Graphene dispersing agent as well as preparation method and application thereof

Abstract

The invention discloses a graphene dispersing agent as well as a preparation method and application thereof, the graphene dispersing agent has a chemical structure as shown in a formula I: # imgabs0 #, n and m are repetitive units respectively, n is equal to 1220-1660, and m is equal to 20-240. The graphene dispersant has a specific structure, not only can efficiently peel graphite to prepare graphene, but also can enable the graphene to be stably dispersed in water and avoid re-accumulation and agglomeration of the graphene, the graphene with small transverse size and few layers is prepared, meanwhile, the quality and yield of the prepared graphene are improved, and the graphene dispersant is suitable for industrial production. The method has important significance for industrial large-scale production of high-quality small-size graphene.

Description

Technical Field

[0001] This application belongs to the technical field of graphene preparation, and specifically relates to a graphene dispersant and a preparation method thereof, and also relates to the application of the graphene dispersant in the preparation of graphene by the aqueous phase exfoliation method. Background Art

[0002] Graphene is a honeycomb two-dimensional carbon nanostructure composed of sp 2 hybridized carbon atoms, with a thickness of only 0.334 nm. The structure of graphene is quite special. Due to its perfect sp 2 hybridized carbon structure, large conjugated bond system, and infinite repetitive periodic structure in the two-dimensional plane, the special and stable crystal structure endows graphene with a series of properties. For example, graphene has excellent optical, electrical, thermal, and mechanical properties. Therefore, graphene has broad application prospects in the fields of energy storage devices, optoelectronics, sensors, semiconductor materials, etc.

[0003] Small-sized graphene generally refers to graphene with a lateral size of 10 nm to 1 μm. Although there is no essential difference in its structure and morphology from that of large-sized graphene, small-sized graphene has better water solubility, so it is easier to disperse and reuse during use; at the same time, the interaction force between the small-sized graphene sheets in the solvent is smaller, making small-sized graphene more suitable for preparing high-concentration graphene solutions. Due to the good dispersion characteristics and uniformity of small-sized graphene, it is more easily used in the fields of conductive and heat-conductive composite materials, heat dissipation coatings, conductive additives, modified fibers, modified plastics, etc.

[0004] Currently, the preparation processes for small-sized graphene are not common. Among them, in some solutions, high-degree oxidative exfoliation of microcrystalline graphite is carried out by introducing concentrated phosphoric acid and increasing the addition amount of strong oxidants, and then small-sized graphene is obtained by combining purification, ultrasonic crushing, and thermal reduction. In other solutions, a mixed solution containing a grinding aid is obtained by mixing an alkali solution dispersed with graphite powder and a soluble salt, and a small-particle-size grinding aid is prepared by the in-situ generation method, which can uniformly enter the graphite interlayer and efficiently exfoliate the graphite sheets, and small-sized graphene with a uniform layer structure can be obtained. In addition, in some solutions, small-sized graphene is prepared by laser cutting after pressing expanded graphite. There are also some solutions where a high-speed rotating rotor drives the fluid to move at a high speed together, generating a high velocity gradient and high shear force, and at the same time, the high-speed fluid collides with the convex platform of the stator hole wall at a high speed to peel and refine the graphite sheets, thereby obtaining a process for small-sized graphene. However, these current processes either have the problem of low safety of the preparation process (involving corrosive reagents such as concentrated acids, strong oxidants, and alkalis), or have the problem of complex processes (requiring multiple steps of treatment), or have the defect of high process costs.

[0005] Liquid phase exfoliation is a mature preparation process for graphene, with the advantages of low cost, environmental protection, short time consumption, and the prepared graphite has fewer structural defects. Although the existing graphene dispersants for liquid phase exfoliation of graphite, such as sodium dodecylbenzene sulfonate (SDBS), gum arabic, polyvinyl pyrrolidone (PVP) and polyethylene glycol, etc., also include organic molecules and high molecular polymers synthesized by themselves, most of the final obtained after these liquid phase exfoliation are not small-sized graphene. In addition, the prior art also discloses that in a mixed system containing polyvinyl alcohol and benzaldehyde, the exfoliation preparation of graphene is realized by strict temperature control, and its process and condition requirements are strict, and the prepared graphene is also not small-sized graphene.

