CN108622887B - Method for preparing graphene through microwave puffing - Google Patents
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Abstract
The invention relates to a method for preparing graphene through microwave puffing, and belongs to the technical field of graphene preparation. The method for preparing graphene through microwave puffing comprises the following steps: 1) mixing a graphite raw material and an intercalating agent for acidification and intercalation to obtain primary intercalation graphite slurry; 2) adding OH into the obtained primary intercalation acidified graphite slurry‑Strong alkali solution with the ion concentration of 0.1-8 mol/L is added until the system is neutral, and secondary intercalation graphite slurry is obtained; 3) and (3) carrying out microwave heating on the obtained secondary intercalated graphite slurry or carrying out microwave heating after drying to obtain the graphite. According to the method, acidizing intercalation treatment is adopted to help open a capillary diffusion channel between graphite sheets, strong base and acid are used for neutralizing the graphite sheets to eliminate an oxidation group introduced by the acidizing intercalation treatment, and then high-efficiency layering of graphite is realized through rapid microwave heating, so that three-dimensional graphene powder particles consisting of ultrathin graphene sheet layer clusters are directly prepared.
Description
Technical Field
The invention relates to the technical field of graphene preparation, in particular to a method for preparing graphene through microwave puffing.
Background
Graphene as a carbon atom with Sp2The monolayer two-dimensional crystal formed by hybridization combination is more and more concerned by people due to the special physical and chemical properties of the crystal. It has been found that the carriers in graphene follow a linear dispersion relationship near the fermi level, similar to the unmassed dirac fermi, which gives it a number of extraordinary properties, such as quantum hall effect and dual-polarization electric field effect. In addition, graphene exhibits non-dispersive transmission characteristics with electron mobilities as high as 1500cm at room temperature2V · s, much higher than conventional semiconductor materials. The graphene has excellent conductivity, transparency, high thermal stability and chemical stability, and is widely applied to the fields of enhancing the specific capacity and the cycling stability of positive and negative electrode materials of metal ion batteries, environmental catalysis substrate materials and the like.
Heretofore, there have been various methods for producing single-layer or few-layer graphene sheets, such as a tape mechanical exfoliation graphite method, a SiC epitaxial growth method, a chemical reduction oxidation graphite method, a graphite liquid phase exfoliation method, a chemical vapor deposition method, and the like. The tape mechanical stripping method is a simple preparation method, but the method has extremely low yield and generates residues of tapes and dispersion solvents to influence the inherent performance of graphene; the SiC epitaxial growth method has higher requirements on preparation conditions and equipment, and the synthesized graphene is difficult to separate from the substrate; a large amount of oxygen-containing functional groups are introduced by a chemical reduction graphite oxide method, the prepared graphene contains a large amount of defects, and a large amount of chemical waste liquid is generated in the preparation process; the traditional graphite liquid phase stripping method has low yield, the prepared graphene sheet layer is agglomerated, and a large amount of chemical waste liquid is caused to pollute the environment; the chemical vapor deposition method has the problems of complex technology, low yield, high cost, inapplicability to the preparation of powder materials and the like.
Patent No. CN102583328B discloses a process for preparing graphene oxide, which comprises the following steps: 1) mixing natural crystalline flake graphite with an oxidant, carrying out constant-temperature reaction, washing, carrying out suction filtration, and drying to obtain graphite particles of an oxidation intercalation; 2) carrying out microwave heating on the graphite particles obtained in the step 1) to obtain expanded graphite; 3) adding a dispersing agent into the expanded graphite obtained in the step 2), and carrying out ultrasonic stripping, suction filtration and drying to obtain graphene oxide. The oxidant is the combination of concentrated sulfuric acid and potassium permanganate, the combination of concentrated nitric acid and perchloric acid or the combination of concentrated phosphoric acid and potassium permanganate. The method relies on a large amount of strong oxidant for intercalation treatment to prepare the interlayer oxidized expanded graphite, and because the expansion rate is poor, the graphene oxide powder is prepared by liquid phase dispersion and ultrasonic exfoliation of the expanded graphite. In addition, as one of the technical variants of the conventional oxidation method, the technology also generates a large amount of chemical waste liquid, and the product defect rate is too high and the yield is not ideal.
Therefore, the method for preparing the low-defect graphene in large quantity with high efficiency, low cost and environmental friendliness is developed, and has great technical significance and wide application prospect.
