Weakly oxidized, large-size graphene and methods of making same

Abstract

The application provides weakly oxidized large-size graphene oxide and a preparation method thereof, and comprises the following steps: S1: after premixing graphite and concentrated sulfuric acid, the temperature in the kettle is reduced to below 10 DEG C by using a water chiller; S2: intercalation agent and protective agent are added to the system in step S1, and an intercalation reaction is completed to obtain intercalated oxide; S3: an oxidizing agent is added to the mixture in step S2, and an oxidation reaction is completed; S4: water is added to the system after the treatment in step S3 to perform a hydration reaction; and S5: weakly oxidized large-size graphene oxide is obtained after suction filtration and washing. Compared with the traditional Hummers method, the amount of oxidizing agent is reduced to 2.0, the cost of the oxidizing agent is reduced by about 33%, the average size of the obtained large-size weakly oxidized GO is about 81 mu m, and the oxygen content is less than or equal to 40%.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of graphene oxide and its preparation method, belong to the technical field of graphene oxide prepared by Hummers method. BACKGROUND

[0002] As the derivative of graphene, graphene oxide has abundant oxygen-containing functional groups, and it has good performance in mechanics, liquid crystal, energy storage and other aspects, so it has been widely used in optical fiber, flexible conductive film, liquid crystal optical material, energy storage material and other fields. At present, the commonly used method for large-scale preparation of graphene oxide is Hummers method, which mainly involves pre-mixing graphite and concentrated sulfuric acid in an ice water bath, then adding a certain proportion of potassium permanganate, and strictly controlling the temperature to obtain. Because the preparation of graphene oxide using small size graphite raw material can only obtain small size and high oxidation degree of graphene oxide, small flake diameter and high oxidation degree will affect the various properties of graphene, such as conductivity, thermal conductivity and regularity of flake stacking, and also increase the probability of flake aggregation, which seriously affects the next step application of graphene. And weak oxidation, large size graphene has good structural integrity and low oxidation degree, which can significantly enhance and increase the conductivity and specific surface area of single structure, and can effectively alleviate the above defects. Moreover, the increase of size makes the large size graphene-based material have higher and better mechanical properties, liquid crystal properties and film forming properties. Therefore, to prepare large size graphene, first of all, large size graphene oxide needs to be prepared.

[0003] Generally, graphene with a size greater than 50 micrometers is called large-size graphene. Hummers' rule, a primary method for preparing graphene oxide, requires large-size graphite as the raw material. Chinese patent CN201510042449, "A method for preparing large-size graphene oxide from natural flake graphite," uses untreated flake graphite of 200 mesh to 50 mesh to prepare large-size graphene oxide. However, its process involves dialysis collection, dispersion shearing, and centrifugal purification, increasing the process cycle and steps. Furthermore, the shearing dispersion and centrifugal collection result in uneven particle size distribution, ranging from 1 μm to 100 μm. Because large-size graphite increases the difficulty of oxidant intercalation, it cannot rapidly and effectively prepare large-size graphene oxide. To reduce the difficulty of intercalation of oxidants, patents such as CN201811634588 "A method for preparing large-size graphene oxide and the large-size graphene oxide obtained therefrom" and CN201510786386 "A method for preparing large-sheet graphene oxide" pre-intercalate graphite raw materials to obtain intercalated graphite, which is then oxidized to obtain large-size graphene oxide. However, the intercalation process of graphite raw materials is complex, such as electrochemical intercalation, and the obtained large-size graphene oxide has a high oxygen content and low yield.

