Composite photocatalyst, preparation method thereof and method for producing hydrogen peroxide

Abstract

The invention relates to a composite photocatalyst, a preparation method thereof and a method for producing hydrogen peroxide, the composite photocatalyst comprises hierarchical pore silicon oxide and C3N4 quantum dots, and the C3N4 quantum dots are loaded on the surface of the hierarchical pore silicon oxide; the hierarchical pore silicon oxide is provided with mesopores of 2 to 6 nm and macropores of 26 to 40 nm; on the basis of the total weight of the composite photocatalyst, the weight percentage of the hierarchical pore silicon oxide is 10%-40%, and the weight percentage of the C3N4 is 60%-90%. The composite photocatalyst provided by the invention has relatively high activity, strong stability and high efficiency during preparation of hydrogen peroxide, and can be used for preparing a pure hydrogen peroxide aqueous solution by taking pure water and oxygen as raw materials under the condition of not adding any sacrificial agent. The composite photocatalyst provided by the invention is simple in preparation method and low in raw material price, and meanwhile, the energy consumption generated in the hydrogen peroxide preparation process can be reduced, the pollution is reduced, the production cost is reduced, and the flow process is simplified.

Description

Technical Field

[0001] The invention relates to the technical field of photocatalysis, and in particular to a composite photocatalyst and a preparation method thereof, and a method for producing hydrogen peroxide. Background Art

[0002] Hydrogen peroxide is a clean oxidant widely used in chemical synthesis, disinfection, wastewater treatment and other fields. In recent years, with the gradual promotion of green chemical technology, the demand for hydrogen peroxide has increased year by year. The traditional synthesis method of hydrogen peroxide is the anthraquinone method, which is highly efficient and can be produced on a large scale, and has become the most important hydrogen peroxide production method in industry. However, the preparation of hydrogen peroxide by the anthraquinone method needs to be carried out in an organic solvent, and needs to undergo anthraquinone hydrogenation, oxidation and subsequent extraction, purification, concentration and other series of processes, which has high energy consumption and heavy environmental pollution. In addition, the hydrogenation reaction of alkyl anthraquinone requires precious metal Pd catalysis, which is costly. Most importantly, the raw materials H2 and anthraquinone of this method are both flammable and explosive chemicals, and the concentration of hydrogen peroxide produced is high and oxidizing, resulting in more safety risks in the production and transportation process. Therefore, the development of energy-saving, environmentally friendly and safe hydrogen peroxide synthesis technology has become a research hotspot and market needs.

[0003] Photocatalytic preparation of hydrogen peroxide technology can be carried out at room temperature. It uses solar energy and photocatalysts to convert water and oxygen into hydrogen peroxide. It is a potential more environmentally friendly, energy-saving and safer hydrogen peroxide preparation technology. Under ideal conditions, the reactants are only water and oxygen. However, due to the high Gibbs free energy of the reaction, many photocatalytic systems require the addition of sacrificial agents to promote the generation of hydrogen peroxide. The addition of sacrificial agents will increase the cost of raw materials on the one hand, and will bring difficulties to product separation on the other hand. Therefore, the development of a photocatalyst that can efficiently prepare hydrogen peroxide in pure water is the focus of current research, which is of great significance for improving the efficiency of hydrogen peroxide preparation and reducing energy consumption. Summary of the invention

[0004] The purpose of the present invention is to provide a composite photocatalyst and a preparation method thereof and a method for producing hydrogen peroxide, so as to solve the problems of high energy consumption, low efficiency, heavy pollution, high cost and complicated process in the preparation method of hydrogen peroxide.

[0005] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a composite photocatalyst, which includes multilevel porous silica and C3N4 quantum dots, and the C3N4 quantum dots are loaded on the surface of the multilevel porous silica; the multilevel porous silica has mesopores of 2 to 6 nm and macropores of 26 to 40 nm; based on the total weight of the composite photocatalyst, the weight percentage of the multilevel porous silica is 10% to 40%, and the weight percentage of the C3N4 quantum dots is 60% to 90%.

[0006] Optionally, based on the total weight of the composite photocatalyst, the weight percentage of the multilevel porous silicon oxide 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 m 2 / g.

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

[0008] S1, mixing coal gasification fly ash with an alkaline solution, and subjecting the mixture to microwave heating reaction; subjecting the reaction product to a first solid-liquid separation to obtain a first solid product, desiliconized ash, and a first solution;

[0009] S2, mixing the first solution, a surfactant and acetic acid, and performing hydrothermal crystallization to obtain a second solution;

[0010] S3, performing a second solid-liquid separation on the second solution to obtain a second solid product; mixing the second solid product, deionized water and melamine to obtain a third solution;

[0011] S4, performing a third solid-liquid separation on the third solution to obtain a third solid product; and calcining 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 weight %; the concentration of silicon element 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 calculated as 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 hexadecylpyridinium bromide, preferably hexadecyltrimethylammonium bromide.

