Composite electrode based on ionic liquid / MXene material, preparation method of composite electrode and application of composite electrode in electrochemical detection of phenolic pollutants

Abstract

The invention provides a composite electrode based on an ionic liquid / MXene material, a preparation method of the composite electrode and application of the composite electrode in electrochemical detection of phenolic pollutants. Adding the few-layer MXene into deionized water, carrying out ultrasonic oscillation, slowly dropwise adding the ionic liquid into the aqueous solution of the few-layer MXene, stirring, centrifuging, washing and drying. Adding the ionic liquid / MXene material into deionized water, and oscillating and mixing at the temperature of below 20 DEG C to obtain an ionic liquid / MXene electrode material; and taking the ionic liquid / MXene electrode material, coating the surface of a glassy carbon electrode with the ionic liquid / MXene electrode material, and placing at room temperature to prepare the ionic liquid / MXene material composite electrode. The ionic liquid / MXene material composite electrode prepared by the invention shows excellent electrocatalytic activity, wide linear range and lower detection limit on phenolic compounds, is simple to operate, quick in response and high in sensitivity in the detection process, and is a novel, simple and low-cost electrochemical sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical sensors, and particularly to the preparation of an ionic liquid / MXene material composite electrode and its application in the electrochemical detection of phenolic pollutants. Background Art

[0002] A large number of phenolic compounds such as catechol, hydroquinone, bisphenol A, nonylphenol, genistein, etc. are widely used in different fields and persist as organic pollutants in our environment. Hydroquinone (HQ) is mainly used in the industrial field as a stabilizer and antioxidant. The residue of hydroquinone in industrial wastewater is highly harmful to humans and the environment. Therefore, establishing a simple and accurate method for detecting hydroquinone is of great significance for food safety and environmental monitoring. The detection of phenolic compounds is carried out by various techniques such as high-performance liquid chromatography (HPLC), fluorescence probes, etc. However, these techniques have some disadvantages, such as the need for long and complex pretreatment in sample preparation and relatively high costs. The electrochemical detection of hydroquinone has the advantages of portability, short analysis time, low power consumption, high sensitivity, etc. Summary of the Invention

[0003] The purpose of the present invention is to provide an ionic liquid / MXene material composite electrode for detecting phenolic pollutants. Therefore, the present invention uses an ionic liquid / MXene material to modify the electrode and constructs a sensitive composite electrode for detecting hydroquinone. The composite electrode shows excellent electrocatalytic activity, a wide linear range, and a low detection limit for hydroquinone.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is: Based on the preparation of an ionic liquid / MXene material composite electrode and its application in the electrochemical detection of phenolic pollutants, it is characterized in that the preparation method includes the following steps:

[0005] 1) Preparation of ionic liquid / MXene electrode material: Add an appropriate amount of few-layer MXene to deionized water, control the ultrasonic temperature below 20 °C, ultrasonically oscillate for 30 - 40 min, then slowly drop an appropriate amount of ionic liquid into the aqueous solution of few-layer MXene, magnetically stir at 300 r / min in an N2 atmosphere for 24 h, centrifuge the above mixture, wash it alternately with ethanol and water 6 times, and dry it in vacuum at 50 °C for standby. Take the ionic liquid / MXene material and add it to deionized water, control the ultrasonic temperature below 20 °C, ultrasonically oscillate for 2 h, and mix well to obtain the ionic liquid / MXene electrode material;

[0006] 2) Coat the ionic liquid / MXene electrode material obtained in step 1) on the surface of a glassy carbon electrode, and place it at room temperature for 2 - 3 h to fully combine the electrode material and the surface of the glassy carbon electrode, thus obtaining an ionic liquid / MXene material composite electrode;

[0007] Further, the few-layer MXene mentioned above is prepared by the MILD (Minimally Intense Layer Delamination) method, and the preparation method includes the following steps:

[0008] 1) Add LiF to hydrochloric acid and stir for 10 min to obtain an etchant; gradually add the multi-layer MXene powder to the etchant within 30 min, and react at 35 - 40 °C for 48 h to obtain a mixture;

[0009] 2) The mixture obtained in step 1) is first centrifugally washed twice with dilute hydrochloric acid, centrifuging at 3500 rpm for 5 min each time. After each wash, the supernatant is removed as waste;

[0010] 3) The product obtained in step 2) is further centrifugally washed several times with deionized water, centrifuging at 3500 rpm for 5 min each time. After each wash, the supernatant is removed as waste. When the pH of the supernatant ≥ 5, collect the precipitate;

[0011] 4) Add the product obtained in step 3) to deionized water, under nitrogen protection, ultrasonically oscillate for 2.5 h, centrifuge at 3500 rpm for 1 h, collect the supernatant, and freeze-dry to obtain powdery few-layer MXene.

