A silicon dioxide-coated cubic lead tetroxide catalyst and its preparation method and application

Abstract

The invention discloses a silica-coated cubic lead tetroxide catalyst and its preparation method and application. The preparation method of the catalyst of the present invention is as follows: cubic lead tetroxide catalyst powder and hexadecyltrimethylammonium bromide (CTAB) are ultrasonically dispersed in a solvent system, the resulting mixed solution is transferred to an oil bath at 40-80°C and continuously stirred, and an alkaline solution is added to adjust the pH to alkaline, tetraethyl orthosilicate (TEOS) is added to the resulting mixed solution system and stirred for 0.5-12 hours, the reaction is cooled after completion, the product is collected and washed with ethanol multiple times to remove CTAB, and finally dried to obtain the silica-coated cubic lead tetroxide catalyst. The silica-coated cubic lead tetroxide catalyst prepared by the present invention is low in cost and is applied to the ozone production reaction process of low-pressure water electrolysis at industrial current density, with excellent catalytic activity and stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalysis, and in particular relates to a silicon dioxide-coated cubic lead tetroxide catalyst, a preparation method and an application thereof. Background Art

[0002] Ozone, an allotrope of oxygen, possesses strong oxidizing power. Therefore, it is used as a bleaching agent, fur deodorizer, air purifier, disinfectant, and drinking water disinfectant and deodorizer. In chemical production, ozone can also replace many catalytic oxidation or high-temperature oxidation processes, simplifying production processes and improving productivity. Furthermore, as a strong oxidant, ozone does not cause secondary pollution, and any remaining ozone decomposes into oxygen within a short period of time. Therefore, using ozone for oxidation is a green and efficient method.

[0003] Currently, low-voltage electrolysis, corona discharge, and ultraviolet irradiation are the main methods for artificially producing ozone. Corona discharge, in which dry oxygen-containing gas flows through a silent discharge gap, produces ozone. This method requires high voltage, produces low ozone concentrations, requires large-scale production equipment, and is complex to operate. Furthermore, the ozone production process releases large amounts of nitrogen oxides, which are harmful to the environment and human health. Ultraviolet irradiation, in which air or oxygen is exposed to ultraviolet radiation, produces ozone. This method produces low ozone yields, has a complex structure, and has difficult-to-control wavelengths, making it unsuitable for large-scale ozone production.

[0004] In summary, methods such as corona discharge and ultraviolet irradiation need improvement. Therefore, developing a low-energy, efficient, and environmentally friendly method for ozone production and its widespread application is crucial. Currently, researchers have proposed the low-voltage electrolysis method for ozone production. This method primarily utilizes an ozone generator to produce ozone by electrolyzing water. This device offers advantages such as simplicity, controllable size, and portability. This technology aligns with the development trend of ozone generation technology and is environmentally friendly, energy-efficient, easy to operate, and highly efficient, thus attracting extensive research and attention. During the electrolytic ozone production process, ozone and oxygen are generated at the anode, while hydrogen is generated at the cathode. Selecting an anode material with a high overpotential can effectively suppress oxygen evolution at the anode, thereby improving the current efficiency of ozone generation. Therefore, current research on electrochemical ozone production, both domestically and internationally, focuses primarily on the selection of anode materials. Pt, β-PbO2, boron-doped diamond (BDD), and DSA titanium electrodes have all been used as anode materials for low-voltage electrochemical ozone production. In commercial products, the anode material is typically β-PbO2, which has a high oxygen evolution potential and is relatively inexpensive. However, as the reaction proceeds, β-PbO2 dissolves under strong oxidizing conditions, causing damage to the catalyst structure and lead loss. Therefore, the catalyst's stability remains unsatisfactory under long-term high-current operation, and lead loss can also have a certain impact on the natural environment. Therefore, it is of great significance to develop a low-cost, highly stable anode catalyst for use in the electrolysis of water to produce ozone. Summary of the Invention

[0005] In response to the above-mentioned technical problems existing in the prior art, the present invention aims to provide a silica-coated cubic lead tetroxide catalyst, its preparation method, and application. By employing a strategy of silica-coating cubic lead tetroxide, the catalyst's stability is enhanced. During the preparation of the silica-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2), the amount of CTAB template is controlled to achieve stable growth of the SiO2 coating layer. The thickness of the SiO2 coating layer is controlled by controlling the amount of TEOS. Furthermore, the TEOS hydrolysis is effectively controlled by controlling the dispersion environment of the solvent system, thereby achieving uniform SiO2 coating. The resulting silica-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2) exhibits excellent catalytic activity and stability when used in the electrolysis of water to produce ozone.

[0006] The method for preparing a silicon dioxide-coated cubic lead tetroxide catalyst comprises the following steps:

[0007] 1) Cubic lead tetroxide catalyst powder and cetyltrimethylammonium bromide (CTAB) are ultrasonically dispersed in a solvent system. The resulting mixture is transferred to an oil bath at 40-80°C and stirred continuously. An alkaline solution is added to adjust the pH to alkaline.

