Electrochemical sensor for detecting PFOA (perfluorooctanoic acid) based on fluorine-fluorine interaction and electrochemical detection method of PFOA

Abstract

The invention relates to the technical field of electrochemistry, in particular to an electrochemical sensor for detecting PFOA (perfluorooctanoic acid) based on fluorine-fluorine interaction and an electrochemical detection method of the PFOA. The invention discloses an electrochemical sensor for detecting PFOA (perfluorooctanoic acid) based on fluorine-fluorine interaction. The electrochemical sensor comprises a counter electrode, a reference electrode, a signal acquisition and processing unit, an electrolyte solution and a working electrode, the electrolyte solution is a potassium ferricyanide solution containing 0.1 M of KCl, and the working electrode is formed by dispensing an electrode material F-COF / MWCNTs-NH2 on the electrode; when the working electrode is placed in an electrolyte solution containing PFOA, fluorine atoms in an electrode material F-COF / MWCNTs-NH2 on the working electrode and fluorine atoms on the PFOA adsorb the PFOA on the surface of the working electrode based on fluorine-fluorine interaction, and then potassium ferricyanide is matched to serve as an oxidation-reduction probe, so that electrochemical detection on the PFOA can be effectively realized. Therefore, the detection problem that the PFOA has no electrochemical activity in the prior art is solved, and accurate and high-sensitivity quantitative detection on the PFOA is realized.

Description

Electrochemical Sensors and Electrochemical Detection Methods for PFOA Based on Fluorofluorine Interactions Technical Field

[0001] This invention relates to the field of electrochemical technology, specifically to an electrochemical sensor for detecting PFOA based on fluorine-fluorine interactions and an electrochemical detection method for PFOA. Background Technology

[0002] Perfluorooctanoic acid (PFOA) is one of the most typical and common perfluoroalkyl compounds (PFAS). However, its high physicochemical stability leads to its widespread accumulation and long-term presence in global waters. It can also enter the human body through bioaccumulation, causing hepatotoxicity, immunosuppression, and carcinogenic risks, posing a significant threat to environmental pollution and human health. Current quantitative analysis of PFOA in water is generally performed using liquid chromatography-mass spectrometry (LC-MS). While this method provides accurate and sensitive measurements, it requires large equipment, time-consuming pretreatment, and costly maintenance. Electrochemical techniques have attracted considerable attention due to their high sensitivity, miniaturization, low cost, and ease of operation. However, because PFOA lacks electrochemical activity, current techniques cannot be used for quantitative analysis of PFOA based on electrochemical methods. Summary of the Invention

[0003] To address the technical problem that existing technologies cannot quantitatively analyze PFOA using electrochemical methods due to its lack of electrochemical activity, this invention provides an electrochemical sensor for detecting PFOA based on fluorine-fluorine interactions and an electrochemical detection method for PFOA.

[0004] This invention employs the following technical solution: an electrochemical sensor for detecting PFOA based on fluorine-fluorine interactions, comprising a counter electrode, a reference electrode, a signal acquisition and processing unit, an electrolyte solution, and a working electrode. The electrolyte solution is a potassium ferricyanide solution containing 0.1M KCl. The working electrode is formed by drop-coating electrode material F-COF / MWCNTs-NH2 onto the electrode. When the working electrode is placed in the electrolyte solution containing PFOA, fluorine atoms in the electrode material F-COF / MWCNTs-NH2 and fluorine atoms on PFOA adsorb PFOA onto the surface of the working electrode based on fluorine-fluorine interactions, thereby achieving quantitative detection of PFOA by changing the oxidation peak current value output by the signal acquisition and processing unit in the electrochemical sensor.

[0005] As a further improvement of the present invention, the preparation method of the electrode material F-COF / MWCNTs-NH2 is as follows: MWCNTs-NH2 and F-COF are dispersed in DMF at a mass ratio of 1~3:3~1 and subjected to ultrasonication. After ultrasonication, the materials are washed and dried sequentially to obtain the electrode material F-COF / MWCNTs-NH2. The fluorine atoms in the electrode material and the fluorine atoms on PFOA achieve specific adsorption of PFOA based on fluorine-fluorine interactions.

[0006] As a further improvement of the present invention, the preparation process of F-COF is as follows: 1,3,5-tris(4-aminophenyl)benzene and tetrafluoroterephthalaldehyde are added to acetonitrile with a mass ratio of 17:14 and a volume ratio of 5:7 to tetrafluoroterephthalaldehyde, and then ultrasonicated. Acetic acid with a volume ratio of 1:10 to acetonitrile is then slowly added, and ultrasonication is continued. After ultrasonication, the mixture is washed and dried sequentially to obtain F-COF.

[0007] As a further improvement of this invention, the preparation process of aminated carbon nanotubes (MWCNTs-NH2) is as follows: MWCNTs-COOH is dispersed in MES buffer at a weight ratio of 1:1 and subjected to ultrasonic treatment. EDC-HCl at a mass ratio of 2:1 to MWCNTs-COOH and NHS at a mass ratio of 36:25 to MWCNTs-COOH are then added, and the mixture is stirred at room temperature. Polyethyleneimine at a concentration of 1% and a mass ratio of 1:1 to MWCNTs-COOH is then slowly added, and stirring continues until all raw materials have fully reacted. The mixture is then collected by centrifugation, washed, and dried to obtain MWCNTs-NH2.

[0008] As a further improvement of the present invention, the detection limit of the electrochemical sensor for PFOA is 0.002 nM, and the concentration detection range of the electrochemical sensor for PFOA is 0.01 nM to 20 nM.

