Composite photocatalyst, method for preparing the same, and method for producing hydrogen peroxide

Abstract

The present application relates to a kind of composite photocatalyst and its preparation method and the method for producing hydrogen peroxide, the composite photocatalyst includes hierarchical porous silica and C3N4 quantum dot, the C3N4 quantum dot is loaded on the surface of the hierarchical porous silica;The hierarchical porous silica has 2-6nm mesoporous and 26-40nm macroporous;With the total weight of the composite photocatalyst as benchmark, the weight percentage of the hierarchical porous silica is 10%-40%, and the weight percentage of the C3N4 is 60%-90%.The composite photocatalyst provided by the present application has higher activity when preparing hydrogen peroxide, has strong stability, high efficiency, can be prepared with pure water and oxygen as raw material under the condition of not adding any sacrificial agent, and obtain pure hydrogen peroxide solution.The preparation method of the composite photocatalyst provided by the present application is simple, raw material is low in price, can reduce the energy consumption generated in the process of preparing hydrogen peroxide, reduce pollution, reduce production cost, simplify process technology.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis technology, specifically to a composite photocatalyst, its preparation method, and a method for producing hydrogen peroxide. Background Technology

[0002] Hydrogen peroxide is a clean oxidant widely used in chemical synthesis, disinfection, and wastewater treatment. In recent years, with the gradual promotion of green chemical technologies, the demand for hydrogen peroxide has increased year by year. The traditional synthesis method for hydrogen peroxide is the anthraquinone process, which is highly efficient and can be mass-produced, making it the most important industrial method for hydrogen peroxide production. However, the anthraquinone process requires organic solvents and involves a series of processes including anthraquinone hydrogenation, oxidation, and subsequent extraction, purification, and concentration, resulting in high energy consumption and significant environmental pollution. Furthermore, the hydrogenation reaction of alkyl anthraquinones requires the precious metal Pd catalysis, further increasing costs. Most importantly, both the raw materials H2 and anthraquinone are flammable and explosive chemicals, resulting in high concentrations of hydrogen peroxide with strong oxidizing properties, posing significant safety risks during production and transportation. Therefore, developing energy-saving, environmentally friendly, and safe hydrogen peroxide synthesis technologies has become a research hotspot and a pressing market need.

[0003] Photocatalytic hydrogen peroxide production can be carried out at room temperature, utilizing solar energy and photocatalysts to convert water and oxygen into hydrogen peroxide. It represents a potentially more environmentally friendly, energy-efficient, and safer hydrogen peroxide production technology. Under ideal conditions, the reactants are only water and oxygen. However, due to the high Gibbs free energy of this reaction, many photocatalytic systems require the addition of sacrificial agents to promote hydrogen peroxide formation. Adding sacrificial agents increases raw material costs and complicates product separation. Therefore, developing a photocatalyst that can efficiently produce hydrogen peroxide in pure water is a current research focus, and it is of great significance for improving the efficiency of hydrogen peroxide production and reducing energy consumption. Summary of the Invention

[0004] The purpose of this invention is to provide a composite photocatalyst and its preparation method, as well as a method for producing hydrogen peroxide, to solve the problems of high energy consumption, low efficiency, heavy pollution, high cost, and complex process in existing hydrogen peroxide preparation methods.

[0005] To achieve the above objectives, a first aspect of the present invention provides a composite photocatalyst comprising hierarchical porous silica and C3N4 quantum dots, wherein the C3N4 quantum dots are supported on the surface of the hierarchical porous silica; the hierarchical porous silica has mesopores of 2–6 nm and macropores of 26–40 nm; based on the total weight of the composite photocatalyst, the weight percentage of the hierarchical porous silica is 10%–40%, and the weight percentage of the C3N4 quantum dots is 60%–90%.

