Preparation method of silicon carbide powder for hydrogen production

Abstract

The invention relates to the technical field of silicon carbide, and particularly 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 indium salt into an ethanol water 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, carrying out solid-liquid separation, and drying to obtain a precursor; s2, in an inert atmosphere, transferring the precursor into sintering equipment, and carrying out heating, heat preservation, continuous heating, heat preservation, continuous heating, heat preservation and cooling to obtain a reduction product; s3, immersing the reduction product in hydrofluoric acid, soaking and washing for 2-3 times at the temperature of 20-30 DEG C, carrying out solid-liquid separation, washing, immersing in a hydrogen peroxide solution, heating, reacting, carrying out solid-liquid separation, washing and drying to obtain silicon carbide powder for hydrogen production; the prepared silicon carbide powder for hydrogen production shows relatively 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: A silicon carbide powder preparation method for hydrogen production comprises the following steps: S1: A silicon source, a carbon source, a nitrogen source, an indium salt, and a template agent are added to an ethanol aqueous solution, and the pH is adjusted to 3.0-4.0; the mixture is heated to 50-70 DEG C and stirred for 5-8 hours; the mixture is transferred to a hydrothermal kettle and heated to 160-180 DEG C and reacted for 18-24 hours; the mixture is cooled, solid-liquid separation is performed, and drying is performed to obtain a precursor; S2: The precursor is transferred to a sintering device under an inert atmosphere, heated to 500-600 DEG C and kept for 2-4 hours, continuously heated to 800-1000 DEG C and kept for 30-40 minutes, continuously heated to 1200-1300 DEG C and kept for 60-80 minutes, and cooled to obtain a reduction product; S3: The reduction product is immersed in hydrofluoric acid at 20-30 DEG C, and soaked and washed for 2-3 times; solid-liquid separation is performed; the washed product is immersed in a hydrogen peroxide solution, heated to 80-90 DEG C, and reacted for 4-6 hours; solid-liquid separation is performed, the washed product is dried, and a silicon carbide powder for hydrogen production is obtained; The nitrogen source comprises urea and melamine.

[0008] In the technical scheme, a silicon source, a carbon source, a nitrogen source, an indium salt, and a template agent are pre-hydrothermally compounded to realize uniform mixing and preliminary self-assembly at a 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 a 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.

[0009] Then, sintering reduction is performed, and a two-step heating method is adopted: first, the temperature is kept 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; then, a carbothermal reduction reaction is performed at a higher temperature of 1200-1300 DEG C; in this process, nitrogen atoms are partially doped into the SiC crystal lattice after being reduced, and 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.

[0010] Preferably, 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).

[0011] Preferably, the carbon source includes polyacrylonitrile fiber and graphene.

[0012] Preferably, the mass ratio of the polyacrylonitrile fiber and graphene is (8~12):1.

[0013] In the technical solution, polyacrylonitrile fiber is used as the main carbon source. During high-temperature heat treatment, not only carbon atoms are provided to participate in the carbothermal reduction reaction, but also the cyano groups in the molecular chain of the polyacrylonitrile fiber decompose to generate a nitrogen-doped carbon skeleton in situ, creating favorable conditions for uniform doping of nitrogen. At the same time, the polyacrylonitrile fiber is easy to form an interwoven one-dimensional fibrous structure after carbonization, 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 a 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.

[0014] Preferably, the mass ratio of the urea and melamine is (1~2.5):1.

[0015] Preferably, the template agent includes block polyether and quaternary ammonium salt.

[0016] Preferably, the mass ratio of the block polyether and quaternary ammonium salt is (3~5):1.

[0017] 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 mesoporous 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 reactants and products, ensures the accessibility of active sites, and avoids performance degradation caused by excessively long or blocked pores.

[0018] Preferably, the amount of the template agent is 8% to 12% of the mass of the silicon source.

[0019] 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.

[0020] 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.

[0021] Preferably, the volume fraction of the hydrofluoric acid is 4% to 6%.

[0022] Preferably, the mass fraction of the hydrogen peroxide solution is 25% to 35%.

[0023] Preferably, before use, the pH of the hydrogen peroxide solution is adjusted to 3 to 4.

