WO2019028803A1

WO2019028803A1 - Method and device for electrochemically preparing graphene oxide

Info

Publication number: WO2019028803A1
Application number: PCT/CN2017/096993
Authority: WO
Inventors: 徐海波; 周泉竹
Original assignee: 徐海波
Priority date: 2017-08-11
Filing date: 2017-08-11
Publication date: 2019-02-14
Also published as: CN111032568B; CN111032568A

Abstract

A method and a device for electrochemically preparing graphene oxide. The graphene oxide is prepared by introducing a continuous flowing electrolyte solution (11) onto a surface of a cathode (5) to form a thin electrolyte layer, and then inserting one end of an anode (4) into the electrolyte solution to form a gap with the cathode (5) for electrolysis. The preparation method has higher oxidative expansion dissociation and cutting abilities, and can achieve the effects of small particle size, low layer number, and controlled particle size distribution and oxidation depth of the product.

Description

Method and device for electrochemically preparing graphene oxide

Technical field

The invention belongs to the technical field of nano materials, and particularly relates to a method and a device for electrochemically preparing graphene oxide.

Background technique

Graphene is a two-dimensional (2D) hexagonal planar single layer composed of sp ² hybrid orbitals of carbon atoms and is the basic building block of graphite materials of all other dimensions. It can be packaged as zero-dimensional (0D) fullerenes, rolled into one-dimensional (1D) nanotubes or stacked into three-dimensional (3D) graphite. Graphene oxide is an oxide of graphene having a single atomic layer thickness like graphene, but containing a large amount of other hetero atom functional groups on the carbon base and/or edge. According to the two-dimensional size of the carbon base surface, it can be divided into: 1-100 nm is a graphene oxide quantum dot, and more than 100 nm is a graphene oxide microchip. When the thickness is 2-10 single atomic layer thickness, it is called a small layer of graphene oxide quantum dots or microchips. When the thickness is 11-100 monoatomic layer thickness, it is also called multi-layer graphene oxide quantum dots or microchips. Here, for convenience of description, they are collectively referred to as graphene oxide unless otherwise specified.

A method in which graphene oxide can be industrially produced is a chemical oxidation method. The method mainly utilizes the structural defects existing in the graphite itself, and uses graphite as a raw material to obtain graphite oxide with a significantly larger interlayer spacing than graphite under strong acid, strong oxidant and heating conditions, and then obtains a single atomic layer by means of effective stripping means. Graphene oxide. At present, many companies at home and abroad have released the graphene oxide microchip products capable of mass production of kilograms and tons. These mass production techniques generally use a strong acid, strong oxidant chemical treatment of expanded graphite in order to achieve the oxidative expansion of graphite. The difference is in the implementation and stage of the process or in combination with other technologies, such as Brodie, Staudenmaier and Hummers. Improved techniques for chemical methods. A large number of chemicals such as strong acids and strong oxidants are used, which are highly polluting, and the quality of the products is poor. The range of layer and chip size distribution is too wide and too large, and the dispersion and stability are relatively poor, which directly leads to poor controllability in application. In addition, conventional electrochemical stripping methods have also been adopted, however, there are problems of small operating current density and uneven current distribution, resulting in long processing time, low product purity and quality, wide range of layer and particle size distribution, and later needs. The cumbersome purification step, the product yield is not high.

Graphene quantum dots (including graphene oxide quantum dots) mainly adopt a top-down preparation method, which refers to cutting a large-sized graphene sheet into a small-sized graphene quantum dot by physical or chemical methods. CN102660270A discloses a method for preparing fluorescent graphene quantum dots by solvothermal method, which firstly prepares graphene oxide, and then uses solvothermal heat to cut graphene oxide into quantum dots; CN102616774A discloses a method for preparing graphene quantum dots The method is to add an amine passivating agent in the hydrothermal cutting process; the disadvantages of the two methods are high heat, high energy, and low yield. Electrochemical preparation of luminescent of Chem.Eur.J., 2012 Graphene quantum dots from multi-walled carbon nanotubes and J. Mater. Chem.'s Facile synthesis of water-soluble, highly fluorescent graphene quantum dots as a robust biological label for stem cells The olefinic quantum dots, but the preliminary processing of the raw material graphite takes a long time, the later purification step takes a long time, and the product yield is not high. In addition, a preparation method using a microcrystalline carbon material as a carbon source is also employed: in the Graphene quantum dots derived from carbon fibers published by Nano Letter in 2012, carbon fibers are used as a carbon source, and the graphite deposited in the fibers is peeled off by acid treatment. A large number of graphene quantum dots with different particle size distributions can be obtained in one step. The advantage of this method is that the steps are simple and the raw materials are cheap, but the disadvantage is that a large amount of sulfuric acid and nitric acid are used in the preparation process, which takes a long time, has serious pollution, and has a particle size distribution. The range is very wide and requires subsequent dialysis separation to give a smaller particle size, resulting in an efficient preparation yield.

