MIP / WS2-AC@Cu-MOF-199 modified glassy carbon electrode, its preparation method, and an electrochemical sensing method for detecting perfluorooctane.

Abstract

The application discloses a kind of MIP / WS2-AC@Cu-MOF-199 modified glassy carbon electrode and its preparation method and electrochemical sensing detection perfluorooctane method, with MIP / WS2-AC@Cu-MOF-199 modified glassy carbon electrode as working electrode, Ag / AgCl electrode as reference electrode, platinum as auxiliary electrode, potassium ferricyanide / potassium ferrocyanide as charged probe molecule, and water PFOA is detected quickly using differential pulse voltammetry.The application will tungsten sulfide-activated carbon (WS2-AC) and Cu-MOF (199) are simply modified by ball milling, to strengthen the conductivity of original Cu-MOF material, to establish a simple and low-cost electrochemical sensing detection method.This method has simple detection, raw material source is extensive, and the method can effectively detect PFOA in a wide range and maintain good sensitivity.The application provides a kind of water perfluorooctane sensing detection method based on electrochemistry using MOF material, and has good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of toxic and hazardous substance detection technology, specifically relating to a glassy carbon electrode modified with MIP / WS2-AC@Cu-MOF-199, its preparation method, and an electrochemical sensing method for detecting perfluorooctane. Background Technology

[0002] Perfluorooctane (PFOA) is a typical perfluorinated compound widely used in various products. All hydrogen atoms in the PFOA carbon skeleton are replaced by fluorine atoms, forming multiple strongly bonded CF bonds (426.27 KJ / mol). Therefore, PFOA is highly persistent and almost never degrades under natural conditions. Furthermore, PFOA has a strong ability to accumulate in organisms. After environmental pollution, PFOA can enter the human body through the food chain or respiratory tract and accumulate there. Studies have shown that PFOA has varying degrees of toxicity to the immune system, nervous system, and liver in humans and animals, and has even been classified as a carcinogen. my country has established a limit of 80 ng / L for PFOA in groundwater and surface water. It is worth noting that the concentration of PFOA varies in different environments. For example, the concentration of PFOA in surface water is 10-50 μg / L, while in wastewater treatment plants it can reach 10-100 ng / L, which seriously threatens human health. Due to their recalcitrant nature, water bodies have become a significant accumulation site for PFOA in the environment. Therefore, the detection of PFOA in water bodies is of great importance.

[0003] Commonly used methods for detecting PFOA include high-performance liquid chromatography (HPLC), gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), and liquid chromatography-mass spectrometry (LC-MS). However, while HPLC and LC-MS offer good sensitivity in detecting pollutants, these methods are costly, have long analysis cycles, and require complex sample pretreatment. In recent years, to explore simpler, more convenient, and more accurate detection methods, electrochemical analysis techniques have gradually become a focus for researchers. Electrochemical analysis techniques offer excellent sensitivity, simple and easy-to-operate methods, and low cost advantages, and can accurately determine target pollutants even in complex environments. Combining this with molecular imprinting technology can further improve the accuracy of target pollutant detection, which shows great promise in the field of environmental monitoring.

[0004] Metal-organic frameworks (MOFs), as an emerging type of coordination polymer material, are hybrid porous complexes assembled from metal complexes and organic ligands, representing a novel category of highly crystalline porous materials. MOFs possess unique properties such as ultra-high porosity, large specific surface area, and tunable chemical properties. In recent years, MOFs have been widely applied in pollutant degradation, biochemical analysis, sensing and detection, and drug delivery, becoming an important research direction in multiple branches of chemistry, including inorganic and organic chemistry.

[0005] However, the method for establishing an electrochemical sensing method for detecting PFOA using MOFs is still imperfect, with problems such as low sensitivity and low detection linearity. Commonly used MOF materials have poor conductivity and cannot be well applied to the field of electrochemical sensing detection, especially with low accuracy in monitoring perfluorooctane in water. Summary of the Invention

[0006] To address the aforementioned technical problems, the first objective of this invention is to provide an IPWS2-ACCu-MOF(199) modified glassy carbon electrode and its preparation method. The second objective is to provide a method for electrochemical sensing to detect perfluorooctane (PFOA). The detection is simple, the raw materials are widely available, and this method can effectively detect PFOA over a wide range while maintaining good sensitivity.

