Preparation method and production device of graphene powder

Abstract

The application belongs to the technical field of graphene powder preparation, and particularly relates to a graphene powder preparation method and production device. The method comprises the following steps: pretreatment and intercalation; first-stage oxidation; second-stage oxidation; thermal expansion and peeling; green reduction and defect repair. The application uses a mild sulfonic acid-based aromatic compound to perform pre-intercalation in step 1, thereby creating a channel for subsequent oxidizing agents to enter the interlayer; a relatively mild oxidation-reduction system of persulfate / organic acid is used to perform first-stage oxidation at low temperature in step 2, thereby avoiding instantaneous and violent heat release; and a strong oxidizing agent is slowly added at medium temperature to perform deep oxidation in step 3. This step-by-step and mild oxidation strategy greatly reduces the dependence on strong acid, thereby reducing the generation amount of acidic waste liquid from the source.

Description

Technical Field

[0001] This invention relates to the field of graphene powder preparation technology, specifically to a method and apparatus for preparing graphene powder. Background Technology

[0002] Graphene, as a two-dimensional material with excellent electrical, thermal, and mechanical properties, has always been a core focus of industrialization and applied research in terms of its large-scale preparation technology. Currently, the chemical oxidation-reduction method is considered one of the most promising routes for preparing graphene powder due to its relatively low cost and ease of scale-up production. The core steps of this route typically include: oxidizing and intercalating natural graphite with strong oxidants and strong acids to prepare graphene oxide, followed by expansion exfoliation and reduction to obtain graphene powder.

[0003] The classic Hummers process and its improvements, while widely used, still suffer from several inherent drawbacks. First, environmental pollution and safety issues are prominent: the reaction requires large quantities of hazardous chemicals such as concentrated sulfuric acid and potassium permanganate, generating highly acidic wastewater with high permanganate content, resulting in high treatment costs, and the strongly exothermic reaction carries a risk of runaway. Second, the degree of oxidation is difficult to control precisely: the vigorous oxidation reaction indiscriminately introduces numerous oxygen-containing functional groups (such as epoxy and carboxyl groups) onto the graphite matrix, severely damaging the sp² carbon lattice structure of graphene and generating irreversible lattice defects. This directly leads to a large number of topological defects in the final reduced graphene powder, significantly reducing its intrinsic properties such as electrical and thermal conductivity. Finally, the limitations of traditional reduction methods: commonly used chemical reducing agents such as hydrazine hydrate are highly toxic, while thermal reduction methods are energy-intensive, and graphene sheets are prone to uncontrolled agglomeration and recombination during reduction, making it difficult to obtain single-layer or few-layer graphene powders with high specific surface area and a loose structure.

[0004] Therefore, there is an urgent need in this field to develop a new method that is environmentally friendly, has a safe and controllable process, and can produce low-defect, high-performance graphene powder. Summary of the Invention

[0005] To solve the above-mentioned technical and safety problems, the technical solution adopted by the present invention is as follows: A method for preparing graphene powder includes the following steps: (1) Pretreatment and intercalation: Natural graphite powder is mixed with a solution of intercalating agent A and stirred at 40-80°C for 1-5 hours. Then, solid-liquid separation is performed to obtain pre-intercalated graphite. The intercalating agent A is an aromatic compound containing sulfonic acid groups, and its mass ratio with graphite powder is 1:10 to 1:2. (2) First stage oxidation: The pre-intercalated graphite obtained in step (1) is mixed with the first oxidant B in a low temperature environment, wherein the low temperature environment is 0-10℃, and the reaction is carried out for 0.5-2 hours; the first oxidant B is a mixture of persulfate and organic acid, wherein the molar ratio of persulfate to organic acid is 1:1 to 1:3, and the mass ratio of the first oxidant B to the pre-intercalated graphite is 2:1 to 5:1; (3) Second stage oxidation: Transfer the mixture obtained in step (2) to a medium temperature environment and slowly add the second oxidant C, controlling the addition rate to maintain the reaction temperature at 20-40℃. After the addition is complete, continue the reaction for 2-6 hours. The second oxidant C is potassium permanganate or potassium chlorate, and its addition amount is 0.5 to 2 times the mass of the pre-intercalated graphite. (4) Thermal expansion exfoliation: The product after the reaction in step (3) is washed until neutral and then dried at 80-120°C to obtain expandable graphite oxide; then the expandable graphite oxide is rapidly transferred to a reactor preheated to 800-1200°C under a protective atmosphere and subjected to thermal shock treatment for 10-60 seconds to obtain a fluffy graphene precursor. (5) Green reduction and defect repair: The graphene precursor obtained in step (4) is uniformly dispersed in the vapor atmosphere of reducing agent D and treated at 200-400℃ for 1-4 hours to complete the reduction and defect repair, and the graphene powder is obtained; the reducing agent D is one of ascorbic acid, hydrogen iodide vapor or hydroiodic acid vapor.