[0006] Optionally, based on the total weight of the composite photocatalyst, the weight percentage of the hierarchical porous silica is 15%–35%, and the weight percentage of the C3N4 quantum dots is 65%–85%; the specific surface area of ​​the composite photocatalyst is 600–1000 m². 2 / g.

[0007] A second aspect of the present invention provides a method for preparing the composite photocatalyst provided in the first aspect of the present invention, the method comprising:

[0008] S1. Mix coal gasification fly ash with an alkaline solution and microwave-heat the reaction; perform a first solid-liquid separation on the reaction product to obtain a first solid product, desiliconized ash, and a first solution;

[0009] S2. Mix the first solution, surfactant and acetic acid, and perform hydrothermal crystallization to obtain the second solution;

[0010] S3. Perform a second solid-liquid separation on the second solution to obtain a second solid product; mix and stir the second solid product, deionized water and melamine to obtain a third solution;

[0011] S4. Perform a third solid-liquid separation on the third solution to obtain a third solid product; calcine the third solid product.

[0012] Optionally, the mass ratio of the coal gasification fly ash to the alkali in the alkaline solution is 1:(0.5-1.0); the alkali in the alkaline solution is one or more of NaOH, KOH or LiOH, preferably NaOH; the concentration of the alkaline solution is 10-30% by weight; and the concentration of silicon in the first solution is 3000-8000 mg / L, preferably 4000-7000 mg / L.

[0013] Optionally, the mass ratio of the second solid product to melamine is 1:(2-14), preferably 1:(5-10).

[0014] Optionally, the molar ratio of the surfactant to the first solution based on silicon element is (0.06-0.4):1, preferably (0.1-0.2):1; the surfactant is selected from at least one of hexadecyltrimethylammonium bromide, hexadecyltriethylammonium bromide and hexadecylpyridine bromide, preferably hexadecyltrimethylammonium bromide.

[0015] Optionally, the microwave heating reaction conditions include: a microwave heating temperature of 100-150℃ and a time of 10-50 min; the hydrothermal crystallization conditions include: a temperature of 50-150℃, preferably 100-120℃; a time of 8-48 h, preferably 16-32 h; and the calcination conditions include: a temperature of 400-700℃, preferably 500-600℃; and a time of 1-8 h, preferably 2-5 h.

[0016] A third aspect of the present invention provides a method for producing hydrogen peroxide, the method comprising: contacting deionized water and oxygen with the composite photocatalyst provided in the first aspect of the present invention in a reactor and carrying out a photocatalytic reaction.

[0017] Optionally, the amount of composite photocatalyst added is 0.2 to 2.0 mg / mL, based on the volume of the deionized water.

[0018] Optionally, the conditions for the photocatalytic reaction include: a light intensity of 20–80 mW / cm². 2 The illumination time is 0.5 to 3 hours; the light source is a 300W xenon lamp pre-installed with a 400 to 800nm ​​filter.

[0019] Through the above technical solution, the composite photocatalyst provided by this invention exhibits high activity, strong stability, and high efficiency in the preparation of hydrogen peroxide. It can prepare a pure aqueous solution of hydrogen peroxide using pure water and oxygen as raw materials without adding any sacrificial agents. The preparation method of the composite photocatalyst provided by this invention is simple, uses inexpensive raw materials, and enables high-value utilization of solid waste from coal gasification. Simultaneously, it can reduce energy consumption during hydrogen peroxide preparation, reduce pollution, lower production costs, and simplify the process.

[0020] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0022] Figure 1 This is an electron microscope image of the composite photocatalyst obtained in Example 1 of the present invention;

[0023] Figure 2 This is a pore distribution diagram of the composite photocatalyst obtained in Example 1 of the present invention. Detailed Implementation

[0024] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0025] The first aspect of the present invention provides a composite photocatalyst comprising hierarchical porous silica and C3N4 quantum dots, wherein the C3N4 quantum dots are supported on the surface of the hierarchical porous silica; the hierarchical porous silica has mesopores of 2-6 nm and macropores of 26-40 nm; based on the total weight of the composite photocatalyst, the weight percentage of the hierarchical porous silica is 10%-40%, and the weight percentage of the C3N4 quantum dots is 60%-90%.

