Preparation method and application of molecularly imprinted cathodic photoelectrochemical sensor based on CNQDs@CTP nanocomposite

Abstract

The application belongs to the technical fields of nanomaterials, photoelectrochemical sensing and analysis, and environmental monitoring, and relates to a preparation method of a molecular imprinting cathode photoelectrochemical sensor based on a CNQDs@CTP nanocomposite material and application thereof; the application first provides a preparation method of a nanocomposite material of in-situ synthesis of a covalent organic framework and graphite carbon nitride quantum dots, and a molecular imprinting cathode photoelectrochemical sensor is constructed based on the material combined with a molecular imprinting technology, and the sensor has good selectivity, ion anti-interference, reproducibility and long-term stability. ‑11 -5*10 ‑6 mol*L ‑1 , a detection limit is 5.50*10 ‑12 mol*L ‑1 ; and the design idea proposed in the application can be used for developing a sensing method for detecting other target objects, and has good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical fields of nanomaterials, photoelectrochemical sensing and analysis, and environmental monitoring, and particularly relates to preparation of photoelectric active nanocomposite CNQDs@CTP, construction of a molecular imprinting photoelectrochemical sensor, and application thereof in monitoring of agricultural water environment. BACKGROUND

[0002] Perfluorooctanoic acid (PFOA) is a kind of perfluorinated compound known as a permanent chemical, which has attracted great attention due to its unique chemical properties, wide range of uses and persistence in the environment. PFOA is widely present in surface water, groundwater, soil and atmosphere worldwide due to its extremely high chemical stability and persistence, and is difficult to degrade. This compound can be transmitted in the food chain through the biological accumulation effect, posing a potential threat to wildlife and human health, including endocrine disruption, reproductive disorders, immune system suppression and possible carcinogenicity, causing huge environmental and health problems. Therefore, it is necessary to develop precise and sensitive detection of PFOA.

[0003] Currently available PFOA detection methods include gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), liquid chromatography-tandem mass spectrometry (LC-MS / MS) and photoelectrochemical (PEC) detection methods; among them, the photoelectrochemical (PEC) detection method has the advantages of high sensitivity and good selectivity, and the characteristics of low cost, simple operation and easy miniaturization make it more promising in practical application. The key to photoelectrochemical sensing and analysis performance lies in, on the one hand, the detection signal electrical signal is derived from the absorption and conversion of light energy by the photosensitive material, therefore, the photosensitive material with high photoelectric activity and stable performance is the basis for detection; on the other hand, how to avoid the interference caused by complex components in the environment to realize the selective and specific response of the target PFOA is the key to complete the detection.

[0004] Based on this, the present application aims at the deficiencies of the prior art, and on the basis of preparing nanocomposite CNQDs@CTP with high photoelectric activity and stability, further combining the molecular imprinting technology (MIP) which is called "artificial antibody", finally realizing the sensitive detection of PFOA in actual samples. SUMMARY

[0005] The present application aims to provide a preparation method of a nanocomposite material (CNQDs@CTP) of in-situ synthesized covalent organic framework (CTP) and graphite carbon nitride quantum dots (CNQDs), and to construct a photoelectrochemical sensor based on the material combined with molecular imprinting technology, and to apply it to the detection of PFOA content in water.

[0006] To achieve the above technical purposes, the present application adopts the following technical solutions:

[0007] One kind is prepared by the following steps: a preparation method of CNQDs@CTP nanocomposite, taking tri-sodium citrate dihydrate and urea as the raw materials for synthesizing CNQDs, taking the mixed solution of p-phenylenediamine (Pa) and tetraformylphenyl porphyrin (TFPP) as the precursor for synthesizing CTP, adding the synthesized CNQDs into the precursor solution of CTP, and preparing CNQDs@CTP nanocomposite by stirring at room temperature.

