A / NP-Au Electrode and Method for On-line Monitoring of Hydroquinone Intermediate Benzoquinone in Electrolytic Synthesis Based on this Electrode

Abstract

The present invention discloses an A / NP-Au electrode and a method for on-line monitoring of hydroquinone intermediate p-benzoquinone in electrolytic synthesis based on this electrode. The preparation method of the A / NP-Au electrode comprises the following steps: (1) pretreating the surface of the gold wire to remove the oil stain and oxide layer on the surface, obtaining a bright gold wire electrode surface; (2) using the gold wire as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode, forming a three-electrode system and immersing it in sulfuric acid, and performing anodic oxidation under a constant voltage to obtain an oxidized gold wire; (3) immersing the obtained oxidized gold wire in a mixed solution of ascorbic acid and stannous chloride for 10-100 s to obtain nanoporous gold, denoted as the A / NP-Au electrode. The present invention provides a method for on-line monitoring of hydroquinone intermediate p-benzoquinone in electrolytic synthesis based on this electrode, which has the characteristics of rapidity, simplicity and accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical detection, and particularly relates to an on-line monitoring method for the intermediate product benzoquinone in the electrolytic synthesis of hydroquinone. Background Art

[0002] At present, organic electrosynthesis has been widely used due to its simple operation, short process flow, energy saving and easy control. Regarding the technology of synthesizing hydroquinone by electrochemistry, since the production by electrosynthesis has the characteristics of cheap raw materials, good product quality and short process flow, it has developed rapidly in recent years. Research on the electrolytic synthesis of hydroquinone from benzene or phenol has been carried out at home and abroad. Using benzene or phenol as raw materials, lead dioxide as the anode, graphite, lead or titanium plate as the cathode, and sulfuric acid or potassium sulfate as the supporting electrolyte, the reactants are first oxidized on the anode surface to form benzoquinone or other intermediate products, and then reduced to hydroquinone on the cathode. During the electrolysis of phenol, there are many intermediate by-products and the reaction is relatively complex. The oxide of benzene, benzoquinone, can be further oxidized to maleic acid and finally oxidized to carbon dioxide. Therefore, to increase the yield of hydroquinone, it is necessary to control and monitor the intermediate products, electrolyte acidity, mass transfer process, etc. during the electrolysis process to prevent the deep oxidation of the products on the electrode or to reduce the rate of deep oxidation to a certain extent. Therefore, the on-line monitoring of benzoquinone is necessary for the electrolysis process.

[0003] At present, the reported detection methods for benzoquinone include chromatography, spectrophotometry and electrochemistry (such as CN114264706A). Although chromatography and spectrophotometry can achieve trace analysis of benzoquinone, they have problems such as demanding environmental temperature and pressure, complex operation and high cost, making it difficult to be used for on-site and large-scale detection of benzoquinone. There are relatively few reported related studies on electrochemistry at present, and the detection limit and sensitivity are not ideal. Therefore, it is very necessary to establish a low-cost, simple and fast detection method for benzoquinone.

[0004] Electrochemical methods are instrumental analysis methods for qualitative and quantitative determination of analytes based on the electrochemical properties and variation laws of substances in solution, and on the metrological relationship between electrochemical quantities such as potential, conductance, current and charge and the concentration of the analyte. Electrochemical detection usually has the following advantages: Electrochemical detectors are cheaper than spectroscopic detectors, and electrochemical devices (including electrodes) can be easily minimized to develop portable sensors with simple procedures, and the energy requirement is low, which can be used for laboratory or on-site measurements. Summary of the Invention

[0005] The first technical problem to be solved by the present invention is to provide a preparation method of an A / NP-Au electrode for benzoquinone detection.

[0006] The second problem to be solved by the present invention is to provide a rapid, simple and accurate online monitoring method for hydroquinone intermediate benzoquinone based on the A / NP-Au electrode, which can be directly used for detecting the concentration of benzoquinone in the process of electrolytic synthesis of hydroquinone, and solve the problems of complex operation steps, long detection time and high detection cost in the prior art.

[0007] To achieve the above-mentioned invention object, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a preparation method of an A / NP-Au electrode for benzoquinone detection, including the following steps:

[0009] (1) Pretreatment process: Pretreat the surface of the gold wire to remove the surface oil and oxide layer, obtain a bright gold wire electrode surface. To save costs, the length of the gold wire entering the solution can be controlled, and the excess part of the gold wire electrode is wrapped and protected with a tetrafluoro capillary for the next preparation;

[0010] (2) Surface etching: Use the gold wire as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode to form a three-electrode system and immerse it in sulfuric acid, and perform anodic oxidation under a constant voltage to obtain an oxidized gold wire;

[0011] (3) Chemical reduction: Immerse the obtained oxidized gold wire in a mixed solution of ascorbic acid and stannous chloride for 10-100 s, and the surface of the gold wire is immediately reduced to elemental gold to obtain nanoporous gold, denoted as the A / NP-Au electrode.

