A multi-effect treatment method of graphite intercalation compounds

Abstract

This invention discloses a multi-effect treatment method for graphite intercalation compounds, belonging to the field of graphene preparation technology. The method includes: washing, filtering, and lightly drying a wet-prepared graphite intercalation compound to obtain the graphite intercalation compound; adding the prepared graphite intercalation compound and ammonium carbamate in a certain proportion into a pulverizer to pulverize, mix, and disperse them evenly; introducing the prepared mixture into a reactor, introducing carbon dioxide into the reactor, and stirring the material to ensure a complete reaction, thereby obtaining ammonium bicarbonate-coated graphite intercalation compound powder. This invention pre-treats the washed graphite intercalation compound before the powdering and reduction reaction of graphene oxide, reducing the adverse effects of washing on the intercalation effect and improving the reduction capacity of the graphene oxide reduction process.

Description

Technical Field

[0001] This invention relates to the field of graphene preparation technology, and in particular to a multi-effect treatment method for graphite intercalation compounds. Background Technology

[0002] In existing technologies, the liquid-phase preparation of powdered graphene (such as reduced graphene oxide) commonly uses single-component or multi-component mixtures composed of concentrated sulfuric acid, hydrochloric acid, perchloric acid, concentrated nitric acid, and potassium permanganate. These chemical components are inserted into the interlayer of graphite flakes through soaking, oxidation, and electrolysis in the solution, forming graphite intercalation compounds. These graphite intercalation compounds require further high-temperature powdering and reduction reactions to obtain high-quality reduced graphene oxide products.

[0003] After graphite flake intercalation, the graphite intercalation compound is separated from the oxidant solution by centrifugation, pressure filtration, etc., yielding a wet graphite intercalation compound containing a certain amount of residual oxidant liquid. This residual oxidant liquid is usually washed and replaced with water because the high-temperature conditions in subsequent powdering and reduction processes can cause severe corrosion to the flow equipment, and the residual oxides can also undergo a carbon-consuming reaction with the graphite, reducing the product yield.

[0004] Washing away residual oxidant with water is an essential step in the preparation of graphene powder using the liquid phase method. However, the washing process can cause some of the intercalated oxides to be lost, reducing the intercalation effect. Furthermore, after washing and drying, some moisture will still remain between the intercalated materials, affecting the subsequent exfoliation effect of graphene. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a multi-effect treatment method for graphite intercalation compounds. Before the graphite intercalation compound is powdered and reduced by graphene oxide, the graphite intercalation compound is pretreated after being washed with water to reduce the adverse effects of water washing on the intercalation effect and improve the reduction ability of the graphene oxide reduction process.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] On one hand, the present invention provides a multi-effect treatment method for graphite intercalation compounds, comprising:

[0008] Step 1: The graphite intercalation material prepared by the wet method is washed with water, filtered and lightly dried to obtain the graphite intercalation compound;

[0009] Step 2: Add the graphite intercalation compound prepared in Step 1 and ammonium carbamate to a pulverizer in a certain proportion to pulverize, mix and disperse them evenly;

[0010] Step 3: The mixture prepared in Step 2 is introduced into the reactor, carbon dioxide is introduced into the reactor, and the mixture is stirred to allow it to react fully, thereby obtaining graphite intercalation compound powder coated with ammonium bicarbonate.

[0011] Furthermore, in step 1, the graphite intercalation compound prepared by wet method is specifically prepared by using one or more components selected from concentrated sulfuric acid, hydrochloric acid, perchloric acid, concentrated nitric acid, and potassium permanganate as intercalating agents, through soaking, oxidation, or electrolysis in a tank.

[0012] Preferably, in step 1, the water content of the final graphite intercalation compound is 10-20 wt%.

[0013] Preferably, in step 2, the amount of ammonium carbamate used is 20-40% of the mass of the graphite intercalation compound.

[0014] Preferably, in step 3, the molar ratio of carbon dioxide to ammonium carbamate is ≥1:1; and the reactor temperature is maintained at 5-20℃.

[0015] On the other hand, the present invention also provides a method for preparing graphene, wherein graphene is obtained by using graphite intercalation compound powder prepared by the above method as raw material and subjected to high-temperature expansion treatment.

[0016] Furthermore, the method for preparing the graphene specifically includes:

[0017] First, the graphite intercalation compound powder prepared by the above method is placed in a high-temperature furnace, vacuumed for a period of time, and then an inert gas is introduced to make the oxygen content in the system less than 0.1%.

