Carbon fiber, method for producing the same, and composite material

Abstract

The application provides a carbon fiber, a preparation method thereof and a composite material, and belongs to the technical field of carbon fiber preparation. The preparation method of the carbon fiber comprises the following steps: performing electrochemical oxidation treatment on a carbon fiber substrate after carbonization treatment to obtain an intermediate; and performing ultrasonic treatment on a mixed system containing the intermediate and a treatment solution. The treatment solution contains tannic acid and metal ions. By sequentially performing carbonization treatment and electrochemical oxidation treatment on the carbon fiber substrate, more oxygen-containing functional groups can be introduced to the surface of the carbon fiber, the wettability and adhesion of the carbon fiber can be improved, and the interfacial bonding strength between the carbon fiber and a matrix resin can be improved. Further, by performing ultrasonic treatment on the carbon fiber substrate after electrochemical oxidation treatment in a system containing tannic acid and metal ions, the interfacial bonding strength between the prepared carbon fiber and the matrix resin can be further improved.

Description

Technical Field

[0001] This application relates to the field of carbon fiber preparation technology, and more specifically, to a carbon fiber, a method for preparing the same, and a composite material thereof. Background Technology

[0002] Carbon fiber reinforced resin matrix composites are formed by combining carbon fibers and matrix resins. They possess a variety of excellent physical and mechanical properties, such as lightweight, high strength, and electrical conductivity. They are widely used in the aerospace industry and various mechanical industries. They can significantly replace traditional metal materials as primary and secondary load-bearing structural components, thereby improving the working efficiency and application range of aerospace vehicles.

[0003] However, the interfacial bonding strength between carbon fibers and matrix resin in existing carbon fiber reinforced resin matrix composites needs to be further improved. Summary of the Invention

[0004] The purpose of this application is to provide a carbon fiber, a method for preparing the same, and a composite material thereof, which aim to improve the interfacial bonding strength between the carbon fiber and the matrix resin.

[0005] In a first aspect, this application provides a method for preparing carbon fiber, the method comprising: electrochemically oxidizing a carbonized carbon fiber matrix to obtain an intermediate; and ultrasonically treating a mixture containing the intermediate and a treatment solution. The treatment solution contains tannic acid and metal ions.

[0006] This application introduces more oxygen-containing functional groups onto the carbon fiber surface by sequentially carbonizing and electrochemically oxidizing the carbon fiber matrix, thereby improving the wettability and adhesion of the carbon fiber and enhancing the interfacial bonding strength between the carbon fiber and the matrix resin. Furthermore, this application further enhances the interfacial bonding strength between the electrochemically oxidized carbon fiber matrix and the matrix resin by ultrasonically treating it in a system containing tannic acid and metal ions.

[0007] In conjunction with the first aspect, in an optional embodiment of this application, the total charge of the electrochemical oxidation treatment is 20 to 120 C / g.

[0008] In the above technical solution, the resulting carbon fiber and matrix resin can have a high interfacial bonding strength.

[0009] Optionally, the electrochemical oxidation treatment time is 30–60 s.

[0010] In conjunction with the first aspect, in an optional embodiment of this application, the electrochemical oxidation treatment employs a multi-stage electrochemical oxidation process.

[0011] In the above technical solutions, under the condition that the total amount of electrochemical oxidation treatment is the same, multi-stage electrochemical oxidation treatment can further improve the interfacial bonding strength between the obtained carbon fibers and the matrix resin compared with single-stage electrochemical oxidation treatment.

[0012] Optionally, the number of stages in the multi-stage electrochemical oxidation treatment can be 2, 3, or 4.

[0013] In conjunction with the first aspect, in an optional embodiment of this application, the electrolyte for electrochemical oxidation treatment is selected from sodium hydroxide, sodium bicarbonate, or sulfuric acid.

[0014] In the above technical solution, the electrolyte used in the electrochemical oxidation treatment is the aforementioned substance, which can introduce more oxygen-containing functional groups onto the carbon fiber surface, thereby improving the wettability and adhesion of the carbon fiber and increasing the interfacial bonding strength between the carbon fiber and the matrix resin.

[0015] In conjunction with the first aspect, in an optional embodiment of this application, the carbonization temperature is 1200–1500°C.

[0016] In the above technical solution, the carbon fiber matrix can be fully carbonized, which is beneficial for introducing more oxygen-containing functional groups onto the surface of the carbon fiber after subsequent electrochemical oxidation treatment.

