Carbon-coated nickel composite material and method for preparing the same

Abstract

Provided are a method for preparing a carbon-coated nickel nanocomposite, comprising the following steps: S1, forming a nitrogen-free organic carboxylic acid coordination Ni ion compound as a precursor; and S2, pyrolyzing the precursor under an inert atmosphere or a reducing atmosphere. Also provided is the carbon-coated nickel nanocomposite prepared by the method. The precursor is directly prepared from one or more of Ni(OH)2, NiO, NiCO3 and basic nickel carbonate and a nitrogen-free organic carboxylic acid in an aqueous solution, and the atomic utilization rate of the precursor Ni can reach 100%. The preparation process does not need to use dicyandiamide, melamine and other ligands which are prone to sublimation or decomposition and are prone to generate carbon nanotube-like substances, which are commonly used in traditional methods; and the method overcomes the defects of the prior art, such as the need to use a high-temperature and high-pressure reaction kettle for self-assembly, the large waste of organic solvents and the complicated purification steps. The carbon-coated nickel nanocomposite has a complete structure, good dispersity and uniform size, and has a wide application prospect in the fields of electrocatalysis, wave-absorbing materials, lubricating oil additives, synthesis of chemical products and the like.

Description

Technical Field

[0001] This invention belongs to the field of carbon-coated metal composite material preparation and application, specifically relating to an oxygen-doped carbon-coated nickel nanocomposite material, its preparation method and application. Background Technology

[0002] Nickel nanoparticles have attracted widespread attention due to their excellent optical, electrical, and magnetic properties. However, their high reactivity makes them prone to aggregation, oxidation, and even combustion in air, significantly impacting their performance and applications. Meanwhile, as a non-metallic material, carbon nanoparticles possess advantages such as resistance to acid and alkali corrosion and chemical stability. In recent years, with the surge in research and progress in carbon nanoparticle materials, carbon nanoparticle-coated metal composites have become a research hotspot in carbon nanoparticle-metal composites. These materials consist of a core of metal nanoparticles tightly encased in a shell of single to several layers of curved graphite sheets, physically isolating the nanoparticles from the external environment and greatly improving the stability of the composite material. Furthermore, related studies have shown that the core metal layer and the surface carbon layer of these materials exhibit electronic interactions, demonstrating excellent performance in certain catalytic reactions. Therefore, this unique core-shell structured nanomaterial has broad application prospects in electrocatalysis, microwave absorbing materials, and lubricant additives.

[0003] Currently, methods for carbon-coated metal nanoparticles mainly include the electric arc method, chemical vapor deposition (CVD), and high-temperature pyrolysis. Among these, the electric arc method requires complex equipment, has poor operability, and high energy consumption, making it unsuitable for large-scale material preparation. Compared to the electric arc method, the CVD method has lower cost and higher yield, but its challenge lies in the need to first prepare uniformly sized and well-dispersed metal nanoparticles or their compounds, and the subsequent products often contain carbon nanotubes and amorphous carbon particles. Similar to the CVD method, the structure and properties of the pyrolysis product are significantly influenced by the precursor material. However, the pyrolysis method has advantages such as simple process, low cost, high yield, and controllable metal content, making it one of the most promising methods for large-scale preparation.

[0004] Pyrolysis methods can be broadly classified into two categories. The first category involves directly mixing a carbon source (usually dicyandiamine, melamine, etc.) and a metal source, then subjecting the mixture to high-temperature pyrolysis under an inert or reducing atmosphere. However, carbon sources like dicyandiamine and melamine decompose easily at high temperatures and exhibit weak interaction with metal particles when directly mixed, resulting in low ligand utilization and low carbonization yield. Furthermore, cyanamides, as carbon and nitrogen sources, readily promote the formation of carbon nanotubes. The second category involves first connecting metal ions and organic ligands via self-assembly under specific reaction conditions to form a metal-organic framework compound as a precursor. The preparation of such precursors typically requires the use of organic solvents and high-temperature, high-pressure reactions in a reactor. For example, Chinese patent CN1055965009A discloses a method using aspartic acid and 4,4'-bipyridine as ligands, and methanol and water as solvents, to react with Ni under high-temperature, high-pressure conditions. 2+ A method for preparing carbon-coated nickel nanoparticles was proposed, involving coordination preparation of precursors and high-temperature pyrolysis under an inert atmosphere. An et al. (DOI:10.1039 / c6ta02339h, Mesoporous Ni@C hybrids for a high energy aqueous asymmetric supercapacitor device, Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A) used iminodiacetic acid as the carbon source and Ni(NO3)2 as the metal source to prepare self-packed precursors under high temperature and high pressure conditions, and further prepared carbon-coated nickel nanoparticles by high-temperature pyrolysis under an Ar atmosphere.

