Process for the preparation of graphite intercalation compounds and graphene oxide

Abstract

The application provides a preparation method of a graphite intercalation compound, comprising the following steps: mixing graphite and sulfuric acid, adding hydrogen peroxide into the reaction system, stirring until the mixed system is blue, and obtaining a graphite intercalation compound solution. The application also provides a preparation method of graphene oxide, comprising the following steps: S1: taking the graphite intercalation compound solution prepared by the above method; S2: slowly adding an oxidizing agent into the graphite intercalation compound solution at a first temperature, and stirring; S3: increasing the temperature of the mixed system in the step S2 to a second temperature, and continuously stirring to complete the oxidation reaction; S4: adding water into the system treated in the step S3, and performing a hydration reaction; and S5: washing and separating to obtain graphene oxide. In the synthesis process of the graphene oxide, the amount of the oxidizing agent is reduced to 1-2 times, and the exfoliation state of the graphene oxide is good.

Description

Technical Field

[0001] This invention relates to graphite intercalation compounds and methods for preparing graphene oxide, belonging to the technical field of Hummers method for preparing graphene oxide. Background Technology

[0002] Currently, the Hummers series of methods are used for the mass production of graphene oxide. This method primarily involves preparing graphene oxide under specific solvent conditions, with graphite and an oxidant in a certain ratio, through a strictly controlled temperature, hydration, and purification process. CN110697698A uses a sulfuric acid and phosphoric acid solution, or an acid solution containing sulfuric acid and phosphorus pentoxide, and the oxidant is potassium permanganate and / or potassium ferrate, with a ratio between 1:4 and 1:3. Patent CN112723351A uses at least one of concentrated sulfuric acid, concentrated hydrochloric acid, concentrated nitric acid, and concentrated phosphoric acid as an intercalating agent. The graphene oxide preparation process in this patent involves multiple oxidation and heating steps, with the mass ratio of graphite to the second oxidant and acid solution being 1:3-6:10-40. It is noteworthy that the amount of oxidant used in this type of graphene oxide preparation process is relatively high, generally more than three times the amount of graphite. This also means that a correspondingly large amount of waste salt will be generated later. Furthermore, the reaction systems mentioned above all involve substances such as nitrogen and phosphorus that are harmful to the environment, and the mixed pollutants produced by the mixed acid system have extremely high treatment costs.

[0003] In the development of the Hummers process for preparing graphene oxide, H2O2 is generally added in the later stages of the reaction to consume the remaining oxidant and terminate the reaction. It is rare to add it to the reaction system in the early stages. In patent CN110697698A, H2O2 is added to the reaction solution to form acid-intercalated graphite at 75-85℃. Patent CN112723351A uses H2O2 as the primary oxidant, with a graphite to H2O2 mass ratio of 1:0.5-9. In CN112723351A, H2O2 is used as the primary oxidant at a temperature not exceeding 2℃ for 10-30 minutes. Patent CN103408000B uses H2O2 during mixing, but requires washing and drying to obtain layered graphite before proceeding to the next oxidation experiment. Furthermore, the amount of oxidant used is three times or more than the amount of graphite. A high amount of oxidant means more waste salts are generated later, resulting in higher costs. Summary of the Invention

[0004] In view of the above problems, the present invention provides a method for preparing a graphite intercalation compound, comprising: mixing graphite with sulfuric acid, adding hydrogen peroxide to the reaction system, stirring until the mixture turns blue, and obtaining a graphite intercalation compound solution.

[0005] According to one aspect of the invention, the graphite is natural graphite; preferably, the graphite purity is ≥90wt%; preferably, the graphite particle size is 100-500 mesh. During the synthesis of GO, the different sizes of graphite affect the subsequent GO exfoliation. Particle sizes smaller than 100 mesh, being too large, easily lead to incomplete oxidation, resulting in a large number of black particles in the material; particle sizes larger than 500 mesh, being too small, easily lead to excessive oxidation, reducing the yield. Simultaneously, small-sized GO is more prone to folding and agglomeration, forming thick flakes.

