Graphene and method for producing the same

Abstract

The application relates to the technical field of carbon material processing, and particularly discloses graphene and a preparation method thereof, the preparation method comprising the following steps: performing first heating treatment on a carbon source material under a first temperature; applying a first electric field to the carbon source material subjected to the first heating treatment to obtain an intermediate product; performing second heating treatment on the intermediate product under a second temperature; applying a second electric field to the intermediate product subjected to the second heating treatment to obtain graphene; wherein the first temperature is not lower than 800 DEG C, the second temperature is not higher than 3000 DEG C and higher than the first temperature; the intensity of the first electric field is not lower than 500 N / C, and the intensity of the second electric field is not higher than 20000 N / C and higher than the intensity of the first electric field. The aforementioned preparation method has the characteristics of wide raw material sources, can effectively reduce the dependence on fossil-based carbon sources, and can obtain graphene with few defects, high crystallinity and excellent electric conductivity under a relatively low activation energy.

Description

Technical Field

[0001] This invention relates to the field of carbon material processing technology, specifically to a graphene and its preparation method. Background Technology

[0002] Graphene is a two-dimensional material in which carbon atoms are arranged in a honeycomb pattern. Due to its excellent mechanical, thermal, optical and electrical properties, it has broad application prospects in fields such as heat dissipation devices, high-strength concrete, flexible displays and supercapacitors.

[0003] However, in the current production of graphene, the raw materials mainly rely on fossil-based carbon sources such as petroleum coke and graphite. At the same time, the production process is energy-intensive, environmentally unfriendly, and has high equipment costs, making it difficult to produce on a large scale. Summary of the Invention

[0004] The purpose of this invention is to provide a graphene and its preparation method to solve the problems of existing graphene production being limited by raw materials, environmentally unfriendly production processes, and high production costs.

[0005] The specific technical solution is as follows: A method for preparing graphene includes the following steps: The carbon source material is subjected to a first heat treatment at a first temperature. A first electric field is applied to the carbon source material undergoing the first heat treatment to obtain an intermediate product; The intermediate product is subjected to a second heat treatment at a second temperature. A second electric field is applied to the intermediate product subjected to the second heat treatment to obtain graphene; Wherein, the first temperature is not lower than 800℃, and the second temperature is not higher than 3000℃ but higher than the first temperature; The electric field strength of the first electric field is not less than 500 N / C, and the electric field strength of the second electric field is not more than 20000 N / C and is higher than the electric field strength of the first electric field.

[0006] Furthermore, a graphene is provided, which is prepared using the preparation method described above.

[0007] Beneficial Technical Effects: Compared with existing technologies, this invention employs an electric field-assisted two-stage heating method for the carbon source material. Through the synergistic effect of the electric field and heating, non-graphitizable hard carbon in the carbon source material can be directly converted into graphene at a relatively low activation energy. This method has the advantages of wide availability of raw materials, low cost, effectively reducing dependence on fossil-based carbon sources such as petroleum coke and graphite, low processing temperature and high processing efficiency, and the entire preparation process is not only environmentally friendly but also has low energy consumption. More importantly, the obtained graphene has the characteristics of lower defects, higher graphitization degree, higher lattice order, and superior electrical conductivity. Attached Figure Description

[0008] Figure 1 This is a scanning electron microscope image of the black product in Example 1 of the present invention; Figure 2 This is the Raman spectrum of the black product in Example 1 of the present invention; Figure 3 This is the Raman spectrum of the black product in Example 2 of the present invention; Figure 4 This is the X-ray diffraction (XRD) pattern of the product obtained in step S32 of Embodiment 3 of the present invention; Figure 5 This is the Raman spectrum of the black product in Example 3 of the present invention; Figure 6 This is an XPS image of the black product in Embodiment 3 of the present invention; Figure 7 This is the Raman spectrum of the product in Comparative Example 1 of this invention; Figure 8 This is the Raman spectrum of the product in Comparative Example 2 of this invention; Figure 9 This is the Raman spectrum of the product in Comparative Example 3 of this invention; Figure 10 This is the XRD pattern of the product in Comparative Example 3 of this invention; Figure 11 This is the Raman spectrum of the product in Comparative Example 4 of this invention; Figure 12 This is the XRD pattern of the product in Comparative Example 4 of this invention; Figure 13 This is a comparison diagram of the conductivity of the products at each stage in Example 3 and Comparative Example 4 of the present invention.

[0009] In this context, “Raman Shift” means “Raman shift”, “Intensity” means “intensity”, “Binding Energy” means “binding energy”, and “Pressure” means “pressure”. Detailed Implementation

[0010] The present invention will be further described below with reference to the accompanying drawings and embodiments. In this specification, appropriate interpretations may be made based on actual circumstances.