[0005] It is easy to see that these two types of pyrolysis methods each have their own advantages and disadvantages. Therefore, combining the advantages of the two types of pyrolysis methods to achieve the preparation of organometallic coordination precursors in pure aqueous phase under normal pressure and the subsequent high-temperature pyrolysis preparation of related carbon-coated metal nanocomposites is of great significance for further promoting the application of composite materials. Summary of the Invention

[0006] The purpose of this invention is to provide an oxygen-doped carbon-coated nickel core-shell structured nanomaterial and its simple, green, and efficient preparation method.

[0007] The present invention provides a carbon-coated nickel nanocomposite material, comprising carbon-coated nickel nanoparticles, wherein the carbon-coated nickel nanoparticles are composed of a nickel nanoparticle core and a graphitized carbon layer shell covering the surface of the nickel nanoparticles; the graphitized carbon layer is only oxygen-doped, and the composite material has two distribution peaks with mesopore sizes of 3-4 nm and 6-8 nm.

[0008] According to one embodiment of the present invention, the proportion of the intermediate pore volume of the composite material to the total pore volume is greater than 90%, preferably greater than 95%.

[0009] According to another embodiment of the invention, the content of Ni is 5-85%, the content of C is 14-94%, the content of O is 0.3-5%, and the content of H is 0.1-1.5% based on the total mass of the composite material. Preferably, the content of Ni is 10-80%, the content of C is 20-89%, the content of O is 0.5-3%, and the content of H is 0.1-1.0%.

[0010] According to another embodiment of the present invention, the nickel nanoparticles have a face-centered cubic structure.

[0011] According to another embodiment of the present invention, the pickling loss rate of the composite material is less than 45%, preferably less than 20%, and more preferably less than 1%.

[0012] Another aspect of the present invention provides a method for preparing the above-mentioned carbon-coated nickel nanocomposite material, comprising the following steps: S1, heating and stirring one or more of Ni(OH)2, NiO, NiCO3 and basic nickel carbonate with a nitrogen-free organic carboxylic acid in water to form a homogeneous solution, and then removing the water to form a precursor; S2, pyrolyzing the precursor at high temperature under an inert atmosphere or a reducing atmosphere.

[0013] According to one embodiment of the present invention, the nitrogen-free organic carboxylic acid is one or more of citric acid, maleic acid, fumaric acid, succinic acid, tartaric acid, malic acid, gluconic acid, and pyromellitic acid.

[0014] According to another embodiment of the present invention, Ni in the homogeneous solution 2+ The molar ratio of the group to the carboxyl group is 1:2 to 20, and the heating and stirring temperature is 30 to 150℃.

[0015] According to another embodiment of the present invention, in step S2, the inert atmosphere is nitrogen or argon, the high-temperature pyrolysis is heated to the isothermal zone at a rate of 0.5-30℃ / min, the isothermal zone is maintained for 20-600min, and the isothermal zone temperature is 400-800℃.

[0016] According to another embodiment of the present invention, it further includes: S3, purifying the product obtained in step S2 in an acidic solution to remove the incompletely coated Ni core.

[0017] According to another embodiment of the present invention, the acidic solution in step S3 is one or more aqueous solutions of hydrochloric acid, sulfuric acid and hydrofluoric acid, with a concentration of 0.1 to 3 mol / L.

