Preparation method of graphite oxide

Abstract

The invention provides a preparation method of graphite oxide. The preparation method comprises the following steps: uniformly mixing graphite powder and concentrated sulfuric acid in a reaction kettle; adding an oxidizing agent into the reaction kettle, heating, and carrying out intercalation and first-stage oxidation reaction to obtain a first mixture of which the viscosity is 200cP-1000cP and the graphite powder is not completely oxidized; separating the first mixture to recover concentrated sulfuric acid and obtain a second mixture; standing the second mixture to carry out a second-stage oxidation reaction until the graphite powder is completely oxidized; dispersing the second mixture in water, heating, keeping for a certain time, cooling, and adding hydrogen peroxide to obtain the graphite oxide. According to the preparation method disclosed by the invention, the complete oxidation of the graphite is ensured while the high recovery rate of the concentrated sulfuric acid is realized. In addition, the recovered concentrated sulfuric acid can also be used in a new round of preparation of graphite oxide, so that the purpose of recycling is achieved, and the cost of raw materials for preparing the graphite oxide is also greatly reduced.

Description

Technical Field

[0001] The present application relates to the field of material preparation, and in particular, to a method for preparing graphite oxide. Background Art

[0002] Graphite oxide is generally prepared by a modified Hummer method, but this method consumes a large amount of concentrated sulfuric acid when preparing graphite oxide, thereby generating a large amount of waste acid, which puts great pressure on the environment and has high processing costs, so it is imperative to recycle concentrated sulfuric acid. However, the existing steps for recycling concentrated sulfuric acid are often performed after the preparation of graphite oxide is completed, and after the preparation of graphite oxide is completed, its mixed solution is usually very viscous, which is difficult to separate, and the amount of concentrated sulfuric acid that can be separated is also small. Summary of the invention

[0003] In view of this, it is necessary to provide a method for preparing graphite oxide that can recover more concentrated sulfuric acid while ensuring complete oxidation of graphite.

[0004] A method for preparing graphite oxide comprises: (1) uniformly mixing graphite powder and concentrated sulfuric acid in a reactor; (2) adding an oxidant into the reactor, heating the reactor to perform intercalation and a first-stage oxidation reaction to obtain a first mixture with a viscosity of 200 cP-1000 cP, wherein the graphite powder in the first mixture is not completely oxidized and the oxidation rate of the graphite powder is above 50%; (3) separating the first mixture in the reactor to recover most of the concentrated sulfuric acid and obtain the remaining second mixture; (4) allowing the second mixture to stand to perform a second-stage oxidation reaction until the graphite powder is completely oxidized; (5) dispersing the second mixture after the second-stage oxidation reaction in water, heating and maintaining for a certain period of time, cooling, and adding hydrogen peroxide to obtain the graphite oxide.

[0005] In some possible embodiments, the preparation method further comprises the following steps: (6) uniformly mixing the new and old mixed concentrated sulfuric acid obtained by mixing the concentrated sulfuric acid recovered in step (3) with new concentrated sulfuric acid and new graphite powder; (7) repeating steps (2) to (5) and recovering the concentrated sulfuric acid again in the repeated step (3) in the process of obtaining new graphite oxide.

[0006] In some possible implementations, the mixing ratio of the recovered concentrated sulfuric acid to the new concentrated sulfuric acid is 1:4-4:1.

[0007] In some possible implementations, the recovered concentrated sulfuric acid is 60%-90% of the total amount of concentrated sulfuric acid initially added.

[0008] In some possible implementations, the concentrated sulfuric acid in step (3) is recovered and recycled 1 to 10 times.

[0009] In some possible implementations, in step (1), the graphite powder and the concentrated sulfuric acid are uniformly mixed in the reactor at a ratio of 1 g:15 mL-50 mL, and the concentration of the concentrated sulfuric acid is 82 wt%-98.3 wt%.

[0010] In some possible implementations, in step (2), the oxidation rate of the graphite powder in the first mixture is 50%-90%.

[0011] In some possible embodiments, the intercalation and first-stage oxidation reaction in step (2) are carried out at 20° C.-60° C. for 1 h-10 h.

[0012] In some possible implementations, the time for standing still in step (4) to carry out the second stage oxidation reaction is 6 hours to 72 hours.

[0013] In some possible implementations, in step (5), the remaining second mixture is dispersed in water at a ratio of the graphite powder to the water of 1 g:10 mL-50 mL, and heated to 50° C.-95° C. and maintained for 5 min-80 min.

