Method for preparing graphene quantum dots from retired graphite

Abstract

The application relates to a method for preparing graphene quantum dots from retired graphite, which comprises the following steps: after ball milling activation of retired graphite, activated retired graphite is obtained; the activated retired graphite is added into a mixed solution of concentrated nitric acid and concentrated sulfuric acid, the graphite is uniformly dispersed, then a hydrothermal reaction is carried out in a sealed reaction container while stirring; after the reaction is completed, the solution in the reaction container is cooled to room temperature, then the solution is diluted with deionized water, a hot alkali solution is added to make the solution neutral, centrifugation is carried out, solid-liquid separation is carried out, unreacted graphite is removed, and a first solution is collected; the collected first solution is cooled, solid-liquid separation is carried out, and a second solution is collected; the second solution is dialyzed by using a dialysis bag, the obtained liquid is dried, and graphene quantum dots are obtained; by the method, retired graphite can be effectively converted into graphene quantum dots with high conversion rate, pollution of waste graphite to the environment is avoided, and high-value recycling of low-value waste resources is realized.

Description

Technical Field

[0001] This invention relates to the field of waste battery recycling technology, and more specifically, to a method for preparing graphene quantum dots from decommissioned graphite. Background Technology

[0002] Lithium-ion batteries, as a green and environmentally friendly secondary power source, have been widely used in 3C products and electric vehicles due to their high energy density, long cycle life, and lack of memory effect. Lithium-ion power batteries typically consist of a casing, positive electrode material, negative electrode material, Al / Cu current collector, separator, and electrolyte. Graphite, due to its good conductivity, reversible high lithium storage capacity, and long and stable plateau, is widely used in the negative electrode materials of lithium-ion batteries. However, the rapid development of the lithium-ion battery industry generates a large amount of waste graphite, which is classified as solid waste and faces the problems of low economic value for recycling and serious environmental pollution. If this waste graphite could be processed into high-quality graphene quantum dots, it would improve the economic benefits of graphite negative electrode recycling and avoid environmental pollution. Moreover, the raw material cost of waste graphite is far lower than that of high-purity graphite, making it suitable as a raw material for the production of graphene quantum dots. For example, Chinese patent 201811358813.2 discloses a method for preparing graphene quantum dots from waste lithium-ion batteries. In this method, after removing the current collector of the negative electrode, the resulting graphite-containing mixture is heated and filtered, and then microwave digested, dialyzed, and eluted with molecular sieves to obtain graphene quantum dots. However, the graphite conversion rate in this method is low (approximately 16-18%), resulting in a large waste of retired graphite. Summary of the Invention

[0003] Based on the aforementioned technical problems in the existing technology, the present invention provides a method for preparing graphene quantum dots from decommissioned graphite. The inventors have discovered that the interlayer spacing of recycled decommissioned graphite is larger than that of pure graphite. After activation, it can be easily oxidized and made into uniform graphene quantum dots through a specific method.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] A method for preparing graphene quantum dots from decommissioned graphite includes the following steps:

[0006] S1. After ball milling and activation, decommissioned graphite is obtained;

[0007] S2. The activated decommissioned graphite is added to a mixed solution of concentrated nitric acid and concentrated sulfuric acid to disperse the graphite evenly. Then, a hydrothermal reaction is carried out in a sealed reaction vessel while stirring.

[0008] S3. After the reaction is complete, cool to room temperature, then dilute the solution in the reaction vessel with deionized water, then add an alkaline solution to make the solution neutral, centrifuge, separate the solid and liquid, remove unreacted graphite, and collect the first solution.

[0009] S4. Cool the first solution collected in step S3 to separate the solid and liquid, and collect the second solution.

[0010] S5. Dialyze the second solution using a dialysis bag. After drying the resulting liquid, graphene quantum dots are obtained.

[0011] In some embodiments, during step S1, the ball milling speed is 300-800 rpm / min and the ball milling time is 1-6 h.

[0012] In some embodiments, in step S2, the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:2-6.

[0013] In some embodiments, the concentration of concentrated nitric acid is 65-68%; the concentration of concentrated sulfuric acid is 95-98%.

[0014] In some embodiments, in step S2, the solid-liquid ratio of graphite and the mixed solution is 1g:40-80mL.

[0015] In some embodiments, in step S2, the hydrothermal reaction temperature is 90-120°C; the reaction time is 12-24 hours.

[0016] In some embodiments, in step S3, the alkali includes at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium carbonate, potassium bicarbonate, potassium hydroxide, magnesium hydroxide, zinc hydroxide, magnesium carbonate, lithium carbonate, and ammonia.