[0018] This invention provides a high-temperature pyrolysis precursor prepared directly from one or more of Ni(OH)₂, NiO, NiCO₃, and basic nickel carbonate in an aqueous solution with a nitrogen-free organic carboxylic acid. The atom utilization rate of the Ni precursor can reach 100%. The preparation process eliminates the need for ligands commonly used in traditional methods, such as dicyandiamine and melamine, which are prone to sublimation or decomposition and easily generate carbon nanotubes. It also overcomes the drawbacks of existing technologies for preparing metal-organic framework precursors, which require high-temperature, high-pressure reactors for self-assembly, resulting in significant waste of organic solvents and cumbersome purification steps. Furthermore, by utilizing coordinated, nitrogen-free organic carboxylic acid ligands as reducing agents, carbon sources, and oxygen sources during the high-temperature pyrolysis process, there is no need to introduce flammable gases such as H₂, CH₄, or C₂H₄. The carbon-coated nickel nanocomposite material prepared by this invention exhibits a complete structure, good dispersibility, and uniform size, showing broad application prospects in electrocatalysis, microwave absorbing materials, lubricant additives, and chemical synthesis. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0020] Figure 1 This is a thermogravimetric-differential thermal analysis (TG-DTA) curve of the precursor material prepared in Example 1.

[0021] Figure 2 This is the XRD pattern of the carbon-coated nickel nanocomposite material prepared in Example 1.

[0022] Figure 3 This is an XPS image of the carbon-coated nickel nanocomposite material prepared in Example 1.

[0023] Figure 4A This is the N2 adsorption-desorption isotherm curve of the carbon-coated nickel nanocomposite material prepared in Example 1.

[0024] Figure 4B This is a pore size distribution diagram of the carbon-coated nickel nanocomposite material prepared in Example 1.

[0025] Figure 5 This is a TEM image of the carbon-coated nickel nanocomposite material prepared in Example 2.

[0026] Figure 6A This is the N2 adsorption-desorption isotherm curve of the carbon-coated nickel nanocomposite material prepared in Example 2.

[0027] Figure 6B This is a pore size distribution diagram of the carbon-coated nickel nanocomposite material prepared in Example 2.

[0028] Figure 7 This is the XRD pattern of the carbon-coated nickel nanocomposite material prepared in Example 3.

[0029] Figure 8 This is an XPS image of the carbon-coated nickel nanocomposite material prepared in Example 3.

[0030] Figure 9 This is the XRD pattern of the carbon-coated nickel nanocomposite material prepared in Example 4.

[0031] Figure 10A This is the N2 adsorption-desorption isotherm curve of the carbon-coated nickel nanocomposite material prepared in Example 4.

[0032] Figure 10B This is a pore size distribution diagram of the carbon-coated nickel nanocomposite material prepared in Example 4.

[0033] Figure 11 This is the XRD pattern of the carbon-coated nickel nanocomposite material prepared in Example 5.

[0034] Figure 12 This is a TEM image of the carbon-coated nickel nanocomposite material prepared in Example 5. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustration and explanation only, and are not intended to limit the present invention in any way.

[0036] In this invention, the term "core-shell structure" refers to a core composed of nickel nanoparticles and a shell of oxygen-doped graphitized carbon layers. The "graphitized carbon layer" refers to a layered carbon structure that is clearly observable under a high-resolution transmission electron microscope, rather than an amorphous structure, with an interlayer spacing of approximately 0.34 nm.

[0037] The term "mesopore" is defined as a pore with a diameter in the range of 2–50 nm. Pores with a diameter less than 2 nm are defined as micropores, and pores with a diameter greater than 50 nm are defined as macropores.

[0038] The term "oxygen doping" refers to oxygen element, and the "oxygen content" of the nanocomposite material refers to the content of oxygen element. Specifically, it means that during the preparation of carbon-coated nanocomposite materials, the graphitized carbon layer formed contains oxygen element in various forms, and the "oxygen content" is the total content of all forms of oxygen element.

[0039] The term "mesopore distribution peak" refers to the mesopore distribution peak on the pore distribution curve obtained by calculating the desorption curve according to the Barrett-Joyner-Halenda (BJH) method.

[0040] The term "acid pickling loss rate" refers to the proportion of transition metal lost after acid pickling of a prepared carbon-coated transition metal nanocomposite product. It reflects the tightness of the graphitized carbon layer's coating of the transition metal. If the graphitized carbon layer's coating of the transition metal is not tight, the transition metal in the core will be dissolved and lost by the acid after acid treatment. A higher acid pickling loss rate indicates a lower tightness of the graphitized carbon layer's coating of the transition metal, and a lower acid pickling loss rate indicates a higher tightness of the graphitized carbon layer's coating of the transition metal.