[0014] In summary, the preparation method of graphite oxide of the present application innovatively proposes that when graphite powder is not completely oxidized and the oxidation rate of graphite powder in the first mixture reaches more than 50%, concentrated sulfuric acid is recovered. At this time, because it is in the formation process of graphite oxide, when the viscosity of the first mixture formed by graphite powder, concentrated sulfuric acid and oxide is 200cP-1000cP, that is, the first mixture is not yet viscous, separation operation is performed, which effectively reduces the difficulty of concentrated sulfuric acid recovery, and greatly improves the recovery amount of concentrated sulfuric acid, so as to recover most of the concentrated sulfuric acid, so as to reduce the waste acid output to a great extent and reduce environmental protection costs; In addition, the recovered concentrated sulfuric acid can also be used in the preparation of a new round of graphite oxide, and while achieving the purpose of recycling, the raw material cost of preparing graphite oxide is also greatly reduced. In addition, the preparation method of graphite oxide of the present application is to make up for the problem that graphite oxide powder is not completely oxidized after the first stage oxidation reaction, and the second stage oxidation reaction is added after the concentrated sulfuric acid recovery step, so as to further oxidize the graphite powder, ensure the complete oxidation of graphite, and also achieve a high recovery rate of concentrated sulfuric acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 The present invention is a flow chart of a method for preparing graphite oxide using novel concentrated sulfuric acid according to some embodiments of the present application.

[0017] Figure 2 A flow chart of a method for preparing graphite oxide using recycled concentrated sulfuric acid according to some embodiments of the present application.

[0018] Figure 3 The X-ray diffraction pattern (XRD) of graphite oxide powder according to some embodiments of the present application.

[0019] Figure 4 This is an optical microscope (OM) photograph of an aqueous dispersion of graphite oxide according to some embodiments of the present application.

[0020] Figure 5 This is an infrared spectrum characterization diagram of graphite oxide powder according to some embodiments of the present application. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0022] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may also be a centered element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may also be a centered element. When an element is considered to be "set on" another element, it may be directly set on the other element or there may also be a centered element. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "or / and" used herein includes any and all combinations of one or more related listed items.

[0024] Some embodiments of the present application are described in detail. In the absence of conflict, the following embodiments and features of the embodiments can be combined with each other.

[0025] Ginseng Figure 1 Some embodiments of the present application provide a method for preparing graphite oxide, comprising the following steps: S1: Graphite powder and concentrated sulfuric acid are uniformly mixed in a reaction kettle.

[0026] Specifically, in some embodiments, graphite powder is poured into a reaction kettle, and concentrated sulfuric acid is poured into the reaction kettle, and uniform stirring is started until the graphite powder reaches a uniformly infiltrated state.

[0027] In some embodiments, the graphite powder and the concentrated sulfuric acid are mixed in a ratio of 1 g: 15 mL-50 mL.

[0028] In some embodiments, the graphite powder is at least one of block graphite, earthy graphite, flake graphite, expanded graphite, and intercalated graphite.

[0029] In some embodiments, the graphite powder has a particle size of 10 μm-1000 μm.

[0030] In some embodiments, the concentration of the concentrated sulfuric acid is 82 wt % to 98.3 wt %.

[0031] S2: adding an oxidant into the reactor, raising the temperature to perform intercalation and first-stage oxidation reactions to obtain a first mixture with a viscosity of 200 cP-1000 cP.

[0032] The graphite powder in the first mixture is not completely oxidized and the oxidation rate of the graphite powder is above 50%.

[0033] In some other embodiments, the oxidation rate of the graphite powder in the first mixture is 50%-90%.

[0034] Specifically, in some embodiments, the temperature of the reactor is controlled to be below 15°C, the mass of the oxidant is added according to 2-6 times of the graphite powder, and the time taken to add the oxidant is 0.5h-10h. In the process of adding the oxidant, the temperature in the reactor is always kept below 15°C.

[0035] In other embodiments, the time for adding the oxidant is 0.5h-2h, or 1h-10h, which is adaptively adjusted according to actual conditions and is not limited here.

[0036] In some embodiments, the oxidant is at least one of potassium permanganate, potassium ferrate, and potassium perchlorate.

[0037] In some embodiments, the intercalation and first stage oxidation reactions are performed at 20° C. to 60° C. for 1 h to 10 h.

[0038] In some other embodiments, the intercalation and first stage oxidation reactions are carried out at 20° C.-60° C. for 1 h-5 h.