[0011] Please see Figure 1 and Figure 2 This invention provides a method for preparing graphene, comprising the following steps: The carbon source material is subjected to a first heat treatment at a first temperature. A first electric field is applied to the carbon source material undergoing the first heat treatment to obtain an intermediate product; The intermediate product is subjected to a second heat treatment at a second temperature. A second electric field is applied to the intermediate product subjected to the second heat treatment to obtain graphene; Wherein, the first temperature is not lower than 800℃, the second temperature is not higher than 3000℃, and the second temperature is higher than the first temperature; The electric field strength of the first electric field is not less than 500 N / C, the electric field strength of the second electric field is not more than 20000 N / C, and the electric field strength of the second electric field is higher than that of the first electric field.

[0012] In embodiments of the present invention, both the first and second electric fields are generated by externally applied electric field electrodes arranged opposite each other, and the externally applied electric field electrodes may not be in contact with the sample. By applying the first and second electric fields, the carbon source material and the intermediate product are positioned within the effective electric field strength region. The effective electric field strength region refers to the region located between the two externally applied electric field electrodes, corresponding to the effective distance d between the electrodes. The average electric field strength E within this effective electric field strength region can be determined by the voltage V applied to the externally applied electric field electrodes and the effective distance d, and can be expressed as: E = V / d. Where d is the effective distance between the two externally applied electric field electrodes. In cases of uneven electric field distribution or edge effects, the electric field strength E can be the average electric field strength acting on the main body region of the sample. The unit of electric field strength can be expressed as V / m or N / C (and 1V / m = 1N / C).

[0013] In some embodiments, the carbon source material may be heated by at least one of Joule heating, induction heating, microwave heating, and radiation heating. Specifically, the carbon source material may be placed in any one of a Joule furnace, muffle furnace, tube furnace, and electric arc furnace for the first heating treatment.

[0014] In some embodiments, the container holding the carbon source material can be evacuated, allowing the carbon source material to be heated under vacuum conditions, effectively preventing the influence of impurities in the air on the graphene preparation process. In some embodiments, the container holding the carbon source material can also be evacuated first and then filled with a protective gas, or a protective gas can be continuously introduced, to perform the first heating treatment in a protective gas atmosphere. In some embodiments, the protective gas can be nitrogen, argon, etc.

[0015] In some embodiments, the first temperature is maintained in the range of 800°C to 1500°C for 3 to 5 minutes. For example, the first temperature is maintained in the range of 850°C to 1450°C for 3 to 5 minutes, or in the range of 900°C to 1400°C for 3 to 5 minutes, or in the range of 950°C to 1350°C for 3 to 5 minutes, or in the range of 1000°C to 1300°C for 3 to 5 minutes, or in the range of 1050°C to 1250°C for 3 to 5 minutes. In the example, the temperature can be maintained at 820℃ for 3 minutes, or at 860℃ for 3 minutes, or at 880℃ for 3 minutes, or at 910℃ for 3 minutes, or at 940℃ for 3.2 minutes, or at 980℃ for 3.3 minutes, or at 1020℃ for 3.1 minutes, or at 1080℃ for 3.5 minutes, or at 1120℃ for 3.6 minutes, or at 1160℃ for 3.3 minutes, or at 1180℃ for 3.2 minutes, or at 1220℃ for 3.1 minutes, or at 1260℃ for 3.3 minutes, or at 1280℃ for 3.2 minutes, or at 1320℃. Maintaining the temperature at typical but not limiting temperatures such as 3.6 min, 3.7 min at 1360°C, 3.8 min at 1380°C, 4.1 min at 1420°C, 4.3 min at 1450°C, 4.6 min at 1460°C, 4.8 min at 1480°C, or 3 min at 1490°C, or at any temperature between any two of these temperatures, can effectively carbonize the carbon source material, transforming it into a state with a carbon mass content of approximately 60%, which is beneficial for obtaining high-purity graphene during further processing.

[0016] In some embodiments, the carbon source material is selected from at least one of biomass, hard carbon, plastics, coal, and coke. When the carbon source material is selected from coal or coke, the time of the first heat treatment can be appropriately shortened to remove moisture, volatile compounds, adsorbed gases, and low-temperature impurities, while partially stabilizing and regulating the raw material, without the need for further carbonization. When the carbon source material is biomass, hard carbon, or plastic, the carbon content can reach approximately 60% by mass through the first heat treatment, which is beneficial for graphene formation during further processing.

