Few-layer structure coal-based graphene and preparation method thereof

Abstract

This invention discloses a few-layer coal-based graphene and its preparation method. The preparation method includes the following steps: (1) grinding coal raw material and acid washing to obtain impurity-free coal raw material; (2) mixing the impurity-free coal raw material with a swelling agent and heating under reflux to swell it, to obtain a coal swelling product; (3) ultrasonically treating the coal swelling product to remove the solvent and obtain a coal dissociation product; (4) calcining the coal dissociation product to obtain coal-based graphene. This invention innovatively uses a physical exfoliation method to obtain a free coal-based aromatic conjugated sheet structure, utilizing the molecular structure advantages of coal itself, and directly calcining it without catalyst doping to significantly improve the aromaticity of the material itself, thus obtaining a few-layer coal-based graphene with an aromatic conjugated sheet structure.

Description

Technical Field

[0001] This invention belongs to the field of high-value application technology of coal, specifically relating to a few-layer structure coal-based graphene and its preparation method. Background Technology

[0002] Coal is the world's most abundant and widely used primary energy source, and an indispensable part of global energy consumption. Utilizing high-value coal is an essential development direction for achieving clean and efficient coal utilization. Therefore, actively developing non-energy utilization and high-value-added deep processing of coal has received close attention and high importance from all sectors.

[0003] Existing technologies include methods such as oxidizing coal with strong oxidants and then reducing it to obtain coal-based graphene; and introducing catalysts and treating the coal raw material at high temperatures to significantly increase the graphitization degree, followed by adding strong oxidants and thermal reduction to obtain coal-based graphene. While these methods promise to provide direction for large-scale production of coal-based graphene, the introduction of catalysts and stringent graphitization conditions increase production costs, and the use of strong oxidants severely damages the chemical structure of the coal itself.

[0004] Therefore, if coal in its aggregated state can be dissociated into a free state while maintaining its chemical structure, the structural advantages of coal itself can be greatly utilized and it can be applied to high-value applications. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a few-layer structure coal-based graphene and its preparation method, thus solving the problems mentioned in the background art.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for preparing coal-based graphene with few-layer structure, comprising the following steps:

[0007] (1) Grind the coal raw material and acid wash it to obtain impurity-free coal raw material;

[0008] (2) The impurity-removed coal raw material is mixed with a swelling agent and heated under reflux to swell, thereby obtaining a coal swelling product;

[0009] (3) The coal swelling product is subjected to ultrasonic treatment to remove the solvent and obtain the coal dissociation product;

[0010] (4) The coal dissociation products are calcined to obtain coal-based graphene.

[0011] In a preferred embodiment of the present invention, in step (1), the coal raw material includes anthracite, lignite, or bituminous coal. The particle size of the coal raw material is preferably ≤74μm. When the particle size of the coal raw material does not meet the above requirements, the coal raw material is sequentially crushed, sieved, and ground. The grinding time is preferably 2–4 hours, more preferably 2–3 hours; the grinding method is preferably ball milling.

[0012] The pickling treatment involves sequentially applying either a hydrochloric acid aqueous solution or a hydrofluoric acid aqueous solution. The volume ratio of concentrated hydrochloric acid to water in the hydrochloric acid aqueous solution is 20–100:180–100, more preferably 40–80:160–120. Similarly, the volume ratio of hydrofluoric acid to water in the hydrofluoric acid aqueous solution is 20–100:180–100, more preferably 40–80:160–120. The mass ratio of the coal raw material to the volume of the hydrochloric acid aqueous solution or hydrofluoric acid aqueous solution is 1–5 g:160–240 mL, more preferably 2–4 g:180–220 mL.

[0013] After pickling, the present invention preferably dries the pickled product sequentially to obtain impurity-free coal raw material. The drying temperature is preferably 50-80℃, more preferably 60-70℃; the drying time is preferably 10-14h, more preferably 12-13h.