[0009] As a further improvement of the present invention, the preparation process of the working electrode is as follows: polish the glassy carbon electrode with alumina powder and clean it, and then dry it in N2 stream; drop the F-COF / MWCNTs-NH2 dispersion onto the surface of the dried glassy carbon electrode and dry it at 40°C to obtain the working electrode.

[0010] As a further improvement of the present invention, the ratio between the sum of the masses of MWCNTs-NH2 and F-COF and the volume of DMF is 1:1.

[0011] This invention also provides an electrochemical detection method for PFOA, which uses the electrochemical sensor described above to detect PFOA. The electrochemical detection method includes: placing the working electrode in an electrolyte solution containing PFOA and performing DPV scanning; measuring the change in oxidation peak current corresponding to different concentrations of PFOA; establishing a quantitative relationship between the concentration of PFOA and the change in oxidation peak current; and determining the concentration of PFOA in an unknown sample based on this quantitative relationship.

[0012] As a further improvement of this invention, the quantitative relationship between the concentration of PFOA and the change in oxidation peak current is as follows: ΔI pa =14.2566LogC-12.2177, where: ΔI pa denoted as the change in oxidation peak current, and C represents the concentration of PFOA.

[0013] As a further improvement of the present invention, the scanning parameters of the electrochemical sensor for detecting PFOA are as follows: potential range of -0.1V to 0.5V, amplitude of 0.05V, pulse period of 0.5s, and scanning speed of 100mV·s. -1 .

[0014] The technical solution provided by the present invention has the following beneficial effects: (1) The present invention provides an electrochemical sensor for detecting PFOA based on fluorine-fluorine interaction. The F-COF framework in the electrode material F-COF / MWCNTs-NH2 has CF bonds, which can construct a fluorinated surface on the electrode material F-COF / MWCNTs-NH2, so that the fluorine atoms in the F-COF / MWCNTs-NH2 material can selectively adsorb PFOA based on fluorine-fluorine interaction, thereby enabling the electrode material to specifically bind PFOA. In addition, with potassium ferricyanide as a redox probe, it can effectively realize the electrochemical detection of PFOA, thereby solving the detection problem of no electrochemical activity for PFOA in the prior art, and realizing accurate and highly sensitive quantitative detection of PFOA.

[0015] (2) This invention provides an electrochemical sensor for detecting PFOA based on fluorine-fluorine interactions. The unique structure of F-COF allows for the selective capture and enrichment of trace PFOA molecules through fluorine-fluorine interactions, providing a material basis for high-sensitivity PFOA detection. Simultaneously, the excellent conductivity of MWCNTs-NH2 significantly promotes the electron transfer rate, and, in conjunction with the porous, ordered structure and stability of F-COF, optimizes the interface structure of the working electrode, exposing more active sites and increasing electrocatalytic activity. The synergistic effect of the combination of F-COF and MWCNTs-NH2 results in a detection limit (LOD) for PFOA as low as 0.002 nM, exhibiting excellent response within a wide linear range of 0.01 nM to 20 nM, thus significantly enhancing the electrochemical performance of the constructed electrochemical sensor.

[0016] (3) The present invention provides an electrochemical detection method for PFOA, which utilizes the interaction between fluorine and fluorine to achieve selective adsorption of PFOA, and constructs a standard curve between the change value of oxidation peak current and the logarithm of PFOA concentration to achieve quantitative detection of unknown concentration of PFOA, thereby realizing accurate, rapid and highly sensitive detection of PFOA by electrochemical means. Attached Figure Description

[0017] Figure 1 is a flowchart of the preparation process of electrode materials in the electrochemical sensor for detecting PFOA based on fluorine-fluorine interaction provided in this invention.

[0018] Figure 2 is a flowchart of the preparation process of the working electrode in the electrochemical sensor for detecting PFOA based on fluorine-fluorine interaction provided in this invention.

[0019] Figure 3 is a scanning electron microscope image of the electrode material prepared according to Figure 1.

[0020] Figure 4 shows the X-ray photoelectron spectra of F-COF, MWCNTs-NH2, and F-COF / MWCNTs-NH2 in this invention.

[0021] Figure 5 shows the X-ray photoelectron spectra of the electrode material before and after PFOA adsorption in this invention.

[0022] Figure 6 shows the trend of oxidation peak current change with concentration when the electrochemical sensor provided by the present invention performs DPV detection on PFOA solution and OA solution of different concentrations.

[0023] Figure 7 shows the current-potential curves of the working electrode modified with different materials in this invention in a 5mM potassium ferricyanide solution containing 0.1M KCl.

[0024] Figure 8 is a bar chart showing the changes in oxidation peak current values ​​of F-COF and MWCNTs-NH2 at different mass ratios in this invention.

[0025] Figure 9 is a bar chart showing the relationship between the amount of F-COF / MWCNTs-NH2 dispersion applied and the corresponding change in oxidation peak current in this invention.

[0026] Figure 10 is a bar chart showing the change in oxidation peak current for each of the five independently manufactured F-COF / MWCNTs-NH2 modified glassy carbon electrodes used as working electrodes in a repeatability test.

[0027] Figure 11 shows the DPV curves after detecting PFOA at different known concentrations using the electrochemical sensor provided by this invention.

[0028] Figure 12 is a standard curve plot showing the relationship between the change in oxidation peak current and the logarithm of PFOA concentration constructed using the electrochemical sensor provided by this invention. Detailed Implementation

[0029] The present invention will now be further described in conjunction with specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0030] In the description of this invention, it should be noted that directional terms such as "center," "lateral," "longitudinal," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific scope of protection of this invention. The terms "first," "second," etc., in the specification and claims of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. The terms "comprising" and "having," and any variations thereof, in the specification and claims of this invention, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or devices.