Recently, CN105565297A and CN105600772A disclose graphene oxide and a method for electrochemically oxidizing and cutting carbon fiber and other carbon-based three-dimensional materials, and the main feature is that one end surface of the carbon-based three-dimensional material is used as a working surface parallel to an electrolyte solution liquid surface. Contact, energized electrolysis, the working section as the end face of the working surface is located in the range of -5 mm to 5 mm below the liquid surface of the electrolyte solution, and the end face is in the working section by intermittent or continuous control, so that the end face The upper graphite sheet is disintegrated and cut into oxide graphene microplatelets or graphene oxide quantum dots by electrochemical oxidation expansion. The method has high oxidative expansion dissociation and cutting ability, and can obtain high-quality graphene oxide microplate or graphene oxide with lower layer number and more uniform particle size distribution under the condition of low energy consumption and no pollution. Quantum dots. However, in this method, the liquid level of the electrolyte solution is still, and the relative positions of the working electrode of the carbon-based three-dimensional material and the auxiliary electrode are far away. The consumption of the electrolyte and the bubbles generated by the electrode can only be naturally replenished and discharged during operation, which leads to the bias of the working voltage. Problems such as high energy consumption, large energy consumption, limited operating current, and low production efficiency are still in need of further improvement.

In summary, the development of a high-quality graphene oxide preparation method and corresponding production equipment is still a key problem that needs to be solved in the field of nano-material technology.

Summary of the invention

In order to solve the above technical problems, an object of the present invention is to provide a method and apparatus for electrochemically preparing graphene oxide, which is obtained by forming a thin liquid layer on the surface of a cathode and then electrolyzing the anode in a thin liquid layer to obtain graphene oxide.

In order to achieve the above object, the present invention first provides a method for electrochemically preparing graphene oxide, which comprises the following steps:

The cathode is placed horizontally so that the electrolyte solution continues to flow along the surface of the cathode to form a thin liquid layer;

Inserting the electrolytic end of the anode into the thin liquid layer, but not in contact with the surface of the cathode;

Electrolysis of the anode and the cathode is performed to prepare graphene oxide.

In the above method, after the electrolytic end of the anode is inserted into the thin liquid layer and energized, the graphite sheet layer on the electrolysis end (end surface) of the anode is electrochemically oxidized and expanded to be dissociated and cut into graphene oxide, and dispersed in the electrolyte solution. in.

In the above method, preferably, the thin liquid layer has a thickness of 0.5 to 10 mm.

In the above method, preferably, the electrolyte solution continuously flows at a rate of from 1 to 1000 cm/s.

In the above method, the anode and the cathode are respectively connected to the two poles (ie, the positive electrode and the negative electrode) of the DC power source. Preferably, the DC power is used for electrolysis, and the constant voltage output control mode is adopted, and the voltage is not higher than 50 V, relative to the anode. The working current density of the electrolytic end is 1-300 A/cm ² .

In the above method, the cathode may be a flat, sheet, cloth or mesh cathode made of an inert material. The above inert material is a conductive material having corrosion resistance against an electrolyte solution, and preferably includes one or a combination of stainless steel, titanium, platinum, nickel-based alloy, copper, lead, graphite, and titanium-based oxide.

In the above method, the anode may be an anode made of a carbon-based three-dimensional material, and the carbon-based three-dimensional material is preferably a structure having a regular shape including a graphite layer structure. The carbon three-dimensional material may include graphite sheets made of natural graphite or artificial graphite, paper, plates, wires, tubes, rods, carbon fiber tows, structural felts, cloth, paper, ropes, boards, and the like. One or a combination of tubes or the like.

In the above method, preferably, the graphene oxide obtained after the electrolysis is dispersed in the electrolyte solution, and the method further comprises the step of separating the electrolyte solution containing graphene oxide by physical and/or chemical methods, the physical and / or chemical methods include one or a combination of filtration, vacuum drying, freeze drying, centrifugation, dialysis, distillation, pyrolysis, extraction, and chemical precipitation. The electrolyte and impurities and the like therein can be removed by separation, and an aqueous solution or an organic solution containing graphene oxide or a graphene oxide graphene or a solid graphene oxide can be isolated. When an organic solution containing graphene oxide is obtained, the organic solvent of the organic solution (ie, the organic solvent used in the separation process) is a strong polar organic solvent, and may include ethylene glycol, diethylene glycol, ethylenediamine, A combination of one or more of N-2-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide.

