A method for preparing silicon carbide powder for hydrogen production

Abstract

The application relates to the technical field of silicon carbide, and specifically discloses a preparation method of silicon carbide powder for hydrogen production. The preparation method comprises the following steps: S1: adding a silicon source, a carbon source, a nitrogen source and an indium salt into an ethanol aqueous solution, then adding a template agent, adjusting the pH value to 3.0-4.0, heating, mixing, transferring to a hydrothermal kettle, heating, reacting, cooling, solid-liquid separation, drying, and obtaining a precursor; S2: under an inert atmosphere, transferring the precursor into a sintering equipment, heating, heat preservation, continuously heating, heat preservation, continuously heating, heat preservation, cooling, and obtaining a reduction product; S3: immersing the reduction product into hydrofluoric acid, soaking and washing 2-3 times at 20-30 DEG C, carrying out solid-liquid separation, immersing into a hydrogen peroxide solution after washing, heating, reacting, carrying out solid-liquid separation, washing, drying, and obtaining the silicon carbide powder for hydrogen production. The silicon carbide powder for hydrogen production prepared by the application has good catalytic activity and hydrogen production rate in photocatalytic hydrogen production.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of silicon carbide, and more particularly to a silicon carbide powder preparation method for hydrogen production. BACKGROUND

[0002] Hydrogen energy is regarded as an ideal clean energy due to its high combustion heat value, zero carbon emission and renewability. Among various hydrogen production technologies, the semiconductor photocatalytic water splitting for hydrogen production technology has become a research focus due to its greenness and low energy consumption, and the core of the technology is to develop a photocatalytic material that is efficient, stable and has a visible light response.

[0003] Silicon carbide (SiC) nanomaterials have high specific surface area, suitable band gap and excellent stability, and are a kind of potential photocatalytic materials. However, the band gap of SiC is 2.4-3.3 eV, the wide band gap limits the absorption of visible light, and the photo-generated electron-hole pairs are prone to recombination, resulting in low photo quantum efficiency, which seriously restricts the practical application of SiC in photocatalytic hydrogen production.

[0004] The patent application file with the publication number CN109954509A discloses a preparation method of a silicon carbide-based photocatalyst, which specifically comprises the following steps: (1) pure SiC preparation: SiC powder is calcined at high temperature, and naturally cooled to room temperature to remove impurity carbon; then the SiC is sealed and light-proof soaked in a 2% mass fraction HF solution to remove SiO2 and other oxides; finally, the SiC is repeatedly centrifuged and washed with deionized water until the pH value is 7, and then the SiC is placed in a vacuum drying box to obtain pure SiC; (2) MoS2 suspension: MoS2 is placed in deionized water and uniformly mixed to obtain a MoS2 suspension; (3) mixing: pure SiC, GO and ionic liquid are sequentially added into the MoS2 suspension, and ultrasonic stirring is performed to uniformly mix the SiC, GO and ionic liquid; (4) hydrothermal reaction for preparing a silicon carbide-based photocatalyst: the suspension obtained in step (3) is transferred to a high-temperature reaction kettle, and reacts at 200℃ for a period of time, and then is centrifuged and washed until the pH value is 7, and then is vacuum dried to obtain a photocatalytic material, wherein in the hydrothermal reaction system, the weight percentage of MoS2 is 2%-10% in terms of molybdenum element, and the weight percentage of GO is 0.5%-3% in terms of carbon element.

[0005] In the technical solution, the intrinsic wide band gap characteristic of SiC determines that it can only respond to ultraviolet light, and cannot effectively utilize visible light which accounts for the main part of the solar spectrum, resulting in narrow light absorption range and low solar energy utilization rate; and the simple hydrothermal treatment leads to insufficient interfacial bonding force between MoS2 and the matrix, and the active components are prone to fall off under long-term light irradiation and reaction liquid scouring, resulting in continuous loss of catalytic sites. SUMMARY

[0006] In order to improve the catalytic activity and hydrogen production rate, the application provides a silicon carbide powder preparation method for hydrogen production.

