A nitride / carbide-doped graphene composite material, a preparation method and application thereof

Abstract

The application relates to the technical field of nanometer carbon material preparation, in particular to a nitride / carbide-doped graphene composite material and a preparation method and application thereof. A physical peeling method is used to treat graphite raw materials to obtain intrinsic graphene powder; the intrinsic graphene powder is mixed with powder of at least one oxide ceramic precursor, the intrinsic graphene powder is coated on the surface of the oxide ceramic precursor powder to form a composite precursor; the composite precursor and at least one doping precursor are subjected to high-temperature reaction in a protective atmosphere, the oxide ceramic precursor is reduced and nitrided or carbonized into a corresponding nitride or carbide ceramic phase, meanwhile, the intrinsic graphene is doped to obtain the nitride / carbide-doped graphene composite material. The composite material has excellent heat conduction performance, predictable catalytic activity and mechanical performance, and can be widely applied to heat dissipation of advanced electronic components, high-strength structural ceramics or replacement of noble metals as chemical catalysts.

Description

Technical Field

[0001] This invention relates to the field of nano-carbon material preparation technology, and in particular to a composite material formed by coating nitride / carbide ceramics with doped graphene, its preparation method and application. The composite material forms a three-dimensional network structure with the doped graphene interconnecting each other, and has electrical conductivity, high thermal conductivity and chemical catalytic activity. It can be used for heat dissipation of advanced electronic components, high-strength structural ceramics or to replace noble metals as chemical catalysts, and has great industrial application value. Background Technology

[0002] Graphene, as a typical two-dimensional carbon-based nanomaterial, possesses unique crystal structure that endows it with core performance advantages such as ultra-high electrical conductivity, excellent thermal conductivity, and outstanding mechanical strength. It has already been successfully applied in many fields, including conductive inks, superheaters, catalytic reaction supports, and electronic devices. However, the intrinsic graphene surface is only composed of carbon sp. 2 As an inert surface primarily composed of bonding materials, graphene exhibits extremely low chemical activity, resulting in significant limitations in its dispersibility, interfacial bonding ability, and electronic and thermal conductivity with other materials. Therefore, in practical applications, extremely high contact resistance and interfacial thermal resistance frequently occur between graphene sheets, between graphene and other materials, or between graphene sheets themselves, or between graphene and other materials. This affects electrical and thermal conductivity, leading to product results that often differ significantly from theoretical expectations.

[0003] To improve the surface activity and expand the functions of graphene, existing technologies mostly employ chemical doping or surface modification methods. Among these, nitrogen doping is a commonly used technique to regulate the electronic structure of graphene and enhance its electrochemical and catalytic performance.

[0004] Currently reported methods for preparing nitrogen-doped graphene mainly include the following: Chinese invention patent CN103601175A uses ammonia water and graphene oxide to simultaneously achieve reduction and doping under high-speed stirring; CN104229789A uses citric acid and melamine as raw materials, which are mixed, dried, and then calcined in stages to prepare nitrogen-doped graphene, also relying on nitrogen-containing reducing agents. Although both methods can obtain a nitrogen content of 3-6 wt%, reducing amino groups or pyrolytic free radicals will attack sp. 2The lattice structure shows a significant increase in the Raman D peak, and residual amine and cyano fragments are difficult to completely remove, leading to an increase in the contact resistance of the composite material. Chinese invention patent CN103359710A reduces GO using urea as the nitrogen source in a mixed atmosphere of inert gas and NH3 at 800-1100°C. While this method can achieve a high nitrogen doping level (e.g., 12.3 wt%), the high-temperature process easily leads to an increase in graphene lattice defects, and the process has high energy consumption, which is not conducive to large-scale production. Chinese invention patent CN103626158A utilizes low-temperature doping of active nitrogen-containing compounds in a closed system at 100-300°C. The conditions are relatively mild, but it relies on the decomposition of the precursor and the generation of gas, resulting in poor process controllability and difficulty in ensuring doping uniformity. Chinese invention patent CN109422259A uses dry ball milling of graphite powder and nitrogen-rich carbon precursors, combined with subsequent heat treatment to achieve nitrogen doping, realizing in-situ exfoliation and simultaneous nitrogen doping. Although this method can retain some intrinsic sp... 2 The graphene layer structure is structurally sound, but it is easily damaged under mechanical forces, which can introduce a large number of edge sps. 3 The structure and disordered areas are prone to detachment and aggregation during external processing.

[0005] In general, existing nitrogen doping methods have the following problems: (1) High temperature or strong chemical treatment can easily destroy the intrinsic sp of graphene. 2 (1) The structure introduces too many defects, which leads to a decrease in its electrical and thermal conductivity; (2) Toxic or corrosive reagents are often used in the doping process, which is not environmentally friendly; (3) Most processes are complex and energy-intensive, making it difficult to balance high performance and low-cost mass production.

[0006] To address the aforementioned issues, researchers have recently begun exploring the combination of graphene with functional ceramics such as nitrides and carbides. The aim is to retain the high electrical conductivity of graphene while introducing the high hardness, high thermal conductivity, and good chemical stability of the ceramic phase, thereby constructing composite materials with excellent mechanical, thermal, and electrochemical properties. However, current methods for combining nitrides / carbides with graphene primarily employ physical mixing or post-modification, resulting in weak interfacial bonding and difficulty in achieving atomic-level doping and uniform dispersion, severely impacting the overall material performance.

[0007] Therefore, developing a preparation method that can achieve atomic-level doping of nitrides or carbides at lower temperatures while maintaining the low-defect structure of graphene has become the key to promoting the application of graphene in the field of high-performance composite materials.

[0008] In view of this, the present invention is proposed. Summary of the Invention

[0009] The purpose of this invention is to provide a nitride / carbide-doped graphene composite material and its preparation method, which has excellent thermal conductivity.

