample. The results are listed in Table 2.

[0031] Figure 1 The images show the infrared spectra of the polymer. As can be seen from the infrared spectra, spectrum a is very similar to the standard polypyrrole spectrum, proving that the synthesis of polypyrrole was very successful. After adding N-trifluoromethylpyrrole-3-amine to the pyrrole solution, as shown in Figure b, the polymerized product shows CF vibration peaks at 1200 and 1350, indicating the possibility that N-trifluoromethylpyrrole-3-amine and pyrrole formed a copolymer. After adding perfluorooctanoic acid to the solution of pyrrole and N-trifluoromethylpyrrole-3-amine, as shown in Figure c, the infrared spectrum of the polymerized product shows vibration peaks for the carbonyl group (C=O) at 1720 and the hydroxyl group (-OH) at 3600, indicating that perfluorooctanoic acid was incorporated into the PPy (PFPy) copolymer.

[0032] Comparative example

[0033] (1) Preparation of CDs dispersion Same as the example.

[0034] (2) CDs / PPy-MIP (PFOA) / GCD modified electrode preparation The most fundamental difference between the modified electrode in the comparative example and the example is that no hydrophobic polytrifluoropyrrole was added to the polypyrrole composite film. When preparing the modified electrode, the functional monomer Fpy was not added. Other conditions were the same as in the example.

[0035] (3) Plotting the PFOA standard curve A series of PFOA solutions with concentrations of 0.1 mg / L, 0.75 mg / L, 1.0 mg / L, 3.0 mg / L, 4.0 mg / L, 8.0 mg / L, and 10 mg / L were prepared to create a standard curve. The modified electrode CDs / PPy-MIP was then used. (PFOA) / GCE was placed in the above solution for analysis, and other operations were the same as in the example. The corresponding linear regression equation was obtained as: ΔRct = 1.09C +2.06, with a linear range of 1.0 mg / L to 10 mg / L, and a correlation coefficient R. 2 = 0.9938 The limit of detection is 0.68 mg / L.

[0036] (4) Detection of PFOA in pickled samples Due to the modified electrode CDs / PPy-MIP (PFOA)The sensitivity of / GCD is relatively low. If the sample is diluted 1000 times, the modified electrode will be unable to detect PFOA in the pickling solution. Therefore, the pickling solution is diluted 500 times, and 50 mL of this diluted sample is placed in a 100 mL beaker. The modified electrode CDs / PPy-MIP is then applied. (PFOA) / GCD was enriched in the above sample solution. The sample analysis was performed in the same manner as in the examples. The concentration of PFOA in the pickling solution sample could then be determined. The results are listed in Table 2.

[0037] Table 2 Concentration of PFOA in pickling solution

[0038] As shown in Table 2, the modified electrode CDs / PPy(PFPy)-MIP was used. (PFOA) / GCE performed three parallel tests on the pickling solution sample, with a relative standard deviation of less than 2%, and the measured values ​​were very close to the actual added amounts, demonstrating that the modified electrode CDs / PPy(PFPy)-MIP (PFOA) / GCE demonstrates good accuracy and precision in the analysis of PFOA in pickling solution samples. A comparative example uses modified CDs / PPyMIP. (PFOA) When analyzing PFOA in pickling solution samples, the limit of detection and linear range of the modified electrode / GCE were inferior to those of the modified electrode CDs / PPy(PFPy)-MIP. (PFOA) / GCE, which shows the importance of hydrophobic PFPy membranes.

[0039] The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various corresponding changes without departing from the scope of the present invention. Therefore, all technical solutions formed by equivalent substitutions or equivalent modifications are within the protection scope of the present invention.

Claims

1. An electrochemical sensor for detecting perfluorooctanoic acid based on molecular imprinting, characterized in that, A modified electrode is constructed on the surface of a conductive substrate by co-modification of carbon quantum dots and a molecularly imprinted polymer with a perfluorooctanoic acid molecular structure. The molecularly imprinted polymer is obtained by electropolymerization of pyrrole and N-trifluoromethylpyrrolidine-3-amine. The method for preparing the electrochemical sensor for detecting perfluorooctanoic acid based on molecular imprinting includes the following steps: (1) Prepare a PBS buffer containing pyrrole, N-trifluoromethylpyrrolidine-3-amine, and perfluorooctanoic acid as a template imprinting molecule as an electropolymerization solution; use a three-electrode system to electropolymerize in the electropolymerization solution at room temperature to prepare a molecularly imprinted polymer on the surface of a conductive substrate; remove the template imprinting molecule from the molecularly imprinted polymer to obtain a molecularly imprinted polymer electrode with a perfluorooctanoic acid molecular structure imprinted on it. (2) The carbon quantum dot dispersion was drop-coated onto the surface of the molecularly imprinted polymer electrode and dried to obtain the modified electrode.