[0039] It can be understood that the oxidation rate of graphite powder can be calculated by measuring the oxygen content in graphite. The specific method is an existing method and will not be repeated here.

[0040] S3: separating the first mixture in the reactor to recover most of the concentrated sulfuric acid and obtain the remaining second mixture.

[0041] In some embodiments, the recovered concentrated sulfuric acid is 60%-90% of the total amount of concentrated sulfuric acid initially added.

[0042] In some embodiments, the method of separation is not limited to filtration or centrifugation.

[0043] The specific filtering or centrifuging methods are existing methods and will not be described in detail here.

[0044] S4: leaving the second mixture to stand to perform a second stage oxidation reaction until the graphite powder is completely oxidized.

[0045] It can be understood that during the standing process, the graphite powder in the second mixture continues to react with the remaining small amount of concentrated sulfuric acid and the oxidant therein to perform a second stage oxidation reaction until all the graphite powder is completely oxidized.

[0046] In some embodiments, the standing time is 6 h-72 h.

[0047] In some other embodiments, the standing time is 10 h-50 h.

[0048] In some embodiments, the second mixture is allowed to stand in an ambient temperature of 20°C-60°C.

[0049] S5: dispersing the second mixture after the second stage oxidation reaction in water, heating and maintaining for a certain period of time, and adding hydrogen peroxide after cooling to obtain the graphite oxide.

[0050] Specifically, in some embodiments, during the hydrolysis process, the second mixture obtained by the second stage oxidation reaction is dispersed in water at a ratio of the graphite powder to the water of 1 g:10 mL-50 mL, heated to 50° C.-95° C. and maintained for 5 min-80 min, and then cooled and hydrogen peroxide is added to terminate the experiment to obtain the graphite oxide.

[0051] It can be understood that the oxidation reaction process of graphite powder with concentrated sulfuric acid in the present application is a "fast first, then slow" process: that is, in the first stage oxidation reaction, after a large amount of concentrated sulfuric acid completely soaks the graphite powder, most of the graphite powder will be quickly oxidized in a short time, and then enter the second stage oxidation reaction: the remaining unoxidized graphite powder is slowly completely oxidized in a small amount of concentrated sulfuric acid and oxidant.

[0052] Furthermore, in some embodiments, the mixture in step S5 is filtered, washed, and dried to obtain graphite oxide powder.

[0053] Ginseng Figure 2 In some embodiments, a method for preparing graphite oxide further comprises the following steps: S6: uniformly mix the new and old mixed concentrated sulfuric acid obtained by mixing the concentrated sulfuric acid recovered in step S3 with the new concentrated sulfuric acid and the new graphite powder.

[0054] S7: Repeat steps S2-S5 to obtain new graphite oxide and recover concentrated sulfuric acid again in the repeated step S3.

[0055] In some embodiments, the mixing ratio of the recovered concentrated sulfuric acid to the new concentrated sulfuric acid is 1:4-4:1.

[0056] In some embodiments, the concentrated sulfuric acid is recovered and recycled 1-10 times in step S3, and the specific preparation methods of subsequent third to N-th graphite oxide preparations can refer to the second method (i.e., steps S6-S7) for preparing graphite oxide, which will not be elaborated here.

[0057] As is known to all, the existing graphite oxide obtained by the improved Hummer method, after the completion of oxidation, when concentrated sulfuric acid is recovered, its mixed solution is usually very viscous. The reasons are: first, the graphite powder gradually expands with the increase of oxidation degree and partially peels off; second, as the oxidation reaction proceeds, the metal atoms in the oxidant will be reduced to produce small solid particles, increasing the viscosity; this leads to a series of problems such as high difficulty in separating concentrated sulfuric acid and extremely low recovery rate.

[0058] Thus, the preparation method of graphite oxide of some embodiments of the present application is concentrated sulfuric acid recovery when graphite powder is not completely oxidized. At this time, because it is in the formation process of graphite oxide, when the viscosity of the first mixture formed by graphite powder, concentrated sulfuric acid and oxide is 200cP-1000cP, that is, the first mixture is not yet viscous, the separation operation is performed, which effectively reduces the difficulty of concentrated sulfuric acid recovery, and greatly improves the recovery amount of concentrated sulfuric acid, so as to recover most of the concentrated sulfuric acid, thus greatly reducing the waste acid output and reducing environmental protection costs; in addition, the recovered concentrated sulfuric acid can also be used in the preparation of a new round of graphite oxide, achieving the purpose of recycling, and greatly reducing the raw material cost of preparing graphite oxide. In addition, the preparation method of graphite oxide of the present application is to make up for the problem that the graphite oxide powder is not completely oxidized after the first stage oxidation reaction, and the second stage oxidation reaction is added after the concentrated sulfuric acid recovery step to further oxidize the graphite powder, ensure the complete oxidation of graphite, and also achieve a high recovery rate of concentrated sulfuric acid.

