A polydopamine-graphite sheet electrode and its preparation method and application

Abstract

The present invention discloses a polydopamine-graphite sheet electrode and its preparation method and application. The polydopamine-graphite sheet electrode of the present invention is obtained by polymerizing polydopamine on the surface of a graphite sheet using an electrochemical method; the present invention deposits polydopamine on the surface of a graphite sheet by electropolymerization, and the introduction of nitrogen increases the active sites for oxygen reduction, which can significantly improve the oxygen reduction performance of the electrode. Hydrogen peroxide is produced at different pH values. Even under neutral or alkaline conditions, the deposition of polydopamine inhibits the four-electron reaction of oxygen, thereby improving the selectivity of the two-electron reaction, allowing the electrode to be used under neutral or alkaline conditions, solving the problem that the performance of reducing oxygen to produce hydrogen peroxide is limited by pH. It can be widely used in the process of electrocatalytic production of hydrogen peroxide, has significant practical and economic value, and broadens the application scenarios of the electrode.

Description

Technical Field

[0001] The invention relates to a polydopamine-graphite sheet electrode and a preparation method and application thereof, and belongs to the field of electrocatalytic production. Background Art

[0002] Hydrogen peroxide is a strong oxidant widely used in sterilization, bleaching, chemical synthesis, and environmental treatment. Compared to other oxidants, hydrogen peroxide has a simple molecular structure, and its oxidation and reduction products are oxygen and water, respectively, making it environmentally friendly and clean. In wastewater treatment, the demand for hydrogen peroxide is increasing annually due to the development of Fenton, electro-Fenton, and Fenton-like technologies. Currently, hydrogen peroxide is primarily produced by anthraquinone oxidation, accounting for over 95% of global annual hydrogen peroxide production. This process requires large-scale equipment, consumes significant energy, and generates large amounts of chemical waste. Furthermore, this centralized process produces high concentrations of hydrogen peroxide, posing an explosion hazard and increasing transportation and storage costs. In reality, low concentrations of hydrogen peroxide are sufficient for practical applications. For example, in wastewater treatment, concentrations below 0.1 wt% are sufficient. In situ synthesis of hydrogen peroxide via the oxygen reduction reaction can be performed at ambient temperature and pressure, uses readily available raw materials, and has low production risks, offering broad application prospects.

[0003] In electrocatalytic systems, the negative electrode has excellent reducing properties and can reduce oxygen to produce hydrogen peroxide. Commonly used electrode materials include precious metals, transition metal oxides, carbon materials, and heteroatom-doped materials. However, oxygen can be reduced not only to produce hydrogen peroxide (two-electron reduction), but also to produce water (four-electron reduction). The competition between these two pathways determines the selectivity of oxygen reduction, which is closely related to the performance of the catalyst. Therefore, the choice of catalyst is particularly important. Catalysts such as precious metals are expensive and not suitable for practical production applications. Carbon materials have attracted widespread attention due to their low price and ease of availability. Since carbon materials have weak oxygen binding ability, they help retain the O-O bond and thus have catalytic properties for producing hydrogen peroxide.

[0004] The performance of carbon material electrodes in reducing oxygen to produce hydrogen peroxide is limited by pH. Under acidic conditions, the hydrogen peroxide yield is high. However, when the pH increases to 5 or above, the alkaline conditions promote the four-electron reaction of oxygen, causing the hydrogen peroxide yield to drop rapidly. This seriously limits the practical application of in situ hydrogen peroxide production. In addition, as the voltage increases, the competitiveness of the four-electron reaction increases, resulting in oxygen reduction being limited to low potentials, which slows the reaction rate and increases the time cost. Therefore, it is necessary to develop an electrode that can solve the pH limitation of the performance of reducing oxygen to produce hydrogen peroxide. Summary of the Invention

[0005] Objectives of the invention: The first objective of the present invention is to provide a polydopamine-graphite sheet electrode capable of high hydrogen peroxide production, so as to solve the problem that the performance of reducing oxygen to produce hydrogen peroxide is limited by pH; the second objective of the present invention is to provide a method for preparing the polydopamine-graphite sheet electrode; the third objective of the present invention is to provide the use of the polydopamine-graphite sheet electrode in the electrocatalytic production of hydrogen peroxide.

[0006] Technical solution: The polydopamine-graphite sheet electrode described in the present invention is obtained by polymerizing polydopamine on the surface of a graphite sheet using an electrochemical method.

