A method for preparing coal-based carbon nanometer onion

Abstract

The application discloses a preparation method of coal-based carbon nano-onions, which is prepared by taking coal powder as a carbon source and water-soluble iron salt as a catalyst, adding the coal powder into a nitric acid solution, heating and refluxing to obtain acid-oxidized coal powder, uniformly mixing the acid-oxidized coal powder with the catalyst, and performing in-situ high-temperature pyrolysis catalysis reaction in a tube furnace under an inert atmosphere to obtain a mixture of coal-based CNOs and hollow coal-based CNOs with metal particles. The coal-based carbon nano-onions prepared by the method can be used as a supercapacitor negative material conductive additive and applied to the preparation of supercapacitors.

Description

Technical Field

[0001] This invention belongs to the field of nano-carbon functional materials technology, and relates to the preparation of coal-based nano-carbon materials, particularly a method for preparing coal-based carbon nano-onions. Background Technology

[0002] As the most abundant and widely distributed fossil fuel on Earth, coal and its derivatives, with an annual production of tens of billions of tons, are mainly used as energy sources with low economic efficiency. Therefore, there is an urgent need for in-depth research and development on the conversion and clean utilization of coal, which will also contribute to the sustainable development of resources, environment, and economy in coal mining areas (Cai T, Liu B, Pang E, et al. A review on the preparation and applications of coal-based fluorescent carbon dots[J]. New Carbon Materials , 2020, 35(6): 646-666.).

[0003] Against the backdrop of carbon emission reduction and carbon peaking, the research and development of coal-based carbon nanomaterials is of great significance for broadening the non-combustion, high-value-added utilization pathways of coal and promoting the application of coal from traditional fossil fuels to nanomaterials in energy, information, and biomedicine. Coal contains abundant nanocrystalline carbon domains linked by aliphatic amorphous carbon and polymeric aromatic hydrocarbons, possessing inherent advantages for the large-scale preparation of carbon nanomaterials. Therefore, coal and its derivatives have become an economical and ideal carbon source for the mass production of various carbon nanomaterials.

[0004] Carbon nano-onions (CNOs) are a successor to C 60 Following carbon nanotubes (CNTs) and graphene, fullerenes are another member of the fullerene family. Since the large-scale preparation of CNTs began in 1992... 60 Since then, the various properties of CNOs have gradually attracted the attention of scholars at home and abroad. Initially, the focus was mainly on the controllable preparation of bilayer and trilayer structures and their size effect properties (Gustavo Costa, John K, McDonough, et al. Thermo-chemistry of onion-like carbons[J]. Carbon , 2014, 69: 490-494.).

[0005] Among various forms of carbon nanotubes (CNOs), hollow CNOs play an important role in electronic materials applications due to their low density, large specific surface area, good stability, and good surface wetting properties. Their unique alternating five- and six-membered ring bonds and structure, along with good biocompatibility, make them suitable for drug delivery. Furthermore, their quasi-spherical or spherical nanostructures allow them to be embedded in matrices as composite materials for reinforcing and toughening materials, lubricants, environmental sensors, and biosensors, among many other applications (Barthelmess J, Giordani S. Carbon nano-onions (multi-layer fullerenes): chemistry and applications [J]). Beilstein J. Nanotechnol , 2014, 5: 1980-1998.).

[0006] Furthermore, CNOs containing magnetic metal particles exhibit superior magnetic properties compared to pure magnetic metal particles, and have broad application prospects in magnetic storage materials, electrostatic copying, optical and magnetic recording materials, bioimaging, and biochemical technologies (Gao Y, Zhou YS, et al. Chemical activation of carbon nano-onions for high-rate supercapacitor electrodes[J]. Carbon , 2013, 51: 52-58.).

[0007] Coal has a high carbon content and is rich in amorphous carbon composed of aliphatic hydrocarbons and crystalline carbon domains formed by polymerized aromatic hydrocarbons. Furthermore, its molecular structure shares natural similarities with carbon nanomaterials. Therefore, using coal as a precursor for the industrial production of carbon nanotubes (CNOs) is of guiding significance. Currently, various coal-based CNOs, including hollow and metal-encased types, have been synthesized based on coal and its derivatives.