[0024] In the technical solution, the hydrogen peroxide is acidified after being adjusted to a pH of 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 a thick and inert SiO2 insulating layer generated by violent reaction, thereby optimizing the interface charge transport performance of the heterojunction.

[0025] 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.

[0026] In the technical solution, 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 combine to construct 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 the introduction of too many deep level defects or lattice distortions due to excessive doping, and prevents 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.

[0027] 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.

[0028] 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.

[0029] In summary, the present application has the following beneficial effects: 1. The present application uses an in-situ doping method, and utilizes the decomposition temperature difference between urea and melamine to achieve 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.

[0030] 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, constructs 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.

[0031] 3、In the application, microwave-assisted sintering and double templates are preferably adopted, microwave heating realizes low-temperature rapid synthesis of the material, and effectively inhibits grain coarsening; the double templates accurately control the mesostructure of the product, and successfully construct a composite structure with high specific surface area and hierarchical pores. The structure not only provides abundant active sites for photocatalytic reaction, but also creates excellent reactant mass transfer channels.

[0032] 4、The application further introduces boric acid to realize B / In / N multi-element co-doping. The incorporation of boron element and nitrogen element forms p-n type co-doping, which can form a micro internal built-in electric field in the SiC grain interior, 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, and essentially improves the core kinetics of the photocatalytic reaction. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The XRD pattern of the silicon carbide powder for hydrogen production prepared in Example 3 of the application. DETAILED DESCRIPTION

[0034] The application will be further described below in combination with examples.

[0035] The raw materials of the examples and comparative examples of the application are all ordinary commercial products unless otherwise specified.

[0036] The block polyether is an ethylene oxide-propylene oxide-ethylene oxide triblock copolymer, abbreviated as F127, and the average molecular weight is about 12600; the quaternary ammonium salt is cetyltrimethylammonium bromide.

[0037] Example 1 The silicon carbide powder preparation method for hydrogen production of the example includes the following steps: S1: 20 g of tetraethyl orthosilicate, 18.2 g of polyacrylonitrile fiber, 1.8 g of graphene, 3.4 g of urea, 1.7 g of melamine and 1.5 g of indium nitrate were sequentially added into 500 mL of ethanol aqueous solution, 1.6 g of F127 and 0.4 g of cetyltrimethylammonium bromide were added, the pH was adjusted to 3.5 by using 10% citric acid, the mixture was stirred at 300 rpm / min for 7 h at 60℃, a uniform sol was obtained, the sol was transferred to an autoclave, the temperature was raised to 170℃, and the hydrothermal reaction was carried out for 22 h, then the temperature was cooled to room temperature, centrifugal separation was carried out, and drying was carried out at 60℃ until the weight was constant, to obtain a precursor; S2: the precursor was placed in a microwave sintering furnace, argon was introduced (flow rate 300 mL / min), the temperature was raised to 550℃ at a rate of 5℃ / min, and then the temperature was kept for 3 h, then the temperature was raised to 900℃ at a rate of 5℃ / min, and then the temperature was kept for 35 min, then the microwave was turned on, the power was 400 W, then the temperature was raised to 1250℃ at a rate of 5℃ / min, and then the temperature was kept for 70 min, to obtain a reduced product; S3: immerse the reduction product in hydrofluoric acid with a volume fraction of 5%, a solid-liquid ratio of 1 g:5 mL, soak and wash for 2 times, each for 30 min, centrifugal separation, wash with deionized water until neutral, then add hydrogen peroxide solution with a pH of 3.5 and a mass fraction of 30%, a solid-liquid ratio of 1 g:10 mL, heat to 85℃, reflux for 5 h, centrifugal separation, wash with deionized water until neutral, and dry at 60℃ until constant weight to obtain the silicon carbide powder for hydrogen production.

[0038] The mixed solvent comprises deionized water and ethanol, and the volume ratio of the deionized water to the ethanol is 1:1.