In the above method, preferably, when the anode (carbon three-dimensional material) is a highly oriented pyrolytic graphite sheet, natural graphite paper or artificial graphite paper, the graphene oxide thus prepared is a graphene oxide microchip, and the oxidation The graphene microchip has a thickness of 1-20 monoatomic layers, a particle diameter of 0.1 to 50 μm, and an atomic ratio of carbon to oxygen of 6:1 to 20:1.

In the above method, preferably, when the anode (carbon three-dimensional material) is a polyacrylonitrile-based or pitch-based carbon fiber tow or felt, the graphene oxide thus obtained is a graphene oxide quantum dot, the graphite oxide The olefinic quantum dots have a thickness and a particle diameter of 1 to 5 monoatomic layers (when graphene is a microchip, the particle diameter refers to a dimension in a planar direction) The atomic ratio of carbon to oxygen at 1-50 nm is 1:1 to 5:1.

In the above method, preferably, the electrolyte solution used is a solution having an ion conductive ability, and the electrolyte solution has a conductivity of not less than 5 mS/cm. If the conductivity of the electrolyte solution is too low, the electrochemical processing efficiency will be lowered, the temperature rise of the solution will be too fast, the energy consumption will increase, and the product quality will be degraded.

In the above method, after completing an electrolysis process as needed, that is, after one end surface of the anode is disconnected from the thin liquid layer, the end surface may be newly inserted into the thin liquid layer, and then electrolyzed, and the above process is repeated to form a discontinuity. Working mode; it is also possible to continuously adjust one end surface of the anode to keep in contact with the thin liquid layer during the electrolysis process as needed, and continue the uninterrupted energization electrolysis to form a continuous working mode.

The present invention also provides an apparatus for electrochemically preparing graphene oxide, comprising a member capable of forming a thin liquid layer on a surface of a cathode and a member capable of inserting one end of the anode into a thin liquid layer for electrolysis. Wherein, a member capable of forming a thin liquid layer on the surface of the cathode is used for continuously flowing an electrolyte solution through the surface of the cathode to form a thin liquid layer, and a member capable of inserting one end of the anode into the thin liquid layer for electrolysis is used for the electrolysis end of the anode It is inserted into the thin liquid layer for electrolysis, and any component or device capable of achieving the above functions can be used in the device of the present invention.

According to a specific embodiment of the present invention, preferably, the above device comprises a liquid storage tank, an anode, a cathode, a power source, a circulation pump, an infusion tube, a partition plate, and a concave groove;

Wherein the partition is disposed in the liquid storage tank, and the liquid storage tank is divided into a high liquid level chamber and a low liquid level chamber;

The high liquid level chamber and the low liquid level chamber are connected through the infusion tube, and the circulation pump is provided on the infusion tube;

The concave groove is horizontally disposed at a top of the partition, and the cathode is horizontally disposed in the concave groove;

The electrolytic end of the anode is located above the cathode;

The power source is connected to the anode and the cathode, respectively.

The concave groove is disposed at the top of the partition plate, and the cathode is horizontally disposed in the concave groove, one end of which is located in the high liquid level chamber, and the other end is located in the low liquid level chamber, and the electrolyte solution in the high liquid level chamber is performed during electrolysis The liquid level is slightly higher than the surface of the cathode, and the liquid level in the low liquid level chamber is lower than the surface of the cathode. The electrolyte solution flows through the surface of the cathode to form a thin liquid layer, and then the electrolytic end of the anode is inserted into the thin liquid layer. It is possible to carry out electrolysis to produce graphene oxide.

According to a particular embodiment of the invention, preferably the device further comprises a liftable bracket, the anode being coupled to the bracket. The bracket can control and adjust the height of the anode (the depth at which the anode is inserted into the thin liquid layer), insert the anode into the thin liquid layer (avoiding the cathode and anode short circuit), and fix it at a fixed height for electrolysis, completing an electrolysis process. After the end face of the anode electrolysis end is disconnected from the thin liquid layer, the end surface is again inserted into the thin liquid layer, and then electrolysis is performed, and the above process is repeated to form an intermittent operation mode; or it can be continuously adjusted during the electrolysis process. , The end face of the anode electrolysis end is kept in contact with the thin liquid layer at all times, and the continuous electrolysis is continuously performed to form a continuous operation mode.

