A method and device for easily separating and producing graphene

Abstract

The present invention discloses a method and device for easily separating and producing graphene, which is based on the preparation of graphene by direct current arc plasma discharge method. The method comprises the following steps: mixing carbon source gas with nanocatalyst and then spraying the mixture into a magnetically enhanced plasma reaction chamber through a venturi ejector, dispersing the nanocatalyst into an airflow, and using the nanocatalyst particles as nucleation sites for graphene growth to obtain vertically oriented graphene. The rear end of the reactor is rapidly cooled and a magnetic field is added to weaken the binding force between the catalyst and graphene, thereby making it more conducive to ultrasonic treatment, purification and collection of the product graphene; the method of the present invention can produce relatively pure graphene nanoribbons, which are easy to remove from the catalyst, and can also recover the catalyst, providing a solution for large-scale continuous operation.

Description

Technical Field

[0001] The present invention belongs to the technical field of separation and preparation of graphene, and specifically relates to a method and device for easily separating and producing graphene. Background Art

[0002] Arc discharge technology has been used to mass-produce high-quality carbon nanotube materials. Plasma discharge has also been gradually applied to the graphene production process, and it has been found that plasma technology has lower energy consumption than the thermal CVD process. It can immediately activate the material in a very short time after the discharge is ignited, grow and deposit to form graphene particles, and then deposit them on the cavity wall. However, plasma technology has problems in process control and large-scale production of synthetic graphene. Among them, separation, purification and collection of relatively pure few-layer graphene are still important factors limiting its large-scale production. Application No. CN202010857687.6 is a method of preparing graphene by direct current arc discharge, using graphite as an electrode. However, the consumption of graphite electrodes during arc discharge cannot be guaranteed, and carbon deposits such as multi-walled carbon nanotubes, carbon onions and multi-layer graphene may be produced on the graphite cathode, which are difficult to separate and collect. Yu Honggang et al. (To promote the nucleation and growth of graphene in arc discharge process by magnetic field and H2[J].Materials Letters, 2015, 159: 43-46.) from the Institute of Applied Chemistry of Xinjiang University reported that the prepared Ni-Y2O3 powder was doped into the anode graphite rod as a catalyst. Under the action of the catalyst, the nucleation and growth rate of graphene sheets were improved and gram-level few-layer graphene was prepared. Although this method of adding catalysts can synthesize graphene with high quality and low cost, it is not suitable for large-scale production of graphene. Summary of the invention

[0003] To solve the above problems, the present invention provides a method for easily separating and producing graphene. The method comprises the following steps: fully mixing a gaseous carbon source, a nanocatalyst, an inert gas and hydrogen, and then spraying the mixture into a magnetically enhanced DC plasma discharge device using a venturi ejector. The mixture reacts in a magnetic field-enhanced plasma environment, and vertically oriented graphene is grown using the nanocatalyst as a nucleation site. The reaction product is cooled and subjected to a magnetic field, so that the bonding energy between the catalyst and the graphene is weakened, and part of the graphene is separated from the catalyst. The reaction product is collected on a filter screen, and the reaction product is ultrasonically treated with water to obtain vertical graphene nanosheets.

[0004] The method is based on a magnetically enhanced direct current arc plasma discharge process. First, a carbon source material and argon-hydrogen containing a nano catalyst are mixed in a venturi ejector in a certain proportion. After being fully mixed in a diffuser of the venturi ejector, the mixture enters a magnetically enhanced direct current plasma generating device. Under the action of high-density plasma enhanced by a magnetic field, the carbon source material is decomposed, and graphene is vertically grown with the nano catalyst as a nucleation site. The product is rapidly condensed through a condensation system at the middle and lower end of the reactor, so that the binding force between the graphene and the nano catalyst particles is reduced. A permanent magnet block is arranged at the rear end of the reactor. After rapid cooling, the nano catalyst becomes ferromagnetic and responds to the magnetic field, so that part of the graphene and the catalyst can be separated. After separation, relatively pure graphene and part of the catalyst not separated from the graphene are collected together on a filter net in a product collection chamber. After the collected material is ultrasonically treated with water, purified vertical graphene sheets are obtained.