[0017] Optionally, the carbonization process can be carried out for 40 to 100 seconds.

[0018] In conjunction with the first aspect, in an optional embodiment of this application, the metal ions include Fe. 3+ Na + Cu 2+ and Zn 2+ At least one of the following; or / and, the solvent in the treatment solution is water; or / and, the pH of the treatment solution is 8 to 9.

[0019] In the above technical solution, the resulting carbon fiber and matrix resin can have a high interfacial bonding strength.

[0020] In conjunction with the first aspect, in an optional embodiment of this application, the molar ratio of tannic acid to metal ions is (0.08 to 0.5):1.

[0021] Optionally, the mass concentration of tannic acid in the treatment solution is 0.5–5.0 mg / mL.

[0022] In conjunction with the first aspect, in an optional embodiment of this application, the power of the ultrasonic treatment is 120-200W.

[0023] In the above technical solution, the resulting carbon fiber and matrix resin can have a high interfacial bonding strength.

[0024] Optionally, the ultrasonic treatment time is 30 to 60 minutes.

[0025] Secondly, this application provides a carbon fiber, which is prepared by any of the preparation methods provided in the first aspect above.

[0026] The carbon fiber provided in this application has a high interfacial bonding strength with the matrix resin, which can improve the interlaminar shear strength of the composite material formed by the carbon fiber and the matrix resin.

[0027] Thirdly, this application provides a composite material comprising a matrix resin and the carbon fiber provided in the second aspect above.

[0028] The composite material provided in this application has a high interfacial bonding strength between carbon fibers and matrix resin, and the composite material has a high interlaminar shear strength. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced 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.

[0030] Figure 1 A flowchart illustrating the carbon fiber preparation method provided in this application. Detailed Implementation

[0031] This application provides a method for preparing carbon fiber, which includes: electrochemically oxidizing a carbonized carbon fiber matrix to obtain an intermediate; and ultrasonically treating a mixture containing the intermediate and a treatment solution. The treatment solution contains tannic acid and metal ions.

[0032] This application introduces more oxygen-containing functional groups into the carbon fiber surface by sequentially carbonizing and electrochemically oxidizing the carbon fiber matrix, which can improve the wettability and adhesion of the carbon fiber and thus enhance the interfacial bonding strength between the carbon fiber and the matrix resin.

[0033] Furthermore, this application involves ultrasonic treatment of the electrochemically oxidized carbon fiber matrix in a system containing tannic acid and metal ions. The benzene ring conjugated structure of tannic acid can form π-π bonds with the carbon fiber matrix, thereby allowing tannic acid molecules to be rapidly coated onto the surface of the carbon fiber matrix. The large number of phenolic hydroxyl groups in tannic acid enhances the surface activity of the carbon fiber. The phenolic hydroxyl groups on the carbon fiber surface can react with epoxy groups in the matrix resin to form chemical bonds, thereby further improving the interfacial bonding strength between the obtained carbon fiber and the matrix resin.

[0034] Figure 1 For a flowchart of the carbon fiber preparation method provided in this application, please refer to [link / reference]. Figure 1 The preparation method of carbon fiber includes the following steps:

[0035] S110 is used to electrochemically oxidize the carbonized carbon fiber matrix to obtain an intermediate.

[0036] In this application, the carbonized carbon fiber matrix is ​​used as the anode and placed in an electrolyte solution; anodic electrolysis is used to generate active oxygen to oxidize the carbon fiber surface, thereby introducing more oxygen-containing functional groups onto the carbon fiber surface.

[0037] In some optional embodiments of this application, the total charge of the electrochemical oxidation treatment is 20–120 C / g; this results in a suitable degree of oxidation in the carbon fiber matrix, leading to a higher interfacial bonding strength between the obtained carbon fiber and the matrix resin. If the total charge of the electrochemical oxidation treatment is low, the number of active groups on the carbon fiber surface will decrease, slightly reducing the interfacial bonding strength between the carbon fiber and the matrix resin; conversely, if the total charge of the electrochemical oxidation treatment is high, the carbon fiber matrix will be over-oxidized, also slightly reducing the interfacial bonding strength between the carbon fiber and the matrix resin.

[0038] As an example, the total charge of the electrochemical oxidation treatment can be any value among 20C / g, 40C / g, 60C / g, 80C / g, 100C / g, and 120C / g, or a range between any two.