According to a particular embodiment of the invention, preferably, there is a gap between the electrolysis end of the anode and the cathode to enable the electrolyte solution to continue to flow through the surface of the cathode and form a thin liquid layer.

According to a specific embodiment of the present invention, the liquid level difference between the high liquid level chamber and the low liquid level chamber can be controlled by adjusting the flow rate of the circulation pump, and at the same time, by controlling the width of the concave groove and the thickness of the cathode laid at the bottom of the concave groove, The thickness of the thin liquid layer and the flow rate of the electrolyte solution in the thin liquid layer can be achieved, and preferably, the width of the cathode is equal to the width of the inner wall of the concave groove. In the electrolysis process, the thickness of the thin liquid layer can be controlled to be 0.5 to 10 mm, and the flow rate of the electrolyte solution in the thin liquid layer can be controlled to be 1-1000 cm/s.

According to a particular embodiment of the invention, preferably, the top end of the partition is provided with a square hole in which the concave groove is disposed.

The method provided by the invention introduces a continuous flowing electrolyte solution on the surface of the cathode to form a thin liquid layer, and then inserts one end of the anode and forms a certain gap with the cathode to prepare the graphene oxide by electrolysis. The beneficial effect is that: In space, the anode end face is relatively close to the cathode plane (not more than 10 mm), which is beneficial to reduce the working voltage, delay the heating of the solution, and the current distribution is more uniform; second, the electrolyte solution is flowing in the thin liquid layer, which It is beneficial to timely replenish the consumed electrolyte and quickly remove the bubbles generated by the reaction on the anode and the anode, which can further reduce the working voltage, eliminate the local heating solution, and make the current distribution more uniform. Third, the flowing thin liquid layer can provide additional The mechanical shearing force facilitates the dissociation and cutting of the graphite sheet on the end face of the anode; fourthly, the combined effect of the above effects makes it possible to operate at higher operating current densities (compared to the technologies disclosed in CN105565297A and CN105600772A). Under the scheme), achieving lower operating voltages, as well as additional mechanical shearing forces, resulting in lower production Consumption and higher productivity, but also more uniform current distribution is such that the resulting product graphene oxide on a narrower size distribution and controllable.

Compared with the chemical oxidation method and the conventional electrochemical preparation method, the method for preparing graphene oxide of the invention has higher oxidative expansion dissociation and cutting ability, and can realize small particle size, low layer number and particle size of the product. The distribution and oxidation depth are controllable, and the raw materials are rich in source and low in cost, the production equipment is simple, the preparation process is simple, the energy consumption is low, the production efficiency is high, the yield is high, and the pollution-free industrialized mass production is advantageous.

DRAWINGS

1 is a schematic view of an apparatus for electrochemically preparing graphene oxide based on a thin liquid layer method provided by the present invention;

2a and 2b are atomic force microscope images and heights of the graphene oxide quantum dots provided in Example 1, respectively. Analysis curve

3 is a particle size distribution curve of the graphene oxide quantum dots provided in Example 1;

4 is a fluorescence spectrum diagram of a graphene oxide quantum dot provided in Example 1;

5 is a transmission electron micrograph of the graphene oxide quantum dots provided in Example 1;

6 is a photoelectron spectrum of the graphene oxide quantum dots provided in Example 1;

7a and 7b are atomic force microscope images and height analysis curves of the graphene oxide microchips provided in Example 2, respectively;

8 is a transmission electron micrograph of a graphene oxide microchip provided in Example 2, and a particle size distribution curve thereof;

Fig. 9 is a photoelectron spectroscopy chart of graphene oxide provided in Example 2.

Main component symbol description:

Reservoir 1, low liquid level chamber 2, high liquid level chamber 3, anode 4, cathode 5, power source 6, circulating water pump 7, infusion tube 8, partition 9, square hole 10, electrolyte solution 11, concave groove 12 , lifting bracket 13

Detailed ways

The detailed description of the technical features, the advantages and the advantages of the present invention will be understood by the following detailed description of the invention.