[0041] The "pickling loss rate" is measured and calculated as follows:

[0042] Add 1 g of sample to 20 mL of sulfuric acid aqueous solution (1 mol / L), treat the sample at 90 °C for 8 h, then wash with deionized water until neutral, dry, weigh, and analyze, and calculate the acid washing loss rate according to the following formula.

[0043] Pickling loss rate = [1 - (mass fraction of transition metal in the composite material after pickling × mass of the composite material after pickling) ÷ (mass fraction of transition metal in the composite material to be pickled × mass of the composite material to be pickled)] × 100%. A carbon-coated nickel nanocomposite material of the present invention comprises carbon-coated nickel nanoparticles, wherein the carbon-coated nickel nanoparticles consist of a nickel nanoparticle core and a graphitized carbon layer shell encapsulating the surface of the nickel nanoparticles; the graphitized carbon layer is only oxygen-doped, and the composite material has two distribution peaks for mesopore sizes of 3-4 nm and 6-8 nm.

[0044] In this process, the proportion of mesopore volume in the total pore volume of the composite material is greater than 90%, preferably greater than 95%.

[0045] Based on the total mass of the composite material, the Ni content is 5-85%, the C content is 14-94%, the O content is 0.3-5%, and the H content is 0.1-1.5%. Preferably, based on the total mass of the composite material, the Ni content is 10-80%, the C content is 20-89%, the O content is 0.5-3%, and the H content is 0.1-1.0%.

[0046] Among them, nickel nanoparticles have a face-centered cubic structure.

[0047] The pickling loss rate of the composite material is less than 45%, preferably less than 20%, and more preferably less than 1%.

[0048] The carbon-coated nickel nanocomposite material of the present invention can be prepared by the following method, including the following steps: S1, one or more of Ni(OH)2, NiO, NiCO3 and basic nickel carbonate are heated and stirred in water with a nitrogen-free organic carboxylic acid to form a homogeneous solution, and then the water is removed to form a precursor; S2, the precursor is pyrolyzed at high temperature under an inert atmosphere or a reducing atmosphere.

[0049] In step S1, the precursor can be prepared by the following steps: One or more of Ni(OH)₂, NiO, NiCO₃, and basic nickel carbonate, along with one or more of maleic acid, fumaric acid, succinic acid, tartaric acid, malic acid, gluconic acid, and pyromellitic acid, are heated and stirred in water to form a homogeneous solution. The water is then removed to form the precursor. Ni in the homogeneous solution... 2+ The molar ratio of the group to the carboxyl group is 1:2 to 20, and the heating and stirring temperature is 30 to 150℃.

[0050] In step S2, the inert atmosphere is nitrogen or argon. The high-temperature pyrolysis is carried out at a rate of 0.5-30℃ / min to reach the isothermal zone. The isothermal zone is maintained for 20-600 min, and the isothermal zone temperature is 400-900℃.

[0051] The method of the present invention may further include: S3, purifying the product obtained in step S2 in an acidic solution to remove the incompletely coated Ni core.

[0052] In step S3, the acidic solution is an aqueous solution of a non-oxidizing acid, such as one or more of hydrochloric acid, sulfuric acid, and hydrofluoric acid, with a concentration of 0.1–3 mol / L.

[0053] Preparation of carbon-coated nickel nanocomposites

[0054] Example 1

[0055] Weigh 10 mmol NiCO3 and 10 mmol citric acid and add them to 150 mL of deionized water. Stir at 70 °C to obtain a homogeneous solution and continue heating to evaporate to dryness. Grind the solid to obtain the precursor.

[0056] The obtained precursor was placed in a ceramic boat, which was then placed in the constant temperature zone of a tube furnace. Nitrogen gas was introduced at a flow rate of 100 mL / min, and the temperature was increased to 450°C at a rate of 5°C / min. After holding the temperature for 1 hour, the heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain the composite material.

[0057] The obtained composite material was added to 60 mL of 1 mol / L HCl solution, stirred and refluxed at 85 °C for 4 h, the solution was filtered, washed with deionized water until neutral, and the powder was dried in an oven at 100 °C for 2 h to obtain the purified composite material.

[0058] Example 2

[0059] Weigh 10 mmol Ni(OH)2 and 10 mmol citric acid and add them to 150 mL of deionized water. Stir at 80 °C to obtain a homogeneous solution and continue heating to evaporate to dryness. Grind the solid to obtain the precursor.