[0039] Furthermore, the electrochemical oxidation treatment time is 30–60 seconds, which can result in a high interfacial bonding strength between the prepared carbon fibers and the matrix resin.

[0040] As an example, the electrochemical oxidation treatment time can be any value among 30s, 35s, 40s, 45s, 50s, 55s, and 60s, or any value between both.

[0041] In some optional embodiments of this application, the electrochemical oxidation treatment employs a multi-stage electrochemical oxidation process.

[0042] Under the condition that the total amount of charge in the electrochemical oxidation treatment is the same, the multi-stage electrochemical oxidation treatment can further improve the interfacial bonding strength between the obtained carbon fibers and the matrix resin compared with the single-stage electrochemical oxidation treatment.

[0043] Furthermore, the number of stages in the multi-stage electrochemical oxidation treatment is 2, 3, or 4.

[0044] In some optional embodiments of this application, the electrolyte for electrochemical oxidation treatment is selected from sodium hydroxide, sodium bicarbonate, or sulfuric acid.

[0045] The electrolyte used in the electrochemical oxidation treatment is the aforementioned substance, which can introduce more oxygen-containing functional groups onto the carbon fiber surface, improve the wettability and adhesion of the carbon fiber, and thus enhance the interfacial bonding strength between the carbon fiber and the matrix resin.

[0046] As an example, sodium hydroxide is selected as the electrolyte for electrochemical oxidation treatment.

[0047] In some optional embodiments of this application, the carbonization temperature is 1200–1500°C; this allows the carbon fiber matrix to be fully carbonized, which is beneficial for introducing more oxygen-containing functional groups onto the carbon fiber surface after subsequent electrochemical oxidation treatment.

[0048] As an example, the carbonization temperature can be any value among 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, and 1500°C, or a range between any two.

[0049] Furthermore, the carbonization time is 40–100 seconds; this allows the carbon fiber matrix to be fully carbonized, which is beneficial for introducing more oxygen-containing functional groups onto the carbon fiber surface after subsequent electrochemical oxidation treatment.

[0050] As an example, the carbonization time can be any value among 40s, 50s, 60s, 70s, 80s, 90s, and 100s, or a range between any two.

[0051] In some optional embodiments of this application, the preparation method of the intermediate includes: after electrochemical oxidation treatment, sequentially washing and drying the carbon fiber matrix.

[0052] S120 involves ultrasonically treating a mixture containing intermediates and a processing liquid.

[0053] In this application, the processing solution contains tannic acid and metal ions. The two adjacent phenolic hydroxyl groups on the benzene ring of tannic acid can coordinate with the metal ions in the processing solution as oxygen anions, causing tannic acid to chelate with the metal ions. Tannic acid has excellent adhesion properties; after simple mixing with metal ions, a coating can be formed on the surface of the carbon fiber matrix, enhancing the interfacial adhesion between the carbon fiber and the matrix resin. Furthermore, the tannic acid-metal ion coating can increase the surface roughness of the carbon fiber, generating higher friction between the carbon fiber and the matrix resin, and also enhancing the interfacial bonding performance.

[0054] In some optional embodiments of this application, the metal ions include Fe. 3+ Na + Cu 2+ and Zn 2+ At least one of them.

[0055] The metal ions selected above can chelate with tannic acid to increase the surface roughness of carbon fibers.

[0056] In some optional embodiments of this application, the solvent in the treatment solution is water.

[0057] In some optional embodiments of this application, the pH of the treatment solution is 8 to 9.

[0058] As an example, the pH of the treatment solution can be any value among 8, 8.2, 8.5, 8.7 and 9, or a range between any two.

[0059] In some optional embodiments of this application, the preparation method of the treatment solution includes: mixing an aqueous solution of tannic acid with an aqueous solution of a metal salt, and then adjusting the pH to 8-9.

[0060] As an example, the substance used to adjust the pH can be Tris (aminobutyric acid); the metal salt can be at least one of ferric chloride, sodium chloride, copper chloride, and zinc chloride.

[0061] In some optional embodiments of this application, the molar ratio of tannic acid to metal ions is (0.08 to 0.5):1.

[0062] As an example, the molar ratio of tannic acid to metal ions can be any one of 0.08:1, 0.095:1, 0.1:1, 0.19:1, 0.2:1, 0.25:1, 0.3:1, 0.38:1, and 0.5:1, or any range between the two.