[0010] The first aspect of the present invention provides a method for preparing a nitride / carbide-doped graphene composite material, comprising the following steps: S1. Mix intrinsic graphene powder with powder of at least one oxide ceramic precursor, so that the intrinsic graphene powder coats the surface of the oxide ceramic precursor powder to form a composite precursor. S2. The composite precursor and at least one doped precursor are placed in a high-temperature reaction apparatus and reacted at high temperature under a protective atmosphere to reduce and nitride or carbide the oxide ceramic precursor into the corresponding nitride or carbide ceramic phase, while the intrinsic graphene is doped to obtain a nitride / carbide-doped graphene composite material.

[0011] In the preparation method of the nitride / carbide-doped graphene composite material of the present invention, firstly, intrinsic graphene powder and oxide ceramic precursor powder are uniformly mixed, so that the intrinsic graphene powder uniformly coats the surface of the oxide ceramic precursor powder to form a composite precursor. Further, during the subsequent heat treatment reduction process, carbon elements in the graphene reduce the oxide ceramic precursor. During the process of carbon atoms detaching from the graphene and reducing the oxide ceramic precursor, the thermal decomposition of the doped precursor allows the dopant element to enter the carbon atom detachment sites in the graphene lattice, forming doped graphene. Under a nitrogen atmosphere, the oxide ceramic precursor is reduced to nitride ceramic, or even to carbide ceramic, ultimately forming a nitride / carbide and doped graphene composite structure. This invention achieves an innovative product form of graphene doping and composite with high-performance structural ceramics without severely disrupting the perfect lattice arrangement of intrinsic graphene or introducing other heterogeneous impurities.

[0012] As a preferred embodiment of this technical solution, the present invention does not strictly limit the mass ratio of intrinsic graphene, oxide ceramic precursor and doped precursor. Preferably, the mass ratio of intrinsic graphene, oxide ceramic precursor and doped precursor is (3-5):(1-2):(20-22).

[0013] As a preferred embodiment of this technical solution, the preparation method of intrinsic graphene powder includes: uniformly dispersing natural graphite powder in water or solvent by mechanical stirring to form a graphite solution, then applying at least one physical force to the graphite solution to cause the graphite to swell and peel off into graphene to form a graphene solution, and freeze-drying the graphene solution to obtain intrinsic graphene powder.

[0014] More preferably, the surface tension of the water or solvent used to disperse the natural graphite powder is 30-60 mJ / m. 2 To improve the suspension and exfoliation efficiency of graphene.

[0015] Specifically, natural graphite powder is composed of tens of thousands of graphene molecules stacked together by van der Waals forces, and the surface energy of natural graphite is approximately 50 mJ / m². 2 When the surface tension of water or solvent is comparable to the surface energy of natural graphite, applying a shear force greater than the van der Waals force to the graphite solution will cause natural graphite to gradually exfoliate into graphene. Therefore, the surface tension of the water or solvent used in this invention to disperse natural graphite powder is 30-60 mJ / m. 2 .

[0016] More preferably, the physical stripping method includes any one or more of ultrasonic treatment, focused ultrasonic treatment, high-shear dispersion, and ball milling.

[0017] The above treatment method causes less damage to the crystal lattice of natural graphite, and the resulting graphene has fewer defects, thus maintaining the structure and properties of graphene to the greatest extent.

[0018] More preferably, the intrinsic graphene used in this invention has a bulk density of 0.01-0.03 g / cm³. 3 The thickness is 0.34-5 nm, the sheet diameter is 1-50 μm, and the ratio of the 2D peak to the G peak in the Raman spectrum is I. 2D / I G Greater than 0.5, the ratio of D peak to G peak I D / I G Less than 0.2, oxygen content less than 3 wt%.

[0019] This invention does not strictly limit the physical parameters of intrinsic graphene, but rather uses the actual properties of intrinsic graphene as the standard. Taking the above-mentioned graphene parameter specifications as an example, I 2D / I G A value greater than 0.5 indicates a thin sheet thickness, with an average sheet thickness likely falling between 3 and 5 layers; D / I G A value less than 0.2 indicates that graphene maintains a perfect lattice structure with very few defects. If it is redox graphene, its I... D / I G It is usually greater than 1.

[0020] As a preferred embodiment of this technical solution, step S1 specifically includes: using a mechanical mixing device, placing intrinsic graphene powder and oxide ceramic precursor powder in the mixing device, adding solvent, using the oxide ceramic precursor as the dispersion medium, and uniformly mixing the two using a homogenizing stirrer, planetary ball mill, horizontal ball mill, or a revolution / rotation mixing device, separating the solvent and drying it, so that the intrinsic graphene is coated on the surface of the oxide ceramic precursor powder to obtain a composite precursor.

[0021] During high-speed stirring or rotation, the significant density difference between ceramics and graphene allows the oxide ceramic precursor powder to collide with the intrinsic graphene powder, achieving dispersion. During dispersion, the intrinsic graphene powder adheres to the surface of the oxide ceramic precursor powder. This method not only effectively disperses intrinsic graphene but also enables it to adhere to the surface of the oxide ceramic precursor powder during dispersion.

[0022] More preferably, the intrinsic graphene powder provides a greater molar amount of carbon than the theoretical molar amount of carbon required to completely convert the oxide ceramic precursor into the target nitride or carbide.

[0023] More preferably, the molar ratio of carbon in the intrinsic graphene powder to the target element in the oxide ceramic precursor is between 3:1 and 30:1, ensuring that the intrinsic graphene can completely reduce the metal oxide and that the intrinsic graphene lattice structure is not excessively damaged. The target element is silicon, aluminum, titanium or boron.

[0024] More preferably, the oxide ceramic precursor includes any one or more of alumina, titanium dioxide, silicon dioxide, and boron oxide.

