Purified graphene oxide and method

Abstract

The invention discloses purified graphene oxide and a method, and belongs to the technical field of industrial graphene oxide. According to the purification method disclosed by the invention, the oxalic acid solution is adopted as a solvent, the oxalic acid solution is easy to obtain in the market, low in price and beneficial to large-scale use, oxalic acid only contains carbon, hydrogen and oxygen elements which are the same as the elements of graphene oxide, new impurities are not introduced, introduction of impurity ions such as Cl <-> and Na < + > is avoided, and the method is suitable for industrial production. The contents of K < + >, Mn < 2 + > and S < 2-> in impurity ions in the purified graphene oxide are greatly reduced, and the technical problems that the cost of materials adopted by an existing purification method is high and large-scale production is difficult to realize are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of industrialized graphene oxide, and in particular relates to purified graphene oxide and a method. Background Art

[0002] Graphene, as a material at the forefront of science and technology in the 21st century, is leading the revolution in materials science with its unprecedented properties. Its excellent mechanical properties give graphene unparalleled strength and toughness, far exceeding traditional materials; and its excellent conductivity makes it an ideal choice in the field of electronic devices, opening up new paths for high-speed electronic transmission and miniaturized circuit design. In addition, graphene's chemical stability and large specific surface area not only make it show great potential in chemical fields such as catalyst carriers and gas adsorption separation, but also greatly promote the advancement of lithium battery technology, making it possible to achieve battery systems with higher energy density and longer cycle life.

[0003] Chemical oxidation, as an important way to prepare graphene, is gradually moving towards industrial application due to its advantages of simplicity, high efficiency and ease of large-scale production. This method cleverly uses a strong acid environment as a reaction medium to deeply oxidize graphite through strong oxidants such as potassium permanganate, converting it into graphene oxide rich in interlayer oxygen-containing functional groups. Subsequently, these oxygen-containing groups are removed by thermal reduction or chemical reduction, restoring the conjugated structure of graphene, and finally obtaining high-quality graphene materials. This process not only enriches the preparation methods of graphene, but also lays a solid foundation for the wide application of graphene in physics, electronics, energy, composite materials and automobiles.

[0004] As an important intermediate product of graphene, the market development of graphene heat dissipation film made of graphene oxide is becoming more and more mature. Some high-end models of Huawei and Honor mobile phones have begun to widely use graphene heat dissipation film. In the future, the demand for graphene oxide will gradually increase. However, when preparing graphene oxide by the improved Hummers method, a large amount of concentrated sulfuric acid, potassium permanganate and other oxidants are added, so the obtained graphene oxide will inevitably contain a large amount of K + , Mn 2+ , S 2- ions, which greatly affects the application of graphene oxide in heat dissipation films and other fields. The cleaning and purification of graphene oxide directly affects the development and performance of its application products, so how to purify graphene oxide products at low cost and on a large scale is a crucial issue.

[0005] In the laboratory, graphene oxide is often prepared by multiple centrifugation of deionized water and long-term dialysis. Although this can eventually reduce the K + , Mn 2+ , S 2-The content of plasma, but its cycle is too long and the yield is low, so it is not suitable for large-scale production. At present, the industrial preparation of graphene oxide often adopts the method of filter pressing to achieve solid-liquid separation, but in the actual preparation process, because graphene oxide contains abundant oxygen-containing functional groups, it has a strong affinity for water molecules, and multiple sheets of graphene oxide wrap water molecules, making the entire solution system lose fluidity. Therefore, as the number of cleanings increases, the graphene oxide is gradually peeled off, and the viscosity of the solution will increase significantly until it loses fluidity and becomes a gel. The gel can no longer be subjected to the filter pressing process, and the content of impurity ions in the graphene oxide cannot be further effectively reduced, which will seriously affect the quality of graphene oxide and further affect the application of graphene oxide.

