CN110577210A - preparation method of powder of graphene and graphene derivative - Google Patents
preparation method of powder of graphene and graphene derivative Download PDFInfo
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- CN110577210A CN110577210A CN201810581205.1A CN201810581205A CN110577210A CN 110577210 A CN110577210 A CN 110577210A CN 201810581205 A CN201810581205 A CN 201810581205A CN 110577210 A CN110577210 A CN 110577210A
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Abstract
the invention provides a preparation method of graphene and graphene derivative powder, which comprises the following steps: s1) adding the graphene aqueous solution or the graphene derivative aqueous solution into liquid nitrogen to obtain solidified graphene or a solidified graphene derivative; s2) carrying out vacuum freeze drying on the solidified graphene or the solidified graphene derivative to obtain graphene powder or graphene derivative powder. Compared with the prior art, the method has the advantages that the graphene aqueous solution or the graphene derivative is treated by liquid nitrogen and then is dried in vacuum, so that the phenomena of irreversible superposition and agglomeration of graphene and graphene derivative sheets are effectively avoided, and the obtained graphene and graphene derivative powder is easy to disperse.
Description
Technical Field
The invention belongs to the technical field of graphene, and particularly relates to a preparation method of powder of graphene and derivatives thereof.
Background
Gein prepared and observed single-layer graphene for the first time in 2004, thereby raising the hot trend of research on graphene materials. Graphene is the thinnest and toughest material discovered by people at present, and has high electric conductivity and heat conductivity, so that the graphene plays a great role in multiple fields such as electrochemistry, biomedicine and the like.
Since the discovery of graphene, various methods of preparing graphene have been developed. The commonly used preparation methods at present comprise a micro-mechanical stripping method, an epitaxial growth method, a chemical vapor deposition CVD method, a graphite oxide reduction method and the like.
The micromechanical peeling method is to press the highly oriented pyrolytic graphite sheet to other surfaces by using a transparent adhesive tape to peel off for multiple times, and finally obtain single-layer or multi-layer graphene. The method is simple to operate, high in sample preparation quality and is the main method for preparing single-layer high-quality graphene at present. But the controllability is poor, the prepared graphene has small size and great uncertainty, and meanwhile, the efficiency is low, the cost is high, and the method is not suitable for large-scale production.
The CVD method is considered to be the most promising method for preparing high-quality large-area graphene, and is the most potential method for industrially producing graphene films. The specific process comprises the following steps: introducing hydrocarbon such as methane and ethanol into the surface of Cu and Ni of a metal substrate heated at high temperature, reacting for a certain time, cooling, and forming a plurality of layers or single-layer graphene on the surface of the substrate in the cooling process, wherein the process comprises two parts of dissolution and diffusion growth of carbon atoms on the substrate. The method is similar to a metal catalytic epitaxial growth method, and has the advantages that the method can be carried out at lower temperature, so that the energy consumption in the preparation process can be reduced, and the graphene and the substrate can be easily separated by a chemical metal corrosion method, thereby being beneficial to the subsequent processing of the graphene.
The graphite oxide reduction method is also considered to be one of the best methods for preparing graphene at present. The method is simple to operate and low in preparation cost, can be used for preparing the graphene on a large scale, and becomes an effective way for preparing the graphene. In addition, the method has the advantage that the functionalized graphene-graphene oxide with wide application prospect can be produced firstly. The specific operation process comprises the steps of oxidizing graphite into graphite oxide by using strong oxidants such as concentrated sulfuric acid, concentrated nitric acid and potassium permanganate, inserting oxygen-containing functional groups between graphite layers in the oxidation process so as to increase the distance between the graphite layers, carrying out ultrasonic treatment for a period of time to form single-layer or multi-layer graphene oxide, and reducing the graphene oxide by using strong reducing agents such as hydrazine hydrate and sodium borohydride to obtain the graphene dispersion liquid.
At present, graphene powder is prepared by using a graphene dispersion liquid, and conventional preparation methods comprise filtration, rotary evaporation and the like, but the methods easily cause irreversible superposition and agglomeration of graphene sheets and are not easy to disperse.
Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide a method for preparing powder of graphene and derivatives thereof, wherein the powder of graphene and derivatives thereof prepared by the method is easy to disperse.
The invention provides a preparation method of graphene and graphene derivative powder, which comprises the following steps:
S1) adding the graphene aqueous solution or the graphene derivative aqueous solution into liquid nitrogen to obtain solidified graphene or a solidified graphene derivative;
S2) carrying out vacuum freeze drying on the solidified graphene or the solidified graphene derivative to obtain graphene powder or graphene derivative powder.