[0008] (1) Preparation of CNQDs:

[0009] First, sodium citrate dihydrate (Na3C6H5O7·2H2O) and urea (CH4N2O) are added to water, mixed and dissolved, then transferred to a high-pressure reaction kettle for reaction, and after cooling to room temperature, the reaction solution is dialyzed, freeze-dried to obtain a blue graphite carbon nitride quantum dot solid, which is dissolved in water to obtain a graphite carbon nitride quantum dot solution, denoted as CNQDs solution.

[0010] (2) Preparation of CNQDs@CTP:

[0011] P-phenylenediamine (Pa) is added to acetonitrile (ACN) to obtain a p-phenylenediamine solution; tetraformylphenyl porphyrin (TFPP) is added to dichloromethane (CH2Cl2) to obtain a tetraformylphenyl porphyrin solution; iron trichloride hexahydrate (FeCl3·6H2O) is mixed with acetonitrile (ACN) to obtain a FeCl3 solution.

[0012] First, the p-phenylenediamine solution and the tetraformylphenyl porphyrin solution are mixed, then the FeCl3 solution, CH3COOH and the CNQDs solution prepared in step (1) are added, and after ultrasonic mixing, the reaction is stirred at room temperature, and after centrifugation, washing, drying and grinding, a black-brown powder solid is obtained, denoted as CNQDs@CTP.

[0013] Preferably, in step (1), the amount ratio of sodium citrate dihydrate, urea and water is 1.63g:2g:100mL; the reaction temperature is 180℃, the reaction time is 3h; the dialysis uses a 1000D dialysis bag, and the dialysis time is 6h; the concentration of the graphite carbon nitride quantum dot solution is 100mg / mL.

[0014] Preferably, in step (2), the amount ratio of p-phenylenediamine, acetonitrile, tetraformylphenyl porphyrin, dichloromethane, iron trichloride hexahydrate, acetonitrile, CH3COOH solution and CNQDs solution is 5mg:10mL:5mg:10mL:16.67mg:0.2mL:5mL:15μL;

[0015] The stirring speed of the reaction under the room temperature condition is 350-370 rpm, and the reaction time is 6 h; the centrifugal condition is set to 10000 rpm for 5 min; the washing uses ethanol for washing 3 times; and the drying temperature is 60℃, and the time is 6-8 h.

[0016] II. The method for constructing the molecular imprinting cathode photoelectrochemical sensor based on the CNQDs@CTP nanocomposite material, and the steps are as follows:

[0017] (1) Preparation of the molecular imprinting polymerization solution:

[0018] PFOA and acrylamide (MA) are added in methanol, the obtained mixed solution is oscillated and uniformly mixed at a certain temperature, nitrogen gas (N2) is passed through the mixed solution for a period of time, dimethyl glycol methacrylate (EGDMA) is added into the solution, nitrogen gas is continuously passed through for a period of time, initiator azobisisobutyronitrile (AIBN) is then added, and after ultrasonic dissolution, the molecular imprinting polymerization solution is obtained, which is stored in the dark;

[0019] (2) First, the indium tin oxide (ITO) conductive glass is pretreated to obtain the pretreated ITO conductive glass; then the CNQDs@CTP is dissolved in water to obtain a CNQDs@CTP dispersion liquid; and the CNQDs@CTP dispersion liquid is added dropwise on the surface of the pretreated ITO conductive glass, which is dried at room temperature, and the dried product is marked as CNQDs@CTP / ITO;

[0020] (3) The molecular imprinting polymerization solution prepared in step (1) is added dropwise on the surface of the CNQDs@CTP / ITO obtained in step (2), and a molecular imprinting film is formed after thermal polymerization, that is, the CNQDs@CTP / ITO containing the molecular imprinting film is obtained; the CNQDs@CTP / ITO containing the molecular imprinting film is placed in an eluent for elution, and after elution, it is dried in the dark at room temperature, and a molecular imprinting cathode photoelectrochemical sensor is obtained, which is marked as MIP / CNQDs@CTP / ITO.