[0031] Because perfluorooctanoic acid (PFOA) lacks electrochemical activity, electrochemical detection is generally not considered in the quantitative analysis of PFOA. While liquid chromatography-mass spectrometry (LC-MS) can accurately detect PFOA, the process is cumbersome and time-consuming due to the large amount of equipment required, time-consuming pretreatment, and high maintenance costs. Therefore, this scheme constructs an electrochemical sensor for PFOA detection based on fluorine-fluorine interactions using potassium ferricyanide as a redox probe. The electrochemical sensor includes a counter electrode, a reference electrode, a signal acquisition and processing unit, an electrolyte solution, and a working electrode. The counter electrode, reference electrode, and working electrode form a three-electrode system. The counter electrode (also called the auxiliary electrode) forms a current loop with the working electrode, conducting electrons to complete the electrochemical reaction on the working electrode and preventing polarization. The reference electrode provides a stable reference potential for accurate measurement of the potential change at the working electrode. In this scheme, the reference electrode can be a saturated calomel electrode, and the counter electrode can be a platinum electrode. The electrolyte solution is a potassium ferricyanide solution containing 0.1M KCl. PFOA is indirectly detected by using the potassium ferricyanide solution as a redox probe. The detection principle is as follows: When there is no PFOA in the electrolyte solution, the oxidation peak current value on the working electrode is the same as the oxidation peak current value of potassium ferricyanide. When PFOA is added to the electrolyte solution, PFOA occupies the interfacial active sites of the working electrode, and the electrochemical signal of potassium ferricyanide decreases. Therefore, electrochemical detection of electrochemically inactive PFOA can be performed based on potassium ferricyanide as a redox probe. Specifically: Since PFOA occupies a certain number of interfacial active sites on the working electrode after adsorption, the decrease in the oxidation peak current signal of potassium ferricyanide is converted into a signal of increased PFOA concentration, thereby achieving rapid and sensitive electrochemical detection. The working electrode is formed by drop-coating the electrode material F-COF / MWCNTs-NH2 onto the electrode. When the working electrode is placed in an electrolyte solution containing PFOA, fluorine atoms in the electrode material F-COF / MWCNTs-NH2 and PFOA adsorb PFOA onto the surface of the working electrode through fluorine-fluorine interactions. This alters the oxidation peak current value output by the signal acquisition and processing unit in the electrochemical sensor, thus enabling quantitative detection of PFOA. The change in oxidation peak current can be understood as the difference between the oxidation peak current value after the addition of PFOA and the oxidation peak current value without the addition of PFOA. F-COF is a fluorinated covalent organic framework with poor conductivity; MWCNTs-NH2 is an aminated carbon nanotube, which is composed of sp... 2Composed of a hybrid carbon skeleton, this structure provides highly delocalized π electrons, forming an electron cloud that is not bound to any single atom and can move freely throughout the entire structure. This free-moving electron gives MWCNTs-NH2 excellent electrical conductivity.

[0032] The principle behind the specific recognition of PFOA by fluorine atoms in F-COF / MWCNTs-NH2 and PFOA based on fluorine-fluorine interactions is as follows: The F-COF framework contains CF bonds, enabling the construction of a fluorinated surface on the F-COF / MWCNTs-NH2 electrode material. This allows the fluorine atoms in F-COF / MWCNTs-NH2 to selectively adsorb PFOA based on fluorine-fluorine interactions, thus enabling the electrode material to specifically bind PFOA. Combined with potassium ferricyanide as a redox probe, this allows for effective electrochemical detection of PFOA. Furthermore, the introduction of MWCNTs-NH2 into the electrode material overcomes the poor conductivity of F-COF itself, significantly improving the electron transfer rate of the constructed F-COF / MWCNTs-NH2 electrode material. In addition, the ordered porous structure of F-COF and the large specific surface area of ​​MWCNTs-NH2 provide numerous adsorption sites for PFOA molecules, achieving highly efficient adsorption of PFOA. Furthermore, the high conductivity and large specific surface area of ​​MWCNTs-NH2, combined with the porous and ordered structure and stability of F-COF, optimized the interfacial structure of the constructed working electrode F-COF / MWCNTs-NH2, allowing the interface of the working electrode to expose more active sites and thus increasing electrocatalytic activity. The working electrode was constructed as follows: a glassy carbon electrode (GCE) was polished with 0.3 μm alumina powder and cleaned, then dried in an N2 stream. A 10 μL volume of F-COF / MWCNTs-NH2 dispersion with a concentration of 1.0 mg / mL was drop-coated onto the dried glassy carbon electrode surface and dried at 40 °C to obtain the working electrode F-COF / MWCNTs-NH2 / GCE. This method of constructing a working electrode modified with F-COF / MWCNTs-NH2 has the following advantages: firstly, the excellent conductivity and high specific surface area of ​​MWCNTs-NH2 greatly promote the electron transfer rate and further increase the effective adsorption sites. On the other hand, F-COF can selectively capture and enrich trace PFOA molecules through specific fluorine-fluorine interactions, providing a material basis for high-sensitivity PFOA detection. F-COF possesses a high specific surface area and an ordered porous structure, and its synergistic effect with MWCNTs-NH2 can optimize the electrode interface structure and increase electrocatalytic activity. The synergistic effect of the combination of F-COF and MWCNTs-NH2 results in an electrochemical sensor with a detection limit (LOD) as low as 0.002 nM for PFOA, exhibiting excellent response over a wide linear range of 0.01 nM to 20 nM, thus significantly enhancing the electrochemical performance of the constructed electrochemical sensor.