Preferably, the graphene aqueous solution or graphene derivative aqueous solution is subjected to ultrasound, and then added to liquid nitrogen.
Preferably, the frequency of the ultrasonic wave is 10-100 KHZ; the time of the ultrasonic treatment is 1-5 h.
preferably, the mass fraction of graphene in the graphene aqueous solution is 0.1-0.5%; the mass fraction of the graphene derivative in the graphene derivative aqueous solution is 0.1-0.3%.
Preferably, the volume ratio of the graphene aqueous solution or the graphene derivative aqueous solution to the liquid nitrogen is 1: (2-10).
Preferably, the step S1) is specifically:
And adding the graphene aqueous solution or the graphene derivative aqueous solution into liquid nitrogen in a stirring state to obtain the solidified graphene or the solidified graphene derivative.
Preferably, the stirring speed is 600-1000 rpm.
Preferably, the pre-cooling temperature of the vacuum freeze drying is less than-40 ℃.
preferably, the temperature in the vacuum freeze drying process is-40 ℃ to 2 ℃.
Preferably, the vacuum degree of the vacuum drying is 0.1-0.5 Pa.
The invention provides a preparation method of graphene and graphene derivative powder, which comprises the following steps: s1) adding the graphene aqueous solution or the graphene derivative aqueous solution into liquid nitrogen to obtain solidified graphene or a solidified graphene derivative; s2) carrying out vacuum freeze drying on the solidified graphene or the solidified graphene derivative to obtain graphene powder or graphene derivative powder. Compared with the prior art, the method has the advantages that the graphene aqueous solution or the graphene derivative is treated by liquid nitrogen and then is dried in vacuum, so that the phenomena of irreversible superposition and agglomeration of graphene and graphene derivative sheets are effectively avoided, and the obtained graphene and graphene derivative powder is easy to disperse.
Drawings
Fig. 1 is a photograph showing the appearance of the graphene powder obtained in example 1 of the present invention;
Fig. 2 is a scanning electron micrograph of the graphene powder obtained in example 1 of the present invention;
Fig. 3 is an X-ray diffraction pattern of the graphene powder obtained in example 1 of the present invention;
Fig. 4 is an atomic force micrograph of the graphene powder obtained in example 1 of the present invention;
Fig. 5 is an appearance photograph of the aqueous solution of graphene oxide obtained in example 3 of the present invention;
Fig. 6 is an appearance photograph of the graphene oxide powder obtained in example 3 of the present invention;
Fig. 7 is a scanning electron micrograph of the graphene oxide powder obtained in example 3 of the present invention;
fig. 8 is a scanning electron micrograph of the graphene oxide powder obtained in example 3 of the present invention;
Fig. 9 is an X-ray diffraction pattern of the graphene oxide powder obtained in example 3 of the present invention;
Fig. 10 is an atomic force micrograph of the graphene oxide powder obtained in example 3 of the present invention;
Fig. 11 is a photograph showing the appearance of the graphene oxide powder obtained in comparative example 1 of the present invention;
Fig. 12 is a scanning electron micrograph of the graphene oxide powder obtained in comparative example 1 of the present invention;
Fig. 13 is a photograph showing that the graphene oxide powder obtained in comparative example 1 of the present invention was dissolved in water and ethanol;
fig. 14 is a photograph showing that the graphene oxide powder obtained in example 3 of the present invention was dissolved in water and ethanol;
fig. 15 is a photograph showing the appearance of the graphene oxide powder obtained in comparative example 2 of the present invention;
Fig. 16 is a photograph showing the appearance of the graphene powder obtained in comparative example 3 of the present invention;
Fig. 17 is a scanning electron micrograph of the graphene powder obtained in comparative example 3 of the present invention;
fig. 18 is a photograph showing the appearance of the graphene powder obtained in comparative example 4 of the present invention.
Detailed Description
the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a preparation method of graphene powder, which comprises the following steps: s1) adding the graphene aqueous solution into liquid nitrogen to obtain solidified graphene; s2) carrying out vacuum drying on the solidified graphene to obtain graphene powder.
In the present invention, the source of all raw materials is not particularly limited, and the raw materials may be commercially available or self-made, and in the present invention, the graphene aqueous solution is preferably prepared according to the following method: mixing concentrated sulfuric acid, graphite and fuming nitric acid for reaction, then cooling, adding potassium permanganate, adding water for quenching reaction after mixing reaction, and adding hydrogen peroxide to obtain a graphene oxide aqueous solution; and (2) carrying out ultrasonic treatment on the graphene oxide aqueous solution, then adjusting the pH value of the graphene oxide aqueous solution to be alkaline, adding a reducing agent and an alcohol polymer, and heating to react to obtain the graphene aqueous solution.