[0006] According to one aspect of the invention, the concentration of the sulfuric acid is ≥96%;

[0007] Preferably, the weight ratio of graphite to sulfuric acid is 1:(30-45); more preferably, it is 1:(37-40). In the reaction system, sulfuric acid is used as a solvent. If the amount of sulfuric acid is less than 30%, the reaction system becomes too viscous, resulting in uneven heat exchange and a tendency for localized overheating. If the amount of sulfuric acid is more than 45%, the reaction system becomes too dilute, leading to waste of sulfuric acid. A viscosity ratio of 37-40 is appropriate, neither affecting heat exchange in the reaction system nor causing sulfuric acid waste.

[0008] According to one aspect of the present invention, the concentration of hydrogen peroxide is ≥27.5 wt%, for example, the concentration of hydrogen peroxide is 27.5 wt%-60 wt%; if the concentration of hydrogen peroxide is too high, it is easy to explode, and if the concentration of hydrogen peroxide is too low, the intercalation effect is poor.

[0009] Preferably, the amount of hydrogen peroxide added satisfies the mass ratio of graphite to hydrogen peroxide as 1:(0.15-0.40); more preferably 1:(0.2-0.25). Adding too little H2O2 is not conducive to the formation of blue graphite intercalation compounds, while adding too much will cause a chemical reaction with KMnO4 in the later stage, reducing the amount of KMnO4 available for oxidation, which is not conducive to the preparation of graphene oxide.

[0010] According to one aspect of the present invention, hydrogen peroxide is added at a system temperature of 5-25°C. Under these conditions, H2O2 is not easily decomposed. If H2O2 is added to the reaction system above 25°C, it will decompose and fail to achieve a good intercalation effect. Temperatures below 5°C will affect the intercalation rate. Preferably, hydrogen peroxide is added at a system temperature of 10±2°C. The preferred temperature range will not affect the decomposition of H2O2 or the intercalation reaction rate.

[0011] This invention also provides a method for preparing graphene oxide, comprising:

[0012] S1: Take the graphite intercalation compound solution prepared by the above method;

[0013] S2: At the first temperature, an oxidant is added to the graphite intercalation compound solution. Preferably, the oxidant is added to the graphite intercalation compound solution while stirring, so as to prevent severe local heat release.

[0014] S3: Heat the mixture from step S2 to the second temperature and stir continuously to complete the oxidation reaction;

[0015] S4: Add water to the system after step S3 to carry out the hydration reaction and peel off the graphene oxide;

[0016] S5: Washing and separation yields graphene oxide.

[0017] According to another aspect of the invention, the second temperature is 25-40°C higher than the first temperature. The rate of oxidation reaction is affected by temperature; as the temperature increases, the reaction rate and the heat released per unit time increase exponentially. At low reaction temperatures, the reaction rate is slow and the reaction time is long; at high reaction temperatures, the reaction rate is fast, heat is released too quickly, the reaction is difficult to control, and it may even cause an explosion. Within a given temperature range, the reaction is easy to control and the reaction rate is relatively fast.

[0018] According to another aspect of the invention, the first temperature is 0-5°C. In the reaction system, the addition of the oxidant is itself an exothermic reaction. If the temperature is higher than 5°C, the temperature is prone to runaway and rise suddenly during the addition of the oxidant. Under the condition of 0-5°C, the temperature is easier to control during the addition of the oxidant.

[0019] According to another aspect of the invention, the second temperature is 30-40°C. The rate of oxidation reaction is affected by temperature; as the temperature increases, the reaction rate and the heat released per unit time increase exponentially. At low reaction temperatures, the reaction rate is slow and the reaction time is long; at high reaction temperatures, the reaction rate is fast, heat is released too quickly, the reaction is difficult to control, and it may even cause an explosion. Within a given temperature range, the reaction is easy to control and the reaction rate is relatively fast.

[0020] According to another aspect of the invention, the amount of water added in the hydration reaction is 1-2 times the volume of sulfuric acid; preferably, the system temperature during the hydration reaction is controlled at 70-80°C. Adding water initiates the hydration stripping process; too little or too much water will affect the final stripping of GO, resulting in thick flakes or black particles.

