A method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid

Abstract

The present invention generally relates to the production and preparation technology of graphene oxide. More specifically, the present invention relates to a method for preparing large-scale single-layer graphene oxide by using supercritical fluid technology to assist exfoliation.

Description

Technical Field

[0001] The present invention generally relates to the production and preparation technology of graphene oxide. More specifically, the present invention relates to a method for assisting the exfoliation of large-scale single-layer graphene oxide by using supercritical fluid technology. Background Art

[0002] Graphene is a two-dimensional carbon layer structure formed by connecting six-membered carbon rings, and it is a single-atom layer structure. In the structure of graphene, each carbon atom is connected to three adjacent carbon atoms, forming covalent bonds through sp2 hybridization, with a bond length of 1.42 Å and a bond energy of 345 kJ / mol, thus forming a firm hexagonal network planar structure; and the remaining one free electron forms a delocalized π bond, which can flow freely in the space between layers. The firm and stable hexagonal network planar structure determines that graphene is firm and hard, even harder than diamond, and has strong mechanical properties. The Young's modulus of graphene is 1060 GPa, and its strength is 100 times that of the best steel. Physicists at Columbia University found in the study of the mechanical properties of graphene that the ultimate strength of graphene is 42 N / m. Graphene nanoribbons exhibit semiconductor properties, and the bandgap width can be adjusted by controlling the size. Of course, some functional groups can also be bonded to graphene by chemical modification methods to regulate its conductivity, which also determines its application in the field of chemical research. At room temperature, the electron mobility in graphene can reach 15000 cm 2 / (V·s), about 140 times that of the carrier mobility in semiconductor silicon, thus showing its excellent conductivity. Considering the relatively high theoretical specific surface area of graphene (2600 m 2 / g), graphene is very suitable as an energy storage material, such as for the preparation of supercapacitors, batteries, integrated circuits, etc. In addition, graphene also has excellent thermal conductivity, with a thermal conductivity of 5000 W / (m·K), which is three times that of diamond and ten times that of copper. Since graphene is a single-atom layer material, it has good light transmittance, and the visible light transmittance is 97.7%, that is to say, it only absorbs 2.3% of visible light. However, the increase in the number of graphene layers will lead to a decrease in its light transmittance, and thus its light transmittance can be regulated. Therefore, graphene is a transparent conductive thin film material with excellent conditions in all aspects. Compared with traditional transparent conductive thin film materials (such as indium tin oxide and fluorine-doped tin oxide), it has high strength and is easy to prepare, and can be used as a substitute for the preparation of solar cells and liquid crystal devices.

[0003] Since the discovery of graphene, graphene oxide has received great attention as a precursor for preparing graphene by solution methods. The earliest preparation of graphene oxide can be traced back to 1859. At that time, the British chemist Brodie used potassium chlorate and concentrated nitric acid as strong oxidants to oxidize graphite, obtaining graphite oxide and finding that this graphite oxide could be well dispersed in pure water or alkaline water, but not in acidic water. Subsequently, researchers improved the Brodie method by adding concentrated sulfuric acid and finally obtained an oxide with a C / O ratio of 2. Currently, the commonly used method for preparing graphene oxide was explored by Hummers and Offeman, known as the Hummers method or the modified Hummers method, which uses concentrated sulfuric acid and potassium permanganate as the main oxidants for oxidation. The chemical structure of graphene oxide is amorphous, and the oxidation reaction has a non-stoichiometric property, so it is impossible to accurately determine the exact chemical structure of the obtained graphene oxide. According to the research on graphene oxide (GO), it is considered that each graphene oxide sheet has a multiple functional group network structure added to the carbon skeleton. In the Lerf-Klinowski (LK) model, it is believed that there are two different structural regions randomly distributed in graphene oxide: one is a pure graphene region composed of sp2 hybridized carbon atoms, and the other is a region composed of oxidized functional groups and sp3 hybridized carbon atoms. The oxidized region mainly includes epoxy and hydroxyl functional groups, as well as carboxyl and hydroxyl groups at the edge positions. As an important derivative of graphene-based materials, although the oxidation process destroys the highly conjugated structure of graphene, it still retains special surface properties and a layered structure. The introduction of oxygen-containing groups not only endows graphene oxide with chemical stability but also provides surface modification active sites and a large specific surface area for the synthesis of graphene-based / graphene oxide-based materials. Graphene oxide, as a precursor and support carrier for synthesizing graphene-based composite materials, has natural advantages in the fields of interfacial chemistry and materials science. Graphene oxide also exhibits excellent physical, chemical, optical, and electrical properties. And due to the coexistence of various oxygen-containing functional groups on the basal plane and edge of the graphene sheet skeleton, graphene oxide can modulate its conductivity and bandgap by controlling the type and quantity of the contained oxygen-containing functional groups. This material has a wide range of applications. For example, graphene oxide can be either hydrophilic or hydrophobic, so it is an effective two-dimensional amphiphilic substance. Based on the molecular structure and morphology of graphene oxide, graphene oxide can be regarded as a new type of flexible two-dimensional material. In addition, besides the field of flexible sensors, it has important application values in the fields of optoelectronics, solar cells, and bioengineering materials.

[0004] There are mainly three common methods for preparing graphene oxide: Brodie method, Staudenmaier method and Hummers method. Among them, the Hummers method has relatively good timeliness in the preparation process and is also relatively safe during the preparation process. It is the most commonly used method. The specific method steps are as follows: First, concentrated sulfuric acid is used to enter the graphite sheet layer to form an intercalation compound, and then strong oxidants such as permanganate ions or nitrate ions are used to enter the intercalation for oxidation. Finally, after washing it with sufficient water, due to the formation of many oxygen-containing functional groups on the sheet layer, especially many hydrophilic functional groups, graphene oxide can be easily exfoliated under the action of external forces such as ultrasonic waves, and finally single-layer or multi-layer graphene oxide is obtained. However, this preparation process has the following disadvantages: large consumption of strong oxidants such as concentrated sulfuric acid; a large amount of waste acid and waste water will be generated during the preparation process; the preparation process is relatively complex, and the complete preparation cycle usually takes more than 48 hours; the product quality is uneven; the yield of single-layer graphene oxide is low.

[0005] CN108706581A discloses a method for preparing graphene oxide assisted by supercritical fluid, which includes placing a mixture containing graphite raw material, acid and oxidant in a sealed reactor; injecting supercritical fluid into the mixture to reach the supercritical state, and performing an oxidation intercalation reaction to obtain a first reaction mixture system; controlling the temperature of the first reaction mixture system, adding deionized water, and reducing the pressure in the sealed reactor to normal pressure, and then performing a hydrolysis reaction to obtain a second reaction mixture system; adding hydrogen peroxide to the second reaction mixture system until the obtained reaction mixture is bright yellow, thereby obtaining graphene oxide. However, this method cannot obtain single-layer graphene oxide.

[0006] US10781105B2 provides a method for synthesizing graphene oxide, including: oxidizing ground graphite with sulfuric acid and at least one oxidant in a supercritical fluid medium, wherein the method includes providing a mixture of sulfuric acid and dry ice, the amount of dry ice being sufficient to solidify the mixture, and a mixture of at least one oxidant and dry ice, wherein at least one of the mixtures contains ground graphite; introducing the provided mixture into a high-pressure autoclave at high pressure; and further mixing the reagents. However, the graphene oxide obtained by this method has a relatively thick thickness and a small area.

[0007] With the development of terminal applications, the market demand for large-scale single-layer graphene oxide is becoming increasingly strong. Therefore, the market urgently needs a preparation process for large-scale batch production of high-quality large-scale single-layer graphene oxide to overcome the disadvantages existing in the above-mentioned prior art. Summary of the Invention

[0008] The object of the present invention is to provide a method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid to overcome the disadvantages and deficiencies existing in the above-mentioned prior art.