[0017] In some embodiments, the biomass is selected from lignocellulose. In some embodiments, when the lignocellulose is subjected to the first heat treatment using a Joule furnace, a conductive carbon source is added. Adding the conductive carbon source enhances the conductivity of the lignocellulose, reduces its resistance, and thus improves the efficiency of lignocellulose carbonization. In some embodiments, the conductive carbon source accounts for 1% to 3% of the total mass of the carbon source material. By adding a conductive carbon source accounting for no more than 3% of the total mass of the carbon source material, the conductivity during the first heat treatment process can be effectively improved, thereby ensuring the stability and uniformity of the heating process. In some embodiments, the biomass is selected from the genus *Acacia* (…). Acacia Plant biomass (spp.) can be derived from the whole plant or any part of these plants, such as the whole plant of acacia, the whole plant of Arabian acacia, or the roots, stems, branches, bark, leaves, etc. of these plants, all of which contain a high content of lignocellulose.

[0018] In some embodiments, the conductive carbon source is selected from conductive carbon black, which has good electrical conductivity. When lignocellulose is finally converted into graphene, the conductive carbon black is also converted into graphene.

[0019] In some implementations, the electric field strength of the first electric field is maintained in the range of 500 N / C to 5000 N / C, and the duration of maintaining the electric field strength of the first electric field is 30 s to 6000 s. The first electric field mainly originates from an external electric field, such as by applying an external non-contact electric field. For example, maintain a temperature of 500 N / C to 4550 N / C for 30 to 5550 seconds, or maintain a temperature of 500 N / C to 4500 N / C for 30 to 5500 seconds, or maintain a temperature of 600 N / C to 4000 N / C for 40 to 5000 seconds, or maintain a temperature of 800 N / C to 3500 N / C for 30 to 4000 seconds, or maintain a temperature of 1000 N / C to 3000 N / C for 45 to 3500 seconds, or maintain a temperature of 1500 N / C to 3000 N / C for 50 to 3000 seconds, or maintain a temperature of 2000 N / C to 2800 N / C for 35 to 2600 seconds. In the examples, the temperature was maintained at 500 N / C for 6000 s, or at 600 N / C for 5500 s, or at 700 N / C for 5000 s, or at 900 N / C for 4500 s, or at 1000 N / C for 4000 s, or at 1200 N / C for 3800 s, or at 1500 N / C for 3500 s, or at 2000 N / C for 2000 s, or at 2500 N / C for 1800 s, or at 2800 N / C for... Maintaining the carbon source material at typical but not limiting electric field strengths for corresponding durations—such as 1500s, 1000s at 3000 N / C, 800s at 3500 N / C, 600s at 3800 N / C, 200s at 4200 N / C, 150s at 4500 N / C, 100s at 4800 N / C, or 50s at 5000 N / C—effectively promotes carbonization of the carbon source material, facilitating further graphene formation. Of course, during the first heat treatment, the applied voltage also creates a certain intrinsic electric field, with its strength ranging from 100 N / C to 500 N / C.

[0020] In some embodiments, when the first electric field is applied, the carbon source material is placed within the effective electric field strength region of the first electric field to sufficiently apply the first electric field to the carbon source material and shorten the processing time of the first electric field. In some embodiments, during and / or after the first heat treatment, the carbon source material is placed within the effective electric field region formed by the first electric field, such that the electric field strength... (For example, according to) The defined average electric field strength is applied to the main region of the carbon source material. The first heating treatment can generate Joule heating through the material resistance to promote heating and reaction; at the same time, the synergistic effect of the first electric field and heating can induce carbonization of biomass and promote the structural orientation and framework rearrangement of some carbonized fragments under the action of the electric field, promoting the formation of a semi-ordered carbon framework structure. This can improve the conductivity and structural order of the intermediate product, thereby contributing to the formation and quality improvement of graphene under the synergy of the second heating treatment and the second electric field.

[0021] In some embodiments, the second temperature is in the range of 2000℃ to 3000℃, and the second temperature is maintained for 2.5 min to 5 min. For example, the second temperature is maintained for 2.5 min to 5 min in the range of 2000℃ to 2855℃, or for 3 min to 5 min in the range of 2050℃ to 2850℃, or for 3 min to 5 min in the range of 2150℃ to 2800℃, or for 3 min to 5 min in the range of 2200℃ to 2750℃, or for 3 min to 5 min in the range of 2250℃ to 2700℃, or for 3 min to 5 min in the range of 2300℃ to 2600℃, or for 3 min to 5 min in the range of 2400℃ to 2500℃. In the examples, the temperature was maintained at 2010℃ for 3 minutes, or at 2050℃ for 3 minutes, or at 2110℃ for 3 minutes, or at 2150℃ for 3 minutes, or at 2180℃ for 3.2 minutes, or at 2200℃ for 3.3 minutes, or at 2210℃ for 3.1 minutes, or at 2215℃ for 3.5 minutes, or at 2225℃ for 3.6 minutes, or at 2350℃ for 3.3 minutes, or at 2450℃ for 3.3 minutes, or at 2550℃ for 3.2 minutes, or at 2600℃ for 3.1 minutes, or at 2650℃ for 3.3 minutes. The intermediate product can be treated at typical but not limiting temperatures, such as 2655°C for 3.2 min, 2700°C for 3.6 min, 2750°C for 3.7 min, 2800°C for 3.8 min, 2850°C for 4.1 min, 2900°C for 4.3 min, 2910°C for 4.6 min, 2950°C for 4.8 min, or 2980°C for 3 min, or at any temperature between any two of these temperatures. Treatment within these temperature ranges can effectively grapheneize the intermediate product, transforming it into higher-quality graphene. In some embodiments, during the second temperature treatment, the intermediate product remains in the container used for the first heat treatment.

