Monolayer edge graphene oxide and method for preparing the same

Abstract

The present invention provides single-layer edge-oxidized graphene and a preparation method thereof, which relate to the technical field of graphene materials. In this invention, single-layer edge-oxidized graphene is prepared from single-layer graphene as a raw material by applying ultra-low frequency alternating current and low current density electrolysis. The amount of oxygen radicals generated from the electrolyte is controlled by adjusting the current intensity and frequency of the applied alternating current, so that a small number of oxygen radicals react with the more active edge binding energy of the single-layer graphene. Lower current intensity and shorter current duration prevent the generated oxygen radicals from penetrating sufficiently into the plane of the single-layer graphene, thereby forming single-layer edge-oxidized graphene. The single-layer edge-oxidized graphene prepared by this invention retains the excellent physical and chemical properties of graphene while increasing its polarity, significantly improving the dispersibility of graphene in polar solvents.

Description

[Technical Field]

[0001] <Cross-reference of related applications> This application claims priority to the Chinese patent application filed with the Chinese National Intellectual Property Office on July 4, 2023, with application number CN202310806922.0, titled "Single-layer edge graphene oxide and method for preparing the same," and all contents of that application are incorporated into this application by reference.

[0002] <Technical field> The present invention relates to the technical field of graphene materials, and more particularly to single-layer edge graphene oxide and a method for preparing the same. [Background technology]

[0003] Graphene is a two-dimensional planar material with a thickness of only one layer of carbon atoms. On the plane of graphene, sp 2 The hybridized carbon atoms are densely arranged in a honeycomb lattice. Graphene can curl in various shapes to form carbon nanotubes and fullerenes, and by continuously stacking these, three-dimensional sheet-like graphite can be formed.

[0004] Graphene possesses many excellent properties due to its unique structure. It is the hardest material discovered to date, has extremely excellent mechanical properties (1060 GPa), and its theoretical specific surface area is 2600 m². 2 ·g -1 And it's high, 3000W·m -1 ·K -1 It possesses excellent thermal conductivity up to 20,000 cm². Furthermore, graphene also has good electrical conductivity, with an electron mobility of 20,000 cm² at room temperature. 2 ·V -1 ·s -1 It can reach that level.

[0005] Graphene, as a two-dimensional planar material with a thickness of only one carbon atom, has an extremely large specific surface area and a very high surface activation energy, making it very unstable and difficult to mold, thus limiting its further application in many fields. Therefore, by preparing graphene oxide by introducing oxygen-containing functional groups such as hydroxyl groups and carbonyl groups into a graphene sheet layer, the polarity of graphene can be greatly improved, allowing for stable dispersion in polar solutions and lowering the surface activation energy. Consequently, it has become possible to process and mold graphene to directly prepare various functional materials such as graphene coatings, graphene paper, and graphene conductive films using simple methods.

[0006] To date, the main methods for preparing graphene oxide have been: (1) strong oxidizing agent oxidation. This method involves introducing strong acids or strong oxidizing agents such as concentrated sulfuric acid, potassium permanganate, and hydrogen peroxide to oxidize graphene. The advantage of this method is that it introduces numerous oxygen-containing functional groups to the planar and edge regions of graphene, thereby greatly improving the polarity and modifiable potential of graphene. However, the introduction of strong acids or strong oxidizing agents destroys the two-dimensional planar structure of graphene, resulting in numerous irreparable defects on the graphene's surface, and causing the loss of graphene's inherently excellent physical and chemical properties. At the same time, the introduction of strong acids causes environmental pollution. (2) DC electrolytic method. This method uses multilayer graphite and platinum metal sheets as a pair of electrolytic electrode sheets, and by applying a voltage of 10V, a large amount of hydroxyl radicals are generated in the electrolyte. These active hydroxyl radicals react with the graphite, thereby introducing oxygen-containing functional groups to the surface of the graphite. Simultaneously, ions such as hydroxyl groups and bicarbonate groups in the electrolyte penetrate between the graphite sheet layers, causing an oxidation-reduction reaction under energized conditions to generate gases such as carbon dioxide and oxygen, which physically exfoliate the graphite layer by layer to produce graphene oxide. The advantage of this method is that it is environmentally friendly and allows for the rapid and safe preparation of graphene oxide. However, it has the disadvantage that the degree of oxidation cannot be controlled, and further reduction operations are required, resulting in numerous defects on the graphene surface and a decrease in the optical, electrical, and thermal properties of the graphene material. (3) Physical exfoliation methods, such as the mechanical ball milling method, utilize the collision and friction between crushed balls in a ball milling tank and graphene at high rotational speeds to crush multilayer graphene oxide and reduce the number of graphene layers. Although this method is simple, it is difficult to control the uniformity of the number of layers of exfoliated graphene oxide. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to provide single-layer edge-oxidized graphene and a method for preparing the same. The prepared graphene is single-layer graphene in which only the edges are oxidized, and it has good water solubility and excellent overall properties.