[0012] Preferably, in the step (1), the pretreatment method is: ultrasonically treat the gold wire in deionized water, absolute ethanol and acetone respectively for 5-10 min.

[0013] Preferably, in the step (2), the concentration range of the sulfuric acid is 0.5-2.0 mol / L, and the most preferred is 1.5 mol / L.

[0014] Preferably, in the step (2), the constant voltage range is 1.8-2.6 V, and the most preferred is 2.2 V.

[0015] Preferably, in the step (2), the anodic oxidation time range is 60-140 s, and the most preferred is 100 s.

[0016] Preferably, in the step (3), in the mixed solution of ascorbic acid and stannous chloride, the concentration range of ascorbic acid is 0.1-1.0 mol / L, and the most preferred is 0.8 mol / L; the molar ratio of ascorbic acid to stannous chloride is 1:0.1-0.5, and the most preferred is 1:0.3.

[0017] In a second aspect, the present invention provides an on-line monitoring method for electrolytic synthesis of hydroquinone intermediate p-benzoquinone based on the A / NP-Au electrode. This method uses a detachable on-line monitoring device, which includes a detection cell, a three-electrode monitoring probe, a magnetic stir bar, and a micro-sampler. The magnetic stir bar is placed in the detection cell. The three-electrode monitoring probe is composed of an A / NP-Au electrode prepared by the above preparation method as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The micro-sampler is provided with a sampling tube and a dosing tube. Two holes are provided on the lid of the detection cell, and the two holes are respectively used to fix the three-electrode monitoring probe and the dosing tube. The three-electrode monitoring probe and the dosing tube are respectively fixed by rubber stoppers matching the holes. One end of the three-electrode monitoring probe is connected to an electrochemical workstation, and one end is placed in the detection cell to contact the liquid in the detection cell. The dosing port of the dosing tube is located in the detection cell, and the sampling tube of the micro-sampler is connected to an electrolytic cell;

[0018] The method includes the following steps:

[0019] (a) Add a CH 3 COOH-CH 3 COONa buffer solution with a pH of 2.5 to 6.5 into the detection cell, turn on the magnetic stirrer, and then start the electrochemical workstation to set the applied voltage to 0.12 to 0.16 V and a certain treatment time. After waiting for the initial current to stabilize, add a p-benzoquinone standard solution prepared with a certain amount of CH 3 COOH-CH 3 COONa buffer solution with a pH of 2.5 to 6.5 through the dosing tube of the micro-sampler. p-Benzoquinone is immediately reduced to produce a current value, and the corresponding reduction current value is recorded. Thereafter, at regular intervals, add a certain amount of p-benzoquinone standard solution prepared with CH 3 COOH-CH 3 COONa buffer solution with a pH of 2.5 to 6.5 through the dosing tube of the micro-sampler to obtain their respective corresponding reduction current values; then establish a standard curve and a linear regression equation for the reduction current value of p-benzoquinone and the cumulative concentration of p-benzoquinone in the detection cell at that time;

[0020] (b) Timely and quantitatively collect the electrolyte during the electrolytic synthesis of hydroquinone as a test sample through the sampling tube of the micro-sampler, add it to the detection cell through the dosing tube, obtain the reduction current value of p-benzoquinone under the same measurement conditions as in step (a), and substitute this reduction current value into the standard curve of the reduction current value and concentration of p-benzoquinone obtained in step (a) to calculate the concentration of p-benzoquinone in the test sample.

[0021] Preferably, the concentration range of the p-benzoquinone standard solution is 0.3 μmol / L to 580 μmol / L.

[0022] Preferably, the pH value of the CH 3 COOH-CH 3 COONa buffer solution ranges from 5.

[0023] Preferably, the applied voltage is 0.14V.

[0024] In step (b) of the present invention, for each measurement of a sample to be tested, the detection cell is disassembled and a new CH 3 COOH-CH 3 COONa buffer solution is replaced, and then the next sample to be tested is measured. Since the samples to be tested are sampled at regular intervals, the reaction process of electro-synthesizing hydroquinone can be monitored online.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. The present invention provides an electrochemical detection method for online determination of p-benzoquinone content. The p-benzoquinone is quantitatively determined by using the electrochemical detection method. Compared with the commonly used liquid chromatography method, the biggest advantage of the electrochemical detection method is that the instrument cost is low, the operation is convenient, the detection speed is fast, and the sensitivity is high.

[0027] 2. The electrode used in the electrochemical detection method of the present invention is a gold electrode, which has low production cost, simple and rapid production process. The nanoporous gold sensor has excellent electrochemical sensing performance for detecting p-benzoquinone, with a low detection limit, high stability, good reproducibility and selectivity, thus being suitable for trace detection of p-benzoquinone.