[0033] It is understandable that, in addition to the main fluorine-fluorine interaction mechanism for achieving specific adsorption of PFOA, our scheme may also have other forces that synergistically work with the fluorine-fluorine interaction to achieve specific adsorption of PFOA. These other forces may include one or more of the following: electrostatic interactions, hydrogen bonds, and hydrophobic interactions. Therefore, this scheme achieves specific adsorption of PFOA by leveraging the fluorine-fluorine interaction in conjunction with other possible mechanisms. The specific preparation process of the electrode material F-COF / MWCNTs-NH2 in the working electrode is described below. Please refer to Figure 1: (I) Preparation of F-COF 34 mg of 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 28 mg of tetrafluoroterephthalaldehyde (TFTA) were added to 20 mL of acetonitrile and sonicated at room temperature for 2 min. Then, acetic acid with a concentration of 12 M and a volume of 2 mL was slowly added to the solution after sonication for 2 min, and sonication was maintained for 1 hour. Finally, the product after sonication was washed with acetonitrile and anhydrous ethanol in sequence, and then vacuum dried at 60 °C to obtain F-COF.

[0034] (II) Preparation of MWCNTs-NH2 First, 50 mg of MWCNTs-COOH (carboxylated nanotubes) was dispersed in 50 mg of 0.1 M, pH 5.5 MES buffer and sonicated for 30 min to obtain mixture one. 100 mg of EDC-HCl and 72 mg of NHS were added to mixture one after sonication, and the mixture was stirred at room temperature for 2 hours to obtain mixture two. 50 mg of 1% polyethyleneimine at pH 9.0 was slowly added to mixture two, and the mixture was stirred at room temperature for 24 hours. Finally, the product was collected by centrifugation and washed three times alternately with anhydrous ethanol and water, and then vacuum dried at 60 °C to obtain MWCNTs-NH2.

[0035] (III) Disperse 2.0 mg of MWCNTs-NH2 and 1.0 mg of F-COF in 3 mL of DMF and sonicate for 2 hours to obtain mixture III. Collect the product in mixture III by centrifugation and wash it several times with DMF and anhydrous ethanol in sequence. Dry the washed product under vacuum at 60 °C to obtain F-COF / MWCNTs-NH2.

[0036] MES buffer is an abbreviation for 2-morpholine ethanesulfonic acid buffer. EDC-HCl is an abbreviation for 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride. NHS is an abbreviation for N-hydroxysuccinimide. DMF is an abbreviation for N,N-dimethylformamide, which is a good aprotic polar solvent that can dissolve most organic and inorganic substances and is miscible with water, alcohols, ethers, aldehydes, ketones, esters, halogenated hydrocarbons, and aromatic hydrocarbons.

[0037] In this scheme, the electrode material can be prepared by the above-described preparation method. The excellent conductivity of the prepared electrode material MWCNTs-NH2 greatly promotes the electron transfer rate. Combined with the porous, ordered structure and stability of F-COF, it optimizes the interface structure of the working electrode, exposing more active sites and increasing electrocatalytic activity. Simultaneously, F-COF can selectively capture and enrich trace PFOA molecules through fluorine-fluorine interactions, providing a material basis for high-sensitivity PFOA detection. Specifically, the specifically adsorbed PFOA molecules occupy the active sites on the working electrode surface, hindering electron transfer from the probe molecules (i.e., potassium ferricyanide), leading to a quantitative change in the oxidation peak current. This allows for the quantitative detection of PFOA concentration by establishing a quantitative relationship between PFOA concentration and the change in oxidation peak current. Furthermore, MWCNTs-NH2 in the electrode material has excellent conductivity and high specific surface area. Its combination with F-COF can overcome the problem of poor conductivity of F-COF itself and improve the electron transfer rate of the electrode material. At the same time, the fluorine atoms in F-COF can specifically adsorb PFOA and enhance the electrocatalytic activity in synergy with MWCNTs-NH2 to achieve rapid and sensitive detection of PFOA.

[0038] Based on the electrode material prepared in this way, a method for preparing a working electrode is also provided, as shown in Figure 2. This method includes the following steps: polishing a glassy carbon electrode (GCE) with 0.3 μm alumina powder and cleaning it, then drying it in an N2 stream to obtain a pretreated glassy carbon electrode. Adding 1 mg of F-COF and 2 mg of MWCNTs-NH2 to 3 mL of DMF and ultrasonically mixing for 30 min yields an F-COF / MWCNTs-NH2 dispersion. Accurately measuring 10 μL of the F-COF / MWCNTs-NH2 dispersion and drop-coating it onto the surface of the pretreated glassy carbon electrode, then drying it at 40 °C, thus obtaining the working electrode F-COF / MWCNTs-NH2 / GCE.

[0039] During the preparation of electrode materials, researchers also conducted verification experiments on the prepared electrode materials and intermediate products in the preparation process.

[0040] (1) Scanning electron microscopy experiment The electrode material F-COF / MWCNTs-NH2 prepared by the above scheme was observed under a scanning electron microscope, and Figure 3 was obtained. Through analysis of Figure 3, it can be seen that there are obvious spheres in Figure 3, which is consistent with the theoretical morphology of F-COF. Therefore, it can be preliminarily inferred that F-COF was successfully prepared. The tubular structure in Figure 3 corresponds to MWCNTs-NH2, which is dispersed on the surface and periphery of F-COF, thus forming a tight interfacial contact. This shows that F-COF / MWCNTs-NH2 was successfully composited.