Means for Solving the Problem

[0008] In order to achieve the above object of the present invention, the present invention provides the following technical solutions. The present invention provides a method for preparing single-layer edge oxidized graphene, mixing single-layer graphene, a binder and a dispersant, and drying the resulting slurry to obtain an electrode sheet; electrolytically oxidizing the electrode sheet in an electrolytic cell to obtain single-layer edge oxidized graphene, wherein the electrolytic oxidation is carried out under the condition of ultra-low frequency alternating current, the frequency of the ultra-low frequency alternating current is 0.01~0.02 Hz, the current density of the electrolytic oxidation is 30~50 mA·cm -2 and the time is 50~100 seconds.

[0009] Preferably, the binder is one or more of polyvinylidene fluoride, naphthol, sodium alginate, styrene-butadiene rubber and polyacrylic acid.

[0010] Preferably, the dispersant contains one or more of water, polyethylene-propylene polymer, N-methylpyrrolidone, methanol, ethanol, ethylene glycol, propanol, methyl ether, ethyl ether, dimethyl carbonate, propylene carbonate, diethyl carbonate, ethylene carbonate, ethyl methyl carbonate, diethylene glycol butyl ether acetate, butyl carbitol, butyl carbitol acetate, texanol, ethylene glycol diacetate and terpineol.

[0011] Preferably, the usage ratio of the single-layer graphene to the dispersant is (2~5) mg:(2~5) mL.

[0012] Preferably, the mass of the binder is 7~15% by weight of the mass of the single-layer graphene.

[0013] Preferably, the electrolyte in the electrolytic cell contains one or more of potassium bicarbonate, potassium hydroxide, ammonium acetate, ammonium sulfate, lithium hexafluorophosphate, lithium hexafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, and sodium hexafluorophosphate.

[0014] Preferably, the concentration of the electrolyte in the electrolytic solution is 0.05 - 0.5 mol·L -1 is.

[0015] Preferably, the frequency of the ultra - low - frequency alternating current is 0.017 Hz, and the current density of the electrolytic oxidation is 41.6 mA·cm -2 is.

[0016] The present invention provides monolayer edge - oxidized graphene prepared by the preparation method described in the above technical solution, and the planar structure of the monolayer edge - oxidized graphene has curled edges.

[0017] Preferably, the size of the monolayer edge - oxidized graphene is 20 - 100 nm, and the edge height is 1.5 nm.

Advantages of the Invention

[0018] The present invention provides a method for preparing monolayer edge - oxidized graphene. In the present invention, monolayer graphene is used as the raw material, and by applying ultra - low - frequency alternating current and electrolysis with a low current density, monolayer edge - oxidized graphene is prepared. By adjusting the current intensity and frequency of the applied alternating current to adjust the amount of oxygen radicals generated from the electrolytic solution, a small amount of oxygen radicals react with the more active part of the binding energy of the edges of monolayer graphene, and with a lower current intensity and a shorter current time, the generated oxygen radicals do not fully penetrate into the plane of monolayer graphene, thereby constructing monolayer edge - oxidized graphene.