[0021] Preferably, in step (1), the amount ratio of PFOA, acrylamide (MA), methanol, dimethyl glycol methacrylate (EGDMA) and azobisisobutyronitrile (AIBN) is 24.9 mg:2.85 mg:2 mL:291 μL:82.1 mg; and the nitrogen gas passing time is 10-15 min.

[0022] Preferably, in step (2), the pre-treatment operation is: placing ITO in 1M NaOH and boiling for 20 min, then taking out the ITO and ultrasonic cleaning in ethanol and water in sequence, and drying after cleaning, thereby completing the pre-treatment step; wherein the size of the ITO conductive glass is 1cm*2cm; the concentration of the CNQDs@CTP dispersion liquid is 2mg / mL, and the amount of the CNQDs@CTP dispersion liquid added dropwise is 20μL.

[0023] Preferably, in step (3), the volume of the molecular imprinting solution added dropwise is 6-8μL, the heat polymerization temperature is 60℃, and the time is 5-10min; the eluent is a mixed solution of methanol and acetic acid in a volume ratio of 9:1, and the elution is accompanied by stirring at 150rpm, and the elution time is 30-40min.

[0024] III. The use of the CNQDs@CTP-based molecular imprinting cathode photoelectrochemical sensor for detecting perfluorooctanoic acid, the specific steps comprising:

[0025] S1, first prepare a PFOA standard solution, then immerse the MIP / CNQDs@CTP / ITO in the PFOA standard solution for incubation, take out the MIP / CNQDs@CTP / ITO electrode after incubation, and naturally dry to obtain the incubated MIP / CNQDs@CTP / ITO electrode.

[0026] Take the incubated MIP / CNQDs@CTP / ITO electrode as a working electrode, a saturated Ag / AgCl electrode as a reference electrode, and a platinum wire electrode as a counter electrode to perform electrochemical testing and detect PEC signals; based on the linear relationship between the response value (I) of the PEC signals and the logarithmic value (lgC) of the PFOA standard solution concentration, a standard curve is constructed;

[0027] S2: according to the same method as S1, except that the test solution is replaced by the PFOA standard solution; finally, the response value of the PEC signal is detected, and the response value of the PEC signal is substituted into the standard curve in S1, thereby realizing the concentration detection of PFOA in the test solution.

[0028] Preferably, in step S1, the concentration of the PFOA standard solution is 5.0*10 -12 ~1.0*10 -5 mol·L -1 ; the incubation time is 20-30min; and the electrochemical testing is performed by using CHI 660E to record and detect PEC signals, wherein the PEC signals are detected in 0.1mol·L -1 PBS (pH=7.0).

[0029] The beneficial effects of the present application are:

[0030] (1) The application prepares CNQDs@CTP nanocomposites by an in-situ synthesis method, and the photoelectric performance of the obtained composite is improved compared with CNQDs and CTP, and the generated cathode photocurrent signal has good anti-interference ability.

[0031] (2) The application combines the molecular imprinting technology with the photoelectrochemical analysis method, which improves the selectivity of the sensor on the one hand, and the formation of the thin film protects the electrode interface, so that the generated photoelectric signal is more stable.

[0032] (3) The application uses a thermal polymerization method to prepare a molecular imprinting thin film; the sensor is simple to construct, and the signal response is fast.

[0033] (4) In the detection process, no external bias voltage is applied, and no redox substance is added in the PBS solution, which avoids the interference of multiple factors on the photoelectric signal.

[0034] (5) The photoelectrochemical sensor constructed by the application is used for the detection of PFOA, and has high sensitivity, good stability and wide linear range, and the linear range is 1x10 -11 -5x10 -6 mol·L -1 , and the detection limit is 5.50x10 -12 mol·L -1 .