[0008] 2) Tetraethyl orthosilicate (TEOS) was added to the mixed solution obtained in step 1) and stirred for reaction for 0.5 to 12 hours. After the reaction was completed, the mixture was cooled, the product was collected, washed with ethanol multiple times to remove CTAB, and finally dried to obtain the silica-coated cubic lead tetroxide catalyst.

[0009] Furthermore, in step 1), the amount of cubic lead tetroxide catalyst powder added to the solvent system is 1-2 mg / mL, preferably 1.5 mg / mL; the amount of CTAB added to the solvent system is 4-7.5 mg / mL, preferably 5 mg / mL.

[0010] Furthermore, the solvent system in step 1) is a pure water phase system, a water-ethanol mixed system with a volume ratio of 0.5 to 2:1, or a water-n-hexane mixed system with a volume ratio of 3 to 5:1, preferably a pure water phase system.

[0011] Furthermore, in step 1), the alkaline solution is an ammonia solution with a mass fraction of 25-28%, and the volume ratio of the alkaline solution to the mixed solution is 1:10-50, preferably 1:20.

[0012] Furthermore, in step 2), the ratio of the volume of tetraethyl orthosilicate TEOS to the mass of the cubic lead tetroxide catalyst powder in step 1) is 2-6:1, preferably 4-5:1, the unit of volume is mL, and the unit of mass is g.

[0013] Furthermore, the preparation method of the cubic lead tetroxide catalyst powder comprises the following steps:

[0014] S1: Dissolve the lead salt in deionized water, add an inorganic base to adjust the pH to 14, and disperse uniformly by ultrasonication to obtain a precursor solution. Add a structure-inducing agent, hexadecyltrimethylammonium bromide (CTAB), and stir at 45-55°C for 20-40 minutes. Then, add sodium hypochlorite solution and stir and disperse uniformly to obtain a suspension.

[0015] S2: The suspension obtained in step S1 is transferred to the inner lining of a hydrothermal reactor, and the inner lining is then placed in the hydrothermal reactor. The hydrothermal reaction is carried out at a temperature of 110-130°C for 20-30 hours. After the reaction is completed, the suspension is cooled to room temperature and filtered to obtain a crude product precipitate. The crude product precipitate is washed several times with anhydrous ethanol and deionized water, filtered, and dried to obtain a cubic lead tetroxide catalyst.

[0016] Furthermore, in step S1, the lead salt is lead acetate, the concentration of the lead salt in deionized water is 20-40 mg / mL, and the inorganic base is sodium hydroxide.

[0017] Furthermore, in step S1, the mass ratio of CTAB to lead salt is 1:1-3, preferably 1:1.25-1.5; in step S1, the effective chlorine concentration of the sodium hypochlorite solution is 4%, and the ratio of the volume of the sodium hypochlorite solution to the mass of the lead salt is 3-8:1, preferably 5-6:1, the unit of volume is mL, and the unit of mass is g.

[0018] The silica-coated cubic lead tetroxide catalyst provided by the present invention can be well applied to the electrocatalytic decomposition of water to produce ozone at industrial current density. The application process is as follows: a solid polymer electrolyte ozone generator is used as a reactor; the silica-coated cubic lead tetroxide catalyst is used as the anode material, and a platinum-carbon catalyst with a 10% platinum content is used as the cathode material. The anode material and the cathode material are respectively coated on the anode surface and the cathode surface of a proton exchange membrane. The cathode chamber and the anode chamber of the reactor are separated by the proton exchange membrane. Deionized water is used as the electrolyte. The current is 5A-10A, the cell voltage is 3V-5V, and the electrolysis reaction is carried out at a temperature of 20°C-50°C to produce an ozone product.

[0019] By adopting the above technology, compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1) The present invention synthesizes a silica-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2) via a two-step method. During the catalyst preparation process, the silica coating effect is regulated by controlling the amount of CTAB template, the amount of TEOS, and the dispersion environment of the solvent system, thereby obtaining a water electrolysis ozone catalyst that is conducive to maintaining high activity and high stability.

[0021] 2) By comparing the ozone production performance of the silica-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2) prepared by the present invention and the uncoated cubic lead tetroxide catalyst (cubic-Pb3O4) in electrolysis of water, the cubic-Pb3O4@SiO2 prepared by the present invention has better stability in electrocatalytic ozone production than cubic-Pb3O4 at industrial current density. After long-term power-on operation, the catalytic activity does not decrease significantly, indicating that silica coating is an effective strategy to improve electrocatalytic stability.

[0022] 3) Under the same test conditions, the cubic-Pb3O4@SiO2 catalyst prepared in the present invention exhibited a higher Faradaic efficiency (18-22%) than the Faradaic efficiency (≤15%) of lead-containing catalysts reported in the literature for electrocatalytic ozone production, indicating that the catalyst material has higher catalytic activity in the electrocatalytic production of ozone.

