Method for preparing silicon carbide nano material from solid waste

Abstract

The invention belongs to the technical field of nano material preparation, and particularly relates to a method for preparing a silicon carbide nano material by using solid waste. According to the preparation method, the coal gangue is taken as a silicon source, the high-carbon solid waste is taken as a carbon source, specific step-by-step extraction and utilization are performed according to composition characteristics of different solid wastes, high-purity raw materials are not needed, the silicon carbide nano material is prepared at low cost, and the silicon carbide nano material has higher forbidden bandwidth, excellent specific capacity and higher resistivity; wider application prospects are shown in the fields of third-generation semiconductors, national defense and military industry, 5G communication, new energy automobiles, smart power grids, high-temperature devices and the like. According to the method, complementary resource high-value utilization of solid wastes such as the coal gangue and the high-carbon solid wastes is realized, the preparation cost of silicon carbide is greatly reduced, the environmental problem and the safety problem caused by the solid wastes are solved, and meanwhile, the high-performance silicon carbide nano material with high purity and small size is successfully prepared; wide application prospects are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterial preparation, and particularly relates to a method for preparing silicon carbide nanomaterials by using solid waste. Background Art

[0002] Silicon carbide has good chemical stability, high thermal conductivity, strong oxidation resistance, and its hardness is second only to diamond and cubic boron nitride. It is widely used in fields such as high-grade refractory materials, abrasives, and fine ceramics. In addition, due to its wider bandgap width, higher breakdown electric field, thermal conductivity, and electron saturation rate, silicon carbide is suitable for preparing high-temperature, high-frequency, radiation-resistant, and high-power devices, and is also known as the third-generation semiconductor material, which is one of the most popular materials in the new material field currently.

[0003] The traditional synthesis of industrial silicon carbide uses high-purity quartz sand and petroleum coke as raw materials and is smelted in a high-temperature resistance furnace by the Acheson method. This method has high purity requirements for quartz sand (≥99%) and petroleum coke (≥98%), resulting in high preparation costs, poor performance, and limited application scenarios for silicon carbide. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing silicon carbide nanomaterials by using solid waste. The preparation method provided by the present invention does not require high-purity raw materials, has low preparation costs, and better performance.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing silicon carbide nanomaterials by using solid waste, comprising the following steps:

[0007] (1) Activating and acid-leaching coal gangue in sequence to obtain coal gangue silicon slag;

[0008] (2) Mixing the coal gangue silicon slag and high-carbon solid waste for carbothermal reduction reaction, followed by roasting and pickling in sequence to obtain the silicon carbide nanomaterials; the carbon content of the high-carbon solid waste is 70-80 wt%; the purity of the coal gangue is above 95%; the bandgap width of the silicon carbide nanomaterials is above 2.45 ev, the specific capacity is above 270 mAh / g, and the resistivity is above 1190 Ω·cm.

[0009] Preferably, the carbothermal reduction reaction is carried out in a protective atmosphere; the carbothermal reduction reaction includes a heating reaction stage and a heat preservation reaction stage; the heating rate of the heating reaction stage is 5-10 °C / min; the temperature of the heat preservation reaction stage is 1300-1600 °C, and the time of the heat preservation reaction stage is 1-5 h.

[0010] Preferably, the temperature of the roasting is 500-1000 °C, and the heat preservation time is 1-4 h.

[0011] Preferably, the temperature of the activation is 500-1000 °C, and the heat preservation time of the activation is 60-240 min.

[0012] Preferably, before the activation, heating-up is further included; the heating-up rate of the heating-up is 5-10 °C / min.

[0013] Preferably, the temperature of the acid solution for the acid leaching is 80-150 °C, and the heat preservation time of the acid leaching is 1-24 h; the acid leaching is carried out under stirring conditions; the mass ratio of the acid solution to the coal gangue is (1-10) mL:1 g.

[0014] Preferably, the high-carbon solid waste includes one or more of kerosene co-refining residue and pyrolysis-carbonized waste tires.

[0015] Preferably, the preparation method of the pyrolysis-carbonized waste tires is: pyrolysis-carbonizing the waste tires at 500-700 °C.

[0016] Preferably, the molar ratio of carbon in the high-carbon solid waste to silicon in the coal gangue silicon slag is 2-4:1.

[0017] Preferably, the mixing of the coal gangue silicon slag and the high-carbon solid waste is ball milling mixing; the rotation speed of the ball milling mixing is 60%-80%, and the ball milling time is 1-5 min.

[0018] The present invention provides a method for preparing silicon carbide nanomaterials by using solid waste. The present invention uses coal gangue as a silicon source and high-carbon solid waste (carbon content above 70 wt%) as a carbon source, and extracts and utilizes them step by step in a targeted manner according to the composition characteristics of different solid wastes. Without high-purity raw materials, silicon carbide nanomaterials can be prepared at low cost, which have a higher band gap, excellent specific capacity and greater resistivity, and show a broader application prospect in multiple fields such as third-generation semiconductors, national defense and military industries, 5G communications, new energy vehicles, smart grids and high-temperature devices.

