Four-electrode electrochemical detection system and its application in pollutant detection

Abstract

The application discloses a four-electrode electrochemical detection system, which comprises an anode, a cathode, a reference electrode I and a reference electrode II. The four-electrode electrochemical detection system is applied to pollutant detection, and the system is matched with a [EMIM][BF4] and PBS compound electrolyte and three modes of static adsorption catalysis, dynamic electrochemical catalysis and pressurized photoelectric synergistic catalysis, so that high-selectivity detection of trace pollutants can be realized. Compared with a traditional three-electrode system, the application has higher sensitivity, resolution and anti-interference ability, and is suitable for fields of environmental monitoring, food safety and emergency response.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrochemical sensors, and particularly relates to a four-electrode electrochemical detection system for realizing high-sensitivity and high-selectivity rapid detection of microplastics, PFAS and other pollutants in environmental water samples and food substrates. BACKGROUND

[0002] With the advancement of industrialization and urbanization, more and more new chemical substances are widely used in industrial production, agriculture, medical treatment and daily life. Emerging contaminants (ECs) refer to a class of new environmental pollutants that have not been or have just been included in the traditional environmental monitoring and management system. These pollutants include pharmaceuticals and personal care products (PPCPs), perfluoro and polyfluoro alkyl substances (PFASs), hormones, antibiotics, endocrine disruptors, microplastics, nanomaterials and the like. Emerging contaminants have the characteristics of various types, diverse structures, strong biological activity, high concealment, low environmental concentration but potential harm, and have become a research hotspot in the field of global environment and health.

[0003] The content of emerging contaminants in the environment is usually low, and the form is complex, so it is difficult to detect and analyze. The commonly used detection techniques at present include pretreatment techniques such as solid-phase extraction, solid-phase microextraction, liquid-liquid extraction; chromatographic techniques such as gas chromatography-mass spectrometry, high-performance liquid chromatography-mass spectrometry, ultra-high-performance liquid chromatography; mass spectrometry techniques such as triple quadrupole mass spectrometry, quadrupole-time-of-flight mass spectrometry, and high-resolution mass spectrometry. However, these methods are very costly, mainly requiring expensive instruments and equipment, and these methods also require complex pretreatment steps and excessive solvents. Therefore, compared with other analysis methods, electrochemistry has the technical advantages of low cost, easy to use, high sensitivity and rapidity. In addition, electrochemical sensors are smaller in size and use various nanomaterials to modify the surface of the electrode to improve sensitivity and selectivity. Electrochemical sensing technology is considered a clean technology because they do not generate hazardous waste and allow measurements to be made using small amounts of chemicals and samples. The existing four-electrode detection system has significant advantages in improving the accuracy of electrochemical testing and revealing the intrinsic behavior of the electrode / interface, but there are still many technical and theoretical problems to be solved, such as assembly process, reference electrode stability, signal interference, complex data interpretation, test equipment adaptation, miniaturization compatibility, etc. SUMMARY

[0004] The present application provides a four-electrode electrochemical detection system, which realizes rapid and accurate detection of emerging contaminants, especially in the fields of environment and food, by using the four-electrode electrochemical detection system. The four-electrode electrochemical detection system improves the detection sensitivity and resolution through multi-dimensional detection mode, and can effectively detect a variety of emerging contaminants.

[0005] The four-electrode electrochemical detection system of the application comprises an anode, a cathode, a reference electrode I and a reference electrode II.

[0006] The anode is prepared as follows:

[0007] (1) MoS2 nanosheets 1.2-2.0 g are placed in 60-80 mL of distilled water, stirred and mixed, and then subjected to hydrothermal reaction at 175-185 ℃ for 7-9 h, and then naturally cooled, centrifuged, and the supernatant collected to obtain a MoS2 quantum dot solution; ZnO is placed in distilled water, mixed, and then subjected to hydrothermal reaction at 175-185 ℃ for 7-9 h, and then naturally cooled, centrifuged, and the precipitate collected, washed and dried to obtain ZnO quantum dots; 10-15 mL of deionized water is added to 90-110 mg of the ZnO quantum dots, and then ultrasonically mixed to obtain a ZnO quantum dot solution; the MoS2 quantum dot solution is mixed with a 1.0 mM HCl solution to obtain a mixed solution, and the ZnO quantum dot solution is added dropwise to the mixed solution under stirring, and the pH is adjusted to 8-10 during the dropwise addition, and then the reaction is carried out at 55-65 ℃ for 2 h to obtain MoS2 / ZnO core-shell quantum dots;

[0008] The volume ratio of the mixed solution to the ZnO quantum dot solution is 1-3:1, and the volume ratio of the MoS2 quantum dot solution to the HCl solution is 10:1.

[0009] (2) Cu(NO3)2 is added to a Zn(NO3)2 solution, stirred and mixed, and then a thiourea solution is added dropwise to the nitrate mixed solution, and then ethylenediamine is added, sealed, and then subjected to reaction at 190-210 ℃ for 10-15 h, and then naturally cooled, centrifuged, and the precipitate collected, washed and dried, and then annealed at 450-550 ℃ under N2 atmosphere for 2 h, and then cooled to obtain ZnS:Cu quantum dots;

[0010] The mass ratio of Zn(NO3)2 to Cu(NO3)2 is 20-30:1, the mass ratio of Cu(NO3)2 to thiourea is 5-8:1, and the mass-volume ratio mg: μL of Cu(NO3)2 to ethylenediamine is 1:5-10;

[0011] The ZnS:Cu quantum dots are weighed and dispersed in chloroform, and then 3-aminopropyltriethoxysilane is added, and then subjected to reflux reaction at 55-65 ℃, and then centrifuged, and the solid is washed with chloroform for 2-3 times, and then vacuum dried to obtain modified ZnS:Cu quantum dots;

[0012] The mass-volume ratio mg: μL of the ZnS:Cu quantum dots to 3-aminopropyltriethoxysilane is 1:1-3;

[0013] functionalized graphene quantum dots were prepared by dispersing 100-150 mg graphene quantum dots in N,N-dimethylformamide, adding 100 μL carbodiimide, 50 μL N-hydroxysuccinimide, stirring at room temperature for 2 h, then adding 20 mg PVDF-TrFE oligomer, continuing to stir, and freeze-drying after dialysis of the reaction product in a dialysis bag with a molecular weight cut-off of 500 Da for 24 h;

