Preparation method and application of PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor

Abstract

The invention discloses a preparation method of a PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor, which is characterized in that N-doped graphdiyne N-GDY and Ni-COF are creatively used for constructing a heterojunction system, and electron transmission is accelerated and the recombination rate of photon-generated carriers is reduced by regulating and controlling the interface structure of the heterojunction to be matched with an energy band and combining a conductive network of the GDY. The introduction of pyridine type nitrogen in N-GDY can form a p-type semiconductor characteristic, and an II-type heterojunction formed by N-GDY and n-type Ni-COF can effectively expand the light response range and inhibit carrier recombination. Perfluorooctyl mercaptan PFOS-SH is adopted as a functional modification layer, a thiol group at the tail end of the functional modification layer is coordinated with a metal center to form a stable monomolecular layer, and the detection specificity can be remarkably improved through the fluorine-fluorine interaction of a perfluorocarbon chain and PFOA. According to the technical scheme, the application boundary of the COFs and GDY heterojunction in the photoelectric sensing field can be expanded, and theoretical support and technical reserve are provided for solving the problem of perfluorooctanoic acid pollution abatement.

Description

Technical Field

[0001] The present invention relates to the field of photoelectrochemical sensing technology, and in particular to a preparation method and application of a PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor. Background Art

[0002] Per- and polyfluoroalkyl substances (PFASs), a class of emerging pollutants known for their persistence, bioaccumulation, and toxicity, have become a major focus of global environmental analytical chemistry for their environmental monitoring and precise detection. Perfluorooctanoic acid (PFOA), a prominent environmental persistent organic pollutant (POP), is widely present in wastewater, groundwater, drinking water, food, biological matrices, and industrial processes due to its excellent hydrophobicity and chemical stability. However, PFOA's poor environmental degradation and potential toxicity to the human endocrine, immune, and reproductive systems have made it a focus of global environmental and health attention. While government regulations in most countries have yet to be enacted into law, the Environmental Protection Agency (EPA) and many state agencies in the United States have established recommended levels for PFOA in water. Preliminary state guidelines limit PFOA concentrations to below 10 ppt (ng / L), while the EPA's non-regulatory guidelines recommend that PFOA concentrations in drinking water should not exceed 4 ppt. There is an urgent need to develop quantitative analytical techniques to detect relevant concentrations of PFOA in water. Currently, most PFOA detection methods rely on traditional instrumental analysis techniques. Although these methods have high sensitivity, they rely on expensive equipment, complex pre-treatment steps and long detection cycles, which limits their application in rapid on-site detection. Therefore, the development of a new detection technology that is efficient, sensitive and easy to operate is urgent.

[0003] Covalent organic framework materials (COFs) are a type of crystalline porous materials formed by light elements (C, H, O, N, etc.) connected by strong covalent bonds. Due to their designable pore structure, large surface area and excellent light absorption properties, they have attracted much attention in the fields of catalysis, sensing and energy. Among them, TAPT-Bpy-COF (formed by the condensation of 1,3,5-triaminophenyltriazine (TAPT) and 2,2'-bipyridine-5,5'-dicarboxaldehyde (Bpy)) exhibits excellent light capture ability and carrier transport performance due to its nitrogen-rich skeleton and π conjugated system, making it an ideal photoelectric active substrate material. Metal nickel-based TAPT-Bpy-COF is synthesized by introducing Ni 2+ Coordination centers can optimize carrier migration paths and enhance photocurrent response. However, the insufficient conductivity of single COFs materials and the rapid recombination of photogenerated electron-hole pairs still need to be improved through interface engineering strategies.

[0004] Nitrogen-doped graphyne (N-GDY) is a new type of two-dimensional carbon material composed of sp and sp 2 Composed of hybrid carbon atoms, N-GDY possesses a unique π-conjugated structure, high carrier mobility, and a wide spectral response range. Its high conductivity, abundant active sites, and narrow bandgap make it an ideal candidate for heterojunction construction. Studies have shown that combining N-GDY with Ni-TAPT-Bpy-COF can optimize interfacial charge transfer pathways through band matching, significantly improving the photoelectric response of the material. Currently, there are no reports on the construction of GDY / COF heterojunctions and their application in PEC sensing. The synergistic mechanism and specific recognition ability for perfluorooctanoic acid (PFOA) remain to be explored. The Ni deposited on the surface of the N-GDY / Ni-TAPT-Bpy-COF composite can be modified with organosulfur compounds to produce a self-assembled monolayer (SAM). Due to the strong Ni-S bond, a well-organized and dense monolayer and stable thin films can be formed. Perfluorooctyl mercaptan can be used to enhance the selective recognition of PFOA. Summary of the Invention

[0005] In view of the problem that most existing PFOA detection methods rely on expensive equipment, complex pretreatment steps and long detection cycles, which limits their application in on-site rapid detection, the present invention proposes a preparation method and application of a PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor.

[0006] The preparation method of the PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor comprises the following steps:

[0007] S1. Preparation of TAPT-Bpy-COF: Synthesis by solvothermal method;

[0008] S2. Preparation of Ni-TAPT-Bpy-COF: The prepared TAPT-Bpy-COF was dissolved in CHCl3 and NiCl2·6H2O was dissolved in THF. Then, the THF containing NiCl2·6H2O was added dropwise to the CHCl3 solution containing TAPT-Bpy-COF. The mixture was stirred at room temperature and then filtered to collect the solid. The uncoordinated Ni was removed by washing with ethanol three times. 2+ Finally, the Ni-TAPT-Bpy-COF material was obtained by drying in a vacuum oven;

[0009] S3. Preparation of nitrogen-doped graphyne (N-GDY): HEB and melamine were dissolved in pyridine and sonicated to form a homogeneous solution. The solution was then transferred to a quartz boat in a tubular furnace and heated to 600°C at a rate of 5°C / min under argon protection and maintained for 2 h. The solution was then naturally cooled and ground, soaked in HCl to remove unreacted impurities, washed with ultrapure water until neutral, and dried to obtain N-GDY black powder.