[0005] The carbon source and the nanocatalyst are mixed by spraying, the nanocatalyst preliminarily catalytically decomposes the carbon source, and then the short-chain hydrocarbons decomposed under the action of the nanocatalyst and high energy in the direct current plasma discharge process enhanced by the magnetic field are decomposed into carbon free radicals in the plasma ionization process, and nucleate and grow on the catalyst surface to form nanovertical graphene; after rapid cooling and magnetic field environment, the binding force between the nanocatalyst and the graphene is weakened, and part of the catalyst is separated from the product, and the separated product is collected on the filter net together with the unseparated product, and the gas product is collected in a collection tank; the product generated by the above reaction is more easily washed off the nanocatalyst thereon by ultrasound, and the final product can not only obtain the product graphene but also recover and reuse the washed catalyst.

[0006] The carbon source is CH4, C2H2, CO2, CO and other gases.

[0007] The catalyst is one or more of nano-sized particles of Pt, Fe3O4, ZrO2, Y2O3, NiO, Al2O3, Fe-Co, Fe-Ni, etc.

[0008] The magnetically enhanced DC plasma discharge device comprises a shell, a product collection chamber is arranged at the bottom of the shell, a filter screen is arranged at the bottom of the shell and is located in the product collection chamber, a feed port is arranged on one side of the upper part of the shell, a cathode is arranged at the center of the shell, an anode is arranged on the left side of the upper part of the shell and is connected to a high-frequency DC power supply, a magnetic field generator is arranged on the upper part of the shell and is connected to the DC power supply, more than two permanent magnets are arranged at the lower part of the shell, the shell wall at the lower part of the shell is a wall with an interlayer, a water inlet and a water outlet are opened on the interlayer and condensed liquid is passed through, and the feed port is connected to the Venturi ejector.

[0009] A pressure gauge is arranged on the shell.

[0010] The magnetic field generator is an electromagnetic coil.

[0011] The anode material is one of molybdenum-lanthanum alloy, zirconium-copper alloy, and tungsten-molybdenum alloy; the cathode material is one of tungsten-copper alloy, zirconium diboride, and titanium diboride.

[0012] In the magnetically enhanced DC plasma discharge device, a high-frequency DC power supply provides a magnetic field strength of 0.05 to 0.15 T for the magnetic coil; a gas carbon source is doped with 44.94 to 60.53 g / L of a nanocatalyst, mixed and pumped into a venturi ejector at a feed rate of 50 to 100 sccm, and argon and hydrogen are mixed through two-way pipes and enter the venturi ejector, wherein the gas carbon source, argon and hydrogen enter the venturi ejector at a flow rate ratio of 3:5:3 to 4:6:5. After vacuuming, the pressure in the reaction chamber is ensured to be 50 to 70 Kpa, and the reaction time is 10 to 15 minutes.

[0013] Advantages and technical effects of the method of the present invention:

[0014] The present invention can select carbon-containing harmful gas as a carbon source, add a nano catalyst, and grow vertically oriented graphene thereon. A magnetic coil is used to add a magnetic field to the DC plasma reaction, which not only enhances the plasma density but also provides sufficient time for the decomposition reaction of the carbon source molecules. Rapid cooling at the rear end of the reaction and the provision of a permanent magnet block can not only absorb other carbon products, but also enable the nano catalyst to respond to the magnetic field in a high-energy environment, thereby weakening its ability to bind to the product graphene, which is beneficial to the separation and purification of subsequent products. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the structure of a magnetically enhanced DC plasma discharge device;

[0016] Figure 2 A schematic diagram of the structure of a device for implementing the method of the present invention;

[0017] In the figure: 1: argon tank; 2: hydrogen tank; 3: mixing bottle; 4: induced draft fan; 5: gas flow meter; 6: venturi ejector; 7: magnetically enhanced DC plasma discharge device; 8: high-frequency DC power supply; 9: pressure gauge; 10: DC power supply; 11: wall with interlayer; 12: vacuum pump; 13: gas collecting chamber; 14: shell; 15: cathode; 16: anode; 17: water inlet; 18: water outlet; 19: magnetic field generator; 20: permanent magnet; 21: filter screen; 22: product collection chamber. DETAILED DESCRIPTION

[0018] The present invention is described in detail below in conjunction with specific implementation methods, but the protection scope of the present invention is not limited to the described contents; the methods in the embodiments are conventional methods unless otherwise specified.