[0019] The present invention further removes impurities such as SiO2 remaining in the silicon carbide through pickling, and finally obtains high-purity silicon carbide nanomaterials. The present invention prepares silicon carbide nanomaterials by controlling the nucleation and growth of silicon carbide. In the reaction Si-O-C system, it generates nano-silicon carbide nuclei through the heterogeneous gas-solid reaction of SiO vapor and C, thereby promoting the growth of nano-block / sheet silicon carbide, and generates nano-silicon carbide nuclei through the homogeneous gas-gas reaction of SiO and CO to promote the growth of nano-wire silicon carbide.

[0020] The present invention not only realizes the complementary high-value utilization of solid wastes such as coal gangue and high-carbon solid wastes, greatly reduces the preparation cost of silicon carbide, comprehensively reduces the cost by 50% - 70%, and solves the environmental problems and safety problems caused by solid wastes. At the same time, high-purity (>98.9%) and small-scale (<100nm) silicon carbide nanomaterials are successfully prepared, which have broad application prospects. Compared with the silicon carbide materials prepared by traditional industry, the silicon carbide nanomaterials prepared by the present invention have a thinner thickness and a unique nanofibrous shape, and the thickness is not more than 100nm. This structure not only endows the material with a higher specific surface area, but also makes it show excellent properties in terms of optical properties, electron transport properties and energy storage properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0022] Figure 1 It is the cross-linked macromolecular lamellar stacking structure (b) of the hard carbon nanosphere porous carbon material (a) obtained by carbonizing waste tires and kerosene co-refining residue;

[0023] Figure 2 It is the XRD diffraction pattern of the silicon carbide nanomaterials prepared from coal gangue and high-carbon solid wastes;

[0024] Figure 3 It is the silicon carbide nanowires (a - d) prepared with waste tires as the carbon source and the silicon carbide nanosheets (e - h) prepared with kerosene co-refining residue as the carbon source;

[0025] Figure 4 It is the XRD (left) and FT-IR (right) diffraction patterns of the silicon carbide nanomaterials prepared from coal gangue and kerosene co-refining residue;

[0026] Figure 5 It is the SEM (left) and TEM (right) patterns of the silicon carbide nanomaterials prepared from coal gangue and kerosene co-refining residue;

[0027] Figure 6 It is the XRD (left) and FT-IR (right) diffraction patterns of the silicon carbide nanomaterials prepared from coal gangue and waste tires;

[0028] Figure 7 It is the SEM (left) and TEM (right) patterns of the silicon carbide nanomaterials prepared from coal gangue and kerosene co-refining residue;

[0029] Figure 8XRD (left) and FT-IR (right) diffraction patterns of the silicon carbide nanomaterials prepared from coal gangue and waste tires;

[0030] Figure 9 SEM (left) and TEM (right) images of the silicon carbide nanomaterials prepared from coal gangue and waste tires;

[0031] Figure 10 XRD (left) and FT-IR (right) diffraction patterns of the silicon carbide nanomaterials prepared from coal gangue and waste tires;

[0032] Figure 11 SEM (left) and TEM (right) images of the silicon carbide nanomaterials prepared from coal gangue and waste tires;

[0033] Figure 12 XRD (left) and FT-IR (right) diffraction patterns of the silicon carbide materials prepared from petroleum coke and quartz sand;

[0034] Figure 13 SEM images of the silicon carbide materials prepared from petroleum coke and quartz sand;

[0035] Figure 14 UV-Vis diffuse reflectance spectra (left) and band gap diagrams (right) of the silicon carbide nanomaterials prepared from the kerosene co-refining residue and coal gangue in Example 1;

[0036] Figure 15 UV-Vis diffuse reflectance spectra (left) and band gap diagrams (right) of the silicon carbide nanomaterials prepared from waste tires and coal gangue in Example 3;

[0037] Figure 16 UV-Vis diffuse reflectance spectra (left) and band gap diagrams (right) of commercial silicon carbide in Comparative Example 1. Detailed implementation manners

[0038] The present invention provides a method for preparing silicon carbide nanomaterials from solid waste, comprising the following steps:

[0039] (1) Activating and acid-leaching coal gangue in sequence to obtain coal gangue silicon residue;

[0040] (2) Mixing the coal gangue silicon residue and high-carbon solid waste for carbothermal reduction reaction, followed by roasting and pickling in sequence to obtain the silicon carbide nanomaterials; the carbon content of the high-carbon solid waste is 70-80 wt%; the purity of the coal gangue is above 95%; the band gap of the silicon carbide nanomaterials is above 2.45 eV, the specific capacity is above 270 mAh / g, and the resistivity is above 1190 Ω·cm.

[0041] In the present invention, coal gangue is activated and acid-leached in sequence to obtain coal gangue silica residue. In the present invention, before use, the coal gangue can be crushed, ball-milled and screened in sequence.

[0042] In the present invention, the particle size of the coal gangue can be no more than 0.2 mm, specifically it can be 0.2 mm, 0.17 mm, 0.15 mm, 0.12 mm, 0.1 mm, 0.07 mm, 0.05 mm or 0.01 mm.

[0043] In the present invention, the activation temperature can be 500 - 1000 °C, specifically it can be 600 °C or 800 °C, and the activation heat preservation time can be 60 - 240 min, specifically it can be 120 min or 180 min.

[0044] In the present invention, before activation, heating-up may further be included; the heating-up rate can be 5 - 10 °C / min, specifically it can be 7 °C / min or 9 °C / min.