[0006] In general, there are still many difficulties in the quantitative preparation of small-sized graphene. It is very necessary to research and develop new graphene dispersants to achieve the preparation of high-quality small-sized graphene. Summary of the invention

[0007] In view of this, the primary purpose of the present application is to provide a graphene dispersant, which has a specific structure, can efficiently exfoliate graphite to prepare graphene, and make the graphene stably dispersed in water, avoid graphene re-stacking and agglomeration, and can prepare graphene with few layers and small lateral dimensions, while improving the quality and yield of the prepared graphene.

[0008] In order to achieve the above objectives, this application adopts the following technical solutions:

[0009] One aspect of the present application provides a graphene dispersant having a chemical structure as shown in Formula I:

[0010]

[0011] Wherein, n and m are repeating units, n=1220-1660, m=20-240.

[0012] Another aspect of the present application provides a method for preparing the graphene dispersant as described above, comprising the following steps:

[0013] Add polyvinyl alcohol into deionized water and fully dissolve it to form a clear and transparent solution;

[0014] An acid reagent is added to the solution to adjust the pH of the system to 2, and then benzaldehyde is added dropwise, followed by heating to react;

[0015] After the reaction is completed, an alkaline reagent is added to adjust the pH of the system to 7 to obtain a graphene dispersant.

[0016] Another aspect of the present application provides the use of the graphene dispersant as described above or the graphene dispersant prepared by the preparation method as described above in the preparation of graphene by aqueous phase exfoliation of graphite.

[0017] Another aspect of the present application provides a method for preparing graphene by aqueous phase exfoliation of graphite, comprising the following steps:

[0018] After mixing graphite, the graphene dispersant and deionized water, mechanical exfoliation is carried out to separate and obtain a graphene dispersion;

[0019] Wherein, the graphene dispersant is as described above or prepared by the preparation method as described above.

[0020] Advantages of the present application:

[0021] The molecular chain of the graphene dispersant in the present application contains benzene rings, which can be tightly adsorbed to the graphene sp 2 hybrid carbon layer through π-π interaction, weakening the van der Waals force between graphite layers and promoting interlayer exfoliation; the benzene rings are anchored on the graphite surface, enhancing the adsorption stability. At the same time, the hydroxyl groups in the molecular chain of the graphene dispersant can form hydrogen bonds with water molecules, improving the dispersibility of the graphene dispersant and graphene in the aqueous phase and preventing the re-accumulation of graphene. Further, the graphene dispersant is coated on the surface of the graphene sheets to form a spatial barrier, thereby preventing the re-aggregation of the exfoliated graphene; under the action of mechanical shear force or ultrasound, energy is input into the graphite layers to break the interlayer binding force. The graphene dispersant also plays the role of a "lubricant" in this process, reducing the exfoliation resistance, and thus high-concentration graphene can be efficiently exfoliated, a graphene dispersion with small lateral size and few layers can be obtained, high-quality small-size graphene can be prepared, and at the same time, the quality and yield of the prepared graphene are improved.

[0022] The graphene dispersant in the present application is synthesized by a one-step acetal reaction of polyvinyl alcohol and benzaldehyde, has amphiphilic groups, and controls the introduction amount of benzene rings by dropwise adding benzaldehyde to ensure the water solubility of the graphene dispersant. Moreover, deionized water is used in the preparation, which is more environmentally friendly. The preparation process of the graphene dispersant in the present application is simple, low-cost, and the process conditions are mild. By controlling the introduction amount of benzene rings on the polyvinyl alcohol molecular chain, the required graphene dispersant can be obtained, which is suitable for industrial production.

[0023] The graphene dispersant in the present application has excellent graphene exfoliation ability. The graphene prepared by the aqueous phase exfoliation method has few defects, small lateral size, high exfoliation efficiency, is environmentally friendly, and the prepared graphene dispersion is stable without sedimentation, and high-quality and high-yield small-size graphene can be industrially produced. Description of the Drawings

[0024] Figure 1This is a schematic diagram of the reaction for preparing graphene dispersion by exfoliating graphite with the graphene dispersant in this application.

[0025] Figure 2 This is an optical photograph of the graphene dispersion in Example 1 and Comparative Example 1 of this application after standing at room temperature (20 °C) for 7 days.

[0026] Figure 3 This is an infrared spectrum diagram of the graphene dispersant and polyvinyl alcohol in Example 1 of this application.

