Method for preparing graphene oxide and device thereof

Abstract

A method and device for preparing graphene oxide, first, graphite and metal chloride are mixed uniformly and then placed in a high-pressure resistant reaction kettle made of polytetrafluoroethylene, and intercalation reaction is carried out to form a first-order intercalated graphite intercalated with metal chloride; the prepared first-order intercalated graphite is placed in a reaction tank body, a screen is pressed on the top of the first-order intercalated graphite to ensure that the first-order intercalated graphite sheet is not easy to separate from the electrode before being peeled off; the screen and the reaction tank body are connected with the positive electrode of a direct current power supply, water is put into the reaction tank body, a graphite electrode or an inert metal is inserted into the water, and the graphite electrode or the inert metal is not in direct contact with the reaction tank body and the screen and is connected with the negative electrode of the direct current power supply; then, the positive electrode and the negative electrode are electrified to carry out electrochemical oxidation and peeling reaction; after the oxidation and peeling, the graphene oxide aqueous solution is obtained by cleaning, and the graphene oxide is obtained after drying; the method and device have the advantages that no control chemicals such as concentrated sulfuric acid which is easy to be used for drug making and explosive making are used, and the container is not damaged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of graphene preparation, in particular to a preparation method and device of graphene oxide. BACKGROUND

[0002] Graphene oxide is generally obtained by strong acid oxidation of graphite. There are currently three main methods for preparing graphene oxide, which are as follows: Brodie method, Staudenmaier method and Hummers method. Among them, the preparation process of Hummers method has relatively good timeliness and is relatively safe during preparation, and is the most commonly used method at present. Currently, the main method for large-scale preparation of graphene oxide in factories is to oxidize graphite with concentrated sulfuric acid and potassium permanganate. Not only are the raw materials used dangerous, but the temperature also needs to be controlled during operation, and a large amount of concentrated sulfuric acid is consumed, resulting in a large amount of waste acid and great environmental pressure. The electrochemical oxidation method mainly uses electric current for sulfuric acid intercalation in concentrated sulfuric acid and electrochemical oxidation in sulfuric acid above 50%, which is a slow preparation process and also involves concentrated sulfuric acid, which is dangerous to operate.

[0003] Therefore, the current common preparation method of graphene oxide generally has the following disadvantages:

[0004] 1) The potassium permanganate and concentrated sulfuric acid used in the chemical method for preparing graphene oxide are controlled chemicals that are prone to be toxic and explosive, which not only causes serious environmental pollution, but also has the risk of high temperature and explosion during preparation, and additional cooling equipment is needed to control the oxidation process;

[0005] 2) In the conventional electrochemical method for preparing graphene oxide, the conventional electrochemical intercalation still uses concentrated sulfuric acid, and the intercalation process is relatively slow compared to chemical intercalation, and the raw material is usually a pre-prepared graphite sheet, which limits the industrialization and volume expansion;

[0006] 3) The metal chloride intercalation graphite mostly uses two-zone intercalation, and the graphite and metal chloride are placed in different temperature zones in a molten and sealed glass container. Each reaction requires breaking a glass container, and it is not necessarily possible to achieve first-order intercalation.

[0007] Therefore, there is a need in the art to provide a preparation method of graphene oxide that can overcome the above-mentioned disadvantages. SUMMARY

[0008] In view of the above-mentioned deficiencies of the prior art, the present application provides a preparation method of graphene oxide that does not use controlled chemicals prone to be toxic and explosive such as concentrated sulfuric acid, and does not damage the container.