[0045] In the present invention, the acid solution temperature for acid leaching can be 80 - 150 °C, specifically it can be 120 °C, and the acid leaching heat preservation time can be 1 - 24 h, specifically it can be 6 h, 12 h or 18 h. In the present invention, through acid leaching, metal impurities such as aluminum and iron are leached out.

[0046] In the present invention, the acid used for acid leaching can be inorganic acid; the inorganic acid can include one or both of HCl and HNO3.

[0047] In the present invention, the acid leaching can be carried out under stirring conditions; the rotation speed of the stirring can be 60% - 80% (the proportion of the rated rotation speed, the rated rotation speed is 600 r / min), specifically it can be 65% or 80%.

[0048] In the present invention, the mass ratio of the acid solution to the coal gangue can be (1 - 10) mL:1 g, specifically it can be 3 mL:1 g, 5 mL:1 g, 7 mL:1 g or 9 mL:1 g.

[0049] In the present invention, after acid leaching, it may further include successively carrying out solid-liquid separation, washing and drying on the obtained acid leaching system.

[0050] In the present invention, the solid-liquid separation can be centrifugation; the centrifugation rate can be 3500 - 8500 r / min, specifically it can be 4000 r / min, 5000 r / min, 6000 r / min, 7000 r / min or 8000 r / min, and the centrifugation time can be 1 - 10 min, specifically it can be 3 min, 5 min, 7 min or 9 min.

[0051] In the present invention, the washing reagent may include one or more of hydrochloric acid, nitric acid, and hydrofluoric acid; the number of washing times may be more than 3 times, specifically 3 times, 5 times, or 7 times, until the washing liquid is neutral.

[0052] In the present invention, the drying temperature may be 70-100 °C, specifically 85 °C or 90 °C, and the heat preservation time may be 1-24 h, specifically 5 h, 12 h, or 18 h.

[0053] Through the above treatment, the present invention obtains coal gangue silica residue, in which the content of neutral silicon dioxide > 95%, and the specific components are shown in Table 1.

[0054] Table 1 Chemical composition of coal gangue silica residue

[0055]

[0056] After obtaining the coal gangue silica residue, the present invention mixes the coal gangue silica residue and high-carbon solid waste (denoted as the first mixing), conducts a carbothermal reduction reaction, and then performs roasting and pickling in sequence to obtain the silicon carbide nanomaterial. In the present invention, the high-carbon solid waste may include one or more of kerosene co-refining residue and pyrolyzed carbonized waste tires. The specific components of the kerosene co-refining residue and waste tires used in the examples of the present invention are shown in Table 2.

[0057] Table 2 Proximate analysis and ultimate analysis of high-carbon solid waste

[0058]

[0059] The preparation method provided by the present invention can controllably synthesize silicon carbide nanomaterials with different morphologies. The present invention utilizes the differences in the residual carbon morphologies in different high-carbon solid wastes to controllably synthesize silicon carbide nanomaterials with different morphologies (nanowires, nanosheets / blocks). There are significant differences in the residual carbon morphologies in high-carbon solid wastes. The carbon in the kerosene co-refining residue is a cross-linked macromolecular lamellar stacking structure composed of aromatic carbon, and the carbon in the waste tire after carbonization treatment is a hard carbon nanosphere porous carbon material. Compared with the kerosene co-refining residue, the waste tire residual carbon has a more abundant hierarchical micro / mesoporous structure and enriched active sites (specifically as Figure 1 shown). Therefore, when the kerosene co-refining residue is used as the carbon source, in the Si-C-O system, the solid-phase high-temperature carbothermal reduction reaction between silicon dioxide and lamellar carbon is the main reaction, forming silicon carbide nanosheets. When the waste tire is used as the carbon source, in the Si-C-O system, silicon dioxide first reacts with the nanosphere porous carbon to generate SiO and CO, and SiO2 and SiO further react with CO to undergo gas-solid / gas-gas chemical vapor deposition to form silicon carbide nanowires (specifically as Figure 2 and Figure 3 shown).

[0060] Due to their unique structures and properties, nanowire-shaped silicon carbide and nanoplate / bulk silicon carbide exhibit significant advantages in multiple fields: Nanowire-shaped silicon carbide has a high specific surface area. Its wire structure provides a larger active surface, enhancing the surface reactivity of the material and making it perform excellently in fields such as catalyst carriers, adsorption materials, and sensors. At the same time, the continuous wire structure of nanowire-shaped silicon carbide forms an efficient conductive channel, significantly reducing the resistivity and endowing it with excellent electrical conductivity in electronic devices and electrode materials. In addition, the wire structure also gives the material high mechanical strength and flexibility, enabling it to have broad application potential in composite materials and flexible devices. In the field of energy storage, the high specific capacity of nanowire-shaped silicon carbide makes it an ideal electrode material for lithium-ion batteries and supercapacitors.

[0061] In the present invention, the preparation method of the pyrolytic carbonized waste tire can be: pyrolytic carbonizing the waste tire at 500 - 700 °C; the temperature of the pyrolytic carbonization can specifically be 550 °C, 600 °C, or 650 °C.

[0062] In the present invention, before using the high-carbon solid waste, it may further include successively crushing, ball-milling, and screening the high-carbon solid waste.