[0022] In some embodiments, the electric field strength of the second electric field is maintained in the range of 5000 N / C to 20000 N / C, excluding 5000 N / C, and the duration of maintaining the second electric field is 15 s to 150 s. The second electric field mainly originates from an external electric field, such as by applying an external non-contact electric field. For example, maintain a temperature of 5000 N / C to 19950 N / C for 15 to 150 seconds, or 5500 N / C to 19950 N / C for 20 to 150 seconds, or 6000 N / C to 19900 N / C for 25 to 150 seconds, or 6500 N / C to 18500 N / C for 30 to 150 seconds, or 7500 N / C to 17500 N / C for 35 to 150 seconds, or 8500 N / C to 17000 N / C for 40 to 150 seconds, or 9000 N / C to 16500 N / C for 45 to 150 seconds, or 10000 N / C to 15500 N / C for 50 to 150 seconds. In the exemplary cases, the intermediate product is grapheneized by maintaining the electric field at typical but non-limiting electric field strengths for the corresponding durations, such as 5000 N / C for 150 s, 6000 N / C for 140 s, 7000 N / C for 130 s, 9000 N / C for 120 s, 10000 N / C for 110 s, 12000 N / C for 90 s, 15000 N / C for 80 s, 17000 N / C for 60 s, 18000 N / C for 35 s, 19000 N / C for 20 s, or 20000 N / C for 15 s.

[0023] In some embodiments, when the second electric field is applied, the intermediate product is placed within the effective electric field strength region of the second electric field, thus sufficiently applying the second electric field to the intermediate product, shortening the processing time of the second electric field and the graphene generation time, and effectively ensuring the mass percentage of the intermediate product converted into graphene, thereby improving the purity of the graphene. In some embodiments, during and / or after the second heat treatment, the intermediate product is placed within the effective electric field region formed by the second electric field, such that the electric field strength of the second electric field is increased. (For example, according to) The defined average electric field strength acts on the main region of the intermediate product. The second heat treatment, combined with a higher second electric field, can promote further rearrangement and ordering of the carbon framework, promoting the formation of graphene / graphene-like carbon structures. Furthermore, under the same heating conditions and processing time, as the applied electric field strength increases (e.g., increasing...), the... The quality of the obtained graphene can be further improved, for example, by exhibiting lower defect characteristics and / or higher graphitization (which can be reflected by Raman spectroscopy, XRD or conductivity, etc.), thereby improving the consistency and quality stability of graphene products.

[0024] In some embodiments, the graphene obtained after the above treatment has a carbon content of 97% or more and a heteroatom content of no more than 3%.

[0025] The following examples illustrate the preparation method of graphene according to the present invention.

[0026] Example 1 S11. Mix acacia trunk wood with a moisture content of not more than 20% (by mass) with carbon black accounting for 2% of the biomass mass to form a uniform mixture. Fill the mixture into a quartz tube in a Joule furnace. The acacia trunk wood has a particle size of about 1 mm and a mass of about 5 g, the carbon black has a mass of 0.1 g, the inner diameter to length ratio of the quartz tube is 1:10, two graphite electrodes are located at the feed end and the discharge end of the quartz tube respectively, and the two graphite electrodes apply pressure to the mixture to ensure good electrical contact of the mixture.

[0027] S12. Argon gas is continuously introduced into the quartz tube to purge it and form a protective atmosphere. The two graphite electrodes are connected to a DC power supply with a voltage of 45V and a current of 12.5A±0.5A. The temperature of the mixture in the quartz tube is raised to 800℃±5℃ within 5 minutes. Then, it is maintained at this temperature for 180s. During the application of voltage, an internal electric field is naturally generated inside. At the same time, an external non-contact electric field with an intensity of 1000N / C is applied. By utilizing the combined effect of resistance heating and electric field intensity, carbonization of biomass is induced, and some carbonized fragments undergo structural orientation, promoting the formation of a semi-ordered carbon skeleton structure.