[0006] Preferably, the aromatic compound containing a sulfonic acid group is one of p-aminobenzenesulfonic acid, sodium dodecylbenzenesulfonate, or sodium naphthalenesulfonate; the solution of the intercalating agent A is an aqueous solution or an alcohol-water mixture, with a mass concentration of 5%-20%.

[0007] Preferably, in step (2), the persulfate is ammonium persulfate or potassium persulfate; the organic acid is at least one of oxalic acid, citric acid or tartaric acid; the low-temperature mixing is performed under ultrasonic assistance, with an ultrasonic power of 100-500W and an ultrasonic frequency of 20-40kHz.

[0008] Preferably, in step (3), the rate of slow addition is controlled as follows: the second oxidant C is added at a uniform rate over 30-90 minutes; during the reaction, the pH value of the reaction system is monitored by an online pH monitor, and the pH value of the reaction system is dynamically stabilized within the range of 1-3 by adding dilute acid or dilute alkali solution.

[0009] Preferably, in step (4), the protective atmosphere is nitrogen or argon; the thermal shock treatment is carried out in a vertical tube high-temperature furnace, and the expandable graphite oxide is placed in a high-temperature resistant boat. The bottom of the boat is provided with uniformly distributed micropores with a pore size of 10-50 micrometers. The protective gas is introduced from the bottom of the furnace tube and passes through the micropores to fluidize the graphite, ensuring uniform thermal expansion.

[0010] Preferably, in step (5), the vapor of the reducing agent D is obtained by placing the solid or liquid reducing agent D in a separate evaporation chamber and carrying the vapor to the reaction chamber containing the graphene precursor by a carrier gas; the carrier gas is nitrogen or argon and the gas flow rate is 50-200 mL / min.

[0011] Preferably, after step (5), a post-processing step is also included: the reduced graphene powder is subjected to high-temperature annealing in an inert atmosphere, with an annealing temperature of 1500-2500℃ and an annealing time of 10-30 minutes, in order to further eliminate lattice defects and improve electrical conductivity.

[0012] Preferably, the graphene powder obtained in step (5) has 1-5 layers, a specific surface area of ​​500-800 m² / g, an intensity ratio (ID / IG) of D peak to G peak in Raman spectrum of less than 0.2, and an electrical conductivity of greater than 1000 S / cm.

[0013] Preferably, the waste liquid generated in steps (2) and (3) is collected and then oxidized by passing ozone through it to convert the residual manganese ions into manganese dioxide precipitate for recovery. The treated clear liquid is used to prepare the intercalating agent A solution in step (1) to realize the recycling of waste liquid.

[0014] Due to the adoption of the above technical solution, the technical progress achieved by this invention compared to the prior art is as follows: This invention employs a step-by-step, gentle oxidation strategy. Step (1) involves pre-intercalation using a mild sulfonic acid-based aromatic compound to create pathways for the subsequent entry of the oxidant into the interlayer. Step (2) uses a relatively mild redox system of persulfate / organic acid at low temperature for the first stage of oxidation, avoiding sudden and intense exothermic reactions. Step (3) then slowly adds a strong oxidant at a moderate temperature for deep oxidation. This step-by-step, gentle oxidation strategy significantly reduces dependence on strong acids (such as concentrated sulfuric acid), thereby reducing the amount of acidic wastewater generated at the source. Simultaneously, the reaction process is mild and controllable, avoiding safety risks caused by runaway reactions, which aligns with the development direction of green chemistry.