[0060] The obtained precursor was placed in a ceramic boat, which was then placed in the isothermal zone of a tube furnace. Nitrogen gas was introduced at a flow rate of 150 mL / min, and the temperature was increased to 575 °C at a rate of 2.5 °C / min. After holding at this temperature for 2 hours, the heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain the composite material.

[0061] The obtained composite material was added to 50 mL of 1 mol / L H2SO4 solution, stirred and refluxed at 90 °C for 4 h, the solution was filtered, washed with deionized water until neutral, and the powder was dried in an oven at 100 °C for 2 h to obtain the purified composite material.

[0062] Example 3

[0063] Weigh 10 mmol Ni(OH)2, 5 mmol citric acid, 1 mmol pyromellitic acid and 4 mmol malic acid and add them to 150 mL deionized water. Stir at 95 °C to obtain a homogeneous solution and continue heating to evaporate to dryness. Grind the solid to obtain the precursor.

[0064] The obtained precursor was placed in a ceramic boat, and then the ceramic boat was placed in the constant temperature zone of a tube furnace. Nitrogen gas was introduced at a flow rate of 100 mL / min, and the temperature was increased to 600℃ at a rate of 2.5℃ / min. After holding at this temperature for 2 hours, the heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain the composite material.

[0065] The obtained composite material was added to 50 mL of 1 mol / L H2SO4 solution, stirred and refluxed at 80 °C for 6 h, the solution was filtered, washed with deionized water until neutral, and the powder was dried in an oven at 100 °C for 2 h to obtain the purified composite material.

[0066] Example 4

[0067] Weigh 10 mmol Ni(OH)2 and 15 mmol citric acid and add them to 150 mL of deionized water. Stir at 90 °C to obtain a homogeneous solution and continue heating to evaporate to dryness. Grind the solid to obtain the precursor.

[0068] The obtained precursor was placed in a ceramic boat, which was then placed in the constant temperature zone of a tube furnace. Nitrogen gas was introduced at a flow rate of 100 mL / min, and the temperature was increased to 700 °C at a rate of 5 °C / min. After holding the temperature for 3 hours, the heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain the composite material.

[0069] The obtained composite material was added to 70 mL of 0.5 mol / L H2SO4 solution, stirred and refluxed at 90 °C for 6 h, the solution was filtered, washed with deionized water until neutral, and the powder was dried in an oven at 100 °C for 2 h to obtain the purified composite material.

[0070] Example 5

[0071] Weigh 10 mmol Ni(OH)2 and 50 mmol citric acid, add them to 100 mL of deionized water, stir at 80 °C to obtain a homogeneous solution, and continue heating to evaporate to dryness. Grind the solid to obtain the precursor.

[0072] The obtained precursor was placed in a ceramic boat, and then the ceramic boat was placed in the constant temperature zone of a tube furnace. Nitrogen gas was introduced at a flow rate of 80 mL / min, and the temperature was increased to 750℃ at a rate of 2.5℃ / min. After holding at this temperature for 1 hour, the heating was stopped, and the mixture was cooled to room temperature under a nitrogen atmosphere to obtain the composite material.

[0073] The obtained composite material was added to 60 mL of 1 mol / L HCl solution, stirred and refluxed at 90 °C for 6 h, the solution was filtered, washed with deionized water until neutral, and the powder was dried in an oven at 100 °C for 2 h to obtain the purified composite material.

[0074] Performance Characterization

[0075] XRD is used to obtain information such as the composition of materials and the structure or morphology of atoms or molecules inside the materials. The XRD diffractometer used is an XRD-6000 X-ray powder diffractometer (Shimadzu, Japan). The XRD test conditions are: Cu target, Kα rays (wavelength λ = 0.154 nm), tube voltage of 40 kV, tube current of 200 mA, and scanning speed of 10° (2θ) / min.

[0076] The surface morphology of the material was characterized using high-resolution transmission electron microscopy (HRTEM). The HRTEM used was a JEM-2100 (Nippon Electron Ltd.), and the testing conditions were: accelerating voltage of 200 kV. The particle size of the nanoparticles in the sample was measured using HRTEM images.

[0077] The elemental composition of the material surface was determined using X-ray photoelectron spectroscopy (XPS). The XPS used was a VG Scientific ESCALab220i-XL model equipped with Avantage V5.926 software. The XPS analysis conditions were as follows: monochromatic AlKα X-ray excitation source, power 330 W, and a base vacuum of 3 × 10⁻⁶. -9 mbar.