[0007] The method for preparing the polydopamine-graphite sheet electrode of the present invention comprises the following steps:

[0008] (1) Pretreatment of graphite sheets: ultrasonically clean the graphite sheets with sodium hydroxide solution, then clean the graphite sheets with water, then clean the graphite sheets with hydrochloric acid solution, then clean the graphite sheets with water, finally clean the graphite sheets with anhydrous ethanol, then clean the graphite sheets with water, drain the graphite sheets, and calcine at high temperature to obtain pretreated graphite sheets;

[0009] (2) preparing an electrolyte solution: exposing a phosphate buffer solution to nitrogen, adding dopamine hydrochloride, and continuously exposing the solution to nitrogen in the dark to obtain an electrolyte solution;

[0010] (3) A platinum sheet electrode is used as a counter electrode, an Ag / AgCl electrode is used as a reference electrode, and a pretreated graphite sheet is used as a working electrode. The three electrodes are placed in an electrolyte and electropolymerization is performed using cyclic voltammetry. The graphite sheet electrode is taken out, washed with water, and calcined at high temperature to obtain a polydopamine-graphite sheet electrode.

[0011] Wherein, in step (1), the concentration of the hydrochloric acid solution is 0.1-1M, and the concentration of the sodium hydroxide solution is 0.1-1M.

[0012] In step (1), the ultrasonic cleaning time of the graphite sheet is 30-60 minutes, and the high-temperature calcination is to heat the graphite sheet to 250-350° C. within 2 hours and then calcine the graphite sheet for 3-6 hours.

[0013] Wherein, in step (1), the graphite sheet is washed with water until it is nearly neutral.

[0014] Wherein, in step (2), the liquid-to-solid ratio of phosphate buffer to dopamine hydrochloride is 5-1 mL / mg, and the concentration of phosphate buffer is 20-100 mM.

[0015] Wherein, in step (2), the phosphate buffer is aerated with nitrogen at a rate of 1000 mL of nitrogen per mL of phosphate buffer per minute for more than 30 minutes, and the aeration time in the dark is continuously 10-20 minutes.

[0016] Wherein, in step (3), when electropolymerization is performed by cyclic voltammetry, the initial potential and the final potential are both 0 V, the voltage range is -0.5-0.6 V, the cycles are 10-50 times, and the scan rate is 0.01-0.05 V / s.

[0017] Wherein, in step (3), the high temperature calcination is carried out by heating the temperature to 200-240°C at 10°C / min and maintaining the temperature for 2-5h.

[0018] The preparation method involves pretreatment of graphite sheets through acid washing, alkaline washing, ethanol washing, and high-temperature treatment. The graphite sheets are then modified with the biomimetic material polydopamine to enhance the electrode's hydrogen peroxide production capacity and adapt it to a wider range of pH conditions. The polydopamine material is electrochemically polymerized.

[0019] The present invention also includes the use of the polydopamine-graphite sheet electrode in electrocatalytic production of hydrogen peroxide.

[0020] The polydopamine-graphite sheet electrode is used in hydrogen peroxide production using a three-electrode electrocatalytic system. Using oxygen as the raw material, a negative potential is applied to efficiently catalyze the oxygen reduction reaction at a pH of 3-11 to produce hydrogen peroxide. High hydrogen peroxide yields can be achieved even at a pH of 3-9.

[0021] The present invention uses a three-electrode electrocatalytic system in the electrocatalytic production of hydrogen peroxide. Oxygen is used as the raw material and a negative voltage is applied to reduce oxygen to produce hydrogen peroxide. The specific mechanism is shown in Figure 1 Among them, polydopamine inhibits the four-electron reduction reaction of oxygen, thereby improving the selectivity of hydrogen peroxide.

[0022] In the three-electrode electrocatalytic system, the counter electrode is a platinum sheet electrode, the reference electrode is an Ag / AgCl electrode, and the working electrode is the polydopamine-graphite sheet electrode described in the present invention.

[0023] The electrolyte is a sodium sulfate solution, and the concentration of the sodium sulfate solution is 0.05-0.1M.

[0024] Oxygen is introduced into the electrolyte for aeration, with a flow rate of 100-1000 mL of oxygen per liter of electrolyte per minute, and the oxygen exposure time is 30-60 minutes.

[0025] The temperature during the production of hydrogen peroxide is kept constant at 20-40° C., and the magnetic stirring speed is set at 300-900 rpm.

