A method for preparing graphite oxide

Abstract

The application provides a preparation method of graphite oxide, comprising the following steps: uniformly mixing graphite powder and concentrated sulfuric acid in a reaction kettle; adding an oxidizing agent in the reaction kettle, performing intercalation and first-stage oxidation reaction under heating to obtain a first mixture with a viscosity of 200 cP-1000 cP and graphite powder not being completely oxidized; separating the first mixture to recover concentrated sulfuric acid and obtain a second mixture; standing the second mixture to perform second-stage oxidation reaction until the graphite powder is completely oxidized; dispersing the second mixture in water, heating and keeping for a certain time, and then adding hydrogen peroxide after cooling to obtain graphite oxide. The preparation method of the application can realize high recovery rate of concentrated sulfuric acid and also ensure complete oxidation of graphite. In addition, the recovered concentrated sulfuric acid can also be used in the preparation of new round of graphite oxide, so that the purpose of recycling is achieved, and the raw material cost of preparing graphite oxide is greatly reduced.

Description

Technical Field

[0001] This application relates to the field of materials preparation, and more specifically, to a method for preparing graphite oxide. Background Technology

[0002] Graphite oxide is generally produced using a modified Hummer process. However, this method consumes a large amount of concentrated sulfuric acid during preparation, resulting in substantial waste acid, significant environmental pressure, and high treatment costs. Therefore, recycling concentrated sulfuric acid is imperative. However, existing concentrated sulfuric acid recycling steps often occur after graphite oxide preparation. After preparation, the resulting mixed solution is typically very viscous, making separation difficult and yielding a limited amount of concentrated sulfuric acid. Summary of the Invention

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

[0004] A method for preparing graphite oxide includes: (1) uniformly mixing graphite powder and concentrated sulfuric acid in a reaction vessel; (2) adding an oxidant to the reaction vessel, heating to carry out 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 reaches more than 50%; (3) separating the first mixture in the reaction vessel to recover most of the concentrated sulfuric acid and obtain the remaining second mixture; (4) allowing the second mixture to stand to carry out 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 time, cooling and adding hydrogen peroxide to obtain the graphite oxide.

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

[0006] In some possible implementations, the ratio of the recovered concentrated sulfuric acid to the new concentrated sulfuric acid is 1:4 to 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 1-10 times.

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

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

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

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

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

[0014] In summary, the innovative method for preparing graphite oxide proposed in this application involves recovering concentrated sulfuric acid when the graphite powder is not fully oxidized and the oxidation rate of the graphite powder in the first mixture reaches 50% or more. At this point, because the graphite oxide is still forming, the separation operation is performed when the viscosity of the first mixture formed by the graphite powder, concentrated sulfuric acid, and oxide is 200 cP-1000 cP, i.e., when the first mixture is not yet viscous. This effectively reduces the difficulty of concentrated sulfuric acid recovery while significantly increasing the recovery rate, thus recovering most of the concentrated sulfuric acid. This greatly reduces waste acid production and lowers environmental costs. Furthermore, the recovered concentrated sulfuric acid can be used in a new round of graphite oxide preparation, achieving recycling and significantly reducing the raw material cost for graphite oxide preparation. In addition, to address the issue of incomplete oxidation of the graphite powder after the first-stage oxidation reaction, the method for preparing graphite oxide in this application adds a second-stage oxidation reaction after the concentrated sulfuric acid recovery step to further oxidize the graphite powder, ensuring complete oxidation of the graphite while achieving a high recovery rate of concentrated sulfuric acid. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 Flow chart of the method for preparing graphite oxide using fresh concentrated sulfuric acid according to some embodiments of the present application.

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

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

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

[0020] Figure 5 Infrared spectrum characterization diagram of graphite oxide powder according to some embodiments of the present application. Detailed implementation manners

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

[0022] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there may also be a middle element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be a middle element at the same time. When an element is considered to be "disposed on" another element, it can be directly disposed on the other element or there may be a middle element at the same time. 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 commonly understood by those skilled in the art to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific implementation manners and are not intended to limit this application. The term "or / and" used herein includes any and all combinations of one or more of the related listed items.

[0024] Some embodiments of the present application will be described in detail. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0025] Refer Figure 1 , some embodiments of the present application provide a method for preparing graphite oxide, including the following steps:

[0026] S1: Uniformly mix graphite powder and concentrated sulfuric acid in a reaction kettle.

[0027] Specifically, in some embodiments, graphite powder is poured into a reaction vessel, and concentrated sulfuric acid is added to the reaction vessel. Stirring is then started at a constant speed until the graphite powder is uniformly wetted.