[0007] To achieve the aforementioned first objective, the present invention provides the following technical solution: a method for preparing a glassy carbon electrode modified with MIPWS2-ACCu-MOF(199), characterized by comprising the following steps: (1) Preparation of WS2-AC: Thioacetamide and sodium tungstate were added to deionized water and dissolved. Oxalic acid and activated carbon were added and stirred. After the reaction was completed at 180 ±10℃, the mixture was cooled to room temperature, and the black product was taken out. It was washed with deionized water and anhydrous ethanol to remove unreacted impurities and dried for later use. (2) Preparation of Cu-MOF(199): Copper nitrate and pyromellitic acid were dissolved in a mixed solvent of water, ethanol and N,N dimethylformamide. The volume ratio of water, ethanol and N,N dimethylformamide was 1:1:1. The reaction was carried out at 90±5 °C. The mixture was cooled, filtered, washed and dried to obtain powdered Cu-MOF-199 for later use. (3) Weigh WS2-AC and Cu-MOF(199), put them into a ball mill and ball mill to ensure uniformity, and record it as WS2-AC / Cu-MOF(199). Weigh WS2-AC / Cu-MOF(199) and Nafion solution and disperse them evenly in ethanol. Use ultrasound to form a uniform ink, and record it as ink A. (4) Use alumina powder to polish the surface of glassy carbon electrode. Polishing removes impurities from the surface of glassy carbon electrode and gives the surface of glassy carbon electrode a mirror effect. Apply ink A to the surface of glassy carbon electrode and let it dry to serve as initial electrode A. (5) Electropolymerization reaction was carried out in a mixture of acetic acid buffer and methanol containing 0.001 M PFOA and 0.01 M o-phenylenediamine (O-PD). The volume ratio of acetic acid buffer to methanol was 2:1. A three-electrode system was constructed with the initial electrode A as the working electrode, the platinum wire electrode as the counter electrode, and the silver / silver chloride electrode as the reference electrode to complete the preparation of molecularly imprinted polymer (MIP) and obtain GCE / WS2-AC@MOF / MIP electrode. Then, the GCE / WS2-AC@MOF / MIP electrode was immersed in the elution solution and stirred to remove the PFOA template to obtain WS2-ACCu-MOF(199) modified glassy carbon electrode.

[0008] In the above scheme: In step (1), the molar ratio of thioacetamide, sodium tungstate, oxalic acid and activated carbon is 10:4:5:15-16. After dissolving, stir for 30 min-60 min and react at 180 ℃ for more than 24 h.

[0009] In the above scheme: in step (2), the mass ratio of copper nitrate and pyromellitic acid is 2:1; in step (4), the amount of ink A for the glassy carbon electrode with a diameter of 5 mm is 2.5-12.5 μL.

[0010] In the above scheme: the mass ratio of WS2-AC and Cu-MOF(199) is 1:3-3:1, and the addition ratio of WS2-AC / Cu-MOF(199) to Nafion solution and ethanol is 4mg WS2-AC / Cu-MOF(199) / 20μL Nafion solution / 2ml ethanol.

[0011] In the above scheme: In step (5), the conditions for the electropolymerization reaction are: within a potential window of 0-1.0 V, cyclic voltammetry (CV) is performed for 15-30 cycles at a scan rate of 100-200 mV / s; the eluent is an ethanol-water mixture, V 乙醇 :V H2O = 1:1.

[0012] The glassy carbon electrode modified with MIPWS2-ACCu-MOF(199) was prepared by the method described above.