[0025] More preferably, the solvent includes any one or more of ethanol, isopropanol, and acetone. The present invention does not strictly limit the type of solvent, as long as sufficient mixing of the intrinsic graphene powder and the oxide ceramic precursor powder is achieved.

[0026] As a preferred embodiment of this technical solution, step S2 specifically includes: placing the composite precursor into a high-temperature furnace, then placing at least one doped precursor, and introducing a protective gas to prevent high-temperature oxidation. At high temperature, the oxide ceramic precursor is reduced and nitrided or carbonized into the corresponding nitride or carbide ceramic phase, while the intrinsic graphene is doped to obtain a nitride / carbide-doped graphene composite material.

[0027] More preferably, the doped precursor includes any one or more compounds of Group IIIA and Group VA elements.

[0028] More preferably, the doped precursor includes any one or more of urea, melamine, dicyandiamide, and boron oxide.

[0029] These doped precursors can be thermally decomposed before reaching the reduction reaction temperature to form a gas phase doped precursor, which then provides nitrogen or boron atoms to dope the graphene into n-type or p-type graphene.

[0030] Specifically, when the composite precursor formed by intrinsic graphene and oxide ceramic precursor is heated at high temperature, the doped precursor will first thermally decompose into a gaseous phase containing dopant elements such as nitrogen or boron. Upon further heating, carbon atoms in the intrinsic graphene lattice will detach from the graphene lattice and undergo a thermal carbon reduction reaction, taking oxygen atoms from the oxide ceramic precursor to form carbon dioxide. At this time, the nitrogen or boron elements in the doped precursor will fill the carbon atom vacancies in the graphene lattice, causing the graphene to form doped graphene. When the protective gas contains nitrogen, nitrogen molecules will fill the oxygen atom vacancies in the oxide ceramic precursor, causing it to transform into nitrides. When the ambient temperature is higher, the nitrides will further react to generate carbides.

[0031] Taking the combination of alumina and graphene as an example, if urea is used as the doping precursor, alumina can undergo a thermal carbon reduction reaction with carbon atoms in intrinsic graphene at high temperature in a nitrogen-containing atmosphere to form aluminum nitride, as shown in the following reaction formula: Al2O3(s) + N2(g) + 3C(g) ->2AlN(s) + 3CO(g) Therefore, a composite powder of aluminum nitride and nitrogen-doped graphene can be obtained in the end.

[0032] As a preferred embodiment of this technical solution, in step S2, the protective atmosphere is any one or more of the following mixed gases: argon, nitrogen, and ammonia. Specifically, it can be any one of high-purity argon, high-purity nitrogen, ammonia, or a nitrogen / argon mixed atmosphere.

[0033] As a preferred embodiment of this technical solution, in step S2, when the high-temperature reaction is carried out, the reaction temperature is controlled at 1400-1700℃ and the holding time is 0.5-8h.

[0034] Generally, the thermal carbon reduction reaction of nitrides begins at temperatures between 1400-1600℃. When the temperature reaches 1600-1700℃, with sufficient carbon source, further reactions can occur to form carbides. Although the thermal carbon reduction reaction mainly occurs in the high-temperature region above 1400℃, the doped precursor used in this invention begins to gradually thermally decompose during the heating stage of 300℃-600℃. Nitrogen gas, due to its extremely high bond energy (946 kJ / mol), is difficult to directly break chemical bonds and enter the graphene lattice at high temperatures. Furthermore, the solid-state doped precursor decomposes at lower temperatures, releasing highly reactive nitrogen / boron-containing gaseous intermediates, such as NH3, -CN, HCN, or B. x O yDuring the heating process, these active intermediates are pre-adsorbed physically or chemically onto the surface and interlayer of graphene. When the temperature is further increased to the thermal carbon reduction initiation temperature, the graphene lattice begins to release carbon atoms due to the reduction reaction and generates highly active lattice defects. At that moment, the active nitrogen / boron elements adsorbed around it can immediately fill the vacancies left by the carbon atoms with an extremely low activation energy barrier. Compared with simply introducing nitrogen gas, this adsorption-in-situ insertion reaction pathway can significantly increase the doping ratio and promote the formation of specific active sites such as pyridine nitrogen or graphitic nitrogen. This is the key to the excellent technical effect of this invention.

[0035] It is worth noting that in the preparation method of this invention, although graphene provides the carbon source to participate in the thermal carbon reduction reaction of oxide ceramics, the intrinsic graphene will not be completely consumed or severely lose its crystal structure integrity. To achieve this, one of the core features of this invention is the stoichiometric design of the excess carbon source. The number of carbon moles in graphene is designed to be greater than the theoretical number of carbon moles required for the complete reduction of oxide ceramics. This means that only a very small portion of high-energy carbon atoms located at the interface between graphene and oxide ceramic particles and at the edges of graphene sheets will participate in the reduction reaction as sacrificial templates, transforming into carbon monoxide or carbon dioxide and escaping. The vast majority of graphene sp... 2 The framework structure is preserved intact as an excess reactant, forming the final composite material network. Secondly, during the high-temperature reduction process, when carbon atoms at the interface detach from the graphene lattice and combine with oxygen in the oxide ceramic, vacancy defects are left on the graphene lattice. Since the reaction system also contains high concentrations of active nitrogen or boron elements from the doping precursor, these doping elements will quickly enter to fill the newly formed carbon vacancies, performing in-situ repair and forming an in-situ defect repair and doping mechanism. This mechanism not only prevents the graphene structure from disintegrating due to the loss of a large number of carbon atoms, but also utilizes the vacancies generated by the reduction reaction as doping sites, achieving highly efficient lattice substitution doping, thereby obtaining high-quality doped graphene.

[0036] A second aspect of the present invention provides a nitride / carbide-doped graphene composite material prepared using the above method, which should also fall within the scope of protection of the present invention.