[0026] The C3N4 in the composite photocatalyst provided by this invention exists in the form of quantum dots. The hierarchical porous silica has a hierarchical pore structure and a large specific surface area. The composite photocatalyst formed with C3N4 quantum dots has many active reaction sites, exhibiting good photocatalytic activity and stability. It is highly efficient when used to produce hydrogen peroxide and can prepare a pure aqueous solution of hydrogen peroxide from pure water and oxygen without adding any sacrificial agents.

[0027] According to the present invention, optionally, based on the total weight of the composite photocatalyst, the weight percentage of the hierarchical porous silica is 15% to 35%, and the weight percentage of the C3N4 quantum dots is 65% to 85%; the specific surface area of ​​the composite photocatalyst is 600 to 1000 m². 2 / g. The above embodiments can improve the photocatalytic performance of the composite photocatalyst, thereby producing hydrogen peroxide more efficiently.

[0028] A second aspect of the present invention provides a method for preparing the composite photocatalyst provided in the first aspect of the present invention, the method comprising:

[0029] S1. Mix coal gasification fly ash with an alkaline solution and microwave-heat the reaction; perform a first solid-liquid separation on the reaction product to obtain a first solid product, desiliconized ash, and a first solution;

[0030] S2. Mix the first solution, surfactant and acetic acid, and perform hydrothermal crystallization to obtain the second solution;

[0031] S3. Perform a second solid-liquid separation on the second solution to obtain a second solid product; mix and stir the second solid product, deionized water and melamine to obtain a third solution;

[0032] S4. Perform a third solid-liquid separation on the third solution to obtain a third solid product; calcine the third solid product.

[0033] The composite photocatalyst preparation method provided by this invention is simple, uses inexpensive raw materials, and enables high-value utilization of solid waste from coal gasification. The resulting composite photocatalyst is more conducive to light absorption and exhibits better photocatalytic activity in the production of hydrogen peroxide.

[0034] According to the present invention, optionally, the mass ratio of the coal gasification fly ash to the alkali in the alkaline solution is 1:(0.5-1.0); the alkali in the alkaline solution is one or more of NaOH, KOH, or LiOH, preferably NaOH; the concentration of the alkaline solution is 10-30% by weight; the concentration of silicon in the first solution is 3000-8000 mg / L, preferably 4000-7000 mg / L. In this invention, coal gasification fly ash is used as a silicon source to prepare a hierarchical porous silica precursor, while simultaneously enabling the resource utilization of the coal gasification fly ash.

[0035] According to the present invention, optionally, the mass ratio of the second solid product to melamine is 1:(2-14), preferably 1:(5-10).

[0036] According to the present invention, optionally, the molar ratio of the surfactant to the first solution based on silicon element is (0.06-0.4):1, preferably (0.1-0.2):1; the surfactant is selected from at least one of hexadecyltrimethylammonium bromide, hexadecyltriethylammonium bromide and hexadecylpyridine bromide, preferably hexadecyltrimethylammonium bromide.

[0037] According to the present invention, optionally, the microwave heating reaction conditions include: a microwave heating temperature of 100-150℃ and a time of 10-50 min; the hydrothermal crystallization conditions include: a temperature of 50-150℃, preferably 100-120℃; a time of 8-48 h, preferably 16-32 h; and the calcination conditions include: a temperature of 400-700℃, preferably 500-600℃; and a time of 1-8 h, preferably 2-5 h.

[0038] A third aspect of the present invention provides a method for producing hydrogen peroxide, the method comprising: contacting deionized water and oxygen with the composite photocatalyst provided in the first aspect of the present invention in a reactor and carrying out a photocatalytic reaction.

