A method for preparing silicon carbide nanomaterials using solid waste

Abstract

The present application belongs to the technical field of nanometer material preparation, and particularly relates to a method for preparing silicon carbide nanometer material by using solid waste. The present application uses coal gangue as a silicon source and high-carbon solid waste as a carbon source, and the silicon carbide nanometer material is prepared by step-by-step extraction and utilization according to the composition characteristics of different solid wastes without high-purity raw materials at a low cost. The silicon carbide nanometer material has a higher band gap, excellent specific capacity and greater resistivity, and shows a broader application prospect in the third-generation semiconductor, national defense and military industry, 5G communication, new energy vehicle, smart grid and high-temperature device and other fields. The present application realizes the complementary resourceization and high-value utilization of coal gangue, high-carbon solid waste and other solid waste, greatly reduces the preparation cost of silicon carbide, solves the environmental problems and safety problems caused by solid waste, successfully prepares high-purity, small-scale and high-performance silicon carbide nanometer material, and has a broad application prospect.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, specifically relating to a method for preparing silicon carbide nanomaterials using solid waste. Background Technology

[0002] Silicon carbide possesses excellent chemical stability, high thermal conductivity, and strong oxidation resistance. Its hardness is second only to diamond and cubic boron nitride, making it widely used in advanced refractory materials, abrasives, and fine ceramics. Furthermore, due to its wider bandgap, higher breakdown electric field, thermal conductivity, and electron saturation velocity, silicon carbide is suitable for fabricating high-temperature, high-frequency, radiation-resistant, and high-power devices, and is thus known as a third-generation semiconductor material, making it one of the most sought-after materials in the field of new materials.

[0003] Traditional industrial silicon carbide is synthesized using high-purity silica sand and petroleum coke as raw materials, smelted in a high-temperature electric resistance furnace via the Atchison process. This method requires high purity of silica sand (≥99%) and petroleum coke (≥98%), resulting in high production costs, poor performance, and limited application scenarios for silicon carbide. Summary of the Invention

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

[0005] To achieve the above objectives, the present invention provides the following technical solution:

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

[0007] (1) The coal gangue was activated and acid-leached in sequence to obtain coal gangue silica slag;

[0008] (2) The coal gangue silicon slag and high-carbon solid waste are mixed and subjected to carbothermic reduction reaction, followed by roasting and acid washing to obtain the silicon carbide nanomaterial; 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 nanomaterial is above 2.45 eV, the specific capacity is above 270 mAh / g, and the resistivity is above 1190 Ω·cm.

[0009] Preferably, the carbothermic reduction reaction is carried out in a protective atmosphere; the carbothermic reduction reaction includes a heating reaction stage and a holding reaction stage; the heating rate of the heating reaction stage is 5-10℃ / min; the temperature of the holding reaction stage is 1300-1600℃, and the holding reaction stage lasts for 1-5 hours.

[0010] Preferably, the roasting temperature is 500–1000°C, and the holding time is 1–4 hours.

[0011] Preferably, the activation temperature is 500–1000°C, and the activation holding time is 60–240 min.

[0012] Preferably, the activation process further includes heating; the heating rate is 5-10°C / min.

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

[0014] Preferably, the high-carbon solid waste includes one or more of the following: coal-oil co-refining residue and waste tires after pyrolysis and carbonization.

[0015] Preferably, the method for preparing the pyrolysis carbonized waste tires is as follows: the waste tires are pyrolyzed and carbonized 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 to 4:1.

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

[0018] This invention provides a method for preparing silicon carbide nanomaterials from solid waste. Using coal gangue as the silicon source and high-carbon solid waste (carbon content above 70 wt%) as the carbon source, this invention targets and utilizes different solid wastes in a stepwise manner, without requiring high-purity raw materials, to prepare silicon carbide nanomaterials at low cost. These nanomaterials exhibit a wider bandgap, excellent specific capacitance, and higher resistivity, showing broader application prospects in multiple fields such as third-generation semiconductors, defense and military industries, 5G communications, new energy vehicles, smart grids, and high-temperature devices.