[0012] Further, in the above-mentioned ionic liquid / MXene material composite electrode, in step 1), the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4).

[0013] Further, in the above-mentioned ionic liquid / MXene material composite electrode, in step 1), the concentration of the hydrochloric acid is 9 M.

[0014] Further, in the above-mentioned ionic liquid / MXene material composite electrode, in step 2), the concentration of the hydrochloric acid is 1 M.

[0015] The present invention provides the application of the ionic liquid / MXene material composite electrode in the electrochemical detection of phenolic pollutants.

[0016] Further, the phenolic pollutant is hydroquinone.

[0017] Further, the method is as follows: Use the ionic liquid / MXene material composite electrode as the working electrode, the Ag / AgCl electrode as the reference electrode, and the platinum wire as the counter electrode. Place the three-electrode system in a phosphate buffer solution containing hydroquinone, and use an electrochemical workstation for electrochemical determination. Electrochemical tests are carried out using cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance.

[0018] Further, in the phosphate buffer solution containing hydroquinone, the concentration of hydroquinone is 5×10 -6 M - 2×10 - 4 M, and the pH of the phosphate buffer solution containing phenolic pollutants is 7.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. In the present invention, by mixing the exfoliated MXene with an ionic liquid, the imidazole cation of the ionic liquid can be intercalated between the MXene layers, expanding its layer spacing, enhancing the stability of MXene, and preventing the collapse of the MXene sheet edges. The exfoliated MXene has a relatively large specific surface area and good conductivity, which can increase the specific surface area of the electrode.

[0021] 2. In the present invention, by using an ionic liquid to address the problems of easy stacking of MXene and poor stability in aqueous media and air, and utilizing the extraction effect of the ionic liquid, it is easy to enrich the substrate to the electrode surface for electrocatalytic reactions. The MXene and the ionic liquid are jointly used to construct a modified electrode, and their synergistic effect is used to better improve the catalytic performance of the modified electrode.

[0022] 3. In the present invention, the technical parameters in the detection process are controlled, and the raw materials of the electrode material are rationally matched, thereby improving the sensitivity of the electrochemical sensor, improving the reliability of the detection result of the hydroquinone content, and reducing the detection cost of the hydroquinone content in the environment. The composite electrode of the present invention and the hydroquinone electrochemical sensor constructed based on it have the advantages of a wide detection range, a low detection limit, good stability, high sensitivity, and low cost. Description of the Drawings

[0023] Figure 1 is the SEM morphology diagram of the MXene material before and after etching;

[0024] Among them, A, B: MAX; C, D: MXene

[0025] Figure 2 is the infrared spectrum of MXene, ionic liquid, and ionic liquid / MXene.

[0026] Figure 3 is the XRD pattern of MAX (a), MXene (b), and ionic liquid / MXene (c).

[0027] Figure 4 is the electrochemical impedance diagram of different modified electrodes in [Fe(CN)6] 3- / 4- solution;

[0028] Among them, a: bare glassy carbon electrode; b: ionic liquid / MXene material composite electrode; c: MXene electrode

[0029] Figure 5 are cyclic voltammograms of hydroquinone detected at different modified electrodes in PBS with pH = 7;

[0030] Among them, a: bare glassy carbon electrode; b: MXene electrode; c: ionic liquid / MXene material composite electrode

[0031] Figure 6 are cyclic voltammograms of 1 mM hydroquinone detected at the ionic liquid / MXene material composite electrode in PBS with pH = 7 at different scan rates.

[0032] Figure 7 is a linear graph of the scan rate versus the oxidation peak current and reduction peak current of hydroquinone.

[0033] Figure 8 are differential pulse voltammograms at different hydroquinone concentrations.

[0034] Figure 9 is a calibration graph of the peak current versus the change in hydroquinone concentration. Specific implementation manners

[0035] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0036] Example 1 Preparation of ionic liquid / MXene material composite electrode

[0037] (I) The preparation method is as follows

[0038] 1. Preparation of few-layer MXene

[0039] 1) Add 2.0 g of LiF to 40 mL of 9M hydrochloric acid and stir for 10 min to fully dissolve it. Gradually add 1.0 g of Ti3AlC2 powder to the above etching agent within 30 min and react at 35 - 40 °C for 48 h to obtain a mixture.