[0041] (2) X-ray photoelectron spectroscopy analysis: The F-COF, MWCNTs-NH2, and F-COF / MWCNTs-NH2 prepared by the above scheme were analyzed by an X-ray photoelectron spectroscopy analyzer, and the X-ray photoelectron spectra are shown in Figure 4. In Figure 4(a), the X-ray photoelectron spectrum of F-COF is shown. In Figure 4(b), the X-ray photoelectron spectrum of MWCNTs-NH2 is shown. In Figure 4(c), the X-ray photoelectron spectrum of F-COF / MWCNTs-NH2 is shown. Analysis of Figure 4 shows that the F-COF / MWCNTs-NH2 composite material has the characteristic peaks of both F-COF and MWCNTs-NH2. Specifically, Figure 4(a) shows the characteristic peak of C=N at 286.2 eV and the characteristic peak of CF at 287.8 eV, which are consistent with the theoretical chemical combination of F-COF, thus proving that F-COF was successfully prepared. Looking at Figure 4(b), the CN characteristic peak at 285.9 eV proves that MWCNTs-NH2 was successfully prepared. Figure 4(c) shows characteristic peaks for both F-COF and MWCNTs-NH2, thus proving that F-COF / MWCNTs-NH2 was successfully combined.

[0042] (3) Verification of the fluorine-fluorine interaction between fluorine atoms in F-COF / MWCNTs-NH2 and fluorine atoms on PFOA: X-ray photoelectron spectroscopy (XPS) and differential pulse voltammetry (DPV) were used to prove the specific fluorine-fluorine interaction between F-COF / MWCNTs-NH2 and PFOA molecules. The specific steps are as follows: Two sets of electrode materials F-COF / MWCNTs-NH2 were prepared, divided into group a and group b. 10 mg of group a electrode material F-COF / MWCNTs-NH2 was added to a 20 μM PFOA solution with a volume of 20 mL to obtain mixture four. Group b electrode material F-COF / MWCNTs-NH2 was added to 20 mL of water to obtain mixture five. Mixture four and mixture five were simultaneously placed in a shaker and incubated for 30 min. After incubation for 30 minutes, the products were collected by centrifugation, washed with water, and dried at 60°C to obtain Sample 1 (corresponding to group a electrode material) and Sample 2 (corresponding to group b electrode material).

[0043] XPS analysis was performed on samples 1 and 2, respectively, as shown in Figure 5. The XPS spectrum before adsorption in Figure 5 is that of sample 2; the XPS spectrum after adsorption is that of sample 1. Analysis of Figure 5 shows that the XPS spectrum after PFOA adsorption exhibits -CF2 (689.9 eV) and -CF3 (691 eV) peaks belonging to PFOA in the F1s region, indicating successful PFOA adsorption. This demonstrates that the proposed method using the F-COF / MWCNTs-NH2 electrode material can effectively achieve PFOA adsorption. Furthermore, comparing the XPS spectra before and after adsorption reveals that, compared to the binding energy of the CF peak in F-COF / MWCNTs-NH2 before PFOA adsorption (688.2 eV), the binding energy of the CF peak in F-COF / MWCNTs-NH2 after adsorption is 688.4 eV, indicating an increase in the binding energy of the CF peak. This suggests a decrease in the electron cloud density of the CF bond in the F-COF / MWCNTs-NH2 material, which may be due to fluorine-fluorine interactions or hydrogen bonding between the PFOA molecules and F-COF / MWCNTs-NH2.

[0044] Comparative Example: 0.1 nM, 1 nM, and 10 nM PFOA solutions and octanoic acid (OA) solutions were prepared respectively. The constructed electrochemical sensor was used to detect the DPV of PFOA and OA solutions at different concentrations. The results are shown in Figure 6. Analysis of Figure 6 shows that the electrochemical sensor detects the change in the oxidation peak current ∆I of PFOA. pa The change in oxidation peak current is consistently greater than that of PFOA, indicating that the working electrode interface of the electrochemical sensor exhibits a specific adsorption enhancement effect on PFOA. Since the forces on the non-fluorinated portions of both are similar (electrostatic interactions, hydrogen bonding, hydrophobic interactions), this enhancement can be attributed to a specific interaction between the perfluoroalkyl chain of PFOA and the fluorinated surface of the working electrode of the electrochemical sensor, namely, fluorine-fluorine interaction. This demonstrates that a fluorine-fluorine interaction exists between the fluorine atoms in the electrode material F-COF / MWCNTs-NH2 and the fluorine atoms on PFOA, achieving specific adsorption of PFOA. Therefore, this specific adsorption effectively enables the quantitative detection of PFOA using electrochemical methods, solving the technical problem in existing technologies where the lack of electrochemical activity of PFOA prevents its quantitative analysis using electrochemical methods.

[0045] In summary, this method directly observed the shift in the CF bond binding energy in the composite material after PFOA adsorption through XPS analysis, confirming at the electronic level that a specific fluorine-fluorine interaction occurred between F-COF / MWCNTs-NH2 and PFOA.

[0046] Through DPV comparison experiments, it was found that the oxidation peak current change value of the electrochemical sensor for OA, a structurally similar but fluorine-free substance, was significantly lower than that for PFOA. This ruled out the dominant role of other forces and strongly proved that the selective capture and enrichment of PFOA molecules is achieved through a specific fluorine-fluorine interaction between the perfluoroalkyl chain of PFOA and the fluorinated surface of the working electrode of the electrochemical sensor.