[0078] The pore structure properties of the material were determined using the BET test method. Specifically, a Quantachrome AS-6B analyzer was used for measurement. The specific surface area of ​​the catalyst was obtained by the Brunauer-Emmett-Taller (BET) method, and the pore distribution curve was calculated from the desorption curve using the Barrett-Joyner-Halenda (BJH) method.

[0079] Carbon, hydrogen, and oxygen elemental analysis was performed using an Elementar Micro Cube elemental analyzer. The specific operating procedures and conditions were as follows: 1-2 mg of sample was weighed and placed in a tin cup, then placed in the autosampler tray. The sample entered the combustion tube through a ball valve and was burned at 1000℃ (helium was used for purging to remove atmospheric interference during sample introduction). The resulting carbon dioxide and water were separated by three desorption columns and then detected sequentially by a thermal conductivity detector (TCD). Oxygen analysis utilized high-temperature decomposition; under the action of a carbon catalyst, oxygen in the sample was converted to CO, which was then detected by a TCD.

[0080] The metal element content is the normalized result after deducting the carbon, hydrogen, and oxygen content of the material.

[0081] Figure 1 This is a thermogravimetric-differential thermal analysis (TG-DTA) curve of the precursor material prepared in Example 1. From... Figure 1 It can be seen that the precursor exhibits two distinct endothermic peaks during the heating process. The endothermic peak at 366℃ corresponds to the high-temperature pyrolysis and carbonization of the precursor and the Ni... 2+ The process of reducing it to elemental Ni. Furthermore, the precursor's mass remains relatively stable after 400℃. Figure 2 This is the XRD pattern of the carbon-coated nickel nanocomposite material prepared in Example 1. From... Figure 2 The diffraction peaks of the carbon material and fcc-Ni can be observed. According to the Scherrer equation, the average particle size of the Ni nanoparticles is 8.6 nm. Figure 3 This is the XPS image of the carbon-coated nickel nanocomposite material prepared in Example 1. The electron binding energy peaks of C, O, and Ni are clearly visible. Figure 4A This is the N2 adsorption-desorption isotherm curve of the carbon-coated nickel nanocomposite material prepared in Example 1. Figure 4B This is a pore size distribution diagram of the carbon-coated nickel nanocomposite material prepared in Example 1. From... Figure 4A It can be seen that this material exhibits a significant hysteresis loop between p / p0 = 0.4 and 1.0. From... Figure 4B It can be seen that the pore size distribution of this material exhibits two peaks at diameters of 3.5 nm and 6.9 nm. The specific surface area of ​​this nanocomposite material is 301 m². 2 / g, pore volume is 0.453cm³ 3 / g, of which mesoporous volume accounts for 100% of the total pore volume. Elemental analysis determined the nanomaterial's C content to be 39.80%, H content to be 1.01%, O content to be 2.50%, and normalized Ni content to be 56.69%. Measured and calculated according to the methods described in the terminology section, the acid washing loss rate of the composite material before purification in this example was 43%, while the acid washing loss rate of the purified material was less than 1%. Based on the methods described in the terminology section, further increasing the acid washing time did not significantly change the acid washing loss rate.

[0082] Figure 5 This is a TEM image of the carbon-coated nickel nanocomposite material prepared in Example 2. From... Figure 5 (a) It can be seen that the nanoparticles are uniform in size and well dispersed. From Figure 5 (b) It can be seen that the outer layer of the nickel nanoparticles is coated with a carbon layer with a certain degree of graphitization, forming a complete core-shell structure. In addition, according to the Scherrer equation, the average particle size of the Ni nanoparticles is 8.4 nm. Figure 6A This is the N2 adsorption-desorption isotherm curve of the carbon-coated nickel nanocomposite material prepared in Example 2. Figure 6B This is a pore size distribution diagram of the carbon-coated nickel nanocomposite material prepared in Example 2. From... Figure 6A It can be seen that this material exhibits a significant hysteresis loop between p / p0 = 0.4 and 1.0. From... Figure 6B It can be seen that the pore size distribution of this material exhibits two peaks at diameters of 3.3 nm and 6.3 nm. The specific surface area of ​​this nanocomposite material is 168 m². 2 / g, pore volume is 0.246cm³ 3 / g, of which mesoporous volume accounts for 100% of the total pore volume. Elemental analysis determined the nanomaterial's C content to be 28.60%, H content to be 0.40%, O content to be 1.94%, and normalized Ni content to be 69.06%. Measured and calculated according to the methods described in the terminology section, the acid washing loss rate of the composite material before purification in this example was 16%, while the acid washing loss rate of the purified material was less than 1%. Based on the methods described in the terminology section, further increasing the acid washing time did not significantly change the acid washing loss rate.