Disclosure of Invention
The invention aims to provide a method for preparing graphene through microwave puffing, which can solve the technical problem that the graphene prepared in the prior art has high defects.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a method for preparing graphene through microwave puffing comprises the following steps:
1) mixing a graphite raw material with an intercalation agent for acidification intercalation to obtain primary intercalation graphite slurry;
2) adding OH into the primary intercalation graphite slurry obtained in the step 1)-Strong alkali solution with the ion concentration of 0.1-8 mol/L is added until the system is neutral, and secondary intercalation graphite slurry is obtained;
3) microwave heating the secondary intercalated graphite slurry obtained in the step 2), or microwave heating the dried secondary intercalated graphite slurry obtained in the step 2) to obtain three-dimensional graphene powder particles; the microwave heating is to heat the materials in the microwave oven to 400-1000 ℃ within 5-300 s.
According to the method for preparing graphene through microwave puffing, the graphite raw material is subjected to acid-alkali two-step efficient intercalation treatment and then rapid microwave heating treatment. After the graphite is subjected to acidification primary intercalation, a strong alkaline solution is adopted for secondary intercalation treatment to greatly enhance the intercalation effect, and then three-dimensional graphene powder particles are directly prepared through microwave rapid heating treatment. The primary acidification intercalation treatment helps to open capillary diffusion channels among graphene sheet layers, and during the secondary intercalation treatment, acid and alkali are subjected to neutralization reaction among the layers to generate salt and water, so that acidic molecules among the layers introduced by the primary intercalation treatment are eliminated, and oxidation groups are avoided or eliminated. Particularly, the microwave heating of the secondary intercalation graphite slurry can cause the rapid gasification of interlayer water of the secondary intercalation graphite, and the graphite layering effect is fully improved.
In order to avoid the loss of interlayer water introduced by secondary intercalation, the temperature adopted during the drying treatment of the intercalation graphite slurry is not more than 80 ℃, and the drying time is preferably 20-40 min. When the conditions are adopted to dry the secondary intercalation graphite slurry, the water on the surface layer of the secondary intercalation graphite particles can be removed, and meanwhile, the loss of interlayer water introduced by the secondary intercalation is avoided, so that the secondary intercalation graphite dry material is obtained.
According to the invention, the intercalation treatment is carried out by acid-alkali neutralization, and the secondary intercalation treatment brought by strong alkali solution can effectively improve the intercalation effect, and the intercalation efficiency is enhanced by cooperating with the primary acidification intercalation, so that the rapid explosion layering is facilitated, and the three-dimensional reduced graphene particles formed by petal-shaped thin graphene sheets are directly prepared; meanwhile, the microwave power can be effectively reduced, acid mist cannot be generated during microwave heating, corrosion to equipment and harm to human health are reduced, and the microwave heating device is green, environment-friendly, efficient and energy-saving.
The method for preparing graphene through microwave puffing has the advantages of simple process and low cost, and graphene oxide is prepared without oxidizing graphite and then reduced to obtain graphene; and the three-dimensional graphene powder particles with extremely low defect rate are directly prepared by one-time microwave puffing treatment, so that the method is suitable for large-scale production of high-quality low-defect graphene, and has great technical significance and wide application prospect.
Preferably, the particle size of the graphite raw material is less than 2 mm. More preferably, the particle size mesh number of the graphite raw material is 10-500 meshes. More preferably, the particle size mesh number of the graphite raw material is 30-500 meshes.
Preferably, in the step 1), the acidification intercalation is to mix the graphite raw material with the intercalation agent and then to stand at normal temperature, and the standing time is 20min to 3 h. Standing at normal temperature can greatly reduce the oxidation of the intercalation agent to graphite.
The mass ratio of the graphite raw material to the intercalation agent is 1 (2-10).
The intercalation agent is at least one of concentrated nitric acid and concentrated phosphoric acid, or a mixture of potassium permanganate and at least one of concentrated nitric acid and concentrated phosphoric acid. The concentration of the concentrated nitric acid is not less than 65 wt%. The concentration of the concentrated phosphoric acid is not less than 85 wt%.
The intercalation agent is mixed acid of concentrated nitric acid and concentrated phosphoric acid, and H in the mixed acid3PO4With HNO3Is not more than 5.
The intercalation agent contains potassium permanganate, and the mass ratio of the potassium permanganate to the graphite raw material is not more than 1.5. It must be noted that excessive potassium permanganate can introduce oxidation defects, which is not favorable for preparing high-quality graphene products.