[0040] 2) Hydrochloric acid washing: Wash the mixture obtained in step 1) twice with 1M hydrochloric acid by centrifugation (3500 rpm, 5 min each time). After each washing, remove the supernatant as waste by pouring.

[0041] 3) Water washing: The product obtained in step 2) was washed several times with deionized water by centrifugation (3500 rpm, 5 min each time). After each washing, the acidic supernatant was removed as waste by pouring. Repeat the water washing until the pH of the supernatant ≥ 5, collect the precipitate, dissolve it in 100 mL of deionized water, under the protection of nitrogen atmosphere, ultrasonically oscillate for 2.5 h, centrifuge at 3500 rpm for 1 h, at this time collect the supernatant and freeze-dry it.

[0042] 2. Preparation of ionic liquid / MXene electrode material

[0043] Dissolve 0.5 g of few-layer MXene in 500 mL of deionized water, ultrasonically oscillate for 0.5 h, slowly drop 1.0 g of ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (dissolved in 30 mL of methanol solution) into the above-mentioned MXene, and magnetically stir at 300 r / min for 24 h under N2 atmosphere. Centrifuge the above mixture, and wash it alternately with ethanol and water by centrifugation 6 times (centrifuge at 3500 r / min for 5 min each time), and dry it in vacuum at 50 °C for standby. Take the ionic liquid / MXene material and add it to deionized water, control the ultrasonic temperature below 20 °C, ultrasonically oscillate for 2 h, and mix well to obtain the ionic liquid / MXene electrode material.

[0044] 3. Pretreatment of the electrode

[0045] Polish the glassy carbon electrode with 0.3 μm Al2O3. Then, ultrasonically wash it with ethanol and ultrapure water for 3 min in turn. Dry it with high-purity nitrogen for standby.

[0046] 4. Preparation of ionic liquid / MXene material composite electrode

[0047] Take the ionic liquid / MXene electrode material obtained in step 2, coat it on the surface of the glassy carbon electrode, and place it at room temperature for 2 - 3 h to make the electrode material and the surface of the glassy carbon electrode fully combine, thus obtaining the ionic liquid / MXene material composite electrode.

[0048] (2) Detection

[0049] Figure 1 are the SEM morphology diagrams of the MXene material before and after etching. From Figure 1 It can be seen that the SEM images of MAX shown in Figures A and B present a dense three-dimensional layered structure. The MAX etched with LiF / HCl is shown in Figures C and D. The structure of the MAX phase etched by LiF and HCl shows a transformation from a blocky shape to a sheet-like shape. It can be seen from Figures C and D that the thin sheet-like structure, because a large amount of HCl can provide a higher concentration of H + , and make it combine with Li +Ion exchange is carried out to produce expanded clay-like MAX, which is more prone to delamination, has larger dimensions, more regular flakes and no defects at the edges.

[0050] Figure 2 are the infrared spectra of MXene, ionic liquid and ionic liquid / MXene. As can be Figure 2 seen, the absorption band observed near 3445 cm -1 belongs to the absorption peak of -OH, reflecting the hydrophilicity of MXene. The signals at 620 cm -1 and 1654 cm -1 represent Ti-O and C=O respectively. The characteristic stretching vibration peak of C=N appears in the range of 1700 - 1500 cm -1 , while the peak at 1160 cm -1 is attributed to the imidazole ring, and the B-F characteristic peak at 1063 cm -1 further confirms the presence of EMIMBF4 (1-ethyl-3-methylimidazolium tetrafluoroborate).

[0051] Figure 3 are the XRD patterns of MAX (a), MXene (b) and ionic liquid / MXene (c). As can be Figure 3 seen, the characteristic peak of (002) of the etched few-layer MXene shifts to the left, and the characteristic peak of (002) of ionic liquid / MXene shifts further, indicating that the interlayer spacing of MXene becomes larger, thus indicating the successful synthesis of the ionic liquid / MXene material.

[0052] Example 2 Application of ionic liquid / MXene material composite electrode in detecting phenolic pollutants

[0053] The method is as follows: Using the ionic liquid / MXene material composite electrode as the working electrode, Ag / AgCl electrode as the reference electrode, and platinum wire as the counter electrode, place the three-electrode system in a phosphate buffer solution containing hydroquinone, and use a CHI660e electrochemical workstation for electrochemical measurement. Cyclic voltammetry, differential pulse voltammetry and electrochemical impedance are used for electrochemical testing. Draw a standard electrochemical curve according to the electrochemical measurement electrochemical signal data. In the phosphate buffer solution containing hydroquinone, the concentration range of hydroquinone measured is 5×10 -6 M - 2×10 -4 M, and the pH of the phosphate buffer solution is 7.