[0004] The most crucial step in the preparation process is the oxidation reaction. When potassium permanganate is added to a mixture of graphite and concentrated sulfuric acid, HSO4 is generated. ～ ions, HSO4 ～ Intercalation of graphite and widening of the interlayer spacing allow the subsequently formed Mn2O7 to enter the interlayer for oxidation. This process is limited by the reaction conditions and the activity of graphite. Summary of the Invention

[0005] In view of the above problems, the present invention provides a simple, efficient, and scalable method for preparing weakly oxidized, large-size graphene oxide, characterized by comprising:

[0006] S1: After graphite is premixed with concentrated sulfuric acid, the temperature inside the reactor is lowered to below 10°C using a chiller to prevent the intercalating agent and oxidizing agent in S2 from decomposing violently due to heat.

[0007] S2: Add intercalating agent and protective agent to the system of step S1, and complete the intercalation reaction to obtain intercalated oxide;

[0008] S3: Add an oxidizing agent to the mixture from step S2 to complete the oxidation reaction;

[0009] S4: Add water to the system after step S3 to carry out a hydration reaction;

[0010] S5: After filtration and washing, weakly oxidized, large-sized graphene oxide is obtained.

[0011] Optionally, the steps S1 to S5 are completed in the same reactor.

[0012] Optionally, the graphite is flake graphite or expandable graphite.

[0013] Optionally, the carbon content of the graphite is more than 95%.

[0014] Optionally, the particle size of the flake graphite or expandable graphite is 50-200 mesh.

[0015] Optionally, the mass ratio of the graphite to concentrated sulfuric acid is 1:20-30; preferably 1:24.

[0016] Optionally, in step S2, the intercalation agent is hydrogen peroxide, preferably 27.5%-30% industrial grade reagent.

[0017] Optionally, in step S2, the protective agent is concentrated phosphoric acid, preferably 98% analytical pure reagent.

[0018] Optionally, in step S2, the amount of hydrogen peroxide and concentrated phosphoric acid added is 0.1-0.5 equivalent concentration and 2-3 equivalent concentration, respectively. Excessive addition of hydrogen peroxide will consume the oxidizing agent in the subsequent step, causing negative effects on the reaction. For the intercalation agent and the protective agent, separate addition of the intercalation agent can promote the exfoliation effect, but separate addition of the protective agent cannot promote the exfoliation.

[0019] Optionally, in step S2, the temperature of the intercalation reaction system is controlled to maintain at 5-20℃.

[0020] Optionally, in step S2, after adding the intercalation agent and the protective agent, the temperature is raised to 5-20℃ and maintained for 2-3h, so that the reactants are fully converted to indigo blue.

[0021] Optionally, in step S3, the oxidizing agent is potassium permanganate.

[0022] Optionally, the temperature of the oxidation reaction system is controlled to 30-40℃.

[0023] Optionally, the oxidation reaction time is 3-3.5h, so that the reactants are fully converted to grayish brown.

[0024] Optionally, in step S3, the amount of potassium permanganate added is 1.5-3 equivalent concentration, the temperature of the oxidation reaction system is controlled to 30-40℃, and the reaction is maintained for 3-3.5h, so that the reactants are fully converted to grayish brown.

[0025] Optionally, in step S4, the amount of water added for the hydration reaction is 1-2 times the amount of sulfuric acid.

[0026] Optionally, the temperature of the hydration reaction system is controlled at 70–80°C.

[0027] Optionally, the preparation method of weakly oxidized, large-size graphene oxide includes the following steps.

[0028] S1: After premixing graphite with concentrated sulfuric acid, the temperature inside the reactor is lowered to below 10°C using a chiller;

[0029] S2: Add H2O2 and H3PO4 to the system in step S1, and maintain the temperature below 10℃ for 2 to 3 hours to complete the intercalation reaction and obtain the intercalated oxide;

[0030] S3: Add potassium permanganate to the mixture from step S2 and keep it at 30-40°C for 3-3.5 hours to complete the oxidation reaction;

[0031] S4: Add twice the amount of deionized water as sulfuric acid to the system after step S3 to carry out the hydration reaction;

[0032] S5: After filtration and washing, weakly oxidized, large-sized graphene oxide is obtained.