[0009] The object of the present invention is also to meet the demand for the continuous development of graphite oxide preparation technology towards high quality, large scale and high single-layer rate.

[0010] The inventors of the present invention surprisingly found that the above object of the present invention can be achieved by the method described and claimed below and the graphene oxide prepared thereby.

[0011] The present invention utilizes supercritical fluid-assisted intercalation oxidation technology to provide a novel method for preparing graphene oxide.

[0012] Specifically, the present invention provides a method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid, including the following steps, preferably consisting of the following steps:

[0013] 1) Graphite and an oxidant are ground and then fully mixed to form a graphite-oxidant mixture;

[0014] 2) The graphite-oxidant mixture formed in step 1) is subjected to supercritical treatment;

[0015] 3) The product obtained in step 2) is subjected to ultrasonic-assisted exfoliation treatment to obtain graphene oxide;

[0016] 4) The graphene oxide obtained in step 3) and a solid acid catalyst are fully mixed, and then the graphene oxide-solid acid catalyst mixture is vacuum-dried in a reaction kettle under high temperature conditions to obtain self-crosslinked graphene oxide;

[0017] 5) The self-crosslinked graphene oxide obtained in step 4) and an oxidant are fully mixed to form a self-crosslinked graphene oxide-oxidant mixture;

[0018] 6) The self-crosslinked graphite oxidant mixture formed in step 5) is subjected to supercritical treatment;

[0019] 7) The product obtained in step 6) is subjected to ultrasonic-assisted exfoliation treatment to obtain large-scale single-layer graphene oxide.

[0020] In some embodiments of the present invention, the supercritical treatment in step 2) includes the following steps, preferably consisting of the following steps:

[0021] a) Under a low-temperature environment, an acid is mixed with a low-temperature supercritical medium to form a strongly acidic supercritical medium;

[0022] b) The graphite-oxidant mixture obtained in step 1) and the strongly acidic supercritical medium obtained in step a) are mixed and added to a closed high-pressure reaction kettle;

[0023] c) Heat and pressurize the reaction kettle, and carry out supercritical fluid-assisted intercalation oxidation graphene reaction on the graphite mixture in the reaction kettle.

[0024] In some embodiments of the present invention, the specific reaction process in step 4) is as follows:

[0025]

[0026] where is a simplified structural schematic diagram of graphene oxide;

[0027] The solid acid catalyst includes SnO, rare earth oxides (such as Sm2O3 or Nd2O3), or a combination thereof, preferably SnO;

[0028] The mass ratio of graphene oxide to solid acid catalyst in the graphene oxide and solid acid catalyst mixture is 1:0.0003 - 1:0.006, preferably 1:0.0005 - 1:0.005, more preferably 1:0.0008 - 1:0.004;

[0029] The self-crosslinking reaction temperature of the graphene oxide and solid acid catalyst mixture in the reaction kettle is 90 - 200 °C, preferably 100 °C - 180 °C, more preferably 110 °C - 160 °C;

[0030] The vacuum drying time of the graphene oxide and solid acid catalyst mixture in the reaction kettle is 1 - 9 hours, preferably 2 hours - 8 hours, more preferably 2.5 hours - 7 hours;

[0031] The vacuum drying means that the vacuum degree is <200 Pa, preferably <160 Pa, more preferably <140 Pa.

[0032] In one embodiment of the present invention, the supercritical treatment in step 6) includes the following steps, preferably consisting of the following steps:

[0033] d) Mix the self-crosslinked graphene oxide oxidant mixture obtained in step 5) above and the strongly acidic supercritical medium obtained in step 2) and add them to a closed high-pressure reaction kettle;

[0034] e) Heat and pressurize the reaction kettle, and carry out supercritical fluid-assisted secondary intercalation oxidation graphene reaction on the mixture in the reaction kettle.

[0035] In the preferred embodiment of the present invention, the graphite includes but is not limited to expandable graphite, natural flake graphite or artificially prepared highly oriented graphite, or a combination thereof, preferably natural flake graphite or artificially prepared highly oriented graphite, or a combination thereof.

[0036] In a preferred embodiment of the present invention, the oxidants used in each step include, but are not limited to, hydrogen peroxide, peroxides (such as alkali metal peroxides, preferably sodium peroxide, etc.), permanganates, dichromates, perchlorates, or combinations thereof, preferably potassium / sodium permanganate, potassium / sodium dichromate, or potassium / sodium perchlorate, or combinations thereof.

[0037] In a preferred embodiment of the present invention, the mass ratio of graphite to oxidant in the graphite oxidant mixture in step 1) is 1:0.5 - 1:6, preferably 1:1 - 1:5, more preferably 1:1.5 - 1:4.5.

[0038] In a preferred embodiment of the present invention, the mass ratio of self-crosslinked graphene oxide to oxidant in the self-crosslinked graphene oxide oxidant mixture in step 5) is 4:1 - 1:4, preferably 3:1 - 1:3, more preferably 2.8:1 - 1:2.8.

[0039] In a preferred embodiment of the present invention, the mass ratio of acid to supercritical medium in the strongly acidic supercritical medium in step a) is 1:0.5 - 1:4, preferably 1:1 - 1:3, more preferably 1:1.2 - 1:2.5. In a preferred embodiment of the present invention, the acid in step a) includes concentrated acids, and the concentrated acids include, but are not limited to, concentrated sulfuric acid, concentrated nitric acid, or combinations thereof, preferably selected from concentrated sulfuric acid.

[0040] In a preferred embodiment of the present invention, the molar concentration of concentrated sulfuric acid ≥ 16 mol / L, preferably ≥ 16.6 mol / L, more preferably the molar concentration is about 18.4 mol / L.

[0041] In a preferred embodiment of the present invention, the molar concentration of concentrated nitric acid ≥ 13 mol / L, preferably ≥ 14 mol / L, more preferably the molar concentration is about 16 mol / L.

[0042] In a preferred embodiment of the present invention, the low temperature in step a) should be lower than the melting point or boiling point of the supercritical medium. For example, it can cause carbon dioxide to form dry ice or nitrogen to form liquid nitrogen to facilitate mixing with strong acids (such as concentrated sulfuric acid).

[0043] In a preferred embodiment of the present invention, the low temperature in step a) needs to ensure that it is lower than the melting point or boiling point of the supercritical medium, making the supercritical medium a liquid or a solid.

[0044] In a preferred embodiment of the present invention, the supercritical media used in each step include carbon dioxide, ethanol, methane, ethane, propane, n-pentane, chloroform, ammonia, nitrogen, or combinations thereof, preferably dry ice or liquid nitrogen.

[0045] In a preferred embodiment of the present invention, the above steps c) and e) are carried out under the condition of rotational oscillation in a closed high-pressure reactor.

[0046] In a preferred embodiment of the present invention, the temperatures in steps c) and e) are independently 30 - 70 °C, preferably 32 - 60 °C, and more preferably 33 - 55 °C.

[0047] In a preferred embodiment of the present invention, the pressures in steps c) and e) are independently 1 MPa - 50 MPa, preferably 2 MPa - 45 MPa, and more preferably 5 MPa - 42 MPa.

[0048] In a preferred embodiment of the present invention, the reaction times of the supercritical fluid-assisted intercalation of graphene oxide in step c) or the supercritical fluid-assisted secondary intercalation of graphene oxide in step e) are independently 0.5 - 5 hours, preferably 1 - 4 hours, and more preferably 1.3 - 3.5 hours.

[0049] In a preferred embodiment of the present invention, the mass ratio of the graphite oxidant mixture to the strongly acidic supercritical medium in step b) is 1:1 - 1:6, preferably 1:2 - 1:5, and more preferably 1:2.5 - 1:4.5.

[0050] In a preferred embodiment of the present invention, the rotation speed of the closed high-pressure reactor in steps c) and e) is 6 - 60 rpm, preferably 8 - 50 rpm, and more preferably 9 - 45 rpm.