[0023] 4) The electrocatalytic process of the present invention uses tap water as the electrolyte, which is low-cost, green and pollution-free, easy to control, and suitable for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1a Schematic diagram of a transmission electron microscope image of the uncoated cubic lead tetroxide catalyst (cubic-Pb3O4) obtained in Example 1 at 0.2 μm;

[0025] Figure 1b Schematic diagram of transmission electron microscopy of the uncoated cubic lead tetroxide catalyst (cubic-Pb3O4) obtained in Example 1 at 50 nm;

[0026] Figure 2a Schematic diagram of a transmission electron microscope image of the silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2) obtained in Example 1 at 0.2 μm;

[0027] Figure 2b Schematic diagram of a transmission electron microscope of the silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2) obtained in Example 1 at 100 nm;

[0028] Figure 3a Schematic diagram of a transmission electron microscope image of the silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2) obtained in Example 2 at 0.2 μm;

[0029] Figure 3b Schematic diagram of transmission electron microscopy of the silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2) obtained in Example 2 at 50 nm;

[0030] Figure 4 Schematic diagram of a transmission electron microscope image of the silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2) obtained in Example 3 at 0.5 μm;

[0031] Figure 5Schematic diagram of a transmission electron microscope image of the silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2) obtained in Example 4 at 0.2 μm;

[0032] Figure 6a Schematic diagram of a scanning transmission electron microscope at 200 nm of the silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@mSiO2) obtained in Example 1 after a long reaction of water electrolysis to produce ozone;

[0033] Figure 6b Schematic diagram of a transmission electron microscope at 50 nm of the silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@mSiO2) obtained in Example 1 after a long reaction of water electrolysis to produce ozone;

[0034] Figure 7a Schematic diagram of a scanning transmission electron microscope at 200 nm of the uncoated cubic lead tetroxide catalyst (cubic-Pb3O4) obtained in Comparative Example 1 after a long reaction of water electrolysis to produce ozone;

[0035] Figure 7b Schematic diagram of a transmission electron microscope at 50 nm of the uncoated cubic lead tetroxide catalyst (cubic-Pb3O4) obtained in Comparative Example 1 after a long reaction of electrolyzing water to produce ozone;

[0036] Figure 8 The XRD results of the silica-coated cubic lead tetroxide catalyst (cubic-Pb3O4@mSiO2) and the uncoated cubic lead tetroxide catalyst (cubic-Pb3O4) obtained in Example 1 are compared with the standard card.

[0037] Figure 9 Graphs of ozone production during long-term reactions of water electrolysis using the silica-coated cubic lead tetroxide catalyst (cubic-Pb3O4@mSiO2) and the uncoated cubic lead tetroxide catalyst (cubic-Pb3O4) obtained in Example 1.

[0038] Figure 10 Graphs of ozone Faraday efficiency corresponding to the long-term reaction of using the silica-coated cubic lead tetroxide catalyst (cubic-Pb3O4@mSiO2) and the uncoated cubic lead tetroxide catalyst (cubic-Pb3O4) obtained in Example 1 for electrolysis of water to produce ozone. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0040] Example 1: Preparation of a silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2), comprising the following steps:

[0041] 1) Weigh 3000 mg of lead acetate and dissolve it in 100 mL of deionized water. Ultrasonicate for 5 minutes and stir to form a homogeneous solution. Adjust the pH of the homogeneous solution to 14 with 20 mL of 1 mol / L NaOH solution, ultrasonicate for 5 minutes, and continue stirring to obtain a homogeneous precursor solution.

[0042] 2) Transfer 40 mL of the precursor solution obtained in step 1) to a 100 mL inner liner. Add 959.4 mg of CTAB to the inner liner, mix thoroughly, and heat the mixture to 50°C in a water bath. After incubating in a constant temperature water bath for 30 minutes, add 6.4 mL of NaClO solution (4% available chlorine concentration) dropwise to the inner liner and stir for 1-3 minutes to evenly disperse the mixture to obtain a suspension.

[0043] 3) The liner was placed in a hydrothermal reactor and subjected to a hydrothermal reaction at 120°C for 24 hours. After the reaction, the mixture was cooled to room temperature and filtered to obtain a crude product precipitate. The crude product precipitate was washed with anhydrous ethanol and deionized water 3-5 times each, then filtered. The filter residue was placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain a cubic lead tetroxide catalyst (cubic-Pb3O4).

[0044] 4) Weigh 540 mg of the dried cubic-Pb3O4 catalyst sample from step 3) and 1800 mg of CTAB, disperse them in 360 mL of deionized water (500 mL flask), and sonicate for 20 min to obtain a uniform suspension.

[0045] 5) Transfer the uniformly dispersed suspension obtained in step 4) to a 40°C oil bath and continue stirring (400 rpm). Slowly add 18 mL of ammonia solution (28 wt%) to adjust the pH of the mixture to 11-12.

[0046] 6) Add 2.16 mL of TEOS to the mixed solution obtained in step 5) and stir at 400 rpm for 30 min. After the reaction is completed and the system is cooled, the product is collected (washed with ethanol several times to remove CTAB) and placed in a vacuum drying oven at 60°C-80°C for 20-24 h to obtain a silica-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2).