[0063] In the present invention, the particle size of the high-carbon solid waste can be no more than 0.2 mm, specifically 0.2 mm, 0.17 mm, 0.15 mm, 0.12 mm, 0.1 mm, 0.07 mm, 0.05 mm, or 0.01 mm.

[0064] In the present invention, the molar ratio of carbon in the high-carbon solid waste to silicon in coal gangue silicon slag can be 2 - 4:1, specifically 2:1, 2.4:1, 2.7:1, 3:1, 3.2:1, 3.5:1, 3.7:1, or 4:1. Through the raw materials with the above molar ratio, the present invention can improve the reaction efficiency and product purity; control the product composition, morphology, and size; reduce energy consumption and costs, improve the material properties, and simplify the subsequent treatment.

[0065] In the present invention, the first mixing can be ball-milling mixing; the rotation speed of the ball-milling mixing can be 60% - 80%, specifically 65% or 75%, and the ball-milling time can be 1 - 5 min, specifically 3 min; the equipment for the ball-milling mixing can be a ball mill. Through ball-milling, the present invention can mix the reaction raw materials more fully.

[0066] In the present invention, the carbothermal reduction reaction can be carried out in a protective atmosphere; the protective atmosphere can be an inert gas or nitrogen; the inert gas can be argon; the equipment for the carbothermal reduction reaction can be a high-temperature tube furnace; the carbothermal reduction reaction can include a heating reaction stage and a heat preservation reaction stage. Through the carbothermal reduction reaction, silicon carbide is prepared in the present invention.

[0067] In the present invention, the heating rate in the heating reaction stage can be 5 to 10 °C / min, specifically it can be 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min or 10 °C / min.

[0068] In the present invention, the temperature in the heat preservation reaction stage can be 1300 to 1600 °C, specifically it can be 1300 °C, 1350 °C, 1400 °C, 1450 °C, 1500 °C, 1550 °C or 1600 °C, and the time of the heat preservation reaction stage can be 1 to 5 h, specifically it can be 1 h, 2 h, 3 h, 4 h or 5 h.

[0069] In the present invention, the temperature of the roasting can be 500 to 1000 °C, specifically it can be 700 °C or 800 °C, and the heat preservation time can be 1 to 4 h, specifically it can be 2 h or 3 h. In the present invention, unreacted residual carbon is removed by roasting.

[0070] In the present invention, the mass ratio of the acid used for pickling to the roasting product can be 5 to 10:1, specifically it can be 7:1; the acid used for pickling can be a HCl-HF mixed acid; the temperature of the pickling can be 30 °C, and the acid leaching time can be 12 h.

[0071] In the present invention, after pickling, it may further include washing and drying the obtained pickling product in sequence.

[0072] In the present invention, the reagent used for washing can include one or several of hydrochloric acid, nitric acid and hydrofluoric acid; the number of washing times can be more than 3 times, specifically it can be 3 times, 5 times or 7 times until the washing liquid is neutral.

[0073] In the present invention, the temperature of the drying can be 70 to 100 °C, specifically it can be 85 °C or 95 °C, and the heat preservation time can be 1 to 24 h, specifically it can be 12 h or 16 h.

[0074] Compared with traditional industrial silicon carbide, the silicon carbide nanomaterials obtained by the preparation method provided by the present invention have many advantages. For example, they have a higher specific surface area, which improves the reaction activity and adsorption capacity; enhanced electrical properties, which increase the resistivity and are suitable for high-frequency and high-power devices; environmental protection and low cost, using coal gangue, waste tires, and co-refining residues of kerosene as raw materials, reducing production costs and realizing the resource utilization of waste; the nanoscale structure makes the material superior to traditional silicon carbide in electrical, optical and other properties and is suitable for a wider range of applications. Moreover, the silicon carbide nanomaterials with different morphologies in the present invention have significant differences in band gap, specific capacity, and resistivity, and exhibit different excellent properties in different application scenarios. Nanoscale flake and nanoscale wire silicon carbide materials show some unique performance advantages due to their special microstructure and nanoscale size effect, and have greater application potential in fields such as energy storage, field emission, and electromagnetic wave absorption devices. ① Band gap advantage and application scenarios: The silicon carbide nanomaterials prepared by the present invention have a higher band gap, which enables them to have better stability and reliability in extreme environments such as high temperature and high pressure. The increase in the band gap means that the material can maintain a lower leakage current under high temperature conditions, thereby reducing energy loss and improving the efficiency and lifespan of the device. In the fields of aerospace and national defense, this high-temperature stability is crucial for the reliable operation of equipment such as satellites and missiles in extreme environments. In addition, its application in 5G communication base stations can improve the efficiency and stability of key components such as power amplifiers, reduce signal distortion, and enhance communication quality. ② Specific capacity advantage and application scenarios: The excellent specific capacity characteristics make the silicon carbide nanomaterials prepared by the present invention have significant advantages in the field of energy storage. The increase in specific capacity means that more electrical energy can be stored under the same volume or weight, which is of great significance for application scenarios with high requirements for energy storage density such as new energy vehicles and smart grids. In new energy vehicles, the battery using this silicon carbide material can achieve a longer cruising range and a faster charging speed, while also improving the cycle life of the battery and reducing the usage cost. In a smart grid, it can be used in energy storage systems to effectively balance the grid load and improve the stability and reliability of the grid. ③ Resistivity advantage and application scenarios: A larger resistivity helps to reduce the leakage current during the operation of the device, improving the insulation performance and stability of the device. In the field of power electronics, such as high-voltage direct current transmission equipment and industrial frequency converters, the silicon carbide nanomaterials prepared by the present invention can reduce energy loss, improve conversion efficiency, and at the same time reduce the requirements for the cooling system, realizing the miniaturization and lightweight of the equipment. In the field of microelectronics, its high resistivity characteristics are conducive to manufacturing high-performance insulated gate bipolar transistor (IGBT) and other devices, improving the operating speed and stability of electronic devices, and being suitable for the power management and signal processing parts of electronic products such as computers and smartphones.

