Method for producing graphene oxide

Abstract

To provide a method for producing graphene oxide that enables graphene oxide to be safely produced in comparison with conventional production methods.SOLUTION: Using a monitoring mechanism comprising a) a mixing section that mixes a gas a, which contains dimanganese heptoxide gas generated during production of graphene oxide in a reaction vessel, with hydrogen peroxide solution, and b) measuring means that measures the oxygen gas concentration in a gas b, which is present in the mixing section and contains oxygen gas generated by the mixing, a permanganate aqueous solution is supplied to a mixed liquid containing graphite and sulfuric acid in the reaction vessel.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing graphene oxide, and more particularly to a method that can produce graphene oxide more safely than conventional production methods. [Background technology]

[0002] Graphene oxide (GO) is a sp 2 It has a structure in which functional groups containing oxygen (oxygen functional groups), such as hydroxyl groups and carboxyl groups, have been introduced into graphene, which has a layered structure in which carbon atoms are arranged in a plane by bonds. Focusing on the unique structure and physical properties of graphene oxide, research into its use and application has been progressing in various technical fields in recent years, and it is expected that graphene oxide will be used and utilized, for example, as a catalyst material, an electrode active material for batteries, an electrode material for capacitors, a thermoelectric conversion material, a light-emitting material, a lubricant material, etc.

[0003] As for graphene oxide, which is expected to be used in various technical fields, a method for producing it by adding potassium permanganate as an oxidizing agent to graphene under ice-cooling in a reaction system to oxidize the graphene, known as the "Hummers method" has been widely known (see Non-Patent Document 1). In recent years, in order to improve safety during production and to improve the quality of the obtained graphene oxide, various production methods that are improvements on the Hummers method as described above and production methods derived from the Hummers method have been proposed (see Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-148701 A [Patent Document 2] JP 2002-53313 A [Patent Document 3] JP 2017-88450 A [Non-patent literature]

[0005] [Non-Patent Document 1] William S. Hummers, et.al, Journal of American Chemical Society, 1958, 80, 1339 Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, it is known that graphene oxide can be synthesized (manufactured) by oxidizing graphite with dimanganese heptoxide (Mn2O7), and in the conventional manufacturing method described above, graphene oxide is produced by utilizing this oxidation reaction. Dimanganese heptoxide (Mn2O7) is produced by dehydrating permanganate with concentrated sulfuric acid. In the dehydration reaction, the presence of water in the reaction system is considered to be unfavorable. Therefore, the permanganate used in the conventional graphene oxide manufacturing method is generally in the form of a solid rather than an aqueous solution. However, solid permanganate is a hazardous material that exhibits strong alkalinity, and various measures are required to ensure the safety of workers in the conventional graphene oxide manufacturing method using such a solid permanganate.

[0007] Under such circumstances, the inventors have conducted intensive research into a method for safely producing graphene oxide compared to conventional production methods, and have confirmed that even when an aqueous permanganate solution is used, the reaction proceeds to an extent comparable to that when solid permanganate is used, making it possible to produce graphene oxide. Furthermore, they have discovered that, with regard to the dehydration reaction of permanganate using concentrated sulfuric acid, by understanding the amount of dimanganese heptaoxide (Mn2O7) gas generated during the reaction, graphene oxide can be produced safely without allowing the dehydration reaction to proceed excessively, and have completed the present invention.

[0008] In other words, the present invention has been made under such circumstances, and a problem to be solved by the present invention is to provide a method for producing graphene oxide that can produce graphene oxide more safely than conventional production methods. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention can be suitably implemented in various aspects as listed below. It should be understood that the aspects and technical features of the present invention are not limited to those described below, but can be recognized based on the inventive idea that can be grasped from the entire description of the specification.

[0010] (1) A process for supplying a permanganate aqueous solution to a mixed liquid containing graphite and sulfuric acid in a reaction tank, The aqueous permanganate solution is supplied into the reaction tank using a monitoring mechanism including: a) a mixing section for mixing a gas a containing manganese heptaoxide gas generated during graphene oxide production in the reaction tank with hydrogen peroxide water; and b) a measuring means for measuring an oxygen gas concentration in the gas b in the mixing section containing oxygen gas generated by such mixing. A method for producing graphene oxide, comprising the steps of: (2) The mixing section has a storage tank for storing hydrogen peroxide solution and a gas-liquid mixer, In the gas-liquid mixer, the hydrogen peroxide solution introduced from the storage tank and the gas A introduced from the reaction tank are mixed, and then the mixture of the hydrogen peroxide solution and the gas A is returned to the storage tank; The method for producing graphene oxide according to aspect (1), wherein the gas b is a gas in the storage tank containing oxygen gas generated by mixing the gas a in the reaction tank with hydrogen peroxide water. (3) The method for producing graphene oxide according to aspect (1) or (2), further comprising a stopping mechanism for stopping the supply of the permanganate aqueous solution when the oxygen gas concentration measured by the measuring means becomes equal to or higher than a specified value. (4) The method for producing graphene oxide according to aspect (1) or (2), further comprising a warning means that is activated when the oxygen gas concentration measured by the measuring means becomes equal to or higher than a predetermined value. (5) The method for producing graphene oxide according to aspect (1) or (2), wherein the storage tank includes an oxidation-reduction potentiometer for measuring an oxidation-reduction potential of a liquid in the tank, and a supplying means for supplying hydrogen peroxide solution. (6) The method for producing graphene oxide according to aspect (1) or (2), wherein the permanganate is sodium permanganate or potassium permanganate. (7) The method for producing graphene oxide according to aspect (1) or (2), wherein the concentration of the aqueous permanganate solution is 30 to 50 wt %. Effect of the Invention