[0028] 3. The detection period of the present invention is short and it is suitable for online monitoring. The test process can be completed in about 2 minutes. The electrochemical workstation is small in volume and the equipment is easy to carry. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the preparation flow chart of the A / NP-Au electrode;

[0030] Figure 2 is the scanning electron microscope image of the A / NP-Au electrode before and after reduction;

[0031] Figure 3a and 3b are respectively the I-t curve of continuously adding p-benzoquinone solutions with different concentrations in the buffer solution and the I-C linear fitting curve of the corresponding current response values of different concentrations;

[0032] Figure 4 is the schematic diagram of the online monitoring process of p-benzoquinone;

[0033] Figure 5 is the schematic diagram of the monitoring probe;

[0034] Figure 6 I-t curve of the A / NP-Au electrode in the presence of hydroquinone and interfering substances of the same concentration. Detailed implementation mode

[0035] The following is a further description of the present invention in combination with embodiments. The present invention relates to an electrochemical detection method for on-line monitoring of hydroquinone content, but the protection scope of the present invention is not limited to these embodiments.

[0036] The detection principle of the electrochemical method of the present invention is as follows: Since hydroquinone containing a C=O double bond can be reduced and broken on the electrode surface, and then a hydrogenation reaction occurs to generate hydroquinone with two phenolic hydroxyl groups. The current value in the electrochemical reaction process is recorded by chronoamperometry or linear sweep voltammetry, and its reduction current is linearly related to the hydroquinone concentration within a certain range. Accordingly, quantitative analysis of hydroquinone can be achieved.

[0037]

[0038] The three-electrode monitoring probe used in the embodiment of the present invention is as Figure 5 shown, with an A / NP-Au electrode as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode to form a three-electrode monitoring probe.

[0039] The detachable on-line monitoring device used in the embodiment of the present invention is as Figure 4 shown, including a detection cell, a three-electrode monitoring probe, a magnetic stirrer and a micro-syringe. The micro-syringe is provided with a sampling tube and a dosing tube. Two holes are provided on the lid of the detection cell, and the two holes are respectively used to fix the three-electrode monitoring probe and the dosing tube. The three-electrode monitoring probe and the dosing tube are respectively fixed by rubber stoppers matching the holes. One end of the three-electrode monitoring probe is connected to an electrochemical workstation, and one end is placed in the detection cell to contact the buffer solution in the detection cell. The dosing port of the dosing tube is located inside the detection cell, and the sampling tube of the micro-syringe is connected to an electrolytic cell.

[0040] The micro-syringe used in the embodiment of the present invention is an intelligent flow type peristaltic pump, brand: Chuangrui, model: BT100LC.

[0041] Example 1

[0042] This embodiment provides a preparation method for rapidly preparing an A / NP-Au electrode, including the following steps

[0043] (1) Pretreatment process: The surface of the gold wire (φ = 0.5 mm) was pretreated. The gold wire was placed in deionized water, absolute ethanol, and acetone respectively for ultrasonic treatment, and the ultrasonic time was maintained for 5 min. The oil stains and oxide layers on the surface of the gold wire electrode were removed, and a bright gold wire electrode surface was obtained. The excess part was wrapped with a Teflon capillary, and the length of the gold wire immersed in the solution was 2 mm;

[0044] (2) Surface etching: The gold wire was used as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode to form a three-electrode system and immerse it in 1.5 mol / L sulfuric acid. Anodic oxidation was carried out under a constant voltage, with an oxidation potential of 2.2 V and an oxidation time of 100 s to obtain oxidized gold wire;

[0045] (3) Chemical reduction: The obtained oxidized gold wire was immersed in a mixed solution of ascorbic acid and stannous chloride. The concentration of ascorbic acid was 1.0 mol / L, and the molar ratio of ascorbic acid to stannous chloride was 1:0.3. The surface of the gold wire was immediately reduced to elemental gold to obtain nanoporous gold, denoted as A / NP-Au electrode;

[0046] Figure 1 is the preparation flow chart of the A / NP-Au electrode, Figure 2 are the scanning electron microscope images of the electrode surface before and after reduction. The surface of the oxidized nanoporous gold is a flaky structure with a length of about 10 μm. The roughness of the reduced nanoporous gold increases, and gold nanoparticles are stacked on the surface, with a length of about 50 nm. This method can not only achieve the rapid preparation of the electrode, but also greatly improve the electrochemical active surface area of the nanoporous gold.

[0047] Example 2

[0048] Refer to Example 1 to prepare the A / NP-Au electrode, and only change the sulfuric acid concentration during anodic oxidation in step (2) to 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, and 2.0 mol / L to investigate the effects of different sulfuric acid concentrations on ECSA (electrochemical active surface area) and Rf (roughness factor).