[0026] The voltage is set to -0.4 to -1 V, oxygen is continuously exposed throughout the entire reaction process, and the reaction lasts for 1 to 5 hours.

[0027] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0028] (1) The present invention modifies the surface pores of the graphite sheet by acid-base washing and high-temperature treatment, and deposits polydopamine on the surface of the graphite sheet by electropolymerization, thereby enriching the functional group structure on the graphite sheet. Among them, the introduction of nitrogen increases the active sites for oxygen reduction, which can significantly improve the oxygen reduction performance of the electrode.

[0029] (2) Under neutral or alkaline conditions, the yield of hydrogen peroxide decreases due to the occurrence of the four-electron reduction reaction of oxygen, while the deposition of polydopamine inhibits the four-electron reaction of oxygen, thereby improving the selectivity of the two-electron reaction. This broadens the application scenarios of the electrode, that is, it can be used under neutral or alkaline conditions.

[0030] (3) Increasing the voltage can increase the reaction rate, but the four-electron reduction reaction of oxygen has a higher reaction activation energy. The increase in voltage allows the four-electron reaction to occur, which reduces the selectivity of the two-electron reduction of oxygen to produce hydrogen peroxide. Polydopamine can inhibit the four-electron reaction of oxygen.

[0031] (4) The polydopamine-graphite sheet electrode of the present invention produces hydrogen peroxide at different pH values, with the highest productivity at pH 3. When the pH increases to 5 and above, the hydrogen peroxide productivity does not decrease significantly. Even at a pH of 11, the high hydrogen peroxide productivity is maintained. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the mechanism of electrocatalytic production of hydrogen peroxide by the polydopamine-graphite sheet electrode of the present invention.

[0033] Figure 2 This is a scanning electron microscope image of the polydopamine-graphite sheet electrode in Example 1;

[0034] Figure 3 This is a photoelectron spectrum analysis diagram of the polydopamine-graphite sheet electrode and the graphite sheet electrode in Example 1;

[0035] Figure 4 This is a graph showing the hydrogen peroxide production of polydopamine-graphite sheet and graphite sheet under natural pH conditions;

[0036] Figure 5 This is the hydrogen peroxide concentration diagram of the polydopamine-graphite sheet group at -0.41V;

[0037] Figure 6 The linear voltammograms of polydopamine-graphite sheets under different pH conditions;

[0038] Figure 7The linear voltammograms of graphite sheets under different pH conditions;

[0039] Figure 8 The kinetic diagram of bisphenol A removal by polydopamine-graphite sheet group under different pH conditions;

[0040] Figure 9 The kinetic diagram of bisphenol A removal by graphite sheets under different pH conditions. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0042] Example 1 Preparation of Polydopamine-Graphite Sheet Electrode and Graphite Sheet Electrode

[0043] (1) Select a new graphite sheet material, use 0.1M sodium hydroxide solution to ultrasonically clean it for 30 minutes, and then use ultrapure water to clean it until the supernatant is nearly neutral (pH = 6.5-7.0). Use the same method to ultrasonically clean it for 30 minutes with 0.1M hydrochloric acid solution, and then use ultrapure water to clean it until the supernatant is nearly neutral (pH = 6.5-7.0). Then use ethanol to clean it, ultrasonically clean it for 30 minutes, and then use ultrapure water to clean it until the supernatant is nearly neutral (pH = 6.5-7.0). All the above operations are carried out at room temperature (20-25℃). After cleaning, drain it and treat it at high temperature in a muffle furnace, raise the temperature to 300℃ within 2 hours, and then maintain it for 5 hours to obtain a pretreated graphite sheet.

[0044] (2) In a reaction dish 50 mm long, 20 mm wide, and 100 mm high, 50 mL of phosphate buffer solution (20 mM concentration) was prepared. After nitrogen aeration (nitrogen flow rate of 50 mL / min) for 30 min, 47.8 mg of dopamine hydrochloride was added. The entire reaction dish was then protected from light and aerated with nitrogen for 20 min to obtain an electrolyte solution.