[0028] S13. The control capacitor discharge system discharges with a 280V pulse. The pulse generates a peak current of 1800A±100A in the partially carbonized material. This instantaneous Joule heating process heats the mixture to 2300℃±50℃ within 500ms. This temperature is then maintained for 150s. The applied voltage naturally generates an internal electric field, while an external non-contact electric field of 6200N / C is applied simultaneously, further promoting the ordered layered stacking of the carbon structure. This causes the carbon structure to rearrange and form a more continuous sp... 2 Carbon layer structure to obtain black product.

[0029] S14. Stop heating and applying the electric field, continue to purge with argon gas until cooled to room temperature, then collect the black product. Scan the sample of the black product using a scanning electron microscope to obtain the following results: Figure 1 The scanning electron microscope image shown is illustrated. Raman spectroscopy was used for detection, and the results are as follows. Figure 2 As shown, clearly identifiable 2D characteristic peaks were found in the black product, and the D peak and G peak were clearly separated. The intensity ratio of the 2D peak to the G peak was... The intensity ratio of the D peak to the G peak is approximately 0.85. The full width at half maximum (FWHM) of the 2D peak is approximately 0.64. The black product exhibits a few-layer graphene morphology with fewer structural defects. Furthermore, the mass yield of the black product is approximately 29% of the starting biomass dry weight. This demonstrates that a two-stage heat treatment process combined with an applied electric field can promote carbon structural ordering while maintaining a high yield.

[0030] Example 2 S21. Mix whole acacia plants with a moisture content of not more than 20% (by mass) with carbon black accounting for 2% of the biomass mass to form a uniform mixture. Fill the mixture into a quartz tube in a Joule furnace. The particle size of the whole acacia plants is about 1 mm and about 5 g, the mass of the carbon black is 0.1 g, the ratio of the inner diameter to the length of the quartz tube is 1:10, two graphite electrodes are located at the feed end and the discharge end of the quartz tube respectively, and the two graphite electrodes apply pressure to the mixture.

[0031] S22. Argon gas is continuously introduced into the quartz tube to purge it and form a protective atmosphere. The two graphite electrodes are connected to a DC power supply with a voltage of 45V and a current of 12.5A±0.5A. The temperature of the mixture in the quartz tube is controlled to rise to 800℃±5℃ within 5 minutes. Then, the temperature is maintained at this temperature for 180s, while an external non-contact electric field with an intensity of 2000N / C is applied to induce the polarization orientation of carbon fragments during carbonization and promote the formation of a semi-ordered carbon framework structure.

[0032] S23. The control capacitor discharge system discharges with a 280V pulse. The pulse generates a peak current of 1800A±100A in the partially carbonized material. This instantaneous Joule heating process rapidly heats the mixture to 2300℃±50℃ within 500ms. This temperature is then maintained for 150s while an external non-contact electric field of 9500N / C is applied, further promoting the ordering and layered stacking of the carbon structure, causing the carbon structure to rearrange and form a more continuous sp... 2 A carbon layer structure is used to obtain a black product.

[0033] S24. Stop heating and applying the electric field, continue to purge with argon gas until cooling to room temperature, then collect the black product. Detection is performed using Raman spectroscopy, and the results are as follows: Figure 3 As shown. By Figure 3 It was found that the product contained clearly distinguishable 2D characteristic peaks, and the D peak and G peak could be clearly separated. The intensity ratio of the 2D peak to the G peak was... The intensity ratio of the D peak to the G peak is approximately 0.95. The full width at half maximum (FWHM) of the 2D peak is approximately 0.34. The black product is granular, and its microstructure exhibits the morphology of few-layer graphene with fewer structural defects. The product's mass yield is approximately 32% of the starting biomass dry weight. This demonstrates that the two-stage heat treatment combined with an external electric field can promote the ordering of carbon structures while maintaining a high material yield.

[0034] Example 3 S31. Mix acacia with a moisture content of no more than 20% (by mass) with carbon black accounting for 2% of the mass of acacia to form a uniform mixture. Load the mixture into a quartz tube of a Joule furnace. The acacia has a particle size of about 1 mm and a mass of about 5 g, and the carbon black has a mass of 0.1 g. Two graphite electrodes are respectively set at both ends of the reaction vessel, and appropriate pressure is applied to the mixture to ensure good electrical contact.

[0035] S32. Argon gas is continuously purged into the quartz tube to create a protective atmosphere. A direct current of 45V and 12.5A±0.5A is applied to raise the temperature inside the quartz tube to 800℃±50℃ within 5 minutes and maintain this temperature for 180 seconds. Simultaneously, an external non-contact electric field of 4600N / C is applied to induce the polarization orientation of carbon fragments during carbonization, promoting the formation of a semi-ordered carbon framework structure. The product after X-ray diffraction treatment yields the following... Figure 4 The XRD pattern shown.