[0049] Using the A / NP-Au prepared in Example 2 as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl as the reference electrode to construct a three-electrode probe as Figure 5 shown. As in Figure 4Add 0.5 M sulfuric acid solution to the detection cell of the detachable on-line monitoring device shown. Perform cyclic voltammetry scanning in 0.5 M sulfuric acid solution. There is an obvious reduction peak at 0.90 V for the oxidized gold on the surface of the A / NP-Au electrode. By calculating the charge integration of the reduction peak, the ECSA (0.77 - 1.58) and Rf (23.31 - 47.88) of the A / NP-Au electrodes prepared at different sulfuric acid concentrations are obtained. The results are shown in Table 1. The results show that when the sulfuric acid concentration is 1.5 mol / L, the ECSA and Rf on the electrode surface reach the maximum values, which are 1.58 and 47.88 respectively.

[0050] Table 1. ECSA and Rf values corresponding to different sulfuric acid concentrations

[0051] Sulfuric acid concentration / mol / L ECSA Rf 0.5 0.77 23.31 1.0 1.08 32.63 1.5 1.58 47.88 2.0 1.33 40.30

[0052] Example 3

[0053] Refer to Example 1 to prepare the A / NP-Au electrode, and only change the oxidation potential during anodic oxidation in step (2) to 1.8 V, 2.0 V, 2.2 V, 2.4 V, 2.6 V, and investigate the effects of different oxidation potentials on the ECSA and Rf of the A / NP-Au electrode.

[0054] Use the A / NP-Au prepared in Example 3 as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl as the reference electrode to construct a three-electrode probe as shown in Figure 5 shown. Add 0.5 M sulfuric acid solution to the detection cell of the detachable on-line monitoring device as shown in Figure 4 shown. Perform cyclic voltammetry scanning in 0.5 M sulfuric acid solution. There is an obvious reduction peak at 0.90 V for the oxidized gold on the electrode surface. By calculating the charge integration of the reduction peak, the ECSA (0.56 - 1.54) and Rf (17.09 - 46.67) of the A / NP-Au electrodes prepared at different oxidation potentials are obtained. See Table 1 for details. The results show that when the oxidation potential is 2.2 V, the ECSA and Rf on the electrode surface reach the maximum values, which are 1.54 and 46.67 respectively.

[0055] Table 2. ECSA and Rf values corresponding to different oxidation potentials

[0056] Oxidation potential / V ECSA Rf 1.8 0.56 17.09 2.0 0.72 21.76 2.2 1.54 46.67 2.4 1.49 45.07 2.6 0.97 29.53

[0057] Example 4

[0058] Refer to Example 1 to prepare the A / NP-Au electrode, and only change the anodic oxidation time in step (2) to 60 s, 80 s, 100 s, 120 s, 140 s, and investigate the effects of different oxidation times on ECSA and Rf.

[0059] Using the A / NP-Au prepared in Example 4 as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode, a three-electrode probe as shown in Figure 5 was constructed. Add 0.5 M sulfuric acid solution to the detection cell of the detachable on-line monitoring device as shown in Figure 4 . Perform cyclic voltammetry scanning in the 0.5 M sulfuric acid solution. There is an obvious reduction peak at 0.90 V for the gold oxide on the electrode surface. By calculating the charge integration of the reduction peak, the ECSA (0.92 - 1.61) and Rf (27.97 - 48.78) of the A / NP-Au electrodes prepared at different oxidation times were obtained, as shown in Table 3 for details. The results show that when the oxidation time is 100 s, the ECSA and Rf on the electrode surface reach the maximum values, which are 1.61 and 48.78 respectively.

[0060] Table 3. ECSA and Rf values corresponding to different oxidation times

[0061] Oxidation time / s ECSA Rf 60 0.92 27.97 80 1.38 41.96 100 1.61 48.78 120 1.35 40.91 140 1.14 34.54

[0062] Example 5

[0063] Refer to Example 1 to prepare the A / NP-Au electrode, and only change the mixed solution of ascorbic acid and stannous chloride during chemical reduction in step (3) to ascorbic acid solution, and the concentrations of ascorbic acid are 0.1 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, and 1.0 M to obtain the A / NP-Au electrodes. Investigate the influence of ascorbic acid with different concentrations on the electrode performance.

[0064] Using the A / NP-Au prepared in Example 5 as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode, a three-electrode probe as shown in Figure 5 was constructed. Add a CH 3 COOH-CH 3 COONa buffer solution with a pH of 5 to the detection cell of the detachable on-line monitoring device as shown in Figure 4 , and add p-benzoquinone to obtain a 5 mM p-benzoquinone buffer solution. Perform LSV curve testing in the p-benzoquinone solution. Set the initial potential to 0.4 V, the termination potential to 0 V, and the scan rate to 50 mV / s. A reduction peak current of p-benzoquinone is generated at 0.17 V. The test results are shown in Table 4.

[0065] Table 4. Current response values corresponding to different concentrations of ascorbic acid

[0066] Ascorbic acid concentration / mol / L Current response value / μA 0.1 -45.34 0.2 -60.57 0.4 -82.43 0.6 -90.71 0.8 -93.82 1.0 -93.29

[0067] Example 6

[0068] Prepare the A / NP-Au electrode with reference to Example 1. Only in the mixed solution of ascorbic acid and stannous chloride during chemical reduction in step (3), fix the concentration of ascorbic acid at 0.8 mol / L, and change the molar ratio of ascorbic acid to stannous chloride to 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5 to obtain the A / NP-Au electrode. Investigate the influence of ascorbic acid with different concentrations on the performance of detecting p-benzoquinone.