[0033] According to another aspect of the present invention, a weakly oxidized, large-size graphene oxide is provided, which is prepared according to the above method, wherein the average size D3,2 of the graphene oxide is 81 μm.

[0034] Optionally, the oxygen content of the graphene oxide is ≤40%.

[0035] Optionally, the graphene oxide obtained by the method is prepared into a thermally conductive film with a thermal conductivity of 1500 W / mK or higher.

[0036] Given that the existing Hummers process for preparing large-size graphene uses large-size (50-200 mesh) graphite as raw material, it increases the difficulty of the oxidant in the intercalation stage and suffers from problems such as complex processes, high oxidant consumption, expensive oxidant, uneven size distribution of the produced graphene oxide, and over-oxidation. This invention, through multi-directional and comprehensive research, ultimately addresses the intercalation and oxidation problems of large-size graphite raw materials, achieving large-scale production of highly exfoliated, weakly oxidized graphene oxide while reducing oxidant consumption. The traditional Hummers process typically uses more than 3.0 equivalents of oxidant; compared to the traditional Hummers process, this invention reduces the oxidant consumption to 2.0, lowering the oxidant cost by approximately 33%.

[0037] Compared with the prior art, the method can expand the layer spacing of the graphite sheet layer, so that the oxidant is more easily entered between the graphite layers, the oxidation and peeling efficiency in the later stage is improved, and the amount of the oxidant is reduced; the phosphoric acid is added at the same time to avoid over-oxidation of the GO and protect the large-size structure.

[0038] The preparation method of the application omits centrifugal purification and dispersion shearing steps, avoids damage to the structure of the graphene oxide, and the obtained graphene oxide has an average size of 81 mu m and a narrow particle size distribution.

[0039] The weakly oxidized and large-size graphene oxide prepared by the method has an oxygen content of ≤40% and a D3,2≥50 mu m.

[0040] The graphene oxide prepared by the application has the characteristics of weak oxidation, large size and high peeling. In the laser flash method heat conduction test, the thermal conductivity coefficient can reach 1500 W / mK, and the conductive direction surface resistance test can reach the order of magnitude of ten squared. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is the optical microscope characterization of the graphene oxide in Comparative Example 1;

[0042] Figure 2 is the optical microscope characterization of the graphene oxide in Comparative Example 2;

[0043] Figure 3 is the optical microscope characterization of the graphene oxide in Comparative Example 3;

[0044] Figure 4 is the optical microscope characterization of the graphene oxide in Example 1;

[0045] Figure 5 is the particle size analyzer test result of the graphene oxide in Example 1 (refer to D3,2 area average diameter data);

[0046] Figure 6 is the particle size distribution histogram of the graphene oxide in Example 1;

[0047] Figure 7 is the optical microscope characterization of the graphene oxide in Example 2;

[0048] Figure 8 is the particle size analyzer test result of the graphene oxide in Example 2 (refer to D3,2 area average diameter data);

[0049] Figure 9is a particle size distribution histogram of the graphene oxide in Example 2; DETAILED DESCRIPTION

[0050] In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It can be evident, however, that such embodiment(s) can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more embodiments.

[0051] Various embodiments according to the present application will be described in detail below with reference to the accompanying drawings.

[0052] Example 1:

[0053] A method for preparing weakly oxidized, large-size graphene oxide, comprising the following steps:

[0054] (1) 25 g of 100-150 mesh flake graphite and 600 g of concentrated sulfuric acid are introduced into a reaction kettle for pre-mixing, and the temperature is reduced to below 10°C.

[0055] (2) 7.5 g of hydrogen peroxide and 50 g of phosphoric acid are added to the reaction kettle, and the intercalation reaction is carried out at 15°C to obtain an intercalation compound.

[0056] (3) 50 g of potassium permanganate is added to the mixture of step 2) and the temperature is raised for oxidation reaction.