[0014] After obtaining the impurity-removed coal raw material, the present invention mixes the impurity-removed coal raw material with a swelling agent and heats and refluxes it to maximize the swelling degree of the coal. In this state, the intermolecular interaction forces such as π-π bonds and van der Waals forces in the coal structure can be significantly weakened.

[0015] In a preferred embodiment of the present invention, in step (2), the swelling agent is N-methylpyrrolidone / carbon disulfide, pyridine / xylene, or N,N-dimethylformamide / toluene, and the volume ratio of the two components in the swelling agent is 40-60:60-40, preferably 50:50. The mass ratio of the impurity coal raw material to the volume ratio of the swelling agent is 0.1-0.5g:80-120mL, preferably 0.2-0.4g:90-110mL. The heating temperature for the reflux is 60-100℃, and the reflux reaction time is 12-36h, preferably 80-100℃ and 18-30h.

[0016] After swelling, the present invention directly ultrasonically treats the mixture of impurity-removed coal and swelling agent in the swollen state. Under the continuous action of the cavitation effect generated by ultrasound, the coal in the solution will remain in a thermally swollen state and undergo sufficient dissociation, thereby obtaining a free coal-based aromatic conjugated lamellar structure.

[0017] In a preferred embodiment of the present invention, in step (3), ultrasonic treatment is performed under ice bath conditions, with an ultrasonic power of 20-25kW and a duration of 3-10h, preferably 3-5h.

[0018] The product treated by ultrasound is filtered, washed, and freeze-dried to remove the solvent, yielding the coal dissociation product. In this invention, the coal dissociation product is dispersed in tert-butanol, and the tert-butanol solution is freeze-dried. Freeze-drying reduces the agglomeration of the coal dissociation product. In this invention, the mass ratio of the coal dissociation product to the volume of tert-butanol is preferably 0.1–0.5 g: 80–120 mL, more preferably 0.2–0.4 g: 90–110 mL. In this invention, the freeze-drying time is preferably 36–50 h.

[0019] High-temperature calcination removes most of the sulfur, nitrogen, and oxygen elements as gaseous compounds, while preserving the aromatic conjugated lamellar structure. In this invention, the calcination atmosphere is preferably argon; the calcination apparatus is preferably a tube furnace.

[0020] In a preferred embodiment of the present invention, in step (4), the heating rate of the calcination treatment is 5-10°C / min, the calcination temperature is 1000-1500°C, and the duration is 1-3 hours, preferably 1200-1500°C for 2-3 hours. In the present invention, the rate of heating to the high-temperature calcination temperature is preferably 5-10°C / min.

[0021] The present invention also provides a few-layer coal-based graphene with an aromatic conjugated sheet structure prepared by the above method.

[0022] Compared with the prior art, this technical solution has the following advantages:

[0023] 1. The present invention can obtain a free coal-based aromatic conjugated sheet structure by dissociating coal in the aggregated state, and obtain coal-based graphene by direct calcination treatment without catalyst doping.

[0024] 2. This invention uses coal as raw material and takes advantage of the inherent molecular structure of coal. First, ash and mineral impurities in the coal are removed by acid washing. Then, the coal is mixed with a swelling agent and heated under reflux to put it in a swollen state. This significantly weakens the intermolecular interactions such as π-π bonds and van der Waals forces in the coal structure. Under the continuous action of the cavitation effect generated by ultrasound, the swollen coal dissociates, resulting in a free coal-based aromatic conjugated sheet structure. Finally, the structure is directly subjected to high-temperature calcination, which removes most of the heteroatoms (sulfur, nitrogen, and oxygen elements) in the form of gaseous compounds, retaining the aromatic conjugated sheet structure. Moreover, high-temperature calcination does not cause the agglomeration of the sheet structure material, ensuring the specific surface area of ​​the product coal-based graphene.