[0027] Figure 4 This is a Raman spectrum diagram of the graphene in Example 1 of this application.

[0028] Figure 5 This is an SEM image of the graphene prepared in Example 1 of this application. Detailed implementation manners

[0029] The following will clearly and completely describe the implementation manners of this application. The technical solutions in the following described implementation manners are exemplary and only possible technical implementations of this application, not all possible implementations. Those skilled in the art can fully combine the implementation manners of this application and obtain other implementation manners without creative labor, and these implementation manners are also within the protection scope of this application.

[0030] The first aspect of this application discloses a graphene dispersant, and the graphene dispersant has a chemical structure shown in Formula I:

[0031]

[0032] Wherein, n and m are repeating units respectively, n = 1220 - 1660, m = 20 - 240.

[0033] The molecular chain structure of the graphene dispersant in this application contains benzene rings and hydroxyl groups. On the one hand, the benzene rings can be tightly adsorbed to graphene through strong π-π bond interactions, weakening the van der Waals forces between graphite layers. Under the action of shear force or ultrasound, it promotes the exfoliation of graphite, and finally exfoliates to form graphene. On the other hand, the hydroxyl groups in the molecular chain structure can form hydrogen bonds with water molecules, improving the dispersion stability of graphene in the aqueous phase and preventing graphene from re-accumulating. At the same time, the graphene dispersant molecules are coated on the surface of the graphene sheets, which can form a spatial barrier to prevent the exfoliated graphene from re-aggregating. This can not only improve the quality and yield of the prepared graphene, but also the prepared graphene has a small lateral size and few layers. In this application, n and m represent repeating units, wherein, n = 1220 - 1660, m = 20 - 240, so as to control the introduction amount of benzene rings, ensure the water solubility of this graphene dispersant, and improve its dispersion and exfoliation effects.

[0034] The second aspect of the present application discloses a method for preparing a graphene dispersant as described above, which is prepared by condensation reaction using polyvinyl alcohol and benzaldehyde as starting materials. It should be noted that deionized water is used as the reaction medium in the present application to improve the environmental friendliness of the reaction, while benzaldehyde is added dropwise, and the amount of benzene ring introduced is controlled by gradually introducing benzaldehyde to ensure the water solubility of the graphene dispersant. In addition, in some examples, the graphene dispersant obtained in the present application can be directly dissolved in deionized water, without purification and drying, thereby simplifying the process.

[0035] In the present application, the preparation of the graphene dispersant comprises the following steps:

[0036] Add polyvinyl alcohol into deionized water and fully dissolve it to form a clear and transparent solution;

[0037] An acid reagent is added to the solution to adjust the pH of the system to 2, and then benzaldehyde is added dropwise, followed by heating to react;

[0038] After the reaction is completed, an alkaline reagent is added to adjust the pH of the system to 7 to obtain a graphene dispersant.

[0039] In the present application, the composition of the final product can be adjusted by adjusting the ratio of polyvinyl alcohol, benzaldehyde and deionized water to optimize the performance of the product. Those skilled in the art can explore and determine it through experiments without special requirements. In some examples, the mass ratio of polyvinyl alcohol, benzaldehyde and deionized water is 8: (0.1-4): (100-500); in some examples, the average degree of polymerization of polyvinyl alcohol is ≥1700, and the number average molecular weight is ≥75000; preferably, the average degree of polymerization of polyvinyl alcohol is 1700-2500, and the number average molecular weight is 75000-125000.

[0040] It is understood that the acid reagent and the alkaline reagent described in the present application are reagents conventionally used in the art to adjust the pH of the reaction system. Specifically, the pH of the system is adjusted to be acidic by the acid reagent, so as to facilitate the control of the reaction. The types of acid reagents that can be used include but are not limited to one of hydrochloric acid, sulfuric acid, phosphoric acid, and Lewis acid. Among them, the concentration of the acid reagent can be selected as needed. For example, in some examples, the mass concentration of the acid reagent is 0.1% to 5%.

[0041] The purpose of adding an alkaline agent in the present application is to adjust the pH of the system to be neutral, thereby neutralizing the acid agent in the reaction system, preventing excessive acetalization, and inhibiting the hydrolysis and side reactions of the graphene dispersant, thereby protecting the integrity of the molecular structure of the graphene dispersant. In some examples, the alkaline agent is one of sodium hydroxide and potassium hydroxide, but is not limited thereto.

