A method for preparing graphene by polyacid intercalation

Abstract

The invention discloses a method for preparing graphene by polyacid intercalation, wherein a graphite sheet is used as a working electrode and a platinum sheet is used as a counter electrode, a constant voltage is applied, and electrochemical intercalation is performed in a sulfuric acid solution, and sulfuric acid molecules are intercalated into the graphite interlayer under the driving of an electric field to obtain a graphite intercalation compound; the obtained graphite intercalation compound is ground, and the bottom product is collected by centrifugation after being fully mixed with a phosphoric acid solution; concentrated phosphoric acid is added to the bottom product and heated, and then a sodium tungstate solution is added to fully react and generate polyacids between graphite layers; the product after the reaction is washed with deionized water for several times, the washed product is redispersed in a dispersant, and the product is allowed to stand after ultrasound to obtain a graphene dispersion; the supernatant of the graphene dispersion after standing is taken, filtered, washed, and dried to obtain graphene. The method of the invention can synthesize high-quality graphene in a short time, and the obtained graphene has a large size, a small number of layers, and an extremely low oxygen content.

Description

Technical Field

[0001] The invention belongs to the technical field of graphene material synthesis, and particularly relates to a method for preparing graphene by polyacid intercalation. Background Art

[0002] Graphene is a two-dimensional layered material with carbon atoms arranged in a "honeycomb" shape. It has excellent conductivity, large specific surface area and high mechanical strength. It has broad application prospects in energy storage devices, nanocomposites and electronic information materials. The synthesis methods of graphene include mechanical exfoliation, ball milling, epitaxial growth, chemical vapor deposition, redox method, etc. The yield of graphene obtained by mechanical exfoliation is low and it is difficult to produce in a quantitative manner; the number of graphene layers obtained by ball milling is uneven and it is difficult to ensure the quality; although epitaxial growth and chemical vapor deposition can obtain high-quality graphene, they have high requirements for experimental conditions and high costs. Redox method is currently one of the main ways to prepare graphene on a large scale, but the electronic structure and crystal integrity of graphene are destroyed by strong oxidants, resulting in large defects. These preparation methods fundamentally limit the large-scale application of graphene.

[0003] The preparation of graphene by electrochemical exfoliation has the advantages of being clean, pollution-free, low-cost, and simple in process. It has attracted extensive attention from researchers and society in recent years, and the quality and yield of graphene can be improved by adjusting the electrolyte and voltage. However, the prepared graphene has a small lateral size, and the introduction of oxygen-containing functional groups is inevitable during the exfoliation process, which seriously damages the excellent properties of graphene such as electrical conductivity and thermal conductivity. Therefore, it is still a severe challenge to mass-produce high-quality graphene with low oxygen content and few layers in a fast and simple way. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing graphene by polyacid intercalation to overcome the shortcomings of existing graphene preparation methods. The method of the present invention can synthesize high-quality graphene in a short time, and the obtained graphene has a large size, a small number of layers, and an extremely low oxygen content.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A method for preparing graphene by polyacid intercalation comprises the following steps:

[0007] a. Using graphite sheet as working electrode and platinum sheet as counter electrode, applying constant voltage, electrochemical intercalation is carried out in sulfuric acid solution. Driven by the electric field, sulfuric acid molecules are intercalated into the graphite layers to obtain graphite intercalation compounds;

[0008] b. grinding the obtained graphite intercalation compound, mixing it thoroughly with the phosphoric acid solution, and then centrifuging to collect the bottom product;

[0009] c. Add concentrated phosphoric acid to the bottom layer product obtained in step b and heat it, then add sodium tungstate solution to fully react and generate polyacid between graphite layers;

[0010] d. Wash the product after the reaction in step c with deionized water for several times, redisperse the washed product in a dispersant, and allow to stand after ultrasonic treatment to obtain a graphene dispersion;

[0011] e. Taking the supernatant of the graphene dispersion after standing, filtering, washing and drying to obtain graphene.

[0012] Furthermore, the graphite material of the working electrode in step a is one of commercial graphite sheets, expanded graphite aggregates, natural graphite aggregates, synthetic graphite aggregates, highly oriented pyrolytic graphite, graphite fibers and graphite films.