[0025] 3. The few-layer coal-based graphene obtained in this invention retains the aromatic conjugated layered structure, forming a two-dimensional layered material composed of periodically and closely packed carbon atom stacks with benzene ring structures (i.e., hexagonal honeycomb structures), possessing a large specific surface area (615.2 m²). 2 It also has excellent wave absorption performance, with a minimum reflection loss of -34.2dB. Attached Figure Description

[0026] Figure 1 This is a diagram illustrating the exfoliation mechanism in the preparation method;

[0027] Figure 2 This is a schematic diagram of the structure of the coal-based graphene prepared in Example 1;

[0028] Figure 3 In Figures a and b, both are SEM images (different fields of view) of the coal-based graphene prepared in Example 1;

[0029] Figure 4 The image in 'ac' is a TEM image (at different magnifications) of the coal-based graphene prepared in Example 1.

[0030] Figure 5 The image shows the microwave absorption properties of the coal-based graphene prepared in Example 1. Detailed Implementation

[0031] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] Example 1

[0033] This embodiment discloses a method for preparing coal-based graphene with a few-layer structure, comprising the following steps:

[0034] (1) The anthracite coal blocks are crushed and then sieved to obtain coal powder with a particle size of no more than 74 μm; the above coal powder (weighed 3 g) is soaked and acid washed with a hydrochloric acid aqueous solution prepared with 50 mL concentrated hydrochloric acid and 150 mL deionized water. After the hydrochloric acid acid washing is completed, the filter cake is filtered and then dispersed in a hydrofluoric acid aqueous solution prepared with 50 mL concentrated hydrofluoric acid and 150 mL deionized water. After the hydrofluoric acid washing is completed, the filter cake is filtered and dried at 60 °C for 12 h to obtain the impurity-free coal raw material.

[0035] (2) Take 0.3g of the above-mentioned cleaned coal raw material and mix it with 100mL of N-methylpyrrolidone / carbon disulfide swelling agent (the volume ratio of N-methylpyrrolidone to carbon disulfide is 50mL:50mL). Under magnetic stirring at 400r / min, heat the oil bath to 100℃ and reflux for 24h to obtain coal swelling product;

[0036] (3) After heating, the above mixed solution was sonicated at a frequency of 20 kHz for 5 h, and the entire sonication process was carried out under ice bath conditions; the above solution was filtered, and the filter cake was washed three times with tert-butanol, with each washing using 50 mL of tert-butanol. After washing, the filter cake was dispersed in 100 mL of tert-butanol, and the coal dissociation product tert-butanol dispersion was cooled and dried for 48 h to obtain the coal dissociation product.

[0037] (4) The coal dissociation product is placed in a tube furnace, and then heated to 1200°C at a rate of 5°C / min under argon protection. After holding at the temperature for 3 hours, coal-based graphene is obtained.

[0038] The peeling mechanism in this embodiment is as follows: Figure 1 Coal-based graphene, obtained by direct calcination of coal dissociation products, retains its aromatic conjugated sheet structure, as shown in the following diagram. Figure 2 As shown. The coal-based graphene prepared in Example 1 was observed under a scanning electron microscope and a transmission electron microscope, respectively, and the microstructure was obtained as shown. Figure 3 a, b and Figure 4 As shown in Figure ac, the coal-based graphene prepared in this embodiment exhibits a distinct two-dimensional sheet structure.

[0039] Microwave absorption performance testing: The prepared coal-based graphene was mixed with paraffin at a ratio of 0.015g:0.085g to obtain a test sample, and the microwave absorption performance was tested. The test results are shown in [Figure number missing]. Figure 5 As can be seen from the figure, the coal-based graphene prepared by this invention has excellent wave absorption properties, with a minimum reflection loss of -34.2 dB.

[0040] Example 2

[0041] (1) The anthracite coal blocks are crushed and then sieved to obtain coal powder with a particle size of no more than 74 μm; the above coal powder (weighed 3 g) is soaked and acid washed with a hydrochloric acid aqueous solution prepared with 50 mL concentrated hydrochloric acid and 150 mL deionized water. After the hydrochloric acid acid washing is completed, the filter cake is filtered and then dispersed in a hydrofluoric acid aqueous solution prepared with 50 mL concentrated hydrofluoric acid and 150 mL deionized water. After the hydrofluoric acid washing is completed, the filter cake is filtered and dried at 60 °C for 12 h to obtain the impurity-free coal raw material.