Preferably, in step 2), the solute of the alkali solution is at least one of sodium hydroxide, potassium hydroxide or lithium hydroxide. During intercalation, the secondary intercalation brought by the strong alkaline solution can effectively improve the intercalation effect, and the intercalation efficiency is enhanced by cooperating with the primary acidification intercalation, thereby being beneficial to layering through rapid explosion and expansion and simultaneously neutralizing the primary intercalation agent. When nitrate or/and phosphate is used as an acid intercalation agent and sodium hydroxide and/or potassium hydroxide solution is used as strong alkali solution, the generated waste liquid can be directly used as chemical fertilizer, and the method is green and environment-friendly.
At 20 deg.C, only 12.8g of lithium hydroxide can be dissolved in 100g of water, and when the strong alkali solution is lithium hydroxide solution, OH in the solution is at the use temperature-The ion concentration does not necessarily reach 8mol/L, the highest is OH which can be reached at the temperature-The highest concentration of ions may be used.
Preferably, the intercalating agent used contains concentrated phosphoric acid, and the solute of the strongly alkaline solution is at least one of sodium hydroxide, potassium hydroxide or lithium hydroxide.
Preferably, in the step 3), when the secondary intercalated graphite slurry is heated by microwave, the mass percentage of water in the secondary intercalated graphite slurry is not more than 10%. Using strong alkaline solution of OH-When the ion concentration is low, the water content in the obtained secondary intercalated graphite slurry is relatively high, and a large amount of solvent can be removed before microwave heating, so that the water content (mass percentage) is not more than 10%. For example, a large amount of the solvent may be removed by direct filtration or heating at a temperature not exceeding 80 ℃.
When the secondary intercalation graphite slurry or the secondary intercalation graphite dry material is subjected to microwave heating, water between secondary intercalation graphite layers can be rapidly heated and gasified, and the effect of stripping secondary intercalation graphite is achieved.
The power of microwave heating is related to the material quality. Preferably, the microwave heating power is 80-600W/g, namely the microwave heating power is set according to the power of 80-600W corresponding to each g of materials. Generally, the heating power is 0.3-3000 kW.
The method for preparing graphene through microwave puffing can also comprise the step of performing ball milling on the three-dimensional graphene powder particles subjected to microwave heating in the step 3) to prepare graphene powder. The rotation speed of the ball milling is 300-450 rpm, and the ball milling time is 1-3 h.
The ball milling can adopt dry ball milling or wet ball milling. The dispersant adopted by the wet ball milling is a polyvinylpyrrolidone water solution. For example, 5 to 15g of polyvinylpyrrolidone can be dissolved in 100ml of deionized water to obtain a dispersant. Centrifuging the graphene suspension obtained after wet ball milling for 15-25 min at the rotating speed of 2500-3500 rpm, then centrifuging the upper layer of suspension at 7000-9000 rpm, taking the precipitate, and drying to further obtain graphene powder with the layer number less than 3.
The method for preparing graphene through microwave puffing further comprises the steps of washing the three-dimensional graphene particles obtained in the step 3) by using a neutral solvent, and then drying for 0.5-3 hours at the temperature of 60-120 ℃. And washing the three-dimensional graphene powder particles by using a neutral solvent to remove residual salt in the graphene.
Drawings
Fig. 1 is a scanning electron micrograph (a) of crystalline flake graphite (S0) and graphene (S2) of example 1;
fig. 2 is a raman spectrum of crystalline flake graphite (S0), neutral graphite dry material (S1), and graphene (S2) in example 1.
Fig. 3 is raman spectra of graphene obtained in example 2(S4) and example 3(S5) and graphene oxide (S3) of a comparative example.
Detailed Description
The technical solution of the present invention is further described below with reference to the specific embodiments, and the technical parameter ranges protected by the present invention include, but are not limited to, the following cases.
In the specific embodiment, the concentrated nitric acid and the concentrated phosphoric acid are analytically pure.
Example 1
The graphite adopted in the embodiment is crystalline flake graphite with the granularity of 50 meshes; the mass fraction of the adopted concentrated nitric acid is 65 percent, and the mass fraction of the adopted concentrated phosphoric acid is 85 percent; the adopted strong alkali solution is NaOH solution with the concentration of 1 mol/L.