[0019] This invention further removes impurities such as SiO2 remaining in silicon carbide through acid washing, ultimately obtaining high-purity silicon carbide nanomaterials. This invention prepares silicon carbide nanomaterials by controlling the nucleation and growth of silicon carbide. In the Si-OC reaction system, nano-silicon carbide nuclei are generated through a heterogeneous gas-solid reaction of SiO vapor and C, thereby promoting the growth of bulk / sheet silicon carbide. Simultaneously, nano-silicon carbide nuclei are generated through a homogeneous gas-gas reaction of SiO and CO, promoting the growth of nanowire silicon carbide.

[0020] This invention achieves complementary resource utilization of solid wastes such as coal gangue and high-carbon solid waste, significantly reducing the preparation cost of silicon carbide by 50%–70%, and solving environmental and safety issues caused by solid waste. Simultaneously, it successfully prepares high-purity (>98.9%) and small-scale (<100nm) silicon carbide nanomaterials with broad application prospects. Compared with traditionally industrially prepared silicon carbide materials, the silicon carbide nanomaterials prepared in this invention have a thinner thickness and a unique nanofiber structure, with a thickness not exceeding 100nm. This structure not only endows the material with a higher specific surface area but also gives it excellent properties in optical performance, electron transport performance, and energy storage performance. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

[0023] Figure 2 XRD diffraction patterns of silicon carbide nanomaterials prepared from coal gangue and high-carbon solid waste;

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

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

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

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

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

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

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

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

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

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

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

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

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

[0037] Figure 16 The image shows the UV-Vis diffuse reflectance (left) and bandgap (right) of commercial-grade silicon carbide in Comparative Example 1. Detailed Implementation

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

[0039] (1) The coal gangue was activated and acid-leached in sequence to obtain coal gangue silica slag;

[0040] (2) The coal gangue silicon slag and high-carbon solid waste are mixed and subjected to carbothermic reduction reaction, followed by roasting and acid washing to obtain the silicon carbide nanomaterial; 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 nanomaterial is above 2.45 eV, the specific capacity is above 270 mAh / g, and the resistivity is above 1190 Ω·cm.

[0041] This invention involves sequentially activating and acid-leaching coal gangue to obtain coal gangue silica slag. In this invention, the coal gangue can be sequentially crushed, ball-milled, and screened before use.

[0042] In this invention, the particle size of the coal gangue may not be greater 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.

[0043] In this invention, the activation temperature can be 500-1000℃, specifically 600℃ or 800℃, and the activation holding time can be 60-240min, specifically 120min or 180min.

[0044] In this invention, the activation process may further include heating; the heating rate may be 5 to 10 °C / min, specifically 7 °C / min or 9 °C / min.

[0045] In this invention, the acid temperature for acid leaching can be 80–150°C, specifically 120°C, and the holding time for acid leaching can be 1–24 hours, specifically 6 hours, 12 hours, or 18 hours. This invention uses acid leaching to remove metallic impurities such as aluminum and iron.

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

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

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

[0049] In this invention, the acid leaching process may further include sequentially performing solid-liquid separation, washing, and drying on the resulting acid leaching system.

[0050] In this invention, the solid-liquid separation can be centrifugation; the centrifugation rate can be 3500-8500 r / min, specifically 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 3 min, 5 min, 7 min or 9 min.

[0051] In this invention, the washing reagent may include one or more of hydrochloric acid, nitric acid and hydrofluoric acid; the number of washing cycles may be more than three, specifically three, five or seven, until the washing solution is neutral.

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

[0053] Through the above-mentioned treatment, the present invention obtains coal gangue silica slag with a neutral silica content of >95%, and the specific composition is shown in Table 1.

[0054] Table 1 Chemical composition of coal gangue and silica slag

[0055]

[0056] After obtaining coal gangue silica slag, this invention mixes the coal gangue silica slag with high-carbon solid waste (denoted as the first mixture) and performs a carbothermal reduction reaction, followed by calcination and acid washing to obtain the silicon carbide nanomaterials. In this invention, the high-carbon solid waste may include one or more of the following: kerosene co-refining residue and pyrolytic carbonized waste tires. The specific compositions of the kerosene co-refining residue and waste tires used in the embodiments of this invention are shown in Table 2.