According to a preferred embodiment of the present invention, the method for electrochemically preparing graphene oxide provided by the present invention may comprise the steps of: using one carbon-based three-dimensional material as an anode and another flat or mesh-shaped inert material as a cathode, respectively The two poles of the power source (ie, the positive electrode and the negative electrode) are connected, and the cathode is horizontally placed to allow the electrolyte solution to flow through the surface of the cathode to form a thin liquid layer; during electrolysis, one end surface of the anode is inserted into the thin liquid layer and must not be in contact with the cathode; At the beginning of energization, during the electrolysis electrolysis, the anode end surface is contacted with the thin liquid layer intermittently or continuously, so that the graphite sheet layer on the end surface of the carbon-based three-dimensional material is disintegrated and cut into graphene oxide by electrochemical oxidation expansion. And dispersing in the electrolyte solution to obtain an electrolyte solution containing graphene oxide; and then physically and/or chemically removing the electrolyte and impurities therein to obtain a water/organic solution containing graphene oxide or a colloidal state or a solid state Graphene oxide.

Based on the above thin liquid layer method, the present invention also provides an apparatus for electrochemically preparing graphene oxide, the structure of which is shown in FIG. The device comprises a liquid storage tank 1 for containing an electrolyte solution 11, which is divided into two chambers by a partition 9, a chamber is a high liquid level chamber 3, and the other chamber is a low liquid level chamber 2, a high liquid The circulating chamber 7 and the infusion tube 8 are communicated between the chamber 3 and the low level chamber 2, and a square hole 10 is formed in the partition plate 9 and is provided with a concave groove 12, which is fitted and concave in the concave groove 12. a cathode 5 made of a flat plate or a mesh-like inert material having an inner wall of the groove 12, directly above the cathode 5 An anode 4 made of a carbon-based three-dimensional material is disposed, and the anode 4 is manually or automatically moved up and down by the lifting bracket 13, and the cathode 5 and the anode 4 are respectively connected to the negative electrode and the positive electrode of the DC power source 6.

The technical solution of the present invention will be further described below by way of specific embodiments.

Example 1

This embodiment provides a method for preparing graphene oxide quantum dots, which comprises the following steps:

Using 24K (24000 monofilament) polyacrylonitrile-based carbon fiber tow as raw material, the carbon fiber has a monofilament diameter of 7 μm, and the tip end surface of 72 bundles of carbon fiber tow is trimmed, and the bundle is vertically fixed in the lifting and lowering shown in FIG. On the bracket 13, the trimmed tip faces downward as the anode working surface (ie, the electrolytic end face of the anode 4); an SS304 stainless steel plate having an area of 100 cm ² is placed as a cathode 5 in a concave groove (acrylic material), and the cathode 5 The anode 4 is connected to the negative and positive electrodes of the direct current power source by cables; the electrolyte solution (2M ammonium sulfate) is charged into the circulating liquid storage tank 1 (made of UPVC material), and the electrolyte solution is added in an amount not less than high. The liquid level chamber 3 corresponds to the capacity along the liquid level on the concave groove 12. During operation, the circulating water pump 7 (polytetrafluoroethylene corrosion resistant pump) is connected to the power source, and the low liquid level chamber 2 is passed through the infusion tube 8 (UPVC material). The solution is transferred to the high liquid level chamber 3, and the solution in the high liquid level chamber 3 is again returned to the low liquid level chamber 2 through the concave groove 12 on the partition plate 9, thus forming on the surface of the stainless steel plate as the cathode 5. a stable stratosphere, that is, the thin liquid layer referred to in the present invention, thereby changing the flow rate of the circulating water pump 7 Adjusting the level difference between the two chambers, and the thickness of solution flow and thin liquid layer, the thickness of the control layer is a thin liquid herein is 3mm, the flow rate of the electrolyte solution is 1 m / sec;

Manually or electrically adjust the lifting bracket 13 so that the anode working surface is just in contact with the thin liquid layer, turn on the DC power supply (100V, 100A), and adjust the constant output voltage to 20V. At this time, the working current density of the opposite end face area is 40A/ Cm ² , electrolytic processing starts, when a large amount of bubbles generated on the cathode 5 and the anode 4 are carried into the low liquid level chamber 2 by the liquid flow, and are directly discharged into the atmosphere; as the electrolysis proceeds, the anode carbon fiber tow It is dissociated and cut by electrochemical oxidation expansion, and continuously dissolves into the solution. The distance between the working end face of the anode and the cathode 5 is gradually increased, and the working current is gradually reduced until the working end face of the anode is disconnected from the thin liquid layer, and the current is reduced to 0. At this time, the lifting bracket 13 is adjusted again, so that the anode working surface is in contact with the thin liquid layer, and the electrolysis process is restarted; the above process is continuously repeated, and the color of the solution gradually changes from light yellow, bright yellow, dark yellow, yellow brown to time. Dark brown, correspondingly increasing the concentration of the graphene oxide quantum dots, thereby obtaining a graphene oxide quantum dot electrolyte solution containing a concentration not higher than 50 mg/mL;

Finally, after filtering off the large particle carbon fiber fragments in the solution, the filtrate was dialyzed several times to remove ammonium sulfate, thereby obtaining an aqueous solution containing only graphene oxide quantum dots.