[0019] The device for completing the method of the present invention in the following embodiment includes an argon tank 1, a hydrogen tank 2, a mixing bottle 3, a venturi ejector 6, a magnetically enhanced DC plasma discharge device 7, a vacuum pump 12, and a gas collecting chamber 13; the magnetically enhanced DC plasma discharge device includes a shell 14, a product collection chamber 22 is provided at the bottom of the shell 14, a stainless steel filter 21 is provided at the bottom of the shell and is located in the product collection chamber 22, a feed port is provided on one side of the upper part of the shell, a cathode 15 is provided at the center of the shell, an anode 16 is provided on the left side of the upper part of the shell and is connected to a high-frequency DC power supply 8, and a magnetic field generator 1 is provided on the upper part of the shell. 9 (electromagnetic coil) and connected to a DC power supply 10, three permanent magnets 20 are arranged in the lower part of the shell, the lower shell wall of the shell is a wall 11 with an interlayer, the interlayer is provided with a water inlet 17 and a water outlet 18 and condensed liquid is introduced, a pressure gauge 9 is arranged on the magnetically enhanced DC plasma discharge device, an argon tank 1 and a hydrogen tank 2 are connected to a venturi ejector 6 through a valve and a gas flowmeter 5 respectively, a mixing bottle 3 is connected to the venturi ejector 6 through an induced draft fan 4 and a gas flowmeter, the venturi ejector 6 is connected to the feed port of the magnetically enhanced DC plasma generating device 7, and a gas collecting chamber 13 is communicated with the shell through a vacuum pump 12;

[0020] Example 1

[0021] The vacuum pump 12 is turned on, and the pressure in the shell of the magnetically enhanced DC plasma discharge device is controlled to be 50 kPa after evacuation. The argon tank 1 is turned on, 15 sccm, 10 minutes, and the air in the reaction chamber is blown away. Then, the mixture of CO2 gas and nanocatalyst NiO in the mixing bottle 3 is introduced into the venturi ejector 6 through the induced draft fan 4 at a flow rate of 90 sccm, wherein the content of the nanocatalyst is 58.76 g / L. The gases in the argon tank 1 and the hydrogen tank 2 enter the venturi ejector 6 at flow rates of 140 and 108 sccm, respectively. After being evenly mixed in the venturi ejector, they enter the magnetically enhanced DC plasma discharge device 7 together. The anode 16 uses a high-temperature resistant zirconium-copper electrode, and the cathode 15 uses a high-temperature resistant tungsten-copper electrode. The electromagnetic coil is powered by a high-frequency DC power supply 8 so that the magnetic field strength generated by the magnetic field generator 19 is The reaction temperature is controlled at 0.05T and the reaction is carried out for 15 minutes in a magnetic field enhanced plasma environment. At this time, CO2 is activated, decomposed and nucleated on the nanocatalyst, and is cooled by the condensed liquid in the interlayer wall 11 to grow graphene in a vertical orientation. The product graphene and nanocatalyst mixture responds to the magnetic field under the action of the permanent magnet 20, and the binding force between the catalyst and the graphene is weakened, and there is a little separation. The separated catalyst is absorbed on the surface of the permanent magnet 20 to produce relatively pure graphene and falls on the stainless steel filter 21 in the product collection chamber 22 together with the remaining part of the product. The gas in the reaction process is introduced into the gas collection chamber 13, and the solid product is collected, immersed in deionized water, and ultrasonically treated for 30 minutes. The collected floating matter and precipitate are dried in a vacuum oven at 100°C overnight to obtain relatively pure graphene and nanocatalyst respectively.

[0022] Example 2

[0023] The pressure in the reaction chamber is controlled at 60 kPa by the vacuum pump 12, and then the argon tank 1 is opened at a low flow rate for 10 minutes, and the CH4 gas and the nanocatalyst Pt in the mixing bottle 3 are introduced into the venturi ejector 6 through the induced draft fan 4 at a flow rate of 50 sccm, wherein the content of the nanocatalyst is 50 g / L, and the gases in the argon tank 1 and the hydrogen tank 2 enter the venturi ejector 6 at a volume flow rate of 120 and 70 sccm respectively, and are then sprayed into the magnetically enhanced DC plasma discharge device 7, wherein the anode 16 uses a high-temperature resistant zirconium-copper electrode and the cathode 15 uses a high-temperature resistant tungsten-copper electrode, and reacts for 10 minutes in a magnetic field enhanced plasma environment with a magnetic field strength of 0.12 T, and CO is activated, Decompose and nucleate on the nanocatalyst, and cool through the condensed liquid in the interlayer wall 11 to grow graphene in a vertical orientation. The product graphene and nanocatalyst mixture responds to the magnetic field under the action of the permanent magnet 20, and the binding force between the catalyst and the graphene is weakened, and there is a little separation. The small amount of catalyst after separation is absorbed on the surface of the permanent magnet 20 to produce relatively pure graphene and falls on the stainless steel filter 21 in the product collection chamber 22 together with the remaining part of the product. The gas in the reaction process is introduced into the gas collection chamber 13, and the solid product is collected, immersed in deionized water, and ultrasonically treated for 30 minutes. The collected floating matter and precipitate are dried in a vacuum oven at 100°C overnight to obtain relatively pure graphene and nanocatalyst respectively.