[0015] This invention achieves a "meticulous refinement" of the oxidation degree of graphene precursors through staged oxidation and precise control of the addition rate of the second oxidant and the reaction pH value, ensuring that the precursors are fully exfoliated while preserving the integrity of the sp² carbon skeleton to the maximum extent. More importantly, step (5) uses a reducing agent vapor for gas-phase reduction, allowing vapor molecules to penetrate deep between the graphene sheets, resulting in a more thorough and uniform reduction. Compared to liquid-phase reduction, this effectively avoids the re-stacking and agglomeration of sheets caused by solvent surface tension. Furthermore, the gas-phase reduction process can also repair some defects such as carbon vacancies generated during oxidation, resulting in graphene powder with extremely low ID / IG values ​​and high electrical conductivity, and its structural integrity and electrical properties are close to theoretical values.

[0016] This invention relates to a wastewater recycling scheme. The manganese-containing wastewater generated during the oxidation stage is treated with ozone oxidation to recover manganese ions as economically valuable manganese dioxide, thus turning heavy metal resources from waste into valuable resources. The treated clarified liquid can be used to prepare the initial intercalating agent solution, forming a closed-loop cycle that significantly reduces the consumption of fresh water and wastewater discharge. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the steps of a method for preparing graphene powder according to the present invention. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to embodiments: according to Figure 1 A method for preparing graphene powder includes the following steps: A method for preparing graphene powder includes the following steps: 1. Pretreatment and intercalation: Mix natural graphite powder with a solution of intercalating agent A, stir at 40-80℃ for 1-5 hours, and then perform solid-liquid separation to obtain pre-intercalated graphite; intercalating agent A is an aromatic compound containing sulfonic acid groups, and its mass ratio with graphite powder is 1:10 to 1:2. 2. First stage oxidation: The pre-intercalated graphite obtained in step 1 is mixed with the first oxidant B in a low-temperature environment of 0-10℃ for 0.5-2 hours; the first oxidant B is a mixture of persulfate and organic acid, wherein the molar ratio of persulfate to organic acid is 1:1 to 1:3, and the mass ratio of the first oxidant B to the pre-intercalated graphite is 2:1 to 5:1; 3. Second stage oxidation: Transfer the mixture obtained in step 2 to a medium temperature environment and slowly add the second oxidant C, controlling the addition rate to maintain the reaction temperature at 20-40℃. After the addition is complete, continue the reaction for 2-6 hours. The second oxidant C is potassium permanganate or potassium chlorate, and its addition amount is 0.5 to 2 times the mass of the pre-intercalated graphite. 4. Thermal expansion exfoliation: The product after the reaction in step 3 is washed until neutral and then dried at 80-120℃ to obtain expandable graphite oxide; then the expandable graphite oxide is rapidly transferred to a reactor preheated to 800-1200℃ under a protective atmosphere and subjected to thermal shock treatment for 10-60 seconds to obtain a fluffy graphene precursor. 5. Green reduction and defect repair: The graphene precursor obtained in step 4 is uniformly dispersed in the vapor atmosphere of reducing agent D and treated at 200-400℃ for 1-4 hours to complete the reduction and defect repair, and obtain graphene powder; the reducing agent D is one of ascorbic acid, hydrogen iodide vapor or hydroiodic acid vapor.

[0019] Preferably, in step (1), the aromatic compound containing a sulfonic acid group is one of p-aminobenzenesulfonic acid, sodium dodecylbenzenesulfonate, or sodium naphthalenesulfonate; the solution of intercalating agent A is an aqueous solution or an alcohol-water mixture, with a mass concentration of 5%-20%. In this specific embodiment, the stirring speed is 300-600 rpm to ensure that the intercalating agent molecules can be fully and uniformly embedded into the graphite interlayer structure; more preferably, the alcohol in the alcohol-water mixture is ethanol or isopropanol, and the volume ratio of alcohol to water is 1:4 to 1:1. This ratio helps to improve the solubility and penetration efficiency of the nonpolar intercalating agent in the system.

