A method for synthesizing multilayer graphene in one step using frozen diatoms

Abstract

The present invention provides a method for one-step synthesis of multi-layer graphene using frozen diatoms. After uniformly mixing the pretreated magnesium powder with the frozen diatoms, the mixture is placed in a tube furnace. To ensure that there is no oxygen in the tube furnace, vacuum pumping is carried out for 30 to 60 minutes before injecting a CO2 (99.99%) atmosphere. Then, the tube furnace is heated to the required reaction temperature through a temperature program, and kept at this temperature for 120 minutes. After the reaction is completed, the tube furnace is cooled to room temperature. During the whole reaction process, a constant CO2 flow rate is provided under atmospheric pressure. After the reaction is completed, the oxidation products and the remaining unreacted metal Mg are removed to obtain multi-layer graphene. The present invention first uses biomass diatoms as raw materials to synthesize a new type of multi-layer graphene material in one step, which can effectively solve the problems of complex preparation process, low quality, and relatively high cost of multi-layer graphene materials.

Description

Technical Field

[0001] The invention relates to the field of graphene preparation, and in particular to a method for synthesizing multilayer graphene in one step by utilizing frozen diatoms. Background Art

[0002] Graphene is a new material with a single-layer two-dimensional honeycomb lattice structure of carbon atoms tightly stacked by sp2 hybridization. Graphene has excellent optical, electrical and mechanical properties, and has important application prospects in materials science, micro-nano processing, energy, biomedicine and drug delivery. It is considered to be a revolutionary material in the future. Andre Geim and Konstantin Novoselov, physicists at the University of Manchester, successfully separated graphene from graphite by micromechanical exfoliation, and thus jointly won the 2010 Nobel Prize in Physics. Common methods for producing graphene powders are mechanical exfoliation, redox method, SiC epitaxial growth method, Hemer method, and chemical vapor deposition (CVD).

[0003] At present, there are mainly the following methods for producing graphene:

[0004] 1. Mechanical stripping method

[0005] Mechanical exfoliation is a method of obtaining graphene thin layers by using friction and relative motion between an object and graphene. This method is simple to operate, and the graphene obtained usually maintains a complete crystal structure. In 2004, two British scientists used transparent tape to peel off natural graphite layer by layer to obtain graphene, which was also classified as mechanical exfoliation. This method was once considered to have low production efficiency and could not be mass-produced industrially. This method can prepare micron-sized graphene, but its controllability is low, and it is difficult to achieve large-scale synthesis.

[0006] 2. Redox method

[0007] The redox method is to oxidize natural graphite by using chemical reagents such as sulfuric acid and nitric acid and oxidants such as potassium permanganate and hydrogen peroxide to increase the spacing between graphite layers and insert oxides between graphite layers to obtain graphite oxide (Graphite Oxide). The reactants are then washed with water, and the washed solids are dried at low temperature to obtain graphite oxide powder. The graphite oxide powder is peeled off by physical peeling, high-temperature expansion and other methods to obtain graphene oxide. Finally, the graphene oxide is reduced by chemical methods to obtain graphene (RGO). This method is simple to operate and has high yield, but the product quality is low. The redox method uses strong acids such as sulfuric acid and nitric acid, which is very dangerous, and a large amount of water must be used for cleaning, which brings great environmental pollution.

[0008] Graphene prepared by the redox method contains abundant oxygen-containing functional groups and is easy to modify. However, it is difficult to control the oxygen content of the reduced graphene when reducing graphene oxide. At the same time, graphene oxide will continue to reduce under the influence of external factors such as sunlight and high temperature in the carriage during transportation. Therefore, the quality of graphene produced by the redox method is often inconsistent from batch to batch, and it is difficult to control the quality.

[0009] 3. Epiphyseal method

[0010] The epitaxial method uses the atomic structure of the growth matrix to "seed" graphene. First, carbon atoms are allowed to infiltrate ruthenium at 1150°C, and then cooled. After cooling to 850°C, a large number of carbon atoms previously absorbed will float to the surface of ruthenium, and finally a single layer of carbon atoms in the shape of a lens will grow into a complete layer of graphene. After the first layer is covered, the second layer begins to grow. The bottom layer of graphene will have a strong interaction with ruthenium, and after the second layer, it will almost completely separate from ruthenium, leaving only weak electrical coupling. However, the graphene flakes produced by this method often have uneven thickness, and the adhesion between graphene and the matrix will affect the properties of the carbon layer.