[0019] The present invention conducts electrolysis using mild electrolysis conditions (ultra-low frequency alternating current and lower current density), resulting in a low degree of oxidation and damage to graphene. Therefore, the graphene sheet layer retains its complete inherent structure, and various excellent properties of graphene can be maximally maintained. At the same time, the oxygen-containing functional groups introduced at the edges (such as hydroxyl groups and ketone groups) endow graphene with good water solubility. The mechanical, thermal, and electrical properties of the graphene material mainly depend on the single-layer structure and planar structure defects of the graphene sheet layer. However, the edge-oxidized graphene prepared by the present invention has a single-layer structure and polar oxidation functional groups at the edges. Therefore, the single-layer edge-oxidized graphene prepared by the present invention retains the excellent physical and chemical properties of graphene while increasing its polarity, significantly improving the dispersion ability of graphene in polar solvents.

[0020] The method of the present invention can adjust the degree of oxidation of graphene oxide by adjusting the current intensity and frequency of the applied alternating current, thereby preparing single-layer edge-oxidized graphene with a controllable degree of oxidation. At the same time, it also solves the problem that it is difficult to control the number of single-layer graphene oxide layers in the physical exfoliation method. The method for preparing single-layer edge-oxidized graphene based on low-frequency alternating current provided by the present invention is safe, simple, pollution-free, and easy to operate.

Brief Description of the Drawings

[0021] [Figure 1] It is a flowchart for preparing single-layer edge-oxidized graphene according to the present invention. [Figure 2] It is a photograph of the single-layer edge-oxidized graphene aqueous dispersion obtained before concentration in Example 1. [Figure 3] It is a transmission electron microscope image of the single-layer edge-oxidized graphene prepared in Example 1. [Figure 4] It is an atomic force microscope measurement graph of the edge thickness of the single-layer edge-oxidized graphene prepared in Example 1. [Figure 5] It is a transmission electron microscope image of graphene oxide prepared by high-current electrolysis of graphene in Comparative Example 1. [Modes for carrying out the invention]

[0022] The present invention provides a method for preparing single-layer edge graphene oxide. The process involves mixing single-layer graphene, a binder, and a dispersant, and drying the resulting slurry to obtain an electrode sheet. The step includes electrolytic oxidation of the electrode sheet in an electrolytic cell to obtain single-layer edge graphene oxide, The electrolytic oxidation is carried out under conditions of an ultra-low frequency alternating current, the frequency of which is 0.01 to 0.02 Hz. The current density of the electrolytic oxidation described above is 30-50 mA·cm². -2 The duration is 50-100 seconds.

[0023] In this invention, unless otherwise specified, the necessary raw materials and reagents are all commercially available products well known to those skilled in the art.

[0024] In this invention, a single layer of graphene, a binder, and a dispersant are mixed, and the resulting slurry is dried to obtain an electrode sheet.

[0025] In this invention, the single-layer graphene is not particularly limited, and commercially available products well known in the art may be used.

[0026] In the present invention, the binder is preferably one or more of polyvinylidene fluoride, naphthol, sodium alginate, styrene-butadiene rubber, and polyacrylic acid. When the binder is two or more of the above, the present invention is not particularly limited to the blending ratio of different types of binders and can be adjusted according to actual needs. The present invention uses a binder to fix the single-layer graphene powder so that it does not fall off in clumps during the electrolysis process.

[0027] In the present invention, the dispersant preferably comprises one or more of the following: water, polyethylene-propylene polymer, N-methylpyrrolidone, methanol, ethanol, ethylene glycol, propanol, methyl ether, ethyl ether, dimethyl carbonate, propylene carbonate, diethyl carbonate, ethylene carbonate, ethylmethyl carbonate, diethylene glycol butyl ether acetate, butyl carbitol, butyl carbitol acetate, texanol, ethylene glycol diacetate, and terpineol. When the dispersant comprises two or more of the above, the present invention is not particularly limited to the blending ratio of different types of dispersants and can be adjusted according to actual needs.

[0028] In the present invention, the ratio of the amount of single-layer graphene to the amount of dispersant used is preferably (2-5) mg:(2-5) mL, and more preferably 3 mg:5 mL.

[0029] In the present invention, the mass of the binder is preferably 7 to 15% by weight of the mass of the single-layer graphene, and more preferably 9% by weight.