Wherein, the graphite is preferably natural flake graphite; the particle size of the natural crystalline flake graphite is preferably 5-20 μm, more preferably 5-15 μm, still more preferably 8-12 μm, and most preferably 10 μm; the mass ratio of the graphite to the concentrated sulfuric acid is preferably 1: (60 to 80), more preferably 1: (65-75); in some embodiments provided by the present invention, the mass ratio of the graphite to the concentrated sulfuric acid is preferably 1: 73.44, respectively; in other embodiments provided by the present invention, the mass ratio of the graphite to the concentrated sulfuric acid is preferably 1: 68.85, respectively; the mass ratio of the graphite to the fuming nitric acid is preferably 1: (0.9 to 1.8), more preferably 1: (0.9 to 1.6), and preferably 1: (0.9 to 1.4), most preferably 1: (0.9 to 1.3); in some embodiments provided herein, the mass ratio of graphite to fuming nitric acid is preferably 1: 0.9475, respectively; the mass ratio of the fuming nitric acid to the concentrated sulfuric acid is preferably 1: (70-120), more preferably 1: (70-110), and more preferably 1: (70-90), and more preferably 1: (70-80); in some embodiments provided herein, the mass ratio of fuming nitric acid to concentrated sulfuric acid is preferably 1: 77.5; in other embodiments provided by the present invention, the mass ratio of fuming nitric acid to concentrated sulfuric acid is preferably 1: 72.6.
In the invention, preferably, concentrated sulfuric acid and graphite are mixed and stirred firstly, and then fuming nitric acid is added; the mixing and stirring time is preferably 0.5-1.5 h, more preferably 0.8-1.4 h, still more preferably 0.9-1.3 h, and most preferably 1-1.2 h; in some embodiments provided by the present invention, it is preferred to add fuming nitric acid after mixing and stirring for 1 hour. Fuming nitric acid is used as an acid mixing agent and an intercalation agent to improve the reaction effect.
adding fuming nitric acid for mixing reaction; the mixing reaction time is preferably 10-20 h, more preferably 12-17 h, still more preferably 12-16 h, and most preferably 13-15 h; in some embodiments provided herein, a mixing reaction of 14h is preferred.
After mixing and reacting, cooling, preferably cooling to the temperature of the reaction liquid below 10 ℃, and then adding potassium permanganate. The mass ratio of the graphite to the potassium permanganate is preferably 1: (2.8-4), more preferably 1: (3-4), and more preferably 1: (3.5-4); in some embodiments provided herein, the mass ratio of graphite to potassium permanganate is preferably 1: 4.
After adding potassium permanganate, mixing reaction is preferably carried out at room temperature, and mixing reaction is more preferably carried out at 30 ℃; the mixing reaction time is preferably 120-160 h, more preferably 130-150 h, still more preferably 140-150 h, and most preferably 142-146 h; in some embodiments provided herein, the mixing reaction time is preferably 144 h.
After the mixing reaction, water is added to quench the reaction, preferably the temperature of the reaction solution is less than 60 ℃, water is added to quench the reaction, and then the temperature of the reaction solution is controlled to be less than 60 ℃ by a constant pressure dropping funnel to quench the reaction. The mass ratio of graphite to water is preferably 1: (30-60), more preferably 1: (33-60), and more preferably 1: (37-60); in some embodiments provided herein, the mass ratio of graphite to water is preferably 1: 60, adding a solvent to the mixture; in other embodiments provided herein, the mass ratio of graphite to water is preferably 1: 37.5.
Adding water to quench the reaction, preferably heating and then cooling, and then adding hydrogen peroxide; the temperature of the temperature rise is preferably 80-95 ℃, more preferably 85-95 ℃, further preferably 87-92 ℃ and most preferably 90 ℃; after the temperature is increased, the temperature is preferably kept for 2-5 h, more preferably 2-4 h, still more preferably 2.5-3 h, and most preferably 2.5 h; the temperature for reducing the temperature is preferably 50-70 ℃, more preferably 55-65 ℃, and further preferably below 60 ℃; the mass ratio of the added hydrogen peroxide to the graphite is preferably (3-6): 1, more preferably (4-5): 1; the concentration of the hydrogen peroxide is preferably 25 to 35 percent, more preferably 30 to 35 percent, still more preferably 32 to 35 percent, and most preferably 32 percent. The excess oxidant can be reduced by adding hydrogen peroxide.