[0007] The application provides a silicon carbide powder preparation method for hydrogen production, which adopts the following technical scheme:

[0008] A silicon carbide powder preparation method for hydrogen production comprises the following steps:

[0009] S1: The silicon source, carbon source, nitrogen source, and indium salt are added to an ethanol aqueous solution, and then a template agent is added, the pH is adjusted to 3.0-4.0, the temperature is raised to 50-70 DEG C, and the mixture is mixed for 5-8 hours, and then the mixture is transferred to a hydrothermal kettle, the temperature is raised to 160-180 DEG C, and the reaction is carried out for 18-24 hours, and then the mixture is cooled, solid-liquid separation is performed, and drying is performed, to obtain a precursor;

[0010] S2: The precursor is transferred to a sintering device under an inert atmosphere, the temperature is raised to 500-600 DEG C, and the temperature is maintained for 2-4 hours, the temperature is continuously raised to 800-1000 DEG C, and the temperature is maintained for 30-40 minutes, the temperature is continuously raised to 1200-1300 DEG C, and the temperature is maintained for 60-80 minutes, and then the mixture is cooled, to obtain a reduction product;

[0011] S3: The reduction product is immersed in hydrofluoric acid, and the immersion and washing are performed 2-3 times at 20-30 DEG C, solid-liquid separation is performed, the washing is performed, the reduction product is immersed in a hydrogen peroxide solution, the temperature is raised to 80-90 DEG C, and the reaction is carried out for 4-6 hours, solid-liquid separation is performed, the washing is performed, and drying is performed, to obtain the silicon carbide powder for hydrogen production;

[0012] The nitrogen source comprises urea and melamine.

[0013] In the technical scheme, the silicon source, carbon source, nitrogen source, indium salt, and template agent are pre-hydrothermally compounded to realize uniform mixing and preliminary self-assembly at the molecular / atomic level. In this process, the template agent guides the formation of an ordered mesoporous structure, and the nitrogen source (urea and melamine) and the indium salt are preliminarily embedded in the silicon-carbon network to lay a foundation for subsequent uniform doping; the difference in the decomposition temperature of urea and melamine can also produce a step doping effect to improve the doping efficiency of nitrogen elements.

[0014] Then, sintering reduction is performed, and a two-step temperature raising method is adopted: the temperature is maintained at 500-600 DEG C and 800-1000 DEG C to completely remove the template agent and fully carbonize the organic matter to form a uniform carbon skeleton; and then, the carbonthermal reduction reaction is carried out at a higher temperature of 1200-1300 DEG C; in this process, the nitrogen atoms are partially doped into the SiC crystal lattice after being reduced, and the indium atoms mainly enter the SiC crystal lattice in the form of an interstitial. 3+The larger ionic radius is the main reason for the lattice expansion. N and In synergistically regulate the band structure of SiC, extending the light response range; then, surface purification and functionalization are carried out by double treatment of hydrofluoric acid and hydrogen peroxide: hydrofluoric acid treatment aims to dissolve and remove free silicon dioxide and part of the silicon-containing impurities produced in the carbothermal reduction process, purifying the material surface; the subsequent hydrogen peroxide treatment generates an extremely thin, hydroxyl-rich non-stoichiometric silicon dioxide layer on the SiC surface in situ under mild heating conditions, thereby constructing a firm core-shell heterojunction. The heterojunction can effectively promote the separation of photo-generated electron-hole pairs, and the abundant hydroxyl functional groups on the surface also enhance the hydrophilicity of the material and provide more active sites for hydrogen evolution.

[0015] Preferably, the mass ratio of the silicon source, carbon source, nitrogen source and indium salt is 1:(0.8~1.2):(0.18~0.30):(0.05~0.12).

[0016] Preferably, the carbon source includes polyacrylonitrile fibers and graphene.

[0017] Preferably, the mass ratio of the polyacrylonitrile fibers and graphene is (8~12):1.