[0013] The second objective of this invention is achieved as follows: a method for electrochemical sensing detection of perfluorooctane, characterized in that: a glassy carbon electrode modified with the aforementioned MIPWS2-ACCu-MOF(199) is used as the working electrode, an Ag / AgCl electrode is used as the reference electrode, platinum is used as the auxiliary electrode, potassium ferrocyanide / potassium ferricyanide is used as the charged probe molecule, phosphate buffer solution is used as the electrolyte solution, and differential pulse voltammetry is used to rapidly detect PFOA in water.

[0014] In the above scheme, the concentration of potassium ferricyanide / potassium ferrocyanide is 27.15 mM.

[0015] In the above scheme, the working conditions are: within the potential range of -0.20 V to 0.20 V, the differential pulse map is recorded with a pulse height of 25 mV / s, a pulse width of 25 ms, a step height of 4 mV / s, a step width of 75 ms, and a scan rate of 50 mV / s between -0.20 V and 0.20 V.

[0016] In the above scheme, the linear detection range of perfluorooctane is 34 ng / L - 10.20 μg / L, and the detection limit is 33.4 ng / L.

[0017] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention uses a glassy carbon electrode (GCE) modified with WS2-AC / Cu-MOF(199) / MIP as the working electrode, and additionally employs charged external probe molecules as electrochemical signal molecules. When PFOA is absent in water, the charged external probe molecules in the solution can indirectly indicate the current status of the current circuit through redox reactions, generating an electrochemical signal. When PFOA is present in water, the selective recognition effect of MIP and PFOA is utilized (after the two combine, the impedance of the circuit increases, affecting the current), causing the redox reactions of the charged external probe molecules in the solution to be affected. Finally, by recording the changes in the electrochemical signal of the external probe molecules, trace amounts of PFOA in water can be electrochemically detected. A linear relationship between the electrochemical signal and the PFOA concentration is established, and the corresponding linear regression equation is obtained.

[0018] This invention involves simple ball milling modification of tungsten sulfide-activated carbon (WS2-AC) with Cu-MOF (199) to enhance the conductivity of the original Cu-MOF material, establishing a simple and inexpensive electrochemical sensing detection method. This method is simple to implement, uses widely available raw materials, and can effectively detect PFOA over a wide range while maintaining good sensitivity. This invention provides an electrochemical method for detecting perfluorooctane in water using MOF materials, which has promising application prospects. Attached Figure Description

[0019] Figure 1This is a schematic diagram of cyclic voltammetry for modified electrodes under different conditions in the detection method of the present invention; Figure 2 This study investigates the effects of the ratio of WS2-AC and Cu-MOF and the amount of ink A applied in the experimental method.

[0020] Figure 3 This is an electrochemical graph showing the change in electrochemical signal intensity with PFOA concentration according to the present invention; wherein the buffer is a phosphate buffer with pH=7, and the PFOA concentrations are 34 ng / L, 68 ng / L, 340 ng / L, 1.36 μg / L, 3.40 μg / L, 6.8 μg / L, and 10.2 μg / L; the differential pulse voltammetry scan range is -0.2 to -0.2 V, and the scan rate is 50 mV / s.

[0021] Figure 4 This is a standard curve showing the change in electrochemical signal intensity with PFOA concentration. Detailed Implementation

[0022] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0023] Example 1 The preparation of WS2-AC was as follows: 10 mM thioacetamide (TAA) and 4 mM sodium tungstate (Na2WO4·2H2O) were added to 70 mL of deionized water. After dissolution, 5 mM oxalic acid and 15 mM activated carbon were added, and the mixture was stirred for 30 min. The reaction was carried out at 180 ℃ for 24 h. After cooling to room temperature, the black product was taken out and washed three times with deionized water and anhydrous ethanol to remove unreacted impurities. Then, it was placed in a vacuum oven at 60 ℃ overnight for later use. The obtained sample was designated as WS2 / AC.