After adding hydrogen peroxide, preferably cooling to room temperature, finally filtering and cleaning the reaction solution, and after detecting that the sulfate radical content is qualified, more preferably performing ultrasonic treatment to obtain the graphene oxide aqueous solution. The filtration and cleaning are preferably carried out by ceramic membrane filtration equipment; the method of the ultrasound is a method well known to those skilled in the art, and is not particularly limited, and in the present invention, it is preferable to perform ultrasound using energy-gathering ultrasound equipment; the frequency of the ultrasonic wave is preferably 10-100 KHZ, more preferably 10-80 KHZ, further preferably 10-60 KHZ, further preferably 10-40 KHZ, further preferably 20-30 KHZ, and most preferably 20 KHZ.
Subjecting the graphene oxide aqueous solution to ultrasound; the mass concentration of the graphene oxide in the graphene oxide aqueous solution is preferably 0.2% to 0.35%, more preferably 0.25% to 0.35%, and most preferably 0.3%. The mass fraction of the graphene oxide in the graphene oxide aqueous solution is too low, which leads to low efficiency, and too high, which affects subsequent reduction effect, resulting in incomplete reduction and occurrence of agglomeration.
The graphene oxide can be further layered by ultrasonic waves, and the graphene oxide can be dispersed and crushed. The method of the ultrasound is a method well known to those skilled in the art, and is not particularly limited, and in the present invention, it is preferable to perform ultrasound using energy-gathering ultrasound equipment; the frequency of the ultrasonic wave is preferably 10-100 KHZ, more preferably 10-80 KHZ, further preferably 10-60 KHZ, further preferably 10-40 KHZ, further preferably 20-30 KHZ, and most preferably 20 KHZ; the ultrasonic time is preferably 1-5 h, more preferably 2-4 h, and further preferably 2-3 h; in some embodiments provided herein, the ultrasound time is preferably 2 hours.
After ultrasonic treatment, adjusting the pH value of the solution to be alkaline, preferably adjusting the pH value of the solution to be 10.3-10.8, more preferably adjusting the pH value of the solution to be 10.5-10.8, and further preferably adjusting the pH value of the solution to be 10.5-10.6; in some embodiments provided herein, it is preferred to adjust the pH of the solution to 10.5; in other embodiments provided herein, the pH of the solution is preferably adjusted to 10.6.
Then adding a reducing agent and an alcohol polymer; wherein, the reducing agent is known to those skilled in the art, and is not particularly limited, hydrazine hydrate or sodium borohydride is preferably added in the present invention, and hydrazine hydrate is more preferably added as the reducing agent; the mass ratio of the graphene oxide to the reducing agent is preferably 1: (0.5 to 1.2), more preferably 1: (0.5 to 1), and preferably 1: (0.6 to 0.8), most preferably 1: (0.6-0.7); in some embodiments provided herein, the mass ratio of the graphene oxide to the reducing agent is preferably 1: 0.6; the alcohol polymer is added into the solution as a polymerization inhibitor to prevent the generated graphene from aggregating; the alcohol polymer is preferably polyethylene glycol; the mass ratio of the alcohol polymer to the reducing agent is preferably 1: (1-10), more preferably 1: (1-8), and more preferably 1: (1-6), and more preferably 1: (1.5-4), and most preferably 1: (1.5-2); in some embodiments provided herein, the mass ratio of the alcohol polymer to the reducing agent is preferably 1: 1.8.
Adding a reducing agent and an alcohol polymer, and then heating for reaction; the temperature of the heating reaction is preferably 70-95 ℃, more preferably 75-95 ℃, further preferably 80-95 ℃, and most preferably 85-95 ℃; in some embodiments provided herein, the temperature of the heating reaction is preferably 90 ℃; the heating reaction time is preferably 10-20 h, more preferably 12-18 h, still more preferably 12-16 h, and most preferably 13-15 h; in some embodiments provided herein, the heating reaction time is preferably 14 hours.
After the heating reaction, the temperature is preferably naturally reduced, and then washing is performed, more preferably, washing is performed until the pH value is 8, so as to obtain a graphene aqueous solution.