[0039] Example 2 The method for preparing the silicon carbide powder for hydrogen production comprises the following steps: S1: sequentially add 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 into an ethanol aqueous solution 500 mL, add F127 1.2 g and cetyltrimethylammonium bromide 0.4 g, adjust the pH to 4 by using citric acid with a mass fraction of 10%, heat to 50℃, and stir and mix at 300 rpm / min for 8 h to obtain a uniform sol, transfer the sol to an autoclave, heat to 160℃, and perform hydrothermal reaction for 24 h, cool to room temperature, centrifugal separation, and dry at 60℃ until constant weight to obtain a precursor; S2: place the precursor in a microwave sintering furnace, introduce argon (flow rate 300 mL / min), heat to 500℃ at a rate of 5℃ / min, keep the temperature for 4 h, heat to 800℃ at a rate of 5℃ / min, keep the temperature for 40 min, turn on the microwave, continue to heat to 1200℃ at a rate of 5℃ / min, and keep the temperature for 80 min to obtain a reduction product; S3: immerse the reduction product in hydrofluoric acid with a volume fraction of 4%, a solid-liquid ratio of 1 g:5 mL, soak and wash for 3 times, each for 30 min, centrifugal separation, wash with deionized water until neutral, then add hydrogen peroxide solution with a pH of 4 and a mass fraction of 35%, a solid-liquid ratio of 1 g:10 mL, heat to 80℃, reflux for 6 h, centrifugal separation, wash with deionized water until neutral, and dry at 60℃ until constant weight to obtain the silicon carbide powder for hydrogen production.

[0040] The mixed solvent comprises deionized water and ethanol, and the volume ratio of the deionized water to the ethanol is 1:1.

[0041] Example 3 The method for preparing the silicon carbide powder for hydrogen production comprises the following steps: S1: tetraethyl orthosilicate 20 g, polyacrylonitrile fiber 22.2 g, graphene 1.8 g, urea 4.3 g, melamine 1.7 g, and indium nitrate 2.4 g were sequentially added into an aqueous ethanol solution 500 mL, F127 2.0 g and cetyltrimethylammonium bromide 0.4 g were added, the pH was adjusted to 3 using a 10% mass fraction citric acid, the temperature was raised to 70℃, 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 raised to 180℃, and hydrothermal reaction was performed for 18 h, the temperature was then cooled to room temperature, centrifugal separation was performed, and drying was performed at 60℃ until a constant weight was obtained to obtain a precursor; S2: the precursor was placed in a microwave sintering furnace, argon was introduced (flow rate 300 mL / min), the temperature was raised to 600℃ at a rate of 5℃ / min, and the temperature was maintained for 2 h, then the temperature was raised to 1000℃ at a rate of 5℃ / min, and the temperature was maintained for 30 min, the microwave was turned on, the power was 300 W, the temperature was continued to be raised to 1300℃ at a rate of 5℃ / min, and the temperature was maintained for 60 min to obtain a reduction product; S3: the reduction product was immersed in a 6% volume fraction hydrofluoric acid, the solid-liquid ratio was 1 g:5 mL, immersion and washing were performed twice, each for 30 min, centrifugal separation was performed, deionized water was used for washing until neutral, then a 25% mass fraction hydrogen peroxide solution was added, the solid-liquid ratio was 1 g:10 mL, the temperature was raised to 90℃, and reflux reaction was performed for 4 h, centrifugal separation was performed, deionized water was used for washing until neutral, and drying was performed at 60℃ until a constant weight was obtained to obtain a silicon carbide powder for hydrogen production.

[0042] The mixed solvent includes deionized water and ethanol, and the volume ratio of the deionized water to the ethanol is 1:1.

[0043] Example 4 The difference between this example and Example 1 is that: 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 aqueous ethanol solution 500 mL, F127 1.6 g and cetyltrimethylammonium bromide 0.4 g were added, the pH was adjusted to 3.5 using a 10% mass fraction citric acid, the temperature was raised 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 raised to 170℃, and 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℃ until a constant weight was obtained to obtain a precursor; The others are the same as in Example 1.

[0044] Example 5 The difference between this example and Example 4 is that: The amount of boric acid is 0.3 g; The others are the same as in Example 4.