[0051] In a preferred embodiment of the present invention, the mass ratio of the self-crosslinking graphene oxide oxidant mixture to the strongly acidic supercritical medium in step d) is 1:1 - 1:8, preferably 1:1.5 - 1:7, and more preferably 1:1.5 - 1:6.5.

[0052] In a preferred embodiment of the present invention, the ultrasonic-assisted exfoliation treatment in steps 3) and 6) is a treatment method well-known to those skilled in the art. For example, the reaction product is dissolved in deionized water and stirred well to disperse it, and the dispersion is ultrasonically treated in a water bath with a 100 W - 300 W ultrasonic source for 10 - 20 min. After dialysis of the suspension, drying is completed to finish the treatment.

[0053] In a preferred embodiment of the present invention, the method for supercritical fluid-assisted preparation of large-scale single-layer graphene oxide sequentially includes the following steps:

[0054] 1) Grind and thoroughly mix graphite and an oxidant to form a graphite oxidant mixture;

[0055] 2) Mix concentrated sulfuric acid with a low-temperature supercritical medium to form a strongly acidic supercritical medium under a low-temperature environment;

[0056] 3) Mix the graphite oxidant mixture obtained in step 1) and the strongly acidic supercritical medium obtained in step 2) and add them to a closed high-pressure reactor;

[0057] 4) Under the condition of rotational oscillation of the closed high-pressure reactor, heat and pressurize the reactor. The temperature is 30 - 70 °C, and the pressure is 1 MPa - 50 MPa. The graphite mixture in the reactor undergoes a supercritical fluid-assisted intercalation oxidation of graphene reaction, and the reaction lasts for 0.5 - 5 hours;

[0058] 5) Perform ultrasonic-assisted exfoliation treatment on the product obtained in step 4) to obtain graphene oxide;

[0059] 6) After fully mixing the graphene oxide obtained in step 5) and SnO, the graphene oxide and SnO mixture is in the reactor, and under the condition of a vacuum degree < 133 Pa at 90 - 200 °C, vacuum dry for 1 - 9 hours to obtain self-crosslinked graphene oxide;

[0060] 7) Fully mix the self-crosslinked graphene oxide obtained in step 6) and the oxidant to form a self-crosslinked graphene oxide oxidant mixture;

[0061] 8) Mix the self-crosslinked graphene oxide oxidant mixture obtained in step 7) and the strongly acidic supercritical medium obtained in step 2) and add them to a closed high-pressure reactor;

[0062] 9) Under the condition of rotational oscillation of the closed high-pressure reactor, heat and pressurize the reactor. The temperature is 30 - 70 °C, and the pressure is 1 MPa - 50 MPa. The graphite mixture in the reactor undergoes a supercritical fluid-assisted secondary intercalation oxidation of graphene reaction, and the reaction lasts for 0.5 - 5 hours;

[0063] 10) Perform ultrasonic-assisted exfoliation treatment on the product obtained in step 9), and large-scale single-layer graphene oxide is obtained.

[0064] Among them, the graphite in step 1) is natural flake graphite, highly oriented graphite, or expandable graphite.

[0065] The oxidants in step 1) and step 7) are potassium permanganate / sodium, potassium dichromate, or sodium peroxide.

[0066] The mass ratio of graphite to oxidant in the graphite oxidant mixture in step 1) is 1:0.5 - 1:6.

[0067] The molar concentration of the concentrated sulfuric acid in step 2) is about 18.4 mol / L.

[0068] The low-temperature supercritical medium in step 2) is dry ice or liquid nitrogen.

[0069] In step 2), the mass ratio of concentrated sulfuric acid to supercritical medium in the strongly acidic supercritical medium is 1:0.5 - 1:4.

[0070] In step 3), the mass ratio of the graphite oxidant mixture to the strongly acidic supercritical medium is 1:1 - 1:6.

[0071] In step 4), the rotation speed of the closed high-pressure reactor is 6 - 60 rpm.

[0072] In step 6), the mass ratio of graphene oxide to SnO in the graphene oxide and SnO mixture is 1:0.0003 - 1:0.006.

[0073] In step 7), the mass ratio of self-crosslinked graphene oxide to the oxidant in the self-crosslinked graphene oxide oxidant mixture is 4:1 - 1:4.

[0074] In step 8), the mass ratio of the self-crosslinked graphene oxide oxidant mixture to the strongly acidic supercritical medium is 1:1 - 1:8.

[0075] The ultrasonic-assisted exfoliation treatment in steps 5) and 10) is a treatment method well-known to those skilled in the art. For example, the reaction product is dissolved in deionized water and stirred thoroughly to disperse it. The dispersion is ultrasonically treated in a water bath with a 100W - 300W ultrasonic source for 10 - 20 min. The suspension is dried after dialysis to complete the treatment.

[0076] In a particularly preferred embodiment of the present invention, the method for supercritical carbon dioxide-assisted preparation of large-scale single-layer graphene oxide comprises the following steps:

[0077] 1) Thoroughly mix natural flake graphite and potassium permanganate after grinding to form a graphite oxidant mixture;

[0078] 2) At low temperature, grind and mix concentrated sulfuric acid with dry ice to form a strongly acidic supercritical medium;

[0079] 3) Mix the graphite oxidant mixture obtained in step 1) above and the strongly acidic supercritical medium obtained in step 2) and add them to a closed high-pressure reactor;

[0080] 4) Under the condition of rotation and oscillation of the closed high-pressure reactor, heat and pressurize the reactor. The temperature is 40 - 50 °C and the pressure is 15 - 25 MPa. The graphite mixture in the reactor undergoes a supercritical fluid-assisted intercalation oxidation graphene reaction for 2 - 4 hours;

[0081] 5) Perform ultrasonic-assisted exfoliation treatment on the product obtained in step 4) to obtain graphene oxide;

[0082] 6) After thoroughly mixing the graphene oxide and SnO obtained in step 5), the mixture of graphene oxide and SnO is vacuum-dried in a reaction kettle at 130 - 150 °C under a vacuum of <110 Pa for 4 - 6 hours to obtain self-crosslinked graphene oxide;

[0083] 7) Thoroughly mix the self-crosslinked graphene oxide obtained in step 6) and potassium permanganate to form a self-crosslinked graphene oxide oxidant mixture;

[0084] 8) Add the self-crosslinked graphene oxide oxidant mixture obtained in step 7) and the strongly acidic supercritical medium obtained in step 2) to a closed high-pressure reaction kettle;

[0085] 9) Under the condition of rotational oscillation of the closed high-pressure reaction kettle, heat and pressurize the reaction kettle. The temperature is 30 - 40 °C and the pressure is 15 - 25 MPa. The graphite mixture in the reaction kettle undergoes a supercritical fluid-assisted secondary intercalation graphene oxide reaction for 2 - 4 hours;

[0086] 10) Perform ultrasonic-assisted peeling treatment on the product obtained in step 9) to obtain single-layer graphene oxide with a size larger than 50x50 μm.

[0087] In step 1), the mass ratio of graphite to oxidant in the graphite oxidant mixture is 1:3 to 1:4.

[0088] In step 2), the molar concentration of the concentrated sulfuric acid is approximately 18.4 mol / L.

[0089] In step 2), the mass ratio of concentrated sulfuric acid to supercritical medium in the strongly acidic supercritical medium is 1:1.5 to 1:2.5.

[0090] In step 3), the mass ratio of the graphite oxidant mixture to the strongly acidic supercritical medium is 1:2 to 1:4.

[0091] In step 4), the rotational speed of the closed high-pressure reaction kettle is 8 - 12 rpm.

[0092] In step 6), the mass ratio of graphene oxide to SnO in the mixture of graphene oxide and SnO is 1:0.001 to 1:0.003.

[0093] In step 7), the mass ratio of graphene oxide to oxidant in the self-crosslinked graphene oxide oxidant mixture is 1:1 to 1:2.