[0018] Then, the above system is heated to 1000-1200℃ and reacted for a period of time. The powder is blown out using an inert gas (when the gas flow rate is above 6m / s, the dust can be blown out directly), and then cooled down to collect the graphene.

[0019] Preferably, the inert gas is argon or nitrogen. The heating is carried out at a heating rate of 50-60°C / min.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention uses a pulverizer to mix a graphite intercalation compound and ammonium carbamate, and the water in the graphite intercalation compound reacts with the ammonium carbamate in the following reaction: Formula I:

[0022] NH2COONH4+H2O===(NH4)2CO3 (I);

[0023] Then carbon dioxide is introduced into the screw conveyor reactor, and the mixed material comes into contact with the carbon dioxide, undergoing reaction II:

[0024] (NH4)2CO3+CO2+H2O===2NH4HCO3 (II);

[0025] The resulting ammonium bicarbonate replaces the water in the graphite intercalation compound, which is equivalent to further intercalating the graphite and solves the technical problem that water washing reduces the intercalation effect in the existing technology.

[0026] Meanwhile, during the subsequent powdering process, the ammonium bicarbonate-coated graphite intercalation compound powder first decomposes into ammonia, carbon dioxide, and water upon heating. The gas expansion causes graphene to peel off, and the generated ammonia decomposes into nitrogen and hydrogen at higher temperatures. Hydrogen, as an excellent reducing agent, can participate in the reduction reaction of graphene oxide, reduce graphene defects, and improve its conductivity. At the same time, the N2 and CO2 released during the decomposition process are ideal inert gases that can dilute the acidic gases generated during the powdering and reduction processes of the graphite intercalation compound, reducing the amount of these impurity gases adsorbed during powder cooling and packaging.

[0027] After being treated by this invention, the graphite intercalation compound becomes alkaline, which can effectively reduce corrosion of material conveying equipment and reaction equipment, and reduce the contamination of powder by corrosive substances. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the multi-effect treatment device for graphite intercalation compounds used in the embodiments of the present invention; in the embodiments of the present invention, "front end", "rear end" and "end" refer to the material conveying direction. Detailed Implementation

[0029] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments.

[0030] Unless otherwise specified, all materials and reagents used in this invention are commercially available.

[0031] This invention provides a multi-effect treatment method for graphite intercalation compounds, and specific embodiments are as follows.

[0032] Example 1

[0033] A multi-effect treatment method for graphite intercalation compounds includes:

[0034] Step 1: Dissolve 100g of expanded graphite (150 mesh) in 500mL of a mixed solution of 98% concentrated sulfuric acid, 98% concentrated nitric acid, and 60% perchloric acid, with a volume ratio of concentrated H2SO4 / HClO4 / concentrated HNO3 of 0.5:1:1. Stir well, seal the mixture, heat to 80℃, and react for 6 hours. Then wash with water several times and filter until the solution is neutral. Dry the obtained graphite intercalation compound at room temperature and measure the water content to be 15wt%.

[0035] Step 2: Add the graphite intercalation compound prepared in Step 1 and ammonium carbamate into a pulverizer to pulverize, mix and disperse them evenly. The amount of ammonium carbamate is 30 wt% of the amount of graphite intercalation compound.

[0036] Step 3: The mixture prepared in Step 2 is introduced into the reactor, the reactor temperature is maintained at 5-10℃, carbon dioxide is introduced into the reactor, the molar ratio of carbon dioxide to ammonium carbamate is 1:3, and the material is stirred to allow it to react fully to obtain graphite intercalation compound powder coated with ammonium bicarbonate.

[0037] The aforementioned multi-effect treatment method for graphite intercalation compounds can be achieved using conventional devices in the prior art.

[0038] For example, such as Figure 1 The multi-effect treatment device for graphite intercalation compounds shown includes a material tank for storing materials and a crusher 1 for crushing materials connected to the material tank. The bottom of the crusher 1 is provided with a discharge port 2, which is connected to a screw conveyor reactor 3. The end of the screw conveyor reactor 3 is provided with an air inlet 4 and a material collection tank 5. The outside of the screw conveyor reactor 3 may be covered with a cooling jacket 6.

[0039] This invention uses a pulverizer to uniformly mix materials, and then uses a screw conveyor reactor to transport the materials so that they come into contact with gas to react. At the same time, cooling water is injected into the cooling jacket to cool the system and prevent the graphite intercalation compound from expanding due to excessive temperature during the reaction, which would affect the subsequent powdering effect.