[0075] To further illustrate the present invention, the solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0076] Example 1 uses the co - refining residue of kerosene as the carbon source

[0077] (1) The coal gangue and the co - refining residue of kerosene are crushed to less than 0.2 mm. The coal gangue powder is evenly spread horizontally in a corundum crucible, placed in a muffle furnace and activated at a high temperature of 800 °C for 2 h, and the heating rate is 5 °C / min. The activated coal gangue powder is mixed with 20% hydrochloric acid according to a solid - liquid ratio of 1:5 and placed in an oil - bath magnetic stirrer. After acid - leaching at 120 °C for 24 h, it is washed repeatedly until the silicon slag is neutral and then dried to obtain coal gangue silicon slag with a silicon oxide content > 95%.

[0078] (2) According to a molar ratio of C:Si of 3:1, the coal gangue silicon slag and the co - refining residue of kerosene are mixed and ball - milled for 5 min, and then placed in a high - temperature tubular resistance furnace. It is heated to 1600 °C in a protective gas (N2) atmosphere, held for 4 h, and the heating rate is 10 °C / min. After the furnace temperature drops to room temperature, it is taken out, then placed in a muffle furnace and held at 700 °C for 3 h, and the heating rate is 5 °C / min. Then it is taken out and cooled to room temperature. It is treated with a 20% HCl - HF solution according to a solid - liquid ratio of 1:10 at 30 °C for 12 h, and then washed repeatedly until the silicon carbide is neutral and then dried to obtain silicon carbide nanomaterials with a purity of 98.92%. The characterization results are as Figure 6 and Figure 7 shown.

[0079] According to Figure 6 and Figure 7 it can be seen that SiC and SiO2 phases are confirmed to exist in the samples from the XRD and FTIR spectra. From the scanning electron microscope SEM images, the silicon carbide nanomaterials prepared from coal gangue show obvious flaky morphological characteristics. These flaky structures stack and interweave with each other, forming an irregular porous structure with different sizes and a large number of gaps and holes, endowing the material with a large specific surface area. Looking at the transmission electron microscope TEM images, the details of the nanoscale flaky structures can be observed more clearly. Although the edges of these flaky particles are not regular, the flaky morphological characteristics are significant. Some flaky particles agglomerate and connect with each other, forming a complex agglomerate structure, further confirming the flaky morphological characteristics of the silicon carbide nanomaterials of the present invention.

[0080] Example 2 changes the silicon - carbon ratio, with carbon in excess

[0081] (1)Crush the coal gangue and the residue of co - refining with kerosene to less than 0.2 mm. Take the coal gangue powder and spread it evenly in a corundum crucible, place it in a muffle furnace and activate it at a high temperature of 800 °C for 2 h, with a heating rate of 5 °C / min. Mix the activated coal gangue powder with 20% hydrochloric acid according to a solid - liquid ratio of 1:5 and place it in an oil - bath magnetic stirrer. After acid - leaching at 120 °C for 24 h, wash it repeatedly until the silicon slag is neutral and then dry it to obtain coal gangue silicon slag with a silicon dioxide content > 95%.

[0082] (2)According to a molar ratio of C:Si of 4:1, mix the coal gangue silicon slag and the residue of co - refining with kerosene and ball - mill for 5 min, then place it in a high - temperature tubular resistance furnace. Heat it to 1600 °C in a protective gas (N2) atmosphere, keep it warm for 4 h, with a heating rate of 10 °C / min. After the furnace temperature drops to room temperature, take it out, then place it in a muffle furnace and keep it warm at 700 °C for 3 h, with a heating rate of 5 °C / min. Then take it out and cool it to room temperature. Treat it with a 20% HCl - HF solution according to a solid - liquid ratio of 1:10 at 30 °C for 12 h, and then wash it repeatedly until the silicon carbide is neutral and then dry it to obtain silicon carbide nanomaterials with a purity of 99.18%. The characterization results are as Figure 4 and Figure 5 shown.

[0083] According to Figure 4 and Figure 5 it can be seen that Figure 4 and Figure 5 show the characterization results of the synthesized silicon carbide nanomaterials after carbon excess. Figure 4 The left figure is the XRD pattern. The characteristic peaks indicate the presence of SiC in the material, proving the existence of the silicon carbide phase in the product; in the FT - IR spectrum, the absorption peak of the Si - C bond appears at a specific wavenumber, further confirming the existence of the Si - C bond. Figure 5 The SEM image on the left shows that the material presents irregular sheet - like and block - like structures. These structures are stacked on each other, and there are some particles attached to the surface. The shape and distribution of the structures show a certain degree of complexity and disorder; the TEM image on the right observes from the nanoscale that the material is composed of irregular sheet - like or block - like particles. The particles agglomerate with each other to form larger aggregates, and the boundaries of the particles are relatively blurred. By comparing with Example 1, it is found that carbon excess changes the morphological and structural characteristics of the material, including the pore structure, particle morphology, and agglomeration mode, etc.