[0037] More preferably, doped graphene is coated on the surface of nitride and / or carbide ceramic particles and interconnected with the ceramic phase to form a three-dimensional network structure, and they are connected to each other by doped graphene. Preferably, the doped graphene that has undergone thermal carbon reduction and doping reaction exhibits a Raman spectrum with an intensity ratio of ID to GG. D / I GA value between 0.2 and 0.5 indicates that the intrinsic graphene did not suffer serious damage to the lattice due to the doping reaction, thus not affecting the overall physical properties of the intrinsic graphene.

[0038] A third aspect of this invention provides applications of the aforementioned nitride / carbide-doped graphene composite material in the fields of thermal management, high-strength structural ceramics, and electrochemistry and catalysis, which should also fall within the scope of protection of this invention. Since the composite material of this invention is not a simple physical mixture, but rather a chemically bonded interface formed between the doped graphene and ceramic grains through a high-temperature in-situ reaction, it can significantly reduce interfacial thermal resistance and contact impedance.

[0039] Based on these special structures, the composite material of the present invention has the following multifaceted industrial application value: In the field of thermal management, the nitride / carbide-doped graphene composite material prepared by this invention can be used as a thermally conductive filler for high-end thermal interface materials. Compared with traditional spherical alumina, the composite material of this invention has a three-dimensional thermally conductive graphene network, which can significantly improve the overall thermal conductivity of thermal paste, thermal sheet or semiconductor packaging resin. In addition, the composite material can also be sintered to make a high thermal conductivity ceramic substrate, which can be used for heat dissipation of high power LEDs, IGBT modules or new generation semiconductor packaging, solving the heat dissipation bottleneck of high heat flux components.

[0040] In the field of high-strength structural ceramics, when the nitride / carbide-doped graphene composite material prepared by this invention is applied to structural parts such as silicon carbide or silicon nitride, the doped graphene can form a toughening and reinforcing effect at the ceramic grain boundaries. The pull-out effect and crack deflection mechanism of graphene can effectively improve the fracture strength and bending strength of ceramic materials, making them suitable for high-end applications such as armor, aerospace components, precision mechanical bearings and cutting tools.

[0041] In the field of electrochemistry and catalysis, the introduction of heteroatoms such as nitrogen and boron into this invention disrupts the original electrical neutrality of graphene and creates a large number of active sites, making doped graphene highly suitable for replacing noble metal catalysts such as platinum and palladium. It can be used in the electrodes of metal-air batteries and the oxygen reduction reaction catalysts of fuel cells, thereby reducing the cost of noble metals and promoting the development of the field of chemical catalysis.

[0042] A fourth aspect of the present invention provides a catalytic material comprising the above-described nitride / carbide-doped graphene composite material, said catalytic material having catalytic activity.

[0043] The fifth aspect of the present invention provides a high thermal conductivity composite material or structural ceramic comprising the above-described nitride / carbide-doped graphene composite material.

[0044] The method for preparing the nitride / carbide-doped graphene composite material of the present invention has at least the following beneficial effects: 1. The preparation method of this invention couples the carbothermic reduction function of intrinsic graphene with an in-situ self-doping mechanism, forming a synergistic reaction system of "reduction-doping-composite". Specifically, intrinsic graphene not only acts as a carbothermic reducing agent in the high-temperature reaction, reducing the oxide ceramic precursor and converting it into a nitride or carbide ceramic phase; more importantly, the process of carbon atoms detaching from the graphene lattice to participate in the reduction reaction generates lattice vacancies in situ. These vacancies become "intercalation sites" for active nitrogen, boron, and other heteroatoms released by the thermal decomposition of the doped precursor, achieving a synchronous spatiotemporal matching between carbon atom migration and doped atom migration. This mechanism avoids the necessity of introducing additional defects or pre-oxidation to create doping sites, fundamentally solving the structural damage problem of "destruction first, repair later" in traditional doping methods. Furthermore, in this invention, the interface between graphene and the ceramic phase does not rely on physical adsorption or external adhesives, but rather forms a chemically bonded interface through atomic-level contact and in-situ reaction during carbothermal reduction. This in-situ grown interface structure significantly reduces interface thermal resistance and contact resistance, and the interface bonding strength is far superior to traditional mechanical mixing or liquid phase coating processes.

[0045] 2. This invention uses intrinsic graphene as the starting material, and the reaction process does not involve destructive treatments such as strong acid oxidation, strong alkali etching, or plasma bombardment. The graphene component in the final composite material still maintains a low defect density. Compared to the traditional high-temperature ammonia reduction and oxidation process for graphene, the composite material obtained by this invention has a lower sp0 of graphene. 2 The conjugated structure is more fully preserved, and the carrier mobility and thermal conductivity are significantly improved.

[0046] 3. This invention combines "ceramic precursor reduction" and "graphene doping" into a single high-temperature step, eliminating cumbersome processes such as pre-oxidation, pre-reduction, and post-washing. The resulting composite material possesses excellent thermal conductivity, predictable mechanical properties, and catalytic activity, and can be widely applied in the fields of thermal management, high-strength structural ceramics, and electrochemistry and catalysis. Attached Figure Description

[0047] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0048] Figure 1 The image shows the Raman spectrum of the intrinsic graphene powder prepared in Example 1 of this invention. Figure 2 The XRD pattern of the nitride / carbide-doped graphene composite material obtained in Example 2 of this invention; Figure 3 The Raman spectrum of the nitride / carbide-doped graphene composite material obtained in Example 2 of this invention; Figure 4 The XPS spectrum of the nitride / carbide-doped graphene composite material obtained in Example 2 of this invention; Figure 5 The XRD pattern of the nitride / carbide-doped graphene composite material obtained in Example 3 of this invention; Figure 6 The Raman spectrum of the nitride / carbide-doped graphene composite material obtained in Example 3 of this invention; Figure 7 The XPS spectrum of the nitride / carbide-doped graphene composite material obtained in Example 3 of this invention; Figure 8 The image shows a SEM image of the nitride / carbide-doped graphene composite material obtained in Example 4 of this invention (the right image is a partial enlarged view of the left image). Figure 9 The XRD pattern of the nitride / carbide-doped graphene composite material obtained in Example 4 of this invention; Figure 10 The Raman spectrum of the nitride / carbide-doped graphene composite material obtained in Example 4 of this invention; Figure 11 The image shows the XPS spectrum of the nitride / carbide-doped graphene composite material obtained in Example 4 of this invention. Detailed Implementation