[0017] In some embodiments, in step S3, hot sodium carbonate solution is first added to the solution, followed by dropwise heating of sodium hydroxide solution until the solution is neutral; wherein the temperature of the hot sodium carbonate solution is 60-80℃, and the concentration of the sodium carbonate solution is 3.0-3.9 mol / L.

[0018] In some embodiments, the temperature of the hot sodium hydroxide is 70-90°C, and the concentration of the sodium hydroxide solution is 45-50 mol / L.

[0019] In some implementations, in step S1, the decommissioned graphite is obtained by the following method:

[0020] The negative electrode of the waste battery is immersed in ethanol to wash away the electrolyte; then it is immersed in NMP, heated to 70-90℃, kept at this temperature for 4-6 hours, and then the negative electrode is removed. The graphite is scraped off from the current collector and then placed in ethanol for ultrasonication. After ultrasonication, it is left to stand and dried to obtain decommissioned graphite.

[0021] In some implementations, graphite is placed in ethanol and sonicated for 1-2 hours, then left to stand for 84-96 hours, with the ethanol being replaced every 12 hours.

[0022] In some embodiments, the graphene quantum dots are dried at 90-120°C for 24-48 hours. Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The inventors discovered that the interlayer spacing of recycled decommissioned graphite is larger than that of pure graphite. Based on this, they used decommissioned graphite as raw material, activated it, oxidized it with a specific oxidant, and then processed it to obtain graphene quantum dots. This achieves high-value recycling of low-value waste resources, avoids solid waste pollution caused by waste graphite, and activates the decommissioned graphite before oxidation, which helps to improve the conversion rate of decommissioned graphite, so that the yield of graphene quantum dots can reach more than 58%.

[0024] In addition, the alkaline solution used in the neutralization of acid solution in this invention is heated first, which requires less volume compared to using room temperature alkaline solution, resulting in a smaller volume of waste liquid to be treated subsequently. Furthermore, saturated small molecule salts can be precipitated by cooling, reducing dialysis time and the number of water changes, further simplifying the subsequent treatment process. Attached Figure Description

[0025] Figure 1 This is a TEM image of the graphene quantum dot material prepared in Example 1 of the present invention;

[0026] Figure 2 The image shows the XRD pattern of the graphene quantum dot material prepared in Example 1 of this invention.

[0027] Figure 3 The XPS C1s spectrum of the graphene quantum dot material prepared in Example 1 of this invention;

[0028] Figure 4 The XPS O1s spectrum of the graphene quantum dot material prepared in Example 1 of this invention;

[0029] Figure 5 The image shows the FTIR spectrum of the graphene quantum dot material prepared in Example 1 of this invention. Detailed Implementation

[0030] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0032] Example 1

[0033] A method for preparing graphene quantum dots from decommissioned graphite includes the following steps:

[0034] First, the negative electrode of the waste battery is soaked in ethanol for 24 hours to wash away the electrolyte. Then, the negative electrode of the waste battery is soaked in NMP (N-methylpyrrolidone) for 12 hours. The solution is heated to 80°C and kept at that temperature for 5 hours. Then, the negative electrode of the waste battery is removed, and the graphite is scraped off from the copper foil. The waste graphite is placed in ethanol and sonicated for 2 hours, then left to stand for 84 hours, with the ethanol being changed every 12 hours. The broken copper foil in the waste graphite is picked out and placed in a forced-air drying oven at 90°C for 24 hours. After drying, the decommissioned graphite is obtained.

[0035] Retired graphite was ball-milled at 500 rpm for 2 hours, then immediately added to a mixed solution of concentrated HNO3 and H2SO4 (concentrated nitric acid (68%) and concentrated sulfuric acid (98%) in a volume ratio of 1:3, with a total solution volume of 60 ml). The mixture was stirred for 30 minutes, then sonicated for 30 minutes until the retired graphite was uniformly dispersed in the mixed solution. Subsequently, the mixed solution was placed in a sealed high-pressure reactor, heated to 90°C, and subjected to a hydrothermal reaction at 300 rpm for 24 hours. After the reaction was completed, the mixture was allowed to cool naturally. After cooling to room temperature, the solution was diluted with 20 mL of deionized water (DI). Then, 20 g of Na2CO3 was heated and dissolved in 50 mL of deionized water, which was then poured into the mixture to neutralize some of the acid. Next, 55 g of NaOH was heated and dissolved in 30 mL of water, and added dropwise until the pH of the mixture was adjusted to neutral. After centrifugation and filtration, the solution was allowed to stand for 24 h to allow the large amount of supersaturated salt in the system to cool and precipitate. Then, the solution was further dialyzed in a dialysis bag to remove small molecule salts. The liquid obtained after dialysis was freeze-dried to obtain graphene quantum dot powder.