[0063] Furthermore, the mass concentration of tannic acid in the treatment solution is 0.5–5.0 mg / mL.

[0064] As an example, the mass concentration of tannic acid in the treatment solution can be any one of 0.5 mg / mL, 1 mg / mL, 1.5 mg / mL, 2 mg / mL, 2.5 mg / mL, 3 mg / mL, 3.5 mg / mL, 4 mg / mL, 4.5 mg / mL and 5 mg / mL or any range between two.

[0065] In some optional embodiments of this application, the ultrasonic treatment power is 120-200W, which allows the tannic acid-metal ion coating to quickly and fully cover the surface of the carbon fiber matrix, resulting in a high interfacial bonding strength between the carbon fiber and the matrix resin.

[0066] As an example, the power of the ultrasonic treatment can be any value among 120W, 130W, 140W, 150W, 160W, 170W, 180W, 190W and 200W or a range between any two.

[0067] Furthermore, the ultrasonic treatment time is 30–60 minutes.

[0068] As an example, the ultrasound treatment time can be any value among 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, and 60 min, or any value between both.

[0069] Furthermore, in some optional embodiments of this application, the method for preparing carbon fiber further includes: drying the ultrasonically treated carbon fiber after ultrasonic treatment.

[0070] This application provides a carbon fiber, which is prepared using the preparation method described above.

[0071] The carbon fiber provided in this application has a high interfacial bonding strength with the matrix resin, which can improve the interlaminar shear strength of the composite material formed by the carbon fiber and the matrix resin.

[0072] This application also provides a composite material, including a matrix resin and the carbon fiber provided above.

[0073] The composite material provided in this application has good mechanical properties, and the carbon fiber and matrix resin in the composite material have high interfacial bonding strength and high interlaminar shear strength.

[0074] It should be noted that this application does not limit the specific selection of the matrix resin. As an example, the matrix resin can be a thermoplastic resin or a thermosetting resin, for example, the matrix resin can be an epoxy resin.

[0075] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0076] Example 1

[0077] This embodiment provides a method for preparing carbon fiber, the specific steps of which are as follows:

[0078] (1) Carbonization treatment:

[0079] Polyacrylonitrile-based carbon fibers were carbonized at 1200℃ for 50 seconds.

[0080] (2) Electrochemical oxidation treatment:

[0081] Using sodium hydroxide as the electrolyte, the carbon fiber matrix after carbonization in step (1) was subjected to a two-stage electrochemical oxidation treatment; then the carbon fiber matrix after electrochemical oxidation was washed and dried to obtain an intermediate.

[0082] The amount of electricity used in each stage of electrochemical oxidation treatment was 30 C / g, and the time for each stage of electrochemical oxidation treatment was 30 s.

[0083] (3) Ultrasonic treatment:

[0084] Aqueous solutions of tannic acid and ferric chloride were mixed and stirred until homogeneous to obtain a mixed solution. Tris was dissolved in the mixed solution and the pH was adjusted to 8.5 to obtain a treatment solution. The intermediate obtained in step (2) was immersed in the treatment solution and ultrasonically treated at 120W for 50 minutes, followed by drying to obtain carbon fibers.

[0085] The treatment solution contained tannic acid at a mass concentration of 2.0 mg / mL and ferric chloride at a mass concentration of 1.0 mg / mL.

[0086] Example 2

[0087] This embodiment provides a method for preparing carbon fiber. The difference between this embodiment and Embodiment 1 is that the electrochemical oxidation treatment in step (2) has 3 stages, the amount of electricity for each stage of electrochemical oxidation treatment is 20C / g, and the time for each stage of electrochemical oxidation treatment is 20s.

[0088] Example 3

[0089] This embodiment provides a method for preparing carbon fiber. The difference between this embodiment and Embodiment 1 is that the electrochemical oxidation treatment in step (2) has 4 stages, the amount of electricity for each stage of electrochemical oxidation treatment is 15C / g, and the time for each stage of electrochemical oxidation treatment is 15s.

[0090] Example 4

[0091] This embodiment provides a method for preparing carbon fiber. The difference between this embodiment and Embodiment 1 is that the amount of electricity used in each stage of electrochemical oxidation treatment in step (2) is 10C / g.

[0092] Example 5

[0093] This embodiment provides a method for preparing carbon fiber. The difference between this embodiment and Embodiment 1 is that the amount of electricity used in each stage of electrochemical oxidation treatment in step (2) is 50 C / g.