According to the invention, the graphene oxide aqueous solution is subjected to ultrasonic treatment, so that the graphene oxide is further layered and dispersed, and the alcohol polymer is added as a polymerization inhibitor, so that the obtained graphene has high single-layer rate and uniform sheet diameter, and the preparation method is simple and has low cost.
adding the graphene aqueous solution into liquid nitrogen; wherein the mass concentration of the graphene in the graphene aqueous solution is preferably 0.1-0.5%, more preferably 0.1-0.4%, still more preferably 0.1-0.3%, and most preferably 0.1-0.2%; in some embodiments provided herein, the mass concentration of graphene in the graphene aqueous solution is preferably 0.1%.
in the present invention, in order to better disperse the graphene in the aqueous solution, it is preferable to perform ultrasonic treatment and then add the graphene to liquid nitrogen. The method of the ultrasound is a method well known to those skilled in the art, and is not particularly limited, and in the present invention, it is preferable to perform ultrasound using energy-gathering ultrasound equipment; the frequency of the ultrasonic wave is preferably 10-100 KHZ, more preferably 10-80 KHZ, further preferably 10-60 KHZ, further preferably 10-40 KHZ, further preferably 20-30 KHZ, and most preferably 20 KHZ; the time of the ultrasonic treatment is preferably 1-5 h, more preferably 2-4 h, still more preferably 2-3 h, and most preferably 2 h. The volume ratio of the graphene aqueous solution to the liquid nitrogen is preferably 1: (2-10), more preferably 1: (3-8), and more preferably 1: (3-6), most preferably 1: (3-5); in some embodiments provided herein, the volume ratio of the graphene aqueous solution to liquid nitrogen is preferably 1: 5; in other embodiments provided by the present invention, the volume ratio of the graphene aqueous solution to the liquid nitrogen is preferably 3: 10.
In order to better mix the graphene and the liquid nitrogen, the graphene aqueous solution is preferably added into the liquid nitrogen in a stirring state to obtain solidified graphene; the stirring speed is preferably 600-1000 rpm, more preferably 700-900 rpm, still more preferably 750-850 rpm, and most preferably 800 rpm.
Vacuum drying the cured graphene; the vacuum degree of the vacuum drying is preferably 0.1-0.5 Pa, more preferably 0.1-0.3 Pa, still more preferably 0.1-0.2 Pa, and most preferably 0.1 Pa; in the invention, the solidified graphene is preferably subjected to vacuum freeze drying; the pre-cooling temperature of the vacuum freeze drying is preferably less than-40 ℃, more preferably-45 ℃ to-55 ℃, and further preferably-50 ℃; then controlling the temperature of the partition board of the vacuum freeze drying in a segmented manner, wherein the temperature of the partition board is required to be not higher than-2 ℃ to-5 ℃; when the material temperature is higher than 2 ℃, indicating that the graphene is completely dried, introducing inert gas to replace the vacuum degree, and obtaining graphene powder; the inert gas is not particularly limited as long as it is known to those skilled in the art, and argon gas is preferred in the present invention.
according to the invention, the graphene aqueous solution is treated by liquid nitrogen and then is dried in vacuum, so that the phenomena of irreversible superposition and agglomeration of graphene sheets are effectively solved, and the obtained graphene powder is easy to disperse.
The invention also provides a preparation method of the graphene derivative powder, which comprises the following steps: s1) adding the graphene derivative aqueous solution into liquid nitrogen to obtain a solidified graphene derivative; s2) carrying out vacuum drying on the solidified graphene derivative to obtain graphene derivative powder.
The graphene derivative is not particularly limited as long as it is well known to those skilled in the art, and graphene oxide is preferred in the present invention; the graphene oxide may be prepared by self-manufacturing or commercially available, and is not particularly limited, and in the present invention, the graphene oxide is preferably prepared according to the preparation method of graphene oxide.
Adding a graphene aqueous solution into liquid nitrogen, wherein the mass fraction of the graphene derivative in the graphene derivative aqueous solution is preferably 0.1-0.3%, more preferably 0.1-0.2%, and still more preferably 0.1%.
in the present invention, in order to disperse the graphene derivative in the aqueous solution better, it is preferable to perform ultrasonic treatment first and then add the solution to liquid nitrogen. The method of the ultrasound is a method well known to those skilled in the art, and is not particularly limited, and in the present invention, it is preferable to perform ultrasound using energy-gathering ultrasound equipment; the frequency of the ultrasonic wave is preferably 10-100 KHZ, more preferably 10-80 KHZ, further preferably 10-60 KHZ, further preferably 10-40 KHZ, further preferably 20-30 KHZ, and most preferably 20 KHZ; the time of the ultrasonic treatment is preferably 1-5 h, more preferably 2-4 h, still more preferably 2-3 h, and most preferably 2 h. The volume ratio of the graphene derivative aqueous solution to liquid nitrogen is preferably 1: (2-10), more preferably 1: (3-8), and more preferably 1: (3-6), most preferably 1: (3-5); in some embodiments provided herein, the volume ratio of the graphene derivative aqueous solution to liquid nitrogen is preferably 1: 5.