[0028] In some embodiments, the graphite powder and the concentrated sulfuric acid are mixed in a ratio of 1g:15mL-50mL.

[0029] In some embodiments, the graphite powder is at least one of block graphite, earthy graphite, flake graphite, expanded graphite, and intercalated graphite.

[0030] In some embodiments, the particle size of the graphite powder is 10 μm-1000 μm.

[0031] In some embodiments, the concentration of the concentrated sulfuric acid is 82 wt% to 98.3 wt%.

[0032] S2: Add an oxidant to the reactor and heat it to carry out intercalation and first-stage oxidation reactions to obtain a first mixture with a viscosity of 200 cP-1000 cP.

[0033] In the first mixture, the graphite powder is not completely oxidized and the oxidation rate of the graphite powder reaches more than 50%.

[0034] In some other embodiments, the graphite powder in the first mixture has an oxidation rate of 50%-90%.

[0035] Specifically, in some embodiments, the temperature of the reactor is controlled below 15°C, the oxidant is added at a mass of 2-6 times that of the graphite powder, and the time for adding the oxidant is 0.5-10 hours. Throughout the process of adding the oxidant, the temperature inside the reactor is maintained below 15°C.

[0036] In other embodiments, the time for adding the oxidant is 0.5h-2h or 1h-10h, which can be adjusted according to the actual situation and is not limited here.

[0037] In some embodiments, the oxidant is at least one of potassium permanganate, potassium ferrate, and potassium perchlorate.

[0038] In some embodiments, the intercalation and first-stage oxidation reactions are carried out at 20°C-60°C for 1-10 hours.

[0039] In some other embodiments, the intercalation and first-stage oxidation reactions are carried out at 20°C-60°C for 1-5 hours.

[0040] It is understandable 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 elaborated here.

[0041] S3: Separate the first mixture in the reactor to recover most of the concentrated sulfuric acid and obtain the remaining second mixture.

[0042] In some implementations, the recovered concentrated sulfuric acid is 60%-90% of the total amount of concentrated sulfuric acid initially added.

[0043] In some implementations, the separation method is not limited to filtration or centrifugation.

[0044] The specific filtration or centrifugation methods are existing and will not be elaborated here.

[0045] S4: Allow the second mixture to stand for a second-stage oxidation reaction until the graphite powder is completely oxidized.

[0046] It is understandable that during the settling process, the graphite powder in the second mixture continues to react with the remaining small amount of concentrated sulfuric acid and oxidant to carry out a second-stage oxidation reaction until all the graphite powder is completely oxidized.

[0047] In some implementations, the settling time is 6h-72h.

[0048] In some other implementations, the settling time is 10h-50h.

[0049] In some embodiments, the second mixture is left to stand at an ambient temperature of 20°C-60°C.

[0050] S5: The second mixture after the second stage oxidation reaction is dispersed in water, heated and maintained for a certain time, cooled and then hydrogen peroxide is added to obtain the graphite oxide.

[0051] Specifically, in some embodiments, during the hydrolysis process, the second mixture after the second stage oxidation reaction is dispersed in water according to the ratio of graphite powder to water of 1g:10mL-50mL, heated to 50℃-95℃ and maintained for 5min-80min, and then cooled before adding hydrogen peroxide to stop the experiment, thereby obtaining the oxidized graphite.

[0052] It is understood that the oxidation reaction of graphite powder by concentrated sulfuric acid in this application is a "fast first, slow later" process: that is, after a large amount of concentrated sulfuric acid completely wets the graphite powder in the first stage of the oxidation reaction, most of the graphite powder will be rapidly oxidized in a short time, and then enter the second stage of the oxidation reaction: the remaining unoxidized graphite powder is slowly and completely oxidized in a small amount of concentrated sulfuric acid and oxidant.

[0053] Further, in some embodiments, the mixture in step S5 is filtered, washed, and dried to obtain graphite oxide powder.

[0054] Refer Figure 2 , in some embodiments, a method for preparing graphite oxide further comprises the following steps:

[0055] S6: Uniformly mix the old and new mixed concentrated sulfuric acid obtained by mixing the recycled concentrated sulfuric acid in step S3 and new concentrated sulfuric acid with new graphite powder.

[0056] S7: Repeat steps S2 - S5 to recycle concentrated sulfuric acid again in the repeated step S3 during the process of obtaining new graphite oxide.

[0057] In some embodiments, the mixing ratio of the recycled concentrated sulfuric acid to the new concentrated sulfuric acid is 1:4 - 4:1.