[0006] 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. - and organic solvents, Cl - It will seriously corrode stainless steel and affect downstream equipment. - The addition of acetone will increase the difficulty and cost of wastewater treatment, and it is impossible to achieve low cost; some researchers use organic acids such as citric acid, salicylic acid, malic acid and tartaric acid to clean and purify graphene oxide, but the above organic acids belong to the food, medicine and cosmetics industries, the cost is relatively high and they are not widely used in the chemical industry. Many reports are also mostly seen in laboratories. Therefore, a cleaning and purification method that can be scaled up, low-cost, and does not increase the difficulty of wastewater treatment is crucial for the preparation and application of graphene oxide. Summary of the invention

[0007] The purpose of the present invention is to provide a purified graphene oxide and a method to solve the technical problem that the existing purification methods use high material costs and are difficult to achieve large-scale production.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: The invention discloses a method for purifying graphene oxide, comprising the following steps: Adding the graphene oxide filter cake into the oxalic acid solution and dispersing it evenly to obtain a graphene oxide dispersion; The graphene oxide dispersion is subjected to sedimentation and pressure filtration to obtain a solid-phase graphene oxide filter cake; The solid-phase graphene oxide filter cake is washed and dried to obtain purified graphene oxide.

[0009] Furthermore, the oxalic acid solution is obtained by mixing oxalic acid and deionized water; the mass fraction of oxalic acid in the oxalic acid solution is 0.1%-1%.

[0010] Furthermore, the concentration of the graphene oxide dispersion is 50-150 g / L.

[0011] Furthermore, the graphene oxide filter cake is added to the oxalic acid solution and dispersed uniformly by shearing and stirring; The shearing speed is 500-1000 r / min, the stirring speed is 100-400 r / min, and the stirring time is 10-60 min.

[0012] Furthermore, the pressing pressure used in the sedimentation filtration is 0.6-0.8Mpa, and the pressing time is 30-60min.

[0013] Furthermore, the drying temperature is 70-100°C, and the drying time is 3-5 h.

[0014] Furthermore, the graphene oxide filter cake is prepared by using an improved Hummers method.

[0015] Furthermore, the pH value of the filtrate obtained after the sedimentation filtration is 5-6.

[0016] The invention also discloses purified graphene oxide prepared by the preparation method.

[0017] Furthermore, the K in the purified graphene oxide + , Mn 2+ With S 2- The mass concentration was less than 0.01%.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a method for purifying graphene oxide. Oxalic acid solution is used as a solvent. Oxalic acid solution is easily available in the market and is cheap, which is conducive to large-scale use. Oxalic acid contains only carbon, hydrogen and oxygen elements, which are the same as the elements of graphene oxide. No new impurities are introduced, and the introduction of impurities such as Cl is avoided. - 、Na + impurity ions, so that the K + , Mn 2+ , S 2- The contents are greatly reduced, solving the technical problem that the existing purification methods use high material costs and are difficult to achieve large-scale production.

[0019] Furthermore, the use of oxalic acid solution as a solvent can effectively make the graphene oxide filter cake evenly dispersed therein, avoid the increase of graphene oxide viscosity and gelation, which is beneficial to solid-liquid separation and greatly improves the cleaning and purification efficiency of graphene oxide. Compared with the existing graphene oxide purification process, the effect of oxalic acid on the anti-gelation of graphene oxide is different from that of existing hydrochloric acid or other acids. The oxalic acid structure contains groups such as carboxyl, carbon-oxygen double bonds and hydroxyl groups, and graphene oxide also contains similar groups. Therefore, on the basis of providing an acidic environment, the oxalic acid solution can be used as an anticoagulant for graphene oxide by dissolving oxalic acid molecules therein. Due to the repulsive force between the same functional groups, the presence of all oxalic acid molecules hinders the mutual adsorption of water by graphene oxide sheets, and the effect of multiple graphene sheets wrapping water molecules cannot be achieved, thereby achieving a decrease in the viscosity of graphene oxide. Because of this dual effect, the amount of oxalic acid added can be controlled within 1%, and the small amount added can control the increase in system cost.

[0020] Furthermore, in terms of wastewater treatment, the introduction of oxalic acid will not increase the COD of the wastewater, reducing the difficulty of wastewater treatment. At the same time, oxalic acid is easily decomposed by heating, and the decomposition products are carbon dioxide, carbon monoxide and water. When the wastewater passes through the multiple-effect evaporator, oxalic acid naturally decomposes, and there is no need to add treatment processes or equipment. The treatment process is extremely convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a process flow chart of the graphene oxide purification method of the present invention; Figure 2 This is a diagram showing the sedimentation effect of graphene oxide dispersion without oxalic acid and after adding oxalic acid. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0023] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0024] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0025] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0026] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0027] like Figure 1 As shown, the present invention provides a method for purifying graphene oxide, comprising the following steps: Graphene oxide filter cake was prepared by improved Hummers method; Dissolve industrial oxalic acid in deionized water to obtain an oxalic acid solution of a certain concentration; The graphene oxide filter cake is added to an oxalic acid solution of a certain concentration and dispersed evenly to obtain a graphene oxide dispersion. The graphene oxide dispersion is subjected to sedimentation and pressure filtration to obtain a solid-phase graphene oxide filter cake. The solid-phase graphene oxide filter cake is washed multiple times until the ion concentration reaches the standard and dried to obtain purified graphene oxide.