[0020] Preferably, the persulfate is ammonium persulfate or potassium persulfate; the organic acid is at least one of oxalic acid, citric acid or tartaric acid; the low-temperature mixing is carried out under ultrasonic assistance, with an ultrasonic power of 100-500W and an ultrasonic frequency of 20-40kHz. In this specific embodiment, organic acid and persulfate constitute a redox system, which generates free radicals in situ at low temperature. These free radicals can gently and effectively attack the graphite edges and interlayers to achieve initial oxidation. At the same time, organic acid ions can serve as intercalation aids. Ultrasonic assistance is performed in an intermittent mode, such as working for 2 seconds and then pausing for 1 second, to prevent local overheating and ensure the uniformity and controllability of the oxidation reaction.

[0021] Preferably, the slow addition rate is controlled as follows: the second oxidant C is added at a uniform rate over 30-90 minutes; during the reaction, the pH value of the reaction system is monitored by an online pH monitor, and the pH value of the reaction system is dynamically stabilized within the range of 1-3 by adding dilute acid or dilute alkali solution dropwise. In this specific embodiment, the dilute acid is sulfuric acid or hydrochloric acid with a concentration of 5%-10%, and the dilute alkali is sodium carbonate or sodium hydroxide solution with a concentration of 5%-10%. By precisely controlling the pH within this strong acid range, the oxidation efficiency of oxidants such as potassium permanganate can be optimized, while the occurrence of side reactions (such as the formation of chlorine pentoxide) can be suppressed to the maximum extent, ensuring the structural integrity of the final product.

[0022] Preferably, the protective atmosphere is nitrogen or argon; the thermal shock treatment is carried out in a vertical tube high-temperature furnace, and the expandable graphite oxide is placed in a high-temperature resistant boat. The bottom of the boat has uniformly distributed micropores with a pore size of 10-50 micrometers. The protective gas is introduced from the bottom of the furnace tube and fluidizes the graphite through the micropores to ensure uniform thermal expansion. In this specific embodiment, the heating rate of the thermal shock treatment is extremely high, reaching over 1000°C / second. The graphite particles undergo tremendous thermal stress in an instant, thereby achieving efficient exfoliation. The boat is made of high-temperature ceramic or porous graphite, which can withstand repeated rapid heating and cooling processes.

[0023] Preferably, the vapor of reducing agent D is obtained by placing solid or liquid reducing agent D in a separate evaporation chamber and carrying the vapor to a reaction chamber containing the graphene precursor by a carrier gas; the carrier gas is nitrogen or argon, and the gas flow rate is 50-200 mL / min. In this specific embodiment, when the reducing agent D is ascorbic acid, the temperature of the evaporation chamber is controlled at 120-180℃; when the reducing agent D is hydroiodic acid, the temperature of the evaporation chamber is controlled at 80-120℃. This gas-phase reduction method avoids the problem of graphene sheets re-stacking and agglomerating due to the surface tension of the solvent in liquid-phase reduction. Vapor molecules can penetrate deep into the interlayer, resulting in more thorough reduction and repairing some defects such as carbon vacancies caused by oxidation.

[0024] Preferably, after step (5), a post-processing step is also included: the reduced graphene powder is subjected to high-temperature annealing in an inert atmosphere, the annealing temperature is 1500-2500℃ and the annealing time is 10-30 minutes, in order to further eliminate lattice defects and improve electrical conductivity. In this specific embodiment, the high-temperature annealing treatment is carried out in a graphitization furnace or an electric arc furnace, with a heating rate of 5-20°C / minute. Through this high-temperature process, topological defects such as five-membered rings and seven-membered rings in the graphene carbon six-membered ring network can be effectively "annealed", significantly reducing carrier scattering, thereby making the conductivity close to the level of ideal graphene.