[0035] (6) The photoelectrochemical sensor constructed by the application has good selectivity, ion anti-interference, reproducibility and long-term stability.

[0036] (7) The sensor constructed by the application can be used for actual sample detection, and the design idea proposed in the application can be used for developing a sensing method for detecting other target substances, and has good application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is a schematic diagram of the construction and detection process of the sensor in the application, wherein A is the preparation process of CNQDs, B is the preparation process of CNQDs@CTP, and C is the construction process of the sensor;

[0038] Figure 2 It is a mechanism diagram for PFOA detection in the application, wherein the left drawing is an electron transfer path, and the right drawing is a photocurrent response schematic diagram;

[0039] Figure 3(a) is a transmission electron microscope (TEM) image of CNQDs; (b) is a scanning electron microscope (SEM) image of CTP; (c) is a scanning electron microscope (SEM) image of CNQDs@CTP; (d) is a high-resolution transmission electron microscope (HRTEM) image of CNQDs; (e) is a transmission electron microscope (TEM) image of CTP; (f) is a transmission electron microscope (TEM) image of CNQDs@CTP.

[0040] Figure 4 To ensure the stability of continuous optical scanning of the working electrode (the incubated MIP / CNQDs@CTP / ITO electrode) in this invention, the concentration of PFOA is 1 nM;

[0041] Figure 5 In the table, (a) represents the PEC response corresponding to different concentrations of PFOA; and (b) represents the linear relationship between the logarithm of different concentrations of PFOA and the change in their PEC response.

[0042] Figure 6 (a) shows the selectivity of the molecularly imprinted photoelectrochemical sensor for substances similar to the target analyte (octanoic acid (S1), sodium fluoride (S2), sodium trifluoroacetate (S3), pentafluoropropionic acid (S4), perfluoroheptanoic acid (S5)). 5) (a) Perfluorononanoic acid (S6), perfluorooctyl sulfonic acid (S7), MIX+ perfluorooctanoic acid (S8), perfluorooctanoic acid (S9); (b) Ion interference resistance of the molecularly imprinted photoelectrochemical sensor; (c) Reproducibility among the six molecularly imprinted photoelectrochemical sensors; (d) 14-day stability of the molecularly imprinted photoelectrochemical sensor. Detailed Implementation

[0043] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0044] It should be understood that the terminology used herein is merely for describing particular embodiments and is not intended to limit the invention. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0045] Many modifications and variations to the illustrative embodiments described herein will be apparent to those of ordinary skill in the art from this specification, which is to be construed as exemplary only. Other embodiments of the application will be apparent to those of ordinary skill in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples provided should be considered exemplary only.

[0046] As Figure 1 Fig. 1 shows the construction and detection process of the sensor in the present application. The specific process is as follows: 20 μL of the uniform dispersion of CNQDs@CTP is added to the interface of the circular working electrode with an area of 0.2826 cm 2 After the electrode interface is dried, 8 μL of the molecularly imprinted polymerization solution containing the PFOA template molecule, the functional monomer acrylamide (MA), the crosslinking agent ethylene glycol dimethacrylate (EGDMA), and the initiator azobisisobutyronitrile (AIBN) is added to the electrode surface. After thermal polymerization, a molecularly imprinted film is obtained. The prepared electrode is eluted in a mixed solution of methanol:acetic acid = 9:1 (V:V) for 30 min to remove the template molecules on the molecularly imprinted film, and an identification site that can specifically bind to PFOA is obtained. At this time, because there are a large number of cavities on the film, photo-generated electrons can be transferred to the electrolyte solution, so the photocurrent response is large. After the eluted electrode is dried, it is immersed in a solution containing the template molecule for 20 min, and then washed to determine the photocurrent response at this time, which is recorded as I. At this time, because the target substance blocks the cavities on the molecularly imprinted film, electron transfer is hindered, so the photocurrent signal decreases. The concentration of PFOA in an unknown sample can be determined by the relationship between the photocurrent response and the concentration of the target substance.