[0028] Preferably, the mass fraction of oxalic acid in deionized water is 0.1% to 1%.

[0029] Preferably, the concentration of the graphene oxide dispersion is 50-150 g / L.

[0030] Preferably, the graphene oxide filter cake is added to the oxalic acid solution and uniformly dispersed by shear stirring.

[0031] Preferably, the shearing speed is 500-1000 r / min, the stirring speed is 100-400 r / min, and the stirring time is 10-60 min.

[0032] Preferably, the pressing pressure during filtration is 0.6-0.8Mpa, and the pressing time is 30-60min.

[0033] Preferably, the drying temperature is 70-100° C. and the drying time is 3-5 h.

[0034] Preferably, K in the purified graphene oxide + , Mn 2+ With S 2- The content is less than 0.01%.

[0035] The present invention uses industrial oxalic acid solution as a solvent, which can effectively disperse the graphene oxide filter cake evenly therein, avoid the increase of graphene oxide viscosity and gelation, facilitate solid-liquid separation, and greatly improve the cleaning and purification efficiency of graphene oxide. Compared with the existing graphene oxide purification process, the effect of oxalic acid on the anti-gelation of graphene oxide is different from that of existing hydrochloric acid or other acids. The oxalic acid structure contains carboxyl, carbon-oxygen double bonds and hydroxyl groups, as shown in the following formula: ; Graphene oxide also contains similar groups, as shown in the following formula: ; Therefore, on the basis of providing an acidic environment, the oxalic acid molecules dissolved in the oxalic acid solution can be used as an anticoagulant for graphene oxide. Due to the repulsion between the same functional groups, the presence of all oxalic acid molecules hinders the mutual adsorption of water by the graphene oxide sheets, and the effect of multiple graphene sheets wrapping water molecules cannot be achieved, thereby achieving a decrease in the viscosity of graphene oxide. The effect of the graphene oxide solution after adding oxalic acid is shown in the attached figure. Figure 2 As shown in the figure, the viscosity of the graphene oxide solution without oxalic acid is very high and cannot be precipitated, while the viscosity of the graphene oxide solution with oxalic acid is significantly reduced, and rapid precipitation can be achieved. It is precisely because of this dual effect that the amount of oxalic acid added can be controlled within 1%. A small amount of addition can control the increase in system costs. In addition, oxalic acid is a very common organic acid in industry. It is easy to obtain in the market and cheap, which is conducive to large-scale use. Oxalic acid only contains carbon, hydrogen and oxygen elements, which are the same as the elements of graphene oxide. No new impurities are introduced, and the introduction of impurities such as Cl is avoided. - 、Na + Impurity ions such as oxalic acid are beneficial to the downstream application development of graphene oxide. In terms of wastewater treatment, the introduction of oxalic acid will not increase the COD of wastewater, reducing the difficulty of wastewater treatment. At the same time, oxalic acid is easy to decompose when heated, and the decomposition products are carbon dioxide, carbon monoxide and water. The decomposition equation is shown below: ; It can be seen that oxalic acid is naturally decomposed when the wastewater passes through the multiple-effect evaporator. There is no need to add treatment processes or equipment, and the treatment process is extremely convenient.