[0030] The present invention is not particularly limited to the mixing of the single-layer graphene, binder and dispersant, and is applicable to uniformly mixing the materials according to processes well known in the art.

[0031] In the present invention, after the mixing of the single-layer graphene, binder, and dispersant is completed, preferably the slurry obtained by the mixing is injected into an electrode mold and dried to obtain an electrode sheet. The present invention is not particularly limited to the electrode mold, and any electrode mold known in the art may be used. Specifically, in the embodiments of the present invention, a rectangular parallelepiped mold with a length of 25 mm, a width of 20 mm, and a height of 2 mm is used.

[0032] The present invention is not particularly limited to the drying described above, and the slurry is dried according to a process well known in the art.

[0033] After obtaining an electrode sheet, the present invention electrolytically oxidizes the electrode sheet in an electrolytic cell to obtain a single-layer edge graphene oxide.

[0034] In this invention, preferably, the electrode sheet is placed in an electrolytic cell, an electrolyte is added so that the electrode sheet is immersed in the electrolyte, and the positive and negative electrodes of an electrochemical workstation are connected to perform electrolytic oxidation. In this invention, the present invention is not particularly limited to the electrochemical workstation and its positive and negative electrodes, and any corresponding apparatus well known in the art may be used.

[0035] In the present invention, the electrolyte in the electrolyte solution used in the electrolytic cell preferably contains one or more of the following: potassium bicarbonate, potassium hydroxide, ammonium acetate, ammonium sulfate, lithium hexafluorophosphate, lithium hexafluoroborate, lithium hexafluoroarsenate, lithium bistrifluoromethanesulfonimide, and sodium hexafluorophosphate. When the electrolyte consists of two or more of the above, the present invention is not particularly limited to the mixing ratio of different types of electrolytes and can be adjusted to suit actual needs.

[0036] In the present invention, the concentration of the electrolyte in the electrolyte solution is preferably 0.05 to 0.5 mol·L. -1 More preferably, 0.2 mol·L -1 The solvent used in the electrolyte is preferably water.

[0037] In this invention, the electrolytic oxidation is carried out under ultra-low frequency AC conditions, the frequency of the ultra-low frequency AC is 0.01 to 0.02 Hz, more preferably 0.017 Hz, and the current density of the electrolytic oxidation is 30 to 50 mA·cm². -2 More preferably, 41.6 mA·cm -2 The time is 50 to 100 seconds, preferably 60 seconds. By using an ultra-low frequency alternating current for electrolysis, the present invention prevents the generation of excessive hydroxyl radicals in the electrolysis process, and ensures that the oxidation reaction occurs only in the part of the graphene edge where the reaction energy is more active, thereby preparing a single layer graphene nanosheet in which only the edge is oxidized.

[0038] After the electrolytic oxidation is completed, the present invention preferably adds the obtained product to deionized water and dialyzes it until the aqueous solution becomes neutral, then centrifugates it, removes the upper layer of solution and sequentially filters it (to remove residual electrolyte metal ions and precipitates), concentrates it (to remove 95% of the water), and freeze-dries it to obtain a single-layer edge-oxide graphene nanosheet. The rotation speed of the centrifugation is preferably 8500 rpm, and the time is preferably 3 minutes. In the present invention, the filtration, concentration, and freeze-drying are not particularly limited and may be carried out according to processes well known in the art.

[0039] The present invention provides single-layer edge graphene prepared by the preparation method described in the above technical solution, wherein the planar structure of the single-layer edge graphene has curled edges. The edges of the single-layer edge graphene prepared by the present invention are curled because oxygen-containing functional groups such as hydroxyl groups and ketone groups are present on the edges of the planar structure.

[0040] In the present invention, the size of the single-layer edge graphene oxide is preferably 20 to 100 nm, and the edge height is preferably 1.5 nm.

[0041] Figure 1 is a flowchart for the preparation of single-layer edge graphene oxide according to the present invention (for example, polyvinylidene fluoride and N-methylpyrrolidone are used). As shown in Figure 1, in the present invention, graphene, polyvinylidene fluoride and N-methylpyrrolidone are mixed and stirred, the resulting slurry is made into a graphene electrolytic electrode sheet, an aqueous potassium bicarbonate solution is used as the electrolyte, and AC conditions (0.01~0.02Hz, 30~50mA·cm) are applied. -2 Edge graphene oxide is obtained by electrolysis using ).