[0018] In the technical solution, polyacrylonitrile fibers are used as the main carbon source, which not only provides carbon atoms for the carbothermal reduction reaction during high-temperature heat treatment, but also generates nitrogen-doped carbon skeletons in situ by the decomposition of the cyano groups in the molecular chains, creating favorable conditions for uniform nitrogen doping. At the same time, the carbonized polyacrylonitrile fibers are easy to form interwoven one-dimensional fibrous structures, which can effectively support and connect SiC grains, prevent pore collapse during sintering, and help form a stable porous structure. Graphene mainly acts as an electronic transmission enhancer and secondary carbon source, constructing an electronic transmission network inside the composite material to efficiently extract and transport photo-generated electrons generated by SiC, thereby greatly inhibiting the recombination of electron-hole pairs and improving quantum efficiency.

[0019] Preferably, the mass ratio of the urea and melamine is (1~2.5):1.

[0020] Preferably, the template agent includes block polyether and quaternary ammonium salt.

[0021] Preferably, the mass ratio of the block polyether and quaternary ammonium salt is (3~5):1.

[0022] In the technical solution, the block polyether and the quaternary ammonium salt are used in a specific proportion, the block polyether ensures that the main skeleton has ordered mesopores with high specific surface area, and the addition of the quaternary ammonium salt can create additional through holes and windows in the skeleton, thereby constructing a hierarchical porous structure, which not only further increases the specific surface area, but more importantly, greatly optimizes the mass transfer and diffusion efficiency of the reactants and products, ensures the accessibility of active sites, and avoids performance degradation caused by excessively long or blocked pores.

[0023] Preferably, the amount of the template agent is 8% to 12% of the mass of the silicon source.

[0024] Preferably, in step S2, the sintering equipment is a microwave sintering furnace, and when the temperature is continuously raised to 1200 to 1300 DEG C, the microwave function is simultaneously turned on, and the microwave power is controlled to be 300 to 500 W.

[0025] In the technical solution, microwave-assisted heating can significantly reduce the reaction activation energy, promote rapid nucleation and growth of crystals at low temperature, and ensure uniform distribution of doped elements.

[0026] Preferably, the volume fraction of the hydrofluoric acid is 4% to 6%.

[0027] Preferably, the mass fraction of the hydrogen peroxide solution is 25% to 35%.

[0028] Preferably, before use, the pH of the hydrogen peroxide solution is adjusted to 3 to 4.

[0029] In the technical solution, the hydrogen peroxide is acidified after adjusting the pH to 3 to 4 with dilute nitric acid, which is beneficial to control the oxidation rate, generate a relatively uniform thin layer rich in hydroxyl groups, rather than generate a thick and inert SiO2 insulating layer through violent reaction, thereby optimizing the interface charge transport performance of the heterojunction.

[0030] Preferably, in step S1, after the indium salt, the step of adding boric acid is further included, and the mass ratio of the indium salt to boric acid is (4 to 5):1.

[0031] The introduction of boric acid can produce a new synergistic effect with N and In, further fine-tune the energy band structure of SiC, and widen the absorption range of visible light; in addition, a small amount of boric acid can form a suitable amount of and uniformly distributed micro P-type region in the N-doped SiC matrix, and the dispersed P-type region and the N-type matrix can form a strong and continuous built-in electric field network in the material. The built-in electric field provides a strong additional driving force for the directional separation of photo-generated electron-hole pairs, greatly inhibits the recombination probability, and thus realizes the synergistic effect of multiple doped elements. Controlling the boron content at this low level avoids excessive doping and the introduction of too many deep level defects or lattice distortions, preventing these defects from becoming new charge recombination centers, thereby improving the charge separation efficiency while ensuring excellent intrinsic crystal quality and photocatalytic activity of the material.

[0032] Preferably, in step S3, after hydrogen peroxide treatment, immerse in a thiourea solution with a mass fraction of 8% to 10% and a pH of 3.0 to 4.0, react at 75 to 85°C for 120 to 150 minutes, solid-liquid separation, washing, drying, and obtain the silicon carbide powder for hydrogen production.

[0033] In the technical solution, by using thiourea for post-treatment, under weak acidic conditions at 75 to 85°C, the sulfhydryl ions or sulfur ions produced by the slow hydrolysis of thiourea can react with the Si-H bonds or Si-OH bonds on the surface of SiC, introduce sulfur-containing functional groups, increase the hydrogen evolution reaction active sites, reduce the hydrogen evolution overpotential, and improve the surface reaction kinetics.