[0059] The scheme of the present application will be explained below in conjunction with the embodiments. Those skilled in the art will understand that the following examples are only used to explain the present application and cannot be construed as limiting the present application. Unless otherwise stated, the reagents, software and instruments not specifically stated in the following embodiments are all conventional commercial products or open source.

[0060] Example 1: Preparation of graphite oxide using new concentrated sulfuric acid (1) Pour 10 g of 325 mesh natural graphite powder into a reactor, and pour 300 mL of 98 wt% concentrated sulfuric acid into the reactor, and then start stirring at a constant speed to mix the two until they are evenly wetted; (2) After the temperature in the reactor is lowered to 10°C, 30 g of potassium permanganate is slowly added into the reactor at a rate of 10 g / 40 min. During the addition of potassium permanganate, the temperature in the reactor must be maintained at no more than 15°C. (3) heating the mixture obtained in step (2) at 25° C. and reacting at the temperature for 100 min to obtain a first mixture having a viscosity of 200 cP-1000 cP; (4) using a Buchner funnel to quickly filter the first mixture obtained in step (3) to obtain about 220 mL of recovered concentrated sulfuric acid and a semi-dried filter cake (i.e., the second mixture), wherein the filter screen of the Buchner funnel is a 500-mesh stainless steel screen; wherein the recovery rate of concentrated sulfuric acid is 73.3%; (5) After the semi-dried filter cake is stored at 25°C for 24 h, it is dispersed in 500 mL of water and heated to 90°C for 30 min.

[0061] (6) After cooling, add 10 mL of 30 wt% hydrogen peroxide; (7) After filtering, washing and drying, graphite oxide powder is obtained.

[0062] like Figure 3 As shown, the graphite oxide powder was characterized by X-ray diffraction (XRD), which showed a characteristic peak of graphite oxide at 11.4° and no other impurity peaks, indicating that the graphite oxidation degree was complete.

[0063] like Figure 4 As shown, the aqueous dispersion of graphite oxide was characterized by an optical microscope (OM), and it can be seen that the graphite oxide is transparent flakes without unevenly oxidized black particles, which also proves that the degree of graphite oxidation is complete.

[0064] like Figure 5 As shown in the figure, infrared spectroscopy analysis shows that graphite oxide contains a large number of hydroxyl groups, carboxyl groups, carbonyl groups and epoxy groups, proving that the degree of graphite oxidation is complete.

[0065] The mass fractions of various elements in graphite oxide measured by combustion method are: carbon 51.5%, oxygen 43.7%, nitrogen 0.2%, hydrogen 3.3%, and sulfur 1.3%, proving that the degree of graphite oxidation is high.

[0066] In summary, according to the above data of XRD characterization, OM characterization, infrared spectroscopy analysis and combustion method, it can be concluded that the preparation method of graphite oxide in some embodiments of the present application recovers concentrated sulfuric acid when the graphite powder has not been completely oxidized and the viscosity is 200cP-1000cP, thereby achieving a high recovery rate of concentrated sulfuric acid and ensuring complete oxidation of graphite.

[0067] Example 2: Preparation of graphite oxide using concentrated sulfuric acid recovered in Example 1 (1) taking 200 mL of the concentrated sulfuric acid recovered in step (4) of Example 1 and mixing it with 100 mL of new concentrated sulfuric acid to obtain 300 mL of new and old mixed concentrated sulfuric acid; (2) Pour 10 g of 325 mesh natural graphite powder into a reactor, and pour 300 mL of new and old mixed concentrated sulfuric acid into the reactor, and then start stirring at a constant speed to mix the two evenly until they are evenly infiltrated; (3) After the temperature in the reactor is lowered to 10°C, 25g of potassium permanganate is slowly added into the reactor at a rate of 10g / 40min. During the addition of potassium permanganate, the temperature in the reactor must be kept below 15°C. (4) heating the mixture obtained in step (3) at 25° C. and reacting at the temperature for 80 min to obtain a first mixture with a viscosity of 200 cP-1000 cP; (5) using a Buchner funnel to quickly filter the first mixture obtained in step (4) to obtain about 200 mL of recovered concentrated sulfuric acid and a semi-dried filter cake (i.e., the second mixture), wherein the filter screen of the Buchner funnel is a 500-mesh stainless steel screen; wherein the recovery rate of concentrated sulfuric acid is 66.7%; (6) After the semi-dried filter cake was stored at 25°C for 12 h, it was dispersed in 500 mL of water and heated to 90°C for 30 min.