[0042] This invention controls the degree of oxidation of single-layer graphene by controlling the conditions of electrolytic oxidation, so that the oxidation reaction of single-layer graphene occurs only at the edges of the graphene material, preventing defects from occurring on the planes of the graphene material due to oxidation, and ensuring that the two-dimensional honeycomb structure of graphene is perfect.

[0043] The technical solutions of the present invention are described below clearly and completely with reference to embodiments of the present invention. Obviously, the embodiments described are only a part of the embodiments of the present invention, not all embodiments. All other embodiments that can be obtained by those skilled in the art without creative effort based on embodiments of the present invention are included within the scope of protection of the present invention.

[0044] In the following embodiment, the electrochemical workstation used is the CHI660E, and both the positive and negative electrodes are graphene electrodes.

[0045] Example 1 3 g of single-layer graphene powder and 9 wt.% polyvinylidene fluoride relative to the mass of the single-layer graphene are dissolved in 5 mL of N-methylpyrrolidone and uniformly mixed. The resulting slurry is then poured into a cubic mold measuring 25 mm in length, 20 mm in width, and 2 mm in height, and dried and solidified to obtain a graphene electrolytic electrode sheet. The graphene electrolytic electrode sheet is placed in the electrolytic cell, and a concentration of 0.2 mol / mL is added. -1 After adding the potassium bicarbonate aqueous solution and connecting it to the positive and negative electrodes of the electrochemical workstation, the reading was 41.6 mA·cm. -2 An alternating current of 0.017 Hz was applied and electrolysis was carried out for 60 seconds. After electrolysis, the solution obtained was dialyzed in deionized water until the aqueous solution became electrically neutral. Then, after high-speed centrifugation at 8500 rpm for 3 minutes, it was filtered, and the resulting black graphene aqueous dispersion was concentrated and freeze-dried to obtain edge-oxide graphene nanosheets.

[0046] Figure 2 is a photograph of the single-layer edge-oxide graphene aqueous dispersion obtained before concentration in Example 1. As can be seen from Figure 2, the single-layer graphene nanosheet layer is uniformly distributed in the aqueous solution without forming concentration differences or precipitation phenomena, which proves that edge-oxide graphene has excellent dispersibility in an aqueous solution system.

[0047] Figure 3 is a transmission electron microscope image of the single-layer edge graphene oxide prepared in Example 1. As can be seen from Figure 3, the edges of the graphene curl due to the generation of hydrogen bonds by the introduction of oxygen-containing functional groups such as hydroxyl, carbonyl, and carboxyl. This proves that oxygen-containing functional groups are introduced into the graphene edges and that their size distribution is within the range of 20 to 100 nm.

[0048] Figure 4 is an atomic force microscopy graph of the edge thickness of the single-layer edge graphene oxide prepared in Example 1. As shown in Figure 4, the height of the edge graphene oxide is 1.5 nm, which proves that it is an electrolytically treated single-layer graphene-based material.

[0049] Comparative Example 1 3 g of single-layer graphene powder and 9 wt.% polyvinylidene fluoride relative to the mass of the single-layer graphene are dissolved in 5 mL of N-methylpyrrolidone and uniformly mixed. The resulting slurry is then poured into a cubic mold measuring 25 mm in length, 20 mm in width, and 2 mm in height, and dried and solidified to obtain a graphene electrolytic electrode sheet. The graphene electrolytic electrode sheet is placed in the electrolytic cell, and a concentration of 0.2 mol / mL is added. -1 After adding the potassium bicarbonate aqueous solution and connecting it to the positive and negative electrodes of the electrochemical workstation, the current was set to 50 mA·cm. -2 An alternating current of 0.017 Hz was applied and electrolysis was carried out for 60 seconds. After electrolysis, the solution obtained was dialyzed in deionized water until the aqueous solution became electrically neutral. Then, after high-speed centrifugation at 8500 rpm for 3 minutes, it was filtered, and the resulting black graphene aqueous dispersion was concentrated and freeze-dried to obtain graphene oxide.