[0034] In summary, the present application has the following beneficial effects:

[0035] 1. The present application uses an in-situ doping method, and utilizes the decomposition temperature difference between urea and melamine to realize synergistic doping with indium salt, so that nitrogen elements enter the silicon carbide lattice in the form of substitution, and indium elements enter the silicon carbide lattice in the form of interstitial, effectively optimizing and narrowing the band gap of SiC, significantly expanding the light response range from the ultraviolet region to the visible region, and greatly improving the utilization efficiency of the solar spectrum.

[0036] 2. In the present application, polyacrylonitrile fibers and graphene are preferably used as double carbon sources, which are complementary and synergistic. The polyacrylonitrile fibers can generate nitrogen-doped carbon skeletons in-situ during pyrolysis, providing a uniform nitrogen source for the material bulk phase; and the graphene, with its excellent electrical conductivity, forms a high-speed electron transport network. The combination of the two greatly promotes the separation and migration rate of photo-generated carriers, effectively inhibits their recombination, and thus significantly improves the photo quantum efficiency.

[0037] 3、The application preferably adopts microwave-assisted sintering and double templates. Microwave heating realizes low-temperature rapid synthesis of the material, effectively inhibiting grain coarsening. The double templates precisely control the mesostructure of the product, successfully constructing a composite structure with high specific surface area and hierarchical pores. This structure not only provides abundant active sites for photocatalytic reactions, but also creates excellent reactant mass transfer channels.

[0038] 4、The application further introduces boric acid, realizing B / In / N multi-element co-doping. The incorporation of boron elements and nitrogen elements forms p-n type co-doping, which can form a micro internal electric field inside the SiC crystal grains, providing an additional driving force for the directional separation of photo-generated electron-hole pairs. This multi-element doping strategy realizes the synergistic effect between different elements, essentially improving the core kinetics of the photocatalytic reaction. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The XRD pattern of the silicon carbide powder for hydrogen production prepared in Example 3 of the application. DETAILED DESCRIPTION

[0040] The application will be further described in conjunction with the examples below.

[0041] The raw materials of the examples and comparative examples of the application are all ordinary commercial products unless otherwise specified.

[0042] The block polyether is an ethylene oxide-propylene oxide-ethylene oxide triblock copolymer, abbreviated as F127, with an average molecular weight of about 12600; the quaternary ammonium salt is cetyltrimethylammonium bromide.

[0043] Example 1

[0044] The method for preparing the silicon carbide powder for hydrogen production of the present embodiment comprises the following steps:

[0045] S1: Add tetraethyl orthosilicate 20 g, polyacrylonitrile fiber 18.2 g, graphene 1.8 g, urea 3.4 g, melamine 1.7 g, and indium nitrate 1.5 g into ethanol aqueous solution 500 mL in sequence, add F127 1.6 g and cetyltrimethylammonium bromide 0.4 g, adjust the pH to 3.5 with 10% mass fraction citric acid, heat to 60℃, and stir the mixture at 300 rpm / min for 7 h to obtain a uniform sol. Transfer the sol to an autoclave, heat to 170℃, and hydrothermally react for 22 h. Cool to room temperature, centrifugally separate, and dry at 60℃ to constant weight to obtain a precursor;

[0046] S2: The precursor was placed in a microwave sintering furnace, argon was introduced (flow rate 300 mL / min), and the temperature was raised to 550°C at a rate of 5°C / min, and held for 3 h, then raised to 900°C at a rate of 5°C / min, and held for 35 min, the microwave was turned on, the power was 400 W, and the temperature was continued to be raised to 1250°C at a rate of 5°C / min, and held for 70 min, to obtain a reduction product;

[0047] S3: The reduction product was immersed in hydrofluoric acid with a volume fraction of 5%, the solid-liquid ratio was 1 g:5 mL, and the immersion washing was performed twice, each for 30 min, centrifugal separation was performed, deionized water was used for washing until neutral, then a hydrogen peroxide solution with a pH of 3.5 and a mass fraction of 30% was added, the solid-liquid ratio was 1 g:10 mL, the temperature was raised to 85°C, and reflux reaction was performed for 5 h, centrifugal separation was performed, deionized water was used for washing until neutral, and drying was performed at 60°C until the weight was constant, to obtain the silicon carbide powder for hydrogen production.