[0008] Liu Xuguang et al. (Fu DJ, Liu XG, Lin X, et al. Synthesis of encapsulating and hollow onion-like fullerenes from coal[J]. Journal of Materials Science(2007, 42(11): 3805-3809.) Microwave plasma and radio frequency plasma were used to study the preparation of CNOs from different coal types by changing process parameters. The results showed that the properties of the coal were closely related to the yield of CNOs. The higher the carbon content and the lower the ash content of the coal, the higher the yield of CNOs. Other elements in the raw coal had little effect on the yield. However, this method of synthesizing CNOs has problems such as complex experimental equipment, high cost, complex preparation process, and low yield, which cannot meet the requirements of large-scale industrial production.

[0009] Qiu JS, Li YF, Wang YP, et al. Preparation of carbon-coated magnetic iron nanoparticles from composite rods made from coal and iron powders[J]. Fuel Processing Technology (2004, 86(3): 267-274.) Using a coal-based carbon rod prepared by mixing anthracite and iron in a 1:1 ratio as the anode and a graphite rod as the cathode, and high-purity helium as the buffer medium, Fe-coated CNOs were prepared by arc discharge, with a particle size between 25-60 nm. However, this method involves very intense discharge, which generates a certain amount of amorphous carbon spheres. The preparation process has many uncontrollable factors and consumes a huge amount of energy, which is not conducive to industrial production. Summary of the Invention

[0010] The purpose of this invention is to provide a method for preparing coal-based carbon nanotube onions suitable for industrial-scale mass production, so as to prepare coal-based CNOs in a low-cost and high-yield manner.

[0011] The method for preparing coal-based carbon nanotube onions according to the present invention uses coal powder as a carbon source and water-soluble iron salt as a catalyst. The coal powder is added to a 30-40 wt% nitric acid solution and heated under reflux to obtain acid-oxidized coal powder. The coal powder is then mixed evenly with the catalyst and subjected to a high-temperature pyrolysis catalytic reaction in situ under an inert atmosphere in a tube furnace to synthesize coal-based CNOs.

[0012] In the preparation method of coal-based carbon nanoparticle onion of the present invention, the reaction temperature of the high-temperature pyrolysis catalytic reaction should be maintained at 1500-2000℃, and the reaction time should be not less than 0.5h.

[0013] Furthermore, the reaction time is 30–120 min.

[0014] Specifically, in the preparation method of the present invention, the coal powder used as the carbon source is mainly coking coal or anthracite.

[0015] More specifically, the present invention involves pulverizing the primary coking coal or anthracite into coal powder of 200 mesh or less for use.

[0016] In the preparation method of coal-based carbon nano-onion described in this invention, the purpose of acid oxidation treatment of coal powder is to remove ash and impurities such as S and Si, while opening the bridging bonds between polymeric aromatic hydrocarbons and aliphatic amorphous carbon, thereby improving the reactivity of coal.

[0017] Specifically, the coal powder is heated and refluxed in a nitric acid solution at 50-70°C for 10-12 hours.

[0018] Furthermore, the present invention can also be applied to coal powder that has been pretreated with hydrochloric acid and then subjected to acid oxidation treatment by heating and reflux with nitric acid solution.

[0019] Specifically, the hydrochloric acid pretreatment involves placing coal powder in a 5 mol / L hydrochloric acid solution and heating it in a water bath at 50–70°C for 40–80 minutes.

[0020] Furthermore, in this invention, the acid-oxidized coal powder is thoroughly washed until neutral and dried before undergoing a subsequent high-temperature pyrolysis catalytic reaction.

[0021] More specifically, in the preparation method of coal-based carbon nano-onion of the present invention, the water-soluble iron salt used as catalyst is preferably ferric nitrate or ferric chloride.

[0022] Furthermore, in the preparation method of the present invention, the mass ratio of coal powder to water-soluble iron salt is 0.5 to 6:1.

[0023] Furthermore, the preferred mass ratio of the pulverized coal to the water-soluble iron salt is 3 to 5:1.

[0024] Furthermore, in the preparation method described in this invention, it is preferable to use a raw material premixing treatment method, in which acid-oxidized coal powder and water-soluble iron salt are mixed and dispersed evenly in anhydrous ethanol, the ethanol is removed, and the mixture is dried and pulverized to obtain the mixture.