[0014] 1.0-2.5 g PVDF-TrFE oligomer and 100-150 mg polyvinylpyrrolidone were added to 0.1 M aqueous N,N-dimethylformamide solution, and the solution was stirred at 60°C until the PVDF-TrFE oligomer was completely dissolved to prepare a PVDF-TrFE solution; the modified ZnS:Cu quantum dots and the functionalized graphene quantum dots were separately dispersed in DMF and ultrasonicated for 30 min; the ultrasonicated modified ZnS:Cu quantum dot solution was added dropwise to the PVDF-TrFE solution, stirred, then the functionalized graphene quantum dot solution was added, ultrasonicated, and stirred at room temperature overnight, and then filtered with a 0.45 μm polytetrafluoroethylene filter membrane to prepare a PVDF-TrFE / ZnS:Cu / GQDs composite solution;

[0015] The mass ratio of the modified ZnS:Cu quantum dots to the PVDF-TrFE oligomer was 1:20-50, and the mass ratio of the functionalized graphene quantum dots to the PVDF-TrFE oligomer was 1:30-50.

[0016] (3) The ITO substrate was sequentially cleaned with distilled water and ethanol, a MoS2 / ZnO core-shell quantum dot layer was prepared on the substrate by a thermal evaporation method, and after drying, the PVDF-TrFE / ZnS:Cu / GQDs composite solution was coated on the MoS2 / ZnO core-shell quantum dot layer, dried, annealed at 140°C for 2 h, cooled, and a PVDF-TrFE / ZnS:Cu / GQDs composite film layer was prepared, and finally an anode was prepared.

[0017] The cathode was prepared as follows:

[0018] A. Fe3O4 nanoparticles were hydrothermally reacted with glucose at 150-200°C for 6 h, centrifuged, and the precipitate was washed 2-3 times and dried to obtain Fe3O4@C quantum dots; a polyaniline solution was mixed with the Fe3O4@C quantum dots-DMF under the condition of pH 1-2, ultrasonically reacted, centrifuged, and the solid was washed and dried to obtain PANI / Fe3O4@C powder;

[0019] The mass ratio of the polyaniline to the Fe3O4@C quantum dots was 1-5:1.

[0020] B. The PANI / Fe3O4@C powder is compounded with a polyacrylonitrile solution by using an electrostatic spinning method to prepare a fiber membrane, the fiber membrane is treated at 250-300 DEG C for 2h in an air atmosphere, naturally cooled to room temperature, then is kept at 750-850 DEG C for 2h in a nitrogen atmosphere, and the carbonized fiber membrane is obtained after cooling; the mass ratio of the PANI / Fe3O4@C powder to the polyacrylonitrile is 1:4-10.

[0021] C. ZnS, CaO, MnCO3 and anhydrous ethanol are mixed, grinded and uniformly mixed, then are reacted at 750-850 DEG C for 6h in a nitrogen atmosphere to prepare CaZnOS:Mn 2+ nanoparticles; the CaZnOS:Mn 2+ nanoparticles are added into anhydrous ethanol to prepare a suspension by ultrasonic dispersion; the carbonized fiber membrane is soaked in the suspension, dried at 200 DEG C, and the cathode is prepared;

[0022] The mass ratio of the ZnS to the CaO is 1-2:1, and the mass ratio of the ZnS to the MnCO3 is 5-10:1.

[0023] The reference electrode I is prepared by mixing zirconia, sodium silicate, sodium phosphate and anhydrous ethanol, grinded and uniformly mixed, then 4-6% polyvinyl alcohol solution is added and grinded, and the dispersion is ultrasonically dispersed; the dispersion is spin-coated on the surface of a ZrO2 ceramic electrode, dried, then kept at 280-320 DEG C for 2h, kept at 1000 DEG C for 4h, naturally cooled to room temperature, soaked in a 0.1M HCl solution for 30min, washed to neutral, dried, then Pt paste is coated on the surface of the dried electrode and a platinum wire is fixed, and the reference electrode I is prepared by sintering at 750-850 DEG C for 30min.

[0024] The mass ratio of the zirconia to the sodium silicate is 1:1-2, and the mass ratio of the sodium silicate to the sodium phosphate is 1-2:1; the Pt paste is prepared by adding 5-20mg platinum powder into 0.5-2mL anhydrous ethanol, ultrasonically treating for 10-30min, adding 200-300μL 5% Nafion solution dropwise, and stirring and uniformly mixing.

[0025] The reference electrode II is a silver / silver chloride electrode.

[0026] Another object of the application is to apply the four-electrode electrochemical detection system to pollutant detection.

[0027] The four-electrode electrochemical detection system is used in the following manner:

[0028] 1. Static adsorption catalysis

[0029] Without the application of voltage, the working electrode utilizes the catalytic activity of quantum dots to react with new pollutants, generating products with electrochemical signals. By measuring changes in the concentration of these products, changes in pollutants in the environment can be monitored in real time.

[0030] The specific adsorption of pollutants by surface defect sites on quantum dots, and the monitoring of adsorption layer thickness changes by surface plasmon resonance (SPR), achieves a sensitivity on the order of 0.1 nm. The adsorption of pollutants by surface defect sites on quantum dots, and the monitoring of adsorption layer thickness changes by SPR, also achieves a sensitivity of 0.1 nm / μg·L. -1 .

[0031] 2. Dynamic electrochemical catalysis

[0032] Under low voltage and piezoelectric stimulation, the working electrode interacts with pollutants through an electrochemical catalytic reaction, exciting electron flow and thus generating a current signal. In this mode, the intensity of the electrochemical signal is positively correlated with the pollutant concentration, exhibiting high sensitivity and selectivity. Applying a scanning voltage of -0.5 to 1.2 V, a built-in electric field is formed at the quantum dot heterojunction interface, accelerating electron transfer. The redox peak current is detected by differential pulse voltammetry (DPV).