[0048] The mixed solvent comprises deionized water and ethanol, and the volume ratio of the deionized water to the ethanol is 1:1.

[0049] Example 2

[0050] The method for preparing the silicon carbide powder for hydrogen production in the example comprises the following steps:

[0051] S1: Tetraethyl orthosilicate 20 g, polyacrylonitrile fiber 14.2 g, graphene 1.8 g, urea 1.8 g, melamine 1.8 g, and indium nitrate 1 g were sequentially added into an ethanol aqueous solution 500 mL, F127 1.2 g and cetyltrimethylammonium bromide 0.4 g were added, a 10% mass fraction citric acid was used to adjust the pH to 4, the temperature was raised to 50°C, and stirring mixing was performed at 300 rpm / min for 8 h to obtain a uniform sol, the sol was transferred to an autoclave, the temperature was raised to 160°C, and hydrothermal reaction was performed for 24 h, the temperature was cooled to room temperature, centrifugal separation was performed, and drying was performed at 60°C until the weight was constant, to obtain a precursor;

[0052] S2: The precursor was placed in a microwave sintering furnace, argon was introduced (flow rate 300 mL / min), and the temperature was raised to 500°C at a rate of 5°C / min, and held for 4 h, then raised to 800°C at a rate of 5°C / min, and held for 40 min, the microwave was turned on, the power was 500 W, and the temperature was continued to be raised to 1200°C at a rate of 5°C / min, and held for 80 min, to obtain a reduction product;

[0053] S3: The reduction product was immersed in hydrofluoric acid with a volume fraction of 4%, the solid-liquid ratio was 1 g:5 mL, and the immersion washing was performed three times, each for 30 min, centrifugal separation was performed, deionized water was used for washing until neutral, then a hydrogen peroxide solution with a pH of 4 and a mass fraction of 35% was added, the solid-liquid ratio was 1 g:10 mL, the temperature was raised to 80°C, and reflux reaction was performed for 6 h, centrifugal separation was performed, deionized water was used for washing until neutral, and drying was performed at 60°C until the weight was constant, to obtain the silicon carbide powder for hydrogen production.

[0054] The mixed solvent comprises deionized water and ethanol, and the volume ratio of the deionized water and the ethanol is 1:1.

[0055] Example 3

[0056] The silicon carbide powder preparation method for hydrogen production of the embodiment comprises the following steps:

[0057] S1: 20 g of tetraethyl orthosilicate, 22.2 g of polyacrylonitrile fiber, 1.8 g of graphene, 4.3 g of urea, 1.7 g of melamine, and 2.4 g of indium nitrate were sequentially added into 500 mL of an ethanol aqueous solution, 2.0 g of F127 and 0.4 g of cetyltrimethylammonium bromide were added, the pH was adjusted to 3 by using 10% citric acid, the temperature was increased to 70°C, and the mixture was stirred at 300 rpm / min for 5 h to obtain a uniform sol, the sol was transferred to an autoclave, the temperature was increased to 180°C, and hydrothermal reaction was performed for 18 h, the temperature was cooled to room temperature, centrifugal separation was performed, and drying was performed at 60°C until a constant weight was obtained to obtain a precursor;

[0058] S2: the precursor was placed in a microwave sintering furnace, argon was introduced (flow rate: 300 mL / min), the temperature was increased to 600°C at a rate of 5°C / min, and then the temperature was kept at 600°C for 2 h, the temperature was then increased to 1000°C at a rate of 5°C / min, and then the temperature was kept at 1000°C for 30 min, the microwave was turned on, the power was 300 W, the temperature was then increased to 1300°C at a rate of 5°C / min, and then the temperature was kept at 1300°C for 60 min to obtain a reduction product;

[0059] S3: the reduction product was immersed in 6% hydrogen fluoride by volume, the solid-liquid ratio was 1 g:5 mL, the immersion and washing were performed twice, each time for 30 min, centrifugal separation was performed, deionized water was used for washing until the solution was neutral, then a 25% hydrogen peroxide solution was added, the pH was 3, the solid-liquid ratio was 1 g:10 mL, the temperature was increased to 90°C, and reflux reaction was performed for 4 h, centrifugal separation was performed, deionized water was used for washing until the solution was neutral, and drying was performed at 60°C until a constant weight was obtained to obtain the silicon carbide powder for hydrogen production.