[0036] from Figure 4 It can be seen that, under the application of an external non-contact electric field, a sharp (002) diffraction peak appears at 25.9°, and a clearer (100) / (101) characteristic peak appears at 42.8°, indicating that the order and crystallinity of the carbon sheet structure are significantly improved. Thus, it can be seen that the external electric field can promote the orientation of carbon atoms and the formation of layered graphite structure during the first stage of heating.

[0037] S33. The control capacitor discharge system discharges with a 280V pulse. The pulse generates a peak current of 1800A±100A in the partially carbonized material. This instantaneous Joule heating process heats the mixture to 2300℃±50℃ within 500ms. Then, it is maintained at this temperature for 150s while an external non-contact electric field with an intensity of 18000N / C is applied to further promote the ordering and layered stacking of the carbon structure, causing the carbon structure to rearrange and form a more continuous sp² carbon layer structure, thereby obtaining a black product.

[0038] S34. Stop heating and applying the electric field, continue to purge with argon gas until cooling to room temperature, then collect the black product. Detection is performed using Raman spectroscopy, and the results are as follows: Figure 5 As shown.

[0039] Depend on Figure 5 It can be seen that the product contains clearly distinguishable 2D characteristic peaks, and the D peak and G peak can be clearly separated. The intensity ratio of the 2D peak to the G peak is... The intensity ratio of the D peak to the G peak is approximately 1.23. The full width at half maximum (FWHM) of the 2D peak is approximately 0.25. The black product exhibits a few-layer graphene morphology with fewer structural defects, and the product's mass yield is approximately 30% of the starting biomass dry weight. This demonstrates that the two-stage heat treatment combined with an external electric field can promote the ordering of carbon structures while maintaining a high material yield.

[0040] The black product obtained in step S34 was subjected to XPS processing, and the results are as follows: Figure 6 As shown. By Figure 6 It can be seen that the doping of other atoms in the finished product is less than 1%, which effectively echoes the... Figure 5 Results showing fewer structural defects in the mid-Raman spectrum.

[0041] Comparative Example 1 D11. Mix acacia trunk wood with a moisture content of no more than 20% (by mass) with carbon black accounting for 2% of the mass of the acacia trunk wood to form a uniform mixture. Fill the mixture into a quartz tube in a Joule furnace. The acacia trunk wood has a particle size of about 1 mm and a weight of about 5 g. The carbon black has a mass of 0.1 g. The ratio of the inner diameter to the length of the quartz tube is 1:10. Two graphite electrodes are located at the feed end and the discharge end of the quartz tube, respectively, and the two graphite electrodes apply pressure to the mixture.

[0042] D12. Argon gas is continuously purged into the quartz tube to form a protective atmosphere. The two graphite electrodes are connected to a DC power supply with a voltage of 45V and a current of 12.5A±0.5A. The temperature of the mixture in the quartz tube is controlled to rise to 800℃±5℃ within 5 minutes. Then, it is maintained at this temperature for 180s. During the heating process, an internal electric field is generated by the applied voltage, and no external non-contact electric field is applied throughout the entire process.

[0043] D13. Subsequently, the intermediate obtained in the first stage is subjected to a second stage of heat treatment. The capacitor discharge system is controlled to discharge with a pulse of 280V. The pulse generates a peak current of 1800A±100A in the partially carbonized material. This instantaneous Joule heating process heats the mixture to a second temperature of 2300℃±50℃ within 500ms. It is then maintained at this temperature for 150s. During the second stage of energized heating, an internal electric field is generated inside the material by the applied voltage. No external non-contact electric field is applied throughout the entire process to promote the high-temperature rearrangement and graphitization of the carbon structure.

[0044] D14. Stop heating, continue to purge with argon gas until cooling to room temperature, then collect the black product. Perform Raman spectroscopy analysis on the obtained product. Figure 7 The display shows identifiable 2D characteristic peaks, and the D peak and G peak are clearly distinguishable, but their Approximately 0.7, Approximately 0.8, 2D peak FWHM approximately The product yield is approximately 28% of the dry weight of the starting biomass.

[0045] Compared with Examples 1-3, the carbon structure of Comparative Example 1 was converted into graphene to a limited extent and had more structural defects, showing that the two-stage heat treatment combined with an external electric field can promote the ordering of the carbon structure and the conversion into graphene with fewer structural defects.

[0046] Comparative Example 2 D21. Mix acacia trunk wood with a moisture content not exceeding 20% ​​(by mass) with carbon black accounting for 2% of the mass of the acacia trunk wood to form a uniform mixture. Fill the mixture into a quartz tube in a Joule furnace. The acacia trunk wood has a particle size of approximately 1 mm and a weight of approximately 5 g, the carbon black has a mass of 0.1 g, and the ratio of the inner diameter to the length of the quartz tube is 1:10. Two graphite electrodes are located at the feed end and the discharge end of the quartz tube, respectively, and the two graphite electrodes apply pressure to the mixture to ensure good electrical contact.