[0025] Specifically, the preparation method of the present invention involves first heating a tube furnace to 1200-1400°C at a rate of 5-10°C / min, then heating it to 1600-2000°C at a rate of 2-5°C / min, and holding it at that temperature for 30-120 min to carry out a high-temperature pyrolysis catalytic reaction.

[0026] After the reaction was completed and cooled to room temperature, the reaction products were collected, yielding a mixture of coal-based CNOs containing metal particles and hollow coal-based CNOs.

[0027] This invention uses inexpensive and widely available coal as a carbon source and employs a thermocatalytic method to synthesize coal-based CNOs in situ. It has the advantages of simple process, low production cost, and easy industrial-scale mass production.

[0028] The coal-based carbon nanotube onion preparation method provided by this invention can promote the transformation of coal from a traditional fossil fuel to a nanomaterial, applicable to the fields of energy conversion and storage. The high-yield internally encapsulated metal particles and hollow coal-based CNOs prepared using coal as a carbon source possess excellent electromagnetic properties, electrical conductivity, and superior thermal and chemical stability, making them novel carbon nanomaterials for electronic components, sensors, electrode materials, and energy storage materials, thus showing promising application prospects in many fields such as sensing and electrochemical energy storage.

[0029] In particular, the coal-based carbon nanotube onion material prepared by this invention can be used as a conductive additive for the negative electrode material of supercapacitors and applied in the preparation of supercapacitors. Attached Figure Description

[0030] Figure 1 This is a high-resolution transmission electron microscope (HRTEM) image of the coal-based CNOs solid powder material prepared in Example 1.

[0031] Figure 2 This is a high-resolution transmission electron microscope (HRTEM) image of the coal-based CNOs solid powder material prepared in Example 2.

[0032] Figure 3 This is a high-resolution transmission electron microscope (HRTEM) image of the coal-based CNOs solid powder material prepared in Example 3.

[0033] Figure 4 This is a high-resolution transmission electron microscope (HRTEM) image of the coal-based CNOs solid powder material prepared in Example 4.

[0034] Figure 5 These are high-resolution transmission electron microscopy (HRTEM) images of carbon nanoparticle solid powder materials prepared in Comparative Examples 1 and 2.

[0035] Figure 6 These are scanning electron microscope (SEM) images of the solid powder materials prepared in Examples 1-3 and Comparative Examples 1 and 2.

[0036] Figure 7 These are X-ray diffraction (XRD) patterns of the solid powder materials prepared in Examples 1-3 and Comparative Examples 1 and 2.

[0037] Figure 8 These are the Raman spectra of the coal-based CNOs solid powder materials prepared in Examples 1-3. Implementation

[0038] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, so that those skilled in the art can better understand and utilize the present invention, and are not intended to limit the scope of protection of the present invention.

[0039] Unless otherwise specified, the production processes, experimental methods, or testing methods involved in the embodiments and comparative examples of this invention are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the art, which are very clear and distinct in the relevant application fields. Those skilled in the art can understand the conventional process steps based on the names and apply the corresponding equipment to implement them according to conventional conditions or conditions recommended by the manufacturer.

[0040] The various instruments, equipment, raw materials or reagents used in the embodiments of this invention are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels and can be prepared according to conventional methods known to those skilled in the art. Example

[0041] Example 1.

[0042] Weigh 10g of 200-mesh prime coking coal powder and add it to 50ml of 5mol / L hydrochloric acid solution. Stir thoroughly to completely wet the powder, heat in a water bath at 60℃ for 60min, and filter. Then slowly add 100ml of 30% concentrated nitric acid and heat in a water bath at 60℃ under reflux for 12h, and filter. Wash with distilled water until pH=7, and dry in a forced-air drying oven for 5-6h to obtain acid-oxidized prime coking coal powder.

[0043] Weigh 1.000g of acid-oxidized coking coal powder and 0.500g of Fe(NO3)3·9H2O into a 100mL beaker, add 20mL of anhydrous ethanol, seal with a sealing film, place on an ultrasonic disperser, and ultrasonically disperse at a frequency of 60kHz for 30min to obtain a mixed solution.