[0010] S4. Preparation of N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode: wash the ITO glass with acetone, ethanol and water in sequence; then immerse the ITO glass in an ethanol / NaOH solution to activate the surface and rinse with pure water; add Ni-TAPT-Bpy-COF and N-GDY powders to the ethanol solution, then vacuum degas the reagents and ultrasonically disperse them to obtain an N-GDY / Ni-TAPT-Bpy-COF dispersion; drop-coat the N-GDY / Ni-TAPT-Bpy-COF solution on the surface of the ITO glass electrode, and dry it under an infrared lamp to obtain an N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode;

[0011] S5. Preparation of PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor: Immerse the N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode in an ethanol solution containing PFDT and let it stand for 12 hours in the dark. After taking it out, rinse it with ethanol to remove the physically adsorbed molecules and blow dry it with nitrogen to obtain a PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor.

[0012] In a preferred embodiment of the present invention, the preparation method of TAPT-Bpy-COF in S1 is as follows: 0.15 mmol of Bpy-DCA and 0.1 mmol of TAPT are placed in a high-pressure glass reactor, dissolved in 1 mL of a v / v = 3 / 1 mixture of mesitylene / 1,4-dioxane, and ultrasonically treated for 20 minutes; then 0.1 mL of a 6 M aqueous acetic acid solution is added, and the mixture is subjected to three vacuum degassing cycles; finally, the mixture is placed in an oven at 120° C. under nitrogen protection for 3 days; after the hydrothermal reaction, the reaction is cooled to room temperature, the precipitate is filtered, washed with DMF, acetone and tetrahydrofuran, and finally dried in a vacuum oven at 100° C. for 12 hours to obtain yellow powder TAPT-Bpy-COF.

[0013] Furthermore, the preparation method of Ni-TAPT-Bpy-COF in S2 is as follows: 0.052 g of the prepared TAPT-Bpy-COF is dissolved in 2 mL of CHCl3, and 0.2 mmol of NiCl2·6H2O is dissolved in 1 mL of THF, and then the THF containing NiCl2·6H2O is added dropwise to the CHCl3 solution containing TAPT-Bpy-COF; the mixture is stirred at room temperature for 10 hours, and then filtered to collect the solid; the uncoordinated Ni is removed by washing with ethanol three times. 2+ Finally, the Ni-TAPT-Bpy-COF material was obtained by drying in a vacuum oven at 60°C for 12 h.

[0014] Furthermore, the preparation method of nitrogen-doped graphyne N-GDY in S3 is as follows: 0.1 mmol of HEB and 0.15 mmol of melamine are dissolved in 20 mL of pyridine, ultrasonically treated for 30 min to form a homogeneous solution; transferred to a tubular furnace quartz boat, heated to 600 °C at 5 °C / min under argon protection and maintained for 2 h; ground after natural cooling, soaked in 0.1 M HCl to remove unreacted impurities, washed with ultrapure water until neutral, and dried at 60 °C to obtain N-GDY black powder.

[0015] Furthermore, the preparation method of the N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode in S4 is as follows: washing the ITO glass with acetone, ethanol and water in sequence; then immersing the ITO glass in a 1M ethanol / NaOH solution with a v / v ratio of 1:1 for 15 minutes to activate the surface and then rinsing it with pure water; adding Ni-TAPT-Bpy-COF and N-GDY powders in a ratio of 2 mg:1 mg to 2 mL of ethanol solution, and then vacuum degassing the reagents and ultrasonically dispersing them for 10 minutes to obtain an N-GDY / Ni-TAPT-Bpy-COF dispersion; dropping 50 μL of the N-GDY / Ni-TAPT-Bpy-COF solution on the surface of the ITO glass electrode, and drying under an infrared lamp to obtain an N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode;

[0016] Furthermore, the preparation method of the PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor in S5 is as follows: immersing the N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode in an ethanol solution containing 1 mM PFDT and allowing it to stand for 12 hours in the dark; after taking it out, rinsing it with ethanol to remove the physically adsorbed molecules, and blowing it dry with nitrogen to obtain the PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor.

[0017] The PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor prepared by the above method is used for trace monitoring of PFOA in wastewater, groundwater, drinking water, food, biological matrices and industrial production.

[0018] The implementation of the embodiments of the present invention has the following beneficial effects:

[0019] The present invention innovatively constructs a heterojunction system by combining nitrogen-doped graphene (N-GDY) with Ni-COF. By regulating the interface structure and energy band matching of the heterojunction and combining the conductive network of GDY, electron transport is accelerated and the recombination rate of photogenerated carriers is reduced. The introduction of pyridinic nitrogen in N-GDY can form p-type semiconductor characteristics, and the type II heterojunction formed with n-type Ni-COF can effectively expand the light response range and inhibit carrier recombination. Perfluorooctylthiol (PFOS-SH) is used as a functionalized modification layer, and its terminal thiol group coordinates with the metal center to form a stable monolayer, while the fluorine-fluorine interaction between the perfluorocarbon chain and PFOA can significantly improve the detection specificity. The present invention provides a rapid and highly sensitive PFOA photoelectrochemical detection platform, providing a new method for monitoring trace persistent pollutants in the environment.

[0020] The technical solution of the present invention not only helps to expand the application boundaries of COFs and GDY heterojunctions in the field of photoelectric sensing, but also provides theoretical support and technical reserves for solving the problem of perfluorooctanoic acid pollution control.