[0024] The preparation of Cu-MOF(199) was as follows: 2.4 g of copper nitrate (Cu(NO3)·3H2O) and 1.2 g of trimesic acid (H3BTC) were dissolved in a mixed solvent of 60 mL of water, ethanol and N,N dimethylformamide (DMF) (volume ratio of 1:1:1). The mixture was treated at 90 °C for 20 h, cooled, filtered, washed and dried to obtain powdered Cu-MOF-199 for later use.

[0025] Weigh out WS2-AC and Cu-MOF(199) at mass ratios of 3:1, 2.5:1.5, 2:2, 1.5:2.5, and 1:3 respectively, and ball mill them for 30 min to ensure uniformity. This mixture is WS2-AC / Cu-MOF(199). Weigh out 4 mg of WS2-AC / Cu-MOF(199) and 20 μL of Nafion solution, disperse them evenly in 2 mL of ethanol, and sonicate to form a uniform ink, which is denoted as Ink A.

[0026] The surface of the glassy carbon electrode was polished sequentially using 0.3 μm and 0.05 μm alumina powders. Polishing removed impurities from the surface of the glassy carbon electrode, giving it a mirror-like finish. A certain volume of ink A was dropped onto the surface of the glassy carbon electrode and allowed to dry, serving as the initial electrode A.

[0027] Electropolymerization was carried out in a solution containing 0.001 M PFOA and 0.01 M o-phenylenediamine (O-PD) in acetate buffer and methanol (acetic acid buffer:methanol, V:V = 2:1, 0.1 M, pH = 5.8). A three-electrode system was constructed using initial electrode A as the working electrode, a platinum wire electrode as the counter electrode, and a silver / silver chloride electrode as the reference electrode to prepare the molecularly imprinted polymer (MIP). The working parameters were within a potential window of 0-1.0 V, and cyclic voltammetry (CV) was performed for 25 cycles at a scan rate of 200 mV / s. The resulting GCE / WS2-AC@MOF / MIP (denoted as the "MIP electrode") was obtained.

[0028] The GCE / WS2-AC@MOF / NIP electrode was obtained using the same method without adding a PFOA template. The MIP electrode was then immersed in the elution solution (V... 乙醇 :V H2O The mixture was stirred in a 1:1 solution for 8 min to remove the PFOA template (denoted as "MIP-PFOA electrode"). The electrode was washed three times with deionized water before further electrochemical characterization. The electrochemical characteristics of the initial electrode, MIP electrode, and NIP electrode were determined using cyclic voltammetry, with the above electrodes serving as the working electrode, platinum wire as the counter electrode, and silver / silver chloride electrode as the reference electrode. The electrolyte was a phosphate buffer solution containing probe molecules (probe molecules were potassium ferricyanide / potassium ferrocyanide at a concentration of 27.15 mM, and the electrolyte solution was a phosphate buffer solution (0.1 M, pH=7)).

[0029] The CV operating conditions are -0.6 to 0.6V, with 30 CV scans performed at a speed of 0.05mV / s.

[0030] PFOA at a concentration of 340 ng / L was added to an electrochemical apparatus containing 30 mL of electrolyte (phosphate buffer solution containing probe molecules) (pH=7.0). The MIP electrode was incubated in the electrolyte with stirring at 400 rpm for 12 min to reach adsorption equilibrium. A three-electrode system was used for rapid detection of PFOA in water, specifically with GCE / WS2-AC@MOF / MIP as the working electrode, a platinum wire electrode as the counter electrode, and a silver / silver chloride electrode as the reference electrode. (The electrochemical method was mainly differential pulse voltammetry (DPV), with operating conditions of a pulse height of 25 mV / s, a pulse width of 25 ms, a step height of 4 mV / s, and a step width of 75 ms within a potential range of -0.20 V to 0.20 V. Differential pulse maps were recorded at a scan rate of 50 mV / s between -0.20 V and 0.20 V.) The current effect was recorded.

[0031] Figure 2 In Figure (a), the effect of the ratio of WS2-AC to Cu-MOF on the detection method in this experiment is shown. Figure 2 In (a), the amount of ink A dropped onto the glassy carbon electrode with a diameter of 5 mm is 5 μL. Figure 2 As can be seen from (a), the current response is optimal when the mass ratio of WS2-AC to Cu-MOF(199) is 2:2.

