A method for self-assembly of macro-quantity of low-defect graphene under hot melt state, and low-defect graphene prepared by the method

Abstract

The application provides a method for self-assembling and macro-preparing low-carbon-defect graphene in a hot melt state, and the prepared low-carbon-defect graphene, wherein a metal hydroxyl carboxylate is heated to a melting point and kept constant, then heated to a carbonization temperature, and kept constant at the carbonization temperature, and the low-carbon-defect graphene is obtained.Compared with the prior art, the method of the application uses a hydroxyl carboxylate of a metal ion as a carbon source precursor to self-assemble and prepare graphene in a molten state; by adjusting the self-assembly time of the hydroxyl carboxylate of the metal ion in the molten state, the macro self-assembly preparation of the low-carbon-defect graphene is realized.The preparation method is simple, green, environmentally friendly, controllable and scalable, and the product quality can be guaranteed, and the purity is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of new functional materials, and particularly relates to a method for self-assembling and macro-preparing low-carbon-defect graphene in a hot melt state and low-carbon-defect graphene prepared by the method. BACKGROUND

[0002] Since the professors Geim and Novoselov of Manchester University in the UK successfully separated graphene by innovative adhesive tape peeling method in 2004, this material has become the focus and research hotspot in the academic field due to its unique structural characteristics and excellent performance. The connection mode and electronic structure of carbon atoms of graphene together endow it with excellent physical and chemical properties. Specifically, graphene has extremely large specific surface area, which provides unlimited possibilities for it in the fields of electrochemistry and material science; meanwhile, its extremely high mechanical strength means that it can withstand various extreme conditions; in addition, its excellent thermal conductivity and ultra-high carrier mobility make graphene also show great application potential in the fields of biomedicine and optics. These excellent performances indicate that graphene will possibly lead a revolution in the field of material science and open a brand-new technological era.

[0003] Although the application prospect of graphene material is broad, the existence of carbon defects in graphene greatly limits its application. Carbon defects can reduce the electrical conductivity of graphene, enhance polarization loss, and significantly affect the transmission ability of electrons, so the preparation of low-carbon-defect graphene is very important for industrial application. However, the mass production of low-carbon-defect graphene faces a series of challenges and limitations. For example, although the mechanical exfoliation method can simply and cheaply prepare low-carbon-defect graphene, its limitation is that the size of the obtained graphene is difficult to accurately control, and the yield is limited. This method is mainly suitable for small-scale laboratory preparation, and it is difficult to meet the production needs of large-scale and industrialization. The supercritical fluid exfoliation method provides an efficient way for the preparation of low-carbon-defect graphene and can quickly produce graphene. However, this method can easily make macromolecules such as surface active substances adhere to the surface of graphene during the reaction, thereby affecting the purity and quality of graphene. In addition, since this method needs to be carried out in a high-temperature and high-pressure environment, it brings significant safety hazards, limiting its widespread application in large-scale production. The graphene prepared by the oxidation-reduction method can obtain graphene with relatively complete structure, but the toxic and harmful gases generated during the reaction will pollute the environment and need to be treated, and the structure and integrity of graphene are often severely damaged by the oxidation of the oxidizing agent, resulting in a decrease in the quality of graphene and many structural defects. The chemical vapor deposition method for preparing low-carbon-defect graphene can prepare graphene with complete structure, good quality and large size, and the number of graphene layers can be changed according to the changes in growth time, growth temperature and other conditions, which has strong controllability and can promote the large-scale production of graphene. However, its preparation process is complex and the production cost is high, thereby limiting the application and promotion of this method.

[0004] In summary, low-carbon-defect graphene is often difficult to be applied on a large scale due to the complexity and low yield of existing preparation methods. Therefore, how to realize a simple, green, controllable and scalable preparation method for low-carbon-defect graphene is worthy of further study. SUMMARY

[0005] The purpose of the present application is to provide a method for self-assembly of low-carbon-defect graphene in a hot melt state. The method uses metal hydroxyl carboxylate as a carbon source precursor to prepare graphene in a molten state. By adjusting the self-assembly time in the molten state, the macro self-assembly preparation of low-carbon-defect graphene is realized. The preparation method is simple, green, controllable and scalable. Moreover, it can ensure product quality and greatly improve purity.