[0049] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0050] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0051] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Example 1 This embodiment provides a method for preparing intrinsic graphene, including the following steps: Take 80-mesh natural graphite powder and place it in N-methylpyrrolidone solvent at a concentration of 1 g / L. Then, place a high-shear dispersion device into the solution for high-shear dispersion and continue the treatment for 72 h. After that, centrifuge at 1000 rpm for 5 min, remove the bottom precipitate, and dry the solution by spray drying to obtain intrinsic graphene powder.

[0053] Figure 1 This is the Raman spectrum of the intrinsic graphene powder obtained in this embodiment, where I D / I G It is 0.154, and I 2D / I G It is 0.508.

[0054] Example 2 This embodiment provides a method for preparing a nitride / carbide-doped graphene composite material, including the following steps: S1. Weigh 25 parts of the intrinsic graphene prepared in Example 1 and 5 parts of silicon dioxide (SiO2), add them to ethanol solvent, mix them in a horizontal ball mill for 4 hours, filter and dry them so that the intrinsic graphene powder is coated on the surface of silicon dioxide to form an intrinsic graphene and silicon dioxide composite precursor. The intrinsic graphene-silica composite precursor was placed in a clean ceramic boat, and 110 parts of urea were placed in another separate clean ceramic boat as a nitrogen source and pore-forming agent.

[0055] S2. Place the ceramic boat containing the composite precursor in the isothermal zone of the tube furnace (or downstream of the gas flow), and place the ceramic boat containing urea at the gas inlet end of the tube furnace (upstream of the gas flow) to ensure that the gaseous products generated by urea pyrolysis can flow with the carrier gas and fully contact the composite precursor. High-purity argon (Ar) is continuously introduced into the tube furnace as a protective gas at a flow rate of 60 mL / min. The tube furnace is heated to 1600℃ at a heating rate of 5℃ / min and held at this temperature for 1 hour. Under high temperature conditions, the active ammonia-containing gas (NH3) generated by urea decomposition can effectively penetrate the graphene lattice to achieve nitrogen doping. Simultaneously, the high temperature promotes the reaction between graphene and silicon dioxide at the interface; both reactions occur simultaneously, ultimately achieving the in-situ synthesis of the nitrogen-doped composite material.

[0056] After naturally cooling to room temperature, the mixture of graphene and silica was taken out and dispersed in 50 mL of deionized water. The mixture was then separated by gravity sedimentation. The upper graphene and the sedimented silica were collected. The separated sample was then placed in a vacuum drying oven and dried to constant weight to obtain a nitride / carbide-doped graphene composite material.

[0057] Figure 2 The XRD pattern of the nitride / carbide-doped graphene composite material obtained in this embodiment is shown below. Figure 3 The Raman spectrum of the nitride / carbide-doped graphene composite material obtained in this embodiment is shown below. Figure 4 The image shows the XPS spectrum of the nitride / carbide-doped graphene composite material obtained in this embodiment.

[0058] Depend on Figure 2-4 It can be seen that the XRD pattern shows sharp and high-intensity diffraction peaks at 2θ = 35.6°, 41.4°, and 60.0°, indicating the formation of trace amounts of SiC. Figure 2 The Raman spectrum showed no obvious SiC peaks and a lower Ig concentration. D / I G The ratio indicates that the graphene matrix maintains a highly ordered sp_structure. 2 Conjugate structure ( Figure 3 As shown in the XPS full-spectrum scan, the characteristic peaks of C, N, Si, and O elements were clearly detected in the full-spectrum scan. Among them, the C 1s peak was significantly intense, indicating that graphene constitutes the conductive framework of the material. The presence of Si 2p and N 1s peaks confirmed that the silicon and nitrogen sources were successfully introduced into the system and chemically bonded at a high temperature of 1600℃. The appearance of Si 2p and N 1s peaks confirmed that the silicon and nitrogen sources were successfully introduced at high temperature and chemically reacted with the carbon substrate. Figure 4 d). The fine 2p spectrum of Si shows the main peak at approximately 100.3 eV, corresponding to the binding energy of the Si-C bond. This indicates that nano-SiO2 underwent a carbothermic reduction reaction with the carbon source at high temperature, resulting in the in-situ formation of the silicon carbide (SiC) phase. Figure 4 c). The unexpected Al-N peak may be due to the carbothermic reduction nitridation reaction that occurs in the alumina ceramic boat at high temperatures. Figure 4 b).

[0059] Example 3 This embodiment provides a method for preparing a nitride / carbide-doped graphene composite material, including the following steps: S1. Weigh 20 parts of the intrinsic graphene prepared in Example 1 and 5 parts of silicon dioxide (SiO2) and add them to isopropanol solvent. Mix them in a horizontal ball mill for 6 hours. After filtration and drying, graphene powder is coated on the surface of silicon dioxide to form an intrinsic graphene and silicon dioxide composite precursor. The intrinsic graphene-silica composite precursor was placed in a clean ceramic boat, and 110 parts of urea were placed in another separate clean ceramic boat as a nitrogen source and pore-forming agent.