[0094] In step 8), the mass ratio of the self-crosslinked graphene oxide oxidant mixture to the strongly acidic supercritical medium is 1:2 to 1:4.

[0095] The ultrasonic-assisted exfoliation treatment described in step 5) and step 10) is specifically as follows: The reaction product is dissolved in deionized water and stirred well to disperse. The dispersion is ultrasonically treated with an ultrasonic source in a bath. After dialysis of the suspension, drying is carried out to complete the treatment.

[0096] The graphene oxide prepared according to the above preferred and particularly preferred embodiments can achieve a high monolayer ratio (e.g., 90%), and can make the area of a single graphene sheet larger than 50×50 μm 2 .

[0097] In another aspect of the present invention, there is provided a large-scale single-layer graphene oxide prepared by the preparation method as described in the context. The graphene oxide prepared by the method for supercritical fluid-assisted preparation of large-scale single-layer graphene oxide of the present invention is detected to have an average thickness of about 0.75 - about 1.075 nm, and the area of a single graphene sheet can be larger than 15×15 μm 2 , preferably larger than 20×20 μm 2 , preferably larger than 30×30 μm 2 , even more preferably larger than 50×50 μm 2 .

[0098] Unless otherwise stated, the above embodiments of the present invention can be combined with each other.

[0099] Advantages of the present invention

[0100] The beneficial effect of the present invention is that the present invention utilizes secondary supercritical fluid-assisted intercalation and self-crosslinking technology. Compared with the existing method of preparing graphene using supercritical media, the present invention has the advantages of high monolayer rate (monolayer rate above 90%) and large scale of single-sheet graphene oxide sheets, and therefore has greater application value. For example, single-layer graphene is superior to multilayer graphene in conductivity, antibacterial and lubrication, while larger-scale single-sheet graphene oxide has better application value in the biomedical field and other fields. For example, the literature (Chen Xiaojie, He Xing, Han Zhuo. Research progress on size classification and cytotoxicity of graphene oxide [J]. Nonferrous Metal Materials and Engineering, 2021, 42(6): 48-54) states that small-sized graphene oxide shows higher toxicity at low concentrations of 10 to 20 μg / mL, while large-sized graphene oxide shows higher toxicity at higher concentrations. It is generally believed that small-sized GO exhibits stronger cytotoxicity than large-sized GO. In antibacterial experiments, large-sized graphene oxide can better cover the surface of E. coli cells, resulting in the isolation of cells from the culture medium, and then the cells cannot absorb sufficient nutrients from the culture medium and cannot proliferate, thereby achieving the purpose of sterilization. Therefore, large-sized GO has better bactericidal performance. In addition, as described in the literature (Zhang, P., He, P., Zhao, Y., Yang, S., Yu, Q., Xie, X., Ding, G., Oxidating Fresh Porous Graphene Networks toward Ultra-Large Graphene Oxide with Electrical Conductivity. Adv. Funct. Mater. 2022, 2202697.): Large-sized high-quality graphene has good water-phase dispersibility and can be assembled to form a layered macroscopic membrane. Unlike the insulating traditional graphene oxide film, the large-sized, high-quality graphene macroscopic film exhibits good conductivity without reduction treatment. Compared with the small-sized graphene oxide, the macroscopic film constructed by large-sized, high-quality graphene has excellent mechanical properties. More importantly, large-sized, high-quality graphene shows obvious advantages in constructing graphene thermal conductive thick films. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] The invention is explained in more detail below by way of example using exemplary embodiments with reference to the accompanying drawings.

[0102] Figure 1 It is a schematic flow diagram of a method for preparing a large-scale monolayer graphene oxide with the assistance of a supercritical fluid according to the present invention;

[0103] Figure 2 is a scanning electron microscope (SEM) image of a graphene oxide sample prepared according to Example 1 of the present invention;

[0104] Figure 3 It is a scanning electron microscope (SEM) image of a graphene oxide sample prepared according to Example 2 of the present invention;

[0105] Figure 4 It is a scanning electron microscope (SEM) image of a graphene oxide sample prepared according to Example 3 of the present invention;

[0106] Figure 5 It is a scanning electron microscope (SEM) image of a graphene oxide sample prepared according to Example 4 of the present invention;

[0107] Figure 6 It is a scanning electron microscope (SEM) image of a graphene oxide sample prepared by the improved Hummers method (Comparative Example 1). The improved Hummers method refers to the following literature: Marcano D C, Kosynkin D V, Berlin J M, et al., Improved synthesis of graphene oxide. [J]. Acs Nano, 2010, 4(8): 4806, which is incorporated herein by reference in its entirety;

[0108] Figure 7 It is a scanning electron microscope (SEM) image of a graphene oxide sample prepared by the method of preparing graphene oxide with supercritical carbon dioxide (Comparative Example 2). The method of preparing graphene oxide with supercritical carbon dioxide refers to the patent: US10781105B2, which is incorporated herein by reference in its entirety;

[0109] Figure 8 It is a scanning electron microscope (SEM) image of a graphene oxide sample prepared by the method of preparing graphene oxide by supercritical fluid-assisted intercalation (Comparative Example 3). The method of preparing graphene by supercritical fluid-assisted intercalation refers to the patent application: CN108706581A, which is incorporated herein by reference in its entirety. Detailed implementation manners

[0110] For the purposes of the present invention, it should be understood that, unless explicitly stated to the contrary, the present invention may adopt various alternative variations and step sequences. In addition, except in any operating examples or otherwise indicated, all numerical values representing the amounts of ingredients used in the specification and claims should be understood to be modified in all cases by the term "about". Therefore, unless stated to the contrary, the numerical parameters set forth in the following specification and appended claims are approximations, which may vary depending on the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in accordance with the number of significant digits reported and by applying ordinary rounding techniques.

[0111] Although the numerical ranges and parameters setting forth the broad scope of the present invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0112] In addition, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10.

[0113] As used in the specification and the appended claims, the articles "a", "an", and "the" include plural referents unless expressly and unambiguously limited to one referent.

[0114] As used herein, the transitional term "comprising" (and other comparable terms such as "containing" and "including") is "open-ended" and is used to refer to a composition, method, and its respective essential component(s) (one or more), but still allows for the possibility of the presence of substances not specified.

[0115] In addition, unless specifically stated otherwise, the use of "or" means "and / or".

[0116] Embodiments of the present invention will be described in detail below by way of examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and not for limiting the scope of the present invention. Various objects and advantageous aspects of the present invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments. Unless otherwise specified, all parts and percentages throughout the examples and the entire specification are by weight.

[0117] Example 1: Preparation of large-scale single-layer graphene oxide assisted by supercritical carbon dioxide.

[0118] A method for preparing large-scale single-layer graphene oxide assisted by supercritical carbon dioxide, comprising the following steps:

[0119] 1) Grind and thoroughly mix natural flake graphite (purchased from Sigma-Aldrich, product number: 808091) and potassium permanganate to form a graphite oxidant mixture;

[0120] 2) At a low temperature environment of -79 °C, grind and mix concentrated sulfuric acid and dry ice to form a strongly acidic supercritical medium;

[0121] 3) mixing the graphite oxidant mixture obtained in step 1) and the strongly acidic supercritical medium obtained in step 2) and adding them into a closed high-pressure reactor;

[0122] 4) Under the condition of rotating and shaking in a closed high-pressure reactor, the reactor is heated and pressurized to a temperature of 50° C. and a pressure of 8 MPa, and the graphite mixture in the reactor undergoes a supercritical fluid-assisted intercalation graphene oxide reaction, and the reaction lasts for 1.5 hours;

[0123] 5) subjecting the product obtained in step 4) to ultrasonic-assisted exfoliation to obtain graphene oxide;

[0124] 6) After the graphene oxide obtained in step 5) is fully mixed with SnO, the mixture of graphene oxide and SnO is vacuum dried in a reactor at 150° C. for 3 hours under the condition of maintaining a vacuum degree of <133 Pa to obtain self-crosslinked graphene oxide;

[0125] 7) fully mixing the self-crosslinked graphene oxide obtained in step 6) with potassium permanganate to form a self-crosslinked graphene oxide oxidant mixture;

[0126] 8) mixing the self-crosslinked graphene oxide oxidant mixture obtained in step 7) and the strongly acidic supercritical medium obtained in step 2) into a closed high-pressure reactor;

[0127] 9) Under the condition of rotating and shaking in a closed high-pressure reactor, the reactor is heated and pressurized to a temperature of 50° C. and a pressure of 8 MPa, and the graphite mixture in the reactor is subjected to a supercritical fluid-assisted secondary intercalation graphene oxide reaction, and the reaction lasts for 2 hours;

[0128] 10) The product obtained in step 9) is subjected to ultrasonic-assisted exfoliation treatment to obtain a large-scale single-layer graphene oxide.