[0069] Use the A / NP-Au prepared in Example 6 as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl as the reference electrode to construct a three-electrode probe as shown in Figure 5 as shown. Add a CH Figure 4 COOH-CH 3 COONa buffer solution with a pH of 5 into the detection cell of the detachable on-line monitoring device as shown in 3 as shown, and add p-benzoquinone to obtain a 5 mM p-benzoquinone buffer solution. Perform LSV curve tests in the 5 mM p-benzoquinone buffer solution. Set the initial potential to 0.4 V, the termination potential to 0 V, and the scanning rate to 50 mV / s. A reduction peak current of p-benzoquinone is generated at 0.17 V, and record the corresponding current response value. The test results are shown in Table 5.

[0070] The enediol group in ascorbic acid has reducibility and can reduce gold oxide. The concentration range of ascorbic acid is 0.1 - 1.0 M. Within a certain range, the higher the concentration of ascorbic acid, the better the reduction performance of p-benzoquinone. When the concentration exceeds 0.8 M, the performance reaches a steady state. 0.8 M ascorbic acid is the most preferred. The reduction current value range of p-benzoquinone is -93.82 to -45.34 μA, and the optimal value is -93.82 μA. Stannous chloride is an inorganic substance with strong reducibility, but it is easily decomposed into precipitates in neutral aqueous solutions and exists stably in acidic solutions. The alcoholic hydroxyl group of ascorbic acid is easily dissociated to release H + with the properties of an acid. Therefore, consider the mixture of ascorbic acid and stannous chloride as a reducing agent to reduce gold oxide. The molar ratio range of ascorbic acid to stannous chloride is 1:0.1 - 0.5. Within a certain range, the lower the ratio of ascorbic acid to stannous chloride, the better the reduction performance of p-benzoquinone. When the ratio exceeds 1:0.3, the mixture solution becomes turbid, suspecting that excessive hydrolysis of stannous chloride produces precipitates and affects its reduction performance. Therefore, when the molar ratio of ascorbic acid to stannous chloride is 1:0.3, it is the most preferred. The reduction current value range of p-benzoquinone is -101.18 to -20.96 μA, and the optimal value is -100.18 μA.

[0071] Table 5. Current response values corresponding to different molar ratios of ascorbic acid and stannous chloride

[0072] Ascorbic acid: Stannous chloride (mol) Current response value / μA 1:0.1 -53.74 1:0.2 -82.37 1:0.3 -101.18 1:0.4 -45.59 1:0.5 -20.96

[0073] Example 7

[0074] This example was to investigate the 3 COOH-CH 3 effect of different pH values of the COONa buffer solution on the performance of the A / NP-Au electrode, and LSV curve tests were carried out.

[0075] Using the A / NP-Au electrode prepared in Example 1 as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode, a three-electrode probe as shown in Figure 5 was constructed. In the detection cell of the detachable on-line monitoring device as shown in Figure 4 CH with pH values of 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, and 6.5 were respectively added 3 COOH-CH 3 COONa buffer solution, and then p-benzoquinone was added to obtain a 5 mM p-benzoquinone buffer solution. LSV curve tests were carried out in the 5 mM p-benzoquinone buffer solution. The initial potential was set to 0.4 V, the termination potential was 0 V, and the scanning rate was 50 mV / s. A p-benzoquinone reduction peak current was generated at 0.17 V. The results showed that as the pH value (2.5, 3, 3.5, 4, 4.5) increased, the reduction peak current also increased. When the pH value further increased to 5, 5.5, 6, and 6.5, the peak current decreased. When the pH values were 4.5 and 5, the peak currents were not much different and the reaction potential was lower at pH 5. Therefore, pH 5 was selected as the optimal condition for detecting p-benzoquinone.

[0076] Example 7

[0077] This example was to investigate the effect of different applied voltages on the p-benzoquinone reduction current.

[0078] Using the A / NP-Au electrode prepared in Example 1 as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode, a three-electrode probe as shown in Figure 5 was constructed. In the detection cell of the detachable on-line monitoring device as shown in Figure 4 CH with pH 5 was added 3 COOH-CH 3 COONa buffer solution, and chronoamperometry tests were carried out in this buffer solution.

[0079] First, turn on the magnetic stirrer, and then start the electrochemical workstation to set the electrochemical parameters: the applied voltages are set to 0.12V, 0.13V, 0.14V, 0.15V, and 0.16V respectively, and the time is set to 800s. After the current becomes stable, start adding 50 μmol / L of p-benzoquinone solution (this concentration is the final concentration of the system after addition) at 200s. The p-benzoquinone is immediately reduced and a current value appears. Thereafter, add 50 μmol / L of p-benzoquinone solution every 50s through the sampling tube of the micro-syringe for I-t test. The results show that as the applied voltage increases, the current shows a downward trend. When the applied voltage reaches 0.14V, the current decline reaches the maximum value, but further increase will have a decaying effect on the current value. The preferred applied voltage is 0.14V as the application condition for A / NP-Au electrochemical detection.