[0042] It is understandable that the control of the reaction time is generally determined by the concentration of the reaction and the amount of reaction raw materials input, while the control of the reaction temperature is generally determined by the speed of the reaction rate. In this application, there are no special requirements for the reaction temperature and reaction time, and they can be adjusted according to actual needs. Those skilled in the art have such capabilities. In some examples, the reaction temperature of the heating reaction is 60-100 °C, and the time is 6-10 h.

[0043] The third aspect of this application discloses the use of the graphene dispersant as described above or the graphene dispersant prepared by the preparation method as described above in the preparation of graphene by aqueous phase exfoliation of graphite. Especially in the preparation of small-sized graphene (with a lateral size below 1000 nm).

[0044] In view of the excellent performance of the graphene dispersant in this application, when it is applied to the preparation of graphene by aqueous phase exfoliation of graphite, it can not only improve the yield and quality of graphene, but more importantly, the prepared graphene has a small lateral size and few layers.

[0045] The fourth aspect of this application discloses a method for preparing graphene by aqueous phase exfoliation of graphite. For the specific exfoliation process, reference can be made to Figure 1 , including the following steps:

[0046] After mixing graphite, graphene dispersant and deionized water, through mechanical exfoliation, a graphene dispersion is separated;

[0047] Among them, the graphene dispersant is as described above or prepared by the preparation method as described above.

[0048] In this application, there are no special requirements for the type and particle size of the graphite, and conventional selections in the art can be used. For example, the type of graphite can be one of expandable graphite, expanded graphite, natural flake graphite, artificial graphite, etc. For the size of the graphite, it can be 32-10000 mesh, but neither the type nor the size is limited to the examples in this application.

[0049] It should be noted that the ratio among the graphene dispersant, graphite and deionized water affects the final exfoliation effect of the graphite. Those skilled in the art can select a suitable ratio based on needs, and there are no special requirements. In some examples, the mass ratio of the graphite, graphene dispersant (polyvinyl alcohol benzal) and deionized water is (1-10):(0.25-2):(50-100).

[0050] In this application, the mechanical exfoliation can adopt conventional methods in the art, such as one of sanding, homogenization, and ultrasonic treatment. The specific parameters can be selected or optimized according to the exfoliation method and exfoliation effect. Those skilled in the art have such capabilities.

[0051] In some examples, the mechanical exfoliation is carried out by sanding, and the rotational speed of the sanding is 500 - 3000 rpm, and the time is 5 - 12 h.

[0052] In other examples, the mechanical exfoliation is carried out by homogenization, and the rotational speed of the homogenization is 3000 - 30000 rpm, and the time is 5 - 12 h.

[0053] In other examples, the power of the ultrasound is 100 - 1200 W, and the time is 5 - 12 h

[0054] In this application, the separation method is centrifugation well-known in the art. In some examples, the rotational speed of the centrifugation is 3000 - 5000 rpm, and the time is 30 - 60 min.

[0055] The following are specific examples of this application. It should be noted that the following specific examples are only for illustrative purposes and do not limit the scope of this application in any way.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0057] In addition, unless otherwise specified, the methods without specific conditions or steps recorded are conventional methods, and the reagents and materials used can be obtained from commercial channels.

[0058] The polyvinyl alcohol used in the following examples has a degree of polymerization of 1700 and a number-average molecular weight of 75000.

[0059] Example 1

[0060] In this example, a preparation method of a graphene dispersant is first provided, and the specific steps are as follows:

[0061] 12.0 g of polyvinyl alcohol is added to 384.0 g of deionized water and dissolved evenly to form a homogeneous mixed solution;

[0062] Then, 1 g of hydrochloric acid with a mass concentration of 2% is added to the above mixed solution to adjust the pH = 2, the temperature is raised to 80 °C, and 3.0 g of benzaldehyde is added dropwise, and mechanical stirring reaction is carried out for 8 h. After the reaction is completed, the system is adjusted to neutral to obtain the graphene dispersant shown in Formula I (solid content 3.75%, n = 1348, m = 176).