[0047] D22. Argon gas is continuously introduced into the quartz tube to purge it and create a protective atmosphere. The two graphite electrodes are connected to the capacitor discharge system.

[0048] D23. Under an inert atmosphere, the mixture is subjected to a single-stage heat treatment. The capacitor discharge system is controlled to discharge with a 280V pulse. The pulse generates Joule heating in the material, carbonizes the material, and generates a peak current of 1800A±100A. This instantaneous Joule heating process heats the mixture to a second temperature of 2300℃±50℃ within 500ms. It is then maintained at this temperature for 150s. During the energized heating process, an internal electric field is formed by the applied voltage. No external non-contact electric field is applied throughout the entire process.

[0049] D24. Stop heating and stop applying the electric field, continue to introduce argon gas until it cools to room temperature, and then collect the black product. Figure 8 Raman spectroscopy analysis revealed identifiable 2D characteristic peaks, with the D peak clearly distinguishable from the G peak, but its... Approximately 0.55, Approximately 1.1, 2D peak FWHM approximately The product yield is approximately 15% of the dry weight of the starting biomass.

[0050] Compared to Comparative Example 1, Comparative Example 2 showed a poorer degree of carbon structure transformation into graphene and higher structural defects, indicating that the two-stage heat treatment combined with an external electric field can promote the ordering of the carbon structure and the transformation into graphene with fewer structural defects. Furthermore, the mass yield of the product was only 15% of the dry weight of the starting biomass, indicating that the material underwent excessive gasification and ablation under single-stage high-temperature long-term treatment conditions.

[0051] Comparative Example 3 D31. Place acacia trunk wood with a moisture content of no more than 20% (by mass) into an alumina crucible and then place it into a quartz tube. The acacia trunk wood has a particle size of about 1 mm and weighs about 5 g. The quartz tube is equipped with a tungsten plate electrode and is placed parallel to the reaction zone to provide an external non-contact electric field.

[0052] D32. Argon gas is continuously purged into the quartz tube to create a protective atmosphere. The tube is heated at a rate of 10°C / min until it reaches the first temperature range of 800°C ± 5°C, and maintained for 30 minutes. This promotes the removal of volatiles and carbonization of the biomass, forming carbonization intermediates. During this first stage, an external non-contact electric field with a strength of approximately 4600 N / C is simultaneously applied. This external electric field is applied independently of the heating method and is used to induce the polarization and orientation of carbon fragments during carbonization, thereby promoting the formation of a semi-ordered carbon framework structure.

[0053] Heating and the applied electric field were stopped, while argon gas was continuously introduced until cooling to room temperature. The black product was then collected. The mass yield of the product was approximately 40% of the dry weight of the starting biomass. The structure of the black product was characterized by Raman spectroscopy, and the results are as follows: Figure 9 As shown.

[0054] from Figure 9 As can be seen, the product obtained under an applied external electric field exhibits identifiable 2D characteristic peaks in its Raman spectrum, while the overlap between the D and G peaks decreases, resulting in clearer separation. These spectral characteristics indicate that the carbon structure of this product no longer displays the typical Raman response of highly amorphous carbon, but rather shows carbon structural ordering and rearrangement and expansion of the sp² carbon domains. The Raman spectroscopy results show that the product exhibits a graphitization trend, forming a layered sp² carbon structure with graphene-like characteristics. Furthermore… Figure 10The results show that under the applied electric field, the XRD pattern exhibits a distinct and sharp (002) diffraction peak near a broad peak at approximately 23.9° and at approximately 25.9°, with an even clearer (100) / (101) characteristic peak at 42.8°, indicating a significant improvement in the orderliness and crystallinity of the carbon sheet structure. This demonstrates that the applied electric field can promote the orientation of carbon atoms and the formation of the layered graphite structure during the first-stage heating process.

[0055] Comparing Comparative Example 3 with Examples 1-3, it was found that an external non-contact electric field can induce a limited degree of carbon structure ordering under a single thermal stage, but this ordering remains in the graphitization intermediate state; however, when the external electric field is combined with a two-stage thermal process, a complete transformation from amorphous carbon to a highly ordered layered sp² carbon structure can be achieved.

[0056] Comparative Example 4 D41. Place acacia trunk wood with a moisture content of no more than 20% (by mass) into an alumina crucible and then place it into a quartz tube. The acacia grains are approximately 1 mm in diameter and weigh approximately 5 g.

[0057] D42. Argon gas is continuously purged into the quartz tube to create a protective atmosphere. The tube is heated to a first temperature of 800℃±5℃ at a heating rate of 10℃ / min and maintained for 30 min. Heating is then stopped, but argon gas is continuously purged until the tube cools to room temperature. The black product is then collected. The product yield is approximately 40% of the dry weight of the starting biomass.