[0080] Example 8

[0081] This example is about the application of the A / NP-Au sensor in p-benzoquinone solutions with different concentrations. Under the preferred conditions, I-t test is carried out in the CH 3 COOH-CH 3 COONa solution.

[0082] Use the A / NP-Au electrode prepared in Example 1 as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode to form a three-electrode probe as shown in Figure 5 shown. Add the CH with pH 5 in the detection cell of the detachable on-line monitoring device as shown in Figure 4 Figure 4 3 COOH-CH 3 COONa buffer solution, and carry out chronoamperometry test in this buffer solution.

[0083] First, turn on the magnetic stirrer, and then turn on the electrochemical workstation to set the electrochemical parameters: the applied voltage is 0.14V and the time is 2100s. After the current becomes stable, start adding a certain concentration of p-benzoquinone solution every 50s through the sampling tube of the micro-syringe at 200s. The concentration settings are shown in Figure 3 for details.

[0084] As shown in Figure 3, draw the p-benzoquinone current (I)-concentration (C) standard curve according to the current values and the cumulative concentrations of the corresponding p-benzoquinone standard solutions, and obtain the linear regression equation I (μA) = -0.063C BQ (μM) - 0.705 (R 2 = 0.999), C BQ : 0.39 μM–575.74 μM, where I represents the average current value in the time period of 50 - 100s after adding p-benzoquinone with different concentrations, C represents the p-benzoquinone concentration, and R represents the correlation coefficient.

[0085] Example 9

[0086] This example is for the monitoring of the phenol electrolysis reaction process.

[0087] Assemble a diaphragm plate-and-frame electrolytic cell: Use a PbO 2 electrode as the anode, a lead mesh electrode as the cathode, and a Nafion114 cation exchange membrane as the diaphragm. Prepare the electrolyte: The cathode electrolyte is H 2 SO 4 solution (concentration 1.0 mol / L), and the anode electrolyte is a mixture of a phenol solution (concentration 5 g / L) and H 2 SO 4 solution (concentration 1.0 mol / L). Control the electrolysis temperature at 30 °C, and conduct an electrolysis experiment in the electrolytic cell using a regulated DC power supply, controlling the current density at 10 mA·cm -2 , and the electrolysis time at 4 h. During the electrolysis process, collect the electrolyte at regular intervals and in fixed amounts through the sampling tube of a micro-syringe. Set the parameters of the micro-syringe as follows: the sampling volume is 6 μL, the sampling time is 1 s, and press "start" to sample every certain electrolysis time. At the same time, collect a certain amount of electrolyte from the electrolytic cell at regular intervals for HPLC liquid-phase detection.

[0088] Use the A / NP-Au electrode prepared in Example 1 as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode to form a three-electrode probe as shown in Figure 5 . Add a CH Figure 4 COOH-CH 3 COONa buffer solution with a pH of 5 to the detection cell of the detachable on-line monitoring device as shown in 3 .

[0089] First, turn on the magnetic stirrer, then start the electrochemical workstation and set the applied voltage to 0.14 V. After waiting for the initial current to stabilize, directly inject a fixed amount of electrolyte into the detection cell through the sampling tube of the micro-sampler. The benzoquinone is immediately reduced and a current value appears. The concentration can be calculated from the reaction current value. Then disassemble the detection cell and replace it with a new CH 3 COOH-CH 3 COONa buffer solution with a pH of 5. Then, take the electrolyte at regular intervals to detect the benzoquinone concentration. Repeat the above operations, sample regularly, and the data is visually observable to monitor the reaction process. The monitoring results are shown in Table 6. By comparing the electrochemical detection results with the HPLC detection results, it can be seen that the method of the present invention can well on-line monitor the phenol electrolysis reaction process.

[0090] Table 6. Monitoring of the content of the intermediate product benzoquinone in the phenol electrolysis reaction process by the A / NP-Au electrode

[0091]

[0092] Example 11

[0093] This example is to investigate the anti-interference ability of the A / NP-Au electrochemical sensor.

[0094] Using the A / NP-Au electrode prepared in Example 1 as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode, a three-electrode probe as shown in Figure 5 is constructed. In the detection cell of the detachable on-line monitoring device as shown in Figure 4 , add a CH 3 COOH-CH 3 COONa buffer solution with a pH of 5, and perform chronoamperometry tests in this buffer solution.