[0044] The mixed solution was placed in a constant temperature magnetic stirrer and heated in an 80°C water bath to evaporate the ethanol until it became a paste. It was then dried in a forced-air drying oven for 12 hours, removed, ground, and transferred to a crucible.

[0045] The crucible was placed in a tube furnace, and argon gas was introduced as a protective gas to completely purge the air from the tube furnace. The temperature was then increased to 1300°C at a rate of 10°C / min, and then increased to 1600°C at a rate of 5°C / min. The temperature was held for 90 minutes to carry out high-temperature pyrolysis catalysis.

[0046] After cooling to room temperature at the same rate, the product in the crucible was collected, yielding a mixture of coal-based CNOs containing metal particles and hollow coal-based CNOs. Its morphology was observed under a high-resolution transmission electron microscope as follows: Figure 1 As shown.

[0047] Example 2.

[0048] Weigh 1.000g of the acid-oxidized prime coking coal powder from Example 1 and 0.250g of Fe(NO3)3·9H2O into a 100mL beaker, add 20mL of anhydrous ethanol, seal with a sealing film, place on an ultrasonic disperser, and ultrasonically disperse at a frequency of 60kHz for 45min to obtain a mixed solution.

[0049] The mixed solution was placed in a constant temperature magnetic stirrer and heated in a 78°C water bath to evaporate the ethanol until it became a paste. It was then dried in a forced-air drying oven for 12 hours, removed, ground, and transferred to a crucible.

[0050] The crucible was placed in a tube furnace, and argon gas was introduced as a protective gas to completely purge the air from the tube furnace. The temperature was then increased to 1400℃ at a rate of 10℃ / min, and then increased to 1600℃ at a rate of 4℃ / min. The temperature was held for 60 minutes to carry out high-temperature pyrolysis catalysis.

[0051] After cooling to room temperature at the same rate, the product in the crucible was collected, yielding a mixture of coal-based CNOs containing metal particles and hollow coal-based CNOs. Its morphology was observed under a high-resolution transmission electron microscope as follows: Figure 2 As shown.

[0052] Example 3.

[0053] Weigh 1.000g of the acid-oxidized coking coal powder from Example 1 and 0.200g of Fe(NO3)3·9H2O into a 100mL beaker, add 20mL of anhydrous ethanol, seal with a sealing film, place on an ultrasonic disperser, and ultrasonically disperse at a frequency of 60kHz for 60min to obtain a mixed solution.

[0054] The mixed solution was placed in a constant temperature magnetic stirrer and heated in an 80°C water bath to evaporate the ethanol until it became a paste. It was then dried in a forced-air drying oven for 12 hours. After being removed, it was ground into powder and transferred to a crucible.

[0055] The crucible was placed in a tube furnace, and argon gas was introduced as a protective gas to completely purge the air from the tube furnace. The temperature was then increased to 1400°C at a rate of 10°C / min, and then increased to 1800°C at a rate of 5°C / min. The temperature was held for 30 minutes to carry out high-temperature pyrolysis catalysis.

[0056] After cooling to room temperature at the same rate, the product in the crucible was collected, yielding a mixture of coal-based CNOs containing metal particles and hollow coal-based CNOs. Its morphology was observed under a high-resolution transmission electron microscope as follows: Figure 3 As shown.

[0057] Example 4.

[0058] Weigh 10g of 200-mesh prime coking coal powder, add 100ml of 30% concentrated nitric acid, stir thoroughly until completely wetted, heat in a 60℃ water bath under reflux for 12h, filter; wash with distilled water until pH=7, and dry in a forced-air drying oven for 5-6h to obtain acid-oxidized prime coking coal powder.

[0059] Weigh 1.000g of acid-oxidized coking coal powder and 0.250g of Fe(NO3)3·9H2O into a 100mL beaker, add 20mL of anhydrous ethanol, seal with a sealing film, place on an ultrasonic disperser, and ultrasonically disperse at a frequency of 60kHz for 30min to obtain a mixed solution.

[0060] The mixed solution was placed in a constant temperature magnetic stirrer and heated in an 80°C water bath to evaporate the ethanol until it became a paste. It was then dried in a forced-air drying oven for 12 hours, removed, ground, and transferred to a crucible.