In order to better mix the graphene derivative with liquid nitrogen, the graphene derivative aqueous solution is preferably added to the liquid nitrogen under stirring to obtain a solidified graphene derivative; the stirring speed is preferably 600-1000 rpm, more preferably 700-900 rpm, still more preferably 750-850 rpm, and most preferably 800 rpm.
vacuum drying the cured graphene derivative; the vacuum degree of the vacuum drying is preferably 0.1-0.5 Pa, more preferably 0.1-0.3 Pa, still more preferably 0.1-0.2 Pa, and most preferably 0.1 Pa; in the present invention, it is more preferable to freeze-dry the cured graphene derivative in vacuum; the pre-cooling temperature of the vacuum freeze drying is preferably less than-40 ℃, more preferably-45 ℃ to-55 ℃, and further preferably-50 ℃; then controlling the temperature of the partition board of the vacuum freeze drying in a segmented manner, wherein the temperature of the partition board is required to be not higher than-2 ℃ to-5 ℃; the temperature in the vacuum freeze drying process is preferably-40 ℃ to 2 ℃, and more preferably-40 ℃ to-5 ℃; when the material temperature is higher than 2 ℃, indicating that the graphene derivative is completely dried, introducing inert gas to replace the vacuum degree, and obtaining graphene derivative powder; the inert gas is not particularly limited as long as it is known to those skilled in the art, and argon gas is preferred in the present invention.
The method comprises the steps of quickly freezing an aqueous solution of the graphene derivative by liquid nitrogen to enable the graphene derivative to be solid powder in a short time, and then continuously sublimating solvent water by freezing under a vacuum condition to obtain a powder product. The method has the advantage of dispersing the macroscopic solution into fine particles, greatly reducing the possibility of agglomeration. And the whole drying process is kept at the temperature of minus 2 ℃ to ensure that the active target of the graphene derivative, especially the graphene oxide, is not damaged by heat.
in order to further illustrate the present invention, the following describes in detail a method for preparing a powder of graphene and a derivative thereof, which is provided by the present invention, with reference to examples.
The reagents used in the following examples are all commercially available.
Example 1
1.1 dispersing 20g (1.667mol) of natural crystalline flake graphite with the particle size of 10 μm in 800ml of 98% concentrated sulfuric acid at room temperature, stirring for 1 hour, adding 10ml of fuming nitric acid, reacting for 14 hours, controlling the reaction temperature to be lower than 10 ℃, adding 80g of potassium permanganate, and reacting for 144 hours at constant temperature of 30 ℃. And (3) dropwise adding 1.2L of high-purity water at the temperature of lower than 60 ℃ by using a constant-pressure dropping funnel, heating to 90 ℃ for reaction for 2.5h, cooling to below 60 ℃, adding 40ml of hydrogen peroxide, naturally cooling, cleaning by using ceramic membrane cleaning equipment, and performing ultrasonic treatment to obtain a single-layer graphene oxide solution.
1.2 carrying out ultrasonic treatment on 2L of graphene oxide aqueous solution with the concentration of 0.3% for 2h under the power of 2KW at 20KHz, adjusting the pH value to 10.5 by using ammonia water, adding 3.6g of hydrazine hydrate and 2g of polyethylene glycol, stirring, controlling the reaction temperature to be 90 ℃, and reacting for 14 h. And naturally cooling, and washing with water until the pH value is 8 to obtain the graphene aqueous solution. And adding pure water to prepare a 0.1% graphene solution for later use.
1.3 starting the vacuum freeze dryer, setting the precooling temperature to be 50 ℃ below zero, and precooling for four hours. Taking 5L of liquid nitrogen, adding a mechanical stirrer, and slowly adding 1L of 0.1% graphene solution into the liquid nitrogen at the rotating speed of 800rpm to obtain cured graphene; and (3) putting the solidified graphene into a vacuum freeze dryer, starting a vacuum pump, and keeping the vacuum degree at 0.1 Pa. And when the temperature of the material is higher than 2 ℃, closing the vacuum stop valve, opening the inflation valve, slowly enabling the internal pressure to reach the atmospheric pressure, and taking out the graphene powder.
Fig. 1 is a photograph showing the appearance of the graphene powder obtained in example 1. As can be seen from fig. 1, the product density is much less than that of graphite.