[0011] As described above, in the graphene oxide production method according to the present invention, permanganate is used in the form of an aqueous solution, which is easier to handle compared to a solid form, and a monitoring mechanism having a predetermined configuration is used to monitor the generation status of manganese heptaoxide gas generated during graphene oxide production. Therefore, it is possible to proceed with the production of graphene oxide without excessively progressing the dehydration reaction of permanganate by sulfuric acid, making the method safer than conventional graphene oxide production methods. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is an explanatory diagram illustrating a schematic diagram of an example of a production unit used when producing graphene oxide according to the present invention. [Diagram 2] FIG. 1 is an explanatory diagram illustrating a schematic diagram of another example of a production unit used when producing graphene oxide according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will now be described in detail with reference to the drawings.

[0014] 1 is a schematic diagram of an example of a production unit used for producing graphene oxide according to the present invention. In the diagram, reference numeral 10 denotes a reaction tank, 12 denotes a storage tank for storing an aqueous manganese peroxide salt solution, 14 denotes a flow path, and 16 denotes a pump. The aqueous permanganate solution in the storage tank 12 is supplied to the reaction tank 10 through the flow path 14 by operation of the pump 16, and the operation, flow rate adjustment, and stop of the pump 16 can be controlled by a control device 18. Note that the reaction tank 10 is preferably a thermostatic tank in order to prevent the graphene oxide synthesis reaction from progressing rapidly due to heat.

[0015] Meanwhile, reference numeral 20 denotes a storage tank for storing hydrogen peroxide solution, and 22 denotes a gas-liquid mixer. The hydrogen peroxide solution in storage tank 20 is supplied to gas-liquid mixer 22 through flow path 26a by operation of pump 24, where it is mixed with the gas (gas a) in reaction tank 10 supplied through flow path 28, and the mixture of hydrogen peroxide solution and gas a is returned to storage tank 20 through flow path 26b. Reference numeral 30 denotes a filter device for removing manganese oxide (MnO2) generated by mixing hydrogen peroxide solution and gas a.

[0016] In addition, an oxygen concentration measuring device 32 for measuring the oxygen gas concentration of the gas inside the storage tank 20 is attached to the storage tank 20. The measurement data in the oxygen concentration measuring device 32, specifically, the oxygen gas concentration of the gas (gas b) inside the storage tank 20 measured by the oxygen concentration measuring device 32, is configured to be transmitted to the control device 18 one by one.

[0017] 1, a hydrogen peroxide storage tank 34 separate from the hydrogen peroxide storage tank 20 is connected to the storage tank 20 via a flow path 36. A pump 38 is disposed midway along the path of the flow path 36, and the operation and stopping of the pump 38 can be controlled by a control device 40. The control device 40 is configured to receive the numerical value (measurement value) of the oxidation-reduction potential of the hydrogen peroxide solution (more precisely, a mixture of the hydrogen peroxide solution and the gas a) in the storage tank 20 measured by an oxidation-reduction potentiometer 42 attached to the storage tank 20, and is configured to supply the hydrogen peroxide solution from the storage tank 34 to the storage tank 20 by operating the pump 38 in accordance with the measurement value measured by the oxidation-reduction potentiometer 42. The concentrations of the hydrogen peroxide water stored in storage tank 34 and the hydrogen peroxide water stored in storage tank 20 described above are not particularly limited, and an appropriate concentration may be selected and used from hydrogen peroxide water of general concentrations. Furthermore, the concentration of the hydrogen peroxide water stored in storage tank 34 may be the same as or different from the concentration of the hydrogen peroxide water stored in storage tank 20 described above.