[0061] The crucible was placed in a tube furnace, and argon gas was introduced as a protective gas to completely purge the air from the tube furnace. The temperature was then increased to 1400°C at a rate of 10°C / min, and then increased to 1700°C at a rate of 5°C / min. The temperature was held for 60 minutes to carry out high-temperature pyrolysis catalysis.

[0062] After cooling to room temperature at the same rate, the product in the crucible was collected, yielding a mixture of coal-based CNOs containing metal particles and hollow coal-based CNOs. Its morphology was observed under a high-resolution transmission electron microscope as follows: Figure 4 As shown.

[0063] Example 5.

[0064] Weigh 10g of 200-mesh anthracite powder and add it to 50ml of 5mol / L hydrochloric acid solution. Stir thoroughly to completely wet the powder, heat in a water bath at 60℃ for 60min, and filter. Then slowly add 100ml of 30% concentrated nitric acid, heat in a water bath at 60℃ under reflux for 12h, and filter. Wash with distilled water until pH=7, and dry in a forced-air drying oven for 5-6h to obtain acid-oxidized anthracite powder.

[0065] Weigh 1.000g of acid-oxidized anthracite powder and 0.250g of Fe(NO3)3·9H2O into a 100mL beaker, add 20mL of anhydrous ethanol, seal with a sealing film, place on an ultrasonic disperser, and ultrasonically disperse at a frequency of 60kHz for 30min to obtain a mixed solution.

[0066] The mixed solution was placed in a constant temperature magnetic stirrer and heated in an 80°C water bath to evaporate the ethanol until it became a paste. It was then dried in a forced-air drying oven for 12 hours, removed, ground, and transferred to a crucible.

[0067] The crucible was placed in a tube furnace, and argon gas was introduced as a protective gas to completely purge the air from the tube furnace. The temperature was then increased to 1400℃ at a rate of 10℃ / min, and then increased to 1700℃ at a rate of 5℃ / min. The temperature was held for 90 minutes to carry out high-temperature pyrolysis catalysis.

[0068] After cooling to room temperature at the same rate, the product in the crucible was collected to obtain a mixture of coal-based CNOs containing metal particles and hollow coal-based CNOs.

[0069] Example 6.

[0070] Weigh 10g of 200-mesh anthracite powder, add 100ml of 30% concentrated nitric acid, stir thoroughly until completely wetted, heat in a 60℃ water bath under reflux for 12h, filter; wash with distilled water until pH=7, and dry in a forced-air drying oven for 5-6h to obtain acid-oxidized anthracite powder.

[0071] Weigh 1.000g of acid-oxidized anthracite powder and 0.167g of FeCl3·6H2O into a 100mL beaker, add 20mL of anhydrous ethanol, seal with a sealing film, place on an ultrasonic disperser, and ultrasonically disperse at a frequency of 60kHz for 30min to obtain a mixed solution.

[0072] The mixed solution was placed in a constant temperature magnetic stirrer and heated in an 80°C water bath to evaporate the ethanol until it became a paste. It was then dried in a forced-air drying oven for 12 hours, removed, ground, and transferred to a crucible.

[0073] The crucible was placed in a tube furnace, and argon gas was introduced as a protective gas to completely purge the air from the tube furnace. The temperature was then increased to 1400°C at a rate of 10°C / min, and then increased to 1700°C at a rate of 5°C / min. The temperature was held for 60 minutes to carry out high-temperature pyrolysis catalysis.

[0074] After cooling to room temperature at the same rate, the product in the crucible was collected to obtain a mixture of coal-based CNOs containing metal particles and hollow coal-based CNOs.

[0075] Comparative Example 1.

[0076] Weigh 1.000g of the acid-oxidized prime coking coal powder from Example 1, add 20mL of anhydrous ethanol without adding any catalyst, seal with a sealing film, place on an ultrasonic disperser, and ultrasonically disperse at a frequency of 60kHz for 30min to obtain a mixed solution.

[0077] The mixed solution was placed in a constant temperature magnetic stirrer and heated in an 80°C water bath to evaporate the ethanol until it became a paste. It was then dried in a forced-air drying oven for 12 hours, removed, ground, and transferred to a crucible.