[0054] The working electrodes are respectively selected as:

[0055] 1) The ionic liquid / MXene material composite electrode prepared in Example 1

[0056] 2) A bare glassy carbon electrode as the working electrode

[0057] 3) MXene electrode: Dissolve MXene in deionized water to form a 1 mg / mL solution. Take 6 μL of the above solution and place it on the surface of a glassy carbon electrode. Let it stand at room temperature for 2 - 3 h. Wait for the water to evaporate to form a MXene thin film on the electrode surface, obtaining a MXene modified electrode.

[0058] (I) Electrochemical responses of ionic liquid / MXene material composite electrode, MXene electrode, and bare glassy carbon electrode in [Fe(CN)6] 3- / 4- KCl solution

[0059] Take 10 mL of a solution containing 5 mM [Fe(CN)6] 3- / 4- and 0.1 M KCl solution and place them in a beaker. Use a three - electrode system, with an Ag / AgCl electrode as the reference electrode, a platinum wire as the counter electrode, and the working electrodes being the ionic liquid / MXene material composite electrode, MXene electrode, and bare glassy carbon electrode respectively. For electrochemical measurement, use a CHI660e type electrochemical workstation to conduct electrochemical impedance testing. The test results are as Figure 4 shown.

[0060] Figure 4 are the electrochemical impedance diagrams of the bare glassy carbon electrode, MXene electrode, and ionic liquid / MXene material composite electrode in [Fe(CN)6] 3- / 4- solution. As can be Figure 4 seen, the charge transfer resistance of the ionic liquid / MXene material composite electrode is greatly reduced, proving that the ionic liquid / MXene material composite electrode can accelerate electron transfer.

[0061] (II) Detection performance of ionic liquid / MXene material composite electrode, MXene electrode, and bare glassy carbon electrode

[0062] Take 10 mL of a 0.2 mol / L phosphate buffer solution with a pH of 7 and place it in a beaker. Then add hydroquinone to the beaker to make its concentration 1 mM and mix evenly.

[0063] Use a three - electrode system, with an Ag / AgCl electrode as the reference electrode, a platinum wire as the counter electrode, and the working electrodes being the ionic liquid / MXene material composite electrode, MXene electrode, and bare glassy carbon electrode respectively. For electrochemical measurement, use a CHI660e type electrochemical workstation, and the potential scanning range is - 0.2 - 0.6 V. Detect hydroquinone. The test results are as Figure 5 shown.

[0064] Figure 5 are the CV diagrams of different electrodes for detecting hydroquinone in PBS with a pH of 7. Among them, a: bare glassy carbon electrode; b: MXene electrode; c: ionic liquid / MXene material composite electrode. As can beFigure 5 It can be seen that the current response of the ionic liquid / MXene composite electrode is the strongest, proving that the ionic liquid / MXene improves the electron transfer rate and further enhances the detection signal of the electrode.

[0065] (III) Catalytic detection performance of the ionic liquid / MXene composite electrode for hydroquinone at different concentrations

[0066] The effect of the scan rate on the peak current was studied by cyclic voltammetry in the range of 25 - 300 mV / s. As Figure 6 shown, when the scan rate increased from 25 mV / s to 400 mV / s, the oxidation peak and reduction peak currents of hydroquinone increased accordingly. After linear fitting, the obtained results are as Figure 7 shown. The oxidation peak current of hydroquinone shows a linear relationship with the scan rate. It can be seen from the equation that the oxidation peak current and reduction peak current of hydroquinone are proportional to the first power of the scan rate, indicating that the electrochemical reaction of hydroquinone is an adsorption-controlled process.

[0067] Hydroquinone was added to the phosphate buffer solution with pH = 7 to make the concentrations of hydroquinone 5, 7, 8, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200 μM respectively. The ionic liquid / MXene composite electrode prepared in Example 1 was used as the working electrode, the Ag / AgCl electrode was used as the reference electrode, and the platinum wire was used as the counter electrode. The CHI660e electrochemical workstation was selected for electrochemical measurement, and the potential scan range was -0.1 - 0.2 V. Hydroquinone was detected. The test results are as Figure 8 shown

[0068] Figure 8 are differential pulse voltammograms at different hydroquinone concentrations. Figure 9 is the calibration graph of the peak current changing with the hydroquinone concentration. As Figure 8 shown, when the concentration of hydroquinone in the phosphate buffer solution gradually increases, the oxidation peak current of the composite electrode also increases accordingly, proving that the ionic liquid / MXene composite electrode prepared in the present invention has good catalytic recognition performance for hydroquinone. As Figure 9 shown, there is a good linear relationship between the oxidation peak current and the hydroquinone concentration in the range of 5 μM - 200 μM. In the range of 5 μM - 10 μM, the linear equation is I(A) = 2.68846×10 -8 C(μM) - 3.23846×10 -8 (R 2 = 0.99718), and in the range of 10 μM - 200 μM, the linear equation is I(A) = 1.28246×10 -8 C(μM) + 1.63879×10 -7(R 2 = 0.99879), and the detection limit was 0.088 μM.