[0057] Table 2 Industrial and elemental analysis of high-carbon solid waste

[0058]

[0059] The preparation method provided by this invention enables the controllable synthesis of silicon carbide nanomaterials with different morphologies. This invention utilizes the differences in the morphology of residual carbon in various high-carbon solid wastes to controllably synthesize silicon carbide nanomaterials (nanowires, nanosheets / blocks) with different morphologies. The morphology of residual carbon in high-carbon solid wastes varies significantly. The carbon in kerosene co-refining residue is a layered, cross-linked macromolecular structure composed of aromatic carbons, while the carbon from waste tires after carbonization is a porous carbon material of hard carbon nanospheres. Compared to kerosene co-refining residue, waste tire residual carbon has a richer multi-level micro / mesoporous structure and more enriched active sites (specifically, as shown in...). Figure 1 (As shown). Therefore, when using kerosene co-refining residue as a carbon source, the solid-phase high-temperature carbothermic reduction reaction between silicon oxide and layered carbon dominates in the Si-CO system, forming silicon carbide nanosheets. When using waste tires as a carbon source, in the Si-CO system, silicon oxide first reacts with porous carbon nanospheres to generate SiO and CO. SiO2 and SiO further react with CO to undergo gas-solid / gas-gas chemical vapor deposition, forming silicon carbide nanowires (specifically as shown). Figure 2 and Figure 3 (As shown).

[0060] Nanowire silicon carbide and nanosheet / bulk silicon carbide exhibit significant advantages in multiple fields due to their unique structure and properties: Nanowire silicon carbide possesses a high specific surface area, and its linear structure provides a larger active surface, enhancing the material's surface reactivity and making it outstanding in catalyst supports, adsorbent materials, and sensors. Simultaneously, the continuous linear structure of nanowire silicon carbide forms highly efficient conductive channels, significantly reducing resistivity and giving it excellent conductivity in electronic devices and electrode materials. Furthermore, the linear structure endows the material with high mechanical strength and flexibility, making it widely applicable in composite materials and flexible devices. In the field of energy storage, the high specific capacity of nanowire silicon carbide makes it an ideal electrode material for lithium-ion batteries and supercapacitors.

[0061] In this invention, the method for preparing the pyrolysis carbonized waste tires can be: pyrolysis carbonizing the waste tires at 500-700°C; the specific temperature of the pyrolysis carbonization can be 550°C, 600°C or 650°C.

[0062] In this invention, the high-carbon solid waste may be further subjected to crushing, ball milling and screening in sequence before use.

[0063] In this invention, the particle size of the high-carbon solid waste may not be greater 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 this invention, the molar ratio of carbon in the high-carbon solid waste to silicon in the coal gangue 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. By using the above molar ratios of raw materials, this invention can improve reaction efficiency and product purity; control product composition, morphology, and size; reduce energy consumption and cost; improve material performance; and simplify subsequent processing.

[0065] In this invention, the first mixing can be ball milling; the rotation speed of the ball milling can be 60% to 80%, specifically 65% ​​or 75%, and the milling time can be 1 to 5 minutes, specifically 3 minutes; the ball milling equipment can be a ball mill. This invention, through ball milling, enables more thorough mixing of the reactants.

[0066] In this invention, the carbothermic 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 carbothermic reduction reaction can be a high-temperature tube furnace; the carbothermic reduction reaction can include a heating reaction stage and a holding reaction stage. This invention prepares silicon carbide through a carbothermic reduction reaction.

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

[0068] In this invention, the temperature of the heat preservation reaction stage can be 1300-1600℃, specifically 1300℃, 1350℃, 1400℃, 1450℃, 1500℃, 1550℃ or 1600℃, and the time of the heat preservation reaction stage can be 1-5h, specifically 1h, 2h, 3h, 4h or 5h.