[0078] The crucible was placed in a tube furnace, and argon gas was introduced as a protective gas to completely purge the air from the tube furnace. The temperature was then increased to 1300°C at a rate of 10°C / min, and then increased to 1600°C at a rate of 5°C / min. The temperature was held for 90 minutes to carry out high-temperature pyrolysis catalysis.

[0079] After cooling to room temperature at the same rate, the product in the crucible was collected to obtain carbon nanomaterials composed of graphitic carbon and amorphous carbon.

[0080] Comparative Example 2.

[0081] Weigh 1.000g of untreated coking coal powder and 0.250g of Fe(NO3)3·9H2O into a 100mL beaker, add 20mL of anhydrous ethanol, seal with a sealing film, place on an ultrasonic disperser, and ultrasonically disperse at 60kHz for 30min to obtain a mixed solution.

[0082] The mixed solution was placed in a constant temperature magnetic stirrer and heated in an 80°C water bath to evaporate the ethanol until it became a paste. It was then dried in a forced-air drying oven for 12 hours. After being removed, it was ground into powder and transferred to a crucible.

[0083] The crucible was placed in a tube furnace, and argon gas was introduced as a protective gas to completely purge the air from the furnace. The furnace was heated to 1400°C at a rate of 10°C / min, and then to 1600°C at a rate of 5°C / min. The temperature was held for 60 min for high-temperature pyrolysis catalysis. The furnace was then cooled to room temperature at the same rate, and the product in the crucible was collected to obtain carbon nanomaterials composed of carbon nanotubes and amorphous carbon.

[0084] A small amount of the products collected in Examples 1-4 and Comparative Examples 1 and 2 were ultrasonically dispersed in ethanol to obtain a suspension. The suspension was then dropped onto a copper grid for transmission electron microscopy, dried, and its morphology was observed using a high-resolution transmission electron microscope. The results are as follows: Figures 1-5 As shown.

[0085] in, Figures 1-4 TEM images of coal-based CNOs solid powder materials prepared in Examples 1-4 are given respectively; Figure 5 (a, b) are TEM images of carbon nanoparticle solid powder materials prepared in Comparative Example 1, and (c, d) are TEM images of carbon nanoparticle solid powder materials prepared in Comparative Example 2.

[0086] from Figures 1-4 It can be seen that the products prepared in Examples 1-4 are spherical or quasi-spherical encapsulated metal CNOs with a core-shell structure: the interior consists of metal nanoparticles encapsulated by a carbon shell, and the particle size is relatively uniform. Figure 1 and Figure 3It can be seen that the product also contains some hollow CNOs, indicating that the encapsulated metal particles have "escaped". The particle size of the CNOs ranges from 20 to 70 nm.

[0087] And from Figure 5 TEM images of the carbon nanotube solid powder materials prepared in Comparative Examples 1 and 2 show that the products exhibit amorphous and strip-like shapes, with irregular and disordered forms. This indicates that the product of Comparative Example 1 is a mixture of graphitic carbon and amorphous carbon, while the product of Comparative Example 2 is a mixture of carbon nanotubes and amorphous carbon.

[0088] and then, Figure 6 SEM images of coal-based CNOs solid powder materials prepared in Examples 1, 2, and 3 are shown in (a, b, and c). The images show that most of the CNOs are spherical or near-spherical, with a small amount of carbon nanotubes present. Figure 6 In the middle (d, e), there are SEM images of carbon nanoparticle solid powder materials prepared in comparative examples 1 and 2. It can be seen from the images that they exhibit a lamellar and tubular structure, which is different from the spherical or quasi-spherical structure of CNOs.

[0089] The above results demonstrate that acid oxidation treatment of coal powder and the addition of catalysts are essential in the process of synthesizing coal-based CNOs solid powder materials.

[0090] Figure 7 Furthermore, XRD spectra of coal-based CNOs solid powder materials prepared in Examples 1, 2, and 3, and carbon nanoparticle solid powder materials prepared in Comparative Examples 1 and 2 are provided.