[0036] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0037] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0038] Example 1 A method for purifying graphene oxide comprises the following steps: Graphene oxide was prepared by improved Hummers method, and the liquid phase was removed by filtration to obtain graphene oxide filter cake; 0.4 g of industrial oxalic acid was weighed and dissolved in 400 g of deionized water, and stirred at 400 r / min for 15 min to dissolve it, to obtain a clear oxalic acid solution, and the mass fraction of oxalic acid was 0.1%; Weigh 60 g of graphene oxide filter cake into oxalic acid solution, stir at a shear speed of 800 r / min and a stirring speed of 300 r / min for 40 min to obtain a graphene oxide dispersion with a concentration of 150 g / L; The graphene oxide dispersion was subjected to sedimentation and pressure filtration to collect the solid product, the pressing pressure was 0.6 MPa, the pressing time was 30 min, and the pH value of the filtrate was measured to obtain a solid-phase graphene oxide filter cake; The solid phase graphene oxide filter cake was washed and purified six times until the pH of the supernatant was 5.5, and the solid product was filtered and dried in a drying oven at 80 °C until its quality was stable. The drying time was 4 hours to obtain purified graphene oxide. Determination of K in purified graphene oxide using ICP + , Mn 2+ , S 2- The contents are 0.0024%, 0.0008% and 0.0068% respectively.

[0039] Example 2 A method for purifying graphene oxide comprises the following steps: Graphene oxide was prepared by improved Hummers method, and the liquid phase was removed by filtration to obtain graphene oxide filter cake; 2 g of industrial oxalic acid was weighed and dissolved in 400 g of deionized water, and stirred at 500 r / min for 10 min to dissolve it, to obtain a clear oxalic acid solution, and the mass fraction of oxalic acid was 0.5%; Weigh 20 g of graphene oxide filter cake in oxalic acid solution, stir at a shear speed of 900 r / min and a stirring speed of 200 r / min for 30 min to obtain a graphene oxide dispersion with a concentration of 50 g / L; The graphene oxide dispersion was subjected to sedimentation and pressure filtration to collect the solid product, the pressing pressure was 0.8 MPa, the pressing time was 60 min, and the pH value of the filtrate was measured to obtain a solid-phase graphene oxide filter cake; The solid phase graphene oxide filter cake was washed and purified six times until the pH of the supernatant was 5.0, and the solid product was filtered and dried in a drying oven at 70 °C until its quality was stable. The drying time was 5 h to obtain purified graphene oxide. Determination of K in purified graphene oxide using ICP + , Mn 2+ , S 2- The contents are 0.0018%, 0.0005% and 0.0048% respectively.

[0040] Example 3 A method for purifying graphene oxide comprises the following steps: Graphene oxide was prepared by the improved Hummers method, and the liquid phase was removed by filtration to obtain a graphene oxide filter cake; 4 g of industrial oxalic acid was weighed and dissolved in 400 g of deionized water, and stirred at a speed of 300 r / min for 20 min to dissolve it, to obtain a clear oxalic acid solution with a mass fraction of 1%; Weigh 40 g of graphene oxide filter cake in oxalic acid solution, stir for 25 min at a shear speed of 1000 r / min and a stirring speed of 350 r / min to obtain a graphene oxide dispersion with a concentration of 100 g / L; The graphene oxide dispersion was subjected to sedimentation and pressure filtration to collect the solid product, the pressing pressure was 0.8 MPa, the pressing time was 40 min, and the pH value of the filtrate was measured to obtain a solid-phase graphene oxide filter cake; The solid phase graphene oxide filter cake was washed and purified six times until the pH of the supernatant was 6.0, and the solid product was filtered and dried in a drying oven at 90° C. until its quality was stable. The drying time was 3 h to obtain purified graphene oxide. Determination of K in purified graphene oxide using ICP + , Mn 2+ , S 2- The contents are 0.0014%, 0.0007% and 0.0056% respectively.

[0041] Example 4 A method for purifying graphene oxide comprises the following steps: Graphene oxide was prepared by the improved Hummers method, and the liquid phase was removed by filtration to obtain a graphene oxide filter cake; 4 g of industrial oxalic acid was weighed and dissolved in 400 g of deionized water, and stirred at a speed of 300 r / min for 20 min to dissolve it, to obtain a clear oxalic acid solution with a mass fraction of 1%; Weigh 40 g of graphene oxide filter cake into oxalic acid solution, stir for 10 min at a shear speed of 800 r / min and a stirring speed of 120 r / min to obtain a graphene oxide dispersion with a concentration of 100 g / L; The graphene oxide dispersion was subjected to sedimentation and pressure filtration to collect the solid product, the pressing pressure was 0.8 MPa, the pressing time was 40 min, and the pH value of the filtrate was measured to obtain a solid-phase graphene oxide filter cake; The solid phase graphene oxide filter cake was washed and purified six times until the pH of the supernatant was 6.0. The solid product was filtered and dried in a drying oven at 90° C. until its quality was stable. The drying time was 3 h to obtain purified graphene oxide.