[0013] Furthermore, the constant voltage in step a is 1V to 6V.

[0014] Furthermore, the sulfuric acid solution in step a is concentrated sulfuric acid with a mass fraction greater than or equal to 70%.

[0015] Furthermore, the electrochemical intercalation time in step a is 60s to 3600s.

[0016] Furthermore, the phosphoric acid solution in step b is concentrated phosphoric acid with a mass fraction greater than or equal to 70%, and the mixing time is 1 h to 48 h.

[0017] Furthermore, in step c, the reaction temperature is 20 to 140° C., and the reaction time is 1 to 12 hours.

[0018] Furthermore, the molar ratio of sodium tungstate to H3PO4 added in step c is 1:2 to 1:16.

[0019] Furthermore, the dispersant in step d is any one of N-methylpyrrolidone, isopropanol and N,N-dimethylformamide.

[0020] Furthermore, in step d, the ultrasonic time is 0.5h to 3h, and the standing time is 1h to 72h.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] The present invention firstly electrochemically intercalates graphite with concentrated sulfuric acid to preliminarily expand the graphite interlayer spacing, and then generates polyacids by in-situ reaction between graphite intercalation compounds. In the process of in-situ generation of polyacids between layers, due to the large size of polyacid clusters, the graphite interlayer spacing can be significantly expanded and the interlayer Van der Waals force can be weakened; and the intercalation process is slow, the intercalation effect is obvious, no redox reaction occurs with graphite, and no gas is released, which can ensure that the chemical structure and properties of graphite will not be destroyed, and graphene with fewer layers, flatness, and large lateral size can be easily separated. The prepared graphene has fewer layers, extremely low oxygen content, and few structural defects. The entire experimental process is green and fast, and has the potential for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 This is a transmission electron microscope photo of the graphene prepared in Example 1 of the present invention;

[0025] Figure 2 The XRD pattern of the graphene prepared in Example 1 of the present invention;

[0026] Figure 3 The Raman spectrum of the graphene prepared in Example 1 of the present invention;

[0027] Figure 4 This is the XPS spectrum of the graphene prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] The embodiments of the present invention are described in further detail below:

[0029] A method for preparing graphene by polyacid intercalation, the preparation method comprising the following steps:

[0030] a. Using a graphite sheet as a working electrode and a platinum sheet as a counter electrode, applying a constant voltage, and performing electrochemical intercalation in a sulfuric acid solution; the graphite material of the working electrode is one of commercial graphite sheets, expanded graphite aggregates, natural graphite aggregates, synthetic graphite aggregates, highly oriented pyrolytic graphite, graphite fibers, and graphite films; the constant voltage is 1V to 6V; the sulfuric acid solution is concentrated sulfuric acid, with a mass fraction greater than or equal to 70%; the electrochemical intercalation time is 60s to 3600s;

[0031] b. Grinding the obtained graphite intercalation compound, and fully mixing it with phosphoric acid for a period of time, and then centrifuging and collecting the bottom product; the phosphoric acid is concentrated phosphoric acid, with a mass fraction greater than or equal to 70%; the mixing time is 1 hour to 48 hours;

[0032] c. Add phosphoric acid to the product obtained in step b and heat it to a certain temperature, then add sodium tungstate solution to fully react and generate polyacid between graphite layers; the reaction temperature is 20-140°C, and the reaction time is 1-12 hours; the dispersant is any one of N-methylpyrrolidone, isopropanol or N,N-dimethylformamide; the molar ratio of sodium tungstate to phosphoric acid is 1:2-1:16;

[0033] d. Wash the reaction product with deionized water for several times, redisperse the washed product in a dispersant, and allow to stand after ultrasonic treatment to obtain a graphene dispersion; the dispersant is any one of N-methylpyrrolidone, isopropanol or N,N-dimethylformamide, the ultrasonic time is 0.5h to 3h, and the standing time is 1h to 72h.