The method for preparing graphene through microwave puffing comprises the following steps:
1) 3g of flake graphite, concentrated nitric acid and concentrated phosphoric acid are mixed according to the mass ratio m (flake graphite): m (HNO)3)：m(H3PO4) 1: 2: 1, and standing for 30min to obtain primary intercalated graphite slurry;
2) adding a strong base solution into the primary intercalated graphite slurry obtained in the step 1) until the system is neutral, and then heating at the temperature of below 80 ℃ to evaporate water to obtain a secondary intercalated graphite slurry with the water mass percent of no more than 10%;
3) putting the secondary intercalated graphite slurry obtained in the step 2) into a microwave oven, setting microwave power according to the proportion of 300W (power) per g of secondary intercalated graphite slurry, and heating the neutral graphite slurry for 20s by microwave to enable the temperature of the neutral graphite slurry to reach more than 500 ℃ (slightly higher than 500 ℃ and not more than 1000 ℃) to obtain three-dimensional graphene powder particles.
The scanning electron microscope test is performed on the flake graphite adopted in the embodiment and the prepared graphene, and the result is shown in fig. 1. As can be seen from fig. 1, after the flake graphite is processed, the morphology is converted into three-dimensional graphene particles composed of petal-shaped flake clusters.
Raman spectrum test is performed on the crystalline flake graphite adopted in the embodiment, the neutral graphite dry material obtained by drying the neutral graphite slurry obtained in the step 2), and the prepared graphene, and the obtained raman spectrum is shown in fig. 2. In fig. 2, the D peak intensity of the graphene (S2) is lower than that of the neutral dry graphite (S1) and approaches zero, which indicates that the obtained graphene has extremely low defect rate (the relative intensity of the D peak is equivalent to that of the flake graphite raw material); the 2D peak of graphene (S2) was well-symmetric, and the main peak was shown to be relative to graphiteThe red shift of 10.1 wave numbers is generated, and the fingerprint Raman characteristics of the single-layer graphene are met; in addition, the acid-alkali secondary composite intercalation causes the obvious splitting phenomenon of the G peak of the swelling graphene (S2), and the main peak G is-The blue shift of 6.2 wave numbers is shown, the blue shift amount of the G peak of the single-layer graphene is corresponded, and the single-layer graphene is further proved to be the main phase composition; minor G peak (G)+) Blue shift is about 1, and the corresponding layer number is not more than 5.
Example 2
The graphite adopted in the embodiment is crystalline flake graphite with the granularity of 100 meshes; the mass fraction of the adopted concentrated nitric acid is 65 percent, and the mass fraction of the adopted concentrated phosphoric acid is 85 percent; the adopted strong alkali solution is KOH solution with the concentration of 1 mol/L.
The method for preparing graphene through microwave puffing comprises the following steps:
1) preparing the flake graphite, potassium permanganate, concentrated nitric acid and concentrated phosphoric acid according to the mass ratio m (flake graphite): m (potassium permanganate): m (HNO)3)：m(H3PO4) 1: 0.2: 1: 4, uniformly mixing, and standing for 3 hours to obtain primary intercalated graphite slurry;
2) adding a strong base solution into the primary intercalated graphite slurry obtained in the step 1) until the system is neutral to obtain a secondary intercalated graphite slurry;
3) drying the secondary intercalation slurry obtained in the step 2) at 60 ℃ for 30min to obtain secondary intercalation graphite dry material, then placing the secondary intercalation graphite dry material into a microwave oven, setting microwave power according to the proportion of 270W (power) corresponding to each g of secondary intercalation graphite dry material, and heating the secondary intercalation graphite dry material by microwave for 20s to enable the temperature of neutral graphite slurry to reach more than 450 ℃ (slightly higher than 450 ℃ and not more than 1000 ℃) to obtain three-dimensional graphene powder particles;
the graphene prepared by the method used in this example is subjected to raman spectroscopy, and the obtained raman spectrogram is shown in fig. 3 (S4). The result shows that the defect of the graphene is extremely low, and the three-dimensional graphene mainly consists of petal-shaped single-layer graphene sheets and a small number of few-layer graphene sheets with the number of layers not more than 4 according to the change of Raman offset of a G peak and a 2D peak.
Example 3
The graphite adopted in the embodiment is natural graphite with the granularity of 100 meshes; the mass fraction of the adopted concentrated nitric acid is 65 percent, and the mass fraction of the adopted concentrated phosphoric acid is 85 percent; the adopted strong alkali solution is KOH solution with the concentration of 1 mol/L.