[0091] As can be seen from the figure, the CNOs prepared in Examples 1, 2, and 3 exhibit a set of strong diffraction peaks at 2θ = 26.2°, corresponding to the (002) crystal plane of graphitic carbon. The high intensity and sharp peak shape of the diffraction peaks indicate that the products have a high degree of graphitization and good crystallinity. The diffraction peak appearing at approximately 2θ = 43.2° corresponds to the (100) crystal plane of C; the diffraction peaks appearing at approximately 2θ = 44.6°, 64.9°, and 82.2° correspond to the (110), (200), and (211) crystal planes of α-Fe; and the diffraction peaks appearing at approximately 2θ = 35.0° and 57.3° correspond to the (311) and (511) crystal planes of Fe3O4.

[0092] In the products prepared in Comparative Examples 1 and 2, the diffraction peaks corresponding to the C(002) crystal plane have a large half-width, relatively low peak intensity, and contain a lot of impurity peaks, indicating that the graphitization degree of the products is relatively low and the crystallinity is poor. Combined with the analysis of SEM and TEM spectra, it is shown that there are almost no coal-based CNOs in the products of coal powder without acid oxidation treatment and without the addition of catalyst for high-temperature pyrolysis reaction.

[0093] Figure 8Raman spectra of coal-based CNOs solid powder materials prepared in Examples 1, 2, and 3 are given. The figures show that the D peak and G peak are located at 1398 cm⁻¹. −1 Left and right sides and 1586cm −1 The locations represent the vibrations at the edges of graphite crystals and graphitic carbon crystals, respectively, and also represent sp... 3 Hybrid bonds and sp 2 Hybridized bonds. The figure shows that the G peak is higher than the D peak, and I... G / I D The values ​​are 1.9, 2.1, and 2.0, respectively, indicating that the CNOs materials prepared by the three methods have a high degree of graphitization, very little amorphous carbon, and few defects.

[0094] The above embodiments of the present invention do not describe all details exhaustively, nor do they limit the present invention to the embodiments described above. Various changes, modifications, substitutions, and variations made by those skilled in the art to these embodiments without departing from the principles and spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing coal-based carbon nanoparticles of onion, comprising using coking coal or anthracite pulverized coal as a carbon source and water-soluble iron salt as a catalyst, wherein the pulverized coal is added to a 30-40 wt% nitric acid solution and heated under reflux to obtain acid-oxidized pulverized coal, which is then mixed uniformly with the catalyst and subjected to a high-temperature pyrolysis catalytic reaction in situ at 1500-2000℃ in an inert atmosphere in a tube furnace for no less than 0.5 h to synthesize coal-based carbon nanoparticles of onion, wherein the mass ratio of pulverized coal to water-soluble iron salt is 0.5-6:

1.

2. The method for preparing coal-based carbon nanoparticles of onion according to claim 1, characterized in that: The mass ratio of the pulverized coal to the water-soluble iron salt is 3 to 5:

1.

3. The method for preparing coal-based carbon nanoparticles of onion according to claim 1, characterized in that: The water-soluble iron salt is ferric nitrate or ferric chloride.

4. The method for preparing coal-based carbon nanoparticles of onion according to claim 1, characterized in that: The reaction time is 30–120 min.

5. The method for preparing coal-based carbon nanoparticles of onion according to claim 1, characterized in that: The pulverized coal is heated and refluxed in a nitric acid solution at 50-70°C for 10-12 hours.

6. The method for preparing coal-based carbon nanoparticles of onion according to claim 1, characterized in that: It also includes pretreating the coal powder with hydrochloric acid before acid oxidation treatment, placing the coal powder in a 5 mol / L hydrochloric acid solution and heating it in a water bath at 50-70°C for 40-80 minutes.

7. The method for preparing coal-based carbon nanoparticles of onion according to claim 1, characterized in that: The acid-oxidized coal powder and water-soluble iron salt were mixed and dispersed evenly in anhydrous ethanol, the ethanol was removed, and the mixture was dried and pulverized to obtain the final mixture.

8. The coal-based carbon nanoparticle onion prepared according to the preparation method of claim 1 is a mixture of coal-based carbon nanoparticle onion with encapsulated metal particles and hollow coal-based carbon nanoparticle onion.

9. The application of the coal-based carbon nanoparticles of claim 8 as a conductive additive for the negative electrode material of a supercapacitor in the preparation of a supercapacitor.

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