The graphene powder obtained in example 1 was analyzed by a scanning electron microscope to obtain a scanning electron micrograph, which is shown in fig. 2. As can be seen from fig. 2, it is a single-layer structure and no agglomeration occurs.
the graphene powder obtained in example 1 was analyzed by X-ray diffraction, and an X-ray diffraction pattern thereof was obtained as shown in fig. 3.
The graphene powder obtained in example 1 was analyzed by an atomic force microscope to obtain an atomic force micrograph, which is shown in fig. 4. As can be seen from FIG. 4, the thickness of the graphene obtained in example 1 was 2 to 4 nm.
Example 2
2.1 dispersing 60g (5mol) of natural crystalline flake graphite with the particle size of 10 mu m in 2.25L 98% concentrated sulfuric acid at room temperature, stirring for 1 hour, adding 30ml fuming nitric acid, reacting for 14 hours, controlling the reaction temperature to be lower than 10 ℃, adding 240g of potassium permanganate, and reacting for 144 hours at the constant temperature of 30 ℃. 2.25L of high purity water was added dropwise at a temperature of less than 60 ℃ using a constant pressure dropping funnel. Heating to 90 deg.C, reacting for 2.5h, cooling to below 60 deg.C, and adding 125ml hydrogen peroxide. And naturally cooling, cleaning by using ceramic membrane cleaning equipment, and carrying out ultrasonic treatment to obtain a single-layer graphene oxide solution.
2.2, carrying out ultrasonic treatment on 4L of graphene oxide aqueous solution with the concentration of 0.3% for 2h under the power of 2KW at 20KHz, adjusting the pH value to 10.5 by using ammonia water, adding 7.2g of hydrazine hydrate, controlling the reaction temperature to be 90 ℃, and reacting for 14 h. And naturally cooling, and washing with water until the pH value is 8 to obtain the graphene aqueous solution. And adding pure water to prepare a 0.1% graphene solution for later use.
2.3 starting the vacuum freeze dryer, setting the precooling temperature to be 50 ℃ below zero, and precooling for four hours. Taking 10L of liquid nitrogen, adding a mechanical stirrer, and slowly adding 3L of 0.1% graphene solution into the liquid nitrogen at the rotating speed of 800rpm to obtain cured graphene; and (3) putting the solidified graphene into a vacuum freeze dryer, starting a vacuum pump, and keeping the vacuum degree at 0.1 Pa. And when the temperature of the material is higher than 2 ℃, closing the vacuum stop valve, opening the inflation valve, slowly enabling the internal pressure to reach the atmospheric pressure, and taking out the graphene powder.
example 3
3.1 preparing graphene oxide solution. Dispersing 60g (5mol) of natural crystalline flake graphite with the particle size of 10 mu m in 2.25L 98% concentrated sulfuric acid at room temperature, stirring for 1 hour, adding 30ml of fuming nitric acid, reacting for 14 hours, controlling the reaction temperature to be lower than 10 ℃, adding 180g of potassium permanganate, and reacting for 72 hours at constant temperature of 30 ℃. 2.25L of high purity water was added dropwise at a temperature of less than 60 ℃ using a constant pressure dropping funnel. Heating to 90 deg.C, reacting for 2.5h, cooling to below 60 deg.C, and adding 125ml of 32% hydrogen peroxide. And naturally cooling, cleaning by using ceramic membrane cleaning equipment until the sulfate radical content in the penetrating fluid is less than 20 ppm. And detecting the solid content of the graphene oxide aqueous solution, and preparing to obtain the graphene oxide aqueous solution with the solid content of 0.1%.
3.2 starting the vacuum freeze drier, wherein the precooling temperature is-50 ℃. Setting the freezing process temperature to be-40 ℃ to-5 ℃; 5L of liquid nitrogen is taken, mechanical stirring is carried out, and 1L of 0.1% graphene oxide solution is slowly added into the liquid nitrogen at the rotating speed of 800 rpm. With the continuous gasification of the liquid nitrogen, a proper amount of liquid nitrogen needs to be added into the stirring container in time to ensure that the liquid does not splash due to bumping. And (4) putting the graphene oxide solution into a vacuum drier after the graphene oxide solution is completely changed into solid particles. Starting a vacuum pump, keeping vacuum, and carrying out vacuum drying at the drying temperature of 40-5 ℃.
and when the material temperature probe is higher than 2 ℃, replacing the vacuum with argon, keeping a drying environment, and taking out the graphene oxide powder.