[0060] The mixed solvent comprises deionized water and ethanol, and the volume ratio of the deionized water and the ethanol is 1:1.

[0061] Example 4

[0062] The difference between the embodiment and the embodiment 1 is that:

[0063] S1: tetraethyl orthosilicate 20 g, polyacrylonitrile fiber 18.2 g, graphene 1.8 g, urea 3.4 g, melamine 1.7 g, indium nitrate 1.5 g and boric acid 0.38 g were sequentially added into an ethanol aqueous solution 500 mL, F127 1.6 g and cetyltrimethylammonium bromide 0.4 g were added, the pH was adjusted to 3.5 by using 10% citric acid, the temperature was increased to 60℃, and the mixture was stirred at 300 rpm / min for 7 h to obtain a uniform sol, the sol was transferred to an autoclave, the temperature was increased to 170℃, and the hydrothermal reaction was performed for 22 h, the temperature was cooled to room temperature, centrifugal separation was performed, and drying was performed at 60℃ until the weight was constant to obtain a precursor;

[0064] The other steps are the same as in Example 1.

[0065] Example 5

[0066] The difference between this example and Example 4 is that:

[0067] The amount of boric acid is 0.3 g;

[0068] The other steps are the same as in Example 4.

[0069] Example 6

[0070] The difference between this example and Example 5 is that:

[0071] S3: the reduced product was immersed in 5% hydrofluoric acid, the solid-liquid ratio was 1 g:5 mL, and the immersion and washing were performed twice for 30 min each time, centrifugal separation was performed, deionized water was used for washing until neutral, then a hydrogen peroxide solution with a pH of 3.5 and a mass fraction of 30% was added, the solid-liquid ratio was 1 g:10 mL, the temperature was increased to 85℃, and the reflux reaction was performed for 5 h, centrifugal separation was performed, deionized water was used for washing until neutral, the product was immersed in a thiourea solution with a mass fraction of 8% and a pH of 3.0, the solid-liquid ratio was 1 g:5 mL, the temperature was increased to 75℃, and the reaction was performed for 150 min, centrifugal separation was performed, deionized water was used for washing until neutral, and drying was performed at 60℃ until the weight was constant to obtain the silicon carbide powder for hydrogen production.

[0072] The other steps are the same as in Example 5.

[0073] Example 7

[0074] The difference between this example and Example 6 is that:

[0075] S3: The reduction product is immersed in 5% volume fraction hydrofluoric acid, solid-liquid ratio is 1g:5mL, soaking and washing for 2 times, 30min each time, centrifugal separation, washing with deionized water until neutral, then adding 30% mass fraction hydrogen peroxide solution with pH 3.5, solid-liquid ratio is 1g:10mL, heating to 85℃, refluxing for 5h, centrifugal separation, washing with deionized water until neutral, immersing in 10% mass fraction thiourea solution with pH 4.0, solid-liquid ratio is 1g:5mL, heating to 85℃, reacting for 120min, centrifugal separation, washing with deionized water until neutral, drying at 60℃ until constant weight, obtaining silicon carbide powder for hydrogen production.

[0076] Other same as example 6.

[0077] Comparative example 1

[0078] The difference between this comparative example and example 1 is that:

[0079] S1: Tetraethyl orthosilicate 20g, polyacrylonitrile fiber 20g, urea 3.4g, melamine 1.7g and indium nitrate 1.5g are sequentially added into 500mL ethanol aqueous solution, F127 1.6g and cetyltrimethylammonium bromide 0.4g are added, pH is adjusted to 3.5 by using 10% mass fraction citric acid, heating to 60℃, stirring and mixing at 300rpm / min for 7h, obtaining uniform sol, the sol is transferred to an autoclave, heating to 170℃, hydrothermal reaction for 22h, cooling to room temperature, centrifugal separation, drying at 60℃ until constant weight, obtaining precursor;

[0080] Other same as example 1.