[0033] 3. Photoelectrocatalysis

[0034] Under combined voltage and pressure conditions, the photoelectrocatalytic activity of quantum dot materials is significantly enhanced. This mode, by controlling variations in voltage, current, and pressure, enables the acquisition of high-resolution electrochemical reaction data in the shortest possible time, further improving the sensor's ability to detect new pollutants. The generation of the photoelectrochemical reaction provides additional detection information, aiding in the accurate measurement of pollutant concentrations. Under pressures of 1.2–3.0 MPa, quantum dots generate photogenerated electron-hole pairs, which are expressed through photocurrent density (nA / cm²). 2 Synergistic analysis of (level) and electrochemical impedance spectroscopy (EIS).

[0035] Advantages and technical effects of the present invention:

[0036] The anode of the four-electrode electrochemical sensing system of the application adopts MoS2 / ZnO core-shell quantum dots, ZnS:Cu quantum dots, graphene quantum dots and PVDF-TrFE composite film and the like materials, which combines the excellent electrochemical catalytic activity of MoS2 / ZnO core-shell quantum dots, the large specific surface area of quantum dots to expose more active sites, and enhances the electron transfer efficiency and adsorption capacity. The ZnS:Cu quantum dots have unique photoelectric response characteristics, and the graphene quantum dots have excellent electrical conductivity, and the two form a film layer with PVDF-TrFE, which not only fixes the quantum dots by the mechanical stability of PVDF-TrFE, but also strengthens the electron transfer by the conductive network of graphene quantum dots, so that the oxidation reaction of pollutants is more likely to occur, the detection signal is significantly amplified, the catalytic efficiency and the pollutant adsorption performance are improved, and the detection response is further strengthened.

[0037] The “adsorption-catalysis” dual-function design of the cathode, the magnetism of Fe3O4 can enhance the targeted adsorption of pollutants containing polar groups, and the carbon shell can improve the electrical conductivity; polyaniline (PANI) as a conductive polymer can construct an efficient electron transport channel to accelerate the reduction reaction of pollutants. The carbonized fiber membrane has a high specific surface area, CaZnOS:Mn 2+ The nanoparticles as a luminescent material can produce energy transfer under excitation in a photoelectric synergistic mode, and the combination of the two can increase the adsorption capacity of pollutants and further activate the catalytic reaction, forming an “oxidation-reduction” closed loop with the anode to strengthen the symmetry and stability of the detection response.

[0038] The reference electrode I uses zirconium oxide, sodium silicate and sodium phosphate as the base material, and the conductivity is improved after modification of Pt, which can stably output the reference potential; the double reference can correct the potential drift in real time, and ensure that the working potential of the anode and the cathode is always in the best interval, thereby fundamentally improving the anti-interference ability.

[0039] The “multi-dimensional” effect of the three catalytic modes, the static adsorption catalysis can make trace pollutants adhere to the electrode surface without external interference through the high adsorption of the electrode material, thereby solving the problem that low-concentration pollutants are difficult to contact active sites; the dynamic electrochemical catalysis can increase the collision frequency of pollutants and electrodes, reduce the mass transfer resistance, and make more pollutants participate in electrochemical reaction, thereby improving the detection efficiency; the pressurized photoelectric synergistic catalysis can promote the diffusion of pollutants to the electrode surface through the pressurized environment, and at the same time, the ZnS:Cu and CaZnOS:Mn 2+ quantum dots produce photo-generated electron-hole pairs, and form a “light-electricity-pressure” synergy with electrochemical catalysis to accelerate the oxidation and reduction of pollutants, and the detection line can reach ppb level. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 Figure 1 is a PET microplastic (MP) concentration and peak current standard curve diagram of Example 1.

[0041] Figure 2 Ciprofloxacin (CIP) concentration vs. peak current standard curve for Example 1 6+ Ciprofloxacin (CIP) concentration vs. peak current standard curve for Example 1

[0042] Figure 3 Ciprofloxacin (CIP) concentration vs. peak current standard curve for Example 1

[0043] Figure 4 Phthalate ester (PAEs) concentration vs. peak current standard curve for Example 2 PET

[0044] Figure 5 Perfluorooctane sulfonate (PFOS) concentration vs. peak current standard curve for Example 2 PET

[0045] Figure 6 Naphthalene (NAP) concentration vs. peak current standard curve for Example 2 PET DETAILED DESCRIPTION

[0046] The application will be further described in the following examples without limiting the scope of the application to what is described therein, and the methods used in the examples are conventional methods unless otherwise specified, and the reagents used are conventional commercially available reagents or reagents prepared according to conventional methods.

[0047] 1. Preparation of anode

[0048] (1) MoS2nanosheets 1.6g were placed in 70mL of distilled water, stirred and mixed uniformly, and then subjected to hydrothermal reaction at 180℃ for 8h, and then naturally cooled, centrifuged at 8000rpm for 15min, and the supernatant was collected to obtain a MoS2quantum dot solution; 0.81g of ZnO was placed in 70mL of distilled water, mixed uniformly, and then subjected to hydrothermal reaction at 180℃ for 8h, and then naturally cooled, centrifuged at 8000rpm for 15min, and the precipitate was collected, washed and dried to obtain ZnO quantum dots, 10mL of deionized water was added to 100mg of ZnO quantum dots, and then ultrasonically mixed to obtain a ZnO quantum dot solution; 20mL of the MoS2quantum dot solution was mixed with 2mL of 1.0mM HCl solution to obtain a mixed solution, and 10mL of the ZnO quantum dot solution was added dropwise to the mixed solution under stirring, and the pH was adjusted to 9 during the dropwise addition, and then the mixture was reacted at 60℃ for 2h to obtain MoS2 / ZnO core-shell quantum dots.