[0069] In this invention, the calcination temperature can be 500–1000°C, specifically 700°C or 800°C, and the holding time can be 1–4 hours, specifically 2 hours or 3 hours. This invention removes unreacted residual carbon through calcination.

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

[0071] In this invention, the pickling process may further include washing and drying the resulting pickled product sequentially.

[0072] In this invention, the washing reagent may include one or more of hydrochloric acid, nitric acid and hydrofluoric acid; the number of washing cycles may be more than three, specifically three, five or seven, until the washing solution is neutral.

[0073] In this invention, the drying temperature can be 70-100°C, specifically 85°C or 95°C, and the heat preservation time can be 1-24 hours, specifically 12 hours or 16 hours.

[0074] Compared to traditional industrial silicon carbide, the silicon carbide nanomaterials prepared by the method provided in this invention have several advantages, such as a higher specific surface area, improving reactivity and adsorption capacity; enhanced electrical properties, increasing resistivity, making them suitable for high-frequency, high-power devices; environmental friendliness and low cost, using coal gangue, waste tires, and kerosene co-refining residues as raw materials, reducing production costs and realizing waste resource utilization; and nanostructures that give the materials superior electrical and optical properties compared to traditional silicon carbide, making them suitable for a wider range of applications. Furthermore, the silicon carbide nanomaterials of this invention exhibit significant differences in bandgap, specific capacity, and resistivity, demonstrating different superior performances in different application scenarios. Nanosheet and nanowire silicon carbide materials, due to their unique microstructure and nanoscale effect, exhibit some unique performance advantages, showing greater application potential in energy storage, field emission, and electromagnetic wave absorption devices. ① Bandgap advantage and application scenarios: The silicon carbide nanomaterials prepared by this invention have a higher bandgap, which makes them more stable and reliable under extreme environments such as high temperature and high pressure. The increased bandgap means that the material can maintain a lower leakage current under high-temperature conditions, thereby reducing energy loss and improving device efficiency and lifespan. In the aerospace and defense industries, this high-temperature stability is crucial for the reliable operation of satellites, missiles, and other equipment in extreme environments. Furthermore, 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 give the silicon carbide nanomaterials prepared in this invention significant advantages in the energy storage field. Increased specific capacity means that more electrical energy can be stored in the same volume or weight, which is of great significance for applications with high energy density requirements, such as new energy vehicles and smart grids. In new energy vehicles, batteries using this silicon carbide material can achieve longer driving range and faster charging speeds, while also improving battery cycle life and reducing operating costs. In smart grids, it can be used in energy storage systems to effectively balance grid load and improve grid stability and reliability. ③ Resistivity Advantage and Application Scenarios: Higher resistivity helps reduce leakage current during device operation, improving the device's insulation performance and stability. In the field of power electronics, such as high-voltage direct current transmission equipment and industrial frequency converters, the silicon carbide nanomaterials prepared by this invention can reduce energy loss, improve conversion efficiency, and simultaneously reduce the requirements for cooling systems, enabling miniaturization and weight reduction of equipment. In the field of microelectronics, its high resistivity is beneficial for manufacturing high-performance insulated-gate bipolar transistors (IGBTs) and other devices, improving the operating speed and stability of electronic equipment, and is suitable for power management and signal processing sections of electronic products such as computers and smartphones.

[0075] To further illustrate the present invention, the following detailed description of the invention's solutions, in conjunction with the accompanying drawings and embodiments, is provided, but should not be construed as limiting the scope of protection of the present invention.

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

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

[0078] (2) The coal gangue silicon slag and kerosene co-refining residue were mixed and ball-milled for 5 min according to a C:Si molar ratio of 3:1. The mixture was then placed in a high-temperature tubular resistance furnace and heated to 1600℃ in a protective atmosphere (N2) for 4 h at a heating rate of 10℃ / min. After the furnace temperature dropped to room temperature, the mixture was removed and placed in a muffle furnace at 700℃ for 3 h at a heating rate of 5℃ / min. After cooling to room temperature, the mixture was treated with a 20% HCl-HF solution at a solid-liquid ratio of 1:10 at 30℃ for 12 h. After repeated washing until the silicon carbide was neutral, the mixture was dried to obtain silicon carbide nanomaterials with a purity of 98.92%. The characterization results are as follows: Figure 6 and Figure 7 As shown.