The aqueous solution containing the graphene oxide quantum dots was transferred to a flat silicon wafer, dried naturally, and subjected to atomic force microscopy. The results are shown in Fig. 2a and Fig. 2b. The maximum height of the graphene oxide quantum dots is 1.5 nm, which corresponds to the thickness of the two layers of graphene, and the average height of the particle size distribution is 0.7 nm, which is equivalent to the height of the single-layer graphene oxide quantum dots. And the distribution is relatively uniform.

The dynamic light scattering (DLS) particle size distribution analysis was carried out directly on the aqueous solution containing the graphene oxide quantum dots, and the analysis results are shown in FIG. It can be seen from the analysis results that the particle size distribution of the graphene oxide quantum dots ranges from 5 to 15 nm, and the distribution interval is narrow. Further, the fluorescence spectrum is analyzed. The analysis results are shown in Fig. 4. The graphite oxide is excited at a wavelength of 360 nm. The emission wavelength of the ene quantum dots is 420 nm.

The aqueous solution containing the graphene oxide quantum dots was subjected to 2000D membrane dialysis treatment to obtain a graphene oxide quantum dot (solution) having a particle size distribution of 5 to 10 nm, and the results are shown in FIG.

The solution containing the graphene oxide quantum dots is vacuum dried or freeze-dried to obtain a solid phase graphene oxide quantum dot, and photoelectron spectroscopy (XPS) analysis is performed, and the analysis results are shown in FIG. 6. From the analysis results, it can be obtained that the graphene oxide quantum dots have a carbon/oxygen atomic ratio of 1.2:1. The graphene oxide quantum dots obtained here are nitrogen-doped because the polyacrylonitrile-based carbon fiber raw material itself contains nitrogen.

Example 2

This embodiment provides a method for preparing a graphene oxide microchip, and the main difference from the embodiment 1 is that a natural graphite paper having a thickness of 0.5 mm is used as a raw material, and an end surface of the longitudinal direction of the graphite paper is used as a working surface. The electrolyte is 0.1 M sodium hydroxide; the cathode is a 100 cm ² nickel sheet; the constant output voltage is controlled to 10 V, and the initial working current density is 280 A/cm ² ;

As the electrolysis progresses, the anode graphite paper is disintegrated and cut by electrochemical oxidation expansion, and is continuously dissolved into the solution. The distance between the working end face of the anode and the cathode is gradually increased. When the current density is reduced to 100 A/cm ² , the motor is passed through the motor. The lifting bracket is automatically adjusted so that the distance between the anode working surface and the cathode is re-approxed until the working current density is restored to 280 A/cm ² , and the lifting bracket stops moving downward, thereby realizing an automatic continuous electrolytic production process; 100 mg/mL graphene oxide microplate electrolyte solution.

The graphene oxide microchip slurry was obtained by multiple centrifugation and water washing. Further, the graphene oxide microchip slurry was dried, and ultrasonically dispersed in ethylene glycol to obtain an ethylene glycol dispersion of graphene oxide microchip.

7a and 7b are respectively an atomic force microscope image and a height analysis curve of the obtained graphene oxide microchip, wherein the graphene oxide microchip has a height distribution ranging from 0.4 to 4 nm, which is equivalent to 1-10 monoatomic layer thicknesses; The graphene oxide microchip has a sheet size of 1-10 μm as shown in Fig. 8; the photoelectron spectroscopy results are shown in Fig. 9, and the graphene oxide microchip has a carbon/oxygen atomic ratio of 9:1.

Example 3

This embodiment provides a method for preparing graphene oxide quantum dots, and the main difference from the embodiment 1 is that the tip end surface of 100 bundles of T300 12K (12000 monofilament) polyacrylonitrile-based carbon fiber tow is used as an anode and a cathode. A 100 cm ² titanium electrode is used; the thickness of the thin liquid layer is controlled to be 8 mm, the flow rate of the electrolyte solution is 0.1 m/sec; the constant output voltage of the regulating power source is 30 V, and the working current density of the opposite end face area is 30 A/cm ² . Intermittent mode electrolytic machining.

The prepared graphene oxide quantum dots have an average thickness of 1 nm, a particle size distribution ranging from 2 to 8 nm, and a carbon/oxygen atomic ratio of 2:1.