[0083] Figure 7 This is the XRD pattern of the carbon-coated nickel nanocomposite material prepared in Example 3. (Compared to...) Figure 2 Similarly, from Figure 7 The diffraction peaks of carbon materials and fcc-Ni can be observed. According to the Scherrer equation, the average particle size of Ni nanoparticles is 8.3 nm. Figure 8This is the XPS plot of the carbon-coated nickel nanocomposite material prepared in Example 3. The electron binding energy peaks of C, O, and Ni are clearly visible. Elemental analysis determined the nanomaterial's C content to be 23.51%, H content to be 0.54%, O content to be 1.66%, and the normalized Ni content to be 74.29%. Furthermore, BET analysis showed that the specific surface area of ​​this nanocomposite material is 154 m². 2 / g, pore volume is 0.240cm³ 3 / g, wherein the mesoporous volume accounts for 100% of the total pore volume. Measured and calculated according to the method described in the terminology section, the acid washing loss rate of the composite material before purification obtained in this embodiment is 13%, and the acid washing loss rate of the purified material is less than 1%. Based on the method described in the terminology section, further increasing the acid washing time does not significantly change the acid washing loss rate.

[0084] Figure 9 This is the XRD pattern of the carbon-coated nickel nanocomposite material prepared in Example 4. (Compared to...) Figure 2 Similarly, from Figure 9 The diffraction peaks of the carbon material and the fcc-Ni material can be observed. According to the Scherrer equation, the average particle size of the Ni nanoparticles is 8.8 nm. Figure 10A This is the N2 adsorption-desorption isotherm curve of the carbon-coated nickel nanocomposite material prepared in Example 4. Figure 10B This is a pore size distribution diagram of the carbon-coated nickel nanocomposite material prepared in Example 4. From... Figure 10A It can be seen that this material exhibits a significant hysteresis loop between p / p0 = 0.4 and 1.0. From... Figure 10B It can be seen that the pore size distribution of this material exhibits two peaks at diameters of 3.9 nm and 6.3 nm. The specific surface area of ​​this nanocomposite material is 172 m². 2 / g, pore volume is 0.270cm³ 3 / g, of which mesoporous volume accounts for 100% of the total pore volume. Elemental analysis determined the nanomaterial's C content to be 32.48%, H content to be 0.41%, O content to be 1.01%, and normalized Ni content to be 66.10%. Measured and calculated according to the methods described in the terminology section, the acid washing loss rate of the composite material before purification in this example was 17%, while the acid washing loss rate of the purified material was less than 1%. Based on the methods described in the terminology section, further increasing the acid washing time did not significantly change the acid washing loss rate.

[0085] Figure 11 This is the XRD pattern of the carbon-coated nickel nanocomposite material prepared in Example 5. (Compared to...) Figure 2 Similarly, from Figure 11 The diffraction peaks of the carbon material and the fcc-Ni material can be observed. According to the Scherrer equation, the average particle size of the Ni nanoparticles is 8.5 nm. Figure 12This is a TEM image of the carbon-coated nickel nanocomposite material prepared in Example 5. From... Figure 12 The nickel nanoparticles are coated with a graphitized carbon layer, and some incompletely coated nickel nanoparticles have been removed by acid washing, leaving behind empty graphitic carbon shells. BET testing shows that the specific surface area of ​​this nanocomposite material is 386 m². 2 / g, pore volume is 0.441cm³ 3 / g, of which mesoporous volume accounts for 100% of the total pore volume. Elemental analysis determined the nanomaterial's C content to be 61.27%, H content to be 0.58%, O content to be 0.94%, and normalized Ni content to be 37.21%. Measured and calculated according to the methods described in the terminology section, the acid washing loss rate of the composite material before purification in this example was 44%, while the acid washing loss rate of the purified material was less than 1%. Based on the methods described in the terminology section, further increasing the acid washing time did not significantly change the acid washing loss rate.