[0079] according to Figure 6 and Figure 7 As can be seen from the XRD and FTIR spectra, the presence of SiC and SiO2 phases in the sample is confirmed. Scanning electron microscopy (SEM) images reveal that the silicon carbide nanomaterials prepared from coal gangue exhibit a distinct sheet-like morphology. These sheet-like structures are stacked and interwoven, forming an irregular porous structure of varying sizes with numerous gaps and pores, resulting in a large specific surface area. Transmission electron microscopy (TEM) images further clarify the details of the nanoscale sheet-like structures. Although the edges of these sheet-like particles are irregular, their sheet-like morphology is significant. Some of these particles aggregate and connect to form complex aggregate structures, further confirming the sheet-like morphology of the silicon carbide nanomaterials of this invention.

[0080] Example 2: Changing the silicon-to-carbon ratio, with excess carbon.

[0081] (1) The residue from the co-refining of coal gangue and kerosene is crushed to below 0.2 mm. Coal gangue powder is evenly spread horizontally in a corundum crucible and activated in a muffle furnace at 800℃ for 2 hours with a heating rate of 5℃ / min. The activated coal gangue powder is mixed with 20% hydrochloric acid at a solid-liquid ratio of 1:5 and placed in an oil bath magnetic stirrer. After acid leaching at 120℃ for 24 hours, it is repeatedly washed until the silica slag is neutral and then dried to obtain coal gangue silica slag with a silica content >95%.

[0082] (2) The coal gangue silicon slag and kerosene co-refining residue were mixed and ball-milled for 5 min according to a C:Si molar ratio of 4:1. The mixture was then placed in a high-temperature tubular resistance furnace and heated to 1600℃ in a protective atmosphere (N2) for 4 h at a heating rate of 10℃ / min. After the furnace temperature dropped to room temperature, the mixture was removed and placed in a muffle furnace at 700℃ for 3 h at a heating rate of 5℃ / min. After cooling to room temperature, the mixture was treated with a 20% HCl-HF solution at a solid-liquid ratio of 1:10 at 30℃ for 12 h. After repeated washing until the silicon carbide was neutral, the mixture was dried to obtain silicon carbide nanomaterials with a purity of 99.18%. The characterization results are as follows: Figure 4 and Figure 5 As shown.

[0083] according to Figure 4 and Figure 5 It can be seen that, Figure 4 and Figure 5 The characterization results of silicon carbide nanomaterials synthesized with excess carbon are presented. Figure 4 The left figure shows the XRD pattern, and the characteristic peaks indicate the presence of SiC in the material, proving that there is a silicon carbide phase in the product; the right figure shows the FT-IR pattern, which shows the absorption peak of Si-C bond at a specific wavenumber, further confirming the presence of Si-C bond. Figure 5 The SEM image on the left shows that the material exhibits irregular sheet-like and blocky structures, which are stacked together with some particles attached to the surface. The shape and distribution of the structure show a certain degree of complexity and disorder. The TEM image on the right shows that the material is composed of irregular sheet-like or blocky particles at the nanoscale. 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 was found that excess carbon changed the morphology and structural characteristics of the material, including pore structure, particle morphology, and aggregation mode.

[0084] Example 3: Using waste tires as a carbon source

[0085] (1) Crush coal gangue and waste tires to below 0.2 mm. Spread coal gangue powder evenly in a corundum crucible and activate it in a muffle furnace 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 repeatedly until the silica slag is neutral and then dry to obtain coal gangue silica slag with a silica content >95%.

[0086] (2) The crushed waste tires were placed in a high-temperature tubular resistance furnace and heated to 700°C for 10 min in a protective atmosphere (N2). The heating rate was 5°C / min. After cooling to room temperature, carbonized waste tires with a fixed carbon content of 78.84 wt% were obtained.