The method for preparing graphene through microwave puffing comprises the following steps:
1) mixing natural graphite, potassium permanganate, concentrated nitric acid and concentrated phosphoric acid according to the mass ratio m (natural graphite): m (potassium permanganate): m (HNO)3)：m(H3PO4) 1: 0.6: 1: 4, uniformly mixing, and standing for 3 hours to obtain acidified graphite slurry;
2) adding a strong base solution into the acidified graphite slurry obtained in the step 1) until the system is neutral to obtain a secondary intercalated graphite slurry;
3) drying the secondary intercalated graphite slurry obtained in the step 2) at 50 ℃ for 40min to obtain a secondary intercalated graphite dry material, then placing the secondary intercalated graphite dry material into a microwave oven, setting microwave power according to the proportion of 130W (power) per g of secondary intercalated graphite dry material, and heating the secondary intercalated graphite dry material by microwave for 5s to enable the temperature of the neutral graphite slurry to reach more than 400 ℃ (slightly higher than 400 ℃ and not more than 1000 ℃) to obtain three-dimensional graphene powder particles;
the raman spectrum of the graphene prepared by the method used in this example is shown in fig. 3 (S5). The result shows that the graphene mainly consists of single-layer graphene, and the number of corresponding layers of a small amount of few-layer graphene is not more than 7.
Example 4
The graphite adopted in the embodiment is crystalline flake graphite with the granularity of 200 meshes; the mass fraction of the adopted concentrated nitric acid is 65 percent; the adopted strong alkali solution is LiOH solution with the concentration of 1 mol/L.
The method for preparing graphene through microwave puffing comprises the following steps:
1) the scale graphite and the concentrated nitric acid are mixed according to the mass ratio m (scale graphite): m (HNO)3) 1: 2, standing for 20min to obtain primary intercalated graphite slurry;
2) adding a strong base solution into the primary intercalated graphite slurry obtained in the step 1) until the system is neutral, and then filtering redundant liquid to obtain a secondary intercalated graphite slurry with the water mass percent not more than 10%;
3) putting the secondary intercalated graphite slurry obtained in the step 2) into a microwave oven, setting microwave power according to the proportion of every g of secondary intercalated graphite slurry corresponding to 360W (power), and heating the secondary intercalated graphite slurry for 20s by microwave to enable the temperature of the neutral graphite slurry to reach above 700 ℃ (slightly higher than 700 ℃ and not more than 1000 ℃) to obtain three-dimensional graphene powder particles;
4) adding 300mg of the three-dimensional graphene powder particles obtained in the step 3) into a 250ml agate ball milling tank, adding 8g of PVP (polyvinylpyrrolidone) into 100ml deionized water, performing ultrasonic dispersion for 15min, adding a PVP solution into the ball milling system, performing wet milling treatment at the rotating speed of 450rpm for 1h, centrifuging the obtained suspension at the rotating speed of 3000rpm for 20min, centrifuging and cleaning the upper layer of suspension at 8000rpm, drying the precipitate for 8h, and collecting graphene with the number of layers less than 3.
Example 5
The graphite adopted in the embodiment is crystalline flake graphite with the granularity of 200 meshes; the mass fraction of the adopted concentrated nitric acid is 65 percent, and the mass fraction of the adopted concentrated phosphoric acid is 85 percent; the adopted strong alkali solution is NaOH solution with the concentration of 1.5 mol/L.
The method for preparing graphene through microwave puffing comprises the following steps:
1) preparing the flake graphite, potassium permanganate, concentrated nitric acid and concentrated phosphoric acid according to the mass ratio m (flake graphite): m (potassium permanganate): m (HNO)3)：m(H3PO4) 1: 0.05: 2: 2, standing for 40min to obtain primary intercalated graphite slurry;
2) adding a strong base solution into the primary intercalated graphite slurry obtained in the step 1) until the system is neutral, and then filtering redundant liquid to obtain a secondary intercalated graphite slurry with the mass percent of water not exceeding 10%;
3) putting the secondary intercalated graphite slurry obtained in the step 2) into a microwave oven, setting microwave power according to the proportion of 400W (power) per g of secondary intercalated graphite slurry, and heating the neutral graphite slurry by microwave for 30s to enable the temperature of the neutral graphite slurry to reach more than 800 ℃ (slightly higher than 800 ℃ and not more than 1000 ℃) to obtain three-dimensional graphene powder particles with the layer number not more than 7, thus obtaining the three-dimensional graphene powder particles.
