A method for purifying graphene oxide

Abstract

The invention discloses a method for purifying graphene oxide, wherein a graphene oxide filter cake is prepared by improving the Hummers method; citric acid, salicylic acid, malic acid and tartaric acid are dissolved in deionized water to obtain a mixed acid solution; the graphene oxide filter cake is added to the mixed acid solution, uniformly dispersed to obtain a graphene oxide dispersion, and filtered multiple times until the pH of the upper clear liquid is 5-6, and dried to obtain purified graphene oxide. The present invention adopts a mixed acid solution containing citric acid, salicylic acid, malic acid and tartaric acid as a solvent, which can effectively make the graphene oxide filter cake uniformly dispersed therein, avoid the increase of the viscosity of the graphene oxide and gelation, is conducive to solid-liquid separation, greatly improves the cleaning and purification efficiency of the graphene oxide, and avoids the introduction of such as Cl ‑ 、Na + The invention has simple process, low cost, high purification efficiency and avoids the introduction of other impurity ions.

Description

Technical Field

[0001] The invention relates to the field of graphene oxide production, and in particular to a method for purifying graphene oxide. Background Art

[0002] As an emerging material in the 21st century, graphene has been widely used in many fields such as physics, electronics, lithium batteries, composite materials, and automobiles due to its excellent mechanical properties, electrical conductivity, chemical stability, and large specific surface area. Chemical oxidation is a simple and easy-to-industrial graphene preparation method. It mainly involves oxidizing graphite with strong oxidants such as potassium permanganate in a strong acid environment to obtain graphene oxide, and then obtaining graphene through thermal reduction or chemical reduction.

[0003] When preparing graphene oxide by the improved Hummers method, concentrated sulfuric acid, potassium permanganate, and hydrogen peroxide are used as raw materials, and graphene oxide is prepared by intercalation oxidation exfoliation. Sodium nitrate in the Hummers method system is not used during the reaction, and no toxic gas is produced. The specific preparation process includes: using graphite as a raw material, using concentrated sulfuric acid to enlarge the graphite interlayer spacing to form graphite oxide, and then using potassium permanganate to exfoliate the graphite oxide into graphene oxide, and finally using hydrogen peroxide to remove the unreacted potassium permanganate in the system, and washing to obtain a graphene oxide filter cake. Since sulfuric acid and potassium permanganate are used in the preparation process, it is inevitable that a large amount of K + , Mn 2+ , S 2- ion.

[0004] In the improved Hummers method, the purification and cleaning of graphene oxide directly affects the performance of subsequent products, so how to improve the purity of graphene products is a crucial issue. At present, most purification processes use deionized water as a solvent and use multiple washing centrifugation, sedimentation filtration or dialysis to gradually reduce the K content in graphene oxide. + , Mn 2+ , S 2- The content of plasma. In the synthesis process of graphene oxide, the byproducts are mainly salts and acids. These byproducts and graphene oxide are highly water-soluble. However, after multiple washings, as the content of impurity ions decreases and the pH of the solution increases, the viscosity of graphene oxide increases and gradually gels. Gelation will hinder the washing process, making water washing impossible. This will seriously affect the quality of graphene oxide and will further affect the application of graphene oxide.

[0005] A large number of researchers have optimized the purification process of graphene oxide. Some researchers have proposed a two-step method using hydrochloric acid and acetone as solvent to wash graphene oxide. That is, first wash the graphene oxide with hydrochloric acid, and then use excess acetone to remove the hydrochloric acid. This method improves the washing efficiency to a certain extent, but it will introduce new impurity ions Cl into graphene oxide. - In addition, the subsequent washing of acetone requires a large amount of deionized water. This will increase the wastewater that needs to be treated, which increases the production cost. Some researchers have also used dialysis, cross-flow filtration and other methods to purify graphene oxide. The purification cycle of this method is too long and is not suitable for industrial production. Therefore, the purification process of graphene oxide needs to be further optimized. Summary of the invention

[0006] In order to overcome the shortcomings of the existing graphene oxide cleaning and purification process, such as long cycle and introduction of other impurity ions, the present invention provides a simple and efficient method for purifying graphene oxide without introducing other impurity ions.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A method for purifying graphene oxide comprises the following steps:

[0009] Graphene oxide filter cake was prepared by improved Hummers method;

[0010] Dissolving citric acid, salicylic acid, malic acid and tartaric acid in deionized water to obtain a mixed acid solution;

[0011] The graphene oxide filter cake is added to the mixed acid solution and evenly dispersed to obtain a graphene oxide dispersion. The graphene oxide dispersion is filtered multiple times until the pH of the upper clear liquid is 5-6, and then dried to obtain purified graphene oxide.