[0049] (2) Take 2.88 g Zn(NO3)2·6H2O into a beaker, add 30 mL deionized water, and stir magnetically until completely dissolved. Take 115 mg Cu(NO3)2·3H2O, add to the beaker, and continue to stir until uniform. Transfer to a 50 mL volumetric flask, dilute to volume, and shake well (mass ratio of Zn(NO3)2to Cu(NO3)2is 25:1) to obtain a mixed solution. Take 19.1 mg thiourea (mass ratio of Cu(NO3)2·3H2O to thiourea is 6:1), pour into a beaker, add 20 mL deionized water, and stir at room temperature until dissolved. Dilute to 30 mL, and shake well. Slowly add the thiourea solution to the above mixed solution, and add 690 μL ethylenediamine chelating agent (mass-volume ratio of Cu(NO3)2·3H2O to ethylenediamine is 1:6 mg: μL) to form a white ZnS precursor precipitate. Transfer the mixture to a 100 mL polytetrafluoroethylene-lined reaction kettle, seal, and react at 200°C for 12 h. After natural cooling, centrifuge at 8000 rpm for 10 min, collect the precipitate, wash with deionized water and anhydrous ethanol 3 times each, dry at 60°C for 12 h, and anneal at 500°C for 2 h under N2atmosphere. After cooling, ZnS:Cu quantum dots are obtained;

[0050] Take 120 mg ZnS:Cu quantum dots, disperse in 20 mL chloroform, and add 120 μL 3-aminopropyltriethoxysilane. Reflux at 60°C for 2 h, centrifuge at 10000 rpm for 10 min, and wash the solid with chloroform 3 times. Dry at 60°C under vacuum to obtain modified ZnS:Cu quantum dots;

[0051] Disperse 100 mg graphene quantum dots in 10 mL N,N-dimethylformamide, add 100 μL carbodiimide and 50 μL N-hydroxysuccinimide, stir at room temperature for 2 h, then add 20 mg PVDF-TrFE oligomer, and continue to stir. Dialyze the reaction product in a dialysis bag with a molecular weight cutoff of 500 Da for 24 h, and freeze-dry to obtain functionalized graphene quantum dots;

[0052] A PVDF-TrFE solution was prepared by adding 1.8 g of PVDF-TrFE oligomer and 120 mg of polyvinylpyrrolidone into 50 mL of 0.1M N,N-dimethylformamide aqueous solution, and stirring at 60°C until completely dissolved; the modified ZnS:Cu quantum dots and the functionalized graphene quantum dots were respectively dispersed in DMF and ultrasonically treated for 30 min; the modified ZnS:Cu quantum dot solution after ultrasonic treatment was added dropwise into the PVDF-TrFE solution (the mass ratio of the modified ZnS:Cu quantum dots to the PVDF-TrFE oligomer was 1:30), stirred, and then the functionalized graphene quantum dot solution (the mass ratio of the functionalized graphene quantum dots to the PVDF-TrFE oligomer was 1:40) was added, ultrasonically treated for 1 h, and stirred at room temperature overnight, and then filtered with a 0.45 μm polytetrafluoroethylene filter membrane to prepare a PVDF-TrFE / ZnS:Cu / GQDs composite solution.

[0053] (3) The ITO substrate was sequentially cleaned with distilled water and ethanol, a MoS2 / ZnO core-shell quantum dot layer was prepared on the substrate by a thermal evaporation method, and after drying, the PVDF-TrFE / ZnS:Cu / GQDs composite solution was coated on the MoS2 / ZnO core-shell quantum dot layer, dried, annealed at 140°C for 2 hours, cooled, and a PVDF-TrFE / ZnS:Cu / GQDs composite film layer was prepared, and finally an anode was prepared.

[0054] 2. Preparation of a cathode

[0055] A. Fe3O4 nanoparticles 500 mg and glucose 1.0 g were hydrothermally reacted at 180°C for 6 h, centrifuged at 8000 rpm for 10 min, the precipitate was washed with deionized water for 3 times, and dried at 60°C to obtain Fe3O4@C quantum dots; 260 mg of a polyaniline solution was mixed with 130 mg of Fe3O4@C quantum dots-DMF under the condition of pH 1 (the mass ratio of the polyaniline to the Fe3O4@C quantum dots was 2:1), and after ultrasonic reaction, centrifugation, and washing of the solid with deionized water, the PANI / Fe3O4@C powder was dried at 60°C.

[0056] B. The PANI / Fe3O4@C powder 100 mg was compounded with polyacrylonitrile solution 8 g by an electrospinning method to prepare a fiber membrane (the mass ratio of the PANI / Fe3O4@C powder to the polyacrylonitrile was 1:8), the fiber membrane was treated at 280°C in an air atmosphere for 2 h, naturally cooled to room temperature, and then heat-treated at 800°C in a nitrogen atmosphere for 2 h, and cooled to obtain a carbonized fiber membrane.

[0057] C. 97 mg of ZnS, 56 mg of CaO, 229 mg of MnCO3, and 15 mL of anhydrous ethanol were mixed, ground and uniformly mixed, and then reacted at 800°C in a nitrogen atmosphere for 6 h to obtain CaZnOS:Mn2+ nanoparticles; CaZnOS:Mn 2+ nanoparticles 50 mg

[0058] The carbon fiber membrane was immersed in the suspension for 30 min, repeated for 3 times, and dried at 200°C for 4h to prepare the cathode.

[0059] 3、Reference electrode I was prepared by mixing zirconia 61 mg, sodium silicate 122 mg, sodium phosphate 81 mg, and 5 mL of anhydrous ethanol, grinding and mixing uniformly, then adding 5% polyvinyl alcohol solution and grinding, and ultrasonic dispersion; the dispersion was spin-coated on the surface of the ZrO2 ceramic electrode, dried, then heat treated at 300°C for 2h, and at 1000°C for 4h, naturally cooled to room temperature, soaked in 0.1M HCl solution for 30 min, then washed with deionized water until neutral, dried at 60°C; Pt paste was coated on the surface of the dried electrode and a platinum wire was fixed, and sintered at 800°C for 30 min to prepare, wherein the Pt paste was prepared by adding 10 mg of platinum powder to 1 mL of anhydrous ethanol, ultrasonic treatment for 20 min, adding 250 μL of 5% Nafion solution dropwise, and stirring and mixing uniformly.

[0060] 4、The four-electrode electrochemical sensing system was used to simultaneously detect PET microplastics (MPs), Cr 6+ and ciprofloxacin (CIP)

[0061] a、Test instruments and conditions:

[0062] The four-electrode electrochemical sensor included an electrochemical workstation, an electrolytic cell, the anode, the cathode, and the reference electrode I prepared in steps 1, 2, and 3; a silver / silver chloride reference electrode II.