[0025] Preferably, the graphene powder obtained in step (5) has 1-5 layers, a specific surface area of ​​500-800 m² / g, an intensity ratio (ID / IG) of D peak to G peak in Raman spectrum of less than 0.2, and an electrical conductivity of greater than 1000 S / cm. In this specific embodiment, the graphene powder exhibits a typical three-dimensional fluffy porous network morphology under a scanning electron microscope, with abundant lamellar folds and cross-linking. This structure is beneficial for its mechanical interlocking and stress transfer with the matrix in the composite material. Its BET specific surface area is preferably 650-750 m² / g, and its ID / IG value is preferably less than 0.15, which indicates that it has extremely high structural integrity and lattice quality.

[0026] Preferably, the waste liquid generated in steps (2) and (3) is collected and then oxidized by passing ozone through it to convert the residual manganese ions into manganese dioxide precipitate for recovery. The treated clear liquid is used to prepare the intercalating agent A solution in step (1) to realize the recycling of waste liquid. In this specific embodiment, the ozone injection rate is 10-50 mg of ozone per liter of waste liquid for 0.5-1 hour. The reaction endpoint is determined by the removal of the characteristic color (such as pink or brown) from the waste liquid. The precipitated manganese dioxide can be sold as a chemical raw material after filtration and drying. This not only realizes the recovery of heavy metal resources, but also significantly reduces the discharge and treatment costs of high-salinity wastewater, making the entire production process conform to the principles of green chemistry. Example

[0027] Includes the following steps: 1. Pretreatment and intercalation: Mix natural graphite powder with a solution of intercalating agent A, stir at 40-80℃ for 1-5 hours, and then perform solid-liquid separation to obtain pre-intercalated graphite; intercalating agent A is an aromatic compound containing sulfonic acid groups, and its mass ratio with graphite powder is 1:10 to 1:2. 2. First stage oxidation: The pre-intercalated graphite obtained in step 1 is mixed with the first oxidant B in a low-temperature environment of 0-10℃ for 0.5-2 hours; the first oxidant B is a mixture of persulfate and organic acid, wherein the molar ratio of persulfate to organic acid is 1:1 to 1:3, and the mass ratio of the first oxidant B to the pre-intercalated graphite is 2:1 to 5:1; 3. Second stage oxidation: Transfer the mixture obtained in step 2 to a medium temperature environment and slowly add the second oxidant C, controlling the addition rate to maintain the reaction temperature at 20-40℃. After the addition is complete, continue the reaction for 2-6 hours. The second oxidant C is potassium permanganate or potassium chlorate, and its addition amount is 0.5 to 2 times the mass of the pre-intercalated graphite. 4. Thermal expansion exfoliation: The product after the reaction in step 3 is washed until neutral and then dried at 80-120℃ to obtain expandable graphite oxide; then the expandable graphite oxide is rapidly transferred to a reactor preheated to 800-1200℃ under a protective atmosphere and subjected to thermal shock treatment for 10-60 seconds to obtain a fluffy graphene precursor. 5. Green reduction and defect repair: The graphene precursor obtained in step 4 is uniformly dispersed in the vapor atmosphere of reducing agent D and treated at 200-400℃ for 1-4 hours to complete the reduction and defect repair, and obtain graphene powder; the reducing agent D is one of ascorbic acid, hydrogen iodide vapor or hydroiodic acid vapor.

[0028] The present invention has been described in detail above. However, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, any modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A method for preparing graphene powder, characterized in that, Includes the following steps: (1) Pretreatment and intercalation: Natural graphite powder is mixed with a solution of intercalating agent A and stirred at 40-80°C for 1-5 hours. Then, solid-liquid separation is performed to obtain pre-intercalated graphite. The intercalating agent A is an aromatic compound containing sulfonic acid groups, and its mass ratio with graphite powder is 1:10 to 1:

2. (2) First stage oxidation: The pre-intercalated graphite obtained in step (1) is mixed with the first oxidant B in a low temperature environment, wherein the low temperature environment is 0-10℃, and the reaction is carried out for 0.5-2 hours; the first oxidant B is a mixture of persulfate and organic acid, wherein the molar ratio of persulfate to organic acid is 1:1 to 1:3, and the mass ratio of the first oxidant B to the pre-intercalated graphite is 2:1 to 5:1; (3) Second stage oxidation: Transfer the mixture obtained in step (2) to a medium temperature environment and slowly add the second oxidant C, controlling the addition rate to maintain the reaction temperature at 20-40℃. After the addition is complete, continue the reaction for 2-6 hours. The second oxidant C is potassium permanganate or potassium chlorate, and its addition amount is 0.5 to 2 times the mass of the pre-intercalated graphite. (4) Thermal expansion exfoliation: The product after the reaction in step (3) is washed until neutral and then dried at 80-120°C to obtain expandable graphite oxide; then the expandable graphite oxide is rapidly transferred to a reactor preheated to 800-1200°C under a protective atmosphere and subjected to thermal shock treatment for 10-60 seconds to obtain a fluffy graphene precursor. (5) Green reduction and defect repair: The graphene precursor obtained in step (4) is uniformly dispersed in the vapor atmosphere of reducing agent D and treated at 200-400℃ for 1-4 hours to complete the reduction and defect repair, and the graphene powder is obtained; the reducing agent D is one of ascorbic acid, hydrogen iodide vapor or hydroiodic acid vapor.

2. The method for preparing graphene powder according to claim 1, characterized in that, In step (1), the aromatic compound containing sulfonic acid group is one of p-aminobenzenesulfonic acid, sodium dodecylbenzenesulfonate or sodium naphthalenesulfonate; the solution of intercalating agent A is an aqueous solution or an alcohol-water mixture, with a mass concentration of 5%-20%.

3. The method for preparing graphene powder according to claim 1, characterized in that, In step (2), the persulfate is ammonium persulfate or potassium persulfate; the organic acid is at least one of oxalic acid, citric acid or tartaric acid; the low-temperature mixing is carried out under ultrasonic assistance, with an ultrasonic power of 100-500W and an ultrasonic frequency of 20-40kHz.

4. The method for preparing graphene powder according to claim 1, characterized in that, In step (3), the rate of slow addition is controlled as follows: the second oxidant C is added at a uniform rate over 30-90 minutes; during the reaction, the pH value of the reaction system is monitored by an online pH monitor, and the pH value of the reaction system is dynamically stabilized within the range of 1-3 by adding dilute acid or dilute alkali solution.

5. The method for preparing graphene powder according to claim 1, characterized in that, In step (4), the protective atmosphere is nitrogen or argon; the thermal shock treatment is carried out in a vertical tube high-temperature furnace, and the expandable graphite oxide is placed in a high-temperature resistant boat. The bottom of the boat is provided with uniformly distributed micropores with a pore size of 10-50 micrometers. The protective gas is introduced from the bottom of the furnace tube and passes through the micropores to fluidize the graphite, ensuring uniform thermal expansion.

6. The method for preparing graphene powder according to claim 1, characterized in that, In step (5), the vapor of the reducing agent D is obtained by placing the solid or liquid reducing agent D in a separate evaporation chamber and carrying the vapor to the reaction chamber containing the graphene precursor by a carrier gas; the carrier gas is nitrogen or argon and the gas flow rate is 50-200 mL / min.

7. The method for preparing graphene powder according to claim 1, characterized in that, After step (5), a post-processing step is also included: the reduced graphene powder is subjected to high-temperature annealing in an inert atmosphere at a temperature of 1500-2500℃ for 10-30 minutes to further eliminate lattice defects and improve electrical conductivity.

8. The method for preparing graphene powder according to claim 1, characterized in that, The graphene powder obtained in step (5) has 1-5 layers, a specific surface area of ​​500-800 m² / g, an intensity ratio (ID / IG) of D peak to G peak in Raman spectrum of less than 0.2, and an electrical conductivity of greater than 1000 S / cm.

9. The method for preparing graphene powder according to claim 1, characterized in that, After the waste liquid generated in steps (2) and (3) is collected, ozone is introduced for oxidation treatment to convert the residual manganese ions into manganese dioxide precipitate for recovery. The treated clear liquid is used for the preparation of intercalating agent A solution in step (1) to realize the recycling of waste liquid.

10. A production apparatus for graphene powder, characterized in that, The method comprising any one of claims 1-9.

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