[0047] Example 1:

[0048] I. Preparation steps of nanocomposite CNQDs@CTP:

[0049] (a) Preparation of graphite carbon nitride quantum dots (CNQDs):

[0050] A hydrothermal synthesis method is used. 1.63 g of citric acid dihydrate and 2 g of urea are dissolved in 100 mL of water, then transferred to a 200 mL high-pressure reaction kettle, heated to 180°C for 3 h, and then cooled to room temperature. The reacted solution is dialyzed with a 1000D dialysis bag, and then freeze-dried to obtain a blue solid. The graphite carbon nitride quantum dot solution is obtained by dissolving the blue solid in water, and is recorded as CNQDs solution with a concentration of 100 mg / mL.

[0051] (b) Preparation of covalent organic framework (CTP):

[0052] 5 mg of TFPP and 5 mg of Pa were dissolved in 10 mL of CH2Cl2and 10 mL of ACN respectively to obtain a Pa solution and a TFPP solution; 16.67 mg of iron trichloride hexahydrate (FeCl3·6H2O) was mixed with 0.2 mL of acetonitrile (ACN) to obtain a FeCl3solution;

[0053] First, the Pa solution was mixed with the TFPP solution, and the FeCl3solution was added, and then 5 mL of CH3COOH and 15 μL of CNQDs solution were added. After stirring at room temperature for 6 h, centrifugation was performed at 10000 rpm for 5 min, and the precipitate obtained by centrifugation was washed with ethanol for 3 times; the washed product was dried at 60°C for 8 h to obtain a dry product, and then ground to obtain a black-brown powder solid, which was recorded as CNQDs@CTP.

[0054] Figure 3 Figures (a) TEM image of CNQDs, (b) SEM image of CTP, (c) SEM image of CNQDs@CTP, (d) HRTEM image of CNQDs, (e) TEM image of CTP, (f) TEM image of CNQDs@CTP;

[0055] By Figure 3 It can be seen from (b) and (c) that the morphology of CNQDs@CTP changes from a solid sphere to a unique hollow sphere.

[0056] II. Molecularly imprinted cathodic photoelectrochemical sensor based on CNQDs@CTP nanocomposite

[0057] (a) Preparation of a molecularly imprinted polymer solution:

[0058] Methanol was used as an organic solvent, 24.9 mg of a detection target PFOA was dissolved in 2 mL of methanol, 2.85 mg of a functional monomer acrylamide (MA) was added, and the obtained mixed solution was fully oscillated and mixed at a certain temperature, then nitrogen gas (N2) was passed for 10 min, 291 μL of a crosslinking agent ethylene glycol dimethacrylate (EGDMA) was added to the mixed solution, nitrogen gas was continued to pass for 10 min, 82.1 mg of an initiator azobisisobutyronitrile (AIBN) was added, and after ultrasonic dissolution, a molecularly imprinted polymer solution was obtained, which was stored in the dark.

[0059] (b) Modification of the electrode with the composite material:

[0060] The ITO conductive glass is boiled in 1M NaOH for 20 min, then ultrasonically cleaned in ethanol and water in sequence, and dried to obtain the pretreated ITO conductive glass, which is used as a working electrode. Then the CNQDs@CTP is dissolved in water to obtain a CNQDs@CTP dispersion; 20 μL of the CNQDs@CTP dispersion with a concentration of 2 mg / mL is added dropwise to the pretreated ITO conductive glass, and the specific dropwise area is 0.2826 cm 2 of the circular working electrode interface; after the electrode interface is dried for standby, the working electrode is marked as CNQDs@CTP / ITO.