[0063] b、Preparation of standard curve

[0064] The electrolyte in the electrolytic cell was 0.1M PBS buffer containing 35% [EMIM][BF4], with a pH of 7.0, and contained 0~3 μmol / L of PET microplastics (MPs), 0~3 μmol / L of Cr 6+ and 0~3 μmol / L of ciprofloxacin (CIP);

[0065] ① On the electrochemical workstation, select differential pulse voltammetry, set the enrichment potential to 0.1V, and the enrichment time to 60 seconds; place the magnetic stir bar in the electrolytic cell, set the stirring speed of the electric stirrer to 300 rpm, and record the current-voltage changes using the electrochemical workstation to obtain the current-voltage curve; ② After the enrichment time is completed, immediately stop stirring the solution in the electrolytic cell, let it stand for 5 seconds, then apply a scanning voltage with a voltage range of -0.5V to 1.2V to the working electrode, and record the current-voltage changes using the electrochemical workstation to obtain the current-voltage curve; ③ Let it stand for another 5 seconds, then apply an external voltage of 1.2-3.0 MPa to the working electrode, and record the current-voltage changes using the electrochemical workstation to obtain the current-voltage curve; ④ Record the characteristic peak currents of the three pollutants, and perform parallel measurements three times for each concentration gradient; PET microplastics (MPs), Cr... 6+ Plot the concentration of ciprofloxacin (CIP) on the x-axis and the peak current value on the y-axis to obtain the PET microplastics (MPs) and Cr. 6+ The standard curve corresponding to ciprofloxacin (CIP) was used for linear regression to obtain the PET microplastics (MPs) and Cr. 6+ The linear relationship between ciprofloxacin (CIP) concentration and peak current; this linear relationship (standard curve) is used for the quantitative detection of PET microplastics (MPs) and Cr. 6+ The concentration of ciprofloxacin (CIP); the PET microplastics (MPs) and Cr corresponding to this working electrode. 6+ The linear relationships between ciprofloxacin (CIP) concentration and peak current are as follows:

[0066] PET microplastics (MPs):

[0067] I p =3.0251×C MPs + 0.0023 (R) 2 =0.9987), MPs concentration ranged from 0.08 to 3.0 μmol / L;

[0068] Cr 6 ⁺:

[0069] I p =4.1063×C Cr6+ +0.0090 (R) 2 =0.9991), Cr 6+ The concentration ranges from 0.08 to 3.0 μmol / L;

[0070] Ciprofloxacin (CIP)

[0071] I p = 2.5960×C CIP+0.0086 (R 2 = 0.9979, CIP concentration was 0.08-3.0 μmol / L;

[0072] c. Calculation of the detection limit

[0073] The detection limit was carried out at the enrichment time of 60 seconds, and the detection limit was calculated by the formula CL= 3Sb / m, where CL, Sb and m were the detection limit (μmol / L), the blank standard deviation (μA) and the standard curve slope (μA / (μmol / L)), respectively. The standard curve slope was obtained by step b, and was PET microplastics (MPs): 3.0251; Cr 6+ : 4.1063; ciprofloxacin (CIP) 2.5960; the blank standard deviation was obtained by taking the standard deviation of the peak current value of the blank water sample scanned 10 times, and was PET microplastics (MPs): 0.0214; Cr 6+ : 0.0297; ciprofloxacin (CIP): 0.0273; finally, the standard curve slope and the blank standard deviation were brought into the formula CL= 3Sb / m to obtain the electrode detection limit, which was PET microplastics (MPs): 0.0291 μmol / L; Cr 6+ : 0.0214 μmol / L; ciprofloxacin (CIP): 0.0267 μmol / L.

[0074] d. Detection of the sample to be tested

[0075] The electrolyte containing 2 μmol / L PET microplastics (MPs), 2 μmol / L Cr 6+ and 2 μmol / L ciprofloxacin (CIP) was detected, and the experimental method was step b, and the peak currents of PET microplastics (MPs), Cr 6+ and ciprofloxacin (CIP) were 5.8104 μA, 7.7700 μA and 4.7074 μA, respectively. Then the peak current values were substituted into the linear equation of step b, and the contents of PET microplastics (MPs), Cr 6+ and ciprofloxacin (CIP) were calculated to be 1.92 μmol / L and 1.89 μmol / L, 1.81 μmol / L, respectively.

[0076] e. Electrode stability test

[0077] The same electrode was placed at room temperature for 30 days, and the test current value at 30 days was 94.1%, 96.8%, 95.3% of the initial value, corresponding to PET microplastics (MPs), Cr 6+ and ciprofloxacin (CIP), which indicated that the sensor had good stability.

[0078] Example 2: Using the four-electrode electrochemical detection system of Example 1 and simultaneously detecting phthalate esters (PAEs), perfluorooctane sulfonic acid (PFOS), and naphthalene (NAP)

[0079] a, Test instrument and conditions

[0080] The four-electrode electrochemical sensor system was prepared and connected as in Example 1.

[0081] b, The preparation method of the standard curve is the same as in Example 1

[0082] The electrolyte containing phthalate esters with a concentration range of 0-3.0 μmol / L, perfluorooctane sulfonic acid with a concentration range of 0-3.0 μmol / L, and naphthalene with a concentration range of 0-3.0 μmol / L was configured. The linear relationship between the concentration of phthalate esters (PAEs), perfluorooctane sulfonic acid (PFOS), and naphthalene (NAP) and the peak current was obtained;

[0083] Phthalate esters (PAEs):

[0084] I p =3.2165×C PAEs + 1.1461(R 2 =0.9987), PAEs concentration was 0.08-3.0 μmol / L;

[0085] Perfluorooctane sulfonic acid (PFOS):

[0086] I p = 2.8541×C PFOS + 0.8767(R 2 =0.9997), PFOS concentration was 0.08-3.0 μmol / L;

[0087] Naphthalene (NAP)

[0088] I p = 3.7856×C NAP + 1.9767(R 2 =0.9979), NAP concentration was 0.08-3.0 μmol / L;

[0089] c, Calculation of the detection limit

[0090] The detection limit was determined at an enrichment time of 60 seconds and was calculated using the formula CL = 3Sb / m, where CL, Sb, and m are the detection limit (μmol / L), blank standard deviation (μA), and standard curve slope (μA / (μmol / L)), respectively. The slopes of the standard curve were obtained in step b, and were as follows: phthalates (PAEs): 3.2165; perfluorooctane sulfonate (PFOS): 2.8541; naphthalene (NAP): 3.7856. The standard deviations of the blank were obtained by scanning 10 blank water samples and taking the standard deviations of the peak current values, and were as follows: phthalates (PAEs): 0.0314; perfluorooctane sulfonate (PFOS): 0.0307; naphthalene (NAP): 0.0373. Finally, the slopes of the standard curve and the standard deviations of the blank were substituted into the formula CL = 3Sb / m to obtain the detection limits of the electrode, which were: phthalates (PAEs): 0.0391 μmol / L; perfluorooctane sulfonate (PFOS): 0.0314 μmol / L; naphthalene (NAP): 0.0467 μmol / L.