[0086] This invention provides a high-temperature pyrolysis precursor directly prepared by reacting one or more of Ni(OH)₂, NiO, and NiCO₃ with a nitrogen-free organic carboxylic acid in an aqueous solution. The atom utilization rate of Ni in the precursor can reach 100%. The preparation process eliminates the need for ligands commonly used in traditional methods, such as dicyandiamine and melamine, which are prone to sublimation or decomposition and easily generate carbon nanotubes. It also overcomes the drawbacks of existing technologies for preparing metal-organic framework precursors, which require high-temperature, high-pressure reactors for self-assembly, resulting in significant waste of organic solvents and cumbersome purification steps. Furthermore, by utilizing coordinated, nitrogen-free organic carboxylic acid ligands as reducing agents, carbon sources, and oxygen sources during the high-temperature pyrolysis process, there is no need to introduce flammable gases such as H₂, CH₄, or C₂H₄. The carbon-coated nickel nanocomposite material prepared by this invention exhibits a complete structure, good dispersibility, and uniform size, showing broad application prospects in electrocatalysis, microwave absorbing materials, lubricant additives, and chemical synthesis.

[0087] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A carbon-coated nickel nanocomposite material, comprising carbon-coated nickel nanoparticles, wherein the carbon-coated nickel nanoparticles consist of a nickel nanoparticle core and a graphitized carbon layer shell encapsulating the surface of the nickel nanoparticles; the graphitized carbon layer is only oxygen-doped, and the composite material has two distribution peaks with mesopore sizes of 3-4 nm and 6-8 nm, the acid pickling loss rate of the composite material is less than 45%, wherein, based on the total mass of the composite material, the content of Ni is 10-80%, the content of C is 20-89%, the content of O is 0.5-3%, and the content of H is 0.1-1.0%.

2. The carbon-coated nickel nanocomposite material according to claim 1, wherein the proportion of mesopore volume to total pore volume in the composite material is greater than 90%.

3. The carbon-coated nickel nanocomposite material according to claim 2, wherein the proportion of mesopore volume to total pore volume in the composite material is greater than 95%.

4. The carbon-coated nickel nanocomposite material according to claim 1, wherein, based on the total mass of the composite material, the Ni content is 5-85%, the C content is 14-94%, the O content is 0.3-5%, and the H content is 0.1-1.5%.

5. The carbon-coated nickel nanocomposite material according to claim 4, wherein the nickel nanoparticles have a face-centered cubic structure.

6. The carbon-coated nickel nanocomposite material according to claim 1, wherein the acid pickling loss rate of the composite material is less than 20%.

7. The carbon-coated nickel nanocomposite material according to claim 6, wherein the acid pickling loss rate of the composite material is less than 1%.

8. A method for preparing the carbon-coated nickel nanocomposite material according to any one of claims 1 to 7, comprising the following steps: S1, one or more of Ni(OH)2, NiO, NiCO3 and basic nickel carbonate are heated and stirred in water with a nitrogen-free organic carboxylic acid to form a homogeneous solution, and then the water is removed to form a precursor; S2, the precursor is pyrolyzed at high temperature under an inert or reducing atmosphere.

9. The preparation method according to claim 8, wherein the nitrogen-free organic carboxylic acid is one or more selected from citric acid, maleic acid, fumaric acid, succinic acid, tartaric acid, malic acid, gluconic acid and pyromellitic acid.

10. The preparation method according to claim 8, wherein the homogeneous solution contains Ni 2+ The molar ratio of the group to the carboxyl group is 1:2 to 20, and the heating and stirring temperature is 30 to 150℃.

11. The preparation method according to claim 8, wherein in step S2, the inert atmosphere is nitrogen or argon, the high-temperature pyrolysis is heated to the isothermal zone at a rate of 0.5-30℃ / min, the isothermal zone is maintained for 20-600min, and the isothermal zone temperature is 400-800℃.

12. The preparation method according to claim 8, further comprising: S3, purify the product obtained in step S2 in an acidic solution to remove the incompletely coated Ni core.

13. The method according to claim 12, wherein the acidic solution in step S3 is one or more aqueous solutions of hydrochloric acid, sulfuric acid and hydrofluoric acid, with a concentration of 0.1 to 3 mol / L.

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