[0069] (IV) Analysis of actual samples of phenolic pollutants in the composite electrode of ionic liquid / MXene material for electrochemical detection

[0070] The recovery rate of the prepared composite electrode of ionic liquid / MXene material in tap water was tested by the standard addition method. The results are shown in Table 1. The recovery rate of hydroquinone was in the range of 92.57 - 109.57%, and its average recovery rate was 98.97%. This indicates that the prepared composite electrode of ionic liquid / MXene material has high accuracy and can be used for the detection of actual samples.

[0071] Table 1. Analysis of recovery rate detected in actual sample tap water

[0072]

Claims

1. Based on an ionic liquid / MXene composite electrode, characterized in that, The preparation method comprises the following steps: 1) Preparation of ionic liquid / MXene electrode material: Add an appropriate amount of few-layer MXene into deionized water, control the ultrasonic temperature below 20 °C, perform ultrasonic oscillation, then slowly drip an appropriate amount of ionic liquid into the aqueous solution of few-layer MXene, stir magnetically under N2 atmosphere, centrifuge the above mixture, wash it alternately with ethanol and water, and dry it in vacuum for standby. Take the ionic liquid / MXene material and add it into deionized water, control the ultrasonic temperature below 20 °C, perform ultrasonic oscillation, and mix well to obtain the ionic liquid / MXene electrode material; 2) Coat the ionic liquid / MXene electrode material obtained in step 1) on the surface of a glassy carbon electrode, and place it at room temperature for 2 - 3 h to fully combine the electrode material and the surface of the glassy carbon electrode, thus obtaining a composite electrode of ionic liquid / MXene material.

2. The composite electrode based on the ionic liquid / MXene material according to claim 1, wherein The preparation method of the few-layer MXene comprises the following steps: 1) Add LiF into hydrochloric acid, stir to obtain an etching agent; gradually add multi-layer MXene powder into the etching agent within 30 min for reaction to obtain a mixture; 2) Wash the mixture obtained in step 1) twice by centrifugation with dilute hydrochloric acid. After each washing, remove the supernatant as waste; 3) Wash the product obtained in step 2) several times by centrifugation with deionized water. After each washing, remove the supernatant as waste. When the pH of the supernatant ≥ 5, collect the precipitate; 4) Add the product obtained in step 3) into deionized water, perform ultrasonic oscillation under nitrogen protection, centrifuge, collect the supernatant, and freeze-dry to obtain powdery few-layer MXene.

3. The composite electrode based on the ionic liquid / MXene material according to claim 2, characterized in that, In step 1), the concentration of the hydrochloric acid is 9 M.

4. The composite electrode based on ionic liquid / MXene material according to claim 2, wherein In step 1), the reaction is carried out at 35 - 40 °C for 48 h.

5. The composite electrode based on ionic liquid / MXene material according to claim 2, characterized in that, The concentration of the dilute hydrochloric acid in step 2) is 1 M.

6. The composite electrode based on the ionic liquid / MXene material according to claim 1, wherein In step 1), the ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate.

7. Application of the composite electrode based on ionic liquid / MXene material according to any one of claims 1 - 6 in the electrochemical detection of phenolic pollutants.

8. The application according to claim 7, characterized in that, The phenolic pollutant is hydroquinone.

9. The application according to claim 8, characterized in that, The method is as follows: Use the composite electrode of ionic liquid / MXene material as defined in claim 1 as the working electrode, an Ag / AgCl electrode as the reference electrode, and a platinum wire as the counter electrode. Place the three-electrode system in a phosphate buffer solution containing hydroquinone, and use an electrochemical workstation for electrochemical determination. Electrochemical tests are carried out by using cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance.

10. The application according to claim 9, characterized in that In a phosphate buffer solution containing hydroquinone, the concentration of hydroquinone is 5×10 -6 M - 2×10 -4 M, and the pH of the phosphate buffer solution is 7.

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