[0087] (3) The coal gangue silicon slag and the carbonized waste tire were mixed and ball-milled for 5 min according to a C:Si molar ratio of 3.5:1. The mixture was then placed in a high-temperature tubular resistance furnace and heated to 1600℃ in a protective atmosphere (N2) for 4 h at a heating rate of 10℃ / min. After the furnace temperature dropped to room temperature, the mixture was removed and placed in a muffle furnace at 700℃ for 3 h at a heating rate of 5℃ / min. After cooling to room temperature, the mixture was treated with a 20% HCl-HF solution at a solid-liquid ratio of 1:10 at 30℃ for 12 h. After repeated washing until the silicon carbide was neutral, the mixture was dried to obtain silicon carbide nanomaterials with a purity of 99.31%. The characterization results are as follows: Figure 8 and Figure 9 As shown.

[0088] according to Figure 8 and Figure 9 It can be seen that, Figure 8 The XRD pattern clearly shows the presence of SiC in the material, confirming the presence of the silicon carbide phase in the product; the FT-IR pattern on the right shows obvious Si-C bond absorption peaks at a specific wavenumber, further confirming the presence of Si-C bonds. Figure 9 The SEM image on the right reveals a distinct fibrous structure. These fibers are interwoven, varying in thickness, and have granular material adhering to their surface. The TEM image on the left clearly shows the microstructure of the fibers at the nanoscale. The fibers have a relatively regular morphology and clear edges, indicating that the material possesses fibrous nanostructure characteristics. These characterization results comprehensively verify the successful preparation of silicon carbide nanofiber materials synthesized from coal gangue and waste tires.

[0089] Example 4: Changing the reaction time

[0090] (1) Crush coal gangue and waste tires to less than 0.2 mm. Spread coal gangue powder evenly in a corundum crucible and activate it in a muffle furnace 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 repeatedly until the silica slag is neutral and then dry to obtain coal gangue silica slag with a silica content >95%.

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

[0092] (3) The coal gangue silicon slag and the carbonized waste tire were mixed and ball-milled for 5 min according to a C:Si molar ratio of 3.5:1. The mixture was then placed in a high-temperature tubular resistance furnace and heated to 1600℃ in a protective atmosphere (N2) for 3 h at a heating rate of 10℃ / min. After the furnace temperature dropped to room temperature, the mixture was removed and placed in a muffle furnace at 700℃ for 3 h at a heating rate of 5℃ / min. After cooling to room temperature, the mixture was treated with a 20% HCl-HF solution at a solid-liquid ratio of 1:10 at 30℃ for 12 h. After repeated washing until the silicon carbide was neutral, the mixture was dried to obtain silicon carbide nanomaterials with a purity >99.12%. The characterization results are as follows: Figure 10 and Figure 11 As shown.

[0093] according to Figure 10 and Figure 11 As can be seen from the XRD and FT-IR spectra, the peak positions and intensities are similar to those after 4 hours of heat preservation, with the characteristic diffraction peaks of SiC still clearly visible. This indicates that silicon carbide phase was successfully synthesized even after 3 hours of heat preservation. The SEM images reveal a fibrous structure with some granular or blocky substances. Compared to the SEM and TEM images after 4 hours of heat preservation, the morphology and distribution of the fibers have changed; for example, the fiber thickness, length uniformity, and degree of interweaving may also differ. These changes are related to the shorter heat preservation time, which affects the growth and aggregation processes of the material. In summary, the silicon carbide materials prepared by 3 hours and 4 hours of heat preservation are basically consistent in phase composition, indicating successful synthesis of silicon carbide. However, there are certain differences in microstructure, suggesting that the heat preservation time affects the micromorphology and internal structure of silicon carbide materials.

[0094] Comparative Example 1

[0095] This comparative example uses commercially available silicon carbide (made from quartz sand and petroleum coke), and its XRD and FTIR diffraction patterns are shown below. Figure 12 As shown, the morphology is as follows Figure 13 As shown.