[0032] Figure 2 In Figure (b), current images are shown for a 5 mm diameter glassy carbon electrode coated with ink A at mass ratios of WS2-AC and Cu-MOF(199) of 1:1, with amounts of 2.5 μL, 5 μL, 7.5 μL, 10 μL, and 12.5 μL, respectively. Figure 2 As can be seen from (b), the optimal ink for drop-coating a 5 mm glassy carbon electrode is A5 μL.

[0033] Different concentrations of PFOA were added to an electrochemical device containing 30 mL of electrolyte (phosphate buffer solution containing probe molecules) (pH=7.0) (concentration gradients of 34 ng / L, 68 ng / L, 340 ng / L, 1.36 μg / L, 3.40 μg / L, 6.8 μg / L, and 10.2 μg / L). The optimal MIP electrode (WS2-AC and Cu-MOF(199) mass ratio 1:1, 5 mm glassy carbon electrode coated with ink A5 μL) was incubated in the electrolyte at 400 rpm for 12 min to reach adsorption equilibrium. A three-electrode system was used for rapid detection of PFOA in water, specifically with GCE / WS2-AC@MOF / MIP as the working electrode, a platinum wire electrode as the counter electrode, and a silver / silver chloride electrode as the reference electrode. (The main electrochemical method is differential pulse voltammetry (DPV), which operates under the following conditions: a potential range of -0.20 V to 0.20 V with a pulse height of 25 mV / s, a pulse width of 25 ms, a step height of 4 mV / s, and a step width of 75 ms. Differential pulse maps are recorded at a scan rate of 50 mV / s between -0.20 V and 0.20 V.) After measurement, immerse GCE / WS2-AC@MOF / MIP in eluent (V 乙醇 :V H2O It can be reused after rinsing in a 1:1 ratio for 8 minutes.

[0034] like Figure 3 The graph shown is a graph showing the changes in electrochemical signals and PFOA concentration. Figure 3 To establish the relationship between the DPV current y and lg(C) by controlling the concentration of PFOA in the electrochemical system (34 ng / L, 68 ng / L, 340 ng / L, 1.36 μg / L, 3.40 μg / L, 6.8 μg / L, 10.2 μg / L), the following method was used: PFOA The linear relationship between concentration x and the given concentration was investigated, resulting in the corresponding linear regression equation y = -21.10788x + 88.76435, with R². 2 =0.99778.

[0035] Limit of detection: According to the formula LOD=3ờ / s, where ờ is the linear slope and is the standard deviation of the detection values ​​of 11 blank samples, the limit of detection is calculated to be 33.4 ng / L within the linear detection range of 34 ng / L-10.20 μg / L. Figure 4 The standard curve showing the change of electrochemical signal intensity with PFOA concentration is presented.

[0036] Case 1: The PFOA content was determined using the above method, with still lake water selected as the actual sample. Specifically, still lake water was taken as the water sample to be tested, centrifuged, and 30 mL of the supernatant was taken as the test solution. Then, 680 ng / L of PFOA was added, and the perfluorooctane content was determined. The recovery rate was calculated to be 118%.

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a glassy carbon electrode modified with MIP / WS2-AC@Cu-MOF-199, characterized in that, Complete the process by following these steps: (1) Preparation of WS2-AC: Thioacetamide and sodium tungstate were added to deionized water and dissolved. Oxalic acid and activated carbon were added and stirred. After the reaction was completed at 180°C, the mixture was cooled to room temperature, and the black product was taken out. It was washed with deionized water and anhydrous ethanol to remove unreacted impurities and dried for later use. (2) Preparation of Cu-MOF-199: Copper nitrate and pyromellitic acid were dissolved in a mixed solvent of water, ethanol and N,N-dimethylformamide. The volume ratio of water, ethanol and N,N-dimethylformamide was 1:1:

1. The reaction was carried out at 90 °C. After cooling, the mixture was filtered, washed and dried to obtain powdered Cu-MOF-199 for later use. (3) Weigh WS2-AC and Cu-MOF-199, put them into a ball mill and ball mill to ensure uniformity, and record it as WS2-AC@Cu-MOF-199. Weigh WS2-AC@Cu-MOF-199 and Nafion solution and disperse them evenly in ethanol. Use ultrasound to form a uniform ink, and record it as ink A. (4) Use alumina powder to polish the surface of glassy carbon electrode. Polishing removes impurities from the surface of glassy carbon electrode and gives the surface of glassy carbon electrode a mirror effect. Apply ink A to the surface of glassy carbon electrode and let it dry to serve as initial electrode A. (5) Electropolymerization reaction was carried out in a mixture of acetic acid buffer and methanol containing 0.001 M perfluorooctane and 0.01 M o-phenylenediamine. The volume ratio of acetic acid buffer to methanol was 2:

1. A three-electrode system was constructed with the initial electrode A as the working electrode, the platinum wire electrode as the counter electrode, and the silver / silver chloride electrode as the reference electrode to complete the preparation of molecularly imprinted polymer (MIP) and obtain the electrode. Then, the electrode was immersed in the elution solution and stirred to remove the perfluorooctane template to obtain the glassy carbon electrode modified with MIP / WS2-AC@Cu-MOF-199.

2. The method for preparing the MIP / WS2-AC@Cu-MOF-199 modified glassy carbon electrode according to claim 1, characterized in that: In step (1), the molar ratio of thioacetamide, sodium tungstate, oxalic acid and activated carbon is 10:4:5:15-16. After dissolution, the mixture is stirred for 30 min-60 min and reacted at 180 ℃ for more than 24 h.

3. The method for preparing the glassy carbon electrode modified with MIP / WS2-AC@Cu-MOF-199 according to claim 1, characterized in that: In step (2), the mass ratio of copper nitrate to pyromellitic acid is 2:

1.

4. The method for preparing the MIP / WS2-AC@Cu-MOF-199 modified glassy carbon electrode according to claim 1, characterized in that: The mass ratio of WS2-AC and Cu-MOF-199 is 1:3-3:

1. The addition ratio of WS2-AC@Cu-MOF-199 to Nafion solution and ethanol is 4mg WS2-AC@Cu-MOF-199:20μL Nafion solution:2ml ethanol. In step (4), the amount of ink A dropped onto the glassy carbon electrode with a diameter of 5mm is 2.5-12.5 μL.

5. The method for preparing the glassy carbon electrode modified with MIP / WS2-AC@Cu-MOF-199 according to any one of claims 1-4, characterized in that: In step (5), the electropolymerization reaction conditions are as follows: 15-30 cycles of cyclic voltammetry are performed within a potential window of 0-1.0 V at a scan rate of 100-200 mV / s; the eluent is an ethanol-water mixture. 乙醇 :V H2O = 1:

1.

6. A glassy carbon electrode modified with MIP / WS2-AC@Cu-MOF-199 prepared by the method of claim 5.

7. A method for detecting perfluorooctane using electrochemical sensing, characterized in that: Using the glassy carbon electrode modified with MIP / WS2-AC@Cu-MOF-199 as described in claim 6 as the working electrode, the Ag / AgCl electrode as the reference electrode, platinum as the auxiliary electrode, potassium ferrocyanide / potassium ferricyanide as the charged probe molecule, and phosphate buffer solution as the electrolyte solution, perfluorooctane in water was rapidly detected by differential pulse voltammetry.

8. The method for electrochemical sensing detection of perfluorooctane according to claim 7, characterized in that: The operating conditions are as follows: within a potential range of -0.20 V to 0.20 V, differential pulse maps are recorded at a scan rate of 50 mV / s with a pulse height of 25 mV, a pulse width of 25 ms, a step height of 4 mV, and a step width of 75 ms, between -0.20 V and 0.20 V.

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