[0060] S2. Place the ceramic boat containing the composite precursor in the isothermal zone (or downstream of the gas flow) of the tube furnace, and place the ceramic boat containing urea in the gas inlet (upstream of the gas flow) of the tube furnace to ensure that the gaseous products generated by urea pyrolysis can flow with the carrier gas and fully contact the composite precursor. High-purity argon (Ar) is introduced into the tube furnace as a protective gas throughout the process, with the gas flow rate set at 60 mL / min. The tube furnace is heated to 1600℃ at a heating rate of 5℃ / min, and then heated to 1700℃ at a heating rate of 2℃ / min, and held at this temperature for 4 hours. Under high temperature conditions, the active ammonia-containing gas (NH3) generated by urea cracking can effectively penetrate into the graphene lattice to achieve nitrogen doping. At the same time, the high temperature promotes the reaction between graphene and silicon dioxide at the interface. The two are completed simultaneously, and finally the in-situ synthesis of nitrogen-doped composite materials is achieved. After naturally cooling to room temperature, the mixture of graphene and silica was taken out and dispersed in 50 mL of deionized water. The mixture was then separated by gravity sedimentation. The upper graphene and the sedimented silica were collected. The separated sample was then placed in a vacuum drying oven and dried to constant weight to obtain a nitride / carbide-doped graphene composite material.

[0061] Figure 5 The XRD pattern of the nitride / carbide-doped graphene composite material obtained in this embodiment is shown below. Figure 6 The Raman spectrum of the nitride / carbide-doped graphene composite material obtained in this embodiment is shown below. Figure 7 The image shows the XPS spectrum of the nitride / carbide-doped graphene composite material obtained in this embodiment.

[0062] Depend on Figure 5-7 It can be seen that the XRD pattern shows sharp and high-intensity diffraction peaks at 2θ = 35.6°, 41.4°, 60.0°, 71.8°, and 75.5°, indicating the formation of SiC with very good crystal quality, resulting in a long-range ordered crystal structure. Figure 5 The presence of two distinct small peaks in the low wavenumber region of the Raman spectrum confirms that silicon carbide was indeed grown in situ on the graphene surface. Figure 6 The XPS plot results show that () Figure 7Higher temperatures significantly promoted the growth of silicon carbide crystals, and the Si-C bond characteristic peaks at 1700℃ showed clear spin-orbit splitting Si-C... 2p3 / 2 and Si-C 2p1 / 2 The bimodal structure, with its split peaks, indicates that silicon carbide possesses high crystallinity and an ordered lattice structure. The presence of Al is likely due to the introduction of trace amounts of aluminum into an alumina ceramic boat at specific high temperatures to modulate the interfacial energy.

[0063] Example 4 This embodiment provides a method for preparing a nitride / carbide-doped graphene composite material, including the following steps: S1. Weigh 22 parts of the intrinsic graphene prepared in Example 1 and 5 parts of silicon dioxide (SiO2) and add them to ethanol solvent. Mix them in a horizontal ball mill for 4 hours. After filtration and drying, the intrinsic graphene powder is coated on the surface of silicon dioxide to form an intrinsic graphene and silicon dioxide composite precursor. The intrinsic graphene-silica composite precursor was placed in a clean ceramic boat, and 110 parts of urea were placed in another separate clean ceramic boat as a nitrogen source and pore-forming agent.

[0064] S2. Place the ceramic boat containing the composite precursor in the isothermal zone (or downstream of the gas flow) of the tube furnace, and place the ceramic boat containing urea in the gas inlet (upstream of the gas flow) of the tube furnace to ensure that the gaseous products generated by urea pyrolysis can flow with the carrier gas and fully contact the composite precursor. High-purity nitrogen (N2) is introduced into the tube furnace throughout the process as a protective gas, and the gas flow rate is set to 60 mL / min. The tube furnace is heated to 1600℃ at a heating rate of 5℃ / min, and then heated to 1650℃ at a heating rate of 2℃ / min, and held at this temperature for 2 hours. Under high temperature conditions, the active ammonia-containing gas (NH3) generated by urea cracking can effectively penetrate into the graphene lattice to achieve nitrogen doping. At the same time, the high temperature promotes the reaction between graphene and silicon dioxide at the interface, and the two are completed simultaneously, ultimately realizing the in-situ synthesis of nitrogen-doped composite materials. After naturally cooling to room temperature, the mixture of graphene and silica was taken out and dispersed in 50 mL of deionized water. The mixture was then separated by gravity sedimentation. The upper graphene and the sedimented silica were collected. The separated sample was then placed in a vacuum drying oven and dried to constant weight to obtain a nitride / carbide-doped graphene composite material.

[0065] Figure 8 The image shows a SEM image of the nitride / carbide-doped graphene composite material obtained in this embodiment. Figure 9 The XRD pattern of the nitride / carbide-doped graphene composite material obtained in this embodiment is shown below. Figure 10The Raman spectrum of the nitride / carbide-doped graphene composite material obtained in this embodiment; Figure 11 The image shows the XPS spectrum of the nitride / carbide-doped graphene composite material obtained in this embodiment.

[0066] Depend on Figure 8 It is known that nanorod structures exist in nitride / carbide-doped graphene composites. This is likely because at a high temperature of 1700°C, silicon dioxide and graphene undergo a carbothermic reduction reaction, generating SiC in situ. The graphene sheets provide nucleation sites for SiC growth, forming silicon carbide nanorods. Figure 9 It can be seen that the XRD pattern of the sample treated at 1650°C exhibits an extremely sharp and strong diffraction peak at 2θ≈26.5°, corresponding to the (002) crystal plane of the graphite lattice, indicating that the material has an extremely high degree of graphitization and complete sp. 2 Carbon framework. Notably, a clear, small diffraction peak was observed at 2θ≈35.6°, attributed to the (111) crystal plane of β-SiC. This result indicates that a carbothermal reduction reaction was successfully triggered within the system at a high temperature of 1650°C, achieving in-situ growth of silicon carbide nanophases on a graphene substrate. Figure 10 It can be seen that the extremely sharp and high-intensity G peak in the carbon characteristic region indicates that the high-temperature treatment at 1650°C significantly enhances the sp content of the carbon matrix. 2 Crystallinity and long-range order. It is worth noting that lower I... D / I G The ratio reflects both the excellent degree of graphitization on a macroscopic level and the presence of retained peaks, confirming the successful doping modification of the graphene lattice by nitrogen-containing active species (derived from urea pyrolysis) and the existence of microscopic defects caused by interfacial reactions. Figure 11 As shown, the C 1s fine spectrum shows a C-Si peak (-283 eV), a crucial small peak that proves silicon atoms are firmly anchored (bonded) to the graphene sheets through C-Si covalent bonds. This constitutes a true molecular-level composite / doping. The Si 2p fine spectrum also confirms the successful formation of Si-C and Si-N covalent bonds. It is evident that the SEM microstructure is consistent with the XRD, XPS, and Raman spectroscopy results.