[0045] (3) A 10×10×0.1mm platinum sheet electrode was selected as the counter electrode and polished clean with suede before use. An Ag / AgCl electrode (Shanghai Chenhua, CH111) was selected as the reference electrode. A pre-treated graphite sheet was selected as the working electrode and fixed with a platinum electrode clamp. The working electrode and the counter electrode were placed in a reaction vessel containing the above electrolyte until the liquid surface was completely covered. The reference electrode sand core should be below the liquid surface and the three electrodes should not touch each other. Voltage was applied using an electrochemical workstation (Gamry Interface 1010E) and cyclic voltammetry was used for electropolymerization. The initial and final potentials were both 0V, the voltage range was -0.5-0.6V, 50 cycles were performed, the scan rate was set to 0.02V / s, and the polymerization process was carried out at room temperature and pressure. After the polymerization was completed, the working electrode, i.e., the polydopamine-graphite sheet electrode, was removed and thoroughly washed with ultrapure water. The polydopamine-graphite sheet electrode was placed in a tube furnace for high-temperature treatment. In a nitrogen atmosphere, the temperature was raised to 240°C at a rate of 10°C / min, maintained for 2 hours, and taken out after the temperature dropped to room temperature to obtain the polydopamine-graphite sheet electrode.

[0046] The polydopamine-graphite sheet electrode obtained in this example was analyzed by scanning electron microscopy. Figure 2 shown. Figure 2 is a scanning electron microscope image of the polydopamine-graphite sheet electrode in Example 1, Figure 2 It can be seen that polydopamine is not a complete thin film, but covers the surface and inside the pores of the graphene sheet.

[0047] The polydopamine-graphite sheet electrode and the pretreated graphite sheet obtained in this example were subjected to photoelectron spectroscopy analysis. The results are as follows: Figure 3 shown. Figure 3 The photoelectron spectrum analysis diagram of the polydopamine-graphite sheet electrode and the graphite sheet electrode in Example 1 is shown in FIG. Figure 3 It can be seen that after loading polydopamine, the content of oxygen and nitrogen elements on the electrode surface increased significantly, and the appearance of nitrogen element proved the deposition of polydopamine.

[0048] Example 2 Polydopamine-graphite sheet electrode for hydrogen peroxide production

[0049] 100 mL of sodium sulfate solution was prepared with ultrapure water to a concentration of 0.05 M. The solution was placed in an electrochemical reactor (cylindrical) with a volume of 100 mL. After exposure to oxygen for 30 minutes, the flow rate was 20 mL / min, and three electrodes were installed. The counter electrode was a 10×10×0.1 mm platinum sheet electrode, which was polished clean with suede before use. The reference electrode was an Ag / AgCl electrode (Shanghai Chenhua, CH111). The working electrode was the polydopamine-graphite sheet electrode prepared in Example 1 and fixed with a platinum electrode clamp. The temperature was kept constant at 30°C; the magnetic stirrer was 2 cm long and had a cross-sectional diameter of approximately 0.5 cm; the rotation speed was set to 500 rpm; the distance between the reference electrode and the counter electrode was 2 cm. A constant potential voltage was applied using an electrochemical workstation (Gamry Interface 1010E), the voltage was set to -1 V, and oxygen exposure was continued. The production of hydrogen peroxide was determined by iodine titration. At the same time, the working electrode was replaced with a graphite sheet for experimental comparison. The results are shown in Tables 1 and Figure 4 shown.

[0050] Table 1. Hydrogen peroxide concentrations of polydopamine-graphite sheet and graphite sheet systems after 1.5 hours

[0051]

[0052] As can be seen from Table 1, the graphite sheet group has a good ability to produce hydrogen peroxide under acidic conditions. However, when the pH increases to 5 or above, the hydrogen peroxide production ability of the graphite sheet group decreases rapidly. However, the polydopamine-graphite sheet group obtained in Example 1 of the present invention still maintains a high activity, which proves that the polydopamine-graphite sheet electrode can be used under a wider range of pH conditions.

[0053] Figure 4 The hydrogen peroxide production diagram of polydopamine-graphite sheet group and graphite sheet group under natural conditions is shown in Figure 2. Figure 4 It can be seen that the 3-hour yield of polydopamine-graphite sheet electrode for electrocatalytic production of hydrogen peroxide increased 11 times compared with the graphite sheet control group. After 3 hours, the hydrogen peroxide concentrations of the graphite sheet group and the graphite sheet group reached 173.4 mg / L and 15.6 mg / L, respectively.