[0084] Example 3 uses waste tires as the carbon source

[0085] (1)Crush the coal gangue and waste tires to less than 0.2 mm. Take the coal gangue powder and evenly spread it horizontally in a corundum crucible, place it in a muffle furnace and activate it at a high temperature of 800 °C for 2 h, with a heating rate of 5 °C / min. Mix the activated coal gangue powder with 20% hydrochloric acid according to a solid-liquid ratio of 1:5 and place it in an oil bath magnetic stirrer. After acid leaching at 120 °C for 24 h, wash it repeatedly until the silicon slag is neutral and then dry it to obtain coal gangue silicon slag with a silicon oxide content > 95%.

[0086] (2) Place the crushed waste tires in a high-temperature tubular resistance furnace, heat them to 700 °C in a protective gas (N2) atmosphere for pyrolysis for 10 min, with a heating rate of 5 °C / min, and then cool them to room temperature to obtain carbonized waste tires with a fixed carbon content of 78.84 wt%.

[0087] (3) According to a C:Si molar ratio of 3.5:1, mix the coal gangue silicon slag and the carbonized waste tires and ball mill them for 5 min, then place them in a high-temperature tubular resistance furnace, heat them to 1600 °C in a protective gas (N2) atmosphere, hold for 4 h, with a heating rate of 10 °C / min. After the furnace temperature drops to room temperature, take it out, then place it in a muffle furnace and hold at 700 °C for 3 h, with a heating rate of 5 °C / min. Then take it out and cool it to room temperature. Treat it with a 20% HCl-HF solution according to a solid-liquid ratio of 1:10 at 30 °C for 12 h, and then wash it repeatedly until the silicon carbide is neutral and then dry it to obtain silicon carbide nanomaterials with a purity of 99.31%. The characterization results are as Figure 8 and Figure 9 shown.

[0088] According to Figure 8 and Figure 9 it can be seen that Figure 8 in the XRD pattern of, the characteristic peaks clearly indicate the presence of SiC in the material, and at the same time confirm the presence of the silicon carbide phase in the product; in the FT-IR spectrum of the right figure, an obvious absorption peak of the Si-C bond appears at a specific wave number, further confirming the presence of the Si-C bond. Figure 9 The SEM image of shows an obvious fibrous structure. These fibers are intertwined with each other, with different thicknesses in morphology, and there are some particulate substances attached to the surface; the TEM image of the right figure clearly shows the microscopic structure of the fibers at the nanoscale. The fibers have a relatively regular morphology and clear edges, indicating that the material has the characteristics of a fibrous nanostructure. Combining these characterization results fully verifies the successful preparation of the silicon carbide nanofiber material synthesized from coal gangue and waste tires.

[0089] Example 4 Change the reaction time

[0090] (1) Crush the coal gangue and waste tires to less than 0.2 mm. Take the coal gangue powder and spread it evenly in a corundum crucible, place it in a muffle furnace and activate it at 800℃ for 2 hours, with a heating rate of 5℃ / min. Mix the activated coal gangue powder with 20% hydrochloric acid at a solid-liquid ratio of 1:5 and place it in an oil bath magnetic stirrer. After acid leaching at 120℃ for 24 hours, wash it repeatedly until the silicon slag is neutral and then dry it to obtain coal gangue silicon slag with a silicon oxide content of >95%.

[0091] (2) The crushed waste tires were placed in a high-temperature tubular resistance furnace, heated to 700°C for pyrolysis for 10 min in a protective gas (N2) atmosphere at a heating rate of 5°C / min, and then cooled to room temperature to obtain carbonized waste tires with a fixed carbon content of 78.84wt%.

[0092] (3) According to the C:Si molar ratio of 3.5:1, the gangue silicon slag and the carbonized waste tire were mixed and ball-milled for 5 minutes, and then placed in a high-temperature tubular resistance furnace, heated to 1600°C in a protective gas (N2) atmosphere, and kept warm for 3 hours at a heating rate of 10°C / min. After the furnace temperature dropped to room temperature, it was taken out and placed in a muffle furnace and kept warm at 700°C for 3 hours at a heating rate of 5°C / min. After that, it was taken out and cooled to room temperature, and mixed with a 20% HCl-HF solution at a solid-liquid ratio of 1:10 at 30°C for 12 hours, and then repeatedly washed until the silicon carbide was neutral and then dried to obtain a silicon carbide nanomaterial with a purity of >99.12%. Its characterization results are as follows: Figure 10 and Figure 11 shown.