[0095] First, turn on the magnetic stirrer, and then turn on the electrochemical workstation to set the electrochemical parameters: the applied voltage is 0.14 V, and the time is 500 s. After the current stabilizes, add a 50 μmol / L p-benzoquinone solution at 100 s, add a 50 μmol / L phenol solution at 150 s, add a 50 μmol / L hydroquinone solution at 200 s, add a 50 μmol / L catechol solution at 250 s, add a 50 μmol / L maleic acid solution at 300 s, add a 50 μmol / L oxalic acid solution at 350 s, and add a 50 μmol / L p-benzoquinone solution at 400 s. Draw the p-benzoquinone current (I)-time (t) curve according to the current values and time. As shown in Figure 6 , the added interfering substances have basically no effect on the current curve.

[0096] Example 12

[0097] This example is to investigate the repeatability, reproducibility, and long-term stability of the A / NP-Au electrochemical sensor.

[0098] Repeatability: Using the A / NP-Au electrode prepared in Example 1 as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode, a three-electrode monitoring probe is constructed. A detachable on-line monitoring device includes a detection cell, a three-electrode monitoring probe, a magnetic stir bar, and a rubber stopper matching the open end of the detection cell. The three-electrode monitoring probe is fixed through the rubber stopper, one end is connected to the electrochemical workstation, and one end is placed in a CH 3 COOH-CH 3In the COONa buffer solution, chronoamperometry tests were carried out in this buffer solution. First, turn on the magnetic stirrer, and then turn on the electrochemical workstation to set the electrochemical parameters: the applied voltage is 0.14 V and the time is 200 s. After the current is stable, add 50 μmol / L p-benzoquinone solution at 100 s. After repeating the experiment 5 times, the relative standard deviation of the current is 1.09%.

[0099] Reproducibility: Using the A / NP-Au electrode prepared in Example 1 as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode to form a three-electrode monitoring probe. A detachable on-line monitoring device includes a detection cell, a three-electrode monitoring probe, a magnetic stir bar, and a rubber stopper matching the open end of the detection cell. The three-electrode monitoring probe is fixed through the rubber stopper, one end of which is connected to the electrochemical workstation and the other end is placed in the CH with a pH of 5 in the detection cell 3 COOH-CH 3 In the COONa buffer solution, chronoamperometry tests were carried out in this buffer solution. First, turn on the magnetic stirrer, and then turn on the electrochemical workstation to set the electrochemical parameters: the applied voltage is 0.14 V and the time is 200 s. After the current is stable, add 50 μmol / L p-benzoquinone solution at 100 s. After testing 5 A / NP-Au electrodes prepared according to the method of Example 1, the relative standard deviation of the current is 3.69%.

[0100] Long-term stability: Using the A / NP-Au electrode prepared in Example 1 as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode to form a three-electrode monitoring probe. A detachable on-line monitoring device includes a detection cell, a three-electrode monitoring probe, a magnetic stir bar, and a rubber stopper matching the open end of the detection cell. The three-electrode monitoring probe is fixed through the rubber stopper, one end of which is connected to the electrochemical workstation and the other end is placed in the CH with a pH of 5 in the detection cell 3 COOH-CH 3 In the COONa buffer solution, chronoamperometry tests were carried out in this buffer solution. First, turn on the magnetic stirrer, and then turn on the electrochemical workstation to set the electrochemical parameters: the applied voltage is 0.14 V and the time is 200 s. After the current is stable, add 50 μmol / L p-benzoquinone solution at 100 s. The electrodes prepared according to the method of Example 1 were stored at room temperature for 1, 3, 7 days and 30 days respectively. After taking the electrodes stored at room temperature for 1, 3, 7 days and 30 days respectively for determination, the current response signal value of p-benzoquinone remained above 90% of the initial measured current value after 7 days and above 80% of the initial measured current value after 30 days.