[0009] To solve the above technical problems, the technical solution adopted by the present application is as follows: a preparation method of graphene oxide, the steps of which include:

[0010] (1) First, mix graphite and metal chloride uniformly, then put them into a high-pressure reaction kettle made of polytetrafluoroethylene, seal it tightly, and then react at a temperature of 240-280℃ for 8-48h; carry out intercalation reaction to form a first-order intercalation graphite intercalated with metal chloride;

[0011] (2) Put the first-order intercalation graphite prepared in step (1) into a reaction tank, and press a layer of screen on top of the first-order intercalation graphite to ensure that the intercalation graphite sheet does not easily fall off the electrode before being peeled off; connect the screen and the reaction tank to the positive electrode of a direct current power supply, put water into the reaction tank, and then take graphite electrode or inert metal (such as platinum gold, etc.) and insert it into the water, and its connection to the negative electrode of the direct current power supply; then, the positive and negative electrodes are powered on to carry out electrochemical oxidation peeling reaction;

[0012] (3) When the electrode of the first-order intercalation graphite is completely oxidized and peeled off, repeatedly wash to remove excess chloride ions and metal ions, and then obtain the graphene oxide aqueous solution, and dry to obtain graphene oxide.

[0013] Further, the metal chloride in step (1) of the present application is in excess of the graphite; it should be noted that when the weight ratio of graphite and metal chloride is 1:2, it is just not excessive, and when it is greater than 1:2, it is excessive.

[0014] Further, the weight ratio of graphite and metal chloride in step (1) of the present application is 1:3-5.

[0015] Further, the graphite in step (1) of the present application is flaky graphite with a particle size of 10-500 mesh.

[0016] Further, the metal chloride in step (1) of the present application is one of ferric chloride and copper chloride.

[0017] Further, before the first-order intercalation graphite in step (2) of the present application is placed in a metal or graphite reaction tank, the first-order intercalation graphite is subjected to high-pressure pressing treatment.

[0018] Further, the high-pressure pressing treatment in the present application is to press the first-order intercalation graphite into a sheet material under a pressure of 18-25MPa.

[0019] Further, the mesh size of the screen in step (2) of the present application satisfies 5-400 mesh; and the material of the reaction tank is metal or graphite material.

[0020] Further, the screen in step (2) of the present application fully covers the first-order intercalation graphite.

[0021] Further, the graphite electrode or inert metal (such as platinum gold, etc.) for connecting the negative pole of the direct current power source in step (2) is located above the screen and in contact with water.

[0022] Further, the screen covering the first-order intercalation graphite in step (2) is a screen made of the same material as the metal reaction tank.

[0023] Further, when the material of the reaction tank in step (2) is metal, the metal is a metal whose activity is not higher than that of trivalent iron ions, which is suitable for the application; specifically, the metal can be any one of gold and platinum gold.

[0024] Further, the screen covering the first-order intercalation graphite in step (2) is a screen made of the same material as the metal reaction tank.

[0025] The application also provides an electrochemical oxidation and stripping device used in the preparation process of graphene oxide, and the structure of the device comprises: a reaction tank (a metal or graphite reaction tank), the reaction tank is placed with first-order intercalation graphite, the first-order intercalation graphite is covered with a screen above, the reaction tank is placed with water, the upper surface of the water is higher than the upper surface of the screen; the screen and the reaction tank are used for connecting the positive pole of the power source; the reaction tank is further provided with a graphite electrode or inert metal (such as platinum gold, etc.), the graphite electrode or inert metal is used for connecting the negative pole of the power source, and the graphite electrode or inert metal is not in contact with the screen.

[0026] Further, the graphite electrode or inert metal in the application is located above the lateral extension surface of the screen and is centrally arranged in the reaction tank.

[0027] The application has the following advantages and beneficial effects:

[0028] 1. The present application first uses a first-order graphite formed by screen and metal chloride intercalation as a positive electrode to prepare graphene oxide, because the first-order intercalated graphite formed by metal chloride intercalation is structurally stable in water and can be placed in water, air, and an environment below 80°C for a long time without delamination, so it can adapt to a wider solution environment for electrochemical oxidation. In addition, more importantly, the first-order intercalated graphite intercalated with metal chloride as a positive electrode during the subsequent exfoliation reaction can continuously release electrolytes in water, so the exfoliation process only requires water and does not need to add additional electrolytes. Moreover, the excess metal chloride on the outer layer of the intercalated graphite does not need to be washed off and can be directly dissolved in water as an electrolyte. After oxidation, dissociation, and exfoliation, the interlayer metal chloride in the subsequent layers will also enter the water to continue to supplement the electrolyte, forming a conductive path. Therefore, the metal chloride in the interlayer can achieve a gradual release effect layer by layer as the exfoliation reaction proceeds, continuously releasing and supplementing into the water to form a conductive path. Each exfoliation of graphite releases a layer of metal chloride, because the metal intercalated graphite is stable in water, so each exfoliation releases a layer, maintaining the stability of the entire electrochemical oxidation process and facilitating the preparation of graphene oxide and improving the preparation efficiency.

[0029] 2. The present application places the first-order intercalated graphite through a screen cover in a container and uses the entire screen as an electrode, so that the intercalated graphite can be effectively fixed and is difficult to separate from the electrode before oxidation and exfoliation, ensuring more complete electrochemical oxidation. The exfoliated graphene oxide formed after exfoliation is flexible and can pass through the screen holes on the screen into the water and disperse, so the oxidation is more complete and effectively avoids incomplete oxidation of the unoxidized raw material due to the stripping of the gas generated by electrolysis of water. Without the screen, the unoxidized graphite to be exfoliated will enter the water, and the gas generated by electrolysis in the water will strip the graphite. Since the graphite is not completely oxidized, the oxidation of the obtained oxidized graphite after exfoliation will be incomplete. The screen of the present application effectively solves the above technical problems.

[0030] 3. The technical solution of the present application effectively combines chemical intercalation and electrochemical oxidation. The chemical intercalation used has lower energy consumption, higher efficiency, and higher yield than existing electrochemical intercalation. The electrochemical oxidation used has more complete oxidation and exfoliation of the layers, more complete oxidation of the single layer, larger layers, higher oxidation, and can form liquid crystal state of graphene oxide.

[0031] 4. The technical solution of the present application uses polytetrafluoroethylene as a reaction kettle for intercalation reaction. The reaction kettle has certain temperature resistance and pressure resistance and can be repeatedly used, thereby effectively reducing the intercalation cost.

[0032] 5. In the intercalation reaction process, the metal chloride must be controlled to be slightly excessive relative to the graphite, because the oxidation stripping needs the excess metal chloride to catalyze, so this slight excess can make the surface of the prepared first-order intercalated graphene have excess metal chloride, when it is used as a positive electrode in water, the metal chloride on its surface can be quickly dissolved in water to form a conductive electrolyte, ensuring the effective progress of electrochemical oxidation.

[0033] 6. Before using the first-order intercalated graphite as a positive electrode, it is also pressed by high pressure, which can obtain more compact first-order intercalated graphite. If it is not pressed, the subsequent electrochemical oxidation process is directly dispersed and stripped, resulting in long processing time and low processing efficiency.

[0034] 7. The electrochemical oxidation and stripping device used in the preparation method of graphene oxide comprises a screen and a first-order intercalated graphite as a positive electrode, and a graphite electrode or an inert metal as a negative electrode. The screen is made of a conductive material such as graphite or metal and is consistent with the material of the reaction tank body. The first-order intercalated graphite is covered below the screen, so that the stability of the position of the first-order intercalated graphite can be maintained during the oxidation and stripping process. The intercalated graphite is fixed and difficult to separate from the electrode before oxidation and stripping, ensuring more complete electrochemical oxidation. After stripping, the graphene oxide is flexible and can pass through a 10-mesh sieve and enter water for dispersion, so that the oxidation degree is better and the unoxidized raw materials are not peeled off by the gas generated by electrolysis of water, resulting in insufficient oxidation. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The electrochemical oxidation and stripping device used in the preparation method of graphene oxide.

[0036] As shown in the drawing: 1. Reaction tank body (in a metal or graphite reaction tank body), 2. First-order intercalated graphite, 3. Screen, 4. Graphite electrode or inert metal.