[0006] Another purpose of the present application is to provide a low-carbon-defect graphene prepared by the above method.

[0007] The specific technical solutions of the present application are as follows:

[0008] The application provides a method for self-assembling and macro-preparing low-carbon defect graphene in a hot melt state, and specifically relates to the following steps: heating metal hydroxyl carboxylate to a melting point under an argon atmosphere, keeping constant temperature, then heating to a carbonization temperature, and keeping constant temperature at the carbonization temperature to obtain the product.

[0009] The metal hydroxyl carboxylate is selected from sodium citrate, preferably sodium citrate dihydrate Na3C6H5O7·2H2O.

[0010] The heating to the melting point refers to heating to the melting point at a heating rate of 1-3 ℃ / min.

[0011] The heating to the melting point and keeping constant temperature refers to keeping constant temperature for 0h

[0012] The heating to the carbonization temperature refers to heating to the carbonization temperature at a heating rate of 5-10 ℃ / min.

[0013] The carbonization temperature is 500-900 ℃.

[0014] The keeping constant temperature at the carbonization temperature refers to keeping constant temperature for 2-8h.

[0015] Further, after carbonization, the obtained material is fully ground to below 60 mesh, hydrochloric acid is added for washing, suction filtration is performed, then water is added for washing to neutral and drying.

[0016] The hydrochloric acid washing uses hydrochloric acid with a concentration of 0.1-0.3 mol / L.

[0017] The drying temperature is 50-100 ℃, and the time is 12-24h.

[0018] In the preparation, hydroxyl carboxylate containing monovalent metal ions is used as a carbon source precursor, and low-carbon defect graphene is synthesized in a hot melt state by self-assembly in one step, and the process can be divided into ring formation reaction, defatting reaction and polymerization reaction. The hydroxyl carboxylate containing monovalent metal ions (sodium citrate dihydrate) has a special structure of sodium carboxylate group and hydroxyl group, and after reaching the hot melt state, the hydroxyl group and the carboxyl group of the hydroxyl carboxylate containing monovalent metal ions serve as a driving force to promote the rearrangement and assembly of the hydroxyl carboxylate, after rearrangement and recombination, an esterification reaction occurs, NaOH is removed, and a carbon ring containing an internal ester group is formed. At the carbonization temperature, the ester group of the carbon ring undergoes a defatting reaction, the carbon-oxygen bond is broken, the free half bond combines with the half bond of the surrounding carbon to form a sigma bond of graphene, and the combination mode is sp 2Hybrid, the preliminary formation of the planar structure, the remaining sodium carboxylate group and the hydroxyl group produced by the carbon ring de-esterification reaction occurs esterification, this reaction realizes the carbon ring polymerization arrangement, completes the self-assembly of carbon process. With the increase of assembly time, the arrangement of carbon source molecules presents the order degree increases, the surface carbon defect of the synthesized carbon material reduces, that is, the graphene with low surface carbon defect can be formed; but if the assembly time is too long, the decarboxylation reaction will occur, which will destroy the ordered structure of graphene. Therefore, by regulating the hydroxycarboxylate of monovalent metal ion self-assembly process in the hot melt state, the one-step macro production of low carbon defect graphene can be realized.

[0019] In the present application, the pre-organized structure formed in the melting self-assembly stage serves as a "template" to guide the ordered arrangement of carbon atoms in the carbonization process and reduce defects; the stepwise heating avoids the violent decomposition of the precursor at a single high temperature, thereby balancing the order and pyrolysis rate. By adjusting the self-assembly time and optimizing the order degree of the intermediate, the structure is fixed by carbonization to realize the macro preparation of low-defect graphene.