[0061] (c) Preparation process of heat-polymerized molecular imprinting:

[0062] Further 8 μL of the molecular imprinting polymerization solution is added dropwise to the surface of the CNQDs@CTP / ITO, and a CNQDs@CTP / ITO containing a molecular imprinting film is obtained after heat polymerization at 60°C; the CNQDs@CTP / ITO containing the molecular imprinting film is placed in an eluent for elution for 30 min, and after elution, it is dried at room temperature in the dark to obtain a molecular imprinting cathode photoelectrochemical sensor, which is marked as MIP / CNQDs@CTP / ITO; wherein the eluent is a mixed solution of methanol:acetic acid = 9:1 (V:V).

[0063] III. Application of the prepared molecular imprinting photoelectrochemical sensor to detection of perfluorooctanoic acid:

[0064] Preparation of different concentrations of PFOA solution: PFOA standard solutions are prepared with concentrations of 5.0×10 -12 , 1.0×10 -11 , 5.0×10 -11 , 1.0×10 -10 , 5.0×10 -10 , 1.0×10 -9 , 5.0×10 -9 , 1.0×10 -8 , 5.0×10 -8 , 1.0×10 -7 , 5.0×10 -7 , 1.0×10 -6 , 5.0×10 -6 , 1.0×10 -5 mol·L -1 ;

[0065] The MIP / CNQDs@CTP / ITO is soaked in the PFOA standard solution for incubation for 20 min, and then the MIP / CNQDs@CTP / ITO electrode is taken out and naturally dried to obtain the incubated MIP / CNQDs@CTP / ITO electrode.

[0066] The incubated MIP / CNQDs@CTP / ITO electrode was used as the working electrode, a saturated Ag / AgCl electrode as the reference electrode, and a platinum wire electrode as the counter electrode, and the PEC signal was recorded and detected by CHI 660E. The PEC signal was recorded in 0.1 mol·L -1 The test was carried out in PBS (pH = 7.0). Figure 4 It can be seen that the photoelectric signal is stable during the switching light scanning for 10 times, and the response value (I) of the PEC signal and the logarithmic value (lg C) of the PFOA concentration are linearly related, and the standard curve between them is drawn as Figure 5 shown, and the linear relationship is I = 97.94lg C (nM) - 844.59 in the concentration range of 1.0 x 10 -11 -5.0 x 10 -6 mol·L -1 , and the detection limit is as low as 5.50 x 10 -12 mol·L -1 .

[0067] In the detection of actual samples with unknown PFOA concentration, the molecularly imprinted photoelectrochemical sensor constructed by the application can avoid the interference of complex components in the actual sample, realize the selective detection of PFOA, and realize the sensitive detection of PFOA within the linear range of the sensor.

[0068] Example 2:

[0069] The molecularly imprinted photoelectrochemical sensor prepared in Example 1 was used to investigate its selectivity for PFOA. When the solution contained different analogues (n-octanoic acid (S1), sodium fluoride (S2), sodium trifluoroacetate (S3), pentafluoropropionic acid (S4), perfluoroheptanoic acid (S5), perfluorononanoic acid (S6), perfluorooctylsulfonic acid (S7), MIX + perfluorooctanoic acid (S8), perfluorooctanoic acid (S9)), wherein MIX is a mixed solution containing all the interferents, the concentration of perfluorooctanoic acid is 1 nM, and the concentration of the interferents is set to 10 nM. From Figure 6 (a) it can be seen that only when the target perfluorooctanoic acid exists in the solution, the sensor will have a larger photoelectric response difference (ΔI), which proves that the constructed sensor has good selectivity.

[0070] The molecularly imprinted photoelectrochemical sensor prepared in Example 1 was used to investigate its ion interference resistance for PFOA. When the solution contained different ions (Na + , K + , Ca 2+ , Mg 2+ , Hg + , Pt2+ Zn 2+ Cu 2+ SO4 2- NO3 - Cl - MIX+PFOA), wherein MIX is a mixed solution containing all interfering ions and PFOA, the concentration of PFOA is 1 nM, and the concentration of interfering ions is set to 10 nM. From Figure 6 (b) it can be seen that the sensor has a larger photocurrent response difference (ΔI) only when the target PFOA exists in the solution, which proves that the constructed sensor has good ion anti-interference performance.