[0096] according to Figure 12 and Figure 13 As can be seen from the XRD and FT-IR spectra, the commercial silicon carbide does indeed contain a silicon carbide crystal structure, and the spectra are basically the same as those of the silicon carbide prepared in this invention. SEM images reveal that the commercial silicon carbide exhibits irregular sheet-like or blocky morphologies, with these sheet-like or blocky particles of varying sizes stacked together. In contrast, the silicon carbide prepared in this invention has a richer and more varied microstructure, endowing the material with unique properties such as a larger specific surface area and more complex interfacial properties, which is beneficial for applications in adsorption, catalysis, and other fields. Its abundant pore structure facilitates the adsorption and diffusion of gases or liquids, offering potential advantages in energy storage, separation, and other fields. Furthermore, the particle morphology and aggregation mode can be flexibly controlled by changing the preparation conditions, especially the unique morphology of nanowire silicon carbide, providing broader scope for expanding the application of silicon carbide in more high-performance fields, such as high-strength composite materials and heat dissipation in electronic devices.

[0097] Test Example 1

[0098] The silicon carbide nanomaterials prepared in Examples 1-4 and the silicon carbide material in Comparative Example 1 were subjected to performance tests. The electrical performance was tested using the optical absorption coefficient method; the specific capacitance was tested using the cyclic voltammetry method; and the resistivity was tested using the van der Bauer method (PPMS). The test results are shown in Table 3.

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

[0100]

[0101]

[0102] As can be seen from Table 3, by comparison, it can be found that the nanosheet-shaped and nanowire-shaped silicon carbide materials prepared by this invention have significant differences from the micron-sized bulk silicon carbide materials in terms of band gap, specific capacitance and resistivity. Moreover, the nanoscale 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 silicon carbide prepared in this invention is 1195.58 Ω·cm, lower than the 2456.81 Ω·cm of nanosheet / bulk silicon carbide, and higher than the resistivity of commercial-grade silicon carbide (761.89 Ω·cm), demonstrating significant advantages in specific applications requiring high resistance. Its high resistivity makes it excellent in the field of insulating materials, effectively preventing current flow and ensuring safe equipment operation, making it suitable for manufacturing high-voltage insulators and cable insulation layers. In certain electronic devices, such as high-precision resistors and specific types of transistors, precise current control is required, and the high resistivity of the silicon carbide nanomaterials of this invention can meet these stringent requirements, ensuring the stability and reliability of the devices. In the biomedical field, its high resistivity can be used to manufacture bioelectrodes and neurostimulators, reducing electrical damage to surrounding tissues. Furthermore, nanoscale silicon carbide can also be used to manufacture high-temperature heating elements and special heating equipment, meeting the demand for high-performance materials in high-end fields such as aerospace and defense.

[0104] Secondly, bandgap is one of the important parameters for evaluating the performance of semiconductor materials. The nanowire silicon carbide prepared in this invention has a bandgap of 2.6 eV, which is higher than the 2.45 eV of nanosheet / bulk silicon carbide and the 2.23 eV of commercial silicon carbide. An increased bandgap generally means better performance in optoelectronic applications, especially in photocatalysis, photodetectors, and solar cells. A higher bandgap allows the material to absorb photons over a wider spectral range, thereby improving photoelectric conversion efficiency. Furthermore, an increased bandgap can enhance the thermal 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 nanowire-shaped silicon carbide and nanosheet / bulk silicon carbide prepared in this invention achieved 285.89 mAh / g and 367.54 mAh / g, respectively, far exceeding the 157 mAh / g of commercially available silicon carbide. This significant improvement in specific capacity indicates the great potential of the material 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, thereby enhancing the electrochemical reactivity of the material. The higher specific capacity of the nanosheet / bulk silicon carbide is due to its sheet-like or bulk structure, which better maintains structural stability during charge and discharge, thus improving the material's cycle performance.