[0020] The low-carbon-defect graphene provided by the present application is prepared by the above method. The low-carbon-defect graphene contains a large amount of sp 2 bonded carbon two-dimensional carbon-based material; only contains a small amount of carbon defects, meets at the Dirac point, and has significant electronic, optical and mechanical properties. The g value intensity of the low-carbon-defect graphene prepared by the present application is less than 0.1, which is low in carbon defects.

[0021] Compared with the prior art, the present application first prepares macro low-carbon-defect graphene in one step through self-assembly of hydroxycarboxylate of monovalent metal ion in the hot melt state, adjusts the self-assembly time of the precursor, and greatly improves the yield of graphene prepared by the melting self-assembly method. The preparation requirements are more simple; compared with the supercritical fluid exfoliation method for preparing graphene, the purity of graphene prepared by the melting self-assembly method is greatly improved, there is no macromolecular impurity, and the preparation conditions of the melting self-assembly method are more simple and easy to realize mass production; compared with the redox method for preparing graphene, the graphene prepared by the melting self-assembly method has fewer structural defects, and the introduction of heteroatoms is avoided. The area of the prepared graphene is also larger, and the conditions for preparing graphene are also more simple; compared with the chemical vapor deposition method, the preparation conditions of the melting self-assembly method are more simple and can realize mass production. In summary, the present application innovatively realizes the design and preparation of low-carbon-defect graphene, the whole operation is more simple and controllable, the reaction conditions are more mild, the controllability and repeatability are better, and the operation process is green and environmentally friendly, and the production cost is low. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 SEM image of graphite carbon prepared in Example 1;

[0023] Figure 2 Raman spectrum of the graphite carbon prepared for Example 1;

[0024] Figure 3 TEM image of the graphite carbon prepared for Example 1;

[0025] Figure 4 SEM image of the graphite carbon prepared for Example 2;

[0026] Figure 5 Raman spectrum of the graphite carbon prepared for Example 2;

[0027] Figure 6 TEM image of the graphite carbon prepared for Example 2;

[0028] Figure 7 SEM image of the graphite carbon prepared for Example 3;

[0029] Figure 8 Raman spectrum of the graphite carbon prepared for Example 3;

[0030] Figure 9 TEM image of the graphite carbon prepared for Example 3;

[0031] Figure 10 SEM image of the graphite carbon prepared for Example 4;

[0032] Figure 11 Raman spectrum of the graphite carbon prepared for Example 4;

[0033] Figure 12 TEM image of the graphite carbon prepared for Example 4;

[0034] Figure 13 EPR image of the graphite carbon prepared for Examples 1, 2, 3 and 4; a is the EPR image of Example 1; b is the EPR image of Example 2; c is the EPR image of Example 3; d is the EPR image of Example 4. DETAILED DESCRIPTION

[0035] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in a clear and complete manner with reference to the embodiments of the present application. Obviously, the described embodiments are only some, but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0036] In the following examples, the test materials and reagents used, etc. can be obtained from commercial channels unless otherwise specified.

[0037] Unless otherwise specified in the examples, the techniques and conditions described in the literature or according to the product instructions are used.

[0038] Example 1 (as a comparison)

[0039] A method for self-assembly of macro-quantity of low-carbon defect graphene in a hot melt state, comprising the following steps:

[0040] a. 5g of sodium citrate dihydrate Na3C6H5O7·2H2O is heated at a heating rate of 1℃ / min to its melting point of 300℃, and after self-assembly in a hot melt state for 0h, it is heated at a heating rate of 5℃ / min to 700℃, and kept constant temperature for 3h, to preliminarily form graphite carbon;

[0041] b. The graphite carbon prepared in step a is put into a mortar and ground to below 60 mesh, 0.1mol / L hydrochloric acid is added for washing, and further suction filtration, water washing to neutral, and finally the obtained product is placed in a drying oven at 70℃ for drying for 24h.