[0054] Example 3

[0055] 100 mL of sodium sulfate solution (0.05 M) was prepared with ultrapure water and placed in a 100 mL cylindrical electrochemical reactor. After exposure to oxygen for 30 minutes at a flow rate of 20 mL / min, three electrodes were installed. The counter electrode was a 10 × 10 × 0.1 mm platinum sheet electrode, polished clean with chamois leather before use. The reference electrode was an Ag / AgCl electrode (Shanghai Chenhua, CH111). The working electrode was the polydopamine-graphite sheet electrode obtained in Example 1, secured with a platinum electrode clamp. The temperature was maintained at 30°C. The magnetic stir bar was 2 cm long and approximately 0.5 cm in diameter. The rotational speed was set to 500 rpm. The distance between the reference and counter electrodes was 2 cm. A constant potential voltage was applied using an electrochemical workstation (Gamry Interface 1010E) at -0.41 V, with continuous exposure to oxygen. Hydrogen peroxide production was determined by iodine titration. Figure 5 The kinetic diagram of hydrogen peroxide production from polydopamine-graphite sheet group at -0.41V is shown in Figure 2. Figure 5 It can be seen that after 3 h, the hydrogen peroxide concentration can reach 92 mg / L.

[0056] Example 4

[0057] A platinum wire counter electrode was used, the polydopamine-graphite sheet in Example 1 was used as the working electrode, Ag / AgCl was used as the reference electrode, 0.05M sodium sulfate was used as the electrolyte, 0.1M sulfuric acid and 0.1M sodium hydroxide were used to adjust the pH, and after aeration with oxygen or nitrogen for 30 minutes, linear voltammetry analysis was performed on the electrochemical workstation with an initial potential of 0V, a final potential of -1V, and a scan rate of 0.02V / s. At the same time, the working electrode was replaced with a graphite sheet for experimental comparison. The results are shown in Figure 2. Figure 6-7 shown. Figure 6 The linear voltammogram of polydopamine-graphite sheet under different pH conditions. Figure 6 It can be seen that there is only one obvious reduction peak in the figure, which is the two-electron reduction peak, and the four-electron reduction peak is very weak or even disappears, indicating good selectivity of two-electron reduction. Figure 7 The linear voltammograms of graphite sheets under different pH conditions. Figure 7 There are two reduction peaks, representing a four-electron reaction and a two-electron reaction. Under the condition of pH = 3, there is only a two-electron reduction peak, which means that when the pH increases, the four-electron reaction occurs, thereby reducing the selectivity of the two-electron reaction and thus reducing the production of hydrogen peroxide.

[0058] Example 5

[0059] (1) Select a new graphite sheet material, use 0.1M sodium hydroxide solution to ultrasonically clean it for 30 minutes, and then use ultrapure water to clean it until the supernatant is nearly neutral (pH = 6.5-7.0). Use the same method to ultrasonically clean it for 30 minutes with 0.1M hydrochloric acid solution, and then use ultrapure water to clean it until the supernatant is nearly neutral (pH = 6.5-7.0). Then use ethanol to clean it, ultrasonically clean it for 30 minutes, and then use ultrapure water to clean it until the supernatant is nearly neutral (pH = 6.5-7.0). All the above operations are carried out at room temperature (20-25℃). After cleaning, drain it and treat it at high temperature in a muffle furnace, raise the temperature to 300℃ within 2 hours, and then maintain it for 5 hours to obtain a pretreated graphite sheet.

[0060] (2) In a reaction dish 50 mm long, 20 mm wide, and 100 mm high, 50 mL of phosphate buffer solution (20 mM concentration) was prepared. After nitrogen aeration (nitrogen flow rate of 50 mL / min) for 30 min, 10 mg of dopamine hydrochloride was added. The entire reaction dish was then protected from light and aerated with nitrogen for 20 min to obtain an electrolyte solution.

[0061] (3) A 10×10×0.1mm platinum sheet electrode was selected as the counter electrode and polished clean with suede before use. An Ag / AgCl electrode (Shanghai Chenhua, CH111) was selected as the reference electrode. A pre-treated graphite sheet was selected as the working electrode and fixed with a platinum electrode clamp. The working electrode and the counter electrode were placed in a reaction vessel containing the above electrolyte until the liquid surface was completely covered. The reference electrode sand core should be below the liquid surface and the three electrodes should not touch each other. Voltage was applied using an electrochemical workstation (Gamry Interface 1010E) and cyclic voltammetry was used for electropolymerization. The initial and final potentials were both 0V, the voltage range was -0.5-0.6V, 50 cycles were performed, the scan rate was set to 0.02V / s, and the polymerization process was carried out at room temperature and pressure. After the polymerization was completed, the working electrode, i.e., the polydopamine-graphite sheet electrode, was removed and thoroughly washed with ultrapure water. The polydopamine-graphite sheet electrode was placed in a tube furnace for high-temperature treatment. Under a nitrogen atmosphere, the temperature was raised to 240°C at a rate of 10°C / min and maintained for 2 hours. After the temperature dropped to room temperature, it was taken out to obtain the polydopamine-graphite sheet electrode. The electrode was used to produce hydrogen peroxide, and the peroxide concentration was 179 mg / L after 3 hours.