[0091] d. Detection of the sample to be tested

[0092] A compound electrolyte containing 2 μmol / L phthalates, 2 μmol / L perfluorooctane sulfonic acid (PFOS), and 2 μmol / L naphthalene (NAP) was tested using the same experimental method as in step b. The peak currents for phthalates (PAEs), PFOS, and NAP were measured to be 7.1609 μA, 5.8123 μA, and 9.3208 μA, respectively. The peak current values ​​were then substituted into the linear equation in step b to calculate the contents of phthalates, PFOS, and naphthalene to be 1.87 μmol / L, 1.91 μmol / L, and 1.94 μmol / L, respectively.

[0093] e. Electrode stability test

[0094] When the same electrode was placed at room temperature for 30 days, the measured current values ​​at 30 days were 96.3%, 95.8%, and 94.3% of its initial value, respectively. These values ​​correspond to phthalates (PAEs), perfluorooctane sulfonic acid (PFOS), and naphthalene (NAP), indicating that the sensor has good stability.

[0095] Example 3: Four-electrode electrochemical detection system and simultaneous detection of PET microplastics (MPs) and Cr 6+ Preparation of Ciprofloxacin (CIP) 1 and Anode

[0096] (1) MoS2 nanosheet 1.2 g was placed in 60 mL of distilled water, stirred and mixed, and then hydrothermally reacted at 185°C for 7 h, naturally cooled, centrifuged at 8000 rpm for 15 min, and the supernatant was collected to obtain a MoS2 quantum dot solution; 0.81 g of ZnO was placed in 70 mL of distilled water, mixed, and then hydrothermally reacted at 180°C for 8 h, naturally cooled, centrifuged at 8000 rpm for 15 min, and the precipitate was collected, washed and dried to obtain ZnO quantum dots; 12 mL of deionized water was added to 95 mg of ZnO quantum dots, ultrasonically mixed, and then a ZnO quantum dot solution was prepared; 20 mL of the MoS2 quantum dot solution was mixed with 2 mL of 1.0 mM HCl solution to obtain a mixed solution, 10 mL of the ZnO quantum dot solution was added dropwise to the mixed solution under stirring, the pH was adjusted to 9 during the dropwise addition, and then the mixture was reacted at 55°C for 2 h to obtain MoS2 / ZnO core-shell quantum dots.

[0097] (2) 2.98 g of Zn(NO3)2·6H2O was weighed into a beaker, 30 mL of deionized water was added, and magnetic stirring was performed until complete dissolution. 149 mg of Cu(NO3)2·3H2O was weighed into the beaker, and stirring was continued until uniform. The mixture was transferred to a 50 mL volumetric flask, and the volume was adjusted and shaken (the mass ratio of Zn(NO3)2 to Cu(NO3)2 was 20:1). 24.8 mg of thiourea (the mass ratio of Cu(NO3)2·3H2O to thiourea was 6:1) was weighed into a beaker, 20 mL of deionized water was added, and stirring was performed at room temperature until dissolution. The volume was adjusted to 30 mL, and shaking was performed. The thiourea solution was slowly added dropwise to the above-mentioned mixed solution, and 1.19 mL of ethylenediamine chelating agent (the mass-volume ratio of Cu(NO3)2·3H2O to ethylenediamine was 1:8) was added to form a white ZnS precursor precipitate. The mixture was transferred to a 100 mL polytetrafluoroethylene-lined reaction kettle, sealed, and then reacted at 200°C for 12 h. After natural cooling, the precipitate was collected by centrifugation at 8000 rpm for 10 min, washed with deionized water and anhydrous ethanol three times, and then dried at 60°C. The dried product was annealed at 500°C under N2 atmosphere for 2 h, and then cooled to obtain ZnS:Cu quantum dots.

[0098] 120 mg of ZnS:Cu quantum dots was weighed, dispersed in 20 mL of chloroform, and then 120 μL of 3-aminopropyltriethoxysilane was added. The mixture was refluxed at 60°C for 2 h, centrifuged at 10000 rpm for 10 min, and the solid was washed with chloroform three times. The modified ZnS:Cu quantum dots were obtained by vacuum drying at 60°C.

[0099] Functionalized graphene quantum dots were prepared by dispersing 100 mg of graphene quantum dots in 10 mL of N,N-dimethylformamide, adding 100 μL of carbodiimide, 50 μL of N-hydroxysuccinimide, stirring at room temperature for 2 h, then adding 20 mg of PVDF-TrFE oligomer, continuing to stir, and freeze-drying the reaction product after dialysis in a dialysis bag with a molecular weight cut-off of 500 Da for 24 h.

[0100] 2.1 g of PVDF-TrFE oligomer and 140 mg of polyvinylpyrrolidone were added to 50 mL of 0.1 M aqueous N,N-dimethylformamide, and the mixture was stirred at 60°C until the PVDF-TrFE oligomer was completely dissolved to prepare a PVDF-TrFE solution; the modified ZnS:Cu quantum dots and the functionalized graphene quantum dots were each dispersed in DMF and ultrasonicated for 30 min; the modified ZnS:Cu quantum dot solution after ultrasonication was added dropwise to the PVDF-TrFE solution (the mass ratio of the modified ZnS:Cu quantum dots to the PVDF-TrFE oligomer was 1:35), and then the functionalized graphene quantum dot solution (the mass ratio of the functionalized graphene quantum dots to the PVDF-TrFE oligomer was 1:42) was added, and the mixture was ultrasonicated for 1 h, stirred at room temperature overnight, and then filtered through a 0.45 μm polytetrafluoroethylene filter membrane to prepare a PVDF-TrFE / ZnS:Cu / GQDs composite solution.