[0094] Example 6

[0095] This embodiment provides a method for preparing carbon fiber. The difference between this embodiment and Embodiment 1 is that the amount of electricity used in each stage of electrochemical oxidation treatment in step (2) is 65 C / g.

[0096] Example 7

[0097] This embodiment provides a method for preparing carbon fiber. The difference between this embodiment and Embodiment 1 is that the amount of electricity used in each stage of electrochemical oxidation treatment in step (2) is 5 C / g.

[0098] Example 8

[0099] This embodiment provides a method for preparing carbon fiber. The difference between this embodiment and Embodiment 1 is that the time for each stage of electrochemical oxidation treatment in step (2) is 15s.

[0100] Example 9

[0101] This embodiment provides a method for preparing carbon fiber. The difference between this embodiment and embodiment 1 is that the mass concentration of tannic acid in the treatment solution of step (3) is 4.0 mg / mL.

[0102] Example 10

[0103] This embodiment provides a method for preparing carbon fiber. The difference between this embodiment and embodiment 1 is that the mass concentration of tannic acid in the treatment solution in step (3) is 1.0 mg / mL.

[0104] Example 11

[0105] This embodiment provides a method for preparing carbon fiber. The difference between this embodiment and embodiment 1 is that the mass concentration of tannic acid in the treatment solution in step (3) is 0.1 mg / mL.

[0106] Example 12

[0107] This embodiment provides a method for preparing carbon fiber. The difference between this embodiment and Embodiment 1 is that the power of ultrasonic treatment in step (3) is 200W.

[0108] Comparative Example 1

[0109] This comparative example provides a method for preparing carbon fiber. The difference between this comparative example and Example 1 is that the electrochemical oxidation treatment and ultrasonic treatment in Example 1 are not performed in this comparative example. The specific steps of this comparative example are as follows:

[0110] Polyacrylonitrile-based carbon fibers were carbonized at 1200℃ for 50 seconds.

[0111] Comparative Example 2

[0112] This comparative example provides a method for preparing carbon fiber. The difference between this comparative example and Example 1 is that the electrochemical oxidation treatment in Example 1 was not performed in this comparative example. The specific steps of this comparative example are as follows:

[0113] (1) Carbonization treatment:

[0114] Polyacrylonitrile-based carbon fibers were carbonized at 1200℃ for 50 seconds.

[0115] (2) Ultrasonic treatment:

[0116] Aqueous solutions of tannic acid and ferric chloride were mixed and stirred until homogeneous to obtain a mixed solution. Tris was dissolved in the mixed solution and the pH was adjusted to 8.5 to obtain a treatment solution. The carbon fiber matrix after carbonization in step (1) was immersed in the aforementioned treatment solution, ultrasonically treated with 120W power for 50 minutes, and then dried to obtain carbon fiber.

[0117] The treatment solution contained tannic acid at a mass concentration of 2.0 mg / mL and ferric chloride at a mass concentration of 1.0 mg / mL.

[0118] Comparative Example 3

[0119] This comparative example provides a method for preparing carbon fiber. The difference between this comparative example and Example 1 is that the ultrasonic treatment in Example 1 is not performed in this comparative example. The specific steps of this comparative example are as follows:

[0120] (1) Carbonization treatment:

[0121] Polyacrylonitrile-based carbon fibers were carbonized at 1200℃ for 50 seconds.

[0122] (2) Electrochemical oxidation treatment:

[0123] Using sodium hydroxide as the electrolyte, the carbon fiber matrix after carbonization in step (1) was subjected to a two-stage electrochemical oxidation treatment; then the carbon fiber matrix after electrochemical oxidation was washed and dried to obtain carbon fiber.

[0124] The amount of electricity used in each stage of electrochemical oxidation treatment was 30 C / g, and the time for each stage of electrochemical oxidation treatment was 30 s.

[0125] Experimental Example

[0126] The water contact angle of the carbon fibers prepared in Examples 1-12 and Comparative Examples 1-3 was tested using the meniscus method. The carbon fibers prepared in Examples 1-12 and Comparative Examples 1-3 were used to prepare composite materials, and the interlaminar shear strength (ILSS) of the composite materials was determined according to GB / T1450.1. The test results are shown in Table 1.