[0071] The reproducibility of the molecularly imprinted photoelectrochemical sensor was evaluated by measuring PFOA in 6 parallel measurements, as shown in Figure 6 (c), the measurement result RSD is 2.16%, indicating that the reproducibility of the molecularly imprinted photoelectrochemical sensor is good. In addition, as shown in Figure 6 (d), the RSD of the molecularly imprinted photoelectrochemical sensor for measuring PFOA for 14 days is 4.91%, indicating that it has good long-term stability.

[0072] In summary, the molecularly imprinted photoelectrochemical sensor constructed in the embodiment has better detection performance than the prior art, and can simply and quickly realize the detection of PFOA. Moreover, the idea provided by the present application can be used to develop a sensing method for detecting other target substances, and has good application prospect.

[0073] It should be understood that although the present specification is described in terms of various embodiments, not every embodiment contains only one independent technical solution, and the description manner of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A method for preparing CNQDs@CTP nanocomposite materials, characterized in that, The steps are as follows: (1) Preparation of CNQDs: First, sodium citrate dihydrate and urea are added to water, mixed and dissolved, and then transferred to a high-pressure reactor for reaction. After the reaction, the mixture is cooled to room temperature. The solution after the reaction is dialyzed and freeze-dried to obtain blue solid graphitic carbon nitride quantum dots. The solid is then dissolved in water to obtain a graphitic carbon nitride quantum dot solution, denoted as CNQDs solution. (2) Preparation of CNQDs@CTP: p-phenylenediamine was added to acetonitrile to obtain a p-phenylenediamine solution; tetraaldehyde phenyl porphyrin was added to dichloromethane to obtain a tetraaldehyde phenyl porphyrin solution; ferric chloride hexahydrate was mixed with acetonitrile to obtain a FeCl3 solution; first, the p-phenylenediamine solution and the tetraaldehyde phenyl porphyrin solution were mixed, and then the FeCl3 solution, CH3COOH and the CNQDs solution prepared in step (1) were added. After thorough ultrasonic mixing, the mixture was stirred and reacted at room temperature. After the reaction, the mixture was centrifuged, washed, dried and ground to obtain a blackish-brown powder solid, denoted as CNQDs@CTP.

2. The method for preparing CNQDs@CTP nanocomposite material according to claim 1, characterized in that, In step (1), the ratio of sodium citrate dihydrate, urea, and water is 1.63g:2g:100mL; the reaction temperature is 180℃ and the reaction time is 3h; dialysis is performed using a 1000D dialysis bag for 6h; and the concentration of the graphite carbon nitride quantum dot solution is 100mg / mL.

3. The method for preparing CNQDs@CTP nanocomposite material according to claim 1, characterized in that, In step (2), the ratio of p-phenylenediamine, acetonitrile, tetraaldehyde phenylporphyrin, dichloromethane, ferric chloride hexahydrate, acetonitrile to CH3COOH solution and CNQDs solution is 5mg:10mL:5mg:10mL:16.67mg:0.2mL:5mL:15μL.

4. The method for preparing CNQDs@CTP nanocomposite material according to claim 1, characterized in that, In step (2), the stirring speed at room temperature is 350-370 rpm and the reaction time is 6 h; the centrifugation conditions are set to 10000 rpm for 5 min; the washing is performed with ethanol 3 times; the drying temperature is 60℃ and the time is 6-8 h.