[0047] XRD test shows that the crystal structure of the uncoated cubic lead tetroxide catalyst (cubic-Pb3O4) and the silicon dioxide coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2) obtained in Example 1 corresponds to PDF#41-1493 (Pb3O4). The XRD test results are as follows: Figure 8 As shown in Figure 2. Since the SiO2 coating content in cubic-Pb3O4@SiO2 is very small, only about 2-3 wt%, the XRD crystal structure of the catalyst here mainly shows Pb3O4. Transmission electron microscopy diagrams of cubic-Pb3O4 catalyst at 0.2 μm and 50 nm are shown in Figure 2. Figure 1a and Figure 1b As shown. Figure 1a and Figure 1b As can be seen in the figure, the cubic-Pb3O4 catalyst particles are cube-shaped with a side length of about 1 μm and a flat surface. Transmission electron microscopy diagrams of cubic-Pb3O4@SiO2 catalyst at 0.2 μm and 100 nm are shown in Figure 2. Figure 2a and Figure 2b As shown. Figure 2a and Figure 2b It can be seen that the cubic-Pb3O4@SiO2 catalyst shows a wrapping structure with cubic-Pb3O4 as the core and a thin layer of SiO2 uniformly wrapped around it, and the SiO2 wrapping thickness is 50-100 nm.

[0048] The silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2) of Example 1 was used in an experiment to produce ozone by electrolysis of water:

[0049] First, a membrane electrode was prepared. Specifically, the cubic-Pb3O4@SiO2 catalyst prepared in Example 1 was used as the anode material, and a platinum-carbon catalyst with a 10% platinum content was used as the cathode material. These catalysts were coated on the anode and cathode surfaces of a Nafion 117 membrane, respectively. The specific preparation process was as follows:

[0050] Preparation of membrane electrode cathode: 200 mg of commercial platinum-carbon catalyst (platinum loading of 10 wt%) and 500 mg of Nafion solution (5 wt%) were dispersed in 10 mL of ethanol, heated in an oil bath to obtain cathode material slurry, which was then coated on the cathode surface of the Nafion117 membrane.

[0051] Preparation of membrane electrode anode: 400 mg of the cubic-Pb3O4@SiO2 catalyst prepared in Example 1 and 500 mg of Nafion solution (5 wt%) were dispersed in 10 mL of ethanol, heated in an oil bath to obtain an anode material slurry, which was coated on the anode surface of the Nafion 117 membrane.

[0052] Hot pressing treatment: After the anode and cathode materials are coated, the hot pressing temperature is set to 100°C and hot pressing treatment is performed to prepare the membrane electrode.

[0053] A solid polymer electrolyte (SPE) ozone generator was used, with the prepared membrane electrode as its core component. The ozone generator's electrolysis chamber had a volume of 3 L (the cathode and anode chambers each had a volume of 1.5 L, separated by the membrane electrode), and tap water was added to the electrolysis chamber. During operation, a constant current of 10 A was set, and the cell voltage was stabilized at 4.0-4.2 V. The ozone gas generated by electrolysis at the anode of the ozone generator was connected to an ozone detector via the anode outlet, enabling real-time detection of the ozone gas concentration. After 36 hours of electrolysis, the gaseous ozone production reached 654 mg / h / (g·catalyst), corresponding to a Faradaic efficiency (FE(O3)) of 22%.

[0054] In order to verify the catalytic stability of cubic-Pb3O4@SiO2 prepared in Example 1, the above ozone generator was operated continuously for 400 h. The corresponding ozone production and Faraday efficiency results are shown in the following table. Figure 9 、 Figure 10 As shown. Figure 9 As can be seen, the ozone concentration produced by the module reached its peak after 36 hours of reaction and then remained stable. Over the 400 hours, the ozone concentration did not decrease significantly over time. This demonstrates the excellent electrocatalytic activity and stability of the cubic-Pb3O4@SiO2 catalyst for ozone production.

[0055] Comparative Example 1 The uncoated cubic lead tetroxide catalyst (cubic-Pb3O4) of Example 1 was applied to the ozone production experiment by electrolysis of water:

[0056] First, a membrane electrode was prepared, and the cubic-Pb3O4 of Example 1 and the platinum-carbon catalyst with a platinum content of 10% were coated on both sides of the Nafion 117 membrane as the anode material and the cathode material, respectively.

[0057] The preparation process of the membrane electrode material of comparative example 1 repeats that of example 1, except that the cubic-Pb3O4@SiO2 catalyst of example 1 is replaced by an equal mass of the cubic-Pb3O4 catalyst of example 1, and the preparation process of the membrane electrode material is the same as that of example 1.