[0037] Figure 2 The Raman spectrum of GO.

[0038] Figure 3 The X-ray photoelectron spectrum of GO.

[0039] Figure 4 The XRD pattern of GO.

[0040] Figure 5 The scanning electron microscope image of GO. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are merely preferred embodiments, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this invention.

[0042] Furthermore, it should be noted that when a component is referred to as being "fixed to" another component, it can be directly on the other component or it may be fixed via another intermediate component. When a component is considered to be "connected to" another component, it can be directly connected to the other component or it may be fixed via another intermediate component. When a component is considered to be "set on" another component, it can be set directly on the other component or it may be fixed via another intermediate component. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0043] As attached Figure 1 The diagram shows the electrochemical oxidation exfoliation apparatus used in the graphene oxide preparation method of this application. The apparatus includes a reaction vessel (in a metal or graphite reaction vessel) 1, inside which is placed a first-order intercalated graphite 2. A sieve 3 covers the top of the first-order intercalated graphite 2 (the sieve can be composed of only laterally extended surfaces, or has both laterally extended and sidewall extended surfaces; it should fit as closely as possible to the inner wall of the reaction vessel to ensure that subsequent graphene oxide only escapes through the sieve openings into the aqueous solution; the sieve opening size is approximately 10 mesh). The reaction vessel is filled with water (water acts as a solvent to dissolve the metal chlorides on the intercalated graphite, causing them to form ions that enter the water and together constitute a conductive electrolyte). The upper surface of the water is higher than the upper surface of the screen 3. The screen 3 and the reaction vessel 1 are connected to the positive terminal of the power supply. The reaction vessel 1 is also equipped with a graphite electrode or an inert metal 4 (as a negative electrode). The graphite electrode or inert metal 4 is used to connect to the negative terminal of the power supply, and the graphite electrode or inert metal 4 does not contact the screen 3. The power supply is a DC power supply.

[0044] As an example, see attached Figure 1 As shown, the graphite electrode or inert metal 4 described in this application is located above the transverse extension surface of the sieve and is centrally located inside the reaction vessel 1.

[0045] The following are specific examples of the preparation of graphene oxide using the above-described apparatus:

[0046] Example 1

[0047] Mix 100g of 50-mesh flake graphite and 300g of anhydrous ferric chloride evenly. Place the mixture in a high-pressure reactor lined with polytetrafluoroethylene (PTFE), seal tightly, and place the reactor in a 280℃ high-temperature environment for 12 hours for high-temperature intercalation. After the reactor cools to room temperature, open the reactor, remove the mixture, and press it into sheet material under 20MPa pressure to obtain a first-order graphite intercalation layer with ferric chloride intercalation. Place the sheet material of the first-order graphite intercalation layer at the bottom of a graphite crucible, and cover it with a 10-mesh graphite sieve structure (the sieve should at least cover the cross-section of the inner cavity of the graphite crucible, i.e., the outer peripheral wall of the sieve should be in close contact with the inner wall of the crucible). Connect the sieve and graphite crucible to the positive terminal of a DC power supply. Connect a graphite rod to the negative terminal of the DC power supply, and add the graphite rod to... Position the graphite rod electrode at the center of the graphite crucible and secure it using a support structure to ensure stability, preventing contact between the rod and the crucible or sieve. Add water to the crucible, ensuring it covers 4 / 5 of the graphite rod electrode length. The pressed ferric chloride intercalated graphite sheets are completely submerged in the water, and excess ferric chloride intercalated into the graphite sheets gradually dissolves, forming chloride and ferric ions. Connect the power supply to 36V to initiate the oxidation reaction. As oxidation progresses, the intercalated graphite electrode begins its own oxidation process, increasing the amount of graphene oxide in the solution. Once the electrode is completely peeled off (complete peeling and oxidation takes approximately 60 minutes), disconnect the power supply and wash the graphene oxide with deionized water to obtain a clean graphene oxide solution. After drying, graphene oxide powder is obtained.