[0012] Furthermore, the mass ratio of citric acid, salicylic acid, malic acid and tartaric acid is (1-2):(1-2):(1-2):(1-2).

[0013] Furthermore, the total mass fraction of citric acid, salicylic acid, malic acid and tartaric acid in the mixed acid solution is 0.1-2%.

[0014] Furthermore, the concentration of the graphene oxide dispersion is 50-150 g / L.

[0015] Furthermore, the graphene oxide filter cake is added into the mixed acid solution and uniformly dispersed by stirring.

[0016] Furthermore, the stirring speed is 400-1000 r / min; and the stirring time is 10-60 min.

[0017] Furthermore, the drying temperature is 70-100° C. and the drying time is 3-5 h.

[0018] Furthermore, the K + , Mn 2+ With S 2- The content is less than 0.01%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] Compared with the existing graphene oxide cleaning and purification process, the present invention uses a mixed acid solution containing citric acid, salicylic acid, malic acid and tartaric acid as a solvent, which can effectively disperse the graphene oxide filter cake evenly, avoid the increase of graphene oxide viscosity and gelation, facilitate solid-liquid separation, and greatly improve the cleaning and purification efficiency of graphene oxide. Since the four acids are all organic acids, they only contain carbon, hydrogen and oxygen elements, which are the same as the elements of graphene oxide, and no new impurities are introduced, and the introduction of impurities such as Cl is avoided. - 、Na + In the later use of graphene oxide, the mixed acid will decompose and volatilize during the high-temperature reduction process of graphene oxide, which will not affect the quality of graphene. After cleaning and purification by this process, the K of impurity ions in graphene oxide + , Mn 2+ , S 2- The content of the present invention is greatly reduced to less than 0.01%. The present invention has simple operation, short implementation period, strong operability, low cost, high purification efficiency and avoids the introduction of other impurity ions, and is convenient for industrial application.

[0021] Furthermore, in the present invention, the concentration of purified graphene oxide can be as high as 150 g / L.

[0022] Furthermore, the present invention uses four organic acids, namely citric acid, salicylic acid, malic acid and tartaric acid, mixed in a mass ratio of (1-2):(1-2):(1-2):(1-2), which can achieve better cleaning results than using hydrochloric acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of a method for purifying graphene oxide in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the embodiments.

[0025] The raw materials and equipment used in the present invention, unless otherwise specified, are all commonly used raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art.

[0026] See also Figure 1 , a method for purifying graphene oxide, comprising the following steps:

[0027] Graphene oxide is prepared by an improved Hummers method, the supernatant is removed by centrifugation, and the solid material is collected to obtain a graphene oxide filter cake.

[0028] Dissolve citric acid, salicylic acid, malic acid and tartaric acid in deionized water in a mass ratio of (1-2):(1-2):(1-2):(1-2), and dissolve them by strong stirring to obtain a mixed acid solution, in which the total mass fraction of citric acid, salicylic acid, malic acid and tartaric acid is 0.1-2%. Weigh a certain mass of graphene oxide filter cake and add it to the mixed acid solution. After high-speed shear dispersion, a uniform graphene oxide dispersion is obtained. Remove the supernatant by suction filtration. Repeat the suction filtration process several times until the pH of the supernatant is between 5-6. After drying for a certain period of time, the purified graphene oxide is obtained, and the impurity ion K in the graphene oxide powder is determined by inductively coupled plasma emission spectroscopy (ICP). + , Mn 2+ , S 2- The content of the cleaning agent is determined based on the test results.

[0029] Example 1

[0030] 1) preparing graphene oxide by an improved Hummers method, removing the supernatant by centrifugation, and obtaining a graphene oxide filter cake;

[0031] 2) 8 g of citric acid, salicylic acid, malic acid and tartaric acid were dissolved in 400 g of deionized water in a ratio of 1:1:1:1, and stirred at 400 r / min for 15 min to dissolve them to obtain a mixed acid solution; the total mass fraction of citric acid, salicylic acid, malic acid and tartaric acid was 2%;

[0032] 3) Weighing 60 g of graphene oxide filter cake into a mixed acid solution, stirring at a speed of 800 r / min for 40 min, to obtain a graphene oxide dispersion with a concentration of 150 g / L;

[0033] 4) collecting the solid product by suction filtration and measuring the pH value of the supernatant;

[0034] 5) Repeat the washing and purification process six times, the pH of the supernatant is 5.5, filter and obtain a solid product, dry it in a drying oven at 80°C until its quality is stable, and the drying time is 4 hours;

[0035] 6) Determination of K in purified graphene oxide using ICP + , Mn 2+ , S 2-The contents are 0.0024%, 0.0008% and 0.0068% respectively.