[0106] In summary, the nanowire-like and nanosheet / bulk silicon carbide prepared by this invention exhibit superior performance compared to commercial-grade silicon carbide in terms of resistivity, bandgap, and specific capacitance. With their wider bandgap, excellent specific capacitance, and higher resistivity, they show broader application prospects in various fields such as aerospace, defense, 5G communications, new energy vehicles, smart grids, and power electronics. These advantages enable them to meet the demands of modern industry for high-performance, high-efficiency, high-reliability, and miniaturized materials, driving technological progress and development in related fields.

[0107] Test Example 2

[0108] The silicon carbide materials of Examples 1, 3, and Comparative Example 1 were subjected to UV-Vis diffuse reflectance and bandgap measurements. The test method involved setting a slit width of 20 nm, using standard barium sulfate as a reference, and measuring the light absorption intensity in the wavelength range of 200–800 nm using a Shimadzu UV-2550 UV-Vis diffuse reflectance spectroscopy (DRS). The reflectance spectra were converted to absorbance using the Kubelka-Munk method. The results are as follows: Figures 14-16 As shown.

[0109] according to Figures 14-16 From the ultraviolet spectra, in terms of absorption spectra, residual SiC prepared from kerosene co-refining residue and coal gangue, tire SiC prepared from waste tires and coal gangue, and commercial-grade SiC all exhibit high absorption at short wavelengths, followed by a decrease in absorption with increasing wavelength. However, the shape and position of the absorption peaks differ among the three, reflecting differences in their microstructure, such as crystal defects and impurity content. Regarding band gap energy, residual SiC is 2.6 eV, tire SiC is 2.45 eV, and commercial-grade SiC is 2.23 eV. Since the band gap energy of silicon carbide determines its electrical and optical properties, a larger band gap energy implies better insulation performance and a higher breakdown electric field strength. Therefore, residual SiC and tire SiC have better insulation performance and higher breakdown electric field strength potential compared to commercial-grade SiC. From this perspective, the silicon carbide nanomaterials prepared in this invention have advantages over commercial-grade silicon carbide in terms of electrical performance-related characteristics.

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

[0111] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, 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, Includes the following steps: (1) Coal gangue is successively activated and acid-leached to obtain coal gangue silica slag, wherein the silica content in the coal gangue silica slag is >95wt%; (2) The coal gangue silicon slag and high-carbon solid waste are mixed and subjected to carbothermic reduction reaction, followed by roasting and acid washing to obtain the silicon carbide nanomaterial; the carbon content of the high-carbon solid waste is 70~80wt%; the purity of the coal gangue is above 95%; the band gap of the silicon carbide nanomaterial is above 2.45eV, the specific capacity is above 270mAh / g, and the resistivity is above 1190Ω·cm; The high-carbon solid waste includes one or more of the following: coal-oil co-refining residue and pyrolysis-carbonized waste tires; the method for preparing the pyrolysis-carbonized waste tires is to pyrolyze and carbonize the waste tires at 500~700℃. The molar ratio of carbon in the high-carbon solid waste to silicon in the coal gangue slag is 2~4:1; The carbothermic reduction reaction is carried out in a protective atmosphere; The carbothermic reduction reaction includes a heating reaction stage and a heat preservation reaction stage; The heating rate during the heating reaction stage is 5~10℃ / min; The temperature of the heat preservation reaction stage is 1300~1600℃, and the heat preservation reaction stage lasts for 1~5 hours.

2. The method according to claim 1, characterized in that, The roasting temperature is 500~1000℃, and the holding time is 1~4h.

3. The method according to claim 1, characterized in that, The activation temperature is 500~1000℃, and the activation holding time is 60~240min.

4. The method according to claim 1 or 3, characterized in that, The activation process also includes heating; The heating rate is 5~10℃ / min.

5. The method according to claim 1, characterized in that, The acid temperature for pickling is 80~150℃, and the pickling time is 1~24h. 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.

6. The method according to claim 1, characterized in that, The coal gangue silica slag and high-carbon solid waste are mixed by ball milling, with the ball milling speed being 60%~80% and the ball milling time being 1~5 minutes.

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