[0048] The products obtained in the examples were tested and characterized: Figure 2 For the Raman spectrum of GO, such as Figure 2 As shown, the D and G peaks of GO can be clearly observed at 1346 cm⁻¹ and 1588 cm⁻¹. The I peaks of GO were calculated. D / I G The value of 0.85 is within the typical range for GO, indicating that the method successfully prepared GO; Figure 3 The X-ray photoelectron spectrum of GO shows that the GO prepared by this method contains abundant oxygen-containing functional groups and has good oxidation degree. Figure 4The XRD pattern of GO is shown in the figure. It can be seen from the figure that GO has an obvious diffraction peak at 2θ = 11.6°, which corresponds to the (111) diffraction peak of GO. The interlayer spacing of GO can be calculated by using the Bragg equation 2dsinθ = λ (where d is the interplanar spacing, θ is the grazing angle, and λ = 0.15418 nm). The interlayer spacing of GO is 0.76 nm. Because GO contains a large number of oxygen-containing functional groups, the interlayer spacing is increased, which indicates that the intercalation, exfoliation and oxidation effects in the preparation of GO by this method are good. Figure 5 The scanning electron microscope image of GO is shown in the figure. The image shows the typical two-dimensional characteristics and flexible features of GO. The average size of GO in the figure is about 102 μm, which indicates the possibility and advantage of preparing large-size GO by this method.

[0049] Example 2

[0050] The difference from Example 1 is that 100 g of 100-mesh flake graphite and 300 g of anhydrous ferric chloride are used, and the corresponding screen mesh is 80 mesh.

[0051] Example 3

[0052] The difference from Example 1 is that 100 g of 300-mesh flake graphite and 300 g of anhydrous ferric chloride are used, and the corresponding screen mesh is 200 mesh.

[0053] Example 4

[0054] The difference from Example 1 is that 100 g of 50-mesh flake graphite and 400 g of anhydrous ferric chloride are used.

[0055] Example 5

[0056] The difference from Example 1 is that 100 g of 50-mesh flake graphite and 500 g of anhydrous ferric chloride are used.

[0057] Comparative Example 1

[0058] Example 1 is basically the same, except that the intercalated graphite is not made into an electrode (not made into an electrode means that high-pressure pressing is not performed), but is directly scattered at the bottom of the graphite crucible. Under the same reaction conditions, the oxidation time is longer than that of Example 1. The oxidation time of this example is 110 min.

[0059] The results show that because the graphite sheets scattered at the bottom of the crucible are not in close contact with the crucible and the graphite electrode is not compacted, the current is large, so the oxidation process is relatively slow compared with the intercalated graphite pressed into an electrode, but both can be completely oxidized.

[0060] Comparative Example 2

[0061] The same as example 1, except that silver crucible silver screen and silver electrode connected to the negative electrode were used, and the obtained graphene oxide surface had silver nanoparticles, indicating that although silver is an inert metal, it can still be oxidized in the presence of ferric chloride solution and under the condition of current oxidation. Such screen and crucible are not suitable for preparing graphene oxide materials.

[0062] Comparative example 3

[0063] The same as example 1, except that no screen was used, and the obtained graphene oxide was not completely oxidized and peeled off to obtain insufficiently oxidized graphite oxide.

[0064] Table 1 below shows the size and oxidation degree of the final graphene oxide obtained in the examples and comparative examples of the present application:

[0065] Table 1 shows the size and oxidation degree of the final graphene oxide obtained in the examples and comparative examples

[0066]

[0067]

[0068] As can be seen from the above examples, if there is no screen, the unoxidized graphite to be peeled off will enter the water, and the gas electrolyzed in the water will then peel off the graphite. However, since the graphite is not completely oxidized, the oxidation of the obtained graphite oxide is insufficient (see comparative example 3). After using the screen, the peeled graphite is flexible and basically separates from the screen holes, and basically does not separate from other positions. It enters the water to separate the peeled graphite from the unpeeled graphite, and to determine when the peeling is complete. When there is no graphite under the screen, the graphite is completely dispersed in the water, which means that the peeling is complete.