[0045] Example 6 The difference between this example and Example 5 is that: S3: immerse the reduction product in hydrofluoric acid with a volume fraction of 5%, the solid-liquid ratio is 1g:5mL, soak and wash for 2 times, each time for 30min, centrifugal separation, wash with deionized water until neutral, then add hydrogen peroxide solution with a mass fraction of 30% and a pH of 3.5, the solid-liquid ratio is 1g:10mL, heat to 85℃, reflux reaction for 5h, centrifugal separation, wash with deionized water until neutral, immerse in thiourea solution with a mass fraction of 8% and a pH of 3.0, the solid-liquid ratio is 1g:5mL, heat to 75℃, react for 150min, centrifugal separation, wash with deionized water until neutral, dry at 60℃ to constant weight, to obtain silicon carbide powder for hydrogen production.

[0046] The rest is the same as Example 5.

[0047] Example 7 The difference between this example and Example 6 is that: S3: immerse the reduction product in hydrofluoric acid with a volume fraction of 5%, the solid-liquid ratio is 1g:5mL, soak and wash for 2 times, each time for 30min, centrifugal separation, wash with deionized water until neutral, then add hydrogen peroxide solution with a mass fraction of 30% and a pH of 3.5, the solid-liquid ratio is 1g:10mL, heat to 85℃, reflux reaction for 5h, centrifugal separation, wash with deionized water until neutral, immerse in thiourea solution with a mass fraction of 10% and a pH of 4.0, the solid-liquid ratio is 1g:5mL, heat to 85℃, react for 120min, centrifugal separation, wash with deionized water until neutral, dry at 60℃ to constant weight, to obtain silicon carbide powder for hydrogen production.

[0048] The rest is the same as Example 6.

[0049] Comparative Example 1 The difference between this example and Example 1 is that: S1: add tetraethyl orthosilicate 20g, polyacrylonitrile fiber 20g, urea 3.4g, melamine 1.7g and indium nitrate 1.5g into ethanol aqueous solution 500mL in turn, add F127 1.6g and cetyltrimethylammonium bromide 0.4g, adjust the pH to 3.5 with citric acid with a mass fraction of 10%, heat to 60℃, stir the mixture at 300rpm / min for 7h to obtain a uniform sol, transfer the sol to an autoclave, heat to 170℃, hydrothermal reaction for 22h, cool to room temperature, centrifugal separation, dry at 60℃ to constant weight, to obtain a precursor; The rest is the same as Example 1.

[0050] Comparative Example 2 The difference between this example and Example 1 is that: S1: tetraethyl orthosilicate 20 g, polyacrylonitrile fiber 18.2 g, graphene 1.8 g, urea 5.1 g, and indium nitrate 1.5 g were sequentially added to 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 using 10% citric acid by mass fraction, the temperature was raised 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 raised to 170℃, and 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℃ until a constant weight was obtained to obtain a precursor; The other is the same as in Example 1.

[0051] Comparative Example 3 The difference between this comparative example and Example 1 is that: S1: tetraethyl orthosilicate 20 g, polyacrylonitrile fiber 18.2 g, graphene 1.8 g, urea 5.1 g, and indium nitrate 1.5 g were sequentially added to 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 using 10% citric acid by mass fraction, the temperature was raised 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 raised to 170℃, and 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℃ until a constant weight was obtained to obtain a precursor; The other is the same as in Example 1.

[0052] Performance detection test 1. Photocatalytic hydrogen production activity test 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 500 W 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℃±2℃. The photocatalytic reaction was performed, and 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. The specific data are shown in Table 1.

[0053] 2. Specific surface area and pore size analysis 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℃ for 6 h, and N2 adsorption-desorption testing was performed at a liquid nitrogen temperature (-196℃). The specific surface area was calculated, and the specific data are shown in Table 1.

[0054] 3. Photocatalytic stability test After the first photocatalytic reaction is completed, without replacing the catalyst, vacuum or Ar is used to evacuate the gas products in the reaction system again, and then the light source is turned on for the next round of cycle testing. This process is repeated 5 times, and the activity retention rate is calculated.

[0055] Table 1 Performance test data of silicon carbide powder for hydrogen production prepared in Examples 1 to 7 and Comparative Examples 1 to 3

[0056] Combined with the test data in Table 1, we can see that: It can be seen from Examples 1 to 3 that by adjusting the ratio and process of the silicon source, carbon source, nitrogen source and indium salt, the silicon carbide powder for hydrogen production obtained has a high specific surface area and excellent photocatalytic hydrogen production performance, indicating that the material system has good controllability and stability.