[0011] 4. Silicon carbide epitaxy

[0012] The SiC epitaxy method is to sublimate silicon atoms from the material in an ultra-high vacuum and high temperature environment, and the remaining C atoms are reconstructed in a self-assembled form to obtain graphene based on the SiC substrate. This method can obtain high-quality graphene, but it has high requirements for equipment.

[0013] 5. Hemer Method

[0014] Graphite oxide is prepared by the Hummer method; graphite oxide is ultrasonically dispersed in water to form a graphene oxide solution with a uniform dispersion and a mass concentration of 0.25g / L to 1g / L, and then ammonia water with a mass concentration of 28% is added to the graphene oxide solution; a reducing agent is dissolved in water to form an aqueous solution with a mass concentration of 0.25g / L to 2g / L; the prepared graphene oxide solution and the reducing agent aqueous solution are mixed evenly, and the obtained mixed solution is placed in an oil bath and stirred. After the reaction is completed, the mixture is filtered, washed, and dried to obtain graphene. However, the graphene prepared by this method has very poor performance to a certain point.

[0015] 6. Chemical Vapor Deposition

[0016] Chemical vapor deposition (CVD) is a method of producing graphene films by vapor deposition using carbon-containing organic gases as raw materials. This is the most effective method for producing graphene films. The graphene produced by this method has the characteristics of large area and high quality, but the cost is relatively high at this stage and the process conditions need to be further improved. Since the thickness of graphene films is very thin, large-area graphene films cannot be used alone and must be attached to macro devices to be useful, such as touch screens, heating devices, etc.

[0017] It can be seen that the current methods for producing multilayer graphene face the problems of high technical difficulty, high equipment requirements, difficult quality control, and environmental pollution during the production process.

[0018] In order to solve the above problems, the present invention is proposed. Summary of the invention

[0019] The present invention provides a method for synthesizing multilayer graphene in one step by using frozen diatoms, comprising the following steps: mixing pretreated magnesium powder and frozen diatoms uniformly and placing the mixture in a tube furnace; injecting CO 2 The (99.99%) atmosphere was evacuated for 30 to 60 minutes before the reaction. The tube furnace was then heated to the desired reaction temperature through a temperature program and kept warm for 120 to 240 minutes. After the reaction was completed, the tube furnace was cooled to room temperature. During the entire reaction process, a constant amount of CO was provided at normal pressure. 2 After the reaction is completed, the product is collected, acid-washed, and dried to obtain multi-layer graphene.

[0020] Preferably, the pretreatment is to first screen and wash the Mg powder, remove oxide scale with HCI, then rinse with deionized water and ethanol, and dry in a nitrogen stream at room temperature.

[0021] Preferably, the screening step is to screen the Mg powder using a sieve with a mesh size of 80-100 meshes.

[0022] Preferably, the cleaning step is to soak the Mg powder in an ethanol solution in a beaker, and place the beaker in an ultrasonic cleaning machine with a working frequency of 40 kHz and a power of 100 W for cleaning for 5 minutes to remove impurities on the surface of the Mg powder.

[0023] Preferably, the HCl concentration is 1.0-2.0M.

[0024] Preferably, the mass ratio of the magnesium powder to the frozen diatom is 1:5 to 1:10.

[0025] Preferably, the heating rate in the tube furnace is 5-10°C min -1 .

[0026] Preferably, the reaction temperature in the tube furnace is 500-700°C.

[0027] Preferably, the CO 2 The flow rate is 20~120mL / min.

[0028] Preferably, the acid washing step is to transfer the obtained product into a 0.5-2M HCI solution, stir at room temperature for 10 hours, separate it with a 4500rpm centrifuge for 3 minutes, and then deposit it in deionized water, assist with an ultrasonic field, and wash it with ethanol.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention uses biomass diatoms as raw materials to synthesize a new type of multilayer graphene material for the first time. The method described in the present invention is simple and can effectively solve the problems of complex preparation process, low quality and relatively high cost of multilayer graphene materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the SEM image of the sample without acid washing after the reaction;

[0032] Figure 2 This is the SEM magnified image of the sample without acid washing after the reaction;

[0033] Figure 3 This is a partially enlarged SEM image of the sample that has not been acid-washed after the reaction (the flocculent layers in the image are multilayer graphene). DETAILED DESCRIPTION

[0034] The present invention is described below in conjunction with specific examples, but the embodiments of the present invention are not limited thereto. Experimental methods without specific conditions in the examples are usually carried out under conventional conditions and conditions described in the manual, or under conditions recommended by the manufacturer. The general equipment, materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified.