[0063] In this example, the application of the graphene dispersant prepared above in the preparation of graphene by aqueous-phase exfoliation of graphite is further provided, and the specific steps are as follows:

[0064] 10.0 g of expanded graphite (400 mesh), 27.0 g of the graphene dispersant prepared in this example, and 63.0 g of deionized water were added to a reaction vessel, mixed evenly, and milled and exfoliated with a sand mill at a speed of 3000 rpm for 6 h; after the exfoliation was completed, the product was centrifuged at a speed of 3000 rpm for 30 min to obtain the upper-layer graphene dispersion liquid.

[0065] Example 2

[0066] In this example, the graphene dispersant was prepared with reference to the implementation method of Example 1.

[0067] In this example, the application of the graphene dispersant prepared above in the preparation of graphene by aqueous-phase exfoliation of graphite was further provided, and the specific steps were as follows:

[0068] 10.0 g of expanded graphite (400 mesh), 27.0 g of the graphene dispersant prepared in this example, and 63.0 g of deionized water were placed in a reaction vessel, mixed evenly, and homogenized and exfoliated with a homogenizer at a speed of 15000 rpm for 6 h; after the exfoliation was completed, the product was centrifuged at a speed of 3000 rpm for 30 min to obtain the upper-layer graphene dispersion liquid.

[0069] Example 3

[0070] In this example, the graphene dispersant was prepared with reference to the implementation method of Example 1.

[0071] In this example, the application of the graphene dispersant prepared above in the preparation of graphene by aqueous-phase exfoliation of graphite was further provided, and the specific steps were as follows:

[0072] 10.0 g of expanded graphite (400 mesh), 27.0 g of the graphene dispersant prepared in this example, and 63.0 g of deionized water were placed in a reaction vessel, mixed evenly, and ultrasonically exfoliated with an ultrasonic machine at a power of 800 W for 6 h; after the exfoliation was completed, the product was centrifuged at a speed of 3000 rpm for 30 min to obtain the upper-layer graphene dispersion liquid.

[0073] Example 4

[0074] In this example, a preparation method of a graphene dispersant was first provided, and the specific steps were as follows:

[0075] 12.0 g of polyvinyl alcohol was added to 385.0 g of deionized water, and dissolved and mixed evenly to form a uniform mixed solution;

[0076] Then, 1 g of 2% hydrochloric acid by mass concentration was added to the above mixed solution, the pH was adjusted to 2, the temperature was raised to 60 °C, and benzaldehyde was added dropwise to 2.0 g. The reaction was stirred mechanically for 8 h. After the reaction was completed, the system was adjusted to neutrality to obtain the graphene dispersant shown in Formula I (solid content 3.5%, n = 1460, m = 120).

[0077] In this example, the application of the graphene dispersant prepared above in the preparation of graphene by aqueous phase exfoliation of graphite was further provided. The specific steps are as follows:

[0078] 10.0 g of expanded graphite (400 mesh), 28.6 g of the graphene dispersant prepared in this example, and 61.4 g of deionized water were placed in a reaction vessel, mixed evenly, and sand-milled at a speed of 3000 rpm for 6 h for exfoliation; after the exfoliation was completed, the product was centrifuged at a speed of 3000 rpm for 30 min to obtain the upper-layer graphene dispersion liquid.

[0079] Example 5

[0080] In this example, a preparation method of a graphene dispersant was first provided. The specific steps are as follows:

[0081] 12.0 g of polyvinyl alcohol was added to 383.0 g of deionized water and dissolved evenly to form a uniform mixed solution;

[0082] Then, 1 g of 2% hydrochloric acid by mass concentration was added to the above mixed solution, the pH was adjusted to 2, the temperature was raised to 80 °C, and benzaldehyde was added dropwise to 4.0 g. The reaction was stirred mechanically for 8 h. After the reaction was completed, the system was adjusted to neutrality to obtain the graphene dispersant shown in Formula I (solid content 4%, n = 1234, m = 233).

[0083] In this example, the application of the graphene dispersant prepared above in the preparation of graphene by aqueous phase exfoliation of graphite was further provided. The specific steps are as follows:

[0084] 10.0 g of natural flake graphite (400 mesh), 50.0 g of the graphene dispersant prepared in this example, and 40.0 g of deionized water were placed in a reaction vessel, mixed evenly, and sand-milled at a speed of 3000 rpm for 6 h for exfoliation; after the exfoliation was completed, the product was centrifuged at a speed of 3000 rpm for 30 min to obtain the upper-layer graphene dispersion liquid.