[0018] When producing graphene oxide according to the present invention using the production unit shown in Fig. 1, first, predetermined amounts of graphite and sulfuric acid are charged into the reaction tank 10. The graphite used when producing graphene oxide according to the present invention is not particularly limited, and can be appropriately selected from conventional graphite. As for sulfuric acid, sulfuric acid with an appropriately adjusted concentration can be used, as in conventional graphene oxide production methods.

[0019] While the graphite and sulfuric acid introduced into the reaction tank 10 are being stirred by the stirrer 44, the pump 16 is operated by the control device 18 to start supplying the aqueous permanganate solution in the storage tank 12 to the reaction tank 10.

[0020] Here, the aqueous permanganate solution used in the present invention is not particularly limited, and may be any aqueous permanganate solution used in the Hummers process, a production method that is an improvement of the Hummers process, or a production method derived from the Hummers process, etc. In the present invention, an aqueous sodium permanganate solution or an aqueous potassium permanganate solution is particularly advantageously used.

[0021] In the graphene oxide production method according to the present invention, if the concentration of the permanganate in the permanganate aqueous solution is too low, problems such as a time required for the synthesis (production) of graphene oxide and difficulty in obtaining graphene oxide at a sufficient yield may occur. On the other hand, if the concentration of the permanganate in the permanganate aqueous solution is too high, even if the supply rate is slowed down (in other words, even if the supply amount of the permanganate aqueous solution per unit time is reduced) when the permanganate aqueous solution is supplied to the graphite and sulfuric acid according to the present invention, the synthesis reaction of graphene oxide may rapidly proceed and manganese heptaoxide may be rapidly and massively generated, which may make it difficult to produce graphene oxide with high safety. For this reason, in the graphene oxide production method according to the present invention, the permanganate aqueous solution used preferably has a concentration of 30 to 50 wt%, and most preferably, a permanganate aqueous solution with a concentration of 40 wt% is used.

[0022] Regarding the supply conditions of the permanganate aqueous solution in the present invention, such as the supply rate (the amount of permanganate aqueous solution supplied per unit time) and whether the supply is continuous or intermittent, it is preferable to carry out a preliminary experiment (production) in advance using the same amounts of graphite and sulfuric acid used, determine various supply conditions based on the results, and carry out the production method of the present invention under those supply conditions.

[0023] By supplying the permanganate aqueous solution to the graphite and sulfuric acid in the reaction tank 10, dimanganese heptaoxide (Mn2O7) is produced together with graphene oxide. A part of this dimanganese heptaoxide becomes gas and is released into the reaction tank 10, and the gas (gas a) in the reaction tank 10 containing the dimanganese heptaoxide gas is supplied to the gas-liquid mixer 22 through the flow path 28. Meanwhile, the hydrogen peroxide solution in the storage tank 20 is also supplied to the gas-liquid mixer 22 through the flow path 26a by the pump 24, which is operated from the start of the supply of the permanganate aqueous solution into the reaction tank 10. As a result, in the gas-liquid mixer 22, the gas a and the hydrogen peroxide solution are mixed to form a mixture, and the mixture is returned to the storage tank 20 through the flow path 26b.

[0024] Manganese heptaoxide (Mn2O7), which is produced simultaneously with graphene oxide, is a very strong oxidizing agent, and when such manganese heptaoxide is mixed with hydrogen peroxide, the two react to generate oxygen. Therefore, when the mixture of gas a and hydrogen peroxide is returned to the storage tank 20, the oxygen generated by the reaction between manganese heptaoxide and hydrogen peroxide becomes gas and is released into the storage tank 20.

[0025] Therefore, in the present invention, the oxygen gas concentration in the gas (gas b) in the storage tank 20 is observed (monitored) by the oxygen concentration measuring device 32, so that the production status of dimanganese heptaoxide in the reaction tank 10 can be grasped. For example, when the oxygen gas concentration measured by the oxygen concentration measuring device 32 increases, it is presumed that the amount of dimanganese heptaoxide produced in the reaction tank 10 is increasing. Although this is a favorable situation in that the production of graphene oxide is active, dimanganese heptaoxide is explosive and is a very dangerous substance, so it is not necessarily a favorable situation from the viewpoint of ensuring the safety of workers, etc. For this reason, in this embodiment, when the oxygen gas concentration measured by the oxygen concentration measuring device 32 reaches a predetermined specified value, the operation of the pump 16 is stopped by an instruction from the control device 18, and the supply of the permanganate aqueous solution to the reaction tank 10 is cut off. By cutting off the supply of the permanganate aqueous solution to the reaction tank 10 in this manner, the excessive production of dimanganese heptaoxide in the reaction tank 10 is also suppressed, making it possible to safely produce graphene oxide.

[0026] It is preferable that the specified value of the oxygen gas concentration in the gas inside the storage tank 20 described above is also determined based on the results of a preliminary experiment (manufacturing) carried out in advance under the same conditions.