[0034] The technical scheme of the present invention is clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Example 1

[0036] The method for preparing graphene by polyacid intercalation of the present invention, the detailed steps of the preparation method are as follows:

[0037] a Commercial graphite sheet was used as the working electrode and platinum sheet as the counter electrode. A voltage of 1.6 V was applied and electrochemical intercalation was performed in a 98 wt % sulfuric acid solution for 1200 s.

[0038] b. grinding the obtained graphite intercalation compound, mixing it thoroughly with 85 wt % phosphoric acid for 12 h, and then centrifuging to collect the bottom product;

[0039] c. Add 10 mL of 85 wt% phosphoric acid to the product obtained in step b and heat to 100°C, then add 10 mL of 2.1 mol / L sodium tungstate solution and react for 6 hours;

[0040] d. The reaction product was washed with deionized water for 5 times, and the washed product was redispersed in N-methylpyrrolidone. After ultrasonic treatment for 1 hour, the product was allowed to stand for 24 hours to obtain a graphene dispersion.

[0041] Depend on Figure 1 It can be seen that the graphene prepared by the present invention has a larger size, a complete structure, and a smaller number of layers. Figure 2 It can be seen that the material has characteristic peaks belonging to the graphite structure near 26° and 54°, indicating that the product has a six-membered "honeycomb" lattice structure of graphene, and no other impurities appear in the spectrum, which shows that the graphene prepared in Example 1 is of high purity and free of other impurities. Figure 3 It can be seen that at 1350cm -1 、1580cm -1 、2710cm -1 The D peak, G peak and 2D peak representing the characteristic peaks of graphene appeared nearby. By calculation, we can get I D / I G The value of is 0.051, indicating that the graphene defect level is low. 2D / I G The value of is 0.49, indicating the few-layer characteristics of graphene. Figure 4 Analysis shows that the carbon-oxygen ratio (C / O) of the prepared graphene is as high as 23.7, indicating that the prepared graphene is of high purity.

[0042] Example 2

[0043] The method for preparing graphene by polyacid intercalation of the present invention, the detailed steps of the preparation method are as follows:

[0044] a With expanded graphite aggregate as working electrode and platinum sheet as counter electrode, 6V voltage was applied and electrochemical intercalation was carried out in 70wt% sulfuric acid solution for 60s;

[0045] b. grinding the obtained graphite intercalation compound, mixing it with 85 wt % phosphoric acid for 18 h, and then centrifuging to collect the bottom product;

[0046] c. Add 10 mL of 80 wt% phosphoric acid to the product obtained in step b and heat to 140°C, then add 10 mL of 1 mol / L sodium tungstate solution and react for 1 hour;

[0047] d. The reaction product was washed with deionized water for 5 times, and the washed product was redispersed in isopropanol. After ultrasonic treatment for 0.5 h, the product was allowed to stand for 48 h to obtain a graphene dispersion.

[0048] Example 3

[0049] The method for preparing graphene by polyacid intercalation of the present invention, the detailed steps of the preparation method are as follows:

[0050] a With highly oriented pyrolytic graphite as the working electrode and platinum sheet as the counter electrode, a voltage of 1 V was applied and electrochemical intercalation was carried out in 80 wt % sulfuric acid solution for 3600 s;

[0051] b. Grinding the obtained graphite intercalation compound, and fully mixing it with 85 wt % phosphoric acid for 24 h, and then centrifuging to collect the bottom product;

[0052] c. Add 17.5 mL of 85 wt% phosphoric acid to the product obtained in step b and heat to 80°C, then add 20 mL of 0.8 mol / L sodium tungstate solution and react for 12 hours;

[0053] d. The reaction product was washed with deionized water for 5 times, and the washed product was redispersed in N-methylpyrrolidone. After ultrasonic treatment for 3 hours, the product was allowed to stand for 72 hours to obtain a graphene dispersion.