Claims

1. A method for preparing graphene oxide, characterized in that: The steps of this method include: (1) First, the graphite and metal chloride are mixed evenly and then placed in a polytetrafluoroethylene high-pressure reactor, sealed tightly, and then reacted at a temperature of 240-280℃ for 8-48h; to carry out the intercalation reaction to form first-order intercalated graphite with metal chloride intercalation. (2) Place the first-order intercalated graphite prepared in step (1) in the reaction vessel, and press a sieve on top of the first-order intercalated graphite to ensure that the first-order intercalated graphite sheet does not easily detach from the electrode before peeling; connect the sieve and the reaction vessel to the positive terminal of the DC power supply, put water in the reaction vessel, and insert another graphite electrode or inert metal into the water, without directly contacting the reaction vessel and the sieve, and connect it to the negative terminal of the DC power supply; then pass electricity through the positive and negative terminals to carry out the electrochemical oxidation peeling reaction; (3) After the first-order intercalated graphite electrode is completely oxidized and stripped, it is repeatedly washed to remove excess chloride ions and metal ions, thus obtaining an aqueous solution of graphene oxide, which is then dried to obtain graphene oxide. The weight ratio of graphite to metal chloride in step (1) is 1:3-5; before the first-order intercalated graphite in step (2) is placed in the reaction vessel, the first-order intercalated graphite is subjected to high-pressure pressing.

2. The method for preparing graphene oxide according to claim 1, characterized in that: The graphite mentioned in step (1) is flake graphite with a particle size of 10-500 mesh.

3. The method for preparing graphene oxide according to claim 1, characterized in that: The metal chloride mentioned in step (1) is either ferric chloride or copper chloride.

4. The method for preparing graphene oxide according to claim 3, characterized in that: The high-pressure pressing process involves pressing first-order intercalated graphite into sheet material under a pressure of 18-25 MPa.

5. The method for preparing graphene oxide according to claim 1, characterized in that: The sieve in step (2) has a mesh size of 5-400 mesh; the reaction vessel is made of metal or graphite.

6. The method for preparing graphene oxide according to claim 1, characterized in that: In step (2), the sieve is fully covered with the first-order intercalated graphite.

7. The method for preparing graphene oxide according to claim 1, characterized in that: The graphite electrode or inert metal used to connect to the negative terminal of the DC power supply in step (2) is located above the screen and in contact with water.

8. The method for preparing graphene oxide according to claim 7, characterized in that: When the first-order intercalated graphite in step (2) is placed in the reaction vessel, the corresponding covering screen is a screen of the same material as the metal reaction vessel; when the first-order intercalated graphite in step (2) is placed in the graphite reaction vessel, the corresponding covering screen is a screen of the same material as the graphite reaction vessel.

9. The method for preparing graphene oxide according to claim 8, characterized in that: When the material of the reaction vessel is metal, the metal is a metal whose elemental activity is not higher than that of ferric ions.

10. An electrochemical oxidation exfoliation apparatus used in the preparation method of graphene oxide according to any one of claims 1-9, characterized in that: The device comprises a reaction vessel containing first-order intercalated graphite, with a screen covering the top of the graphite. The reaction vessel is filled with water, the upper surface of which is higher than the upper surface of the screen. The screen and the reaction vessel are used to connect to the positive terminal of a power supply. A graphite electrode or inert metal is also disposed within the reaction vessel, used to connect to the negative terminal of the power supply, and the graphite electrode or inert metal does not contact the screen.

11. The electrochemical oxidation stripping device according to claim 10, characterized in that: The graphite electrode or inert metal is located above the transverse extension surface of the sieve and is centrally positioned within the reaction vessel.

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