Claims

1. An on-line monitoring method for hydroquinone intermediate p-benzoquinone in electrolytic synthesis based on A / NP-Au electrode, Characterized in that: This method uses a detachable on-line monitoring device, which includes a detection cell, a three-electrode monitoring probe, a magnetic stirrer and a micro-sampler. The magnetic stirrer is placed in the detection cell. The three-electrode monitoring probe is composed of an A / NP-Au electrode as the working electrode, a platinum electrode as the counter electrode, and an Ag / AgCl electrode as the reference electrode. The micro-sampler is provided with a sampling tube and a dosing tube. There are two holes on the lid of the detection cell, which are respectively used to fix the three-electrode monitoring probe and the dosing tube. The three-electrode monitoring probe and the dosing tube are respectively fixed by rubber stoppers matching the holes. One end of the three-electrode monitoring probe is connected to an electrochemical workstation, and one end is placed in the detection cell to contact the liquid in the detection cell. The dosing port of the dosing tube is located in the detection cell, and the sampling tube of the micro-sampler is connected to the electrolytic cell; This method includes the following steps: (a) Add CH with pH 2.5 - 6.5 in the detection cell 3 COOH - CH 3 COONa buffer solution, turn on the magnetic stirrer, then start the electrochemical workstation to set the applied voltage to 0.12 - 0.16 V and a certain treatment time. After waiting for the initial current to stabilize, add the p - benzoquinone standard solution prepared with a certain amount of CH with pH 2.5 - 6.5 3 COOH - CH 3 COONa buffer solution through the sampling tube of the micro - sampler. The p - benzoquinone is immediately reduced and a current value appears. Record the corresponding reduction current value. Thereafter, add a certain amount of p - benzoquinone standard solution prepared with CH with pH 2.5 - 6.5 3 COOH - CH 3 COONa buffer solution through the sampling tube of the micro - sampler at certain intervals to obtain their respective corresponding reduction current values; then establish the standard curve and linear regression equation of the p - benzoquinone reduction current value and the cumulative concentration of p - benzoquinone in the detection cell at that time; (b) Timely and quantitatively collect the electrolyte during the electrolytic synthesis of hydroquinone as a test sample through the sampling tube of the micro-sampler, add it to the detection cell through the dosing tube, obtain the reduction current value of p-benzoquinone under the same measurement conditions as in step (a), and substitute the reduction current value into the standard curve of the reduction current value and concentration of p-benzoquinone obtained in step (a) to calculate the concentration of p-benzoquinone in the test sample; The preparation method of the A / NP-Au electrode includes the following steps: (1) Pretreatment process: Pretreat the surface of the gold wire to remove the surface oil and oxide layer to obtain a bright gold wire electrode surface; (2) Surface etching: Use the gold wire as the working electrode, the platinum electrode as the counter electrode, and the Ag / AgCl electrode as the reference electrode to form a three-electrode system and immerse it in sulfuric acid, and perform anodic oxidation under a constant voltage to obtain oxidized gold wire; (3) Chemical reduction: Immerse the obtained oxidized gold wire in a mixed solution of ascorbic acid and stannous chloride for 10-100 s, and the surface of the gold wire is immediately reduced to elemental gold to obtain nanoporous gold, denoted as A / NP-Au electrode.

2. The on-line monitoring method for hydroquinone intermediate p-benzoquinone in electrolytic synthesis according to claim 1, Characterized in that: The concentration range of the p-benzoquinone standard solution is 0.3 μmol / L to 580 μmol / L.

3. The on-line monitoring method for hydroquinone intermediate p-benzoquinone in electrolytic synthesis according to claim 1, Characterized in that: CH 3 COOH-CH 3 The pH value of the COONa buffer solution is 5.

4. The on-line monitoring method for hydroquinone intermediate p-benzoquinone in electrolytic synthesis according to claim 1, Characterized in that: The applied voltage is 0.14V.

5. The on-line monitoring method for hydroquinone intermediate p-benzoquinone in electrolytic synthesis according to claim 1, Characterized in that: In step (b), for each determination of a sample to be measured, the detection cell is disassembled and a new CH 3 COOH-CH 3 COONa buffer solution is replaced, and then the next sample to be measured is determined.

6. The on-line monitoring method for hydroquinone intermediate p-benzoquinone in electrolytic synthesis according to claim 1, Characterized in that: In step (2), the concentration range of the sulfuric acid is 0.5-2.0 mol / L.

7. The on-line monitoring method for hydroquinone intermediate p-benzoquinone in electrolytic synthesis according to claim 6, Characterized in that: In step (2), the concentration of sulfuric acid is 1.5 mol / L.

8. The on-line monitoring method for p-benzoquinone, the intermediate product of hydroquinone electrolytic synthesis, as claimed in claim 1, is characterized in that: in step (2), the constant voltage range is 1.8 - 2.6 V.

9. The on-line monitoring method for p-benzoquinone, the intermediate product of hydroquinone electrolytic synthesis, as claimed in claim 8, is characterized in that: in step (2), the constant voltage is 2.2 V.

10. The on-line monitoring method for p-benzoquinone, the intermediate product of hydroquinone electrolytic synthesis, as claimed in claim 1, is characterized in that: in step (2), the anodic oxidation time range is 60 - 140 s.

11. The on-line monitoring method for p-benzoquinone, the intermediate product of hydroquinone electrolytic synthesis, as claimed in claim 10, is characterized in that: in step (2), the anodic oxidation time is 100 s.

12. The on-line monitoring method for p-benzoquinone, the intermediate product of hydroquinone electrolytic synthesis, as claimed in claim 1, is characterized in that: in step (3), in the mixed solution of ascorbic acid and stannous chloride, the concentration range of ascorbic acid is 0.1 - 1.0 mol / L; the molar ratio of ascorbic acid to stannous chloride is 1:0.1 - 0.

5.

13. The on-line monitoring method for p-benzoquinone, the intermediate product of hydroquinone electrolytic synthesis, as claimed in claim 12, is characterized in that: in step (3), in the mixed solution of ascorbic acid and stannous chloride, the concentration of ascorbic acid is 0.8 mol / L; the molar ratio of ascorbic acid to stannous chloride is 1:0.3.

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