[0021] According to another aspect of the invention, the oxidant is KMnO4;

[0022] Preferably, the mass ratio of graphite to oxidant is 1:(1.0-2.0); more preferably, it is 1:(1.0-1.2). The difficulty in GO synthesis lies in achieving good GO exfoliation under low oxidant dosage conditions. This is also the focus of our patent. A higher oxidant dosage than 2.0 results in good GO exfoliation, but increases the production cost of GO; a lower oxidant dosage than 1.0 results in low GO oxidation, poor exfoliation, and more black particles and thick flakes.

[0023] Compared to existing patents on graphene oxide preparation based on the Hummers method, this patent can reduce the amount of oxidant used in the graphene oxide synthesis process by 1-2 times, and the graphene oxide exhibits excellent exfoliation properties. The main principle is:

[0024] H₂O₂ + H₂SO₄ → HSO₄ - +H3O + +O

[0025] In the presence of H₂O₂, it can react with sulfuric acid to form HSO₄⁻ ions, which then intercalate into graphite. Figure 1 The graphite of a transforms into Figure 1 The graphite intercalation compound of b, the overall solution appears blue (e.g. Figure 2 Compared to graphite, Figure 1 The interlayer spacing of graphite intercalation compounds (b) increases. The oxidation of graphite sheets by the oxidant is a diffusion-controlled process. The graphite intercalation compounds formed after the addition of H2O2 have a larger interlayer spacing, making it easier for the oxidant to enter the graphite interlayers and oxidize the graphite sheets. It is worth noting that this invention patent clearly explains the role of H2O2 in the formation of blue graphite intercalation compounds and the principle behind reducing the amount of oxidant used. Based on the above principles, a significant reduction in the amount of oxidant used in the synthesis of graphene oxide has been achieved, reducing it to 1-2 times the amount of graphite used. This amount is lower than that of current patents using the Hummers method to synthesize graphene oxide.

[0026] This invention, based on the existing Hummers process, adds a pretreatment step for graphite. A certain amount of H₂O₂ is added to a mixed solution of graphite and concentrated sulfuric acid, forming HSO₄⁻ ions in the solution, which then perform intercalation treatment on the graphite to form… Figure 1The graphite intercalation compound b, in its mixed solution, exhibits a blue color. This method increases the interlayer spacing of the graphite sheets in the intercalated compound, facilitating the entry of subsequent oxidative activity into the interlayer and oxidizing the graphite sheets. Using this H₂O₂ intercalation method to form the graphite intercalation compound can improve the oxidation efficiency of the oxidant, reducing the amount of oxidant required to 1 to 2 times the mass of graphite. Notably, under conditions of 5-30℃, the amount of H₂O₂ required is only 0.15-0.40 times the mass of graphite, which is sufficient to convert graphite into a blue graphite intercalation compound. Simultaneously, the amount of oxidant required is reduced to 1-2 times the amount of graphite. Attached Figure Description

[0027] Figure 1 a- Figure 1 b is a schematic diagram of graphite transforming into a graphite intercalation compound;

[0028] Figure 2 yes Figure 1 A photograph of the graphite intercalation compound b under an optical microscope;

[0029] Figure 3 This is an optical microscope image of graphene oxide from Example 1;

[0030] Figure 4 This is an optical microscope image of graphene oxide from Example 2;

[0031] Figure 5 This is an optical microscope image of graphene oxide from Example 3;

[0032] Figure 6 This is a light microscope image of graphene oxide from Example 4;

[0033] Figure 7 This is an optical microscope image of graphene oxide from Example 5;

[0034] Figure 8 This is an optical microscope image of graphene oxide in Comparative Example 1. Detailed Implementation

[0035] In the following description, numerous specific details are set forth for illustrative purposes and to provide a thorough understanding of one or more embodiments. However, it will be apparent that these embodiments may also be implemented without these specific details. In other instances, well-known structures and devices are shown in block diagram form for ease of description of one or more embodiments.

[0036] The various embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0037] Example 1:

[0038] The preparation method of graphene oxide in this embodiment includes the following steps:

[0039] (1) In a reactor, 100-mesh graphite is mixed with sulfuric acid (the mass ratio of graphite to sulfuric acid is 1:30). Then, at 5°C, H2O2 (the mass ratio of graphite to H2O2 is 1:0.15) is added and stirred for 2 hours to perform pre-intercalation, forming... Figure 1 The graphite intercalation compound of b appears as a blue solution;

[0040] (2) Under ice-water bath conditions (the temperature of the reaction system is controlled at 0-5℃), KMnO4 (the mass ratio of graphite to KMnO4 is 1:1.5) is slowly added to the reactor and stirred.