[0058] A solid polymer electrolyte (SPE) ozone generator was used, with the membrane electrode prepared above as its core component. The ozone generator's electrolysis chamber had a volume of 3 L (the cathode and anode chambers each had a volume of 1.5 L, separated by the membrane electrode), and tap water was added to the electrolysis chamber. During operation, a constant current of 10 A was set, and the cell voltage was stabilized at 4.8-5.5 V during the initial operation. The ozone gas generated by electrolysis at the anode of the ozone generator was connected to an ozone detector via the anode outlet, enabling real-time detection of the ozone gas concentration. After 36 hours of electrolysis, the gaseous ozone production reached 549 mg / h / (g·catalyst), corresponding to a Faradaic efficiency (FE(O3)) of 18%.

[0059] In order to verify the stability of the cubic-Pb3O4 catalyst prepared in Comparative Example 1 for electrocatalytic ozone production, the above ozone generator was continuously operated for 250 h. The corresponding ozone production and Faraday efficiency results are shown in the following table. Figure 9 、 Figure 10 As shown. Figure 9 It can be seen that after 36 hours of reaction, the ozone concentration produced by the module reached its peak. After 180 hours of operation, its ozone production began to drop sharply. After approximately 250 hours of operation, the ozone production dropped to 177 mg / h / (g·catalyst), and the corresponding FE (O3) dropped to 5.9%. This demonstrates that the cubic-Pb3O4 catalyst has poorer electrocatalytic ozone production activity and stability than the cubic-Pb3O4@SiO2 catalyst.

[0060] By comparing the reactivity and stability of the cubic-Pb3O4 catalyst and the cubic-Pb3O4@SiO2 catalyst in the electrocatalytic ozone production process in Example 1, it is speculated that the coating of silicon dioxide has a significant effect on improving the reactivity and stability of cubic-Pb3O4. Figure 6a As shown in Figure 2, the cubic-Pb3O4@SiO2 catalyst maintained a good cubic morphology after stable operation for 400 h at a constant current of 10 A. Figure 6b It can be seen that the surface structure of the cubic-Pb3O4@SiO2 catalyst remains "ordered" even after long-term operation under highly oxidizing conditions, which may explain why the catalyst has excellent catalytic stability. Figure 7a As shown in Figure 2, after 250 h of reaction under the same constant current operating conditions, the cubic structure of the cubic-Pb3O4 catalyst was destroyed, as shown in Figure 2. Figure 7b As shown, its surface structure is in a relatively "disordered" state. Perhaps it is precisely this structural change that leads to a decrease in its activity and stability.

[0061] Example 2: Preparation of a silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2), comprising the following steps:

[0062] 1) Weigh 3000 mg of lead acetate and dissolve it in 100 mL of deionized water. Ultrasonicate for 5 minutes and stir to form a homogeneous solution. Adjust the pH of the homogeneous solution to 14 with 20 mL of 1 mol / L NaOH solution, ultrasonicate for 5 minutes, and continue stirring to obtain a homogeneous precursor solution.

[0063] 2) Transfer 40 mL of the precursor solution obtained in step 1) to a 100 mL inner liner. Add 959.4 mg of CTAB to the inner liner, mix thoroughly, and heat the mixture to 50°C in a water bath. After incubating in a constant temperature water bath for 30 minutes, add 6.4 mL of NaClO solution (4% available chlorine concentration) dropwise to the inner liner and stir for 1-3 minutes to evenly disperse the mixture to obtain a suspension.

[0064] 3) The liner was placed in a hydrothermal reactor and subjected to a hydrothermal reaction at 120°C for 24 hours. After the reaction, the mixture was cooled to room temperature and filtered to obtain a crude product precipitate. The crude product precipitate was washed with anhydrous ethanol and deionized water 3-5 times each, then filtered. The filter residue was placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain a cubic lead tetroxide catalyst (cubic-Pb3O4).

[0065] 4) Weigh 540 mg of the dried cubic-Pb3O4 catalyst sample from step 3) and 2700 mg of CTAB, dissolve them in 360 mL of deionized water (500 mL flask), and sonicate for 20 min to obtain a uniform suspension.

[0066] 5) Transfer the uniformly dispersed suspension obtained in step 4) to a 40°C oil bath and continue stirring (400 rpm). Slowly add 7.2 mL of ammonia solution (28 wt%) to adjust the pH of the mixture.

[0067] 6) Add 2.16 mL of TEOS to the mixed solution obtained in step 5) and stir at 400 rpm for 6 h. After the reaction is complete and the system is cooled, collect the product (wash with ethanol several times to remove CTAB) and dry it in a vacuum drying oven at 60°C-80°C for 20-24 h to obtain a silica-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2).

[0068] Example 2 Transmission electron microscopy diagrams of the cubic-Pb3O4@SiO2 catalyst obtained at 0.2 μm and 50 nm are shown in Figures 2 and 3. Figure 3a and Figure 3b As shown. Figure 3a and Figure 3b As can be seen in the figure, the cubic-Pb3O4@SiO2 catalyst exhibits a semi-encapsulated structure, with the cubic-Pb3O4 core surrounded by a thin layer of SiO2 that is unevenly coated. The reason for this uneven SiO2 coating is likely due to the alkaline environment of the system, which leads to insufficient TEOS hydrolysis and the lack of uniform growth and coating of the SiO2 layer.