Example 6
The graphite adopted in the embodiment is crystalline flake graphite with the granularity of 500 meshes; the mass fraction of the adopted concentrated nitric acid is 65 percent, and the mass fraction of the adopted concentrated phosphoric acid is 85 percent; the adopted strong alkali solution is NaOH solution with the concentration of 1 mol/L.
The method for preparing graphene through microwave puffing comprises the following steps:
1) preparing the flake graphite, concentrated nitric acid and concentrated phosphoric acid according to the mass ratio m (flake graphite): m (HNO)3)：m(H3PO4) 1: 2: uniformly mixing the components in a proportion of 0.05, and standing for 40min to obtain primary intercalated graphite slurry;
2) adding a strong base solution into the primary intercalated graphite slurry obtained in the step 1) until the system is neutral, and then filtering redundant liquid to obtain a secondary intercalated graphite slurry with the mass fraction of water not exceeding 10%;
3) putting the secondary intercalated graphite slurry obtained in the step 2) into a microwave oven, setting microwave power according to the proportion of 450W (power) for each g of secondary intercalated graphite slurry, and heating the neutral graphite slurry by microwaves for 30s to enable the temperature of the neutral graphite slurry to reach above 850 ℃ (slightly higher than 850 ℃ and not higher than 1000 ℃) to obtain three-dimensional graphene powder particles;
4) and (3) adding deionized water into the three-dimensional graphene powder particles obtained in the step (a), washing to remove phosphate and nitrate, and drying at 60 ℃ for 2h to obtain the graphene powder particles.
Example 7
The graphite adopted in the embodiment is crystalline flake graphite with the granularity of 500 meshes; the mass fraction of the adopted concentrated nitric acid is 65 percent, and the mass fraction of the adopted concentrated phosphoric acid is 65 percent; the strong alkali solution is KOH solution with the concentration of 1.5 mol/L.
The method for preparing graphene through microwave puffing comprises the following steps:
1) preparing the flake graphite, concentrated nitric acid and concentrated phosphoric acid according to the mass ratio m (flake graphite): m (HNO)3)：m(H3PO4) 1: 0.05: 2, standing for 20min to obtain primary intercalated graphite slurry;
2) adding a strong base solution into the primary intercalated graphite slurry obtained in the step 1) until the system is neutral, and then filtering redundant liquid to obtain a secondary intercalated graphite slurry with the mass percent of water not exceeding 10%;
3) putting the secondary intercalated graphite slurry obtained in the step 2) into a microwave oven, setting microwave power according to the proportion of 500W (power) corresponding to each g of secondary intercalated graphite slurry, and heating the neutral graphite slurry for 40s by microwave to enable the temperature of the neutral graphite slurry to reach over 900 ℃ (slightly higher than 900 ℃ and not more than 1000 ℃) to obtain three-dimensional graphene powder particles;
4) and (3) adding deionized water into the three-dimensional graphene powder particles obtained in the step (a), washing to remove phosphate and nitrate, and drying at 80 ℃ for 0.5h to obtain the graphene oxide powder.
Example 8
The graphite adopted in the embodiment is crystalline flake graphite with the granularity of 30 meshes; the mass fraction of the adopted concentrated nitric acid is 65 percent, and the mass fraction of the adopted concentrated phosphoric acid is 85 percent; the adopted strong alkali solution is NaOH solution with the concentration of 1.5 mol/L.
The method for preparing graphene through microwave puffing comprises the following steps:
1) preparing the flake graphite, concentrated nitric acid and concentrated phosphoric acid according to the mass ratio m (flake graphite): m (HNO)3)：m(H3PO4) 1: 1: 4, uniformly mixing, and standing for 3 hours to obtain primary intercalated graphite slurry;
2) adding a strong base solution into the primary intercalated graphite slurry obtained in the step 1) until the system is neutral, and then filtering redundant liquid to obtain a secondary intercalated graphite slurry with the water mass percent not more than 10%;
3) putting the secondary intercalated graphite slurry obtained in the step 2) into a microwave oven, setting microwave power according to the proportion of 550W (power) corresponding to each g of secondary intercalated graphite slurry, and heating the neutral graphite slurry for 5 seconds by microwave to enable the temperature of the neutral graphite slurry to reach above 920 ℃ (slightly higher than 920 ℃ and not higher than 1000 ℃) to obtain three-dimensional graphene powder particles;
4) adding 300mg of the three-dimensional graphene powder particles obtained in the step 3) into a 250ml agate ball milling tank, adding 5g of PVP (polyvinylpyrrolidone) into 100ml deionized water, performing ultrasonic dispersion for 10min, adding a PVP solution into the ball milling system, performing wet milling treatment at the rotating speed of 400rpm for 2h, centrifuging the obtained suspension at the rotating speed of 2500rpm for 25min, taking the upper layer of the suspension, centrifuging and cleaning at 7000rpm, and taking the precipitate and drying for 8h to obtain the graphene oxide powder.