[0039] According to the present invention, optionally, the amount of composite photocatalyst added is 0.5 to 2.0 mg / mL, based on the volume of the deionized water.

[0040] According to the present invention, optionally, the conditions for the photocatalytic reaction include: a light intensity of 20–80 mW / cm². 2 The illumination time is 0.5 to 3 hours; the light source is a 300W xenon lamp pre-installed with a 400 to 800nm ​​filter.

[0041] In this invention, the composite photocatalyst exhibits high activity, strong stability, and high efficiency in the photocatalytic preparation of hydrogen peroxide. It can produce a pure aqueous solution of hydrogen peroxide using pure water and oxygen as raw materials without the addition of any sacrificial agents. Simultaneously, it reduces energy consumption, pollution, and production costs during hydrogen peroxide preparation, and simplifies the process.

[0042] The present invention will be further illustrated by the following examples, but the present invention is not limited thereto.

[0043] The coal gasification fly ash used in the examples came from a chemical plant in Anqing and is referred to as Anqing ash. Its main chemical composition (by weight) includes: SiO2 (49.4%), Al2O3 (22.8%), CaO (10.3%), Fe2O3 (8.21%), TiO2 (1.26%), Na2O (1.22%), MgO (0.83%), with the remainder being residual carbon.

[0044] Example 1

[0045] (1) Preparation of composite photocatalyst: Weigh 3g of coal gasification fly ash into a polytetrafluoroethylene digestion tube, add 6mL of 20% NaOH solution, add the same raw materials to four tubes, and place them in a microwave digestion instrument. React for 30min under microwave-assisted heating at 130℃, and then separate the solid and liquid to obtain desiliconized ash and the first solution. Combine the first solutions and adjust the silicon concentration in the first solution to 5g / L. Accurately measure 100 mL of the first solution, add 1.04 g of CTAB, stir well, then add acetic acid to adjust the pH to 11.0, transfer to a 200 mL hydrothermal reactor, and hydrothermally heat at 110 °C for 24 h to obtain the second solution. Centrifuge the second solution to obtain the second solid product, wash the second solid product until neutral, weigh 1.0 g of the second solid product, mix with 30 mL of deionized water and 8.6 g of melamine, stir for 30 min to obtain the third solution. Centrifuge the third solution to obtain melamine-loaded hierarchical porous silica powder. Place the powder in a crucible, cover, and calcine in a muffle furnace at 550 °C for 4 h to obtain the hierarchical porous silica / C3N4 composite photocatalyst. Its electron micrograph is shown below. Figure 1 As shown, the pore distribution is as follows Figure 2 As shown, by Figure 1 and Figure 2 It can be seen that the composite photocatalyst prepared in this embodiment has a hierarchical porous structure. The weight percentage of hierarchical porous silica / C3N4 composite photocatalyst is 15.2%, and the weight percentage of C3N4 quantum dots is 84.8%; the specific surface area of ​​the hierarchical porous silica / C3N4 composite photocatalyst is 755 m². 2 / g.

[0046] (2) Photocatalytic preparation of hydrogen peroxide: The photocatalytic preparation of hydrogen peroxide was carried out in a multifunctional photochemical reactor. The light source used was a 300W xenon lamp pre-installed with a 400-800nm ​​filter (illuminance of 50mW / cm²). 2 25 mg of hierarchical porous silica / C3N4 composite photocatalyst was weighed into a reaction vessel, and 50 mL of ultrapure water was added. After sealing the reaction vessel, oxygen was introduced to achieve oxygen saturation. The light source and stirring were turned on, and oxygen was continuously introduced. After 1 hour, the oxygen, light source, and stirring were turned off. A sample was taken using a 5 mL syringe, filtered, and the concentration of H2O2 in the supernatant was determined using the potassium titanium oxalate method. The H2O2 concentration was 910 μmol / L. The calculated H2O2 formation rate was 1820 μmol·g⁻¹. -1 ·h -1 .