[0129] In step 1), the mass ratio of graphite to oxidant in the graphite-oxidant mixture is 1:3.

[0130] Step 2) The molar concentration of the concentrated sulfuric acid is 18.4 mol / L.

[0131] Step 2) The mass ratio of concentrated sulfuric acid in the strongly acidic supercritical medium to supercritical medium is 1:1.5.

[0132] Step 3) The mass ratio of the graphite oxidant mixture to the strongly acidic supercritical medium is 1:3.

[0133] Step 4) The closed high-pressure reactor rotates at a speed of 12 rpm.

[0134] Step 6) The mass ratio of graphene oxide to SnO in the mixture of graphene oxide and SnO is 1:0.002.

[0135] Step 7) The mass ratio of graphene oxide to oxidant in the self-crosslinking graphene oxide oxidant mixture is 2.5:1.

[0136] Step 8) The mass ratio of the self-crosslinking graphene oxide oxidant mixture to the strongly acidic supercritical medium is 1:2.

[0137] The ultrasonic assisted exfoliation treatment in step 5) and step 10) is specifically to dissolve the reaction product in deionized water and fully stir and disperse it, ultrasonically treat the dispersion in a bath with a 100W ultrasonic source for 20 minutes, and the suspension is dialyzed and then dried to complete the treatment.

[0138] The graphene oxide prepared by the method for preparing large-scale single-layer graphene oxide assisted by supercritical carbon dioxide is tested to have an average thickness of about 0.8nm, a single-layer rate of more than 95%, and an area of ​​a single graphene sheet greater than 15×15μm 2 .

[0139] Example 2: Supercritical nitrogen assisted preparation of large-scale monolayer graphene oxide.

[0140] A method for preparing large-scale single-layer graphene oxide with the assistance of supercritical nitrogen comprises the following steps:

[0141] 1) grinding high-oriented graphite and potassium dichromate and fully mixing them to form a graphite oxidant mixture;

[0142] 2) In a Dewar vessel, concentrated nitric acid and liquid nitrogen are mixed at -196°C to form a strongly acidic supercritical medium;

[0143] 3) mixing the graphite oxidant mixture obtained in step 1) and the strongly acidic supercritical medium obtained in step 2) and adding them into a closed high-pressure reactor;

[0144] 4) Under the condition of rotating and shaking in a closed high-pressure reactor, the reactor is heated and pressurized to a temperature of 35° C. and a pressure of 40 MPa, and the graphite mixture in the reactor undergoes a supercritical fluid-assisted intercalation graphene oxide reaction, and the reaction lasts for 3 hours;

[0145] 5) subjecting the product obtained in step 4) to ultrasonic-assisted exfoliation to obtain graphene oxide;

[0146] 6) After the graphene oxide obtained in step 5) and Sm2O3 are fully mixed, the mixture of graphene oxide and Sm2O3 is vacuum dried in a reactor at 120° C. and maintained at a vacuum degree of <133 Pa for 6 hours to obtain self-crosslinked graphene oxide;

[0147] 7) fully mixing the self-crosslinked graphene oxide obtained in step 6) with sodium peroxide to form a graphene oxide oxidant mixture;

[0148] 8) Mix the self-crosslinked graphene oxide oxidant mixture obtained in step 7) and the strongly acidic supercritical medium obtained in step 2) and add them to a closed high-pressure reaction kettle.

[0149] 9) Under the condition of rotational oscillation of the closed high-pressure reaction kettle, heat and pressurize the reaction kettle. The temperature is 35 °C and the pressure is 40 MPa. Perform a supercritical fluid-assisted secondary intercalation graphene oxide reaction on the graphite mixture in the reaction kettle, and the reaction lasts for 1.5 hours.

[0150] 10) Perform ultrasonic-assisted exfoliation treatment on the product obtained in step 9), and large-scale single-layer graphene oxide is obtained.

[0151] The highly oriented graphite described in step 1) is a graphite material prepared according to patent application CN110451964A, and this patent application is incorporated herein by reference in its entirety.

[0152] In the graphite oxidant mixture in step 1), the mass ratio of graphite to oxidant is 1:4.

[0153] The molar concentration of the concentrated nitric acid described in step 2) is 16.0 mol / L.

[0154] In the strongly acidic supercritical medium described in step 2), the mass ratio of concentrated nitric acid to supercritical medium is 1:2.

[0155] In step 3), the mass ratio of the graphite oxidant mixture to the strongly acidic supercritical medium is 1:4.

[0156] The rotational speed of the closed high-pressure reaction kettle described in step 4) is 40 rpm.

[0157] In the graphene oxide and Sm2O3 mixture described in step 6), the mass ratio of graphene oxide to Sm2O3 is 1:0.001.

[0158] In the self-crosslinked graphene oxide oxidant mixture described in step 7), the mass ratio of graphene oxide to oxidant is 1:2.5.

[0159] In step 8), the mass ratio of the self-crosslinked graphene oxide oxidant mixture to the strongly acidic supercritical medium is 1:6.

[0160] The ultrasonic-assisted exfoliation treatment described in steps 5) and 10) is to dissolve the reaction product in deionized water and stir it evenly, perform ultrasonic treatment on the dispersion liquid in a bath with a 300 W ultrasonic source for 10 min, and the suspension is dried after dialysis to complete the treatment.

[0161] The graphene oxide prepared by the method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid of the present invention is detected to have an average thickness of about 1.0 nm, a single-layer rate greater than 90%, and the area of a single graphene sheet greater than 20×20 μm 2 。

[0162] Example 3: Preparation of large-scale single-layer graphene oxide assisted by supercritical carbon dioxide.

[0163] A method for preparing large-scale single-layer graphene oxide assisted by supercritical carbon dioxide, comprising the following steps:

[0164] 1) Expandable graphite (purchased from Sigma-Aldrich, product number: 808121) and potassium permanganate are ground and fully mixed to form a graphite oxidant mixture;

[0165] 2) At a low temperature environment of -79 °C, a mixture of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 1:1 is ground and mixed with dry ice to form a strongly acidic supercritical medium;

[0166] 3) The graphite oxidant mixture obtained in step 1) and the strongly acidic supercritical medium obtained in step 2) are mixed and added to a closed high-pressure reaction kettle;

[0167] 4) Under the condition of rotational oscillation of the closed high-pressure reaction kettle, the reaction kettle is heated and pressurized, the temperature is 40 °C, the pressure is 8 MPa, and the graphite mixture in the reaction kettle undergoes a supercritical fluid-assisted intercalation oxidation of graphene reaction for 3 hours;

[0168] 5) The product obtained in step 4) is subjected to ultrasonic-assisted peeling treatment to obtain graphene oxide;

[0169] 6) After the graphene oxide obtained in step 5) and SnO are fully mixed, the mixture of graphene oxide and SnO is vacuum-dried in the reaction kettle at 130 °C under a vacuum degree of <120 Pa for 6 hours to obtain self-crosslinked graphene oxide;

[0170] 7) The self-crosslinked graphene oxide obtained in step 6) and sodium permanganate are fully mixed to form a self-crosslinked graphene oxide oxidant mixture;

[0171] 8) The self-crosslinked graphene oxide oxidant mixture obtained in step 7) and the strongly acidic supercritical medium obtained in step 2) are mixed and added to a closed high-pressure reaction kettle;

[0172] 9) Under the condition of rotational oscillation of the closed high-pressure reaction kettle, the reaction kettle is heated and pressurized, the temperature is 35 °C, the pressure is 10 MPa, and the graphite mixture in the reaction kettle undergoes a supercritical fluid-assisted secondary intercalation oxidation of graphene reaction for 2 hours;

[0173] 10) The product obtained in step 9) is subjected to ultrasonic assisted exfoliation treatment to obtain a single layer of graphene oxide having a size greater than 20×20 μm.