[0021] The present invention successfully developed a nickel-centered TAPT-Bpy-COF and nitrogen-doped graphene (N-GDY) heterojunction composite material, and further optimized the sensor performance through the self-assembly strategy of perfluorooctyl mercaptan (PFOS-SH). Based on the self-assembly modification strategy of perfluorooctyl mercaptan, a biomimetic hydrophobic recognition layer was constructed on the heterojunction surface. FT-IR and contact angle tests showed that the long-chain perfluorinated structure of PFOS-SH was directionally anchored on the material surface through thiol-metal bonds, forming a dense hydrophobic microenvironment, achieving efficient and selective capture of the perfluorinated chains in the PFOA molecules. At the same time, the van der Waals force and fluorine-fluorine interaction mechanism between PFOA and the modified layer provide a theoretical basis for specific recognition. The present invention provides theoretical guidance and technical examples for the design of highly selective photoelectrochemical sensors, and at the same time provides a reliable analytical tool for the prevention and control of perfluorinated compound pollution and risk assessment, which has important scientific significance and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 Schematic diagram of the construction of PFOAPEC sensor based on N-GDY / Ni-TAPT-Bpy-COF heterojunction;

[0024] Figure 2 SEM images (A, B) of TAPT-Bpy-COF and Ni-TAPT-Bpy-COF and TEM images (C, D) of TAPT-Bpy-COF; EDS mapping of Ni-TAPT-Bpy-COF (including C element, O element, N element, and Ni element);

[0025] Figure 3 PXRD pattern (A), 13C CPMAS NMR pattern (B), FT-IR pattern (C), and TGA pattern (D) of TAPT-Bpy-COF and Ni-TAPT-Bpy-COF;

[0026] Figure 4 The full XPS spectra of TAPT-Bpy-COF and Ni-TAPT-Bpy-COF;

[0027] Figure 5 Zeta sizer potential diagrams of TAPT-Bpy-COF and N-GDY / Ni-TAPT-Bpy-COF;

[0028] Figure 6 EIS graphs (A) and CV graphs (B) of bare electrode ITO, b. COF / ITO, c. Ni-COF / ITO, d. N-GDY / Ni-TAPT-Bpy-COF / ITO, e. N-GDY / Ni-TAPT-Bpy-COF-PFDT, and f. PFOA-N-GDY / Ni-TAPT-Bpy-COF-PFDT. CV graphs (C) and Ip-v1 / 2 fitting graphs (D) of COF at different scanning speeds.

[0029] Figure 7 DPV electrochemical response of N-GDY / Ni-TAPT-Bpy-COF (A) and the fitted Langmuir isotherm model (B); where af concentrations are: 0 nM (a), 0.5 nM (b), 1 nM (c), 5 nM (d), 10 nM (e), 25 nM (f);

[0030] Figure 8 Mott-Schottky curves (A), UV-visible diffuse reflectance spectra (B), and (αhν)1 / 2 vs Eg curves (C) of Ni-TAPT-Bpy-COF and N-GDY / Ni-TAPT-Bpy-COF;

[0031] Figure 9 Switching photocurrent diagram (A), LSV diagram (B), and OCP diagram (C) of (a) Bare ITO (b) COF, (c) Ni-COF, (d) N-GDY / Ni-TAPT-Bpy-COF, (e) N-GDY / Ni-TAPT-Bpy-COF-PFDT, and (f) PFOA-N-GDY / Ni-TAPT-Bpy-COF-PFDT at 5 mM DA concentration;

[0032] Figure 10 Optimization of N-GDY / Ni-COF under different analytical conditions: (A) Photocurrent intensity in different buffer solutions; (B) Dispersion solution addition amount; (C) N-GDY to COF ratio; (D) Electron pH; (E) Electron donor DA concentration; (F) PFOA adsorption time (error bars: n = 3);

[0033] Figure 11 The working curve (A) and standard curve (B) of PFOA-PECS (a.0M b.10 -10 M c.5×10 - 10 Md.10 -9 Me.5×10 -9 f.10 -8 Mg.5×10 -8 M h.10 -7 Mi.5×10 -7 M j.10 -6 M k.5×10 -6 1.10 -5 M);

[0034] Figure 12 This is the anti-interference diagram of PFOA-PECS. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] See Figure 1 , Figure 1 Schematic diagram of the construction of a PFOAPEC sensor based on an N-GDY / Ni-TAPT-Bpy-COF heterojunction. The preparation method of this PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor includes the following steps:

[0037] S1. Preparation of TAPT-Bpy-COF: 0.15 mmol of Bpy-DCA and 0.1 mmol of TAPT were placed in a high-pressure glass reactor, dissolved in 1 mL of a v / v = 3 / 1 mixture of mesitylene / 1,4-dioxane, and sonicated for 20 minutes; then 0.1 mL of a 6 M aqueous acetic acid solution was added, and the mixture was degassed in a vacuum oven three times; finally, the mixture was placed in a 120°C oven under nitrogen protection for 3 days; after the hydrothermal reaction, the reaction mixture was cooled to room temperature, the precipitate was filtered, washed with DMF, acetone, and tetrahydrofuran, and finally dried in a vacuum oven at 100°C for 12 hours to obtain yellow powdered TAPT-Bpy-COF.

[0038] S2. Preparation of Ni-TAPT-Bpy-COF: 0.052 g of the prepared TAPT-Bpy-COF was dissolved in 2 mL of CHCl3, and 0.2 mmol of NiCl2·6H2O was dissolved in 1 mL of THF. The THF containing NiCl2·6H2O was then added dropwise to the CHCl3 solution containing TAPT-Bpy-COF. The mixture was stirred at room temperature for 10 h, and then filtered to collect the solid. The uncoordinated Ni was removed by washing with ethanol three times. 2+ Finally, the Ni-TAPT-Bpy-COF material was obtained by drying in a vacuum oven at 60°C for 12 h.

[0039] S3. Preparation of nitrogen-doped graphyne N-GDY: 0.1 mmol of HEB and 0.15 mmol of melamine were dissolved in 20 mL of pyridine and sonicated for 30 min to form a homogeneous solution; the solution was transferred to a tubular furnace quartz boat and heated to 600°C at 5°C / min under argon protection and maintained for 2 h; the solution was naturally cooled and ground, and the unreacted impurities were removed by soaking in 0.1 M HCl, washed with ultrapure water until neutral, and dried at 60°C to obtain N-GDY black powder.