Example 4

This embodiment provides a method for preparing a graphene oxide microchip. The main difference from the embodiment 2 is that a flexible graphite sheet having a thickness of 1 mm is used as a raw material, and one end surface in the longitudinal direction is used as an anode working surface, and the cathode is 50 cm ^{2 .} Hastelloy stencil, the electrolyte is 1M sulfuric acid; control constant output voltage 20V, initial working current density is 100A/cm ² , when the current density is reduced to 20A/cm ² , the lifting bracket is automatically adjusted to make the anode working surface The distance from the cathode is redrawn until the operating current density is restored to an automatic continuous electrolytic production process of 100 A/cm ² .

The prepared graphene oxide microchip has a thickness of 5-20 layers, a microchip diameter of 0.4-20 μm, and a carbon/oxygen atomic ratio of 18:1.

Example 5

This embodiment provides a method for preparing graphene oxide quantum dots, and the main difference from the embodiment 4 is that 220 bundles of HM110 4K pitch-based carbon fiber tow are used as raw materials, and the electrolyte is 0.5 M ammonium carbonate; the constant power supply is controlled. The output voltage is 45V, the initial working current density is 80A/cm ² , and when the current density is reduced to 40A/cm ² , the lifting bracket is automatically adjusted, so that the distance between the anode working surface and the cathode is pulled back until the working current density is restored to 80A. /cm ² automatic continuous electrolytic production process.

The number of layers of the graphene oxide quantum dots prepared is 1-2 layers, the particle size distribution ranges from 1 to 5 nm, and the carbon/oxygen atomic ratio is 4:1.

Example 6

The present embodiment provides a method for preparing graphene oxide quantum dots, and the main difference from the embodiment 1 is that 100 bundles of M55J 3K graphite carbon fiber tow are used as raw materials, and the carbon fiber has a monofilament diameter of 5 μm; the electrolyte solution is used. It is 0.2M sodium sulfate; the cathode is 200cm ² of TA2 titanium mesh; the thickness of the thin liquid layer is controlled to 2mm, the flow rate of the electrolyte solution is 6m/s; the constant output voltage is adjusted to 25V, and the working current density of the opposite end face area is 10A/cm ² , electrolytic processing in discontinuous mode.

The number of layers of the graphene oxide quantum dots prepared is 1-3 layers, the particle size distribution ranges from 10 to 25 nm, and the carbon/oxygen atomic ratio is 5:1.

Example 7

The present embodiment provides a method for preparing graphene oxide quantum dots. The main difference from the embodiment 1 is that a pitch-based carbon fiber felt having a thickness of 6 mm is used as a raw material, and one end surface in the longitudinal direction is used as an anode working surface, and the cathode is 50 cm ^{2 .} Reticulated titanium-based cerium oxide coated electrode, electrolyte is 1M hydrogen phosphate diamine; control thin liquid layer thickness is 4mm, flow rate is 2cm / s; control power supply constant output voltage 15V, initial working current density is 10A / cm ^2. When the current density is reduced to 4 A/cm ² , the lifting bracket is automatically adjusted so that the distance between the anode working surface and the cathode is re-pulled until the working current density is restored to an automatic continuous electrolytic production process of 10 A/cm ² .

The number of layers of the graphene oxide quantum dots prepared is 1-5 layers, the particle size distribution ranges from 7 to 30 nm, and the carbon/oxygen atomic ratio is 2:1.

Example 8

This embodiment provides a method for preparing a graphene oxide microchip, and the main difference from the embodiment 2 is that a high-oriented pyrolytic graphite sheet having a thickness of 5 mm is used as a raw material, and one end face in the longitudinal direction is used as an anode working surface and a cathode. Using a 100 cm ² titanium mesh plate, the electrolyte is a mixture of 1.0 M sodium sulfate and 0.1 M sulfuric acid; controlling a constant output voltage of 50 V, an initial working current density of 188 A/cm ² , when the current density is lowered to 90 A/cm ² The lifting bracket is automatically adjusted so that the distance between the anode working surface and the cathode is re-approxed until the working current density is restored to an automatic continuous electrolytic production process of 188 A/cm ² .

The prepared graphene oxide microchip has a thickness of 3-12 layers, a microchip diameter of 10-50 μm, and a carbon/oxygen atomic ratio of 16:1.

Example 9

The graphene oxide quantum dots obtained in Example 3, Example 5 and Example 6 were respectively irradiated by ultraviolet excitation light at a wavelength of 365 nm in an aqueous solution, respectively, and blue, green and yellow fluorescences were respectively exhibited (this may be related to the graphene oxide quantum The particle size distribution of the point is related to the carbon/oxygen ratio).