[0068] (7) After cooling, add 10 mL of 30 wt% hydrogen peroxide; (8) After filtering, washing and drying, graphite oxide powder is obtained.

[0069] Example 3 (1) Pour 1 g of 325 mesh natural graphite powder into a reactor, and pour 30 mL of 98.3 wt% concentrated sulfuric acid into the reactor, and then start stirring at a constant speed to mix the two until they are evenly wetted; (2) After the temperature in the reactor is lowered to 10°C, 3 g of potassium permanganate is slowly added into the reactor at a rate of 10 g / 40 min. During the addition of potassium permanganate, the temperature in the reactor must be maintained at no more than 15°C. (3) heating the mixture obtained in step (2) at a temperature controlled at 25° C. and reacting at the temperature for 4 hours to obtain a first mixture with a viscosity of 200 cP-1000 cP. At this time, the oxidation rate of graphite powder in the first mixture is about 90%; (4) using a Buchner funnel to quickly filter the first mixture obtained in step (3) to obtain about 20 mL of recovered concentrated sulfuric acid and a semi-dried filter cake (i.e., the second mixture), wherein the filter screen of the Buchner funnel is a 500-mesh stainless steel screen; wherein the recovery rate of concentrated sulfuric acid is 66.7%; (5) After the filter cake is stored in an environment of 25°C for 24 hours, it is dispersed in water, heated and maintained for a certain period of time, cooled, and hydrogen peroxide is added. After filtering, washing and drying, graphite oxide powder is obtained.

[0070] The oxidation degree of the graphite oxide powder obtained in step (5) was 100% after testing. The recovery rate of concentrated sulfuric acid was 66.7%.

[0071] Comparative Example 1 (1) Pour 1 g of 325 mesh natural graphite powder into a reactor, and pour 30 mL of 98.3 wt% concentrated sulfuric acid into the reactor, and then start stirring at a constant speed to mix the two until they are evenly wetted; (2) After the temperature in the reactor is lowered to 10°C, 3 g of potassium permanganate is slowly added into the reactor at a rate of 10 g / 40 min. During the addition of potassium permanganate, the temperature in the reactor must be maintained at no more than 15°C. (3) heating the mixture obtained in step (2) at a temperature controlled at 25° C. and reacting at the temperature for 4 hours to obtain a first mixture with a viscosity of 200 cP-1000 cP. At this time, the oxidation rate of graphite powder in the first mixture is about 40%; (4) using a Buchner funnel to quickly filter the first mixture obtained in step (3) to obtain about 23 mL of recovered concentrated sulfuric acid and a semi-dried filter cake (i.e., the second mixture), wherein the filter screen of the Buchner funnel is a 500-mesh stainless steel screen; wherein the recovery rate of concentrated sulfuric acid is 76.7%; (5) After the filter cake is stored in an environment of 25°C for 24 hours, it is dispersed in water, heated and maintained for a certain period of time, cooled, and hydrogen peroxide is added. After filtering, washing and drying, graphite oxide powder is obtained.

[0072] The graphite oxide powder obtained in step (5) was tested and found to have an oxidation degree of less than 100%. The recovery rate of concentrated sulfuric acid was 76.7%.

[0073] Comparative Example 2 (1) Pour 1 g of 325 mesh natural graphite powder into a reactor, and pour 30 mL of 98.3 wt% concentrated sulfuric acid into the reactor, and then start stirring at a constant speed to mix the two until they are evenly wetted; (2) After the temperature in the reactor is lowered to 10°C, 3 g of potassium permanganate is slowly added into the reactor at a rate of 10 g / 40 min. During the addition of potassium permanganate, the temperature in the reactor must be maintained at no more than 15°C. (3) heating the mixture obtained in step (2) at a temperature controlled at 25° C. and reacting at the temperature until the graphite powder is completely oxidized, wherein the viscosity of the mixture after complete oxidation reaches more than 10,000 cP; (4) using a Buchner funnel to quickly filter the mixture obtained in step (3) to obtain about 8 mL of recovered concentrated sulfuric acid and a filter cake, wherein the filter screen of the Buchner funnel is a 500-mesh stainless steel screen; wherein the recovery rate of concentrated sulfuric acid is 26.7%; (5) After the filter cake is stored in an environment of 25°C for 24 hours, it is dispersed in water, heated and maintained for a certain period of time, cooled, and hydrogen peroxide is added. After filtering, washing and drying, graphite oxide powder is obtained.