[0042] Example 5 A method for purifying graphene oxide comprises the following steps: Graphene oxide was prepared by improved Hummers method, and the liquid phase was removed by filtration to obtain graphene oxide filter cake; 0.4 g of industrial oxalic acid was weighed and dissolved in 400 g of deionized water, and stirred at 400 r / min for 15 min to dissolve it, to obtain a clear oxalic acid solution, and the mass fraction of oxalic acid was 0.1%; Weigh 60 g of graphene oxide filter cake into oxalic acid solution, stir at a shear speed of 800 r / min and a stirring speed of 300 r / min for 40 min to obtain a graphene oxide dispersion with a concentration of 150 g / L; The graphene oxide dispersion was subjected to sedimentation and pressure filtration to collect the solid product, the pressing pressure was 0.8 MPa, the pressing time was 35 min, and the pH value of the filtrate was measured to obtain a solid-phase graphene oxide filter cake; The solid phase graphene oxide filter cake was washed and purified six times until the pH of the supernatant was 5.5. The solid product was filtered and dried in a drying oven at 85°C until its quality was stable. The drying time was 4 hours to obtain purified graphene oxide.

[0043] Example 6 A method for purifying graphene oxide comprises the following steps: Graphene oxide was prepared by improved Hummers method, and the liquid phase was removed by filtration to obtain graphene oxide filter cake; 2 g of industrial oxalic acid was weighed and dissolved in 400 g of deionized water, and stirred at 500 r / min for 10 min to dissolve it, to obtain a clear oxalic acid solution, and the mass fraction of oxalic acid was 0.5%; Weigh 20 g of graphene oxide filter cake in oxalic acid solution, stir at a shear speed of 900 r / min and a stirring speed of 200 r / min for 30 min to obtain a graphene oxide dispersion with a concentration of 50 g / L; The graphene oxide dispersion was subjected to sedimentation and pressure filtration to collect the solid product, the pressing pressure was 0.8 MPa, the pressing time was 60 min, and the pH value of the filtrate was measured to obtain a solid-phase graphene oxide filter cake; The solid phase graphene oxide filter cake was washed and purified six times until the pH of the supernatant was 6.0. The solid product was filtered and dried in a drying oven at 100°C until its quality was stable. The drying time was 4 hours to obtain purified graphene oxide.

[0044] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for purifying graphene oxide, characterized in that: The following steps are involved: Adding the graphene oxide filter cake into the oxalic acid solution and dispersing it evenly to obtain a graphene oxide dispersion; The graphene oxide dispersion is subjected to sedimentation and pressure filtration to obtain a solid-phase graphene oxide filter cake; The solid-phase graphene oxide filter cake is washed and dried to obtain purified graphene oxide.

2. A method for purifying graphene oxide according to claim 1, characterized in that: The oxalic acid solution is obtained by mixing oxalic acid and deionized water; the mass fraction of oxalic acid in the oxalic acid solution is 0.1%-1%.

3. 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.

4. A method for purifying graphene oxide according to claim 1, characterized in that: The graphene oxide filter cake is added into the oxalic acid solution and dispersed uniformly by shearing and stirring; The shearing speed is 500-1000 r / min, the stirring speed is 100-400 r / min, and the stirring time is 10-60 min.

5. A method for purifying graphene oxide according to claim 1, characterized in that: The pressing pressure used in the sedimentation filtration is 0.6-0.8Mpa, and the pressing time is 30-60min.

6. 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 3-5 hours.

7. A method for purifying graphene oxide according to claim 1, characterized in that: The graphene oxide filter cake is prepared by adopting an improved Hummers method.

8. A method for purifying graphene oxide according to claim 1, characterized in that: The pH value of the filtrate obtained after the sedimentation and pressure filtration is 5-6.

9. A purified graphene oxide, characterized in that: The product is prepared by the purification method described in any one of claims 1 to 8.

10. The purified graphene oxide according to claim 9, characterized in that: The K in the purified graphene oxide + , Mn 2+ With S 2- The mass concentration was less than 0.01%.

Images