[0069] The cubic-Pb3O4@SiO2 catalyst of Example 2 was used in an experiment to produce ozone by electrolysis of water:

[0070] First, a membrane electrode was prepared. Specifically, the cubic-Pb3O4@SiO2 catalyst prepared in Example 2 was used as the anode material, and a platinum-carbon catalyst with 10% platinum content was used as the cathode material, which were coated on the anode and cathode surfaces of the Nafion 117 membrane, respectively.

[0071] The preparation process of the membrane electrode material of Example 2 repeats Example 1, except that: the added catalyst of Example 1 is replaced by the catalyst prepared in Example 2 of equal mass, and the commercial platinum-carbon catalyst with 10% platinum content in Example 1 is replaced by the commercial platinum-carbon catalyst with 10% platinum content of equal mass. The rest of the preparation process of the membrane electrode material is the same as that of Example 1.

[0072] A solid polymer electrolyte (SPE) ozone generator was used, with the prepared membrane electrode as its core component. The ozone generator's electrolysis chamber had a volume of 3 L (the cathode and anode chambers each had a volume of 1.5 L, separated by the membrane electrode), and tap water was added to the electrolysis chamber. During operation, a constant current of 5 A was set, and the cell voltage was stabilized at 3.5-4 V. The ozone gas generated by electrolysis at the anode of the ozone generator was connected to an ozone detector via the anode outlet, enabling real-time detection of the ozone gas concentration. After 36 hours of electrolysis, the gaseous ozone production reached 272 mg / h / (g·catalyst), corresponding to a Faradaic efficiency (FE(O3)) of 18%.

[0073] Example 3: Preparation of a silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2), comprising the following steps:

[0074] 1) Weigh 3000 mg of lead acetate and dissolve it in 100 mL of deionized water. Ultrasonicate for 5 minutes and stir to form a homogeneous solution. Adjust the pH of the homogeneous solution to 14 with 20 mL of 1 mol / L NaOH solution, ultrasonicate for 5 minutes, and continue stirring to obtain a homogeneous precursor solution.

[0075] 2) Transfer 40 mL of the precursor solution obtained in step 1) to a 100 mL inner liner. Add 959.4 mg of CTAB to the inner liner, mix thoroughly, and heat the mixture to 50°C in a water bath. After incubating in a constant temperature water bath for 30 minutes, add 6.4 mL of NaClO solution (4% available chlorine concentration) dropwise to the inner liner and stir for 1-3 minutes to evenly disperse the mixture to obtain a suspension.

[0076] 3) The liner was placed in a hydrothermal reactor and subjected to a hydrothermal reaction at 120°C for 24 hours. After the reaction, the mixture was cooled to room temperature and filtered to obtain a crude product precipitate. The crude product precipitate was washed with anhydrous ethanol and deionized water 3-5 times each, then filtered. The filter residue was placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain a cubic lead tetroxide catalyst (cubic-Pb3O4).

[0077] 4) Weigh 540 mg of the dried cubic-Pb3O4 catalyst sample from step 3) and 1800 mg of CTAB, dissolve them in 360 mL of a solvent system (90 mL of deionized water + 270 mL of ethanol), and sonicate for 20 min to obtain a uniform suspension.

[0078] 5) Transfer the uniformly dispersed suspension obtained in step 4) to a 40°C oil bath and continue stirring (400 rpm). Slowly add 18 mL of ammonia solution (28 wt%) to adjust the pH of the mixture to 11-12.

[0079] 6) Add 1.44 mL of TEOS to the mixed solution obtained in step 5) and stir at 400 rpm for 30 min. After the reaction is completed and the system is cooled, the product is collected (washed with ethanol several times to remove CTAB) and placed in a vacuum drying oven at 60°C-80°C for 20-24 h to obtain a silica-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2).

[0080] The transmission electron microscopy diagram of the cubic-Pb3O4@SiO2 catalyst obtained in Example 3 at 0.5 μm is shown in the figure below. Figure 4 As shown. Figure 4As can be seen in the figure, the cubic-Pb3O4@SiO2 catalyst is mainly composed of cubic-Pb3O4 as the core, and the SiO2 coating is small and uneven. This may be caused by the uneven dispersion of the mixed system in this solvent system. Insufficient TEOS dosage may also lead to the low SiO2 coating.

[0081] The cubic-Pb3O4@SiO2 catalyst prepared in Example 3 was used in an experiment to produce ozone by electrolysis of water:

[0082] First, a membrane electrode was prepared. Specifically, the cubic-Pb3O4@SiO2 catalyst prepared in Example 3 was used as the anode material, and a platinum-carbon catalyst with 10% platinum content was used as the cathode material, which were coated on the anode and cathode surfaces of the Nafion 117 membrane, respectively.

[0083] The preparation process of the membrane electrode material of Example 3 repeats that of Example 1, except that the catalyst added in Example 1 is replaced with the catalyst prepared in Example 3 of the same mass. The rest of the preparation process of the membrane electrode material is the same as that of Example 1.