[0127] The preparation method of the composite material is as follows: carbon fiber is wound and fixed; AG80 epoxy resin and 4,4'-diaminodiphenyl sulfone (curing agent) are mixed and coated on the carbon fiber, and the composite material is obtained after drying.

[0128] Table 1

[0129]

[0130]

[0131] As can be seen from Table 1, the interlaminar shear strength of the carbon fiber and resin composite materials prepared in Examples 1-12 is significantly higher than that of the carbon fiber and resin composite materials prepared in Comparative Examples 1-3; indicating that sequential carbonization treatment, electrochemical oxidation treatment, and ultrasonic treatment in "tannic acid-metal ion treatment solution" can result in higher interfacial bonding strength between the carbon fiber and resin.

[0132] As can be seen from the comparison of Examples 1 to 3, when the total amount of electrochemical oxidation treatment is the same, the interlaminar shear strength of the composite material increases with the increase of the number of electrochemical oxidation treatment stages.

[0133] A comparison of Examples 1 and Examples 4-7 shows that, when the number of electrochemical oxidation treatment stages is the same, the total amount of electricity used in the electrochemical oxidation treatment will further affect the interlaminar shear strength of the composite material formed by carbon fiber and resin.

[0134] A comparison of Examples 1 and 8 shows that, when the number of electrochemical oxidation treatment stages and the total amount of charge are the same, the time of each stage of electrochemical oxidation treatment has little effect on the interlaminar shear strength of the composite material formed by carbon fiber and resin.

[0135] A comparison of Examples 1 and Examples 9-11 shows that as the mass concentration of tannic acid in the treatment solution increases during ultrasonic treatment, the interlaminar shear strength of the composite material also increases.

[0136] A comparison between Example 1 and Example 12 shows that the ultrasonic power of ultrasonic treatment further affects the interlaminar shear strength of the composite material formed by carbon fiber and resin.

[0137] In summary, this application, by sequentially carbonizing and electrochemically oxidizing the carbon fiber matrix, introduces more oxygen-containing functional groups onto the carbon fiber surface, improving the wettability and adhesion of the carbon fiber and thus enhancing the interfacial bonding strength between the carbon fiber and the matrix resin. Furthermore, this application further enhances the interfacial bonding strength between the electrochemically oxidized carbon fiber matrix and the matrix resin by ultrasonically treating it in a system containing tannic acid and metal ions.

[0138] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A method for preparing carbon fiber, characterized in that, include: The carbonized carbon fiber matrix was subjected to multi-stage electrochemical oxidation treatment to obtain an intermediate. The mixture containing the intermediate and the processing liquid is subjected to ultrasonic treatment; The treatment solution contains tannic acid and metal ions.

2. The preparation method according to claim 1, characterized in that, The total charge of the electrochemical oxidation treatment is 20~120C / g.

3. The preparation method according to claim 2, characterized in that, The electrochemical oxidation treatment lasts for 30-60 seconds.

4. The preparation method according to claim 1, characterized in that, The number of stages in the multi-stage electrochemical oxidation treatment is 2, 3, or 4.

5. The preparation method according to claim 1, characterized in that, The electrolyte used in the electrochemical oxidation treatment is selected from sodium hydroxide, sodium bicarbonate, or sulfuric acid.

6. The preparation method according to claim 1, characterized in that, The carbonization process is carried out at a temperature of 1200~1500℃.

7. The preparation method according to claim 6, characterized in that, The carbonization process takes 40 to 100 seconds.

8. The preparation method according to any one of claims 1 to 7, characterized in that, The metal ions include Fe. 3+ Na + Cu 2+ and Zn 2+ At least one of them; Or / and, the solvent in the treatment solution is water; Or / and, the pH of the treatment solution is 8-9.

9. The preparation method according to any one of claims 1 to 7, characterized in that, The molar ratio of tannic acid to the metal ion is (0.08~0.5):

1.

10. The preparation method according to claim 9, characterized in that, The tannic acid concentration in the treatment solution is 0.5~5.0 mg / mL.

11. The preparation method according to any one of claims 1 to 7, characterized in that, The power of the ultrasonic treatment is 120~200W.

12. The preparation method according to any one of claims 1 to 7, characterized in that, The ultrasonic treatment time is 30-60 minutes.

13. A carbon fiber, characterized in that, The carbon fiber is prepared by the preparation method as described in any one of claims 1 to 12.

14. A composite material, characterized in that, It includes the matrix resin and the carbon fiber as described in claim 13.

Images