[0085] Example 6

[0086] In this example, a preparation method of a graphene dispersant was first provided. The specific steps are as follows:

[0087] 12.0 g of polyvinyl alcohol was added to 384.5 g of deionized water and dissolved evenly to form a uniform mixed solution;

[0088] Then, 1 g of hydrochloric acid with a mass concentration of 2% was added to the above mixed solution, the pH was adjusted to 2, the temperature was raised to 80 °C, and benzaldehyde was added dropwise to 2.5 g. The reaction was mechanically stirred for 8 h. After the reaction was completed, the system was adjusted to neutrality to obtain a graphene dispersant (solid content 3.6%, n = 1398, m = 151).

[0089] In this example, the application of the graphene dispersant prepared above in the preparation of graphene by aqueous phase exfoliation of graphite was further provided. The specific steps are as follows:

[0090] 10.0 g of natural flake graphite (400 mesh), 55.6 g of the graphene dispersant prepared in this example, and 34.4 g of deionized water were placed in a reaction vessel, mixed evenly, and sanded and exfoliated at 3000 rpm for 10 h using a sand mill; after the exfoliation was completed, the product was centrifuged at 3000 rpm for 30 min to obtain an upper-layer graphene dispersion.

[0091] Comparative Example 1

[0092] In this comparative example, a method for preparing graphene by aqueous phase exfoliation of graphite was provided. Referring to the implementation method of Example 1, the difference was only that the graphene dispersant was replaced with a mixture of benzaldehyde and polyvinyl alcohol.

[0093] The specific steps are as follows:

[0094] 10.0 g of expanded graphite (400 mesh), 0.8 g of polyvinyl alcohol (degree of polymerization 1700, number average molecular weight 75000), 0.2 g of benzaldehyde, and 89.0 g of deionized water were placed in a reaction vessel, mixed evenly, and sanded and exfoliated at 3000 rpm for 6 h using a sand mill; after the exfoliation was completed, the product was centrifuged at 3000 rpm for 30 min to obtain an upper-layer graphene dispersion.

[0095] Comparative Example 2

[0096] In this comparative example, a method for preparing graphene by aqueous phase exfoliation of graphite was provided. Referring to the implementation method of Example 1, the difference was only that the graphene dispersant was replaced with polyvinylpyrrolidone (PVPK30).

[0097] The specific steps are as follows:

[0098] 10.0 g of expanded graphite (400 mesh), 1.0 g of polyvinylpyrrolidone (PVPK30), and 89.0 g of deionized water were placed in a reaction vessel, mixed evenly, and sanded and exfoliated at 3000 rpm for 6 h using a sand mill; after the exfoliation was completed, the product was centrifuged at 3000 rpm for 30 min to obtain an upper-layer graphene dispersion.

[0099] Characterization and Testing

[0100] (1) Figure 2 Optical photographs of the graphene dispersions prepared in Example 1 and Comparative Example 1 after standing at room temperature (20 °C) for 7 days. As can be seen from Figure 2 it, the graphene dispersant in Comparative Example 1 showed obvious stratification, while there was no stratification in Example 1, indicating that the graphene dispersion obtained by using the graphene dispersant in this application has excellent dispersion stability and can exist uniformly and stably.

[0101] (2) Figure 3 Infrared spectra of the graphene dispersant and the raw material polyvinyl alcohol in Example 1. As can be seen from Figure 3 it, in the infrared spectrum of the graphene dispersant, the two absorption peaks at 755 cm -1 and 699 cm -1 belong to the out-of-plane bending vibration peaks of C-H in a monosubstituted benzene ring. Compared with the infrared spectrum of PVA, the stretching vibration peak of -OH in the dispersant appears at 3300 cm -1 , and the absorption intensity is significantly weakened, indicating that most of the -OH in the structure of the graphene dispersant has undergone an acetal reaction with benzaldehyde. Therefore, it can be proved by the infrared spectrum that benzaldehyde and PVA have undergone an acetal reaction.

[0102] Furthermore, combined with Figure 4 , Figure 4 Raman spectrum of the graphene prepared in Example 1. It can be seen that three typical peaks appear at about 1350 cm -1 , 1577 cm -1 , and 2712 cm -1 , corresponding to the D, G, and 2D peaks of graphene respectively. The intensity ratio of the 2D / G peak is 0.33, fully indicating that the prepared graphene has the characteristics of few layers.