[0047] Example 2

[0048] (1) Preparation of composite photocatalyst: Weigh 3g of coal gasification fly ash into a polytetrafluoroethylene digestion tube, add 6mL of 20% NaOH solution, add the same raw materials to four tubes, and place them in a microwave digestion instrument. React for 30min under microwave-assisted heating at 130℃, and then separate the solid and liquid to obtain desiliconized ash and the first solution. Combine the first solutions and adjust the silicon concentration in the first solution to 5g / L. Accurately measure 100 mL of the first solution, add 1.04 g of CTAB, stir well, then add acetic acid to adjust the pH to 11.0, transfer to a 200 mL hydrothermal reactor, and hydrothermally heat at 110 °C for 24 h to obtain the second solution. Centrifuge the second solution to obtain the second solid product, wash the second solid product until neutral, weigh 1.2 g of the second solid product, mix with 30 mL of deionized water and 8.6 g of melamine, stir for 30 min to obtain the third solution. Centrifuge the third solution to obtain melamine-loaded hierarchical porous silica powder. Place the powder in a crucible, cover, and calcine in a muffle furnace at 550 °C for 4 h to obtain a hierarchical porous silica / C3N4 composite photocatalyst. The weight percentage of hierarchical porous silica in the hierarchical porous silica / C3N4 composite photocatalyst is 11.1%, and the weight percentage of C3N4 quantum dots is 88.9%; the specific surface area of ​​the hierarchical porous silica / C3N4 composite photocatalyst is 741 m². 2 / g.

[0049] (2) Photocatalytic preparation of hydrogen peroxide: The photocatalytic preparation of hydrogen peroxide was carried out in a multifunctional photochemical reactor. The light source used was a 300W xenon lamp pre-installed with a 400-800nm ​​filter (illuminance of 50mW / cm²). 225 mg of hierarchical porous silica / C3N4 composite photocatalyst was weighed into a reaction vessel, and 50 mL of ultrapure water was added. After sealing the reaction vessel, oxygen was introduced to achieve oxygen saturation. The light source and stirring were turned on, and oxygen was continuously introduced. After 1 hour, the oxygen, light source, and stirring were turned off. A sample was taken using a 5 mL syringe, filtered, and the concentration of H2O2 in the supernatant was determined using the potassium titanium oxalate method. The H2O2 concentration was 860 μmol / L. The calculated H2O2 formation rate was 1720 μmol·g⁻¹. -1 ·h -1 .

[0050] Comparative Example

[0051] (1) Preparation of photocatalyst: 8.6g of melamine was weighed and placed in a crucible. After covering the crucible, it was calcined in a muffle furnace at 550℃ for 4h to obtain C3N4 photocatalyst.

[0052] (2) Photocatalytic preparation of hydrogen peroxide: The photocatalytic preparation of hydrogen peroxide was carried out in a multifunctional photochemical reactor. The light source used was a 300W xenon lamp pre-installed with a 400-800nm ​​filter (illuminance of 50mW / cm²). 2 25 mg of C3N4 photocatalyst was weighed into a reaction vessel, and 50 mL of ultrapure water was added. After sealing the reaction vessel, oxygen was introduced to achieve oxygen saturation. The light source and stirring were turned on, and oxygen was continued to be introduced. After 1 hour, the oxygen, light source, and stirring were turned off. A sample was taken using a 5 mL syringe, filtered, and the concentration of H2O2 in the supernatant was determined using the potassium titanium oxalate method. The H2O2 concentration was 6 μmol / L. The calculated H2O2 formation rate was 12 μmol·g⁻¹. -1 ·h -1 .