Example 9
The graphite adopted in the embodiment is crystalline flake graphite with the granularity of 10 meshes; the mass fraction of the adopted concentrated nitric acid is 65 percent, and the mass fraction of the adopted concentrated phosphoric acid is 85 percent; the adopted strong alkali solution is NaOH solution with the concentration of 8 mol/L.
The method for preparing graphene through microwave puffing comprises the following steps:
1) preparing the flake graphite, potassium permanganate, concentrated nitric acid and concentrated phosphoric acid according to the mass ratio m (flake graphite): m (potassium permanganate): m (HNO)3)：m(H3PO4) 1: 0.15: 2: 3, uniformly mixing, and standing for 2 hours to obtain primary intercalated graphite slurry;
2) adding a strong base solution into the primary intercalated graphite slurry obtained in the step 1) until the system is neutral, and then filtering redundant liquid to obtain a secondary intercalated graphite slurry with the water mass percent not more than 10%;
3) putting the secondary intercalated graphite slurry obtained in the step 2) into a microwave oven, setting microwave power according to the proportion of each g of secondary intercalated graphite slurry corresponding to 600W (power), and heating the neutral graphite slurry for 30s by microwave to enable the temperature of the neutral graphite slurry to reach 1000 ℃ to obtain three-dimensional graphene powder particles;
4) adding 300mg of the three-dimensional graphene powder particles obtained in the step 3) into a 250ml agate ball milling tank, adding 15g of PVP (polyvinylpyrrolidone) into 100ml deionized water, performing ultrasonic dispersion for 25min, adding a PVP solution into the ball milling system, performing wet milling treatment at the rotating speed of 400rpm for 2h, centrifuging the obtained suspension at the rotating speed of 3500rpm for 15min, centrifuging the upper layer of the suspension at 9000rpm, cleaning, and drying the precipitate for 7h to obtain the graphene oxide powder.
Example 10
The graphite adopted in the embodiment is crystalline flake graphite with the granularity of 200 meshes; the mass fraction of the adopted concentrated nitric acid is 65 percent; the adopted strong alkali solution is NaOH solution with the concentration of 7 mol/L.
The method for preparing graphene through microwave puffing comprises the following steps:
1) preparing the flake graphite, concentrated nitric acid and concentrated phosphoric acid according to the mass ratio m (flake graphite): m (potassium permanganate): m (HNO)3)：m(H3PO4) 1: 1.5: 5: 5, uniformly mixing, and standing for 20min to obtain primary intercalated graphite slurry;
2) adding a strong base solution into the primary intercalated graphite slurry obtained in the step 1) until the system is neutral, and then filtering redundant liquid to obtain a secondary intercalated graphite slurry with the water mass percent not more than 10%;
3) putting the secondary intercalated graphite slurry obtained in the step 2) into a microwave oven, setting microwave power according to the proportion of 80W (power) for each g of secondary intercalated graphite slurry, and heating the neutral graphite slurry by microwaves for 300s to enable the temperature of the neutral graphite slurry to reach above 700 ℃ (slightly higher than 700 ℃ and not more than 1000 ℃) to obtain three-dimensional graphene powder particles;
4) adding 300mg of the three-dimensional graphene powder particles obtained in the step 3) into a 250ml agate ball milling tank, adding 10g of PVP (polyvinylpyrrolidone) into 100ml deionized water, performing ultrasonic dispersion for 15min, adding a PVP solution into the ball milling system, performing wet milling treatment at the rotating speed of 300rpm for 3h, centrifuging the obtained suspension at the rotating speed of 3000rpm for 20min, centrifuging the upper layer of the suspension at 7000rpm, washing the precipitate with deionized water, and drying to obtain the graphene oxide powder.