[0040] Furthermore, the material tanks include a first material tank 7 and a second material tank 8. The first material tank 7 is used to store ammonium carbamate, and the second material tank 8 is used to store graphite intercalation compounds. The bottoms of the first material tank 7 and the second material tank 8 are connected to the crusher 1. The cooling jacket 6 has an inlet 9 and an outlet 10 at both ends, respectively. Cooling water flows from the inlet 9 to the outlet 10, in the opposite direction to the material conveying direction of the screw conveyor reactor, facilitating heat dissipation. The inlet 9 is located at the tail end of the screw conveyor reactor, at the front end of the air inlet 4; the outlet 10 is located at the rear end of the outlet 2. In step 3, cooling water (5-10℃) can be introduced into the cooling jacket to prevent the graphite intercalation compounds from expanding due to excessive temperature. Preferably, the screw conveyor reactor 3 can be a screw conveyor.

[0041] The above-mentioned multi-effect treatment device for graphite intercalation compounds has a simple structure. After being treated by this scheme, the graphite intercalation compounds become alkaline, which can effectively reduce the corrosion of material conveying equipment and reaction equipment, and reduce the pollution of powder by corrosive substances.

[0042] Example 2

[0043] A multi-effect treatment method for graphite intercalation compounds, specifically including:

[0044] Step 1: Place 10g of graphite flakes (25 mesh) into a material box and put it into an electrolytic cell. Add electrolyte (60wt% perchloric acid) to the electrolytic cell until it is above the upper edge of the graphite flake material. Then connect the DC power supply and control the current density to 80mA / cm³. 2 The electrolysis time was 5 hours, then the electrolysis was stopped, the material box was removed and the electrolyzed material was collected to obtain the graphite intercalation compound. The obtained graphite intercalation compound was washed, filtered, and dried at room temperature, and the moisture content was measured to be 12 wt%.

[0045] Step 2: Add the graphite intercalation compound prepared in Step 1 and ammonium carbamate into a pulverizer to pulverize, mix and disperse them evenly. The amount of ammonium carbamate is 20 wt% of the amount of graphite intercalation compound.

[0046] Step 3: The mixture prepared in Step 2 is introduced into the reactor, the reactor temperature is maintained at 10-20℃, and excess carbon dioxide (molar ratio of carbon dioxide to ammonium carbamate is 1:2) is introduced into the reactor. The mixture is stirred to allow it to react fully and obtain graphite intercalation compound powder coated with ammonium bicarbonate.

[0047] The method in this embodiment can also be adopted. Figure 1 The multi-effect treatment apparatus for graphite intercalation compounds shown in the figure can, in step 3, introduce cooling water (5-10°C) into the cooling jacket.

[0048] Example 3

[0049] A multi-effect treatment method for graphite intercalation compounds includes:

[0050] Step 1: Same as Step 1 in Example 2;

[0051] Step 2: Add the graphite intercalation compound prepared in Step 1 and ammonium carbamate into a pulverizer to pulverize, mix and disperse them evenly. The amount of ammonium carbamate is 40 wt% of the amount of graphite intercalation compound.

[0052] Step 3: The mixture prepared in Step 2 is introduced into the reactor, the reactor temperature is maintained at 10-15℃, and excess carbon dioxide (molar ratio of carbon dioxide to ammonium carbamate is 1:3) is introduced into the reactor. The mixture is stirred to allow it to react fully, and graphite intercalation compound powder coated with ammonium bicarbonate is obtained.

[0053] The method in this embodiment can also be adopted. Figure 1 The multi-effect treatment apparatus for graphite intercalation compounds shown in the figure can, in step 3, introduce cooling water (5-10°C) into the cooling jacket.

[0054] Example 4

[0055] A multi-effect treatment method for graphite intercalation compounds includes:

[0056] Step 1: Same as Step 1 in Example 2;

[0057] Step 2: Add the graphite intercalation compound prepared in Step 1 and ammonium carbamate into a pulverizer to pulverize, mix and disperse them evenly. The amount of ammonium carbamate is 25 wt% of the amount of graphite intercalation compound.

[0058] Step 3: The mixture prepared in Step 2 is introduced into the reactor, the reactor temperature is maintained at 15-20℃, and excess carbon dioxide (molar ratio of carbon dioxide to ammonium carbamate is 1:2) is introduced into the reactor. The mixture is stirred to allow it to react fully and obtain graphite intercalation compound powder coated with ammonium bicarbonate.