[0074] The oxidation degree of the graphite oxide powder obtained in step (5) was 100% after testing. The recovery rate of concentrated sulfuric acid was 26.7%.

[0075] It can be seen from Example 3, Comparative Example 1 and Comparative Example 2 that in Comparative Example 1, concentrated sulfuric acid is recovered when the oxidation rate of graphite powder in the first mixture is lower than 50%. Although a higher recovery rate of concentrated sulfuric acid is ensured, the oxidation rate of graphite powder in the first mixture is too low, resulting in incomplete oxidation in the subsequent oxidation reaction. Comparative Example 2 collects concentrated sulfuric acid after the graphite powder is completely oxidized. Although the oxidation degree of oxidized graphite is ensured, the viscosity of the graphite powder after complete oxidation is high, resulting in an extremely low recovery rate of concentrated sulfuric acid. In Example 3, concentrated sulfuric acid is recovered when the graphite powder has not been completely oxidized and the oxidation rate of the graphite powder reaches more than 50%. At this time, the viscosity of the first mixture is 200cP-1000cP, so that the concentrated sulfuric acid obtains a higher recovery rate while also ensuring the complete oxidation of graphite.

[0076] The above implementation modes are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the above preferred implementation modes, a person skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for preparing graphite oxide, characterized in that: The preparation method comprises: (1) Evenly mix graphite powder and concentrated sulfuric acid in a reaction kettle; (2) adding an oxidant into the reactor, raising the temperature to perform intercalation and first-stage oxidation reactions to obtain a first mixture with a viscosity of 200 cP-1000 cP, wherein the graphite powder in the first mixture is not completely oxidized and the oxidation rate of the graphite powder is greater than 50%; (3) separating the first mixture in the reactor to recover most of the concentrated sulfuric acid and obtain the remaining second mixture; (4) allowing the second mixture to stand to perform a second stage oxidation reaction until the graphite powder is completely oxidized; (5) Dispersing the second mixture after the second stage oxidation reaction in water, heating and maintaining for a certain period of time, and adding hydrogen peroxide after cooling to obtain the graphite oxide.

2. The method for preparing graphite oxide according to claim 1, characterized in that: The preparation method further comprises the following steps: (6) uniformly mixing the new and old mixed concentrated sulfuric acid obtained by mixing the concentrated sulfuric acid recovered in step (3) with the new concentrated sulfuric acid and the new graphite powder; (7) Repeating steps (2) to (5) to obtain new graphite oxide, the concentrated sulfuric acid is recovered again in the repeated step (3).

3. The method for preparing graphite oxide according to claim 2, characterized in that: The mixing ratio of the recovered concentrated sulfuric acid to the new concentrated sulfuric acid is 1:4-4:

1.

4. The method for preparing graphite oxide according to any one of claims 1 to 3, characterized in that: The recovered concentrated sulfuric acid is 60%-90% of the total amount of concentrated sulfuric acid initially added.

5. The method for preparing graphite oxide according to any one of claims 1 to 3, characterized in that: The concentrated sulfuric acid in step (3) is recovered and recycled 1 to 10 times.

6. The method for preparing graphite oxide according to any one of claims 1 to 3, characterized in that: In step (1), the graphite powder and the concentrated sulfuric acid are uniformly mixed in the reaction kettle at a ratio of 1 g:15 mL-50 mL, and the concentration of the concentrated sulfuric acid is 82 wt%-98.3 wt%.

7. The method for preparing graphite oxide according to any one of claims 1 to 3, characterized in that: In step (2), the oxidation rate of the graphite powder in the first mixture is 50%-90%.

8. The method for preparing graphite oxide according to any one of claims 1 to 3, characterized in that: In step (2), the intercalation and first stage oxidation reaction are carried out at 20°C-60°C for 1h-10h.

9. The method for preparing graphite oxide according to any one of claims 1 to 3, characterized in that: The time for standing still in step (4) to carry out the second stage oxidation reaction is 6h-72h.

10. The method for preparing graphite oxide according to any one of claims 1 to 3, characterized in that: In step (5), the remaining second mixture is dispersed in water according to the ratio of the graphite powder to the water of 1 g:10 mL-50 mL, and heated to 50° C.-95° C. and maintained for 5 min-80 min.

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