[0101] (3) The ITO substrate was sequentially cleaned with distilled water and ethanol, a MoS2 / ZnO core-shell quantum dot layer was prepared on the substrate by a thermal evaporation method, and after drying, the PVDF-TrFE / ZnS:Cu / GQDs composite solution was coated on the MoS2 / ZnO core-shell quantum dot layer, dried, annealed at 140°C for 2 h, cooled, and a PVDF-TrFE / ZnS:Cu / GQDs composite film layer was prepared, and finally an anode was prepared.

[0102] 2. Preparation of a cathode

[0103] A. Fe3O4 nanoparticles 500 mg and glucose 1.0 g were subjected to hydrothermal reaction at 180°C for 6 h, centrifuged at 8000 rpm for 10 min, and the precipitate was washed with deionized water 3 times and dried at 60°C to obtain Fe3O4@C quantum dots; 520 mg of a polyaniline solution was mixed with 130 mg of Fe3O4@C quantum dots-DMF under the condition of pH 1 (the mass ratio of the polyaniline to the Fe3O4@C quantum dots was 4:1), and after ultrasonic reaction, centrifugation, and washing of the solid with deionized water, the PANI / Fe3O4@C powder was dried at 60°C to obtain a PANI / Fe3O4@C powder;

[0104] B, 100 mg of PANI / Fe3O4@C powder is compounded with 6 mL of polyacrylonitrile solution by electrospinning method to prepare a fiber membrane (the mass ratio of PANI / Fe3O4@C powder to polyacrylonitrile is 1:6), the fiber membrane is treated at 280°C for 2 h in air atmosphere, naturally cooled to room temperature, and then heated at 800°C for 2 h in nitrogen atmosphere, and the carbonized fiber membrane is obtained after cooling;

[0105] C, 97 mg of ZnS, 56 mg of CaO, 229 mg of MnCO3, and 15 mL of anhydrous ethanol are mixed, ground and uniformly mixed, and then reacted at 800°C for 6 h in a nitrogen atmosphere to obtain CaZnOS:Mn 2+ nanoparticles; 50 mg of CaZnOS:Mn 2+ nanoparticles

[0106] 20 mL of anhydrous ethanol is added and ultrasonic dispersion is performed to prepare a suspension; the carbonized fiber membrane is soaked in the suspension for 30 min, repeated for 3 times, and dried at 200°C for 4 h to obtain a cathode.

[0107] 3, Reference electrode I is prepared by mixing 61 mg of zirconia, 122 mg of sodium silicate, 81 mg of sodium phosphate, and 5 mL of anhydrous ethanol, grinding and uniformly mixing, then adding 5% polyvinyl alcohol solution and grinding, and ultrasonic dispersion; the dispersion is spin-coated on the surface of a ZrO2 ceramic electrode, dried, and then heated at 300°C for 2 h, heated at 1000°C for 4 h, naturally cooled to room temperature, soaked in 0.1M HCl solution for 30 min, washed with deionized water until neutral, and dried at 60°C; Pt paste is coated on the surface of the dried electrode and a platinum wire is fixed, and the Pt paste is prepared by adding 10 mg of platinum powder to 1 mL of anhydrous ethanol, ultrasonic treatment for 20 min, adding 250 μL of 5% Nafion solution dropwise, and stirring and mixing uniformly, and then sintering at 800°C for 30 min.

[0108] 4, The four-electrode electrochemical sensing system simultaneously detects PET microplastics (MPs), Cr 6+ and ciprofloxacin (CIP)

[0109] a, Test instruments and conditions:

[0110] The four-electrode electrochemical sensor includes an electrochemical workstation, an electrolytic cell, the anode, the cathode, and the reference electrode I prepared in steps 1, 2, and 3; and a silver / silver chloride reference electrode II.

[0111] b, The standard curve preparation method is the same as that in Example 1;

[0112] c, The detection limit is calculated in the same way as in Example 1;

[0113] d, Sample detection

[0114] For products containing 0.6 μmol / L PET microplastics (MPs), 0.6 μmol / L Cr, and Cr 6+ The detection was performed using a compound electrolyte of 0.6 μmol / L ciprofloxacin (CIP) in 0.1 M PBS buffer and 35% wt [EMIM][BF4], following the same experimental method as step b. The PET microplastics (MPs) and Cr were calculated. 6+ The concentrations of ciprofloxacin (CIP) were 0.563 μmol / L and 0.579 μmol / L and 0.591 μmol / L, respectively.

[0115] e. Electrode stability test

[0116] When the same electrode was placed at room temperature for 30 days, the tested current values ​​after 30 days were 94.1%, 93.8%, and 94.6% of their initial values, corresponding to PET microplastics (MPs) and Cr. 6+ The presence of ciprofloxacin (CIP) indicates that the sensor has good stability.