[0103] (3) Figure 5 Scanning electron micrograph of the graphene prepared in Example 1. As can be seen from Figure 5 it, graphite has been exfoliated by the graphene dispersant under the action of mechanical exfoliation, and the prepared graphene has fewer layers, with an average number of layers of about 3.

[0104] (4) The graphene dispersions prepared in Examples 1-6 and Comparative Examples 1 and 2 were observed, and the average number of layers and lateral size were tested. The results are shown in Table 1.

[0105] Table 1 Test results of graphene

[0106] Sample Average number of layers Transverse dimension D50 Dispersion state (visual) Example 1 3 650 nm Stable without sedimentation Example 2 4 800 nm Stable without sedimentation Example 3 5 1 μm Stable without sedimentation Example 4 4 830 nm Stable without sedimentation Example 5 4 680 nm Stable without sedimentation Example 6 3 550 nm Stable without sedimentation Comparative Example 1 10 15 μm Unstable and prone to sedimentation Comparative Example 2 8 6 μm Unstable and prone to sedimentation

[0107] As can be seen from the above characterizations and test results, the graphene dispersant in the present application is applied to the preparation of graphene by aqueous-phase exfoliation of graphite, and a graphene dispersion with stable dispersion and no sedimentation can be prepared. Moreover, the prepared graphene also has the advantages of small lateral size and few layers.

[0108] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same constitution and the same effect within the technical scope of the present application are included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other modes constructed by combining some constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A graphene dispersant, characterized in that: The graphene dispersant has a chemical structure as shown in Formula I: Wherein, n and m are repeating units, n=1220-1660, m=20-240.

2. A method for preparing a graphene dispersant according to claim 1, characterized in that: The following steps are involved: Add polyvinyl alcohol into deionized water and fully dissolve it to form a clear and transparent solution; An acid reagent is added to the solution to adjust the pH of the system to 2, and then benzaldehyde is added dropwise, followed by heating to react; After the reaction is completed, an alkaline reagent is added to adjust the pH of the system to 7 to obtain a graphene dispersant.

3. The preparation method according to claim 2, characterized in that: The mass ratio of the polyvinyl alcohol, benzaldehyde and deionized water is 8: (0.1-4): (100-500); Preferably, the average degree of polymerization of the polyvinyl alcohol is ≥1700, and the number average molecular weight is ≥75000.

4. The preparation method according to claim 2, characterized in that: The acid reagent is one of hydrochloric acid, sulfuric acid, phosphoric acid, and Lewis acid; And / or, the alkaline reagent is one of sodium hydroxide and potassium hydroxide.

5. The preparation method according to claim 2, characterized in that: The temperature of the temperature-raising reaction is 60-100° C. and the time is 6-10 hours.

6. Use of the graphene dispersant according to claim 1 or the graphene dispersant prepared by the preparation method according to any one of claims 2 to 5 in preparing graphene by aqueous phase exfoliation of graphite.

7. The use according to claim 6, characterized in that The graphene is small-sized graphene, and the lateral size of the small-sized graphene is less than 1 μm.

8. A method for preparing graphene by aqueous phase exfoliation of graphite, characterized in that: The following steps are involved: After mixing graphite, graphene dispersant and deionized water, the mixture is subjected to mechanical exfoliation to separate and obtain a graphene dispersion; Wherein, the graphene dispersant is as described in claim 1 or is prepared by the preparation method described in any one of claims 2-5; Preferably, the graphite is one of expandable graphite, expanded graphite, natural flake graphite, and artificial graphite; and / or, the size of the graphite is 32-10000 mesh; Preferably, the separation method is centrifugation, the centrifugation speed is 3000-5000 rpm, and the time is 30-60 min.

9. The method for preparing graphene by aqueous phase exfoliation of graphite as claimed in claim 8, characterized in that: The mass ratio of the graphite, graphene dispersant and deionized water is (1-10): (0.25-2): (50-100).

10. The method for preparing graphene by aqueous phase exfoliation of graphite according to claim 8, characterized in that: The mechanical peeling method is one of sanding, homogenization, and ultrasound; Preferably, the sand milling speed is 500-3000 rpm, and the time is 5-12 hours; Preferably, the homogenization speed is 3000-30000 rpm, and the time is 5-12 hours; Preferably, the power of the ultrasound is 100-1200 W, and the time is 5-12 hours.

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