[0084] A solid polymer electrolyte (SPE) ozone generator was used, with the membrane electrode prepared above as its core component. The ozone generator's electrolysis chamber had a volume of 3 L (the cathode and anode chambers each had a volume of 1.5 L, separated by the membrane electrode), and tap water was added to the electrolysis chamber. During operation, a constant current of 10 A was set, and the cell voltage was stabilized at 4.2-4.5 V. The ozone gas generated by electrolysis at the anode of the ozone generator was connected to an ozone detector via the anode outlet, enabling real-time detection of the ozone gas concentration. After 36 hours of electrolysis, the gaseous ozone production reached 580 mg / h / (g·catalyst), corresponding to a Faradaic efficiency (FE(O3)) of 18% for ozone production.

[0085] Example 4: Preparation of a silicon dioxide-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2), comprising the following steps:

[0086] 1) Weigh 3000 mg of lead acetate and dissolve it in 100 mL of deionized water. Ultrasonicate for 5 minutes and stir to form a homogeneous solution. Adjust the pH of the homogeneous solution to 14 with 20 mL of 1 mol / L NaOH solution, ultrasonicate for 5 minutes, and continue stirring to obtain a homogeneous precursor solution.

[0087] 2) Transfer 40 mL of the precursor solution obtained in step 1) to a 100 mL inner liner. Add 959.4 mg of CTAB to the inner liner, mix thoroughly, and heat the mixture to 50°C in a water bath. After incubating in a constant temperature water bath for 30 minutes, add 6.4 mL of NaClO solution (4% available chlorine concentration) dropwise to the inner liner and stir for 1-3 minutes to evenly disperse the mixture to obtain a suspension.

[0088] 3) The liner was placed in a hydrothermal reactor and subjected to a hydrothermal reaction at 120°C for 24 hours. After the reaction, the mixture was cooled to room temperature and filtered to obtain a crude product precipitate. The crude product precipitate was washed with anhydrous ethanol and deionized water 3-5 times each, then filtered. The filter residue was placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain a cubic lead tetroxide catalyst (cubic-Pb3O4).

[0089] 4) Weigh 540 mg of the dried cubic-Pb3O4 catalyst sample from step 3) and 1800 mg of CTAB, dissolve them in 360 mL of a solvent system (288 mL of deionized water + 72 mL of n-hexane), and sonicate for 20 min to obtain a uniform suspension.

[0090] 5) Transfer the uniformly dispersed suspension obtained in step 4) to a 40°C oil bath and continue stirring (400 rpm). Slowly add 18 mL of ammonia solution (28 wt%) to adjust the pH of the mixture to 11-12.

[0091] 6) Continue to add 720 μL of TEOS to the mixed solution system obtained in step 5), stir at 400 rpm for 30 minutes, wait for the reaction to complete, and cool the system. Collect the product (wash it with ethanol several times to remove CTAB) and place the resulting product in a vacuum drying oven at 60°C-80°C for 20-24 hours to obtain a silica-coated cubic lead tetroxide catalyst (cubic-Pb3O4@SiO2).

[0092] The transmission electron microscopy diagram of the cubic-Pb3O4@SiO2 catalyst obtained in Example 4 at 0.5 μm is shown in the figure below. Figure 5 As shown. Figure 5 As can be seen in the figure, the cubic-Pb3O4@SiO2 catalyst is mainly composed of cubic-Pb3O4 as the core, and the SiO2 coating is very small and uneven. This may be caused by the uneven dispersion of the mixed system in the solvent system. In addition, too little TEOS may also lead to a low SiO2 coating.

[0093] The cubic-Pb3O4@SiO2 catalyst prepared in Example 4 was used in an experiment to produce ozone by electrolysis of water:

[0094] First, a membrane electrode was prepared. Specifically, the cubic-Pb3O4@SiO2 catalyst prepared in Example 4 was used as the anode material, and a platinum-carbon catalyst with 10% platinum content was used as the cathode material, which were coated on the anode and cathode surfaces of the Nafion 117 membrane, respectively.

[0095] The preparation process of the membrane electrode material of Example 4 repeats that of Example 1, except that the catalyst added in Example 1 is replaced with the catalyst prepared in Example 4 of the same mass. The rest of the preparation process of the membrane electrode material is the same as that of Example 1.

[0096] A solid polymer electrolyte (SPE) ozone generator was used, with the prepared membrane electrode as its core component. The ozone generator's electrolysis chamber had a volume of 3 L (the cathode and anode chambers each had a volume of 1.5 L, separated by the membrane electrode), and tap water was added to the electrolysis chamber. During operation, a constant current of 5 A was set, and the cell voltage was stabilized at 3.7-4.2 V. The ozone gas generated by electrolysis at the anode of the ozone generator was connected to an ozone detector via the anode outlet, enabling real-time detection of the ozone gas concentration. After 36 hours of electrolysis, the gaseous ozone production reached 279 mg / h / (g·catalyst), corresponding to a Faradaic efficiency (FE(O3)) of 18.5%.

[0097] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be considered as being limited to the specific forms described in the embodiments.