2. The method for preparing an electrochemical sensor for detecting perfluorooctanoic acid based on molecular imprinting as described in claim 1, characterized in that, The specific steps include the following: (1) Prepare a PBS buffer solution containing functional monomers pyrrole and N-trifluoromethylpyrrolidine-3-amine, and perfluorooctanoic acid as a template imprinting molecule, as an electropolymerization solution; use a three-electrode system to electropolymerize in the electropolymerization solution at room temperature to prepare a molecularly imprinted polymer on the surface of a conductive substrate; remove the template imprinting molecule from the molecularly imprinted polymer to obtain an electrode imprinted with the molecular structure of perfluorooctanoic acid, denoted as PPy(PFPy)-MIP. (PFOA) / GCE; (2) Drop the carbon quantum dot dispersion onto PPy(PFPy)-MIP (PFOA) The GCE surface is dried to obtain a modified electrode, denoted as CDs / PPy(PFPy)-MIP. (PFOA) / GCE.

3. The method for preparing an electrochemical sensor for detecting perfluorooctanoic acid based on molecular imprinting according to claim 2, characterized in that, In the electropolymerization solution, the molar ratio of pyrrole, N-trifluoromethylpyrrolidine-3-amine, and perfluorooctanoic acid is 10:1:1; the concentration of pyrrole in the electropolymerization solution is 1 mmol / L.

4. The method for preparing an electrochemical sensor for detecting perfluorooctanoic acid based on molecular imprinting according to claim 2, characterized in that, The electropolymerization reaction is carried out using a clean GCE electrode as the working electrode, an Ag / AgCl electrode as the reference electrode, and a platinum electrode as the auxiliary electrode. The polymerization conditions were as follows: cyclic voltammetry scans were performed at room temperature in the range of 0–0.8 V for 10–30 cycles at a scan rate of 100 mV / s.

5. The method for preparing an electrochemical sensor for detecting perfluorooctanoic acid based on molecular imprinting according to claim 2, characterized in that, The carbon quantum dot dispersion is obtained by uniformly dispersing carbon quantum dots in N,N-dimethylformamide solvent, with a concentration of 1 mg / mL and a drop volume of 2–5 μL.

6. The application of the electrochemical sensor based on molecular imprinting for detecting perfluorooctanoic acid (PFOA) as described in claim 1 in the electrochemical impedance spectroscopy (EIS) method for detecting PFOA concentration.

7. The application according to claim 6, characterized in that, The detection method includes the following steps: (1) Prepare PBS buffer solutions containing different concentrations of perfluorooctanoic acid as standard solutions, and use the modified electrode CDs / PPy(PFPy)-MIP (PFOA) / GCE was placed in a standard solution and enriched for 10 min at room temperature with stirring. The modified electrode after enrichment was used as the working electrode, with Ag / AgCl as the reference electrode and a platinum wire electrode as the counter electrode to form a three-electrode system. It was placed in a solution containing Fe(CN)6 3- / 4- AC impedance testing was performed in KCl solution; an AC impedance sensor modified electrode CDs / PPy(PFPy)-MIP was established. (PFOA) / GCE combined the relationship curve between the change in charge transfer resistance (ΔRct) of perfluorooctanoic acid and the concentration of PFOA in the standard solution to obtain the corresponding linear regression equation; (2) Modify the electrode CDs / PPy(PFPy)-MIP (PFOA) / GCE is placed in the pickling solution dilution and stirred for 10 min at room temperature. The AC impedance test is performed according to the method in step (1) above. The measured ΔRct is substituted into the linear regression equation of the standard curve to calculate the concentration of perfluorooctanoic acid in the pickling solution.

8. The application according to claim 7, characterized in that, The Fe(CN)6-containing 3- / 4- In KCl solution, Fe(CN)6 3- / 4- The concentration of MgCl2 was 5 mmol / L, and the concentration of KCl was 0.1 mol / L.

9. The application according to claim 7, characterized in that, The parameters for the AC impedance test are: potential 0.2 V, amplitude of the applied sinusoidal potential: 10 mV, frequency range: 1~1×10 5 Hz.

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