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

[0016] The third aspect of the present invention provides a method for producing hydrogen peroxide, which comprises: contacting deionized water and oxygen with the composite photocatalyst provided by the first aspect of the present invention in a reactor and performing a photocatalytic reaction.

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

[0018] Optionally, the conditions for the photocatalytic reaction include: a light intensity of 20 to 80 mW / cm 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 scheme, the composite photocatalyst provided by the present invention has high activity, strong stability and high efficiency in preparing hydrogen peroxide, and can prepare pure hydrogen peroxide aqueous solution with pure water and oxygen as raw materials without adding any sacrificial agent. The preparation method of the composite photocatalyst provided by the present invention is simple, the raw material price is low, and high value-added utilization of coal gasification solid waste can be achieved. At the same time, it can reduce the energy consumption generated in the process of preparing hydrogen peroxide, reduce pollution, reduce production costs, and simplify the process technology.

[0020] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

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

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

[0024] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

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

[0026] The C3N4 in the composite photocatalyst provided by the present invention exists in the form of quantum dots, the multilevel porous silicon oxide has a multilevel porous structure, and the multilevel porous silicon oxide has a large specific surface area. The composite photocatalyst formed with the C3N4 quantum dots has many reaction active sites, has good photocatalytic activity and stability, is highly efficient when used for producing hydrogen peroxide, and can prepare a pure aqueous hydrogen peroxide solution using pure water and oxygen as raw materials without adding any sacrificial agent.

[0027] According to the present invention, optionally, based on the total weight of the composite photocatalyst, the weight percentage of the multilevel porous silicon oxide is 15% to 35%, the weight percentage of the C3N4 quantum dots is 65% to 85%; the specific surface area of ​​the composite photocatalyst is 600 to 1000 m 2 The above-mentioned embodiment can improve the photocatalytic performance of the composite photocatalyst, thereby preparing hydrogen peroxide more efficiently.

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

[0029] S1, mixing coal gasification fly ash with an alkaline solution, and subjecting the mixture to microwave heating reaction; subjecting the reaction product to a first solid-liquid separation to obtain a first solid product, desiliconized ash, and a first solution;

[0030] S2, mixing the first solution, a surfactant and acetic acid, and performing hydrothermal crystallization to obtain a second solution;

[0031] S3, performing a second solid-liquid separation on the second solution to obtain a second solid product; mixing the second solid product, deionized water and melamine to obtain a third solution;

[0032] S4, performing a third solid-liquid separation on the third solution to obtain a third solid product; and calcining the third solid product.

[0033] The composite photocatalyst preparation method provided by the present invention is simple, the raw material price is low, and the high added value utilization of coal gasification solid waste can be achieved. The obtained composite photocatalyst is more conducive to light absorption and has good photocatalytic activity when producing hydrogen peroxide.

[0034] According to the present invention, optionally, the mass ratio of the coal gasification fly ash to the alkali in the alkali solution is 1: (0.5-1.0); the alkali in the alkali solution is one or more of NaOH, KOH or LiOH, preferably NaOH; the concentration of the alkali 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 the present invention, the coal gasification fly ash is used as a silicon source to prepare a multi-level porous silicon oxide precursor, and the coal gasification fly ash can be utilized as a resource.

[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 calculated as silicon element is (0.06-0.4):1, preferably (0.1-0.2):1; the surfactant is selected from at least one of cetyltrimethylammonium bromide, cetyltriethylammonium bromide and cetylpyridinium bromide, preferably cetyltrimethylammonium bromide.

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

[0038] The third aspect of the present invention provides a method for producing hydrogen peroxide, which comprises: contacting deionized water and oxygen with the composite photocatalyst provided by the first aspect of the present invention in a reactor and performing a photocatalytic reaction.

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

[0040] According to the present invention, optionally, the conditions for the photocatalytic reaction include: a light intensity of 20 to 80 mW / cm 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 the present invention, the composite photocatalyst has high activity, strong stability and high efficiency when preparing hydrogen peroxide through photocatalytic reaction, and can prepare pure hydrogen peroxide aqueous solution with pure water and oxygen as raw materials without adding any sacrificial agent. At the same time, it can reduce energy consumption generated in the process of preparing hydrogen peroxide, reduce pollution, reduce production costs, and simplify the process technology.