[0093] according to Figure 10 and Figure 11 It can be seen that from the position and intensity of the peaks in the XRD and FT-IR spectra, similar to the results of 4h insulation, the characteristic diffraction peaks of SiC can still be clearly observed, which shows that the silicon carbide phase is still successfully synthesized under the condition of 3h insulation. From the SEM image, it can be observed that the material presents a fibrous structure, accompanied by some granular or blocky substances. Compared with the SEM and TEM images of 4h insulation, the morphology and distribution of the fibers have changed, such as the thickness and length uniformity of the fibers, and the degree of interweaving between the fibers may also be different. These changes are related to the short insulation time and the affected growth and agglomeration process of the material. On the whole, the silicon carbide materials prepared by insulation for 3h and 4h are basically the same in phase composition, and silicon carbide has been successfully synthesized, but there are certain differences in the microstructure, indicating that the insulation time will affect the micromorphology and internal structure of the silicon carbide material.

[0094] Comparative Example 1

[0095] This comparative example is a commercially available silicon carbide product (with quartz sand and petroleum coke as raw materials), and its XRD spectrum and FTIR diffraction spectrum are as follows: Figure 12 As shown, the appearance is Figure 13 shown.

[0096] according to Figure 12 and Figure 13 It can be seen that the XRD and FT-IR spectra show that the silicon carbide product does contain silicon carbide crystal structure, which is basically the same as the spectrum of silicon carbide prepared by the present invention. From the SEM image, it can be found that the commercial grade silicon carbide presents irregular flake or block morphology, and these flake or block particles are of different sizes and piled together. In contrast, the silicon carbide prepared by the present invention is more varied in microstructure, and can give the material unique properties such as larger specific surface area and more complex interface properties, which is conducive to application in adsorption, catalysis and other fields; the rich pore structure is conducive to the adsorption and diffusion of gas or liquid, and has potential advantages in energy storage, separation and other fields; and the particle morphology and agglomeration mode can be flexibly controlled by changing the preparation conditions, especially the unique morphology of nanowire silicon carbide, which provides a broader space for expanding the application of silicon carbide in more high-performance fields, such as high-strength composite materials, electronic device heat dissipation and other aspects.

[0097] Test Example 1

[0098] The silicon carbide nanomaterials prepared in Examples 1 to 4 and the silicon carbide material of Comparative Example 1 were tested for performance, wherein the electrical performance test method was the light absorption coefficient method; the specific capacity test method was the cyclic voltammetry method; and the resistivity test method was the van der Pauw method (PPMS). The test results are shown in Table 3.

[0099] Table 3 Performance test results of silicon carbide materials of Examples 1 to 4 and Comparative Example 1

[0100]

[0101]

[0102] As can be seen from Table 3, by comparison, it can be found that the nano-sheet and nano-wire silicon carbide materials prepared by the present invention have obvious differences in band gap width, specific capacity and resistivity and other properties compared with the micron-sized block silicon carbide materials, and the nano-sized morphology materials perform better in some performance indicators, which will provide a reference for the selection and optimization of silicon carbide materials in different application scenarios;

[0103] First, from the perspective of resistivity, the resistivity of the nanowire-shaped silicon carbide prepared by the present invention is 1195.58 Ω·cm, lower than that of nanosheet / bulk silicon carbide (2456.81 Ω·cm), and both are higher than the resistivity of commercial-grade silicon carbide (761.89 Ω·cm). It has significant advantages in specific application scenarios that require high resistance. Its high-resistance property enables it to perform excellently in the field of insulating materials, effectively preventing current from passing through and ensuring the safe operation of equipment. It is suitable for manufacturing high-voltage insulators and cable insulation layers. In specific electronic devices, such as high-precision resistors and certain types of transistors, precise control of current is required. The high resistivity of the silicon carbide nanomaterial of the present invention can meet these demanding requirements and ensure the stability and reliability of the devices. In the biomedical field, its high-resistance property can be used to manufacture bioelectrodes and nerve stimulators, reducing the electrical damage to surrounding tissues. In addition, nanoscale silicon carbide can also be used to manufacture high-temperature heating elements and special heating equipment, meeting the requirements for high-performance materials in high-end fields such as aerospace and national defense;

[0104] Secondly, the bandgap is one of the important parameters for measuring the performance of semiconductor materials. The bandgap of the nanowire-shaped silicon carbide prepared by the present invention is 2.6 eV, higher than that of nanosheet / bulk silicon carbide (2.45 eV) and commercial-grade silicon carbide (2.23 eV). An increase in the bandgap generally means better performance of the material in optoelectronic applications, especially in fields such as photocatalysis, photodetection, and solar cells. A higher bandgap allows the material to absorb photons in a wider spectral range, thereby improving the optoelectronic conversion efficiency. In addition, the increase in the bandgap can also enhance the thermal stability and chemical stability of the material, enabling it to exhibit better performance under high-temperature or harsh environments;

[0105] In terms of specific capacity, the specific capacities of the nanowire-shaped silicon carbide and nanosheet / bulk silicon carbide prepared by the present invention reach 285.89 mAh / g and 367.54 mAh / g respectively, far higher than that of commercial-grade silicon carbide (157 mAh / g). The significant increase in specific capacity indicates that the materials of the present invention have great potential in the field of electrochemical energy storage, especially in energy storage devices such as lithium-ion batteries and supercapacitors. The high specific capacity of the nanowire-shaped silicon carbide is attributed to its unique nanowire structure, which provides a larger specific surface area and more active sites, thus enhancing the electrochemical reaction activity of the material. The higher specific capacity of the nanosheet / bulk silicon carbide is due to the fact that its sheet-like or bulk structure can better maintain the structural stability during charge and discharge processes, thereby improving the cycling performance of the material;

[0106] In summary, the nanowire-shaped silicon carbide and nanosheet / bulk silicon carbide prepared by the present invention exhibit superior performance to commercial-grade silicon carbide in terms of resistivity, bandgap width, specific capacitance, etc. With its higher bandgap width, excellent specific capacitance, and larger resistivity, it shows broader application prospects in many fields such as aerospace, national defense, 5G communication, new energy vehicles, smart grids, and power electronics. These advantages enable it to meet the requirements of modern industry for high-performance, high-efficiency, high-reliability, and miniaturized materials, and promote the technological progress and development of related fields.