[0062] Example 6

[0063] (1) Select a new graphite sheet material, use 0.1M sodium hydroxide solution to ultrasonically clean it for 30 minutes, and then use ultrapure water to clean it until the supernatant is nearly neutral (pH = 6.5-7.0). Use the same method to ultrasonically clean it for 30 minutes with 0.1M hydrochloric acid solution, and then use ultrapure water to clean it until the supernatant is nearly neutral (pH = 6.5-7.0). Then use ethanol to clean it, ultrasonically clean it for 30 minutes, and then use ultrapure water to clean it until the supernatant is nearly neutral (pH = 6.5-7.0). All the above operations are carried out at room temperature (20-25℃). After cleaning, drain it and treat it at high temperature in a muffle furnace, raise the temperature to 300℃ within 2 hours, and then maintain it for 5 hours to obtain a pretreated graphite sheet.

[0064] (2) In a reaction dish 50 mm long, 20 mm wide, and 100 mm high, 50 mL of phosphate buffer solution (20 mM concentration) was prepared. After nitrogen aeration (nitrogen flow rate of 50 mL / min) for 30 min, 48.7 mg of dopamine hydrochloride was added. The entire reaction dish was then protected from light and aerated with nitrogen for 20 min to obtain an electrolyte solution.

[0065] (3) A 10×10×0.1mm platinum sheet electrode was selected as the counter electrode and polished clean with suede before use. An Ag / AgCl electrode (Shanghai Chenhua, CH111) was selected as the reference electrode. A pre-treated graphite sheet was selected as the working electrode and fixed with a platinum electrode clamp. The working electrode and the counter electrode were placed in a reaction vessel containing the above electrolyte until the liquid surface was completely covered. The reference electrode sand core should be below the liquid surface and the three electrodes should not touch each other. Voltage was applied using an electrochemical workstation (Gamry Interface 1010E) and cyclic voltammetry was used for electropolymerization. The initial and final potentials were both 0V, the voltage range was -0.5-0.6V, 20 cycles were performed, the scan rate was set to 0.02V / s, and the polymerization process was carried out at room temperature and pressure. After the polymerization was completed, the working electrode, i.e., the polydopamine-graphite sheet electrode, was removed and thoroughly washed with ultrapure water. The polydopamine-graphite sheet electrode was placed in a tube furnace for high-temperature treatment. Under a nitrogen atmosphere, the temperature was raised to 240°C at a rate of 10°C / min and maintained for 2 hours. After the temperature dropped to room temperature, it was taken out to obtain the polydopamine-graphite sheet electrode. The electrode was used to produce hydrogen peroxide, and the peroxide concentration was 167 mg / L after 3 hours.

[0066] The polydopamine-graphite sheet electrodes obtained in Examples 5 and 6 were used for hydrogen peroxide production and linear voltammetric analysis, and the results were similar to those of the polydopamine-graphite sheet electrode obtained in Example 1. This indicates that the methods of the present invention can produce stable polydopamine-graphite sheet electrodes, broadening the application scenarios of the electrodes, allowing them to be used under neutral or alkaline conditions.

[0067] Example 7

[0068] A 100 mL sodium sulfate solution was prepared with ultrapure water to a concentration of 0.05 M. 5 mg / L bisphenol A was added, and the pH was adjusted with 0.1 M sulfuric acid and 0.1 M sodium hydroxide. The solution was placed in a 100 mL cylindrical electrochemical reactor and exposed to oxygen for 30 minutes at a flow rate of 20 mL / min. Three electrodes were installed: a 10 × 10 × 0.1 mm platinum sheet electrode, polished clean with chamois leather before use, a Ag / AgCl electrode (Shanghai Chenhua, CH111), and a working electrode, either the polydopamine-graphite sheet electrode or the graphite sheet obtained in Example 1, secured with a platinum electrode clamp. The temperature was maintained at 30°C. The magnetic stir bar was 2 cm long and approximately 0.5 cm in diameter. The rotational speed was set at 500 rpm. The reference and counter electrodes were separated by 2 cm. A constant potential voltage was applied using an electrochemical workstation (Gamry Interface 1010E) at -1 V, with continuous oxygen exposure. The concentration of bisphenol A was detected by high performance liquid chromatography, and the experiment was carried out at pH = 3, 5, 6, 7, 8, 9, and 11. The results are as follows Figure 8-9 shown.