[0058] D43. The structure of the black product was characterized by Raman spectroscopy, and the results are as follows: Figure 11 As shown. From Figure 11 It is evident that the product obtained under normal heating conditions without an external electric field did not exhibit identifiable 2D characteristic peaks in its Raman spectrum. The D peak and G peak showed significant overlap or fusion, indicating that the material is predominantly a highly amorphous carbon structure and has not formed a layered sp² carbon structure with graphene-like characteristics. Furthermore... Figure 12 The XRD pattern in the first-stage heating process without an applied external electric field shows only a broad peak at approximately 23.9°, accompanied by a weak broad shoulder peak near 43.2°, indicating that the carbon structure is still predominantly amorphous or low-order. This demonstrates that only the first-stage heating process cannot promote the orientation of carbon atoms and the formation of layered graphite structures.

[0059] The product treated in step D41 and the product treated in steps S32 and S33 in Example 3 were subjected to conductivity tests under different compaction conditions. The results are as follows: Figure 13 As shown.

[0060] from Figure 13 As can be seen from this, compared with simple furnace heating, the first stage of applying an electric field (1 st Heating during the first stage process can increase the conductivity of the sample by more than two orders of magnitude, from approximately 0.061 S / cm to approximately 6.1 S / cm. Further, a second stage (2...) is performed. nd After stage process electric field treatment, the conductivity increased to 93.2 S / cm, showing that the electric field can effectively promote the orientation of carbon atoms and the formation of graphitized structure, thereby effectively enhancing the conductivity of the material.

[0061] Based on the above Examples 1-3 and Comparative Examples 1-4, it can be seen that only when the applied electric field is combined with two-stage heating can the transformation from amorphous carbon to highly ordered layered sp32-particle carbon be completed while maintaining yield. 2 The transformation of carbon structure ultimately yields graphene with good morphological integrity, high crystallinity, and excellent electrical conductivity.

[0062] The above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, such as combining different features in various embodiments, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing graphene, characterized in that, Includes the following steps: The carbon source material is subjected to a first heat treatment at a first temperature. A first electric field is applied to the carbon source material undergoing the first heat treatment to obtain an intermediate product; The intermediate product is subjected to a second heat treatment at a second temperature. A second electric field is applied to the intermediate product subjected to the second heat treatment to obtain graphene; Wherein, the first temperature is not lower than 800℃, and the second temperature is not higher than 3000℃ but higher than the first temperature; The electric field strength of the first electric field is not less than 500 N / C, and the electric field strength of the second electric field is not more than 20000 N / C and is higher than the electric field strength of the first electric field.

2. The method for preparing graphene according to claim 1, characterized in that, The carbon source material is selected from at least one of biomass, hard carbon, plastics, coal, and coke.

3. The method for preparing graphene according to claim 2, characterized in that, The biomass is selected from lignocellulose.

4. The method for preparing graphene according to claim 3, characterized in that, When the carbon source material is selected from lignocellulose and the first heat treatment uses a Joule furnace, a conductive carbon source also needs to be added.

5. The method for preparing graphene according to claim 4, characterized in that, The conductive carbon source is selected from conductive carbon black; and / or, The conductive carbon source accounts for 1% to 3% of the total mass of the carbon source material.

6. The method for preparing graphene according to any one of claims 1 to 5, characterized in that, The first temperature is in the range of 800℃ to 1500℃, and the first temperature is maintained for 3 min to 5 min; and / or, The second temperature is in the range of 2000℃ to 3000℃, and the time for maintaining the second temperature is 2.5 min to 5 min.

7. The method for preparing graphene according to any one of claims 1 to 5, characterized in that, The electric field strength of the first electric field is maintained within the range of 500 N / C to 5000 N / C, and the duration of maintaining the first electric field is 30 s to 6000 s; and / or, The electric field strength of the second electric field is maintained in the range of 5000 N / C to 20000 N / C, excluding 5000 N / C, and the duration of the second electric field is maintained from 15 s to 150 s.

8. The method for preparing graphene according to any one of claims 1 to 5, characterized in that, In the graphene, the carbon content reaches 97% or more by mass, and the heteroatom content is no more than 3% by mass; and / or, The carbon source material is placed in any one of a Joule furnace, muffle furnace, tube furnace, or electric arc furnace.

9. The method for preparing graphene according to any one of claims 1 to 5, characterized in that, When the first electric field is applied, the carbon source material is placed within the effective electric field strength region of the first electric field; and / or, When the second electric field is applied, the intermediate product is placed within the effective electric field strength region of the second electric field.

10. A graphene, characterized in that, The graphene is prepared using the preparation method described in any one of claims 1 to 9.

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