[0042] (2) Take 0.3g of the above-mentioned cleaned coal raw material and mix it with 100mL of N-methylpyrrolidone / carbon disulfide swelling agent (the volume ratio of N-methylpyrrolidone to carbon disulfide is 50mL:50mL). Under magnetic stirring at 400r / min, heat the oil bath to 100℃ and reflux for 24h to obtain coal swelling product;

[0043] (3) After heating, the above mixed solution was sonicated at 25 kHz for 5 h, and the entire sonication process was carried out under ice bath conditions. The above solution was filtered, and the filter cake was washed three times with tert-butanol, with 50 mL of tert-butanol used each time. After washing, the filter cake was dispersed in 100 mL of tert-butanol, and the coal dissociation product tert-butanol dispersion was cooled and dried for 48 h to obtain the coal dissociation product.

[0044] (4) The coal dissociation product is placed in a tube furnace, and then heated to 1200°C at a rate of 5°C / min under argon protection. After holding at the temperature for 3 hours, coal-based graphene is obtained.

[0045] Example 3

[0046] (1) The anthracite coal blocks are crushed and then sieved to obtain coal powder with a particle size of no more than 74 μm; the above coal powder (weighed 3 g) is soaked and acid washed with a hydrochloric acid aqueous solution prepared with 50 mL concentrated hydrochloric acid and 150 mL deionized water. After the hydrochloric acid acid washing is completed, the filter cake is filtered and then dispersed in a hydrofluoric acid aqueous solution prepared with 50 mL concentrated hydrofluoric acid and 150 mL deionized water. After the hydrofluoric acid washing is completed, the filter cake is filtered and dried at 60 °C for 12 h to obtain the impurity-free coal raw material.

[0047] (2) Take 0.3g of the above-mentioned cleaned coal raw material and mix it with 100mL of N-methylpyrrolidone / carbon disulfide swelling agent (the volume ratio of N-methylpyrrolidone to carbon disulfide is 50mL:50mL). Under magnetic stirring at 400r / min, heat the oil bath to 100℃ and reflux for 24h to obtain coal swelling product;

[0048] (3) After heating, the above mixed solution was sonicated at 20 kHz for 10 h, and the entire sonication process was carried out under ice bath conditions. The above solution was filtered, and the filter cake was washed three times with tert-butanol, with 50 mL of tert-butanol used each time. After washing, the filter cake was dispersed in 100 mL of tert-butanol, and the coal dissociation product tert-butanol dispersion was cooled and dried for 48 h to obtain the coal dissociation product.

[0049] (4) The coal dissociation product is placed in a tube furnace, and then heated to 1200°C at a rate of 5°C / min under argon protection. After holding at the temperature for 3 hours, coal-based graphene is obtained.

[0050] Example 4

[0051] (1) The anthracite coal blocks are crushed and then sieved to obtain coal powder with a particle size of no more than 74 μm; the above coal powder (weighed 3 g) is soaked and acid washed with a hydrochloric acid aqueous solution prepared with 50 mL concentrated hydrochloric acid and 150 mL deionized water. After the hydrochloric acid acid washing is completed, the filter cake is filtered and then dispersed in a hydrofluoric acid aqueous solution prepared with 50 mL concentrated hydrofluoric acid and 150 mL deionized water. After the hydrofluoric acid washing is completed, the filter cake is filtered and dried at 60 °C for 12 h to obtain the impurity-free coal raw material.

[0052] (2) Take 0.3g of the above-mentioned cleaned coal raw material and mix it with 100mL of N-methylpyrrolidone / carbon disulfide swelling agent (the volume ratio of N-methylpyrrolidone to carbon disulfide is 50mL:50mL). Under magnetic stirring at 400r / min, heat the oil bath to 90℃ and reflux for 24h to obtain coal swelling product.