[0069] Figure 8 The kinetic diagrams of bisphenol A removal by polydopamine-graphite sheet group under different pH conditions, where (a) is the reaction kinetic diagram and (b) is the degradation rate diagram. Figure 9 The graphs are the kinetics of bisphenol A removal by graphite sheets under different pH conditions, where (a) is the reaction kinetics diagram and (b) is the degradation rate diagram. Figure 8 and Figure 9 It can be seen that under -1V conditions, the in situ hydrogen peroxide production technology of the polydopamine-graphite sheet group and the graphite group can be used to remove pollutants. Compared with the graphite sheet group, the polydopamine-graphite sheet group has better resistance to pH shock, which broadens the application scenarios of electrocatalytic removal of pollutants.

Claims

1. A method for preparing a polydopamine-graphite sheet electrode, characterized in that: The following steps are involved: (1) Pretreatment of graphite sheets: ultrasonically clean the graphite sheets with sodium hydroxide solution, then clean the graphite sheets with water, then clean the graphite sheets with hydrochloric acid solution, then clean the graphite sheets with water, finally clean the graphite sheets with anhydrous ethanol, then clean the graphite sheets with water, drain the graphite sheets, and calcine them at high temperature to obtain pretreated graphite sheets; (2) Preparation of electrolyte: Aerate phosphate buffer solution with nitrogen, add dopamine hydrochloride, and continue to aerate with nitrogen in the dark to obtain electrolyte; (3) Platinum sheet electrode is used as counter electrode, Ag / AgCl electrode is used as reference electrode, and pretreated graphite sheet is used as working electrode. The above three electrodes are placed in electrolyte and electropolymerization is performed by cyclic voltammetry. The graphite sheet electrode is taken out, washed with water, and calcined at high temperature to obtain polydopamine-graphite sheet electrode. The high temperature calcination is carried out under nitrogen protection, and the temperature is raised to 200-240℃ at 10℃ / min and maintained for 2-5 hours.

2. The method for preparing the polydopamine-graphite sheet electrode according to claim 1, wherein: In step (1), the concentration of the hydrochloric acid solution is 0.1-1 M, and the concentration of the sodium hydroxide solution is 0.1-1 M.

3. The method for preparing the polydopamine-graphite sheet electrode according to claim 1, wherein: In step (1), the ultrasonic cleaning time of the graphite sheet is 30-60 minutes, the high temperature calcination is to raise the temperature to 250-350 ° C within 2 hours and then calcine for 3-6 hours, and the graphite sheet is washed with water until it is nearly neutral.

4. The method for preparing the polydopamine-graphite sheet electrode according to claim 1, wherein: In step (2), the liquid-to-solid ratio of phosphate buffer to dopamine hydrochloride is 5-1 mL / mg, and the concentration of phosphate buffer is 20-100 mM.

5. The method for preparing the polydopamine-graphite sheet electrode according to claim 1, wherein: In step (2), the phosphate buffer solution is aerated with nitrogen at a rate of 1000 mL of nitrogen per minute per mL of phosphate buffer solution for more than 30 minutes, and the aeration time in the dark is continuously 10-20 minutes.

6. The method for preparing the polydopamine-graphite sheet electrode according to claim 1, characterized in that: In step (3), the initial potential and the final potential of the electropolymerization were both 0 V, the voltage range was -0.5 - 0.6 V, the number of cycles was 20-50, and the scan rate was 0.01-0.05 V / s.

7. The polydopamine-graphite sheet electrode obtained by the preparation method according to any one of claims 1 to 6.

8. Use of the polydopamine-graphite sheet electrode according to claim 7 in electrocatalytic production of hydrogen peroxide.

9. The use according to claim 8, characterized in that Using a three-electrode electrocatalytic system, with oxygen as the raw material, a negative potential is applied to efficiently catalyze the oxygen reduction reaction at a pH of 3-11 to produce hydrogen peroxide.

Images