Claims

A method for electrochemically preparing graphene oxide, comprising the steps of:

The cathode is placed horizontally so that the electrolyte solution continues to flow along the surface of the cathode to form a thin liquid layer;

Inserting the electrolytic end of the anode into the thin liquid layer, but not in contact with the surface of the cathode;

Electrolysis of the anode and the cathode is performed to prepare graphene oxide.
The method of claim 1 wherein said thin liquid layer has a thickness of from 0.5 to 10 mm.
The method according to claim 1, wherein the electrolyte solution continuously flows at a rate of 1-1000 cm/s.
The method according to claim 1, wherein said electrolysis is performed by a direct current power source in a constant voltage output control mode, the voltage is not higher than 50 V, and the operating current density with respect to the electrolysis end of said anode is 1-300 A/cm 2 .
The method according to claim 1, wherein said cathode is a flat, sheet, cloth or mesh cathode made of an inert material.
The method of claim 5 wherein the inert material comprises one or a combination of stainless steel, titanium, platinum, nickel based alloys, copper, lead, graphite, and titanium based oxides.
The method according to claim 1, wherein the anode is an anode made of a carbon-based three-dimensional material, and the carbon-based three-dimensional material is a structure having a regular shape including a graphite layer structure.
The method according to claim 7, wherein the carbon-based three-dimensional material comprises graphite sheets made of natural graphite or artificial graphite, paper, plates, wires, tubes, rods, carbon fiber tows, and structures woven therefrom A combination of one or more of felt, cloth, paper, rope, board, and tube.
The method according to claim 1, wherein the graphene oxide obtained after the electrolysis is dispersed in the electrolyte solution, the method further comprising the step of separating the electrolyte solution containing graphene oxide by physical and/or chemical means, Physical and/or chemical methods include one or a combination of filtration, vacuum drying, freeze drying, centrifugation, dialysis, distillation, pyrolysis, extraction, and chemical precipitation.
The method according to claim 9, wherein the separated aqueous solution or organic solution containing graphene oxide, or colloidal graphene oxide or solid graphene oxide; and the organic solvent of the organic solution includes ethylene A combination of one or more of an alcohol, diethylene glycol, ethylene diamine, N-2-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide.
The method according to claim 7, wherein the anode is a highly oriented pyrolytic graphite sheet, natural graphite paper or artificial graphite paper, and the graphene oxide thus prepared is a graphene oxide microchip, the graphene oxide micro The sheet has a thickness of 1 to 20 monoatomic layers, a particle diameter of 0.1 to 50 μm, and an atomic ratio of carbon to oxygen of 6:1 to 20:1.
The method according to claim 7, wherein the anode is a polyacrylonitrile-based or pitch-based carbon fiber tow or felt, and the graphene oxide thus obtained is a graphene oxide quantum dot, the graphene oxide quantum dot It has a thickness of 1 to 5 monoatomic layers, a particle diameter of 1 to 50 nm, and an atomic ratio of carbon to oxygen of 1:1 to 5:1.
The method according to claim 1, wherein the electrolyte solution is a solution having an ion conductive ability, and the electrolyte solution has a conductivity of not less than 5 mS/cm.
An apparatus for electrochemically preparing graphene oxide, comprising a member capable of forming a thin liquid layer on a surface of a cathode, and a member capable of inserting one end of the anode into a thin liquid layer for electrolysis.
The apparatus according to claim 14, wherein the apparatus comprises a liquid storage tank, an anode, a cathode, a power source, a circulation pump, an infusion tube, a partition, and a concave groove;

Wherein the partition is disposed in the liquid storage tank, and the liquid storage tank is divided into a high liquid level chamber and a low liquid level chamber;

The high liquid level chamber and the low liquid level chamber are connected through the infusion tube, and the circulation pump is provided on the infusion tube;

The concave groove is horizontally disposed at a top of the partition, and the cathode is horizontally disposed in the concave groove;

The electrolytic end of the anode is located above the cathode;

The power source is connected to the anode and the cathode, respectively.
The device of claim 15 wherein the device further comprises a liftable bracket, the anode being coupled to the bracket.
The apparatus according to claim 15, wherein a gap is formed between the electrolytic end of the anode and the cathode, and the gap is smaller than a thickness of the thin liquid layer.
The apparatus according to claim 15, wherein the width of the cathode is equal to the width of the inner wall of the concave groove.
The apparatus according to claim 15, wherein a top end of said partition is provided with a square hole, and said concave groove is provided in said square hole.