[0036] Testing showed that the method in this embodiment achieved a graphene quantum dot yield of 58%.

[0037] The obtained graphene quantum dot material was subjected to TEM and XRD tests, and the results are as follows: Figure 1 and Figure 2 As shown. Among them, Figure 1 This is a TEM image of the graphene quantum dot material. Figure 2 This is the XRD pattern of the graphene quantum dot material.

[0038] like Figure 1As shown, the graphene quantum dot material obtained in this embodiment has a particle size of 2-5 nm, is uniformly distributed, and has no obvious agglomeration phenomenon.

[0039] like Figure 2 As shown, the diffraction peak of graphite at 26.6° disappeared after acid oxidation, indicating that the two-dimensional structure of graphite was destroyed, and GQDs were successfully synthesized by exfoliating graphite.

[0040] like Figure 3 As shown, the high-resolution C1s fine spectrum can be divided into three peaks at 284.8, 286.5, and 288.3 eV, corresponding to the CC / C=C, CO, and OC=O bonds, respectively.

[0041] like Figure 4 As shown, the O 1s XPS spectrum shows four types of peaks at 531.1, 531.5, 532.4 and 535.6 eV, which belong to OC=O, CO, C-OH and H2O, respectively.

[0042] The functional groups of GQDs were detected using Fourier transform infrared (FT-IR). Figure 5 As shown, 1105 and 1619cm -1 The peak at 3433 cm⁻¹ is attributed to the stretching vibrations of the CO and OC=O groups; -1 The broad absorption band at this point indicates the typical stretching vibration of the hydroxyl groups in GQDs. Therefore, it suggests that the GQDs formed after oxidative exfoliation contain abundant oxygen-containing functional groups.

[0043] Example 2

[0044] A method for preparing graphene quantum dots from decommissioned graphite includes the following steps:

[0045] First, the negative electrode of the waste battery was soaked in ethanol for 48 hours to wash away the electrolyte. Then, the negative electrode of the waste battery was soaked in NMP (N-methylpyrrolidone) for 24 hours. The solution was heated to 90°C and kept at that temperature for 6 hours. Then, the negative electrode of the waste battery was removed, and the graphite was scraped off from the copper foil. The waste graphite was placed in ethanol and sonicated for 2 hours, then left to stand for 96 hours, with the ethanol being changed every 12 hours. The broken copper foil in the waste graphite was picked out and placed in a forced-air drying oven at 90°C for 24 hours. After drying, the decommissioned graphite was obtained.

[0046] After ball milling decommissioned graphite at 700 rpm for 2 hours, it was immediately added to a mixed solution of concentrated HNO3 and H2SO4 (concentrated nitric acid (68%) and concentrated sulfuric acid (98%) in a volume ratio of 1:4, with a total solution volume of 50 ml). The mixture was stirred for 30 minutes, followed by sonication for 30 minutes until the decommissioned graphite was uniformly dispersed in the mixed solution. Subsequently, the mixed solution was placed in a sealed high-pressure reactor, heated to 120°C, and subjected to hydrothermal reaction with stirring at 300 rpm for 24 hours. After the reaction was completed, the mixture was allowed to cool naturally. After reaching room temperature, the solution was diluted with 20 mL of deionized water (DI). Then, 20 g of Na2CO3 was heated and dissolved in 50 mL of deionized water, which was then poured into the mixture to neutralize some of the acid. Next, 55 g of NaOH was heated and dissolved in 30 mL of water, and added dropwise until the pH of the mixture was adjusted to neutral. After centrifugation and filtration, the solution was allowed to stand for one day to allow the large amount of supersaturated salt in the system to cool and precipitate. Then, the solution was further dialyzed in a dialysis bag to remove small molecule salts. The liquid obtained after dialysis was freeze-dried to obtain graphene quantum dot powder.

[0047] Testing showed that the method in this embodiment yielded a graphene quantum dot yield of 56.7%.

[0048] The graphene quantum dots obtained by the method of the present invention have a particle size of 3-8 nm, are uniformly distributed, and have no obvious agglomeration.