[0035] Example 1

[0036] Mg powder was first sieved with an 80-mesh screen, and then 3 g of Mg powder was soaked in an ethanol solution in a beaker, and the beaker was placed in an ultrasonic cleaner with an operating frequency of 40 kHz and a power of 100 W for 5 min to remove impurities on the surface of the Mg powder. Subsequently, Mg was transferred to a beaker containing 100 mL of 1.0 M HCl for 2 minutes at room temperature to remove oxide scale, and then rinsed with deionized water and ethanol and dried in a nitrogen stream at room temperature.

[0037] Take 100 mg of magnesium powder after the above pretreatment and 500 mg of frozen triangular brown diatom, mix them evenly and place them in a tube furnace. In order to ensure that there is no oxygen in the furnace, inject CO 2 The atmosphere was evacuated for 30 minutes before the furnace was heated to 99.99%. Then, CO was injected into the furnace at a constant rate of 120 mL / min. 2 , ensuring sufficient CO at room temperature and pressure 2 Fill the furnace. Note that the injected CO 2 It cannot react with Mg and organic matter in biomass at room temperature, so graphene will not be produced under this condition. At the same time, the tube furnace is heated to the required reaction temperature of 500°C through the temperature program. First, the tube furnace is heated from room temperature to the required reaction temperature, and the heating rate is 5°C min -1 , keep warm for 120 minutes, the reaction is completed, and the tube furnace is cooled to room temperature. During the entire reaction process, a constant CO 2 After the reaction, the product was collected to obtain porous magnesium oxide loaded with multilayer graphene. The electron microscope image is shown in Figure 1 , Figure 2 , Figure 3 As shown, Figure 3 The floc-like layers on top are multilayer graphene.

[0038] Acid washing and collection of graphene: First, the above product was transferred to HCI solution (concentration range of 0.5-2.0M), stirred at room temperature for 10 hours, then separated by a 4500rpm centrifuge for 3 minutes, then deposited in deionized water, assisted by an ultrasonic field, and washed with ethanol. Finally, the prepared product was placed in a vacuum drying oven and dried at 80°C for 10 hours to prepare multilayer graphene.

Claims

1. A method for synthesizing multilayer graphene in one step using frozen diatoms, It is characterized in that The following steps are involved: The pretreated magnesium powder was mixed evenly with the frozen diatoms and placed in a tube furnace. 2 The atmosphere was evacuated for 30 to 60 minutes before the reaction. The tube furnace was then heated to the desired reaction temperature through a temperature program and kept warm for 120 to 240 minutes. After the reaction was completed, the tube furnace was cooled to room temperature. During the entire reaction process, a constant CO was provided at normal pressure. 2 After the reaction is completed, the product is collected, acid-washed, and dried to obtain multi-layer graphene; The mass ratio of the magnesium powder to the frozen diatom is 1:5-1:10; The reaction temperature in the tube furnace is 500-700°C; The CO 2 The flow rate is 20 ~ 120 mL / min.

2. The method according to claim 1, It is characterized in that The pretreatment is to first screen and clean the Mg powder, remove the oxide scale with HCI, then rinse with deionized water and ethanol, and dry in a nitrogen stream at room temperature.

3. The method according to claim 2, It is characterized in that The sieving step is to sieve the Mg powder using a sieve with a mesh size of 80-100 meshes.

4. The method according to claim 2, It is characterized in that The cleaning step is to soak the Mg powder in an ethanol solution in a beaker, and place the beaker in an ultrasonic cleaning machine with a working frequency of 40 kHz and a power of 100 W for 5 minutes to remove impurities on the surface of the Mg powder.

5. The method according to claim 2, It is characterized in that The HCl concentration is 1.0~2.0 M.

6. The method according to claim 1, It is characterized in that The heating rate in the tube furnace is 5-10°C min -1 .

7. The method according to claim 1, It is characterized in that The acid washing step is to transfer the obtained product into a 0.5-2M HCl solution, stir it at room temperature for 10 h, separate it with a 4500 rpm centrifuge for 3 min, and then deposit it in deionized water, assist with an ultrasonic field, and wash it with ethanol.

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