[0174] Step 1) The graphite-oxidant mixture has a graphite:oxidant mass ratio of 1:4.

[0175] Step 2) The molar concentration of the concentrated sulfuric acid is 18.4 mol / L, and the molar concentration of the concentrated nitric acid is 16.0 mol / L.

[0176] Step 2) The mass ratio of the mixture of concentrated sulfuric acid and concentrated nitric acid of the strongly acidic supercritical medium to the supercritical medium is 1:2.

[0177] Step 3) The mass ratio of the graphite oxidant mixture to the strongly acidic supercritical medium is 1:3.

[0178] Step 4) The closed high-pressure reactor rotates at a speed of 10 rpm.

[0179] Step 6) The mass ratio of graphene oxide to SnO in the mixture of graphene oxide and SnO is 1:0.003.

[0180] Step 7) The self-crosslinking graphene oxide:oxidant mass ratio of the self-crosslinking graphene oxide to the oxidant mixture is 1:1.

[0181] Step 8) The mass ratio of the self-crosslinking graphene oxide oxidant mixture to the strongly acidic supercritical medium is 1:3.

[0182] The ultrasonic assisted exfoliation treatment in step 5) and step 10) is specifically to dissolve the reaction product in deionized water and fully stir and disperse it, ultrasonically treat the dispersion in a bath with a 200W ultrasonic source for 20 minutes, and the suspension is dialyzed and then dried to complete the treatment.

[0183] The graphene oxide prepared by the method of supercritical carbon dioxide assisted preparation of large-scale single-layer graphene oxide has been tested to have an average thickness of about 1.0nm, a single-layer rate of more than 90%, and an area of ​​a single graphene sheet greater than 30×30μm 2 .

[0184] Example 4: Supercritical carbon dioxide assisted preparation of large-scale single-layer graphene oxide.

[0185] A method for preparing large-scale single-layer graphene oxide with the assistance of supercritical carbon dioxide comprises the following steps:

[0186] 1) grinding natural flake graphite (purchased from Sigma-Aldrich, product number: 808067) and potassium permanganate and mixing them thoroughly to form a graphite oxidant mixture;

[0187] 2) At a low temperature environment of -79 °C, concentrated sulfuric acid and dry ice are ground and mixed to form a strongly acidic supercritical medium;

[0188] 3) The graphite oxidant mixture obtained in the above step 1) and the strongly acidic supercritical medium obtained in step 2) are mixed and added to a closed high-pressure reactor;

[0189] 4) Under the condition of rotational oscillation of the closed high-pressure reactor, the reactor is heated and pressurized. The temperature is 45 °C and the pressure is 20 MPa. The graphite mixture in the reactor undergoes a supercritical fluid-assisted intercalation oxidation of graphene reaction for 3 hours;

[0190] 5) The product obtained in step 4) is subjected to ultrasonic-assisted exfoliation treatment to obtain graphene oxide;

[0191] 6) After the graphene oxide obtained in step 5) and SnO are fully mixed, the graphene oxide and SnO mixture is vacuum-dried in a reactor at 140 °C under a vacuum degree of <100 Pa for 5 hours to obtain self-crosslinked graphene oxide;

[0192] 7) The self-crosslinked graphene oxide obtained in step 6) and potassium permanganate are fully mixed to form a self-crosslinked graphene oxide oxidant mixture;

[0193] 8) The self-crosslinked graphene oxide oxidant mixture obtained in the above step 7) and the strongly acidic supercritical medium obtained in step 2) are mixed and added to a closed high-pressure reactor;

[0194] 9) Under the condition of rotational oscillation of the closed high-pressure reactor, the reactor is heated and pressurized. The temperature is 35 °C and the pressure is 20 MPa. The graphite mixture in the reactor undergoes a supercritical fluid-assisted secondary intercalation oxidation of graphene reaction for 3 hours;

[0195] 10) The product obtained in step 9) is subjected to ultrasonic-assisted exfoliation treatment to obtain single-layer graphene oxide with a size larger than 50x50 μm.

[0196] In step 1), the mass ratio of graphite to oxidant in the graphite oxidant mixture is 1:3.5.

[0197] In step 2), the molar concentration of the concentrated sulfuric acid is 18.4 mol / L.

[0198] In step 2), the mass ratio of concentrated sulfuric acid to supercritical medium in the strongly acidic supercritical medium is 1:2.

[0199] In step 3), the mass ratio of the graphite oxidant mixture to the strongly acidic supercritical medium is 1:3.

[0200] In step 4), the rotational speed of the closed high-pressure reactor is 10 rpm.

[0201] For the graphene oxide and SnO mixture described in step 6), the mass ratio of graphene oxide to SnO is 1:0.002.

[0202] For the self-crosslinked graphene oxide oxidant mixture described in step 7), the mass ratio of graphene oxide to oxidant is 1:1.5.

[0203] For the self-crosslinked graphene oxide oxidant mixture and the strongly acidic supercritical medium described in step 8), the mass ratio is 1:3.

[0204] The ultrasonic-assisted exfoliation treatment described in step 5) and step 10) is specifically as follows: the reaction product is dissolved in deionized water and stirred well to disperse, and the dispersion is ultrasonically treated in a bath with a 100W ultrasonic source for 20 min, and the suspension is dried after dialysis to complete the treatment.

[0205] The graphene oxide prepared by the method for preparing large-scale single-layer graphene oxide assisted by supercritical carbon dioxide has been detected. Its average thickness is about 1.07 nm, the single-layer rate is greater than 90%, and the area of a single graphene sheet is greater than 50×50 μm 2 。

[0206] Comparative Example 1:

[0207] Graphene oxide was prepared by the improved Hummers method. For the specific method, refer to the literature: Marcano D C, Kosynkin D V, Berlin J M, et al., Improved synthesis of graphene oxide. [J]. Acs Nano, 2010, 4(8): 4806.

[0208] Comparative Example 2

[0209] Graphene oxide was oxidized by the method described in US10781105B2.

[0210] Comparative Example 3

[0211] Graphene oxide was prepared by the method in CN108706581A.

[0212] The graphene oxide obtained in Comparative Examples 1 to 3 was respectively compared with the graphene oxide prepared in Examples 1 to 4 of the present invention. The results of the average thickness and average single sheet area are shown in Table 1 below:

[0213] Table 1: Comparison of the average thickness and average single sheet area of graphene oxide prepared by different methods

[0214]

[0215] As can be seen from the accompanying drawings of this application and Table 1 above, compared with the graphene oxide prepared according to the prior art, the graphene oxide prepared according to the embodiments of the present invention is graphene oxide with a high monolayer ratio, and a significantly larger average area of a single graphene sheet is achieved.