[0057] (4) Pure water is added to the graphene oxide treated in step 3), and after being drained in a filter press, it is washed with a washing solution to obtain graphene oxide. The optical microscope characterization results are shown in FIG. 1, all are large-size flakes, the oxygen content of the sample is less than 40%, the average size is about 81 μm measured by nano particle size analysis, and the results are shown in FIG. 2 and FIG. 3, which have the characteristics of weak oxidation, large size and high exfoliation. Figure 4 Figure 5 6

[0058] Example 2:

[0059] A method for preparing weakly oxidized, large-size graphene oxide, comprising the following steps:

[0060] (1) 25 g of 100-150 mesh expandable graphite and 600 g of concentrated sulfuric acid are introduced into a reaction kettle for pre-mixing, and the temperature is reduced to below 10°C.

[0061] (2) 7.5 g of hydrogen peroxide and 50 g of phosphoric acid are added to the reaction kettle, and the intercalation reaction is carried out at 15°C to obtain an intercalation compound.

[0062] (3) 2.0 equivalents of potassium permanganate are added to the mixture of step 2) and the temperature is raised for oxidation reaction.​​​

[0063] (4) To the oxidized graphite treated in step 3), pure water was added, and after being transferred into a filter press and drained, it was washed with a sulfuric acid solution to obtain graphene oxide. The optical microscope characterization results are shown in Figure 4. Figure 7 It was a relatively large flake, as shown in Figure 4. Figure 8 and 9 The average size was about 63 μm, and the oxygen content of the sample was about 43%.

[0064] Comparative Example 1:

[0065] Graphene oxide was prepared by a conventional Hummers method, including the following steps:

[0066] 25 g of 100-150 mesh flake graphite and 600 g of concentrated sulfuric acid were introduced into a reaction kettle for pre-mixing, and the temperature was reduced to below 10°C.

[0067] (2) To the mixture of step 1), 75 g of potassium permanganate was added, and the temperature was increased for oxidation.

[0068] (3) To the oxidized graphite treated in step 2), pure water was added, and after being transferred into a filter press and drained, it was washed with a sulfuric acid solution to obtain graphene oxide. The optical microscope characterization results are shown in Figure 4. Figure 1 A large number of thick flakes were observed, and the oxygen content of the sample was higher than 48%, and the average size was about 21 μm, as determined by nano-particle size analysis.

[0069] Comparative Example 2:

[0070] A method for preparing weakly oxidized graphene, including the following steps:

[0071] (1) 25 g of 100-150 mesh flake graphite and 600 g of concentrated sulfuric acid were introduced into a reaction kettle for pre-mixing, and the temperature was reduced to below 10°C.

[0072] (2) 5 g of hydrogen peroxide was added to the reaction kettle, and an intercalation reaction was carried out at 10°C to obtain an intercalation compound.

[0073] (3) To the mixture of step 2), 62.5 g of potassium permanganate was added, and the temperature was increased for oxidation.

[0074] (4) To the oxidized graphite treated in step 3), pure water was added, and after being transferred into a filter press and drained, it was washed with a sulfuric acid solution to obtain graphene oxide. The optical microscope characterization results are shown in Figure 4. Figure 2 A small number of thick flakes were observed, and the oxygen content of the sample was about 45%, and the average size was about 28 μm, as determined by nano-particle size analysis.

[0075] Comparative Example 3:

[0076] A method for preparing weakly oxidized graphene, including the following steps:

[0077] (1) 25g of 100-150 mesh flake graphite and concentrated sulfuric acid were introduced into the reaction vessel for premixing, and the temperature was lowered to below 10℃.

[0078] (2) Add 7.5g of hydrogen peroxide to the reactor and maintain the intercalation reaction at 10℃ to obtain the intercalated compound.

[0079] (3) Add 55g of potassium permanganate to the mixture in step 2) and raise the temperature to carry out the oxidation reaction.