[0053] As can be seen from the above examples and comparative examples, under conditions without sacrificial agents, the photocatalytic rate of hydrogen peroxide production by the hierarchical porous silica / C3N4 composite photocatalyst is much higher than that of the pure C3N4 photocatalyst, indicating that the composite photocatalyst has high photocatalytic activity. Furthermore, the composite photocatalyst uses inexpensive raw materials and has a simple preparation process, enabling the resource utilization of coal chemical solid waste while simultaneously producing hydrogen peroxide.

[0054] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0055] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0056] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for producing hydrogen peroxide, characterized in that, The method includes: contacting deionized water and oxygen with a composite photocatalyst in a reactor and carrying out a photocatalytic reaction; Based on the volume of the deionized water, the amount of the composite photocatalyst added is 0.2~2.0 mg / mL; The composite photocatalyst comprises hierarchical porous silica and C3N4 quantum dots, wherein the C3N4 quantum dots are loaded on the surface of the hierarchical porous silica. Based on the total weight of the composite photocatalyst, the weight percentage of the hierarchical porous silica is 10%~40%, and the weight percentage of the C3N4 quantum dots is 60%~90%; the specific surface area of ​​the composite photocatalyst is 600~1000 m². 2 / g.

2. The method according to claim 1, wherein, Based on the total weight of the composite photocatalyst, the weight percentage of the hierarchical porous silica is 15% to 35%, and the weight percentage of the C3N4 quantum dots is 65% to 85%.

3. The method according to claim 1 or 2, wherein, The preparation method of the composite photocatalyst includes: S1. Mix coal gasification fly ash with an alkaline solution and microwave-heat the reaction; perform a first solid-liquid separation on the reaction product to obtain a first solid product, desiliconized ash, and a first solution; S2. Mix the first solution, surfactant and acetic acid, and perform hydrothermal crystallization to obtain the second solution; S3. Perform a second solid-liquid separation on the second solution to obtain a second solid product; mix and stir the second solid product, deionized water and melamine to obtain a third solution; S4. Perform a third solid-liquid separation on the third solution to obtain a third solid product; calcine the third solid product.

4. The method according to claim 3, wherein, The mass ratio of the coal gasification fly ash to the alkali in the alkaline solution is 1:(0.5-1.0). The alkali in the alkaline solution is one or more of NaOH, KOH, or LiOH; the concentration of the alkaline solution is 10-30% by weight. The concentration of silicon in the first solution is 3000-8000 mg / L.

5. The method according to claim 4, wherein, The alkali in the alkaline solution is NaOH; The concentration of silicon in the first solution is 4000-7000 mg / L.

6. The method according to claim 3, wherein, The mass ratio of the second solid product to melamine is 1:(2-14).

7. The method according to claim 6, wherein, The mass ratio of the second solid product to melamine is 1:(5-10).

8. The method according to claim 3, wherein, The molar ratio of the surfactant to the first solution, based on silicon element, is (0.06-0.4):1; The surfactant is selected from at least one of hexadecyltrimethylammonium bromide, hexadecyltriethylammonium bromide, and hexadecylpyridine bromide.

9. The method according to claim 8, wherein, The molar ratio of the surfactant to the first solution, based on silicon element, is (0.1-0.2):1; The surfactant is hexadecyltrimethylammonium bromide.

10. The method according to claim 3, wherein, The microwave heating reaction conditions include: microwave heating temperature of 100-150℃ and time of 10-50min; The hydrothermal crystallization conditions include: a temperature of 50-150℃ and a time of 8-48 hours. The calcination conditions include: a temperature of 400-700℃ and a time of 1-8 hours.

11. The method according to claim 10, wherein, The hydrothermal crystallization conditions include: a temperature of 100-120℃ and a time of 16-32 hours. The calcination conditions include: a temperature of 500-600℃ and a time of 2-5 hours.

12. The method according to claim 1, wherein, The conditions for the photocatalytic reaction include: a light intensity of 20~80 mW / cm². 2 The illumination time is 0.5~3h; the light source is a 300W xenon lamp pre-installed with a 400~800nm ​​filter.

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