[0047] (4) Electrochemical performance of different working electrodes. Four different working electrodes were prepared. The first group of working electrodes was a glassy carbon electrode (GCE) without any modification. The second group of working electrodes was a glassy carbon electrode modified with F-COF. The third group of working electrodes was a glassy carbon electrode modified with F-COF / MWCNTs-NH2. The fourth group of working electrodes was a glassy carbon electrode modified with MWCNTs-NH2.

[0048] Four sets of electrochemical sensors were constructed using the four sets of working electrodes described above. All aspects of the four electrochemical sensors were kept identical except for the working electrodes; for example, a saturated calomel electrode was used as the reference electrode, and a platinum electrode was used as the counter electrode to construct a three-electrode system. The performance of the four electrochemical sensors was evaluated using four different working electrodes. The specific procedure is as follows: Cyclic voltammetry was used, placing all four working electrodes in a 5.0 mL solution of 0.1 KCl in 5 mM potassium ferricyanide and voltammetrically increasing the voltage by 100 mV·s. -1 The scanning speed was adjusted to a scanning potential range of -0.2V to 0.6V, resulting in Figure 7. Figure 7 shows the current-potential curves of different working electrodes in a 5mM potassium ferricyanide solution containing 0.1M KCl. As shown in Figure 7, the electrochemical sensor constructed with the first set of working electrodes exhibits a pair of distinct redox peaks. The redox peak of the electrochemical sensor constructed with the second set of working electrodes is slightly smaller than that of the first set, mainly due to the relatively poor conductivity of F-COF. The redox peak of the electrochemical sensor constructed with the third set of working electrodes is significantly higher than that of the first and second working electrodes, indicating that MWCNTs-NH2 modification can effectively improve the conductivity of the working electrodes. On the other hand, the peak potential (E) of the electrochemical sensor constructed with the third set of working electrodes... pThe peak potentials of the electrochemical sensors constructed with the first and fourth working electrodes were significantly lower than those of the first group, which is attributed to the increased electron transfer kinetics due to the addition of F-COF. However, the electrochemical sensor constructed with the F-COF / MWCNTs-NH2 working electrode group showed a significant increase in peak current and a significant decrease in peak potential, indicating that the working electrode formed by modifying the glassy carbon electrode with F-COF / MWCNTs-NH2 material exhibits increased electrocatalytic activity.

[0049] (5) Parameter optimization experiment In this scheme, the researchers also conducted the following studies on the mass ratio of F-COF and MWCNTs-NH2 in the electrode material and the volume of F-COF / MWCNTs-NH2 dispersion added to GCE.

[0050] (5.1) Optimization of the mass ratio of F-COF and MWCNTs-NH2: The effect of the mass ratio of F-COF and MWCNTs-NH2 on the electrochemical response of PFOA was studied using differential pulse voltammetry (DPV). The specific operation in the study process is as follows: Five groups of working electrodes were constructed. The first group of working electrodes was obtained by adding 1 mg of F-COF and 3 mg of MWCNTs-NH2 to 4 mL of DMF and ultrasonically mixing for 30 min to obtain an F-COF / MWCNTs-NH2 dispersion. 10 μL of the F-COF / MWCNTs-NH2 dispersion was accurately measured and dropped onto the surface of the pretreated glassy carbon electrode, and dried at 40 °C to obtain the F-COF / MWCNTs-NH2 modified glassy carbon electrode, which is the first group of working electrodes.

[0051] The processing method for the second group of working electrodes is the same as that for the first group of working electrodes. The difference is that the mass of F-COF in the second group of working electrodes is 1 mg, the mass of MWCNTs-NH2 is 2 mg, and the volume of DMF is 3 mL.

[0052] The processing method for the third group of working electrodes is the same as that for the first group of working electrodes. The difference is that the mass of F-COF in the third group of working electrodes is 1 mg, the mass of MWCNTs-NH2 is 1 mg, and the volume of DMF is 2 mL.

[0053] The processing method for the fourth group of working electrodes is the same as that for the first group of working electrodes. The difference is that the mass of F-COF in the fourth group of working electrodes is 2 mg, the mass of MWCNTs-NH2 is 1 mg, and the volume of DMF is 3 mL.

[0054] The processing method for the fifth group of working electrodes is the same as that for the first group of working electrodes. The difference is that the mass of F-COF in the fifth group of working electrodes is 3 mg, the mass of MWCNTs-NH2 is 1 mg, and the volume of DMF is 4 mL.

[0055] Electrochemical sensors were constructed using the five sets of working electrodes described above, resulting in five sets of electrochemical sensors that differed only in their working electrodes. The working electrodes of the five sensors were placed in 5.0 mL of a 1 mM potassium ferricyanide solution containing 0.1 mM KCl and 1 nMP FOA, and then subjected to a pulse at 100 mV•s. -1 The above sensors were studied using a scanning speed of -0.1V to 0.5V, with an amplitude of 0.05V, a pulse width of 0.05s, and a pulse period of 0.5s. The oxidation peak current changes (∆I) of the five electrochemical sensors were recorded. pa The data obtained are shown in Figure 8. Figure 8 shows that the oxidation peak current variation is largest when the mass ratio of F-COF to MWCNTs-NH2 is 1:2. Excessive F-COF can affect the conductivity of the electrode material; excessive MWCNTs-NH2 may reduce the number of fluorination sites on the working electrode surface. Therefore, in the actual preparation of electrode materials, a mass ratio of F-COF to MWCNTs-NH2 of 1:2 can be selected as an optimal parameter.