[0049] Comparative Example 1

[0050] A method for preparing graphene quantum dots from ordinary graphite includes the following steps:

[0051] Graphite powder was added to a mixed solution of concentrated HNO3 and H2SO4 (the volume ratio of concentrated nitric acid (68%) to concentrated sulfuric acid (98%) was 1:3, and the total solution volume was 60 ml). The solution was stirred for 30 min, then sonicated for 30 min until the degraded graphite was uniformly dispersed in the mixed solution. Subsequently, the mixed solution was placed in a sealed high-pressure reactor, heated to 90°C, and subjected to a hydrothermal reaction at a stirring rate of 300 rpm / min for 24 h. After the reaction was completed, the solution was allowed to cool naturally to room temperature, and then 20 mL of [unspecified solution] was used to [unspecified reaction]. After dilution with deionized water (DI), Na2CO3 (20g) was heated and dissolved in 50mL of deionized water, and poured into the mixture to neutralize some of the acid. Then, NaOH (55g) was heated and dissolved in 30mL of water, and added dropwise until the pH of the mixture was adjusted to neutral. After centrifugation and filtration, the mixture was allowed to stand for 24 hours to cool and precipitate a large amount of supersaturated salt. Then, it was further dialyzed in a dialysis bag to remove small molecule salts. The liquid obtained after dialysis was freeze-dried to obtain graphene quantum dot powder.

[0052] According to the test results, the yield of graphene quantum dots using the comparative method was 25%.

[0053] The graphene quantum dots obtained by the method in this comparative example have a particle size of 5-10 nm and no obvious agglomeration.

[0054] Comparative Example 2

[0055] A method for preparing graphene quantum dots from decommissioned graphite includes the following steps:

[0056] First, the negative electrode of the waste battery was soaked in ethanol for 48 hours to wash away the electrolyte. Then, the negative electrode of the waste battery was soaked in NMP (N-methylpyrrolidone) for 24 hours. The solution was heated to 90°C and kept at that temperature for 6 hours. Then, the negative electrode of the waste battery was removed, and the graphite was scraped off from the copper foil. The waste graphite was placed in ethanol and sonicated for 2 hours, then left to stand for 96 hours, with the ethanol being changed every 12 hours. The broken copper foil in the waste graphite was picked out and placed in a forced-air drying oven at 90°C for 24 hours. After drying, the decommissioned graphite was obtained.

[0057] The decommissioned graphite was ball-milled at 700 rpm / min for 2 hours and then left to stand for 24 hours.

[0058] The ball-milled and settled decommissioned graphite was added to a mixed solution of concentrated HNO3 and H2SO4 (concentrated nitric acid (68%) and concentrated sulfuric acid (98%) in a volume ratio of 1:3, with a total solution volume of 60 ml), stirred for 30 min, and then sonicated for 30 min until the decommissioned graphite was uniformly dispersed in the mixed solution. Subsequently, the mixed solution was placed in a sealed high-pressure reactor, heated to 120 °C, and subjected to hydrothermal reaction at a stirring rate of 300 rpm / min for 24 h. After the reaction was completed, it was naturally cooled to room temperature, and then... After diluting with 0 mL of deionized water (DI), Na2CO3 (20 g) was heated and dissolved in 50 mL of deionized water. This solution was then poured into the mixture to neutralize some of the acid. NaOH (55 g) was then heated and dissolved in 30 mL of water. This solution was added dropwise until the pH of the mixture was adjusted to neutral. After centrifugation and filtration, the mixture was allowed to stand for one day to allow the large amount of supersaturated salt in the system to precipitate. Then, it was further dialyzed in a dialysis bag to remove small molecule salts. The liquid obtained after dialysis was freeze-dried to obtain graphene quantum dot powder.

[0059] Testing showed that the method in this embodiment yielded 48.7% of graphene quantum dots.

[0060] The graphene quantum dots obtained by the method of the present invention have a particle size of 3-9 nm, are uniformly distributed, and have no obvious agglomeration.

[0061] Comparative Example 3

[0062] A method for preparing graphene quantum dots from decommissioned graphite includes the following steps:

[0063] First, the negative electrode of the waste battery is soaked in ethanol for 24 hours to wash away the electrolyte. Then, the negative electrode of the waste battery is soaked in NMP (N-methylpyrrolidone) for 12 hours. The solution is heated to 80°C and kept at that temperature for 5 hours. Then, the negative electrode of the waste battery is removed, and the graphite is scraped off from the copper foil. The waste graphite is placed in ethanol and sonicated for 2 hours, then left to stand for 84 hours, with the ethanol being changed every 12 hours. The broken copper foil in the waste graphite is picked out and placed in a forced-air drying oven at 90°C for 24 hours. After drying, the decommissioned graphite is obtained.