[0024] Example 3

[0025] The vacuum pump 12 is turned on, and the pressure in the reaction chamber is controlled to be 70 kPa after vacuuming. The argon tank 1 is turned on and argon is passed for 10 minutes. Then, the CO gas and the nanocatalyst Al2O3 in the mixing bottle 3 are introduced into the venturi ejector 6 through the induced draft fan 4 at a flow rate of 70 sccm, wherein the content of the nanocatalyst is 44.94 g / L. The gases in the argon tank 1 and the hydrogen tank 2 enter the venturi ejector 6 at flow rates of 103 and 87 sccm, respectively. After being evenly mixed, they enter the magnetic enhanced DC plasma generator 7 together. The anode 16 uses a tungsten-molybdenum high temperature resistant electrode, and the cathode 15 uses a titanium diboride high temperature resistant electrode. The number of turns of the magnetic coil is adjusted to generate a magnetic field strength of 0.1 T. In the magnetic field enhanced plasma environment, 11 reactions are carried out. 15min, the carbon source material can be nucleated on the nanocatalyst, and is cooled by the condensed liquid in the interlayer wall 11 to grow graphene in a vertical orientation. The product graphene and nanocatalyst mixture responds to the magnetic field under the action of the permanent magnet 20, and the binding force between the catalyst and the graphene is weakened, and there is a little separation. The small amount of catalyst after separation is absorbed on the surface of the permanent magnet 20. After separation, the relatively pure graphene and the remaining part of the product fall onto the stainless steel filter 21 in the product collection chamber 22. The gas in the reaction process is introduced into the gas collection chamber 13, and the solid product is collected, immersed in deionized water, and ultrasonically treated for 30min. The collected floating matter and precipitate are dried in a vacuum oven at 100°C overnight to obtain relatively pure graphene and nanocatalyst respectively.

Claims

1. A method for easily separating and producing graphene, characterized in that: After the gaseous carbon source, nanocatalyst, inert gas and hydrogen are fully mixed, the mixture is sprayed into a magnetically enhanced DC plasma discharge device by using a venturi ejector, and the mixture reacts in a magnetic field enhanced plasma environment, and vertically oriented graphene is grown with the nanocatalyst as a nucleation site. The reaction product is cooled and subjected to a magnetic field, so that the bonding energy between the catalyst and the graphene is weakened, and part of the graphene is separated from the catalyst. The reaction product is collected on a filter screen, and the reaction product is ultrasonically treated with water to obtain vertical graphene nanosheets. The magnetically enhanced DC plasma discharge device comprises a shell (14), a product collection chamber (22) is arranged at the bottom of the shell (14), a filter screen (21) is arranged at the bottom of the shell and is located in the product collection chamber (22), a feed port is arranged on one side of the upper part of the shell, a cathode (15) is arranged at the center of the shell, an anode (16) is arranged on the left side of the upper part of the shell and is connected to a high-frequency DC power supply (8), a magnetic field generator (19) is arranged at the upper part of the shell and is connected to the DC power supply (10), two or more permanent magnets (20) are arranged at the lower part of the shell, the lower shell wall is a wall with an interlayer (11), the interlayer is provided with a water inlet (17) and a water outlet (18) and is passed through a condensed liquid, and the feed port is connected to a venturi ejector; The carbon source is selected from gaseous carbon-containing pollutants, and the gaseous carbon-containing pollutants are selected from CH4, C2H2, CO2, and CO; the nanocatalyst is one or more of Pt, Fe3O4, ZrO2, Y2O3, NiO, Al2O3, Fe-Co, and Fe-Ni.

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