[0027] In this embodiment, a hydrogen peroxide storage tank 34 separate from the hydrogen peroxide storage tank 20 is connected to the storage tank 20 via a flow path 36. The hydrogen peroxide in the storage tank 20 reacts with dimanganese heptaoxide in the gas a, resulting in a decrease in the concentration of the hydrogen peroxide in the storage tank 20. Therefore, in order to ensure good reactivity with dimanganese heptaoxide in the gas a, a pump 38 is operated in response to the value of the oxidation-reduction potential measured by an oxidation-reduction potentiometer 42 to supply hydrogen peroxide from the storage tank 34 to the storage tank 20.

[0028] As described above, in the graphene oxide production method according to the present invention, permanganate is used in the form of an aqueous solution, which is easier to handle compared to a solid form, and a monitoring mechanism having a predetermined configuration is used to monitor the generation status of manganese heptaoxide gas generated during graphene oxide production. Therefore, it is possible to proceed with the production of graphene oxide without excessively progressing the dehydration reaction of permanganate by sulfuric acid, making the method safer than conventional graphene oxide production methods.

[0029] Although one representative embodiment of the present invention has been described in detail above, it goes without saying that the present invention is not limited to the above-mentioned embodiment.

[0030] For example, the graphene oxide production method according to the present invention can be advantageously carried out in a production unit as shown in Fig. 2. In the production unit shown in Fig. 2, the same components as those in the production unit shown in Fig. 1 are denoted by the same reference numerals as in Fig. 1, and detailed descriptions thereof will be omitted.

[0031] In the production unit shown in Fig. 2, 50 is a pump that can be manually operated to start and stop, and 52 is a warning device. In this case, when the oxygen gas concentration determined by the oxygen concentration measuring device 32 reaches a predetermined specified value, a warning is issued from the warning device 52. When such a warning is issued, an operator can stop the operation of the pump 50 to suppress excessive progress of the graphene oxide synthesis reaction, thereby ensuring safe production of graphene oxide. Note that any conventionally known warning device, such as one that issues a warning sound or turns on a warning light, can be used as the warning device 52.

[0032] In addition, although not listed individually, it should be understood that, in addition to the specific description above, various changes, modifications, improvements, etc. can be made to the present invention based on the knowledge of those skilled in the art without departing from the spirit of the present invention. [Explanation of symbols]

[0033] 10 Reaction tank 12 Storage tank 14 Flow path 16 Pump 18 Control device 20 Storage tank 22 Gas-liquid mixer 24 Pump 26a, 26b Channel 28 Channel 30 Filter device 32 Oxygen concentration measuring device 34 Reservoir 36 Flow path 38 Pump 40 Control device 42 Oxidation-reduction potentiometer 44 Stirring device 50 Pump 52 Warning device

Claims

1. Supplying a permanganate aqueous solution to a mixed liquid containing graphite and sulfuric acid in a reaction tank, The aqueous permanganate solution is supplied into the reaction tank using a monitoring mechanism including: a) a mixing section for mixing a gas a containing manganese heptaoxide gas generated during graphene oxide production in the reaction tank with hydrogen peroxide water; and b) a measuring means for measuring an oxygen gas concentration in the gas b in the mixing section containing oxygen gas generated by such mixing. A method for producing graphene oxide, comprising the steps of:

2. The mixing unit has a storage tank for storing hydrogen peroxide solution and a gas-liquid mixer, In the gas-liquid mixer, the hydrogen peroxide solution introduced from the storage tank and the gas a introduced from the reaction tank are mixed, and then the mixture of the hydrogen peroxide solution and the gas a is returned to the storage tank; The method for producing graphene oxide according to claim 1 , wherein the gas b is a gas in the storage tank containing oxygen gas generated by mixing the gas a in the reaction tank with hydrogen peroxide water.

3. 3. The method for producing graphene oxide according to claim 1, further comprising a stopping mechanism for stopping the supply of the permanganate aqueous solution when the oxygen gas concentration measured by the measuring means becomes equal to or higher than a specified value.

4. The method for producing graphene oxide according to claim 1 or 2, further comprising a warning means that is activated when the oxygen gas concentration measured by the measuring means becomes equal to or higher than a predetermined value.

5. 3. The method for producing graphene oxide according to claim 1 or 2, wherein the storage tank comprises an oxidation-reduction potentiometer for measuring an oxidation-reduction potential of a liquid in the tank, and a supply means for supplying hydrogen peroxide solution.

6. The method for producing graphene oxide according to claim 1 or 2, wherein the permanganate is sodium permanganate or potassium permanganate.

7. The method for producing graphene oxide according to claim 1 or 2, wherein the concentration of the permanganate aqueous solution is 30 to 50 wt %.

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