Claims

1. A method for preparing a silicon dioxide-coated cubic lead tetroxide catalyst, characterized in that The following steps are involved: 1) Cubic lead tetroxide catalyst powder and cetyltrimethylammonium bromide (CTAB) are ultrasonically dispersed in a solvent system. The resulting mixture is transferred to an oil bath at 40-80°C and stirred continuously. An alkaline solution is added to adjust the pH to alkaline. 2) Tetraethyl orthosilicate (TEOS) was added to the mixed solution obtained in step 1) and stirred for 0.5 to 12 hours. After the reaction was completed, the mixture was cooled, the product was collected, washed with ethanol several times to remove CTAB, and finally dried to obtain the silica-coated cubic lead tetroxide catalyst. In step 1), the amount of cubic lead tetroxide catalyst powder added to the solvent system is 1-2 mg / mL, and the amount of CTAB added to the solvent system is 4-7.5 mg / mL. The solvent system in step 1) is a pure aqueous phase system; In step 1), the alkaline solution is an ammonia solution with a mass fraction of 25-28%, and the volume ratio of the alkaline solution to the mixed solution is 1:20; In step 2), the ratio of the volume of tetraethyl orthosilicate (TEOS) to the mass of the cubic lead tetroxide catalyst powder in step 1) is 2-6:1, the unit of volume is mL, and the unit of mass is g.

2. The method for preparing a silicon dioxide-coated cubic lead tetroxide catalyst according to claim 1, characterized in that In step 1), the amount of cubic lead tetroxide catalyst powder added to the solvent system is 1.5 mg / mL; the amount of CTAB added to the solvent system is 5 mg / mL.

3. The method for preparing a silicon dioxide-coated cubic lead tetroxide catalyst according to claim 1, characterized in that In step 2), the ratio of the volume of tetraethyl orthosilicate (TEOS) to the mass of the cubic lead tetroxide catalyst powder in step 1) is 4-5:1, the unit of volume is mL, and the unit of mass is g.

4. The method for preparing a silicon dioxide-coated cubic lead tetroxide catalyst according to claim 1, characterized in that The preparation method of the cubic lead tetroxide catalyst powder comprises the following steps: S1: Dissolve the lead salt in deionized water, add an inorganic base to adjust the pH to 14, and disperse uniformly by ultrasonication to obtain a precursor solution. Add a structure-inducing agent, hexadecyltrimethylammonium bromide (CTAB), and stir at 45-55°C for 20-40 minutes. Then, add sodium hypochlorite solution and stir and disperse uniformly to obtain a suspension. S2: The suspension obtained in step S1 is transferred to the inner lining of a hydrothermal reactor, and the inner lining is then placed in the hydrothermal reactor. The hydrothermal reaction is carried out at a temperature of 110-130°C for 20-30 hours. After the reaction is completed, the suspension is cooled to room temperature and filtered to obtain a crude product precipitate. The crude product precipitate is washed several times with anhydrous ethanol and deionized water, filtered, and dried to obtain a cubic lead tetroxide catalyst.

5. The method for preparing a silicon dioxide-coated cubic lead tetroxide catalyst according to claim 4, characterized in that In step S1, the lead salt is lead acetate, the concentration of the lead salt in deionized water is 20-40 mg / mL, and the inorganic base is sodium hydroxide.

6. The method for preparing a silicon dioxide-coated cubic lead tetroxide catalyst according to claim 4, characterized in that In step S1, the mass ratio of CTAB to lead salt is 1:1-3; in step S1, the effective chlorine concentration of the sodium hypochlorite solution is 4%, the volume of the sodium hypochlorite solution and the mass ratio of the lead salt are 3-8:1, the unit of volume is mL, and the unit of mass is g.

7. The method for preparing a silicon dioxide-coated cubic lead tetroxide catalyst according to claim 6, characterized in that In step S1, the mass ratio of CTAB to lead salt is 1:1.25-1.5; in step S1, the ratio of the volume of the sodium hypochlorite solution to the mass of the lead salt is 5-6:1, the unit of volume is mL, and the unit of mass is g.

8. A silicon dioxide-coated cubic lead tetroxide catalyst prepared by the method according to any one of claims 1 to 7.

9. Use of the silicon dioxide-coated cubic lead tetroxide catalyst as claimed in claim 8 in the electrocatalytic decomposition of water to produce ozone at industrial current density.

10. The use according to claim 9, characterized in that A solid polymer electrolyte ozone generator is used as a reactor; the silicon dioxide-coated cubic lead tetroxide catalyst is used as the anode material, and the platinum-carbon catalyst with a 10% platinum content is used as the cathode material. The anode material and the cathode material are respectively coated on the anode surface and the cathode surface of the proton exchange membrane. The cathode chamber and the anode chamber of the reactor are separated by the proton exchange membrane. Deionized water is used as the electrolyte. The current is 5A-10A, the cell voltage is 3V-5V, and the electrolysis reaction is carried out at a temperature of 20°C-50°C to produce an ozone product.

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