[0056] (5.2) Optimization of the parameter of the volume of F-COF / MWCNTs-NH2 dispersion added to the glassy carbon electrode: The effect of the volume of F-COF / MWCNTs-NH2 dispersion added to the glassy carbon electrode on the electrochemical response of PFOA was studied using the DPV method. The specific operation in the study process is as follows: Five identical electrochemical sensors were set up. 5 μL of F-COF / MWCNTs-NH2 dispersion with a concentration of 1 mg / mL was dropped onto the pretreated glassy carbon electrode surface of the first electrochemical sensor and dried at 40 °C.

[0057] The second set of electrochemical sensors was constructed in the same way as the first set of electrochemical sensors, except that the volume of the F-COF / MWCNTs-NH2 dispersion dropped onto the glassy carbon electrode surface of the second set of electrochemical sensors was 7 μL.

[0058] The construction method of the third group of electrochemical sensors is the same as that of the first group of electrochemical sensors. The difference is that the volume of F-COF / MWCNTs-NH2 dispersion drop-coated on the glassy carbon electrode surface of the third group of electrochemical sensors is 10 μL.

[0059] The construction method of the fourth group of electrochemical sensors is the same as that of the first group of electrochemical sensors. The difference is that the volume of F-COF / MWCNTs-NH2 dispersion drop-coated on the glassy carbon electrode surface of the fourth group of electrochemical sensors is 13 μL.

[0060] The fifth group of electrochemical sensors was constructed in the same way as the first group of electrochemical sensors, except that the volume of the F-COF / MWCNTs-NH2 dispersion dropped onto the glassy carbon electrode surface of the fifth group of electrochemical sensors was 15 μL.

[0061] The working electrodes of the five electrochemical sensors were placed in 5.0 mL of 1 mM potassium ferricyanide solution containing 0.1 M KCl and 1 nMP FOA, respectively, using the DPV method. The oxidation peak current change ΔI of the five electrochemical sensors was recorded. pa The data obtained is shown in Figure 9. Analysis of Figure 9 reveals that as the amount of F-COF / MWCNTs-NH2 dispersion added increases, the change in oxidation peak current of the electrochemical sensor first increases and then decreases. This is likely because as the loading of F-COF / MWCNTs-NH2 dispersion on the glassy carbon electrode increases, the amount of modified material on the glassy carbon electrode surface increases, significantly increasing the number of active sites available for PFOA binding, thus gradually increasing the change in oxidation peak current of the electrochemical sensor. However, when the loading of F-COF / MWCNTs-NH2 dispersion on the glassy carbon electrode exceeds 10 μL, the modified layer on the glassy carbon electrode surface becomes too thick, masking the active sites and resulting in a decrease in the oxidation peak current, thereby reducing its sensitivity. Therefore, in this scheme, the optimal loading amount of F-COF / MWCNTs-NH2 dispersion on the glassy carbon electrode is 10 μL.

[0062] (6) Repeatability Test To verify the repeatability of the electrochemical sensor constructed in this scheme, five independently manufactured F-COF / MWCNTs-NH2 modified glassy carbon electrodes were used as working electrodes. Each electrode was placed in a 5.0 mL solution of 1 mM potassium ferricyanide containing 0.1 MKCl and 1 nMPFOA for DPV measurement, and the results are shown in Figure 10. Analysis of Figure 10 shows that the ∆I corresponding to the five working electrodes... pa The relative standard deviation (RSD) was 2.42%. This indicates that the electrochemical sensor constructed by the F-COF / MWCNTs-NH2 modified electrode in this invention has good reproducibility.

[0063] Based on the electrochemical sensor constructed above, this scheme also provides an electrochemical detection method for PFOA, which uses the electrochemical sensor described above to quantitatively detect the concentration of PFOA. The electrochemical detection method for PFOA includes the following steps: (1) Constructing a quantitative relationship between PFOA concentration and oxidation peak current change value, that is, plotting the standard curve of PFOA. Construct an electrochemical sensor according to the above optimal parameters, and prepare a series of PFOA solutions with known concentration gradients. The electrochemical sensor constructed is used to detect PFOA solutions with different known concentrations. The detection method can be the DPV method, thereby obtaining multiple sets of oxidation peak current change values ​​corresponding to different known concentrations of PFOA. The specific results can be seen in Figure 11. Figure 11 is the DPV curve of PFOA at different known concentrations. By analyzing Figure 11, it can be seen that the electrochemical sensor constructed in this scheme can effectively respond well to PFOA with concentrations of 0.01nM~20nM, thus proving that the electrochemical sensor constructed in this scheme has high sensitivity and can effectively and sensitively detect PFOA. Furthermore, in this scheme, multiple sets of oxidation peak current changes corresponding to different known concentrations of PFOA were used to construct a standard curve plot between the oxidation peak current changes and the logarithm of the PFOA concentration, as shown in Figure 12. Figure 12 shows that the linear relationship between the oxidation peak current changes and the logarithm of the PFOA concentration is ∆I. pa =14.2566LogC-12.2177, R 2 =0.9985, and its limit of detection (LOD) is 0.002nM.

[0064] (2) Place the unknown concentration of PFOA in a 0.1M KCl potassium ferricyanide solution (i.e. electrolyte solution), and place the working electrode of the constructed electrochemical sensor in an electrolyte solution containing the unknown concentration of PFOA. The signal acquisition and processing unit in the electrochemical sensor outputs the concentration of PFOA based on the standard curve of PFOA, thereby achieving the purpose of quantitative detection of the concentration of PFOA using an electrochemical sensor.