[0053] (4) After heating, the above mixed solution was sonicated at 20 kHz for 5 h, and the entire sonication process was carried out under ice bath conditions. The above solution was filtered, and the filter cake was washed three times with tert-butanol, with 50 mL of tert-butanol used each time. After washing, the filter cake was dispersed in 100 mL of tert-butanol, and the coal dissociation product tert-butanol dispersion was cooled and dried for 48 h to obtain the coal dissociation product.

[0054] (4) The coal dissociation product is placed in a tube furnace, and then heated to 1200°C at a rate of 5°C / min under argon protection. After holding at the temperature for 3 hours, coal-based graphene is obtained.

[0055] Example 5

[0056] (1) The anthracite coal blocks are crushed and then sieved to obtain coal powder with a particle size of no more than 74 μm; the above coal powder (weighed 3 g) is soaked and acid washed with a hydrochloric acid aqueous solution prepared with 50 mL concentrated hydrochloric acid and 150 mL deionized water. After the hydrochloric acid acid washing is completed, the filter cake is filtered and then dispersed in a hydrofluoric acid aqueous solution prepared with 50 mL concentrated hydrofluoric acid and 150 mL deionized water. After the hydrofluoric acid washing is completed, the filter cake is filtered and dried at 60 °C for 12 h to obtain the impurity-free coal raw material.

[0057] (2) Take 0.3g of the above-mentioned cleaned coal raw material and mix it with 100mL of N-methylpyrrolidone / carbon disulfide swelling agent (the volume ratio of N-methylpyrrolidone to carbon disulfide is 50mL:50mL). Under magnetic stirring at 400r / min, heat the oil bath to 100℃ and reflux for 24h to obtain coal swelling product;

[0058] (3) After heating, the above mixed solution was sonicated at 20 kHz for 5 h, and the entire sonication process was carried out under ice bath conditions. The above solution was filtered, and the filter cake was washed three times with tert-butanol, with each wash using 50 mL of tert-butanol. After washing, the filter cake was dispersed in 100 mL of tert-butanol, and the coal dissociation product tert-butanol dispersion was cooled and dried for 48 h to obtain the coal dissociation product.

[0059] (4) The coal dissociation product is placed in a tube furnace, and then heated to 1200°C at a rate of 10°C / min under argon protection. After holding at the temperature for 3 hours, coal-based graphene is obtained.

[0060] Example 6

[0061] (1) The anthracite coal blocks are crushed and then sieved to obtain coal powder with a particle size of no more than 74 μm; the above coal powder (weighed 3 g) is soaked and acid washed with a hydrochloric acid aqueous solution prepared with 50 mL concentrated hydrochloric acid and 150 mL deionized water. After the hydrochloric acid acid washing is completed, the filter cake is filtered and then dispersed in a hydrofluoric acid aqueous solution prepared with 50 mL concentrated hydrofluoric acid and 150 mL deionized water. After the hydrofluoric acid washing is completed, the filter cake is filtered and dried at 60 °C for 12 h to obtain the impurity-free coal raw material.

[0062] (2) Take 0.3g of the above-mentioned cleaned coal raw material and mix it with 100mL of N-methylpyrrolidone / carbon disulfide swelling agent (the volume ratio of N-methylpyrrolidone to carbon disulfide is 50mL:50mL). Under magnetic stirring at 400r / min, heat the oil bath to 100℃ and reflux for 24h to obtain coal swelling product;

[0063] (3) After heating, the above mixed solution was sonicated at 20 kHz for 5 h, and the entire sonication process was carried out under ice bath conditions. The above solution was filtered, and the filter cake was washed three times with tert-butanol, with each wash using 50 mL of tert-butanol. After washing, the filter cake was dispersed in 100 mL of tert-butanol, and the coal dissociation product tert-butanol dispersion was cooled and dried for 48 h to obtain the coal dissociation product.

[0064] (4) The coal dissociation product is placed in a tube furnace and then heated to 1400°C at a rate of 5°C / min under argon protection. After holding at the temperature for 3 hours, coal-based graphene is obtained.