[0041] (3) Heat the mixed solution formed in step (2) to 30°C and stir continuously for 3 hours;

[0042] (4) Add water at a volume 1.5 times that of sulfuric acid to the reactor, and control the temperature of the reaction system below 80℃; then, after washing, separate to obtain graphene oxide, such as... Figure 3 .

[0043] Example 2:

[0044] The method for preparing graphene oxide in this embodiment includes the following steps:

[0045] (1) In a reactor, 200-mesh graphite is mixed with sulfuric acid (the mass ratio of graphite to sulfuric acid is 1:35). Then, at 15°C, H2O2 (the mass ratio of graphite to H2O2 is 1:0.2) is added and stirred for 2 hours to perform pre-intercalation, forming... Figure 1 The graphite intercalation compound of b appears as a blue solution;

[0046] (2) Under ice-water bath conditions, KMnO4 (the mass ratio of graphite to KMnO4 is 1:1.7) is slowly added to the reactor and stirred.

[0047] (3) Heat the mixed solution formed in step (2) to 35°C and stir continuously for 3 hours;

[0048] (4) Add water to the reactor in an amount twice the volume of sulfuric acid, and control the temperature of the reaction system below 80℃; then wash and separate to obtain graphene oxide, such as... Figure 4 .

[0049] Example 3:

[0050] The method for preparing graphene oxide in this embodiment includes the following steps:

[0051] (1) In a reactor, 250-mesh graphite is mixed with sulfuric acid (the mass ratio of graphite to sulfuric acid is 1:35). Then, at 15°C, H2O2 (the mass ratio of graphite to H2O2 is 1:0.3) is added and stirred for 2 hours to perform pre-intercalation, forming... Figure 1 The graphite intercalation compound of b appears as a blue solution;

[0052] (2) Under ice-water bath conditions, KMnO4 (the mass ratio of graphite to KMnO4 is 1:1.6) is slowly added to the reactor and stirred.

[0053] (3) Heat the mixed solution formed in step (2) to 35°C and stir continuously for 4 hours;

[0054] (4) Add water to the reactor in an amount twice the volume of sulfuric acid, and control the temperature of the reaction system below 80℃; then wash and separate to obtain graphene oxide, such as... Figure 5 .

[0055] Example 4:

[0056] The method for preparing graphene oxide in this embodiment includes the following steps:

[0057] (1) In a reactor, 250-mesh graphite is mixed with sulfuric acid (the mass ratio of graphite to sulfuric acid is 1:35). Then, at 15°C, H2O2 (the mass ratio of graphite to H2O2 is 1:0.3) is added and stirred for 2 hours to perform pre-intercalation, forming... Figure 1 The graphite intercalation compound of b appears as a blue solution;

[0058] (2) Under ice-water bath conditions, KMnO4 (the mass ratio of graphite to KMnO4 is 1:1.8) is slowly added to the reactor and stirred.

[0059] (3) Heat the mixed solution formed in step (2) to 35°C and stir continuously for 4 hours;

[0060] (4) Add water at a volume 1.5 times that of sulfuric acid to the reactor, and control the temperature of the reaction system below 80℃; then, after washing, separate to obtain graphene oxide, such as... Figure 6 .

[0061] Example 5:

[0062] The method for preparing graphene oxide in this embodiment includes the following steps:

[0063] (1) In a reactor, 250-mesh graphite is mixed with sulfuric acid (the mass ratio of graphite to sulfuric acid is 1:37). Then, at 12°C, H2O2 (the mass ratio of graphite to H2O2 is 1:0.25) is added and stirred for 2 hours to perform pre-intercalation, forming... Figure 1 The graphite intercalation compound of b appears as a blue solution;

[0064] (2) Under ice-water bath conditions, KMnO4 (the mass ratio of graphite to KMnO4 is 1:1.2) is slowly added to the reactor and stirred.

[0065] (3) Heat the mixed solution formed in step (2) to 35°C and stir continuously for 4 hours;

[0066] (4) Add water at a volume 1.5 times that of sulfuric acid to the reactor, and control the temperature of the reaction system below 80℃; then, after washing, separate to obtain graphene oxide, such as... Figure 7 .