[0081] Comparative example 2

[0082] The difference between this comparative example and example 1 is that:

[0083] S1: Tetraethyl orthosilicate 20g, polyacrylonitrile fiber 18.2g, graphene 1.8g, urea 5.1g and indium nitrate 1.5g are sequentially added into 500mL ethanol aqueous solution, F127 1.6g and cetyltrimethylammonium bromide 0.4g are added, pH is adjusted to 3.5 by using 10% mass fraction citric acid, heating to 60℃, stirring and mixing at 300rpm / min for 7h, obtaining uniform sol, the sol is transferred to an autoclave, heating to 170℃, hydrothermal reaction for 22h, cooling to room temperature, centrifugal separation, drying at 60℃ until constant weight, obtaining precursor;

[0084] Other same as example 1.

[0085] Comparative example 3

[0086] The difference between this comparative example and example 1 is that:

[0087] S1: Tetraethyl orthosilicate 20 g, polyacrylonitrile fiber 18.2 g, graphene 1.8 g, urea 3.4 g, melamine 1.7 g and indium nitrate 1.5 g were sequentially added into an ethanol aqueous solution 500 mL, F127 2 g was added, the pH was adjusted to 3.5 using a 10% mass fraction of citric acid, the temperature was raised to 60°C, and the mixture was stirred at 300 rpm / min for 7 h to obtain a uniform sol, the sol was transferred to an autoclave, the temperature was raised to 170°C, and the hydrothermal reaction was performed for 22 h, the temperature was then cooled to room temperature, centrifugal separation was performed, and drying was performed at 60°C until a constant weight was obtained to obtain a precursor;

[0088] Other same as example 1.

[0089] Performance detection test

[0090] 1. Photocatalytic hydrogen production activity test

[0091] 50 mg of the silicon carbide powder for hydrogen production in examples 1-7 and comparative examples 1-3 was respectively dispersed in a reaction solution composed of 90 mL of deionized water and 10 mL of methanol, placed in a reactor, and bubbled with high-purity Ar gas for 30 min, a 500W xenon lamp (equipped with an AM 1.5G filter to simulate sunlight) was turned on, stirring and cooling water circulation were started, and the reaction temperature was maintained at 20°C±2°C for photocatalytic reaction, the concentration of H2 in the headspace was analyzed every 1 h, the total detection time was 5 h, and the average hydrogen production rate was calculated, and the specific data are shown in Table 1.

[0092] 2. Specific surface area and pore size analysis

[0093] 100 mg of the silicon carbide powder for hydrogen production in examples 1-7 and comparative examples 1-3 was respectively vacuum degassed at 120°C for 6 h, and N2 adsorption-desorption test was performed at liquid nitrogen temperature (-196°C) to calculate the specific surface area, and the specific data are shown in Table 1.

[0094] 3. Photocatalytic stability test

[0095] After the first photocatalytic reaction, the catalyst was not replaced, the gas products in the reaction system were emptied by vacuum or Ar, and then the light source was turned on for the next cycle test, and this process was repeated 5 times to calculate the activity retention rate.

[0096] Table 1 Performance test data of the silicon carbide powder for hydrogen production prepared in examples 1-7 and comparative examples 1-3

[0097]

[0098] According to the detection data in Table 1, it can be seen that:

[0099] From Examples 1-3, it can be seen that by adjusting the ratio of silicon source, carbon source, nitrogen source and indium salt and the process, the silicon carbide powder for hydrogen production prepared has high specific surface area and excellent photocatalytic hydrogen production performance, indicating that the material system has good controllability and stability.

[0100] From the comparison of Examples 1, 4-7, although the introduction of boric acid and thiourea makes the specific surface area of the catalyst decrease slightly, the photocatalytic hydrogen production performance is significantly improved. This shows that the performance enhancement is mainly due to the optimization of the intrinsic properties of the material by boron and sulfur element modification: boron doping helps to form an internal electric field, effectively promoting the separation and migration of photo-generated carriers; and sulfur treatment introduces high-activity surface sites, significantly improving the hydrogen evolution reaction kinetics. The synergistic effect of the two improves the intrinsic catalytic activity of the catalyst, making it exhibit excellent and stable hydrogen production performance under visible light irradiation.