[0040] S4. Preparation of N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode: The ITO glass was washed with acetone, ethanol and water in sequence; the ITO glass was then immersed in a 1 M ethanol / NaOH solution with a v / v ratio of 1:1 for 15 min to activate the surface and then rinsed with pure water; Ni-TAPT-Bpy-COF and N-GDY powders were added to 2 mL of ethanol solution in a ratio of 2 mg:1 mg, and the reagents were then vacuum degassed and ultrasonically dispersed for 10 min to obtain an N-GDY / Ni-TAPT-Bpy-COF dispersion; 50 μL of N-GDY / Ni-TAPT-Bpy-COF solution was drop-coated on the surface of the ITO glass electrode, and after drying under an infrared lamp, an N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode was obtained; in addition, for comparison, Ni-TAPT-Bpy-COF / ITO and TAPT-Bpy-COF / ITO modified electrodes were prepared by the same method.

[0041] S5. Preparation of PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor: Immerse the N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode in an ethanol solution containing 1 mM PFDT and let it stand for 12 h in the dark. After taking it out, rinse it with ethanol to remove the physically adsorbed molecules and blow dry it with nitrogen to obtain the PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor.

[0042] Performance testing:

[0043] Characterization analysis:

[0044] To investigate the microstructure of TAPT-Bpy-COF and Ni-TAPT-Bpy-COF, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the samples. Figure 2 .like Figure 1As shown in A and B in the figure, the prepared pure phase TAPT-Bpy-COF and Ni-TAPT-Bpy-COF exhibit a regular two-dimensional layered stacking structure, with obvious honeycomb-like ordered pores visible on the surface. Figure C shows that TAPT-Bpy-COF has a long-range ordered honeycomb pore array. The submicrostructure of the material was further analyzed by high-resolution transmission electron microscopy (HRTEM). The Fourier transform (FFT) spectrum (inset) shows six-fold symmetrical diffraction spots, indicating that it has a two-dimensional layered lattice with AA stacking. The lattice spacing of 1.19 nm can be measured in the HRTEM image (Figure D), which corresponds to the interlayer π-π stacking distance, which is consistent with the calculation results of the XRD main peak (2θ=4.6°). This shows that the solvothermal method successfully constructed a highly crystalline COF skeleton. The surface scanning results of EDSMapping (Figure E) show that the C, N, O, and Ni elements are evenly distributed, which is consistent with the expected results, and also confirms that Ni 2+ It is anchored to the bipyridine site of COF through coordination.

[0045] See Figure 3 The crystal structures of TAPT-Bpy-COF and Ni-TAPT-Bpy-COF were determined by PXRD. A strong diffraction peak was observed at 2θ=3.5° (corresponding to the (100) crystal plane), indicating that it belongs to AA stacking. The secondary peaks 2θ=5.8° ((110) crystal plane) and 2θ=26.3° ((001) interlayer stacking) further verified the successful synthesis of COF. In order to confirm the maintenance of COF crystallinity during the introduction of metal ions, the PXRD patterns were compared and it was found that Ni-TAPT-Bpy-COF retained all the main diffraction peaks during the entire transformation process. However, the crystal structure underwent subtle intensity changes, and the peak intensity was significantly reduced. It is speculated that the introduction of Ni may cause partial π-π stacking distortion.

[0046] In order to clarify the chemical bonding and coordination environment of TAPT-Bpy-COF and Ni-TAPT-Bpy-COF, 13 The two materials were characterized by C CPMA S NMR. As shown in the figure, the characteristic peak at 150 ppm is attributed to the sp 2Hybridized carbon atoms confirm that TAPT and Bpy (monomers successfully form a covalent skeleton through Schiff base condensation reaction. The aromatic carbon region (110-150ppm) shows multiple splitting peaks: the strong signals at 122.7ppm and 135ppm correspond to the pyridine ring carbon atoms that do not participate in the condensation in the bipyridine unit; the peak at 141.9ppm can be assigned to the C-N bond carbon atom connected to the amino group in the triazine ring. After the introduction of Ni (II) (Figure B), the electronic environment of the bipyridine unit changes significantly: the C = N peak shifts downfield to 151.7 ppm (Δ = +1.7 ppm), indicating that metal coordination leads to an increase in the polarizability of the imine bond. The bipyridine carbon peak splits into two peaks at 123.5 ppm and 137 ppm, consistent with Jahn-Teller distortion caused by bipyridine-Ni chelation. The newly emerged weak peak at 158 ​​ppm may be derived from the deshielding effect of the adjacent carbon ions induced by Ni→N coordination. By comparison, the triazine ring-related peak (141.7 ppm) does not undergo a significant shift, confirming that the metal center is selectively anchored to the bipyridine site rather than the triazine nitrogen atom.

[0047] At the same time, the infrared characterization material is shown in Figure C at 1570 cm -1 The strong peak at 3320cm is attributed to the stretching vibration of C=N bond. -1 The broad peak at 660 cm is the adsorbed water -OH, proving the microporous nature of COF materials. -1 The absorption band is attributed to the stretching vibration of Ni-N bond, which proves that Ni 2+ Coordinate with the N atom of Bpy (the electron cloud density decreases). The above results have confirmed that Ni 2+ Successfully linked to the COF structure. The thermal decomposition behavior of TAPT-Bpy-COF and its nickel coordination product was systematically studied using thermogravimetric analysis (TGA). As shown in Figure D, TAPT-Bpy-COF showed an obvious weight loss peak at 400°C, while Ni-TAPT-Bpy-COF showed obvious weight loss at 100°C. The core reason for the reduced thermal stability of Ni-TAPT-Bpy-COF may be the weakening of the skeleton bonding strength by metal coordination or the catalytic decomposition of Ni. The introduction of metal ions may destroy the conjugated structure or interlayer stacking of the original COF and reduce the crystallinity, which is consistent with the XRD test results, thereby weakening the thermal stability.