[0080] (4) Add pure water to the graphene oxide treated in step 3), transfer it to a filter press to dry it, and then wash it with a washing solution to obtain graphene oxide. The optical microscopy characterization results are shown in the appendix. Figure 3 The graphene oxide was observed to be well exfoliated, with an oxygen content of approximately 43% and an average size of approximately 27 μm as measured by nanoparticle size analysis. Comparative Examples 2 and 3 investigated how adding hydrogen peroxide could promote exfoliation and oxidation, reducing the amount of potassium permanganate required, but failing to achieve large particle sizes. In Examples 1 and 2 of this application, the addition of phosphoric acid enabled both high exfoliation efficiency and large particle sizes.

[0081] The graphene oxide prepared according to the preferred embodiment of the present invention has an average size of about 81 μm (D3,2), and the product with a particle size in the range of 80 to 120 μm accounts for about 70%.

[0082] The preparation method of this invention allows for preferential reaction with sulfuric acid in the presence of H₂O₂ to form HSO₄. ～ Ion intercalation of graphite transforms graphite into... Figure 4 and Figure 7 The graphite intercalation compound in this state exhibits an overall blue color in solution. This contrasts with graphite premixed with sulfuric acid in the Hummers process. Figure 4 and 7 The increased interlayer spacing of graphite intercalation compounds in the graphite state allows oxidants to more easily penetrate the graphite interlayers and oxidize the graphite sheets. Therefore, enhancing the activity of graphite through chemical intercalation can greatly promote its oxidation and exfoliation. Studies have shown that introducing phosphoric acid into a strong oxide system of concentrated sulfuric acid and potassium permanganate can provide in-situ protection for vicinal diols formed on the bottom surface of carbon nanotubes, thereby improving the selectivity of oxidative exfoliation and preventing over-oxidation of carbon nanotubes. This method is also feasible in the preparation of GO.

[0083] The preparation method of this invention is based on the existing Hummers process. It involves intercalation pretreatment by adding an intercalating agent (hydrogen peroxide, H2O2) and a protecting agent (phosphoric acid, H3PO4) to the system to obtain graphene oxide with weak oxidation, large size, and high exfoliation characteristics. Specifically, adding a certain amount of H2O2 to a mixed solution of graphite and concentrated sulfuric acid allows the formation of HSO4 in the solution.～ Ion, pre-intercalation treatment is carried out on graphite to form Figure 4 and Figure 7 The mixture solution exhibits blue color. The method can expand the interlayer spacing of the graphite sheet layer, so that the oxidant can easily enter the graphite interlayer for oxidation, greatly promotes the oxidation and peeling effect, and reduces the later oxidant dosage. At the same time, the introduction of phosphoric acid into the strong oxidant system of concentrated sulfuric acid and potassium permanganate can in-situ protect the adjacent diols formed on the GO, improve the selectivity of oxidation and peeling, prevent the GO from being over-oxidized, and protect the large-size structure.

[0084] Compared with the intercalation oxidation of the reaction of sulfuric acid and potassium permanganate to generate bisulfate, the hydrogen bisulfate is generated one stage earlier by adding hydrogen peroxide, so the highlight is that the hydrogen peroxide makes the concentrated sulfuric acid generate hydrogen bisulfate to intercalate graphite, promotes the later potassium permanganate to enter the interlayer for oxidation, and can reduce the amount of potassium permanganate. The hydrogen peroxide and phosphoric acid intercalate to promote oxidation and peeling, and one protects the large-size structure. The phosphoric acid in-situ protects the adjacent diols formed during the oxidation of GO, thereby preventing over-oxidation.

[0085] The hydrogen peroxide in the present application is added in the early premixing stage to pre-intercalate graphite to form an intercalation compound, so that the later oxidant can be more easily intercalated and oxidized, and the amount of oxidant can be reduced.