Comparative example
The preparation method of graphene oxide of the comparative example includes the steps of:
1) weighing 5g of 350-mesh natural flake graphite, adding 100ml of concentrated sulfuric acid and 10g of potassium permanganate, fully and uniformly stirring, reacting at room temperature for 2 hours, washing the obtained product to be neutral by using 1L of hydrochloric acid with the mass percentage of 10% and distilled water, and then carrying out vacuum filtration and drying at 60 ℃ to obtain graphite particles subjected to oxidation intercalation;
2) placing the graphite particles of the oxidation intercalation obtained in the step 1) in a microwave oven, and heating for 20s at the power of 800W to obtain expanded graphite;
3) putting the expanded graphite obtained in the step 2) into deionized water, ultrasonically stripping, taking the upper suspension, filtering and drying to obtain the expanded graphite; the ultrasonic power is 100W, and the ultrasonic time is 30 min. The lower layer precipitates as graphite, and the graphene oxide yield is only about 28%. Compared with the prior art, the two-stage intercalation treatment method can prepare 100% of three-dimensional graphene powder products only through one-time microwave expansion and explosion treatment.
Raman spectrum test of the graphene obtained by the comparative example was performed, and a raman spectrum was obtained as shown in fig. 3 (S3).
As can be seen from fig. 3, the graphene oxide powder prepared by the method has a large number of defects inherent in graphene oxide due to the introduction of a large amount of oxidant, a raman spectrum is similar to that of standard activated carbon, the defect D peak is wide and high, and the fingerprint information 2D peak of graphene is missing.
Claims (10)
1. A method for preparing graphene through microwave puffing is characterized by comprising the following steps: the method comprises the following steps:
1) mixing a graphite raw material with an intercalation agent for acidification intercalation to obtain primary intercalation graphite slurry;
2) adding OH into the primary intercalation graphite slurry obtained in the step 1)-Strong alkali solution with the ion concentration of 0.1-8 mol/L is added until the system is neutral, and secondary intercalation graphite slurry is obtained;
3) microwave heating the secondary intercalated graphite slurry obtained in the step 2), or microwave heating the dried secondary intercalated graphite slurry obtained in the step 2) to obtain three-dimensional graphene powder particles; the microwave heating is to heat the materials in the microwave oven to 400-1000 ℃ within 5-300 s.
2. The method for preparing graphene by microwave puffing according to claim 1, wherein the method comprises the following steps: the acidification intercalation is to mix the graphite raw material with the intercalation agent and then to stand at normal temperature, and the standing time is 20 min-3 h.
3. The method for preparing graphene by microwave puffing according to claim 1 or 2, wherein the method comprises the following steps: the mass ratio of the graphite raw material to the intercalation agent is 1 (2-10).
4. The method for preparing graphene by microwave puffing according to claim 1, wherein the method comprises the following steps: the intercalation agent is at least one of concentrated nitric acid and concentrated phosphoric acid, or a mixture of potassium permanganate and at least one of concentrated nitric acid and concentrated phosphoric acid.
5. The method for preparing graphene by microwave puffing according to claim 1 or 2, wherein the method comprises the following steps: the intercalation agent is mixed acid of concentrated nitric acid and concentrated phosphoric acid, and H in the mixed acid3PO4With HNO3Is not more than 5.
6. The method for preparing graphene by microwave puffing according to claim 1 or 4, wherein the method comprises the following steps: the intercalation agent contains potassium permanganate, and the mass ratio of the potassium permanganate to the graphite raw material is not more than 1.5.
7. The method for preparing graphene by microwave puffing according to claim 1, wherein the method comprises the following steps: the solute of the strong alkaline solution is at least one of sodium hydroxide, potassium hydroxide or lithium hydroxide.
8. The method for preparing graphene by microwave puffing according to claim 1, wherein the method comprises the following steps: the microwave heating power is 80-600W/g.
9. The method for preparing graphene by microwave puffing according to claim 1, wherein the method comprises the following steps: ball-milling the three-dimensional graphene powder particles obtained after microwave heating in the step 3), wherein the ball-milling speed is 300-450 rpm, and the ball-milling time is 1-3 h.
10. The method for preparing graphene by microwave puffing according to claim 1, wherein the method comprises the following steps: washing the three-dimensional graphene powder particles obtained in the step 3) by using a neutral solvent, and drying at 60-120 ℃ for 0.5-3 h.
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