[0048] See Figure 4The elemental composition and bonding state of TAPT-Bpy-COF and Ni-TAPT-Bpy-COF were investigated using X-ray photoelectron spectroscopy (XPS). As shown in the figure, the full spectrum of the materials shows the coexistence of C, N, and O from TAPT-Bpy-COF and Ni-TAPT-Bpy-COF. The introduction of Ni adds characteristic Ni 2p peaks (855.1 eV and 873 eV) to the full spectrum, indicating strong coordination between the metal center and the COF ligands.

[0049] Zeta potential analysis of N-GDY and Ni-TAPT-Bpy-COF heterojunction:

[0050] To explore the electrostatic interaction mechanism of the self-assembly of N-GDY and Ni-TAPT-Bpy-COF heterojunction, the Zeta potential of Ni-TAPT-Bpy-COF and N-GDY / Ni-TAPT-Bpy-COF in anhydrous ethanol was further studied. Figure 5 The test results show that Ni-TAPT-Bpy-COF presents a positive Zeta potential value of +10.4mV, which is closely related to the Lewis acidity of the nickel center in its skeleton and the protonation tendency of the uncoordinated pyridine nitrogen atom. However, when nitrogen-doped graphyne is introduced, the surface potential of the composite system changes significantly under the same conditions, and the Zeta potential of the heterojunction drops to -13.3mV. The opposite surface potential indicates the existence of electrostatic attraction in the heterojunction, and this complementary surface charge distribution provides a driving force for the self-assembly of the heterojunction. The surface charge stability is improved after the heterojunction is formed. This feature is conducive to the directional coordination of the thiol group and the metal center in the subsequent perfluorooctane thiol (PFOS) modification process, laying the foundation for the construction of a highly sensitive PFOA sensor.

[0051] Electrochemical characterization:

[0052] The conductive properties of photoactive materials are a key factor influencing the photocurrent response of the working electrode in PEC sensors. Improving conductivity helps accelerate the migration of photogenerated carriers to the electrode-electrolyte interface, thereby establishing an efficient photocurrent pathway and reducing the probability of carrier recombination. This study used a 5 mM ferricyanide probe to electrochemically characterize different modified electrodes (bare ITO, COF / ITO, Ni-COF / ITO, and N-GDY / Ni-COF composite systems).

[0053] See Figure 6Based on EIS spectra analysis (Figure A), the charge transfer resistance (Rct) can be quantitatively characterized by the diameter of the semicircle in the Nyquist plot. Experimental data show that the N-GDY / Ni-COF composite electrode exhibits significantly lower impedance than bare ITO (curve d vs. a), which is attributed to the π-π stacking structure of the two-dimensional N-GDY and COF, which constructs a three-dimensional conductive network. The addition of Ni may optimize interfacial charge transfer, further reducing the impedance. The high conductivity of N-GDY significantly reduces the impedance, indicating that the heterojunction effectively improves the charge transfer efficiency. The introduction of PFDT shows a slight increase in Rct (curve e), which may be due to the significant influence of PFDT modification on the interfacial charge transfer behavior of the heterojunction. PFDT covers the heterojunction surface in the form of a self-assembled monolayer, forming a hydrophobic and electrochemically inert interfacial layer. After PFOA adsorption (curve f), the specific binding of the target in the pores of the material hinders the charge transfer path, resulting in a significant increase in impedance.

[0054] The intensity change of the redox peak in the cyclic voltammetry curve shows a good correspondence with the impedance analysis results (Figure B). The N-GDY / Ni-COF modified electrode shows the highest peak current response (curve d), confirming its excellent charge transfer performance. The grafting of PFDT reduces the peak current intensity (curve e), while the peak current further decays after PFOA adsorption (curve f), which is consistent with the electron transport retardation mechanism revealed by the impedance spectrum. In order to quantitatively evaluate the specific surface area characteristics of the material, based on the Randles-Sevcik theoretical model, the linear relationship between the peak current and the square root of the scan rate was established by voltammetry tests at different scan rates (Figures C, D), where n = 1, D = 1×10 -5 cm 2 / s (Typical diffusion coefficient reference value), the concentration C corresponds to 1 mM solution, and the effective reaction area of ​​the N-GDY / Ni-COF electrode is calculated to be 1.61 cm 2 , an increase of 61% compared to the geometric area. This structural advantage not only enhances the light capture capability, but also effectively promotes the rapid migration of carriers by expanding the electrode / solution interface contact area, thereby optimizing the photoelectric conversion efficiency.

[0055] The detection performance of the electrochemical sensing system for perfluorooctanoic acid (PFOA) was systematically evaluated by differential pulse voltammetry. Figure 7The experiment used a three-electrode system, in which a glassy carbon electrode modified with a nanocomposite material served as the working electrode, a platinum wire served as the counter electrode, and an Ag / AgCl electrode served as the potential reference. The specific operation process included placing the modified electrode in a 5mM ferricyanide electrolyte with different PFOA concentrations (0-25nM), and performing a DPV scan after equilibration for 15 minutes under constant stirring conditions. It is worth noting that when the concentration gradient of the target substance increases, the oxidation peak current in the voltammetric curve shows a regular attenuation phenomenon. This change in the electrical signal is due to the specific binding of the molecular recognition sites on the surface of the composite material to PFOA: as more PFOA molecules occupy the recognition sites, the channels for the diffusion of free carriers in the solution to the electrode surface are blocked, resulting in a significant decrease in the electrochemical response signal. To verify the reproducibility of the experiment, three independent tests were performed under each concentration condition, and the data were statistically processed and presented in the form of mean ± standard deviation. Based on the surface binding equilibrium theory, a Langmuir adsorption model was established to analyze the experimental data. The mathematical derivation process shows that there is the following quantitative relationship between the peak current change (ΔI) and the PFOS concentration: ΔI=(C0·K A ·[PFOS]) / (1+K A [PFOS]) was obtained by nonlinear fitting to obtain the adsorption equilibrium constant K A The value is (1.09±0.265)×10 12 cm 3 ·mol -1 This parameter confirms that the composite sensing material has nanomolar-level efficient capture capability for PFOS molecules. The good fit of the binding isotherm shown in Figure B further validates the reliability of the established model and provides an important theoretical basis for subsequent sensor optimization.