[0050] Figure 5 shows a transmission electron microscope image of graphene oxide prepared by high-current electrolysis of graphene in Comparative Example 1. As shown in Figure 5, unlike Example 1, where only the edges of the graphene were oxidized and curled by electrolysis using low current conditions, in Comparative Example 1, the oxidized graphene peeled off and aggregated in clumps after increasing the current intensity, and no edge curling was observed with the transmission electron microscope. This proves that the degree of oxidation spreads throughout the interior of the plane, exhibiting interlayer lamination, and demonstrates that the degree of oxidation of graphene can be controlled by the method of the present invention.

[0051] The above description of the embodiments is used solely to aid in understanding the method and central idea of ​​the present invention. Those skilled in the art should note that several improvements and modifications can be made to the invention without departing from the principles of the invention, and these improvements and modifications are also included within the scope of the claims of the invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not intended to be limited to the embodiments shown herein, but should conform to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing monolayer edge graphene oxide, The process involves mixing single-layer graphene, a binder, and a dispersant, and drying the resulting slurry to obtain an electrode sheet. The step includes electrolytic oxidation of the electrode sheet in an electrolytic cell to obtain single-layer edge graphene oxide, The electrolytic oxidation is carried out under conditions of an ultra-low frequency alternating current, the frequency of which is 0.01 to 0.02 Hz. The current density of the electrolytic oxidation described above is 30 to 41.6 mA / cm². －２ A preparation method characterized by the fact that the time is 50 to 100 seconds.

2. The preparation method according to claim 1, characterized in that the binder is one or more of polyvinylidene fluoride, naphthol, sodium alginate, styrene-butadiene rubber, and polyacrylic acid, and the dispersant is one or more of water, polyethylene-propylene polymer, N-methylpyrrolidone, methanol, ethanol, ethylene glycol, propanol, methyl ether, diethyl ether, dimethyl carbonate, propylene carbonate, diethyl carbonate, ethylene carbonate, ethylmethyl carbonate, diethylene glycol butyl ether acetate, butyl carbitol, butyl carbitol acetate, texanol, ethylene glycol diacetate, and terpineol.

3. The preparation method according to claim 1, characterized in that the dosage ratio of the monolayer graphene to the dispersant is (2-5) mg:(2-5) mL.

4. The preparation method according to claim 1, characterized in that the mass of the binder is 7 to 15% by weight of the mass of the single-layer graphene.

5. The electrolyte in the electrolyte solution used for the electrolytic oxidation described above contains one or more of the following: potassium bicarbonate, potassium hydroxide, ammonium acetate, ammonium sulfate, lithium hexafluorophosphate, lithium hexafluoroborate, lithium hexafluoroarsenate, lithium bistrifluoromethanesulfonimide, and sodium hexafluorophosphate, and the concentration of the electrolyte in the electrolyte solution is 0.05 to 0.5 mol·L. －１ That is The preparation method according to feature 1.

6. The frequency of the aforementioned ultra-low frequency AC is 0.017 Hz, and the current density of the electrolytic oxidation is 41.6 mA·cm². －２ The preparation method according to claim 1, characterized in that it is the same.

7. The preparation method according to any one of claims 1, 5, and 6, characterized in that, after the electrolytic oxidation, the product obtained by the electrolytic oxidation is further added to deionized water and dialyzed, and after the aqueous solution becomes neutral, it is centrifuged, the upper layer of solution is removed and sequentially filtered, and concentrated and freeze-dried to obtain a single-layer edge-oxidized graphene nanosheet.

8. The preparation method according to claim 7, characterized in that the rotational speed of the centrifugal separation is 8500 rpm and the time is 3 minutes.

9. A single-layer edge graphene having a single-layer planar structure, wherein the edges of the planar structure are oxidized, characterized in that the edges of the planar structure of the single-layer edge graphene are curled, the size of the single-layer edge graphene is in the range of 20 to 100 nm, and the edge height is 1.5 nm.

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