[0216] In addition, the present invention relates to the following non-limiting aspects:

[0217] 1. A method for supercritical fluid-assisted preparation of large-scale single-layer graphene oxide, characterized by comprising the following steps:

[0218] 1) Grind graphite and an oxidant and mix them thoroughly to form a graphite-oxidant mixture;

[0219] 2) Perform supercritical treatment on the graphite-oxidant mixture formed in step 1);

[0220] 3) Perform ultrasonic-assisted exfoliation treatment on the product obtained in step 2) to obtain graphene oxide;

[0221] 4) After thoroughly mixing the graphene oxide obtained in step 3) and a solid acid catalyst, vacuum-dry the graphene oxide and solid acid catalyst mixture in a reaction kettle under high-temperature conditions to obtain self-crosslinked graphene oxide;

[0222] 5) Thoroughly mix the self-crosslinked graphene oxide obtained in step 4) and an oxidant to form a self-crosslinked graphene oxide-oxidant mixture;

[0223] 6) Perform supercritical treatment on the self-crosslinked graphite oxidant mixture formed in step 5);

[0224] 7) Perform ultrasonic-assisted exfoliation treatment on the product obtained in step 6), and large-scale single-layer graphene oxide is obtained.

[0225] 2. The method for supercritical fluid-assisted preparation of large-scale single-layer graphene oxide according to aspect 1, characterized in that the supercritical treatment in step 2) comprises the following steps:

[0226] a) Mix an acid with a low-temperature supercritical medium to form a strongly acidic supercritical medium under a low-temperature environment;

[0227] b) Mix the graphite-oxidant mixture obtained in step 1) above and the strongly acidic supercritical medium obtained in step a) and add them to a closed high-pressure reaction kettle;

[0228] c) Heat and pressurize the reaction kettle, and the graphite mixture in the reaction kettle undergoes a supercritical fluid-assisted intercalation oxidation graphene reaction.

[0229] 3. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to aspect 1 or 2, characterized in that the reaction process in step 4) is as follows:

[0230]

[0231] where is a schematic diagram of the simplified structure of graphene oxide;

[0232] The solid acid catalyst includes SnO, rare earth oxides (such as Sm2O3 or Nd2O3), or a combination thereof, preferably SnO;

[0233] The mass ratio of graphene oxide to solid acid catalyst in the mixture of graphene oxide and solid acid catalyst is 1:0.0003 - 1:0.006, preferably 1:0.0005 - 1:0.005;

[0234] The self-crosslinking reaction temperature of the mixture of graphene oxide and solid acid catalyst in the reaction kettle is 90 - 200 °C, preferably 100 °C - 180 °C;

[0235] The vacuum drying time of the mixture of graphene oxide and solid acid catalyst in the reaction kettle is 1 - 9 hours, preferably 2 hours - 8 hours;

[0236] The vacuum drying means that the vacuum degree is <200 Pa.

[0237] 4. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to any one of the foregoing aspects, characterized in that the supercritical treatment in step 5) includes the following steps:

[0238] d) Mix the self-crosslinked graphene oxide oxidant mixture obtained in the above step 5) and the strongly acidic supercritical medium obtained in step 2) and add them to a closed high-pressure reaction kettle;

[0239] e) Heat and pressurize the reaction kettle, and perform a supercritical fluid-assisted secondary intercalation graphene oxide reaction on the mixture in the reaction kettle.

[0240] 5. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to any one of the foregoing aspects, characterized in that the graphite includes expandable graphite, natural flake graphite or artificially prepared highly oriented graphite, or a combination thereof, preferably includes natural flake graphite or artificially prepared highly oriented graphite, or a combination thereof.

[0241] 6. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to any one of the foregoing aspects, wherein the oxidants used in each of the foregoing steps include hydrogen peroxide, peroxide, permanganate, dichromate, perchlorate, or a combination thereof, preferably including potassium / sodium permanganate, potassium / sodium dichromate, or potassium / sodium perchlorate, or a combination thereof.

[0242] 7. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to any one of the foregoing aspects, wherein the mass ratio of graphite to oxidant in the graphite oxidant mixture in step 1) is 1:0.5 - 1:6, preferably 1:1 - 1:5.

[0243] 8. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to any one of the foregoing aspects, wherein the mass ratio of acid to supercritical medium in the strongly acidic supercritical medium in step a) is 1:0.5 - 1:4, preferably 1:1 - 1:3.

[0244] 9. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to any one of the foregoing aspects, wherein the mass ratio of self-crosslinked graphene oxide to oxidant in the self-crosslinked graphene oxide oxidant mixture in step 5) is 4:1 - 1:4, preferably 3:1 - 1:3.

[0245] 10. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to any one of the foregoing aspects, wherein the acid in the above step a) includes concentrated acid, and the concentrated acid includes concentrated sulfuric acid, concentrated nitric acid or a combination thereof.

[0246] 11. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to aspect 10, wherein the molar concentration of concentrated sulfuric acid ≥ 16 mol / L, preferably ≥ 16.6 mol / L.

[0247] 12. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to any one of the foregoing aspects, wherein the low temperature in the above step a) is lower than the melting point or boiling point of the supercritical medium.

[0248] 13. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to any one of the foregoing aspects, wherein the supercritical media used in each step include carbon dioxide, ethanol, methane, ethane, propane, n-pentane, chloroform, ammonia, nitrogen or a combination thereof, preferably dry ice or liquid nitrogen.

[0249] 14. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to any one of the foregoing aspects, wherein the above steps c) and e) are carried out under the condition of rotational oscillation of a closed high-pressure reaction kettle.

[0250] 15. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of the foregoing aspects, characterized in that the temperatures of the above steps c) and e) are independently 30-70 °C, preferably 32-60 °C.

[0251] 16. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of the foregoing aspects, characterized in that the pressures of the above steps c) and e) are independently 1 MPa - 50 MPa, preferably 2 MPa - 45 MPa.

[0252] 17. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of the foregoing aspects, characterized in that the reaction times of the supercritical fluid-assisted intercalation of graphene oxide reaction in step c) or the supercritical fluid-assisted secondary intercalation of graphene oxide reaction in step e) are independently 0.5 - 5 hours, preferably 1 - 4 hours.

[0253] 18. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of the foregoing aspects, characterized in that the mass ratio of the graphite oxidant mixture to the strongly acidic supercritical medium in step b) is 1:1 - 1:6, preferably 1:2 - 1:5.

[0254] 19. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of the foregoing aspects, characterized in that the rotation speed of the closed high-pressure reactor in steps c) and e) is 6 - 60 rpm, preferably 8 - 50 rpm.

[0255] 20. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of the foregoing aspects, characterized in that the mass ratio of the self-crosslinking graphene oxide oxidant mixture to the strongly acidic supercritical medium in step d) is 1:1 - 1:8, preferably 1:1.5 - 1:7.

[0256] 21. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of the foregoing aspects, characterized in that the ultrasonic-assisted peeling treatment in steps 3) and 6) is to dissolve the reaction product in deionized water and stir it sufficiently to disperse, and use a 100W - 300W ultrasonic source to ultrasonically treat the dispersion in a water bath for 10 - 20 min, and the suspension is dried after dialysis.

[0257] 22. Large-scale single-layer graphene oxide prepared by the method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of the foregoing aspects.

[0258] 23. The graphene oxide according to aspect 22, characterized in that its average thickness is about 0.75 - about 1.075 nm, and / or the area of a single graphene sheet is greater than 15×15 μm 2 , preferably greater than 20×20 μm 2 , more preferably greater than 30×30 μm 2 , most preferably greater than 50×50 μm 2 .