5. A method for constructing a molecularly imprinted cathode photoelectrochemical sensor based on the CNQDs@CTP nanocomposite material prepared according to any one of claims 1-4, characterized in that, The steps are as follows: (1) Preparation of molecularly imprinted polymerization solution: PFOA and acrylamide were added to methanol, and the resulting mixed solution was shaken and mixed evenly at a certain temperature. After purging the mixed solution with nitrogen for a period of time, ethylene glycol dimethacrylate was added to the solution. After purging with nitrogen for a period of time, the initiator azobisisobutyronitrile was added. After ultrasonic dissolution, the molecularly imprinted polymer solution was obtained and stored under light-protected conditions. (2) First, ITO conductive glass is pretreated to obtain pretreated ITO conductive glass; Then, CNQDs@CTP was dissolved in water to obtain a CNQDs@CTP dispersion. CNQDs@CTP dispersion was dropped onto the pretreated ITO conductive glass surface and dried at room temperature. The dried product was denoted as CNQDs@CTP / ITO. (3) The molecularly imprinted polymer solution prepared in step (1) is dropped onto the surface of CNQDs@CTP / ITO obtained in step (2). After thermal polymerization, a molecularly imprinted film is formed, thus obtaining CNQDs@CTP / ITO containing the molecularly imprinted film. The CNQDs@CTP / ITO containing the molecularly imprinted film is placed in the elution solution for elution. After elution, it is dried at room temperature in the dark to obtain the molecularly imprinted cathode photoelectrochemical sensor, denoted as MIP / CNQDs@CTP / ITO.

6. The method according to claim 5, characterized in that, In step (1), the ratio of PFOA, acrylamide, methanol, ethylene glycol dimethacrylate and azobisisobutyronitrile is 24.9 mg: 2.85 mg: 2 mL: 291 μL: 82.1 mg; the nitrogen purging time is 10-15 min.

7. The method according to claim 5, characterized in that, In step (2), the pretreatment operation is as follows: ITO is boiled in 1M NaOH for 20 minutes, then the ITO is taken out and ultrasonically cleaned in ethanol and water in sequence, and dried after cleaning to complete the pretreatment step. The ITO conductive glass has a size of 1cm × 2cm; the concentration of the CNQDs@CTP dispersion is 2mg / mL, and the amount of CNQDs@CTP dispersion added is 20μL.

8. The method according to claim 5, characterized in that, In step (3), the volume of the added molecular imprinting solution is 6-8 μL, the temperature of the thermal polymerization is 60℃, and the time is 5-10 min; the eluent is a mixed solution of methanol and acetic acid in a volume ratio of 9:1, and the elution is accompanied by stirring at 150 rpm for 30-40 min.

9. The use of the molecularly imprinted cathode photoelectrochemical sensor prepared according to claim 5 for the detection of perfluorooctanoic acid, characterized in that, The steps are as follows: S1. First, prepare a PFOA standard solution, then immerse the MIP / CNQDs@CTP / ITO in the PFOA standard solution for incubation. After incubation, remove the MIP / CNQDs@CTP / ITO electrode and air dry it to obtain the incubated MIP / CNQDs@CTP / ITO electrode. The incubated MIP / CNQDs@CTP / ITO electrode was used as the working electrode, the saturated Ag / AgCl electrode as the reference electrode, and the platinum wire electrode as the counter electrode. Electrochemical tests were performed to detect the PEC signal. A standard curve was constructed based on the linear relationship between the response value of the PEC signal and the logarithm of the concentration of the PFOA standard solution. S2: Following the same method as S1, except that the test solution is replaced with a PFOA standard solution; finally, the response value of the PEC signal is obtained, and the response value of the PEC signal is substituted into the standard curve in S1 to realize the concentration detection of PFOA in the test solution.

10. The use according to claim 9, characterized in that, In step S1, the concentration of the PFOA standard solution is 5.0 × 10⁻⁶. -12 ~1.0×10 -5 mol·L -1 The incubation time is 20-30 min; the electrochemical test is performed using a CHI 660E to record and detect the PEC signal, wherein the PEC signal is detected at 0.1 mol·L⁻¹. -1 The assay was performed in PBS with a pH of 7.0.

Images