[0059] The method in this embodiment can also be adopted. Figure 1 The multi-effect treatment apparatus for graphite intercalation compounds shown in the figure can, in step 3, introduce cooling water (5-10°C) into the cooling jacket.

[0060] To further illustrate the beneficial effects of the present invention, due to space limitations, only Example 4 is used as an example to construct a comparative case as follows.

[0061] Comparative Example 1

[0062] Steps 2-3 are omitted in this comparative example, and the remaining conditions are the same as in Example 4.

[0063] Comparative Example 2

[0064] Step 3 is omitted in this comparative example, and the remaining conditions are the same as in Example 4.

[0065] Comparative Example 3

[0066] Step 2 is omitted in this comparative example, and the remaining conditions are the same as in Example 4.

[0067] The present invention also provides a method for preparing graphene, and specific embodiments are as follows.

[0068] Example 5

[0069] A method for preparing graphene, specifically as follows:

[0070] The prepared graphite intercalation compound powder is placed in a high-temperature furnace (specifically a tubular furnace). First, a vacuum is applied for 5 minutes, followed by the introduction of argon gas for 30 minutes to prevent external air from entering and affecting the process, ensuring that the oxygen volume content in the system is less than 0.1%. The temperature is then increased to 1100℃ at a rate of 60℃ / min and held for one hour. Then, the argon gas flow rate is increased to 8m / s to blow out the prepared powder, simultaneously cooling the powder. Gas-solid separation can then be performed to collect the graphene.

[0071] The graphenes prepared from the ammonium bicarbonate-coated graphite intercalation compound powders in Examples 1-4 are numbered S-1, S-2, S-3, and S-4, respectively; the graphenes prepared from the graphite intercalation compounds in Comparative Examples 1-3 are numbered D-1, D-2, and D-3, respectively.

[0072] The performance of the obtained graphene powder was tested, and the results are shown in Table 1-2.

[0073] To further illustrate the beneficial effects of the graphene prepared by this invention, comparative examples are provided below.

[0074] Comparative Example 4

[0075] A method for preparing graphene, specifically as follows:

[0076] The graphite intercalation compound prepared in Comparative Example 1 was placed in a high-temperature furnace. A vacuum was first applied for 5 minutes, followed by the introduction of argon gas for 30 minutes to prevent external air from affecting the process and to ensure the oxygen content in the system was less than 0.1%. The temperature was increased to 1100℃ at a rate of 60℃ / min and held for one hour. During the heating process, argon gas was continuously introduced at a rate of 100 sccm, followed by hydrogen gas at a rate of 20 sccm to enhance the reduction effect. The resulting graphene powder (numbered D-4) was subjected to performance tests, and the results are shown in Table 2.

[0077] Table 1

[0078] Serial Number <![CDATA[Specific surface area (m 2 / g)]]> Electrical conductivity (s / m) C / O value S-1 328 <![CDATA[4.2×10 4 ]]> 23.3 S-2 336 <![CDATA[4.3×10 4 ]]> 24.2 S-3 340 <![CDATA[4.3×10 4 ]]> 24.6 S-4 346 <![CDATA[4.4×10 4 ]]> 25.3

[0079] As shown in Table 1, the graphite intercalation compound processed by the device and method of the present invention has a good reduction and repair effect on graphene oxide after powdering and high-temperature treatment.

[0080] This is because the graphite intercalation compound processed by the method of the present invention contains ammonium bicarbonate intercalated into the graphite layer, which will undergo the decomposition reaction of formula III when subjected to high temperatures above 60°C:

[0081] NH4HCO3===NH3+CO2+H2O (III);

[0082] It produces ammonia, carbon dioxide, and water vapor, which participate in the gasification and pulverization process of other intercalated materials, thus amplifying the pulverization effect of the intercalated materials.

[0083] Ammonium bicarbonate, which is mixed with the intercalated compound, undergoes a decomposition reaction to produce ammonia during the simultaneous powdering and reduction of the graphite intercalation compound at temperatures above 1000°C. The ammonia then undergoes Formula IV decomposition to release hydrogen gas.

[0084] 2NH3===N2+3H2(high temperature) (IV);

[0085] The released hydrogen gas can serve as an excellent reducing agent in the reduction reaction of graphene oxide.