[0065] The electrochemical detection method for PFOA described above solves the problem of the lack of electrochemical activity in existing technologies, enabling accurate and highly sensitive quantitative detection of PFOA. Furthermore, the electrochemical detection method offers high sensitivity, simple equipment and operation, and low cost, effectively addressing the technical challenges of existing liquid chromatography-mass spectrometry (LC-MS) methods, which require bulky equipment, time-consuming pretreatment, and high maintenance costs.

[0066] The basic principles, main features, and advantages of this invention have been described above. Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made without departing from the spirit and scope of the invention, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection claimed by this invention is defined by the appended claims and their equivalents.

Claims

1. An electrochemical sensor for detecting PFOA based on fluorine-fluorine interactions, comprising a counter electrode, a reference electrode, and a signal acquisition and processing unit; characterized in that, It also includes an electrolyte solution and a working electrode; the electrolyte solution is a potassium ferricyanide solution containing 0.1M KCl, and the working electrode is formed by coating the electrode material F-COF / MWCNTs-NH2 onto the electrode; when the working electrode is placed in an electrolyte solution containing PFOA, the fluorine atoms in the electrode material F-COF / MWCNTs-NH2 on the working electrode and the fluorine atoms on PFOA adsorb PFOA onto the surface of the working electrode based on fluorine-fluorine interactions, thereby realizing the quantitative detection of PFOA by changing the oxidation peak current value output by the signal acquisition and processing unit in the electrochemical sensor.

2. The electrochemical sensor for detecting PFOA based on fluorine-fluorine interactions as described in claim 1, characterized in that, The preparation method of the electrode material F-COF / MWCNTs-NH2 is as follows: MWCNTs-NH2 and F-COF are dispersed in DMF at a mass ratio of 1~3:3~1 and ultrasonicated. After ultrasonication, the materials are washed and dried sequentially to obtain the electrode material F-COF / MWCNTs-NH2. The fluorine atoms in the electrode material and the fluorine atoms on PFOA achieve specific adsorption of PFOA based on fluorine-fluorine interaction.

3. The electrochemical sensor for detecting PFOA based on fluorine-fluorine interactions as described in claim 2, characterized in that, The preparation process of F-COF is as follows: 1,3,5-tris(4-aminophenyl)benzene and tetrafluoroterephthalaldehyde are added to acetonitrile at a mass ratio of 17:14 and a volume ratio of tetrafluoroterephthalaldehyde of 5:7, and then ultrasonicated. Acetic acid at a volume ratio of 1:10 to acetonitrile is then slowly added, and ultrasonication is continued. After ultrasonication, the mixture is washed and dried sequentially to obtain F-COF.

4. The electrochemical sensor for detecting PFOA based on fluorine-fluorine interactions as described in claim 2, characterized in that, The preparation process of the aminated carbon nanotubes MWCNTs-NH2 is as follows: MWCNTs-COOH is dispersed in MES buffer at a weight ratio of 1:1 and sonicated. EDC-HCl and NHS at a mass ratio of 2:1 to MWCNTs-COOH and a mass ratio of 36:25 to MWCNTs-COOH are added and stirred at room temperature. Polyethyleneimine at a concentration of 1% at a mass ratio of 1:1 to MWCNTs-COOH is then slowly added and stirred until all raw materials have fully reacted. The mixture is then collected by centrifugation, washed and dried to obtain MWCNTs-NH2.

5. The electrochemical sensor for detecting PFOA based on fluorine-fluorine interactions as described in claim 1, characterized in that, The detection limit of the electrochemical sensor for PFOA is 0.002 nM, and the concentration detection range of the electrochemical sensor for PFOA is 0.01 nM to 20 nM.

6. The electrochemical sensor for detecting PFOA based on fluorine-fluorine interactions as described in claim 1, characterized in that, The preparation process of the working electrode is as follows: polish the glassy carbon electrode with alumina powder and clean it, and then dry it in N2 stream; drop the F-COF / MWCNTs-NH2 dispersion onto the surface of the dried glassy carbon electrode and dry it at 40°C to obtain the working electrode.

7. The electrochemical sensor for detecting PFOA based on fluorine-fluorine interactions as described in claim 2, characterized in that, The ratio of the sum of the masses of MWCNTs-NH2 and F-COF to the volume of DMF is 1:

1.

8. An electrochemical detection method for PFOA, characterized in that, It uses an electrochemical sensor as described in any one of claims 1-7 to detect PFOA. The electrochemical detection method includes: placing the working electrode in an electrolyte solution containing PFOA and performing DPV scanning, measuring the change value of the oxidation peak current corresponding to different concentrations of PFOA, and establishing a quantitative relationship between the concentration of PFOA and the change value of the oxidation peak current; and determining the concentration of PFOA in an unknown sample based on the quantitative relationship.

9. The electrochemical detection method for PFOA as described in claim 8, characterized in that, The quantitative relationship between PFOA concentration and the change in oxidation peak current is as follows: ΔI pa =14.2566LogC-12.2177, where: ΔI pa denoted as the change in oxidation peak current, and C represents the concentration of PFOA.

10. The electrochemical detection method for PFOA as described in claim 8, characterized in that, The DPV scanning parameters for the electrochemical sensor when detecting PFOA are: potential range of -0.1V to 0.5V, amplitude of 0.05V, pulse period of 0.5s, and scan speed of 100mV·s. -1 .

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