[0259] Although specific embodiments of the invention have been described above for purposes of illustration, it will be apparent to those skilled in the art that various variations in the details of the invention may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid, characterized in that It includes the following steps: 1) Grind graphite and an oxidant and mix them thoroughly to form a graphite-oxidant mixture; 2) Perform supercritical treatment on the graphite-oxidant mixture formed in step 1); 3) Perform ultrasonic-assisted exfoliation treatment on the product obtained in step 2) to obtain graphene oxide; 4) After thoroughly mixing the graphene oxide obtained in step 3) and a solid acid catalyst, vacuum-dry the graphene oxide and solid acid catalyst mixture in a reaction kettle under high-temperature conditions to obtain self-crosslinked graphene oxide, where the self-crosslinking reaction temperature of the graphene oxide and solid acid catalyst mixture in the reaction kettle is 90 - 200 °C, and the solid acid catalyst includes SnO, Sm2O3, or a combination thereof; 5) Thoroughly mix the self-crosslinked graphene oxide obtained in step 4) and an oxidant to form a self-crosslinked graphene oxide-oxidant mixture; 6) Perform supercritical treatment on the self-crosslinked graphite-oxidant mixture formed in step 5); 7) Perform ultrasonic-assisted exfoliation treatment on the product obtained in step 6), and large-scale single-layer graphene oxide is obtained. It is characterized in that the supercritical treatment in step 2) includes the following steps: a) Under a low-temperature environment, mix an acid with a low-temperature supercritical medium to form a strongly acidic supercritical medium; b) Mix the graphite-oxidant mixture obtained in step 1) above and the strongly acidic supercritical medium obtained in step a) and add them to a closed high-pressure reaction kettle; c) Heat and pressurize the reaction kettle, and perform a supercritical fluid-assisted intercalation oxidation graphene reaction on the graphite mixture in the reaction kettle. The supercritical treatment in step 6) includes the following steps: d) Mix the self-crosslinked graphene oxide-oxidant mixture obtained in step 5) above and the strongly acidic supercritical medium obtained in step 2) and add them to a closed high-pressure reaction kettle; e) Heat and pressurize the reaction kettle, and perform a supercritical fluid-assisted secondary intercalation oxidation graphene reaction on the mixture in the reaction kettle.

2. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 1, wherein The reaction process in step 4) is as follows: Among them is a simplified structural schematic diagram of graphene oxide; The mass ratio of graphene oxide to solid acid catalyst in the graphene oxide and solid acid catalyst mixture is 1:0.0003 - 1:0.006; The vacuum drying time of the graphene oxide and solid acid catalyst mixture in the reaction kettle is 1 - 9 hours; The vacuum drying means that the vacuum degree is <200 Pa.

3. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 2, wherein The solid acid catalyst includes SnO.

4. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 2, wherein The mass ratio of graphene oxide to solid acid catalyst in the graphene oxide and solid acid catalyst mixture is 1:0.0005 - 1:0.

005.

5. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 2, wherein The self-crosslinking reaction temperature of the graphene oxide and solid acid catalyst mixture in the reaction kettle is 100 °C - 180 °C.

6. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 2, characterized in that The vacuum drying time of the graphene oxide and solid acid catalyst mixture in the reaction kettle is 2 hours - 8 hours.

7. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, The graphite includes expandable graphite, natural flake graphite, or artificially prepared highly oriented graphite, or a combination thereof.

8. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 7, characterized in that, The graphite includes natural flake graphite or artificially prepared highly oriented graphite, or a combination thereof.

9. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, The oxidants used in each step include hydrogen peroxide, peroxides, permanganates, dichromates, perchlorates, or a combination thereof.

10. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 9, wherein, The oxidants used in the above steps include potassium permanganate, sodium permanganate, potassium dichromate, sodium dichromate, potassium perchlorate, or sodium perchlorate, or a combination thereof.

11. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, In step 1), the mass ratio of graphite to oxidant in the graphite oxidant mixture is 1:0.5 - 1:

6.

12. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 11, wherein, In step 1), the mass ratio of graphite to oxidant in the graphite oxidant mixture is 1:1 - 1:

5.

13. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, In step a), the mass ratio of acid to supercritical medium in the strongly acidic supercritical medium is 1:0.5 - 1:

4.

14. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 13, wherein In step a), the mass ratio of acid to supercritical medium in the strongly acidic supercritical medium is 1:1 - 1:

3.

15. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, In step 5), the mass ratio of self-crosslinked graphene oxide to oxidant in the self-crosslinked graphene oxide oxidant mixture is 4:1 - 1:

4.

16. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 15, wherein, In step 5), the mass ratio of self-crosslinked graphene oxide to oxidant in the self-crosslinked graphene oxide oxidant mixture is 3:1 - 1:

3.

17. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, The acid in step a) above includes concentrated acids, and the concentrated acids include concentrated sulfuric acid, concentrated nitric acid, or a combination thereof.

18. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 17, wherein, The molar concentration of concentrated sulfuric acid ≥ 16 mol / L.

19. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to claim 18, wherein, The molar concentration of concentrated sulfuric acid ≥ 16.6 mol / L.

20. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, The low temperature in step a) above is lower than the melting point or boiling point of the supercritical medium.

21. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, The supercritical media used in each step include carbon dioxide, ethanol, methane, ethane, propane, n-pentane, chloroform, ammonia, nitrogen, or a combination thereof.

22. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 21, wherein The supercritical medium used in each step is dry ice or liquid nitrogen.

23. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, Steps c) and e) above are carried out under the condition of rotational oscillation in a closed high-pressure reactor.

24. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, The temperatures of steps c) and e) above are independently 30 - 70 °C.

25. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 24, wherein The temperatures of steps c) and e) above are independently 32 - 60 °C.

26. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, The pressures of steps c) and e) above are independently 1 MPa - 50 MPa.

27. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 26, wherein The pressures of steps c) and e) above are independently 2 MPa - 45 MPa.

28. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, The reaction times of the supercritical fluid-assisted intercalation of graphene oxide reaction in step c) or the supercritical fluid-assisted secondary intercalation of graphene oxide reaction in step e) are independently 0.5 - 5 hours.

29. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 28, wherein, The reaction times of the supercritical fluid-assisted intercalation of graphene oxide reaction in step c) or the supercritical fluid-assisted secondary intercalation of graphene oxide reaction in step e) are independently 1 - 4 hours.

30. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, In step b), the mass ratio of the graphite oxidant mixture to the strongly acidic supercritical medium is 1:1 - 1:

6.

31. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 30, wherein In step b), the mass ratio of the graphite oxidant mixture to the strongly acidic supercritical medium is 1:2 - 1:

5.

32. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, The rotational speed of the closed high-pressure reactor in steps c) and e) is 6 - 60 rpm.

33. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 32, wherein, The rotational speed of the closed high-pressure reactor in steps c) and e) is 8 - 50 rpm.

34. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to any one of claims 1 to 6, characterized in that, In step d), the mass ratio of the self-crosslinked graphene oxide oxidant mixture to the strongly acidic supercritical medium is 1:1 - 1:

8.

35. The method for preparing large-scale single-layer graphene oxide by supercritical fluid assistance according to claim 34, characterized in that, In step d), the mass ratio of the self-crosslinked graphene oxide oxidant mixture to the strongly acidic supercritical medium is 1:1.5 - 1:

7.

36. The method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to any one of claims 1 to 6, characterized in that, In steps 3) and 6), the ultrasonic-assisted exfoliation treatment is to dissolve the reaction product in deionized water and stir it thoroughly to disperse, and then use a 100W - 300W ultrasonic source to ultrasonically treat the dispersion in a water bath for 10 - 20 min. The suspension is dried after dialysis. Large-scale single-layer graphene oxide prepared by the method for preparing large-scale single-layer graphene oxide assisted by supercritical fluid according to any one of claims 1 to 36.

38. The graphene oxide according to claim 37, wherein, Its average thickness is 0.75 - 1.075 nm, and / or the area of a single graphene sheet is greater than 15×15 μm 2 .

39. The graphene oxide according to claim 38, wherein, The area of a single graphene sheet is greater than 20×20 μm 2 .

40. The graphene oxide according to claim 38, wherein, The area of a single graphene sheet is greater than 30×30 μm 2 .

41. The graphene oxide according to claim 38, wherein, The area of a single graphene sheet is greater than 50×50 μm 2 .

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