[0065] Example 7

[0066] (1) The anthracite coal blocks are crushed and then sieved to obtain coal powder with a particle size of no more than 74 μm; the above coal powder (weighed 3 g) is soaked and acid washed with a hydrochloric acid aqueous solution prepared with 50 mL concentrated hydrochloric acid and 150 mL deionized water. After the hydrochloric acid acid washing is completed, the filter cake is filtered and then dispersed in a hydrofluoric acid aqueous solution prepared with 50 mL concentrated hydrofluoric acid and 150 mL deionized water. After the hydrofluoric acid washing is completed, the filter cake is filtered and dried at 60 °C for 12 h to obtain the impurity-free coal raw material.

[0067] (2) Take 0.3g of the above-mentioned cleaned coal raw material and mix it with 100mL of N-methylpyrrolidone / carbon disulfide swelling agent (the volume ratio of N-methylpyrrolidone to carbon disulfide is 50mL:50mL). Under magnetic stirring at 400r / min, heat the oil bath to 100℃ and reflux for 24h to obtain coal swelling product;

[0068] (3) After heating, the above mixed solution was sonicated at 25 kHz for 3 hours, and the entire sonication process was carried out under ice bath conditions. The above solution was filtered, and the filter cake was washed three times with tert-butanol, with each wash using 50 mL of tert-butanol. After washing, the filter cake was dispersed in 100 mL of tert-butanol, and the coal dissociation product tert-butanol dispersion was cooled and dried for 48 hours to obtain the coal dissociation product.

[0069] (4) The coal dissociation product is placed in a tube furnace, and then heated to 1200°C at a rate of 5°C / min under argon protection. After holding at the temperature for 3 hours, coal-based graphene is obtained.

[0070] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. 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 therein. Such 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 coal-based graphene with a few-layer structure, characterized in that: Includes the following steps: (1) Grind the coal raw material and acid wash it to obtain impurity-free coal raw material; (2) The impurity-removed coal raw material is mixed with a swelling agent and heated under reflux to swell, thereby obtaining a coal swelling product; the swelling agent is N-methylpyrrolidone / carbon disulfide, pyridine / xylene, or N,N-dimethylformamide / toluene, and the volume ratio of the two components in the swelling agent is 40~60:60~40; the mass ratio of the impurity-removed coal raw material to the volume ratio of the swelling agent is 0.1~0.5g:80~120mL; (3) The coal swelling product is subjected to ultrasonic treatment, and the ultrasonically treated product is filtered, washed and freeze-dried to remove the solvent to obtain the coal dissociation product; (4) The coal dissociation products are calcined to obtain coal-based graphene; the calcination atmosphere is argon, the heating rate of the calcination treatment is 5-10℃ / min, the calcination temperature is 1000-1500℃, and the duration is 1-3h.

2. The method for preparing few-layer coal-based graphene according to claim 1, characterized in that: In step (1), the coal raw material includes anthracite, lignite or bituminous coal, and is ground to a particle size ≤74μm.

3. The method for preparing few-layer coal-based graphene according to claim 1, characterized in that: In step (1), the pickling treatment is carried out sequentially using hydrochloric acid aqueous solution and hydrofluoric acid aqueous solution. The volume ratio of concentrated hydrochloric acid to water in the hydrochloric acid aqueous solution is 20~100:180~100, and the volume ratio of hydrofluoric acid to water in the hydrofluoric acid aqueous solution is 20~100:180~100. The mass ratio of the coal raw material to the volume ratio of hydrochloric acid aqueous solution or hydrofluoric acid aqueous solution is 1~5g:160~240mL.

4. The method for preparing few-layer coal-based graphene according to claim 1, characterized in that: In step (2), the heating temperature of the reflux is 60~100℃ and the reflux reaction time is 12~36h.

5. The method for preparing few-layer coal-based graphene according to claim 1, characterized in that: In step (3), ultrasonic treatment is performed under ice bath conditions, with an ultrasonic power of 20~25kW and a duration of 3~10h.

6. A few-layer coal-based graphene, characterized in that: It is prepared by the method described in any one of claims 1-5.

7. The few-layer coal-based graphene according to claim 6, characterized in that: It has an aromatic conjugated lamellar structure.

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