[0036] Example 2

[0037] 1) preparing graphene oxide by an improved Hummers method, and removing the supernatant by centrifugation to obtain a graphene oxide filter cake;

[0038] 2) dissolving 2 g of citric acid, salicylic acid, malic acid and tartaric acid in a mass ratio of 1:2:1:2 in 400 g of deionized water, stirring at a speed of 500 r / min for 10 min to dissolve them, to obtain a mixed acid solution; the total mass fraction of citric acid, salicylic acid, malic acid and tartaric acid is 0.5%;

[0039] 3) Weigh 20 g of graphene oxide filter cake into the mixed acid solution, and stir at a speed of 600 r / min for 30 min to obtain a graphene oxide dispersion with a concentration of 50 g / L;

[0040] 4) collecting the solid product by suction filtration and measuring the pH value of the supernatant;

[0041] 5) Repeat the washing and purification process three times, the pH of the supernatant is 5.0, and the solid product is dried in a drying oven at 70° C. until its quality is stable, and the drying time is 5 h;

[0042] 6) Determination of K in purified graphene oxide using ICP + , Mn 2+ , S 2- The contents are 0.0018%, 0.0005% and 0.0048% respectively.

[0043] Example 3

[0044] 1) preparing graphene oxide by an improved Hummers method, and removing the supernatant by centrifugation to obtain a graphene oxide filter cake;

[0045] 2) 4 g of citric acid, salicylic acid, malic acid and tartaric acid were dissolved in 400 g of deionized water in a mass ratio of 2:1:2:1, and stirred at 300 r / min for 20 min to dissolve them to obtain a mixed acid solution with a mass fraction of 1%; the total mass fraction of citric acid, salicylic acid, malic acid and tartaric acid was 1%;

[0046] 3) Weighing 40 g of graphene oxide filter cake into a mixed acid solution, stirring at a speed of 800 r / min for 25 min to obtain a graphene oxide dispersion with a concentration of 100 g / L;

[0047] 4) collecting the solid product by suction filtration and measuring the pH value of the supernatant;

[0048] 5) Repeat the washing and purification process five times, the pH of the supernatant is 6.0, and the solid product is dried in a drying oven at 90° C. until its quality is stable, and the drying time is 3 h;

[0049] 6) Determination of K in purified graphene oxide using ICP + , Mn 2+ , S 2- The contents are 0.0014%, 0.0007% and 0.0056% respectively.

[0050] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for purifying graphene oxide, characterized in that: The following steps are involved: Graphene oxide filter cake was prepared by improved Hummers method; Dissolving citric acid, salicylic acid, malic acid and tartaric acid in deionized water to obtain a mixed acid solution; The graphene oxide filter cake is added to the mixed acid solution and evenly dispersed to obtain a graphene oxide dispersion, the graphene oxide dispersion is filtered multiple times until the pH of the supernatant is 5-6, and dried to obtain purified graphene oxide; K in purified graphene oxide + , Mn 2+ With S 2- The content is less than 0.01%; The mass ratio of citric acid, salicylic acid, malic acid and tartaric acid is (1-2):(1-2):(1-2):(1-2); The total mass fraction of citric acid, salicylic acid, malic acid and tartaric acid in the mixed acid solution is 0.1-2%.

2. A method for purifying graphene oxide according to claim 1, characterized in that: The concentration of the graphene oxide dispersion is 50-150 g / L.

3. A method for purifying graphene oxide according to claim 1, characterized in that: The graphene oxide filter cake is added to the mixed acid solution and uniformly dispersed by stirring.

4. A method for purifying graphene oxide according to claim 3, characterized in that: The stirring speed is 400-1000r / min; the stirring time is 10-60min.

5. A method for purifying graphene oxide according to claim 1, characterized in that: The drying temperature is 70-100°C and the drying time is 3-5h.

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