[0107] Test Example 2

[0108] The silicon carbide materials of Example 1, Example 3, and Comparative Example 1 were subjected to ultraviolet-visible diffuse reflectance testing and bandgap testing. The testing method was to set the slit width to 20, use standard barium sulfate as a reference, and measure the light absorption intensity in the wavelength range of 200-800 nm on a Shimadzu UV-2550 ultraviolet-visible diffuse reflectance spectrum (DRS). The Kubelka-Munk method was used to convert the reflection spectrum into absorbance, and the results are as Figures 14 - 16 shown.

[0109] According to Figures 14 - 16 the ultraviolet spectrum, in terms of the absorption spectrum, the residue SiC prepared from co-refined residue of kerosene and coal gangue, the tire SiC prepared from waste tires and coal gangue, and commercial-grade SiC all have relatively high absorption at short wavelengths, and then the absorption decreases as the wavelength increases. However, the shapes and positions of the absorption peaks of the three are different, which reflects the differences in their microstructures such as crystal defects and impurity contents. In terms of bandgap energy, the residue SiC is 2.6 eV, the tire SiC is 2.45 eV, and the commercial-grade SiC is 2.23 eV. Since the bandgap energy of silicon carbide determines its electrical and optical properties, a larger bandgap energy means better insulation performance and higher breakdown electric field strength. Therefore, the residue SiC and tire SiC have better insulation performance and higher potential for breakdown electric field strength in terms of electrical properties compared to commercial-grade SiC. From this perspective, it shows that the silicon carbide nanomaterials prepared by the present invention have more advantages than commercial-grade silicon carbide in terms of characteristics related to electrical properties.

[0110] As can be seen from the above examples, the preparation method provided by the present invention not only realizes the complementary resource high-value utilization of solid wastes such as coal gangue and high-carbon solid wastes, greatly reduces the preparation cost of silicon carbide, and solves the environmental and safety problems caused by solid wastes, but also successfully prepares high-purity and small-scale silicon carbide nanomaterials with broad application prospects.

[0111] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all of them. Other embodiments can also be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing silicon carbide nanomaterials using solid waste, characterized in that: The following steps are involved: (1) activating and acid leaching the coal gangue in sequence to obtain coal gangue silicon slag; (2) The gangue silicon slag and high-carbon solid waste are mixed for carbon thermal reduction reaction, followed by roasting and acid washing in sequence to obtain the silicon carbide nanomaterial; the carbon content of the high-carbon solid waste is 70-80wt%; the purity of the gangue is above 95%; the bandgap width of the silicon carbide nanomaterial is above 2.45ev, the specific capacity is above 270mAh / g, and the resistivity is above 1190Ω·cm.

2. The method according to claim 1, characterized in that The carbothermal reduction reaction is carried out in a protective atmosphere; The carbon thermal reduction reaction includes a temperature rise reaction stage and a temperature insulation reaction stage; The heating rate in the temperature-raising reaction stage is 5 to 10°C / min; The temperature of the heat preservation reaction stage is 1300-1600° C., and the time of the heat preservation reaction stage is 1-5 hours.

3. The method according to claim 1, characterized in that The calcination temperature is 500-1000° C., and the heat preservation time is 1-4 hours.

4. The method according to claim 1, characterized in that: The activation temperature is 500-1000° C., and the activation insulation time is 60-240 minutes.

5. The method according to claim 1 or 4, characterized in that: The activation also includes heating; The heating rate of the heating is 5 to 10° C. / min.

6. The method according to claim 1, characterized in that The acid solution temperature of the acid leaching is 80 to 150° C., and the holding time of the acid leaching is 1 to 24 hours; The acid leaching is carried out under stirring conditions; The mass ratio of the acid solution to coal gangue is (1-10) mL:1 g.

7. The method according to claim 1, characterized in that The high-carbon solid waste includes one or more of kerosene co-refining residue and waste tires after pyrolysis and carbonization.

8. The method according to claim 7, characterized in that The method for preparing the waste tire after pyrolysis and carbonization is as follows: pyrolysis and carbonization of the waste tire is performed at 500-700°C.

9. The method according to claim 1 or 7, characterized in that: The molar ratio of carbon in the high-carbon solid waste to silicon in the coal gangue silicon slag is 2 to 4:

1.

10. The method according to claim 1 or 7, characterized in that: The coal gangue silicon slag and high carbon solid waste are mixed by ball milling, the rotation speed of the ball milling is 60% to 80%, and the ball milling time is 1 to 5 minutes.

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