[0056] Characterization of photoelectric properties of TAPT-Bpy-COF and N-GDY / Ni-TAPT-Bpy-COF:

[0057] This paper uses a multi-dimensional characterization method to systematically analyze the electrochemical behavior and band structure characteristics of covalent organic framework materials. Figure 8As shown in Figure A, through Mott-Schottky electrochemical impedance spectroscopy analysis, it was found that the COF-based material showed a typical positive slope response curve under the test conditions. This feature is consistent with the carrier transport mechanism of n-type semiconductors. Based on classical semiconductor theory, when the vertical axis intercept of the coordinate approaches zero, the Fermi level position of the material system is approximately equal to the flat band potential value. Calculated by linear extrapolation, the flat band potentials of metal Ni-COF and its composite system N-GDY / Ni-TAPT-Bpy-COF are -1.19eV and -1.37eV, respectively. According to the n-type semiconductor band theory, this flat band potential value can be equivalently regarded as the conduction band position. In the study of light absorption characteristics, ultraviolet-visible diffuse reflectance spectroscopy combined with the Tauc curve analysis method was used to construct (αhν) 1 / 2 -hν energy band transition model. Where h=6.63×10 -34 J·s is Planck's constant, ν is the incident light frequency, A is the material characteristic constant, and Eg represents the band gap width. By comparing the goodness of fit of different exponent n values, it was found that the best linear relationship was obtained when n=2, confirming that the material system belongs to an indirect gap semiconductor material. This band structure feature is conducive to achieving efficient photon capture and carrier separation. After linear epitaxial calculation, the band gap widths of metal Ni-COF and its composite system N-GDY / Ni-TAPT-Bpy-COF were determined to be 1.59eV and 1.48eV, respectively. Based on the basic principle of band engineering E VB =E CB +E g The valence band tops of the two materials were deduced to be 0.4 eV and 0.11 eV, respectively. Band structure analysis revealed that the reduced band gap of the composite significantly enhanced the separation kinetics of photogenerated carriers, providing a theoretical basis for optimizing subsequent photoelectrochemical performance. The resulting band structure model for COF-based materials revealed that the conduction band to valence band range of metallic Ni-COF is -1.19 to 0.4 eV, while that of the composite system extends to -1.37 to -0.11 eV.

[0058] In addition, by comparing and analyzing the photoelectric response characteristics of three material systems (TAPT-Bpy-COF, Ni-TAPT-Bpy-COF, N-GDY / Ni-TAPT-Bpy-COF) under no-bias conditions, the performance optimization mechanism of the composite material was revealed. Figure 9 , experimental data show that under the same test conditions, the photocurrent densities of the original COF and Ni-TAPT-Bpy-COF are 3.6μA / cm 2 and 6.7 μA / cm 2 , and the photoelectric response of the N-GDY / Ni-TAPT-Bpy-COF composite system was significantly improved to 10μA / cm 2, and showed better photoelectric signal stability. This performance leap is mainly attributed to the interface engineering strategy of the composite material, which effectively controls the carrier migration dynamics by optimizing the light capture efficiency and energy level matching characteristics. Experiments show (curve e) that when the composite system self-assembles perfluorooctyl mercaptan, the photocurrent density of the heterojunction drops to 5.6μA / cm 2 This concentration-dependent signal attenuation confirms that the insulating nature of PFDT causes it to form an electronic barrier at the heterojunction interface, hindering the migration of photogenerated electrons or holes, increasing the probability of charge recombination, and reducing the charge separation efficiency. After the target adsorption experiment (curve f), the photocurrent of the composite material was significantly reduced to 2.4μA / cm 2 , the PFOA concentration can be quantitatively detected based on the difference in photocurrent signals, and the results prove that the PFOA sensor has been successfully constructed. Through linear sweep voltammetry research (Figure B), it was found that the charge transfer ability of the composite material was significantly improved compared with the original COF, which is consistent with the photocurrent test results. The open circuit potential response analysis (Figure C) further revealed the mechanism of improvement in carrier separation efficiency: the N-GDY / Ni-TAPT-Bpy-COF composite system produced a more significant photovoltage change under light conditions, indicating that it has stronger carrier generation and separation capabilities. Time-resolved photovoltage kinetics tests show that the voltage decay rate of the composite material under dark conditions is lower than that of the COF system. Through the calculation of carrier recombination kinetics parameters, it can be seen that the voltage decay rate is inversely proportional to the lifetime of photogenerated carriers, and its photogenerated carrier lifetime is extended. This performance improvement stems from the regulation of the band structure at the heterojunction interface. Band bending tests show that the Fermi level of the composite material is lower than that of the COF itself. This energy level arrangement promotes the directional migration of photogenerated electrons through the Schottky barrier to the N-GDY layer. At the same time, holes are enriched in the Ni-TAPT-Bpy-COF layer. The resulting built-in electric field reduces the probability of carrier recombination, ultimately achieving a significant improvement in photoelectric conversion efficiency. This research provides an important theoretical basis for the interface engineering design of new photoelectric sensors.