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

[0043] The coal gasification fly ash used in the examples comes from a chemical plant in Anqing, 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%), and the rest is residual carbon.

[0044] Example 1

[0045] (1) Preparation of composite photocatalyst: Weigh 3 g of coal gasification fly ash into a polytetrafluoroethylene digestion tube, add 6 mL of a 20 wt % NaOH solution, add the same raw materials mentioned above into four tubes, and place them in a microwave digestion instrument at the same time. React for 30 min under microwave-assisted heating conditions at 130°C, and then separate the solid and liquid to obtain desiliconized ash and a first solution; combine the first solutions, and adjust the silicon concentration in the first solution to 5 g / L. Accurately measure 100mL of the first solution, add 1.04g CTAB, stir evenly, add acetic acid to adjust the pH to 11.0, transfer to a 200mL hydrothermal kettle, and hydroheat at 110℃ for 24h to obtain a second solution; centrifuge the second solution to obtain a second solid product, wash the second solid product to neutrality, weigh 1.0g of the second solid product and mix with 30mL deionized water and 8.6g melamine and stir for 30min to obtain a third solution; centrifuge the third solution to obtain a multi-level porous silica powder loaded with melamine; put the above powder into a crucible, cover it with a lid, and calcine it in a muffle furnace at 550℃ for 4h to obtain a multi-level porous silica / C3N4 composite photocatalyst. The electron microscope image is as follows Figure 1 As shown, the pore distribution is Figure 2 As shown by Figure 1 and Figure 2 It can be seen that the composite photocatalyst prepared in this embodiment has a dual-level pore structure. The weight percentage of multi-level porous silica in the multi-level 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 multi-level porous silica / C3N4 composite photocatalyst is 755m 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 (light intensity of 50mW / cm2) pre-installed with a 400-800nm ​​filter. 2 ). Weigh 25 mg of multi-level porous silica / C3N4 composite photocatalyst into the reactor, add 50 mL of ultrapure water, seal the reactor, and introduce oxygen to reach oxygen saturation. Turn on the light source and stir, and continue to introduce oxygen. After 1 hour, turn off the oxygen, light source and stirring, use a 5 mL syringe to take samples, filter the samples, and use the potassium titanium oxalate method to determine the H2O2 concentration in the supernatant. The H2O2 concentration is 910 μmol / L. It is calculated that the H2O2 generation rate is 1820 μmol·g -1 ·h -1 .

[0047] Example 2

[0048] (1) Preparation of composite photocatalyst: Weigh 3 g of coal gasification fly ash into a polytetrafluoroethylene digestion tube, add 6 mL of a 20 wt % NaOH solution, add the same raw materials mentioned above into four tubes, and place them in a microwave digestion instrument at the same time. React for 30 min under microwave-assisted heating conditions at 130°C, and then separate the solid and liquid to obtain desiliconized ash and a first solution; combine the first solutions, and adjust the silicon concentration in the first solution to 5 g / L. Accurately measure 100 mL of the first solution, add 1.04 g of CTAB, stir evenly, add acetic acid to adjust the pH to 11.0, transfer to a 200 mL hydrothermal kettle, and hydrothermal at 110°C for 24 hours to obtain a second solution; centrifuge the second solution to obtain a second solid product, wash the second solid product to neutrality, weigh 1.2 g of the second solid product, mix with 30 mL of deionized water and 8.6 g of melamine and stir for 30 minutes to obtain a third solution; centrifuge the third solution to obtain a multi-level porous silica powder loaded with melamine; put the above powder into a crucible, cover it with a lid, and calcine it at 550°C in a muffle furnace for 4 hours to obtain a multi-level porous silica / C3N4 composite photocatalyst. The weight percentage of multi-level porous silica in the multi-level 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 multi-level porous silica / C3N4 composite photocatalyst is 741 m 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 (light intensity of 50mW / cm2) pre-installed with a 400-800nm ​​filter. 2). Weigh 25 mg of multi-level porous silica / C3N4 composite photocatalyst into the reactor, add 50 mL of ultrapure water, seal the reactor, and introduce oxygen to reach oxygen saturation. Turn on the light source and stir, and continue to introduce oxygen. After 1 hour, turn off the oxygen, light source and stirring, use a 5 mL syringe to take samples, filter the samples, and use the potassium titanium oxalate method to determine the H2O2 concentration in the supernatant. The H2O2 concentration is 860 μmol / L. It is calculated that the H2O2 generation rate is 1720 μmol·g -1 ·h -1 .