[0042] The SEM characterization of the synthesized graphite carbon is shown in Figure 1 , which shows that the generated carbon material is a two-dimensional sheet structure; the Raman spectrum is shown in Figure 2 , the D peak value is 1345cm -1 , the G peak value is 1603cm -1 , and there is no obvious 2D peak, indicating that there is no graphene in the graphite carbon; the HRTEM of the graphite carbon is shown in Figure 3 , which shows that the order of the graphite carbon is low. EPR test is performed: using equipment BRUKER EMXPLUS, the intensity of carbon vacancy defects of 20mg sample is scanned, and the vacancy parameters set by CEL-PF300 series xenon lamp system (belonging to high light power full wave band light source, wavelength continuously distributed, spectral coverage UV-Vis-IR 200-1100nm) are CenterField 3510.00G, SweepWidth 100.0G, FrequencyMon 9.843016GHz, Power 3.170mW, PowerAtten 10.0dB, ModAmp 1.000G, ModFreq 100.00kHz, SweepTime 60.00s, TimeConst 5.12ms, to realize the scanning of the intensity of carbon defects. From the EPR shown in Figure 13 a, it can be seen that the carbon material shows high carbon defect intensity, indicating that there are many carbon defects in the material.

[0043] Example 2

[0044] A method for self-assembly of low-carbon defect graphene in a hot melt state, comprising the following steps:

[0045] a. 5g of sodium citrate dihydrate Na3C6H5O7·2H2O precursor is heated to its melting point of 300℃ at a heating rate of 1℃ / min, and after self-assembly in a hot melt state for 12h, it is heated to 700℃ at a heating rate of 5℃ / min and kept constant for 3h to preliminarily form graphite carbon;

[0046] b. The graphite carbon prepared in step a is ground in a mortar to below 60 mesh, washed with 0.1mol / L hydrochloric acid, and further subjected to suction filtration, washed with water until neutral, and finally dried in a drying oven at 70℃ for 24h.

[0047] The SEM characterization of the synthesized graphite carbon is shown in Figure 4 , indicating that the generated carbon material is two-dimensional; the Raman spectrum shown in Figure 5 indicates that the D peak is 1345cm -1 , the G peak is 1603cm -1 , and the 2D peak is 2886cm -1 , indicating that a certain amount of graphene exists in the graphite carbon, and the 2D peak is significantly improved compared with the graphite carbon prepared in Example 1, indicating that the increase of self-assembly time promotes the assembly of graphene; the HRTEM of the graphite carbon is shown in Figure 6 , in which a plurality of parallel short lines are graphene microcrystals distributed in different directions, and the arrangement of the carbon material becomes ordered; as shown in b of Figure 13 , the EPR shows that compared with the graphene prepared in Example 1, reasonably extending the assembly time is beneficial to reducing the carbon defects of the graphite carbon material.

[0048] Example 3

[0049] A method for self-assembly of low-carbon defect graphene in a hot melt state, comprising the following steps:

[0050] a. 5g of sodium citrate dihydrate Na3C6H5O7·2H2O precursor is heated to its melting point of 300℃ at a heating rate of 1℃ / min, and after self-assembly in a hot melt state for 24h, it is heated to 700℃ at a heating rate of 5℃ / min and kept constant for 3h to preliminarily form graphite carbon;

[0051] b. The graphite carbon prepared in step a is ground in a mortar to below 60 mesh, washed with 0.1mol / L hydrochloric acid, and further subjected to suction filtration, washed with water until neutral, and finally dried in a drying oven at 70℃ for 24h.

[0052] The SEM characterization of the synthesized graphite carbon is shown inFigure 7 As shown, this indicates that the generated carbon material is two-dimensional; by Figure 8 The Raman spectrum shows a D peak at 1345 cm⁻¹. -1 G peak value 1603cm -1 2D peak value 2886cm -1 This indicates the presence of a certain amount of graphene in the graphitic carbon, but the intensity of the 2D peak in the Raman spectrum of Example 2 is much higher, indicating a higher content and integrity of graphene. This is due to the extended self-assembly time; the hydrophilic and hydrophobic properties of the hydroxyl and carboxyl groups prolong the assembly time, making the material more ordered, and after carbonization, it becomes an ordered graphene material. Figure 9 HRTEM images of graphene carbon show multiple parallel short lines representing graphene microcrystals distributed in different directions. Compared to Examples 1 and 2, the material in Example 3 exhibits a more ordered arrangement, resulting in a graphene material with fewer defects. Figure 13 As shown in Figure c, the EPR strength of the carbon material prepared in Example 3 is low, indicating that it has few carbon defects. This proves that a reasonable extension of the assembly time is beneficial to reducing carbon defects on the graphene surface.