[0059] Optimization of analytical conditions:

[0060] The present invention establishes an optimal sensing system for PFOA detection through multi-parameter control. The experiment focuses on key influencing factors such as the type of buffer selected, the ratio of composite materials, the amount of dispersion added, the pH value of the buffer, and the adsorption time of the target. Figure 10. In the buffer screening, acetic acid-sodium acetate showed better photogenerated electron transport performance than PBS, citric acid-sodium citrate, and Tris-HCl, and its photoresponse signal intensity was improved compared with the second best option. In terms of nanocomposite interface construction, by regulating the synergistic ratio of nitrogen-doped graphyne and covalent organic framework (COF), it was found that when the mass ratio reached 1:2, the carrier separation efficiency of the heterojunction structure was the highest, and the corresponding photocurrent response was improved. In the optimization of the sensing interface construction parameters, by regulating the coating amount of the composite material dispersion, it was found that when the drop amount reached 50μL, a uniform and dense nanocomposite film was formed on the electrode surface, and the photocurrent response reached a platform value at this time. The optimization of molecular recognition conditions showed that in the acetic acid-sodium acetate buffer system at pH 4.4, the specific binding efficiency of PFOA molecules to the recognition site was the highest, and the photocurrent change value at this time was higher than the average of other pH conditions. The electron donor concentration gradient experiment showed that 5mM DA solution can achieve the best electron transfer efficiency, and too high a concentration would hinder mass transfer due to the increase in solution viscosity. Kinetic studies have shown that when the adsorption time reaches 20 minutes, the sensor surface reaches dynamic adsorption equilibrium, and further extension of the reaction time only increases the signal intensity by less than 3%.

[0061] Based on these studies, the optimal detection conditions were determined to be: N-GDY / Ni-COF (1:2) composite system, 50 μL coating volume, 5 mM DA electron donor, pH 4.4 buffer, and 20 min adsorption time. This optimized solution improved sensor sensitivity compared to the initial conditions, laying the foundation for subsequent quantitative analysis studies.

[0062] Analytical performance of the sensor:

[0063] Under the optimized sensing parameters, the present invention evaluates the performance of the PFOA photoelectrochemical sensor (PFOA-PECS) constructed by the N-GDY / Ni-COF composite system. Figure 11 As shown, the target concentration ranged from 0.1 nM to 1 × 10 4 When the concentration changes in the nM range, the system photocurrent response shows a concentration-dependent decay. The calibration curve (Figure B) established after blank signal correction shows that the linear characteristic changes to ΔI = 0.9649lg (C) + 1.3583 (R 2=0.996). The sensor's detection limit was calculated to be 3.1 nM using the signal-to-noise ratio method (3σ / S, n=11). To verify the device's reliability, repeatability and reproducibility were evaluated: six consecutive tests of the same sensor showed an RSD of 2.3%, while five independently prepared sensors tested in parallel had an RSD of ≤8.6%, confirming the system's excellent operational stability and reproducibility. Compared to reported detection methods, as shown in Table 1, this sensor exhibits a wider linear response range and competitive detection sensitivity, attributed to the unique mass transfer kinetics and signal amplification mechanism of the N-GDY / Ni-COF composite interface.

[0064] Table 1 Comparison of the developed method with other methods for the determination of PFOA

[0065]

[0066] Cross-interference study:

[0067] In the practical application of sensing systems, anti-interference properties are the key indicators that determine the reliability of detection. This paper systematically evaluates the selective response characteristics of PFOA-PECS using a gradient concentration method, selecting five typical derivatives of the perfluorinated compound family (perfluorooctane sulfonic acid - PFOS, pentafluoropropionic acid - PFPRA, heptafluorobutyric acid - PFBA, perfluoropentanoic acid - PFPEA, perfluorohexanoic acid - PFHXA,) and three common cations (Ca 2+ 、Na + Mg 2+ ) as the interference object. In the experimental design, the concentration of the water environment matrix interference was set to 100 times the baseline concentration, and other interferences were tested under extreme conditions using 1000 times excess concentration. Figure 12 As shown, despite the interference of structural similarity, the sensing system still maintains excellent selective recognition ability for PFOA. Experimental data show that the interference response signals of other perfluorocarboxylic acids and inorganic cations are all below the detection threshold, confirming the stable detection performance of the sensor in complex matrices.

[0068] Actual sample analysis:

[0069] Perfluorooctanoic acid (PFOA), as a typical persistent organic pollutant, is widely present in various aquatic systems. The present invention systematically evaluates its analytical efficiency in real environmental samples by constructing an electrochemical sensing platform (PFOA-PECS) based on N-GDY / Ni-COF composite materials. The experiment selected two typical water matrices, municipal water supply and atmospheric precipitation, and used the standard addition method for method validation. Please refer to Table 2. The data in the table show that the target substance presents a recovery efficiency of 82%-121.6% within the spiked concentration range, and the relative standard deviation between each matrix is ​​less than 12%. The key performance indicators confirm that the sensing system has good matrix tolerance and detection reliability, and can be effectively used for on-site rapid detection of trace PFOS in natural water bodies.

[0070] Table 2 PFOA detection in actual samples

[0071]

[0072] The present invention focuses on the construction of a new photoelectrochemical sensor and its application in the detection of perfluorooctanoic acid (PFOA). It has successfully developed a TAPT-Bpy-COF and nitrogen-doped graphene (N-GDY) heterojunction composite material centered on metal nickel, and further optimized the sensor performance through the self-assembly strategy of perfluorooctyl mercaptan (PFOS-SH). Based on the self-assembly modification strategy of perfluorooctyl mercaptan, a biomimetic hydrophobic recognition layer was constructed on the heterojunction surface. FT-IR and contact angle tests show that the long-chain perfluorinated structure of PFOS-SH is directionally anchored on the surface of the material through thiol-metal bonds, forming a dense hydrophobic microenvironment, achieving efficient and selective capture of the perfluorinated chains in the PFOA molecules. At the same time, the van der Waals force and fluorine-fluorine interaction mechanism between PFOA and the modified layer provide a theoretical basis for specific recognition. The present invention provides theoretical guidance and technical examples for the design of highly selective photoelectrochemical sensors, and at the same time provides a reliable analytical tool for the prevention and control of perfluorinated compound pollution and risk assessment, which has important scientific significance and application value.