[0058] In some embodiments, the number of times the concentrated sulfuric acid is recycled and reused in step S3 is 1 - 10 times. The specific preparation method of graphite oxide for the third to the Nth time can refer to the method of preparing graphite oxide for the second time (i.e., steps S6 - S7), which will not be elaborated here.

[0059] As is well known, for the graphite oxide obtained by the existing improved Hummer method, when the concentrated sulfuric acid is recycled after oxidation, the mixed solution is usually very viscous. The reasons are as follows: First, the graphite powder gradually expands and partially exfoliates as the oxidation degree increases; second, as the oxidation reaction proceeds, the metal atoms in the oxidant are reduced to produce solid small 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.

[0060] Thus, in the method for preparing graphite oxide according to some embodiments of the present application, the concentrated sulfuric acid is recycled when the graphite powder is not completely oxidized. At this time, during the formation process of graphite oxide, when the viscosity of the first mixture formed by graphite powder, concentrated sulfuric acid, and oxide is 200 cP - 1000 cP, that is, when the first mixture is not yet viscous, the separation operation is carried out, effectively reducing the difficulty of recycling concentrated sulfuric acid and greatly increasing the recovery amount of concentrated sulfuric acid to recover most of the concentrated sulfuric acid. In this way, the production of waste acid is greatly reduced and the environmental protection cost is lowered. In addition, the recycled 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, to solve the problem that the graphite oxide powder is not completely oxidized after the first - stage oxidation reaction, the method for preparing graphite oxide of the present application also adds a second - stage oxidation reaction after the concentrated sulfuric acid recycling step to further oxidize the graphite powder, ensuring the complete oxidation of graphite while achieving a high recovery rate of concentrated sulfuric acid.

[0061] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the present application. Unless otherwise specified, reagents, software, and instruments involved in the following embodiments are all conventional commercially available products or open-source materials.

[0062] Example 1: Preparation of graphite oxide using fresh concentrated sulfuric acid

[0063] (1) Take 10g of 325 mesh natural graphite powder and pour it into the reaction vessel. Then pour 300mL of 98wt% concentrated sulfuric acid into the reaction vessel and start stirring at a constant speed to mix the two evenly until they are uniformly wetted.

[0064] (2) After the temperature inside the reactor is reduced to 10°C, take 30g of potassium permanganate and slowly add it into the reactor at a rate of 10g / 40min. During the addition of potassium permanganate, the temperature inside the reactor must be kept below 15°C.

[0065] (3) The mixture obtained in step (2) is heated at 25°C and reacted at this temperature for 100 min to obtain a first mixture with a viscosity of 200 cP-1000 cP;

[0066] (4) The first mixture obtained in step (3) was rapidly filtered using a Buchner funnel to obtain approximately 220 mL of recovered concentrated sulfuric acid and a semi-dry filter cake (i.e., the second mixture), wherein the filter screen of the Buchner funnel was a 500-mesh stainless steel mesh; wherein the recovery rate of concentrated sulfuric acid was 73.3%;

[0067] (5) After storing the semi-dry filter cake in an environment of 25°C for 24 hours, disperse it in 500 mL of water, heat it to 90°C and keep it for 30 minutes.

[0068] (6) After cooling, add 10 mL of 30 wt% hydrogen peroxide;

[0069] (7) After filtration, washing and drying, graphite oxide powder is obtained.

[0070] like Figure 3 As shown, the graphite oxide powder was characterized by X-ray diffraction (XRD). The characteristic peak of graphite oxide was observed at 11.4°, with no other impurity peaks, indicating that the graphite oxidation was complete.

[0071] like Figure 4 As shown, the aqueous dispersion of graphite oxide was characterized by an optical microscope (OM). The graphite oxide was transparent and flake-like, without any unevenly oxidized black particles, which also proved that the graphite was completely oxidized.

[0072] like Figure 5 As shown, infrared spectroscopy analysis reveals that graphene oxide contains a large number of hydroxyl, carboxyl, carbonyl, and epoxy groups, proving that the graphene oxidation is complete.

[0073] The mass fractions of various elements in graphite oxide, as determined by combustion, were: carbon 51.5%, oxygen 43.7%, nitrogen 0.2%, hydrogen 3.3%, and sulfur 1.3%, indicating a high degree of graphite oxidation.

[0074] In summary, based on the data from XRD characterization, OM characterization, infrared spectroscopy analysis, and combustion method, it can be concluded that the method for preparing graphite oxide in some embodiments of this application involves recovering concentrated sulfuric acid when the graphite powder is not completely oxidized and its viscosity is 200 cP-1000 cP. This achieves a high recovery rate of concentrated sulfuric acid while ensuring complete oxidation of graphite.