[0053] Example 4 (as a comparison)

[0054] A method for large-scale self-assembly of low-carbon defect graphene in a molten state includes the following steps:

[0055] a. 5g of sodium citrate dihydrate Na3C6H5O7·2H2O precursor was heated to its melting point of 300℃ at a heating rate of 1℃ / min. After self-assembly in the hot-melt state for 48h, it was heated to 700℃ at a heating rate of 5℃ / min and kept at a constant temperature for 3h to initially form graphite carbon.

[0056] b. Grind the graphite carbon prepared in step a in a mortar until it is below 60 mesh, wash it with 0.1 mol / L hydrochloric acid, filter it further, wash it with water until it is neutral, and finally dry the product in a drying oven at 70°C for 24 hours.

[0057] SEM characterization of the synthesized graphite carbon is as follows: Figure 10 As shown, this indicates that the generated carbon material is two-dimensional; by Figure 11 The Raman spectrum shows a D peak at 1345 cm⁻¹. -1 G peak value 1603cm -1 2D peak value 2886cm -1 This indicates the presence of a certain amount of graphene in the graphitic carbon, but the intensity of the 2D peak in the Raman spectrum is lower than that of Example 3, suggesting that the graphene content is not as high as in Example 3 and the integrity is not high. This is because the self-assembly time is too long; if the intermediate assembly is too long, a decarboxylation reaction will occur, destroying the ordered structure of the graphene. Figure 12HRTEM of the graphite carbon shows that the multiple parallel short lines are the graphene microcrystals distributed in different directions. Compared with the material of Example 3, the material has reduced order and increased surface carbon defects. The EPR shown in FIG. 6B indicates that the carbon material has high carbon defect intensity, which indicates that the carbon defects in the material are increased. Figure 13 The EPR shown in FIG. 6B indicates that the carbon material has high carbon defect intensity, which indicates that the carbon defects in the material are increased.

[0058] The above description of the examples is to facilitate the understanding and use of the invention by those of ordinary skill in the art. Those skilled in the art can easily make various modifications to the examples and apply the general principles described herein to other examples without creative labor. Therefore, the invention is not limited to the above examples, and improvements and modifications made by those skilled in the art based on the disclosure of the invention without departing from the scope of the invention should be within the protection scope of the invention.

Claims

1. A method for large-scale self-assembly preparation of low-carbon defect graphene in a molten state, characterized in that, The method specifically involves heating a metal hydroxycarboxylate to its melting point under an argon atmosphere and holding the temperature thereafter, then raising the temperature to the carbonization temperature and holding it thereafter to obtain the final product. The metal hydroxycarboxylic acid salt is selected from sodium citrate; The heating to the melting point and holding at that temperature for a duration of 0 h < holding time < 48 h; The low-carbon defect graphene has a g-value intensity of less than 0.

1.

2. The method according to claim 1, characterized in that, Heating to the melting point means heating to the melting point at a heating rate of 1-3℃ / min.

3. The method according to claim 1, characterized in that, The heating to carbonization temperature refers to heating at a rate of 5-10℃ / min to the carbonization temperature.

4. The method according to claim 1 or 3, characterized in that, The carbonization temperature is 500-900℃.

5. The method according to claim 1, characterized in that, The carbonization temperature is maintained at a constant temperature for 2-8 hours.

6. The method according to claim 1, characterized in that, After carbonization, the resulting material is thoroughly ground, washed with hydrochloric acid, filtered, washed again, and dried.

7. A low-carbon defect graphene prepared by the method according to any one of claims 1-6.

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