[0067] Example 5 This embodiment provides a method for preparing a nitride / carbide-doped graphene composite material, including the following steps: S1. Weigh 20 parts of the intrinsic graphene prepared in Example 1 and 5 parts of alumina respectively, add them to isopropanol solvent, mix them in a horizontal ball mill for 3 hours, filter and dry to obtain intrinsic graphene powder coated on the surface of alumina, forming an intrinsic graphene and alumina composite precursor. The intrinsic graphene-alumina composite precursor was placed in a clean ceramic boat, while 110 parts of melamine were placed in another separate clean ceramic boat as a nitrogen source and pore-forming agent.

[0068] S2. Place the ceramic boat containing the composite precursor in the isothermal zone (or downstream of the gas flow) of the tube furnace, and place the ceramic boat containing melamine in the gas inlet (upstream of the gas flow) of the tube furnace to ensure that the gaseous products generated by the pyrolysis of melamine can flow with the carrier gas and fully contact the composite precursor. High-purity argon (Ar) is introduced into the tube furnace as a protective gas throughout the process, and the gas flow rate is set to 60 mL / min. The tube furnace is heated to 1600℃ at a heating rate of 5℃ / min and held at this temperature for 4 hours. Under high temperature, the ammonia (NH3) generated by the cracking of melamine can effectively penetrate into the graphene lattice to achieve nitrogen doping. At the same time, the high temperature promotes the reaction between graphene and alumina interface. The two reactions are completed simultaneously, and finally the in-situ synthesis of nitrogen-doped composite materials is achieved. After naturally cooling to room temperature, the mixture of graphene and alumina was removed and dispersed in 50 mL of deionized water. The mixture was then allowed to stand and separate using the principle of gravity sedimentation. The upper graphene layer and the precipitated aluminum nitride were collected. The separated sample was then placed in a vacuum drying oven and dried to constant weight to obtain a nitride / carbide-doped graphene composite material.

[0069] Example 6 This embodiment provides a method for preparing a nitride / carbide-doped graphene composite material, including the following steps: S1. Weigh 25 parts of the intrinsic graphene prepared in Example 1 and 5 parts of titanium dioxide (TiO2) and add them to isopropanol solvent. Mix them in a horizontal ball mill for 4 hours. After filtration and drying, the intrinsic graphene powder is coated on the surface of titanium dioxide to form an intrinsic graphene and titanium dioxide composite precursor. The intrinsic graphene-titanium dioxide composite precursor was placed in a clean ceramic boat, and 110 parts of dicyandiamide were placed in another separate clean ceramic boat as a nitrogen source and pore-forming agent.

[0070] S2. Place the ceramic boat containing the composite precursor in the isothermal zone (or downstream of the gas flow) of the tube furnace, and place the ceramic boat containing dicyandiamide in the gas inlet (upstream of the gas flow) of the tube furnace to ensure that the gaseous products generated by the pyrolysis of dicyandiamide can flow with the carrier gas and fully contact the composite precursor. High-purity argon (Ar) is introduced into the tube furnace as a protective gas throughout the process, and the gas flow rate is set to 60 mL / min. The tube furnace is heated to 1600℃ at a heating rate of 5℃ / min and held at this temperature for 1 hour. Under high temperature, the ammonia (NH3) generated by the cracking of dicyandiamide can effectively penetrate into the graphene lattice to achieve nitrogen doping. At the same time, the high temperature promotes the reaction between graphene and titanium dioxide at the interface. The two are completed simultaneously, and finally the in-situ synthesis of nitrogen-doped composite material is achieved. After naturally cooling to room temperature, the mixture of graphene and titanium dioxide was taken out and dispersed in 50 mL of deionized water. The mixture was then separated by gravity sedimentation. The upper graphene layer and the precipitated titanium nitride were collected. The separated sample was then placed in a vacuum drying oven and dried to constant weight to obtain a nitride / carbide-doped graphene composite material.

[0071] Compare with Example 1 This comparative example is basically the same as Example 2, except that: redox graphene is used instead of the intrinsic graphene of this invention, wherein the Raman spectroscopy of the reduced graphene oxide (rGO) powder is performed. D / I G Approximately 1.3 g / cm³, oxygen content approximately 20 wt%, bulk density approximately 0.02 g / cm³ 3 .

[0072] Compare with Example 2 This comparative example is basically the same as Example 2, except that: a method of first composite sintering and then gas phase doping is adopted, that is, the composite precursor is heated to 1600°C in an argon atmosphere and held for 1 h to allow silicon dioxide to be carbothermally reduced to silicon nitride (at this time, no nitrogen gas is introduced and no doping precursor is added) to obtain Si3N4 / graphene composite material; the Si3N4 / graphene composite material is placed in a tube furnace, ammonia gas is introduced, and it is held at 1650°C for 1 h for gas phase nitrogen doping. After separation and drying, the composite material is obtained.

[0073] Compare with Example 3 This comparative example is basically the same as Example 2, except that: intrinsic graphene and silicon dioxide (SiO2) are mixed and ground at a carbon / silicon molar ratio of 2.5:1 to obtain a composite precursor.