[0075] Example 2: Preparation of graphite oxide using concentrated sulfuric acid recovered in Example 1

[0076] (1) Take 200 mL of the concentrated sulfuric acid recovered in step (4) of Example 1 and mix it with 100 mL of new concentrated sulfuric acid to obtain 300 mL of mixed old and new concentrated sulfuric acid;

[0077] (2) Take 10g of 325 mesh natural graphite powder and pour it into the reaction vessel. Then pour 300mL of mixed new and old concentrated sulfuric acid into the reaction vessel and start stirring at a constant speed to mix the two evenly until they are uniformly wetted.

[0078] (3) After the temperature inside the reactor is reduced to 10°C, take 25g of potassium permanganate and slowly add it into the reactor at a rate of 10g / 40min. During the addition of potassium permanganate, the temperature inside the reactor must be kept below 15°C.

[0079] (4) The mixture obtained in step (3) is heated at 25°C and reacted at this temperature for 80 min to obtain a first mixture with a viscosity of 200 cP-1000 cP;

[0080] (5) The first mixture obtained in step (4) was rapidly filtered using a Buchner funnel to obtain approximately 200 mL of recovered concentrated sulfuric acid and a semi-dry filter cake (i.e., the second mixture), wherein the filter screen of the Buchner funnel was a 500-mesh stainless steel mesh; wherein the recovery rate of concentrated sulfuric acid was 66.7%;

[0081] (6) After storing the semi-dry filter cake in an environment of 25°C for 12 hours, disperse it in 500 mL of water, heat it to 90°C and keep it for 30 minutes.

[0082] (7) After cooling, add 10 mL of 30 wt% hydrogen peroxide;

[0083] (8) After filtration, washing and drying, graphite oxide powder is obtained.

[0084] Example 3

[0085] (1) Take 1g of 325 mesh natural graphite powder and pour it into the reaction vessel, and pour 30mL of 98.3wt% concentrated sulfuric acid into the reaction vessel, and then start the uniform stirring to make the two mix evenly until they are uniformly wetted.

[0086] (2) After the temperature inside the reactor is reduced to 10°C, take 3g of potassium permanganate and slowly add it into the reactor at a rate of 10g / 40min. During the addition of potassium permanganate, the temperature inside the reactor must be kept below 15°C.

[0087] (3) The mixture obtained in step (2) is heated at 25°C and reacted at this 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%.

[0088] (4) The first mixture obtained in step (3) was rapidly filtered using a Buchner funnel to obtain approximately 20 mL of recovered concentrated sulfuric acid and a semi-dry filter cake (i.e., the second mixture), wherein the filter screen of the Buchner funnel was a 500-mesh stainless steel mesh; wherein the recovery rate of concentrated sulfuric acid was 66.7%;

[0089] (5) After storing the filter cake in an environment of 25°C for 24 hours, disperse it in water, heat it and keep it for a certain time, cool it and add hydrogen peroxide. After filtration, washing and drying, graphite oxide powder is obtained.

[0090] The graphite oxide powder obtained in step (5) was tested and found to have an oxidation degree of 100%. The recovery rate of concentrated sulfuric acid was 66.7%.

[0091] Comparative Example 1

[0092] (1) Take 1g of 325 mesh natural graphite powder and pour it into the reaction vessel, and pour 30mL of 98.3wt% concentrated sulfuric acid into the reaction vessel, and then start the uniform stirring to make the two mix evenly until they are uniformly wetted.

[0093] (2) After the temperature inside the reactor is reduced to 10°C, take 3g of potassium permanganate and slowly add it into the reactor at a rate of 10g / 40min. During the addition of potassium permanganate, the temperature inside the reactor must be kept below 15°C.

[0094] (3) The mixture obtained in step (2) is heated at 25°C and reacted at this 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%.

[0095] (4) The first mixture obtained in step (3) was rapidly filtered using a Buchner funnel to obtain approximately 23 mL of recovered concentrated sulfuric acid and a semi-dry filter cake (i.e., the second mixture), wherein the filter screen of the Buchner funnel was a 500-mesh stainless steel mesh; wherein the recovery rate of concentrated sulfuric acid was 76.7%;

[0096] (5) After storing the filter cake in an environment of 25°C for 24 hours, disperse it in water, heat it and keep it for a certain time, cool it and add hydrogen peroxide. After filtration, washing and drying, graphite oxide powder is obtained.