[0086] Table 2

[0087] Serial Number <![CDATA[Specific surface area (m 2 / g)]]> Electrical conductivity (s / m) C / O value D-1 208 <![CDATA[3.2×10 4 ]]> 17.5 D-2 292 <![CDATA[3.5×10 4 ]]> 22.2 D-3 212 <![CDATA[3.3×10 4 ]]> 18.1 D-4 265 <![CDATA[4.0×10 4 ]]> 20.6

[0088] As shown in Table 2, the graphite intercalation compound of Comparative Example 1 was not subjected to the treatment of steps 2-3 of the present invention, while the graphite intercalation compound of Comparative Example 3 omitted the addition of ammonium carbamate. After subsequent graphene preparation, the obtained graphene had a small specific surface area and did not undergo the subsequent hydrogen reduction reaction. Its C / O value and conductivity were both small, and the prepared graphene had significant defects.

[0089] In Comparative Example 2, although ammonium carbamate was added, which can react with the moisture between the intercalation compound layers and improve its exfoliation effect to a certain extent, resulting in a slight increase in the specific surface area of ​​the prepared graphene, the increase was limited due to the absence of subsequent reaction with carbon dioxide. At the same time, the improvement in its C / O value and electrical conductivity was not significant.

[0090] In Comparative Example 4, using a method commonly used in the prior art, graphite intercalation compound was first prepared, then exfoliated at high temperature, and then reduced by hydrogen gas. Although this improved its C / O value and electrical conductivity to some extent, the specific surface area of ​​graphene was small, resulting in poor exfoliation effect.

[0091] In summary, this invention first reacts ammonium carbamate with water in the graphite intercalation compound, and then reacts with carbon dioxide, which is equivalent to further intercalation of graphite. The high-temperature reaction process can improve the exfoliation effect of graphene, and at the same time reduce the graphene to a certain extent, thereby reducing defects in the prepared graphene.

[0092] The above description is a preferred embodiment of the present invention. For those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A multi-effect treatment method of graphite intercalation compounds, characterized by, The application relates to a preparation method of a graphite intercalation compound material powder. Step 1: water washing, filtering and slightly drying a graphite intercalation compound prepared by a wet method to obtain a graphite intercalation compound; Step 2: adding the graphite intercalation compound prepared in step 1 and ammonium carbamate into a pulverizer according to a certain proportion to make the graphite intercalation compound, the ammonium carbamate and other materials be pulverized, mixed and dispersed uniformly; Step 3: introducing the mixed material prepared in step 2 into a reactor, introducing carbon dioxide into the reactor, and making the material be fully reacted by stirring to obtain an ammonium bicarbonate-coated graphite intercalation compound material powder.

2. The multi-effect treatment method of graphite intercalation compounds according to claim 1, characterized by, In step 1, the graphite intercalation compound prepared by the wet method is prepared by soaking, oxidizing or in-tank electrolysis by using one or more components of concentrated sulfuric acid, hydrochloric acid, perchloric acid, concentrated nitric acid and potassium permanganate as an intercalation agent.

3. The multi-effect treatment method of graphite intercalation compounds according to claim 1, characterized by, In step 1, the water content of the graphite intercalation compound is 10-20 wt%.

4. The multi-effect treatment method of graphite intercalation compounds according to claim 1, characterized by, In step 2, the amount of ammonium carbamate is 20-40% of the mass of the graphite intercalation compound.

5. The multi-effect treatment method of graphite intercalation compounds according to claim 1, characterized by, In step 3, the molar ratio of carbon dioxide to ammonium carbamate is greater than or equal to 1:1, and the temperature of the reactor is 5-20 DEG C.

6. A method of producing graphene, characterized by, The graphite intercalation compound material powder prepared by the method of any one of claims 1-5 is used as raw material to obtain graphene by high-temperature expansion treatment.

7. The method of claim 6, wherein the graphene is prepared by a method comprising the steps of: The preparation method of the graphene comprises the following steps: ​ Firstly, the graphite intercalation compound material powder prepared by the method of any one of claims 1-5 is put into a high-temperature furnace, vacuum is drawn for a period of time, inert gas is introduced to make the oxygen content in the system less than 0.1%; Then, the system is heated to 1000-1200 DEG C, reacts for a period of time, the powder is blown out by using inert gas, and then the temperature is lowered to collect the graphene.

8. The method of claim 7, wherein the graphene is prepared by a method comprising: The inert gas is argon or nitrogen.

9. The method of claim 7, wherein the graphene is prepared by a method comprising the steps of: The heating is carried out at a heating rate of 50-60 DEG C / min. ​

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