[0057] Comparison of Examples 1, 4, and 7 reveals that while the introduction of boric acid and thiourea slightly decreased the specific surface area of ​​the catalysts, their photocatalytic hydrogen production performance was significantly improved. This suggests that the performance enhancement stems primarily from the optimization of the intrinsic properties of the material by boron and sulfur modification: boron doping contributes to the formation of a built-in electric field, effectively promoting the separation and migration of photogenerated carriers; while sulfur treatment introduces highly active surface sites, significantly improving the kinetics of the hydrogen evolution reaction. These two factors work synergistically to enhance the intrinsic catalytic activity of the catalysts, resulting in excellent and stable hydrogen production performance under visible light irradiation.

[0058] By comparing Example 1 with Comparative Examples 1 to 3, it can be seen that whether a single carbon source or a single template is used, the specific surface area of ​​the material is significantly reduced, and the hydrogen production rate also decreases accordingly; and when only a single nitrogen source is used, although the specific surface area does not change significantly, the hydrogen production rate is still lower than that of Example 1 of the multi-nitrogen source system, indicating that the diversity of nitrogen sources has an important influence on improving nitrogen doping efficiency and photocatalytic activity.

[0059] Combine 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 diffraction peaks appear, indicating that the main crystalline phase of the sample is well-crystallized cubic silicon carbide. All diffraction peaks show a consistent slight negative shift, which is mainly due to the lattice expansion caused by N / In co-doping, where In 3+ Interstitial doping is the primary cause of lattice distortion, and this result confirms the successful introduction of nitrogen and indium into the SiC lattice. Furthermore, no impurities such as free carbon or indium oxide were detected in the spectra, indicating that subsequent purification treatment was effective and the sample was of high purity.

[0060] The embodiments are only illustrative of the present application, and are not intended to limit the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but 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 in that: The steps include: S1: Add silicon source, carbon source, nitrogen source, and indium salt to ethanol aqueous solution, then add template, adjust pH to 3.0-4.0, heat to 50-70°C, mix for 5-8 hours, transfer to hydrothermal reactor, heat to 160-180°C, react for 18-24 hours, cool, separate solid and liquid, and dry to obtain precursor; S2: Under an inert atmosphere, the precursor is transferred into a sintering device, heated to 500-600°C, kept warm for 2-4 hours, then heated to 800-1000°C, kept warm for 30-40 minutes, then heated to 1200-1300°C, kept warm for 60-80 minutes, and cooled to obtain a reduced product; S3: Immerse the reduction product in hydrofluoric acid at 20-30°C, soak and wash 2-3 times, separate the solid and liquid, and then immerse in hydrogen peroxide solution, raise the temperature to 80-90°C, react for 4-6 hours, separate the solid and liquid, wash, and dry to obtain silicon carbide powder for hydrogen production; The nitrogen sources include urea and melamine.

2. The method for preparing silicon carbide powder for hydrogen production according to claim 1, characterized in that: 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).

3. The method for preparing silicon carbide powder for hydrogen production according to claim 1, characterized in that: The carbon source includes polyacrylonitrile fiber and graphene.

4. The method for preparing silicon carbide powder for hydrogen production according to claim 3, characterized in that: The mass ratio of the polyacrylonitrile fiber to the graphene is (8-12):

1.

5. The method for preparing silicon carbide powder for hydrogen production according to claim 1, characterized in that: The mass ratio of the urea to melamine is (1-2.5):

1.

6. The method for preparing silicon carbide powder for hydrogen production according to claim 1, characterized in that: The template comprises a segmented polyether and a quaternary ammonium salt.

7. The method for preparing silicon carbide powder for hydrogen production according to claim 6, characterized in that: The mass ratio of the block polyether to the quaternary ammonium salt is (3-5):

1.

8. The method for preparing silicon carbide powder for hydrogen production according to claim 1, characterized in that: The volume fraction of the hydrofluoric acid is 4% to 6%.

9. The method for preparing silicon carbide powder for hydrogen production according to claim 1, characterized in that: The mass fraction of the hydrogen peroxide solution is 25% to 35%.

10. The method for preparing silicon carbide powder for hydrogen production according to claim 1, characterized in that: 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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