[0054] Example 4

[0055] The method for preparing graphene by polyacid intercalation of the present invention, the detailed steps of the preparation method are as follows:

[0056] a With natural graphite aggregate as working electrode and platinum sheet as counter electrode, 5V voltage was applied and electrochemical intercalation was carried out in 90wt% sulfuric acid solution for 600s;

[0057] b. Grinding the obtained graphite intercalation compound, and fully mixing it with 85 wt % phosphoric acid for 48 hours, and then centrifuging to collect the bottom product;

[0058] c. Add 30 mL of 70 wt% phosphoric acid to the product obtained in step b and heat to 20°C, then add 15 mL of 4 mol / L sodium tungstate solution and react for 10 hours;

[0059] d. The reaction product was washed with deionized water for 5 times, and the washed product was redispersed in N,N-dimethylformamide. After ultrasonic treatment for 2 hours, the product was allowed to stand for 36 hours to obtain a graphene dispersion.

[0060] Example 5

[0061] The method for preparing graphene by polyacid intercalation of the present invention, the detailed steps of the preparation method are as follows:

[0062] a With synthetic graphite aggregate as working electrode and platinum sheet as counter electrode, 3V voltage was applied and electrochemical intercalation was carried out in 98wt% sulfuric acid solution for 2400s;

[0063] b. grinding the obtained graphite intercalation compound, mixing it thoroughly with 85 wt % phosphoric acid for 1 hour, and then centrifuging to collect the bottom product;

[0064] c. Add 10 mL of 75 wt% phosphoric acid to the product obtained in step b and heat to 50°C, then add 10 mL of 3 mol / L sodium tungstate solution and react for 3 hours;

[0065] d. The reaction product was washed with deionized water for 5 times, and the washed product was redispersed in N,N-dimethylformamide. After ultrasonic treatment for 1.5 hours, the product was allowed to stand for 60 hours to obtain a graphene dispersion.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing graphene by polyacid intercalation, characterized in that: The following steps are involved: a. Using graphite sheet as working electrode and platinum sheet as counter electrode, applying constant voltage, electrochemical intercalation is carried out in sulfuric acid solution. Driven by the electric field, sulfuric acid molecules are intercalated into the graphite layers to obtain graphite intercalation compounds; The sulfuric acid solution is concentrated sulfuric acid, with a mass fraction greater than or equal to 70%; b. grinding the obtained graphite intercalation compound, mixing it thoroughly with the phosphoric acid solution, and then centrifuging to collect the bottom product; c. Add concentrated phosphoric acid to the bottom layer product obtained in step b and heat it, then add sodium tungstate solution to fully react and generate polyacid between graphite layers; d. Wash the product after the reaction in step c with deionized water for several times, redisperse the washed product in a dispersant, and allow to stand after ultrasonic treatment to obtain a graphene dispersion; e. Taking the supernatant of the graphene dispersion after standing, filtering, washing and drying to obtain graphene.

2. The method for preparing graphene by polyacid intercalation according to claim 1, characterized in that: The graphite material of the working electrode in step a is one of commercial graphite sheets, expanded graphite aggregates, natural graphite aggregates, synthetic graphite aggregates, highly oriented pyrolytic graphite, graphite fibers and graphite films.

3. The method for preparing graphene by polyacid intercalation according to claim 1, characterized in that: The constant voltage in step a is 1V to 6V.

4. The method for preparing graphene by polyacid intercalation according to claim 1, characterized in that: The electrochemical intercalation time in step a is 60s to 3600s.

5. The method for preparing graphene by polyacid intercalation according to claim 1, characterized in that: The phosphoric acid solution in step b is concentrated phosphoric acid with a mass fraction greater than or equal to 70%, and the mixing time is 1 h to 48 h.

6. The method for preparing graphene by polyacid intercalation according to claim 1, characterized in that: The reaction temperature in step c is 20-140° C., and the reaction time is 1-12 hours.

7. The method for preparing graphene by polyacid intercalation according to claim 1, characterized in that: The molar ratio of sodium tungstate to H3PO4 added in step c is 1:2 to 1:

16.

8. The method for preparing graphene by polyacid intercalation according to claim 1, characterized in that: The dispersant in step d is any one of N-methylpyrrolidone, isopropanol and N,N-dimethylformamide.

9. The method for preparing graphene by polyacid intercalation according to claim 1, characterized in that: The ultrasonic time in step d is 0.5h to 3h, and the standing time is 1h to 72h.

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