[0067] Comparative Example 1:

[0068] The preparation method of graphene oxide in this comparative example includes the following steps:

[0069] (1) Mix 250 mesh graphite with sulfuric acid in a reactor (the mass ratio of graphite to sulfuric acid is 1:35), and then stir for 2 hours at 15°C.

[0070] (2) Under ice-water bath conditions, KMnO4 (the mass ratio of graphite to KMnO4 is 1:1.8) is slowly added to the reactor and stirred.

[0071] (3) Heat the mixed solution formed in step (2) to 35°C and stir continuously for 4 hours;

[0072] (4) Add water at a volume 1.5 times that of sulfuric acid to the reactor, and control the temperature of the reaction system below 80℃; then, after washing, separate to obtain graphene oxide, such as... Figure 8 .

[0073] Depend on Figure 3-7 It can be seen that, under an optical microscope, the graphene oxide produced using the H2O2 intercalation process exhibits a relatively uniform light-colored flake appearance. Figure 3-7 In contrast, the graphene oxide prepared in Comparative Example 1 without the H2O2 intercalation process exhibited a colored, thick sheet-like appearance under an optical microscope. Figure 8 The above comparison of graphene oxide shows that, under conditions of low oxidant dosage, the H2O2 intercalation process can effectively achieve the exfoliation of graphene oxide.

[0074] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing graphene oxide, characterized in that, include: S1: After mixing graphite and sulfuric acid, hydrogen peroxide is added to the reaction system and stirred until the mixture turns blue to obtain a graphite intercalation compound solution. S2: At the first temperature, an oxidant is added to the graphite intercalation compound solution; S3: Heat the mixture from step S2 to the second temperature and stir continuously to complete the oxidation reaction; S4: Add water to the system after step S3 to carry out the hydration reaction; S5: Washing and separation yields graphene oxide; The graphite to oxidant mass ratio is 1:(1.0-2.0); the amount of hydrogen peroxide added satisfies the graphite:hydrogen peroxide mass ratio of 1:(0.15-0.40); the hydrogen peroxide is added at a system temperature of 5-25℃; the first temperature is 0-5℃; the second temperature is 30-40℃; and the oxidant is KMnO4.

2. The method for preparing graphene oxide according to claim 1, characterized in that, An oxidant is added while stirring the graphite intercalation compound solution.

3. The method for preparing graphene oxide according to claim 1, characterized in that, The graphite mentioned is natural graphite.

4. The method for preparing graphene oxide according to claim 3, characterized in that, The graphite purity is ≥90wt%.

5. The method for preparing graphene oxide according to claim 3, characterized in that, The graphite has a particle size of 100-500 mesh.

6. The method for preparing graphene oxide according to claim 1, characterized in that, The concentration of the sulfuric acid is ≥96%.

7. The method for preparing graphene oxide according to claim 1, characterized in that, The weight ratio of graphite to sulfuric acid is 1:(30-45).

8. The method for preparing graphene oxide according to claim 1, characterized in that, The weight ratio of graphite to sulfuric acid is 1:(37-40).

9. The method for preparing graphene oxide according to claim 1, characterized in that, The concentration of the hydrogen peroxide is ≥27.5wt%.

10. The method for preparing graphene oxide according to claim 1, characterized in that, The amount of hydrogen peroxide added satisfies the mass ratio of graphite to hydrogen peroxide of 1:(0.2-0.25).

11. The method for preparing graphene oxide according to claim 1, characterized in that, Hydrogen peroxide was added while maintaining the system temperature at 10±2℃.

12. The method for preparing graphene oxide according to claim 1, characterized in that, The second temperature is 25-40°C higher than the first temperature.

13. The method for preparing graphene oxide according to claim 1, characterized in that, The amount of water added for the hydration reaction is 1-2 times the volume of sulfuric acid.

14. The method for preparing graphene oxide according to claim 1, characterized in that, The temperature of the hydration reaction system is controlled at 70-80℃.

15. The method for preparing graphene oxide according to claim 1, characterized in that, The mass ratio of graphite to oxidant is 1:(1.0-1.2).

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