Fig. 5 is an appearance photograph of the aqueous graphene oxide solution obtained in example 3; fig. 6 is an appearance photograph of the graphene oxide powder obtained in example 3.
The graphene oxide powder obtained in example 3 was analyzed by a scanning electron microscope to obtain scanning electron micrographs, as shown in fig. 7 and 8.
The graphene oxide powder obtained in example 3 was analyzed by X-ray diffraction, and an X-ray diffraction pattern thereof was obtained, as shown in fig. 9.
the graphene oxide powder obtained in example 3 was analyzed by an atomic force microscope to obtain an atomic force micrograph, which is shown in fig. 10.
comparative example 1
the graphene oxide aqueous solution obtained in example 3 was directly placed in a vacuum freeze dryer to be lyophilized, and graphene oxide powder was obtained.
Fig. 11 is a photograph showing the appearance of the graphene oxide powder obtained in comparative example 1.
The graphene oxide powder obtained in comparative example 1 was analyzed by a scanning electron microscope to obtain a scanning electron micrograph, which is shown in fig. 12. As can be seen from FIG. 12, the agglomeration was severe.
The graphene oxide powder obtained in comparative example 1 is dissolved in water and ethanol, as shown in fig. 13, where a is an ethanol solution and B is an aqueous solution, and it is apparent from fig. 13 that the graphene oxide powder is not completely dissolved and has suspended matter.
The graphene oxide powder obtained in example 3 was dissolved in water and ethanol, as shown in fig. 14, where a is an ethanol solution and B is an aqueous solution. It can be seen from fig. 14 that it is completely dissolved.
Comparative example 2
And (3) putting the graphene oxide aqueous solution obtained in the embodiment 3 into an oven for drying to obtain graphene oxide powder.
Fig. 15 is a photograph showing the appearance of the graphene oxide powder obtained in comparative example 2. As is clear from FIG. 15, the particles are distributed in the form of flakes on the glass, and the morphology is greatly different from that of the powder.
comparative example 3
the graphene aqueous solution obtained in example 1 was directly placed in a freeze dryer to be dried under the same freeze drying conditions as in example 1, thereby obtaining a graphene powder.
Fig. 16 is a photograph showing the appearance of the graphene powder obtained in comparative example 3. As can be seen from fig. 16, the appearance was similar to that of the graphene powder obtained in example 1.
The graphene powder obtained in comparative example 3 was analyzed by a scanning electron microscope to obtain a scanning electron micrograph, which is shown in fig. 17. As can be seen from fig. 17, the agglomeration was severe.
Comparative example 4
And directly placing the graphene aqueous solution obtained in the embodiment 1 into an oven for drying to obtain graphene powder.
Fig. 18 is a photograph showing the appearance of the graphene powder obtained in comparative example 4. As can be seen in fig. 18, it agglomerated into a block shape.
Claims (10)
1. A preparation method of graphene and powder of graphene derivatives is characterized by comprising the following steps:
S1) adding the graphene aqueous solution or the graphene derivative aqueous solution into liquid nitrogen to obtain solidified graphene or a solidified graphene derivative;
S2) carrying out vacuum freeze drying on the solidified graphene or the solidified graphene derivative to obtain graphene powder or graphene derivative powder.
2. the method according to claim 1, wherein the aqueous solution of graphene or the aqueous solution of a graphene derivative is subjected to ultrasound and then added to liquid nitrogen.
3. The preparation method according to claim 2, wherein the ultrasonic wave has a frequency of 10 to 100 KHZ; the time of the ultrasonic treatment is 1-5 h.
4. The preparation method according to claim 1, wherein the mass fraction of graphene in the graphene aqueous solution is 0.1-0.5%; the mass fraction of the graphene derivative in the graphene derivative aqueous solution is 0.1-0.3%.
5. The method according to claim 1, wherein the volume ratio of the aqueous graphene solution or the aqueous graphene derivative solution to the liquid nitrogen is 1: (2-10).
6. The preparation method according to claim 1, wherein the step S1) is specifically:
And adding the graphene aqueous solution or the graphene derivative aqueous solution into liquid nitrogen in a stirring state to obtain the solidified graphene or the solidified graphene derivative.
7. The method according to claim 6, wherein the stirring speed is 600 to 1000 rpm.
8. the method of claim 1, wherein the pre-cooling temperature of the vacuum freeze-drying is less than-40 ℃.
9. The method according to claim 1, wherein the temperature during the vacuum freeze-drying is-40 ℃ to 2 ℃.
10. the method according to claim 1, wherein the vacuum degree of the vacuum freeze-drying is 0.1 to 0.5 Pa.
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