[0050] Comparative Example

[0051] (1) Preparation of photocatalyst: 8.6 g of melamine was weighed and placed in a crucible. The crucible was covered with a lid and calcined in a muffle furnace at 550° C. for 4 h to obtain a 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 (light intensity of 50mW / cm2) pre-installed with a 400-800nm ​​filter. 2 ). Weigh 25 mg of C3N4 photocatalyst into a reactor, add 50 mL of ultrapure water, seal the reactor, and introduce oxygen to achieve oxygen saturation. Turn on the light source and stir, and continue to introduce oxygen. After 1 hour, turn off the oxygen, light source and stirring, use a 5 mL syringe to take a sample, filter the sample, and use the potassium titanium oxalate method to determine the H2O2 concentration in the supernatant. The H2O2 concentration is 6 μmol / L. It is calculated that the H2O2 generation rate is 12 μmol·g -1 ·h -1 .

[0053] It can be seen from the above examples and comparative examples that, in the absence of a sacrificial agent, the rate of photocatalytic preparation of hydrogen peroxide by the multi-level porous silicon oxide / C3N4 composite photocatalyst is much higher than that of the pure C3N4 photocatalyst, indicating that the composite photocatalyst has a high photocatalytic activity. In addition, the raw material of the composite photocatalyst is inexpensive, the preparation process is simple, and while preparing hydrogen peroxide by photocatalysis, it can also realize the resource utilization of coal chemical solid waste.

[0054] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to 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 further describe various possible combinations.

[0056] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A composite photocatalyst, characterized in that: The composite photocatalyst comprises multi-level porous silicon oxide and C3N4 quantum dots, wherein the C3N4 quantum dots are loaded on the surface of the multi-level porous silicon oxide; the multi-level porous silicon oxide has mesopores of 2 to 6 nm and macropores of 26 to 40 nm; Based on the total weight of the composite photocatalyst, the weight percentage of the multilevel porous silicon oxide is 10% to 40%, and the weight percentage of the C3N4 quantum dots is 60% to 90%.

2. The composite photocatalyst according to claim 1, wherein Based on the total weight of the composite photocatalyst, the weight percentage of the multilevel porous silicon oxide 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 m 2 / g.

3. A method for preparing the composite photocatalyst according to claim 1 or 2, characterized in that: The method includes: S1, mixing coal gasification fly ash with an alkaline solution, and subjecting the mixture to microwave heating reaction; subjecting the reaction product to a first solid-liquid separation to obtain a first solid product, desiliconized ash, and a first solution; S2, mixing the first solution, a surfactant and acetic acid, and performing hydrothermal crystallization to obtain a second solution; S3, performing a second solid-liquid separation on the second solution to obtain a second solid product; mixing the second solid product, deionized water and melamine to obtain a third solution; S4, performing a third solid-liquid separation on the third solution to obtain a third solid product; and calcining 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 alkali solution is 1:(0.5-1.0); The alkali in the alkali solution is one or more of NaOH, KOH or LiOH, preferably NaOH; the concentration of the alkali solution is 10-30% by weight; The concentration of silicon in the first solution is 3000-8000 mg / L, preferably 4000-7000 mg / L.

5. The method according to claim 3, wherein: The mass ratio of the second solid product to melamine is 1:(2-14), preferably 1:(5-10).

6. The method according to claim 3, wherein: The molar ratio of the surfactant to the first solution calculated as silicon element is (0.06-0.4):1, preferably (0.1-0.2):1; The surfactant is at least one selected from the group consisting of hexadecyltrimethylammonium bromide, hexadecyltriethylammonium bromide and hexadecylpyridinium bromide, preferably hexadecyltrimethylammonium bromide.

7. The method according to claim 3, wherein: The microwave heating reaction conditions include: microwave heating temperature of 100-150°C and time of 10-50min; The hydrothermal crystallization conditions include: temperature of 50-150°C, preferably 100-120°C; time of 8-48h, preferably 16-32h; The calcination conditions include: a temperature of 400-700° C., preferably 500-600° C.; and a time of 1-8 hours, preferably 2-5 hours.

8. A method for producing hydrogen peroxide, characterized in that The method comprises: contacting deionized water and oxygen with the composite photocatalyst described in claim 1 or 2 in a reactor and performing a photocatalytic reaction.

9. The method according to claim 8, wherein: Based on the volume of the deionized water, the added amount of the composite photocatalyst is 0.2-2.0 mg / mL.

10. The method according to claim 8, wherein: The conditions of the photocatalytic reaction include: the light intensity is 20 to 80 mW / cm 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.

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