[0073] The PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor prepared by this method is used for trace monitoring of PFOA in wastewater, groundwater, drinking water, food, biological matrices and industrial production.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor, characterized in that: The following steps are involved: S1. Preparation of TAPT-Bpy-COF: Synthesis by solvothermal method; S2. Preparation of Ni-TAPT-Bpy-COF: The prepared TAPT-Bpy-COF was dissolved in CHCl3 and NiCl2·6H2O was dissolved in THF. Then, the THF containing NiCl2·6H2O was added dropwise to the CHCl3 solution containing TAPT-Bpy-COF. The mixture was stirred at room temperature and then filtered to collect the solid. The uncoordinated Ni was removed by washing with ethanol three times. 2+ Finally, the Ni-TAPT-Bpy-COF material was obtained by drying in a vacuum oven; S3. Preparation of nitrogen-doped graphyne (N-GDY): HEB and melamine were dissolved in pyridine and sonicated to form a homogeneous solution. The solution was then transferred to a quartz boat in a tubular furnace and heated to 600°C at a rate of 5°C / min under argon protection and maintained for 2 h. The solution was then naturally cooled and ground, soaked in HCl to remove unreacted impurities, washed with ultrapure water until neutral, and dried to obtain N-GDY black powder. S4. Preparation of N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode: wash the ITO glass with acetone, ethanol and water in sequence; then immerse the ITO glass in an ethanol / NaOH solution to activate the surface and rinse with pure water; add Ni-TAPT-Bpy-COF and N-GDY powders to the ethanol solution, then vacuum degas the reagents and ultrasonically disperse them to obtain an N-GDY / Ni-TAPT-Bpy-COF dispersion; drop-coat the N-GDY / Ni-TAPT-Bpy-COF solution on the surface of the ITO glass electrode, and dry it under an infrared lamp to obtain an N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode; S5. Preparation of PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor: Immerse the N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode in an ethanol solution containing PFDT and let it stand for 12 hours in the dark. After taking it out, rinse it with ethanol to remove the physically adsorbed molecules and blow dry it with nitrogen to obtain a PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor.

2. The method for preparing the PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor according to claim 1, wherein: The preparation method of TAPT-Bpy-COF in S1 is specifically as follows: 0.15 mmol of Bpy-DCA and 0.1 mmol of TAPT are placed in a high-pressure glass reactor, dissolved in 1 mL of a v / v = 3 / 1 mixture of mesitylene / 1,4-dioxane, and ultrasonically treated for 20 minutes; then 0.1 mL of a 6M acetic acid aqueous solution is added, and the mixture is subjected to three vacuum degassing cycles; finally, the mixture is placed in an oven at 120°C under nitrogen protection for 3 days; after the hydrothermal reaction, the reaction is cooled to room temperature, the precipitate is filtered, washed with DMF, acetone and tetrahydrofuran, and finally dried in a vacuum oven at 100°C for 12 hours to obtain yellow powder TAPT-Bpy-COF.

3. The method for preparing the PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor according to claim 2, characterized in that: The preparation method of Ni-TAPT-Bpy-COF in S2 is as follows: 0.052 g of the prepared TAPT-Bpy-COF is dissolved in 2 mL of CHCl3, and 0.2 mmol of NiCl2·6H2O is dissolved in 1 mL of THF, and then the THF containing NiCl2·6H2O is added dropwise to the CHCl3 solution containing TAPT-Bpy-COF; the mixture is stirred at room temperature for 10 hours, and then the solid is filtered and collected; the uncoordinated Ni is removed by washing with ethanol three times. 2+ Finally, the Ni-TAPT-Bpy-COF material was obtained by drying in a vacuum oven at 60°C for 12 h.

4. The method for preparing the PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor according to claim 3, characterized in that: The preparation method of nitrogen-doped graphyne N-GDY in S3 is specifically as follows: 0.1 mmol of HEB and 0.15 mmol of melamine are dissolved in 20 mL of pyridine, and ultrasonically treated for 30 min to form a homogeneous solution; the solution is transferred to a tubular furnace quartz boat, and the temperature is increased to 600°C at 5°C / min under argon protection and maintained for 2 h; the solution is naturally cooled and then ground, and unreacted impurities are removed by soaking in 0.1 M HCl, washed with ultrapure water until neutral, and dried at 60°C to obtain N-GDY black powder.

5. The method for preparing the PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor according to claim 4, characterized in that: The preparation method of the N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode in S4 is specifically as follows: washing the ITO glass with acetone, ethanol and water in sequence; then immersing the ITO glass in a 1M ethanol / NaOH solution with v / v = 1:1 for 15 minutes to activate the surface and then rinsing it with pure water; adding Ni-TAPT-Bpy-COF and N-GDY powder in a ratio of 2 mg:1 mg to 2 mL of ethanol solution, and then vacuum degassing the reagents and ultrasonically dispersing them for 10 minutes to obtain an N-GDY / Ni-TAPT-Bpy-COF dispersion; 50 μL of the N-GDY / Ni-TAPT-Bpy-COF solution is drop-coated on the surface of the ITO glass electrode, and after drying under an infrared lamp, an N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode is obtained.

6. The method for preparing the PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor according to claim 5, characterized in that: The preparation method of the PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor in S5 is specifically as follows: immersing the N-GDY / Ni-TAPT-Bpy-COF / ITO modified electrode in an ethanol solution containing 1 mM PFDT and allowing it to stand for 12 hours in the dark; after taking it out, rinsing it with ethanol to remove the physically adsorbed molecules, and blowing it dry with nitrogen to obtain the PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor.

7. The method for preparing the PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor according to any one of claims 1 to 6, characterized in that: The prepared PFDT / N-GDY / Ni-TAPT-Bpy-COF sensor is used for trace monitoring of PFOA in wastewater, groundwater, drinking water, food, biological matrices and industrial production.

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