[0074] The thermal conductivity of the composite materials prepared in Examples 2-6 and Comparative Examples 1-3 after mixing with epoxy resin was tested. 30 parts of composite material and 70 parts of epoxy resin were mixed evenly and then pressed into a mold for curing. The thermal conductivity was tested by the hot plate method. The test results are shown in Table 1.

[0075] Table 1 Test Results

[0076] As shown in Table 1, the composite materials prepared in Examples 2-6 of the present invention have excellent thermal conductivity compared to Comparative Examples 1-3.

[0077] In Comparative Example 1, redox graphene (rGO) was used instead of intrinsic graphene. Because rGO itself contains numerous lattice defects and oxygen-containing functional groups, these defects further expand during the high-temperature reaction; simultaneously, the low graphitization degree of rGO severely affects its intrinsic electrical and thermal conductivity. Although this route can achieve nitrogen doping and ceramic conversion, the structural integrity of the graphene component in the resulting composite material is far lower than that of this invention, and both interfacial bonding strength and thermal conductivity are significantly affected. This demonstrates that a low-defect structure in intrinsic graphene is a necessary prerequisite for balancing doping activity and high thermal conductivity.

[0078] Comparative Example 2 employs a method of first composite sintering followed by gas-phase doping. In this method, vacancies for graphene carbon atom migration are generated during the first step of carbothermic reduction, but these vacancies are immediately reconstructed by neighboring carbon atoms. However, during gas-phase doping, the active nitrogen atoms from ammonia decomposition mainly adsorb onto edge defects on the graphene surface and have difficulty entering vacancies within the crystal lattice. Therefore, the resulting product exhibits reduced thermal conductivity due to low doping levels and uneven distribution.

[0079] In Comparative Example 3, the molar ratio of carbon to the target element silicon was reduced to 2.5:1. Under this condition, the carbon provided by graphene was insufficient to completely reduce silicon dioxide to silicon nitride, and a large amount of residual oxide phase was present in the product. At the same time, due to excessive consumption of graphene, almost no graphene coating layer remained after the reaction, the doped graphene network no longer existed, and the composite material degenerated into a non-target product that was "mainly ceramic with insufficient carbon residue", which led to a serious decrease in thermal conductivity.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a nitride / carbide-doped graphene composite material, characterized in that, Includes the following steps: S1. Mix intrinsic graphene powder with powder of at least one oxide ceramic precursor, so that the intrinsic graphene powder coats the surface of the oxide ceramic precursor powder to form a composite precursor. S2. The composite precursor and at least one doped precursor are placed in a high-temperature reaction apparatus and reacted at high temperature under a protective atmosphere to reduce and nitride or carbide the oxide ceramic precursor into the corresponding nitride or carbide ceramic phase, while the intrinsic graphene is doped to obtain a nitride / carbide-doped graphene composite material.

2. The method for preparing the nitride / carbide-doped graphene composite material according to claim 1, characterized in that, In step S1, the intrinsic graphene is prepared by physical exfoliation. Preferably, the physical exfoliation method includes any one or more of ultrasonic treatment, focused ultrasonic treatment, high-shear dispersion, and ball milling; Preferably, the intrinsic graphene has a bulk density of 0.01-0.03 g / cm³. 3 The thickness is 0.34-5 nm, the sheet diameter is 1-50 μm, and the ratio of the 2D peak to the G peak in the Raman spectrum is I. 2D / I G Greater than 0.5, the ratio of D peak to G peak I D / I G Less than 0.2, oxygen content less than 3 wt%.

3. The method for preparing the nitride / carbide-doped graphene composite material according to claim 1, characterized in that, In step S1, the molar amount of carbon provided by the intrinsic graphene powder is greater than the theoretical molar amount of carbon required to completely convert the oxide ceramic precursor into the target nitride or carbide. Preferably, the molar ratio of carbon in the intrinsic graphene powder to the target element in the oxide ceramic precursor is between 3:1 and 30:1, wherein the target element is silicon, aluminum, titanium or boron. Preferably, the oxide ceramic precursor includes any one or more of alumina, titanium dioxide, silicon dioxide, and boron oxide.

4. The method for preparing the nitride / carbide-doped graphene composite material according to claim 1, characterized in that, In step S1, the mixing method includes one or more of ball milling, horizontal ball milling, and planetary mixing (revolution / rotation). Preferably, the mixing is carried out in the presence of a solvent.

5. The method for preparing the nitride / carbide-doped graphene composite material according to claim 1, characterized in that, In step S2, the doped precursor includes any one or more compounds of Group IIIA and Group VA elements; Preferably, the doped precursor includes any one or more of urea, melamine, dicyandiamide, and boron oxide.

6. The method for preparing the nitride / carbide-doped graphene composite material according to claim 1, characterized in that, In step S2, the protective atmosphere is any one or a mixture of argon, nitrogen, and ammonia.

7. The method for preparing the nitride / carbide-doped graphene composite material according to claim 1, characterized in that, In step S2, during the high-temperature reaction, the reaction temperature is controlled at 1400-1700℃, and the holding time is 0.5-8h.

8. A nitride / carbide-doped graphene composite material, characterized in that, The nitride / carbide-doped graphene composite material was prepared according to any one of claims 1-7. Preferably, doped graphene is coated on the surface of nitride and / or carbide ceramic particles and interconnected with the ceramic phase to form a three-dimensional network structure, with doped graphene serving as the connection between them.

9. The nitride / carbide-doped graphene composite material according to claim 8, characterized in that, In the Raman spectrum of the graphene doped in the nitride / carbide-doped graphene composite material, the intensity ratio of the D peak to the G peak is I. D / I G Between 0.2 and 0.

5.

10. The application of the nitride / carbide-doped graphene composite material according to any one of claims 8-9 in the field of thermal management.

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