[0101] From the comparison of Comparative Example 1 and Comparative Examples 1-3, it can be seen that whether a single carbon source or a single template agent is used, the specific surface area of the material is significantly reduced, and the hydrogen production rate also decreases; while using only a single nitrogen source, the specific surface area does not change significantly, but the hydrogen production rate is still lower than that of Example 1 with multiple nitrogen sources, indicating that the diversity of nitrogen sources has an important influence on improving the nitrogen doping efficiency and photocatalytic activity.

[0102] In combination with Figure 1 It can be seen that the diffraction peaks of the silicon carbide powder prepared in Example 3 are located at 2θ of 35.4°, 41.3°, 59.7° and 71.4°, respectively, corresponding to the (111), (200), (220) and (311) crystal planes of cubic SiC, and no impurity phase diffraction peaks appear, indicating that the main crystal phase of the sample is well-crystallized cubic silicon carbide. All the diffraction peaks show consistent slight negative shift, which is mainly due to the lattice expansion caused by N / In co-doping, in which In 3+ Interstitial doping is the main cause of lattice distortion, and this result confirms that N and In have been successfully introduced into the SiC lattice. In addition, no free carbon or indium oxide impurities are detected in the spectrum, indicating that the subsequent purification treatment is effective and the sample has high purity.

[0103] The specific embodiments are merely illustrative of the present application, and are not a limitation on the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the present specification, and as long as the modifications are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing silicon carbide powder for hydrogen production, characterized by, The method comprises the following steps: S1: adding a silicon source, a carbon source, a nitrogen source, and an indium salt into an ethanol aqueous solution, then adding a template agent, adjusting the pH to 3.0-4.0, heating to 50-70 DEG C, mixing for 5-8 hours, transferring to a hydrothermal kettle, heating to 160-180 DEG C, reacting for 18-24 hours, cooling, solid-liquid separation, drying, and obtaining a precursor; S2: under an inert atmosphere, transferring the precursor into a sintering device, heating to 500-600 DEG C, keeping the temperature for 2-4 hours, continuously heating to 800-1000 DEG C, keeping the temperature for 30-40 minutes, continuously heating to 1200-1300 DEG C, keeping the temperature for 60-80 minutes, cooling, and obtaining a reduction product; S3: immersing the reduction product in hydrofluoric acid, soaking and washing for 2-3 times at 20-30 DEG C, solid-liquid separation, immersing in a hydrogen peroxide solution, heating to 80-90 DEG C, reacting for 4-6 hours, solid-liquid separation, washing, and drying, and obtaining a silicon carbide powder for hydrogen production; The nitrogen source comprises urea and melamine; The carbon source comprises polyacrylonitrile fibers and graphene; The template agent comprises a block polyether and a quaternary ammonium salt.

2. The silicon carbide powder production method for hydrogen production according to claim 1, characterized by, The mass ratio of the silicon source, the carbon source, the nitrogen source, and the indium salt is 1:(0.8-1.2):(0.18-0.30):(0.05-0.12).

3. The method for producing silicon carbide powder for hydrogen production according to claim 1, wherein The mass ratio of the polyacrylonitrile fibers and the graphene is (8-12):

1.

4. The silicon carbide powder production method for hydrogen production according to claim 1, characterized by, The mass ratio of the urea and the melamine is (1-2.5):

1.

5. The silicon carbide powder production method for hydrogen production according to claim 1, characterized by, The mass ratio of the block polyether and the quaternary ammonium salt is (3-5):

1.

6. The silicon carbide powder production method for hydrogen production according to claim 1, characterized by, The volume fraction of the hydrofluoric acid is 4%-6%.

7. The method of claim 1, wherein the silicon carbide powder for hydrogen production is prepared by the method, further comprising: The mass fraction of the hydrogen peroxide solution is 25%-35%. ​ 8. The silicon carbide powder production method for hydrogen production according to claim 1, characterized by, In step S1, after the indium salt, a step of adding boric acid is further included, and the mass ratio of the indium salt to the boric acid is (4-5):1.

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