Claims

1. A four-electrode electrochemical detection system, characterized in that: Includes anode, cathode, reference electrode I, and reference electrode II; The anode is prepared as follows: (1) Place 1.2-2.0g of MoS2 nanosheets in 60-80mL of distilled water, stir and mix well, and then perform a hydrothermal reaction at 175-185℃ for 7-9h. After natural cooling, centrifuge and collect the supernatant to obtain the MoS2 quantum dot solution. Place ZnO in distilled water, mix well, and then perform a hydrothermal reaction at 175-185℃ for 7-9h. After natural cooling, centrifuge and collect the precipitate. Wash and dry to obtain ZnO quantum dots. Add 10-15mL of deionized water to 90-110mg of ZnO quantum dots and sonicate to obtain ZnO quantum dot solution. Mix the MoS2 quantum dot solution with 1.0mM HCl solution to obtain a mixed solution. Add the ZnO quantum dot solution dropwise to the mixed solution while stirring. Adjust the pH to 8-10 during the dropwise addition. After the dropwise addition is complete, react at 55-65℃ for 2h to obtain MoS2 / ZnO core-shell quantum dots. (2) Cu(NO3)2 was added to Zn(NO3)2 solution and stirred until well mixed. Thiourea solution was added dropwise to nitrate mixed solution, and then ethylenediamine was added. After sealing, the mixture was reacted at 190-210℃ for 10-15h. After natural cooling, centrifugation was performed, the precipitate was collected, washed and dried, and then annealed at 450-550℃ for 2h under N2 atmosphere. After cooling, ZnS:Cu quantum dots were obtained. Weigh out ZnS:Cu quantum dots and disperse them in chloroform. Add 3-aminopropyltriethoxysilane and reflux at 55-65℃. Centrifuge, wash the solid with chloroform 2-3 times, and dry under vacuum to obtain modified ZnS:Cu quantum dots. 100-150 mg of graphene quantum dots were dispersed in N,N-dimethylformamide, 100 μL of carbodiimide and 50 μL of N-hydroxysuccinimide were added, and the mixture was stirred at room temperature for 2 h. Then, 20 mg of PVDF-TrFE oligomer was added, and the mixture was stirred again. The reaction product was dialyzed through a dialysis bag with a molecular weight cutoff of 500 Da for 24 hours, and then freeze-dried to obtain functionalized graphene quantum dots. 1.0-2.5 g of PVDF-TrFE oligomer and 100-150 mg of polyvinylpyrrolidone were added to a 0.1 MN, N-dimethylformamide aqueous solution and stirred at 60 °C until completely dissolved to obtain a PVDF-TrFE solution. Modified ZnS:Cu quantum dots and functionalized graphene quantum dots were dispersed separately in DMF and sonicated. The sonicated modified ZnS:Cu quantum dot solution was added dropwise to the PVDF-TrFE solution and stirred. Then, the functionalized graphene quantum dot solution was added, sonicated, stirred at room temperature overnight, and filtered through a 0.45 μm polytetrafluoroethylene filter membrane to obtain a PVDF-TrFE / ZnS:Cu / GQDs composite solution. (3) The ITO substrate was cleaned with distilled water and ethanol in sequence. A MoS2 / ZnO core-shell quantum dot layer was prepared on the substrate by thermal evaporation. After drying, the PVDF-TrFE / ZnS:Cu / GQDs composite liquid was coated on the MoS2 / ZnO core-shell quantum dot layer. After drying, it was annealed at 140℃ for 2 hours and cooled to obtain the PVDF-TrFE / ZnS:Cu / GQDs composite film layer. Finally, the anode was obtained. The cathode is prepared as follows: A. Fe3O4 nanoparticles were hydrothermally reacted with glucose at 150-200℃ for 6 hours, centrifuged, and the precipitate was washed 2-3 times and dried to obtain Fe3O4@C quantum dots; under pH 1-2 conditions, polyaniline solution was mixed with Fe3O4@C quantum dot-DMF, ultrasonically reacted, centrifuged, and the solid was washed and dried to obtain PANI / Fe3O4@C powder; B. PANI / Fe3O4@C powder is composited with polyacrylonitrile solution to form a fiber membrane by electrospinning. The fiber membrane is treated at 250-300℃ in air for 2 hours, naturally cooled to room temperature, and then kept at 750-850℃ in nitrogen atmosphere for 2 hours. After cooling, carbonized fiber membrane is obtained. C. Mix ZnS, CaO, MnCO3, and anhydrous ethanol, grind and mix thoroughly, then react at 750-850℃ for 6 hours under a nitrogen atmosphere to obtain CaZnOS:Mn 2+ Nanoparticles; CaZnOS:Mn 2+ Nanoparticles were added to anhydrous ethanol and ultrasonically dispersed to prepare a suspension; a carbon fiber membrane was immersed in the suspension and dried to obtain a cathode. Reference electrode I is prepared by mixing zirconium oxide, sodium silicate, sodium phosphate, and anhydrous ethanol, grinding and mixing them thoroughly, then adding 4-6% polyvinyl alcohol solution and grinding again, followed by ultrasonic dispersion. The dispersion is spin-coated onto the surface of a ZrO2 ceramic electrode, dried, and then kept at 280-320℃ for 2 hours, followed by 1000℃ for 4 hours. After naturally cooling to room temperature, it is soaked in 0.1M HCl solution for 30 minutes, rinsed until neutral, and dried. Pt slurry is coated on the dried electrode surface and platinum wire is fixed in place. The electrode is then sintered at 750-850℃ for 30 minutes.

2. The four-electrode electrochemical detection system according to claim 1, characterized in that: In step (1) of anode preparation, the volume ratio of the mixed solution to the ZnO quantum dot solution is 1-3:1, and the volume ratio of the MoS2 quantum dot solution to the HCl solution is 10:

1.

3. The four-electrode electrochemical detection system according to claim 1, characterized in that: In step (2) of anode preparation, the mass ratio of Zn(NO3)2 to Cu(NO3)2 is 20-30:1, the mass ratio of Cu(NO3)2 to thiourea is 5-8:1, and the mass-volume ratio of Cu(NO3)2 to ethylenediamine (mg: μL) is 1:5-10.

4. The four-electrode electrochemical detection system according to claim 1, characterized in that: In step (2) of anode preparation, the mass-to-volume ratio of ZnS:Cu quantum dots to 3-aminopropyltriethoxysilane (mg: μL) is 1:1-3; the mass ratio of modified ZnS:Cu quantum dots to PVDF-TrFE oligomers is 1:20-50; and the mass ratio of functionalized graphene quantum dots to PVDF-TrFE oligomers is 1:30-50.

5. The four-electrode electrochemical detection system according to claim 1, characterized in that: In step A of cathode preparation, the mass ratio of polyaniline to Fe3O4@C quantum dots is 1-5:1; in step B, the mass ratio of PANI / Fe3O4@C powder to polyacrylonitrile is 1:4-10.

6. The four-electrode electrochemical detection system according to claim 1, characterized in that: In the cathode preparation, the mass ratio of ZnS to CaO is 1-2:1, and the mass ratio of ZnS to MnCO3 is 5-10:

1.

7. The four-electrode electrochemical detection system according to claim 1, characterized in that: The mass ratio of zirconium oxide to sodium silicate is 1:1-2, and the mass ratio of sodium silicate to sodium phosphate is 1-2:

1. The Pt slurry is prepared by adding 5-20 mg of platinum powder to 0.5-2 mL of anhydrous ethanol, ultrasonicating for 10-30 min, adding 200-300 μL of 5% Nafion solution dropwise, and stirring until homogeneous.

8. The four-electrode electrochemical detection system according to claim 1, characterized in that: Reference electrode II is a silver / silver chloride electrode.

9. The application of the four-electrode electrochemical detection system according to claim 1 in pollutant detection.

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