[0086] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for limiting the present application, although the foregoing detailed description of the present application is made with reference to the foregoing embodiments, for those skilled in the art, it still can be modified to the technical solutions recorded in the foregoing embodiments, or equivalent replacement of some technical features. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing weakly oxidized, large-size graphene oxide, characterized by, The method comprises the following steps: S1: graphite is premixed with concentrated sulfuric acid, and the temperature in the reactor is reduced to below 10 DEG C by a water cooling machine; S2: an intercalation agent and a protective agent are added to the system of step S1, and an intercalation reaction is completed to obtain an intercalated oxide; the intercalation agent is hydrogen peroxide, which makes hydrogen sulfate intercalate into graphite; the temperature of the system in the intercalation reaction is controlled to be 5-20 DEG C; S3: an oxidizing agent is added to the mixture of step S2, and an oxidation reaction is completed; S4: water is added to the system after the treatment of step S3 to complete a hydration reaction; S5: weakly oxidized and large-size graphene oxide is obtained after filtration and washing; the protective agent is concentrated phosphoric acid; the oxidizing agent is potassium permanganate; the temperature of the system in the oxidation reaction is controlled to be 30-40 DEG C; the oxidation reaction time is 3-3.5 h, so that the reactants are fully changed into grayish brown; the average size D[3,2] of the graphene oxide is 81 μm; the oxygen content of the graphene oxide is less than or equal to 40%; the graphene oxide is prepared into a heat-conducting film, and the heat conductivity coefficient of the heat-conducting film is more than 1500 W / mK.

2. The method of claim 1, wherein the weakly oxidized, large-sized graphene oxide is characterized by, The steps S1-S5 are all completed in the same reactor.

3. The method for preparing weakly oxidized, large-size graphene oxide according to claim 1, characterized in that, The graphite is flake graphite or expandable graphite.

4. The method for preparing weakly oxidized, large-size graphene oxide according to claim 1, characterized in that, The carbon content of the graphite is more than 95%.

5. The method for preparing weakly oxidized, large-size graphene oxide according to claim 3, characterized in that, The particle size of the flake graphite or expandable graphite is 50-200 mesh.

6. The method of claim 1, wherein the weakly oxidized, large-sized graphene oxide is characterized by, In step S1, the mass ratio of graphite to concentrated sulfuric acid is 1:20-30.

7. The method for preparing weakly oxidized, large-size graphene oxide according to claim 6, characterized in that, In step S1, the mass ratio of graphite to concentrated sulfuric acid is 1:

24.

8. The method of claim 1, wherein the weakly oxidized, large-sized graphene oxide is characterized by, The hydrogen peroxide is an industrial grade reagent with a concentration of 27.5%-30%.

9. The method of claim 1, wherein the weakly oxidized, large-sized graphene oxide is characterized by, The concentrated phosphoric acid is an analytical pure reagent with a purity of 98%.

10. The method of claim 1, wherein the weakly oxidized, large-sized graphene oxide is characterized by, After the intercalation agent and the protective agent are added, the temperature is raised to 5-20 DEG C and maintained for 2-3 h, so that the reactants are fully changed into indigo blue.

11. The method of claim 1, wherein the weakly oxidized, large-sized graphene oxide is characterized by, The amount of water added in the hydration reaction is 1-2 times that of sulfuric acid.

12. The method of claim 1, wherein the weakly oxidized, large-sized graphene oxide is characterized by, The temperature of the system in the hydration reaction is controlled to be 70-80 DEG C.

13. Weakly oxidized, large-size graphene oxide, characterized in that, The average size D[3,2] of the graphene oxide prepared by the method according to any one of claims 1-12 is 81 μm.

14. The weakly oxidized, large-size graphene oxide according to claim 13, characterized in that, The oxygen content of the graphene oxide is less than or equal to 40%.

15. The weakly oxidized, large-size graphene oxide of claim 13, wherein, The graphene oxide is prepared into a heat-conducting film, and the heat conductivity coefficient of the heat-conducting film is more than 1500 W / mK.

Images