[0064] Retired graphite was ball-milled at 500 rpm for 2 hours, then immediately added to a mixed solution of concentrated HNO3 and H2SO4 (concentrated nitric acid (68%) and concentrated sulfuric acid (98%) in a volume ratio of 1:3, with a total solution volume of 60 ml). The mixture was stirred for 30 minutes, then sonicated for 30 minutes until the retired graphite was uniformly dispersed in the mixed solution. Subsequently, the mixed solution was placed in a sealed high-pressure reactor and heated to 90°C for a hydrothermal reaction for 24 hours. After the reaction was completed, it was naturally cooled to room temperature and then... After diluting with 1 mL of deionized water (DI), Na2CO3 (20 g) was heated and dissolved in 50 mL of deionized water. This solution was then poured into the mixture to neutralize some of the acid. NaOH (55 g) was then heated and dissolved in 30 mL of water. This solution was added dropwise until the pH of the mixture was adjusted to neutral. After centrifugation and filtration, the mixture was allowed to stand for 24 h to allow a large amount of supersaturated salt in the system to precipitate. Then, the mixture was further dialyzed in a dialysis bag to remove small molecule salts. The liquid obtained after dialysis was freeze-dried to obtain graphene quantum dot powder.

[0065] Testing showed that the method in this embodiment yielded 42% of graphene quantum dots.

[0066] The graphene quantum dots obtained by the method of the present invention have a particle size of 4-9 nm, are uniformly distributed, and have no obvious agglomeration.

[0067] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method of preparing graphene quantum dots from decommissioned graphite, the method comprising: The method comprises the following steps: ​ S1, activating the retired graphite by ball milling to obtain activated retired graphite; S2, adding the activated retired graphite into a mixed solution of concentrated nitric acid and concentrated sulfuric acid to uniformly disperse the graphite, and then performing a hydrothermal reaction in a sealed reaction container while stirring; S3, after the reaction is completed, cooling to room temperature, then diluting the solution in the reaction container with deionized water, then adding a hot alkali solution to neutralize the solution, centrifuging, solid-liquid separation, removing unreacted graphite, and collecting a first solution; S4, cooling the first solution collected in step S3 to precipitate supersaturated salts neutralized by the hot alkali, solid-liquid separation, and collecting a second solution; S5, dialyzing the second solution with a dialysis bag, drying the obtained liquid to obtain graphene quantum dots; The retired graphite is obtained by the following method: immersing the negative electrode of the waste battery in ethanol, washing away the electrolyte, then immersing in NMP, heating to 70-90℃, taking out the negative electrode after 4-6h of heat preservation, scraping the graphite off the current collector, then ultrasonically treating in ethanol, standing after the ultrasonic treatment is completed, and drying to obtain the retired graphite.

2. The method of claim 1, wherein the method comprises: In step S1, the ball milling speed is 300-800rpm / min, and the ball milling time is 1-6h.

3. The method of claim 1, wherein the method comprises: In step S2, the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:2-6.

4. The method of claim 1, wherein the method comprises: In step S2, the solid-liquid ratio of graphite to the mixed solution is 1g:40-80mL.

5. The method of claim 1, wherein the method further comprises the step of: 5.

1. removing the graphene quantum dots from the reactor. In step S2, the hydrothermal reaction temperature is 90-120℃, and the reaction time is 12-24h.

6. The method of claim 1, wherein the method further comprises: In step S3, the alkali includes at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium carbonate, potassium bicarbonate, potassium hydroxide, magnesium hydroxide, zinc hydroxide, magnesium carbonate, lithium carbonate, and ammonia water.

7. The method of claim 1, wherein the method further comprises the step of: In step S3, first add a hot sodium carbonate solution into the solution, then drop a hot sodium hydroxide solution until the solution is neutral; the temperature of the hot sodium carbonate solution is 60-80℃, the concentration of the sodium carbonate solution is 3.0-3.9mol / L; and / or, the temperature of the hot sodium hydroxide is 70-90℃, and the concentration of the sodium hydroxide solution is 45-50mol / L. ​ 8. The method of claim 1, wherein the method is characterized by, In step S4, the collected first solution is cooled by an ice water bath, the temperature of the ice water bath is 3-10℃, and the ice water bath time is 6-10h.

9. The method for preparing graphene quantum dots from decommissioned graphite according to claim 1, characterized in that, Ultrasonically treat the graphite in ethanol for 1-2h, and stand for 84-96h, replacing the ethanol every 12h.

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