[0097] 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%.

[0098] Comparative Example 2

[0099] (1) Take 1g of 325 mesh natural graphite powder and pour it into the reaction vessel, and pour 30mL of 98.3wt% concentrated sulfuric acid into the reaction vessel, and then start the uniform stirring to make the two mix evenly until they are uniformly wetted.

[0100] (2) After the temperature inside the reactor is reduced to 10°C, take 3g of potassium permanganate and slowly add it into the reactor at a rate of 10g / 40min. During the addition of potassium permanganate, the temperature inside the reactor must be kept below 15°C.

[0101] (3) The mixture obtained in step (2) is heated at 25°C and reacted at this temperature until the graphite powder is completely oxidized, wherein the viscosity of the mixture after complete oxidation reaches more than 10,000 cP.

[0102] (4) The mixture obtained in step (3) was rapidly filtered using a Buchner funnel to obtain approximately 8 mL of recovered concentrated sulfuric acid and filter cake. The filter screen of the Buchner funnel was a 500-mesh stainless steel mesh. The recovery rate of the concentrated sulfuric acid was 26.7%.

[0103] (5) After storing the filter cake in an environment of 25°C for 24 hours, disperse it in water, heat it and keep it for a certain time, cool it and add hydrogen peroxide. After filtration, washing and drying, graphite oxide powder is obtained.

[0104] The graphite oxide powder obtained in step (5) was tested and found to have an oxidation degree of 100%. The recovery rate of concentrated sulfuric acid was 26.7%.

[0105] Based on the combined results of Example 3, Comparative Example 1, and Comparative Example 2, it can be seen that Comparative Example 1, where the oxidation rate of graphite powder in the first mixture is less than 50%, recovers concentrated sulfuric acid. While this ensures a high recovery rate, the low oxidation rate of graphite powder in the first mixture leads to incomplete oxidation in subsequent oxidation reactions. Comparative Example 2, where concentrated sulfuric acid is collected after complete oxidation of graphite powder, ensures the degree of graphite oxidation, but the high viscosity of the fully oxidized graphite powder results in an extremely low recovery rate. Example 3, however, recovers concentrated sulfuric acid when the graphite powder is not completely oxidized and its oxidation rate reaches more than 50%. At this point, the viscosity of the first mixture is 200 cP-1000 cP, allowing for a high recovery rate of concentrated sulfuric acid while ensuring complete oxidation of the graphite.

[0106] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A method for preparing graphite oxide, characterized in that, The preparation method includes: (1) Graphite powder and concentrated sulfuric acid are mixed uniformly in a reaction vessel at a ratio of 1 g: 15 mL-50 mL, wherein the concentration of the concentrated sulfuric acid is 82 wt%-98.3 wt%. (2) An oxidant is added to the reactor, and an intercalation and first-stage oxidation reaction is carried out at a temperature of 20 ℃-60 ℃ for 1 h-4 h 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 50%-90%; (3) The first mixture in the reactor is separated by filtration or centrifugation to recover 60%-90% of the total amount of concentrated sulfuric acid initially added, and to obtain the remaining second mixture; (4) The second mixture is left to stand at an ambient temperature of 20 ℃-60 ℃ for 6 h-72 h to carry out the second stage oxidation reaction until the graphite powder is completely oxidized; (5) Disperse the second mixture after the second stage oxidation reaction in water according to the graphite powder to water ratio of 1 g: 10 mL-50 mL, heat to 50 ℃-95 ℃ and keep for 5 min-80 min, cool and add hydrogen peroxide to obtain the graphite oxide.

2. The method for preparing graphite oxide as described in claim 1, characterized in that, The preparation method further includes the following steps: (6) Mix the recovered concentrated sulfuric acid and the new concentrated sulfuric acid obtained by mixing the old and new concentrated sulfuric acid in step (3) and mix them evenly with the new graphite powder; (7) Repeat steps (2)-(5) to recover concentrated sulfuric acid again in the repeated step (3) during the process of obtaining new graphite oxide.

3. The method for preparing graphite oxide as described in claim 2, characterized in that, The mixing ratio of the recovered concentrated sulfuric acid to the new concentrated sulfuric acid is 1:4 to 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, In step (3), concentrated sulfuric acid is recovered and recycled 1-10 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 mixed uniformly in the reaction vessel at a ratio of 1g:15mL-50mL, and the concentration of the concentrated sulfuric acid is 82wt%-98.3wt%.

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

8. 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 at a ratio of graphite powder to water of 1g:10mL-50mL, heated to 50℃-95℃ and held for 5min-80min.

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