Method for preparing single-layer graphene by catalytic reduction of CO2

Abstract

The application discloses a method for preparing single-layer graphene by catalytic reduction of CO2, which comprises the following steps: introducing CO2 gas into a fluidized bed reactor through a raw gas inlet, preparing CO and CO2 containing gas under the action of a reducing agent in an oxygen-free environment at 1000-1300 DEG C, introducing the CO and CO2 containing gas and a mixture containing nano catalyst into a two-stage Venturi jet unit from a product outlet and a mixed gas tank respectively, fully mixing and uniformly distributing the mixture, and preparing single-layer graphene under the action of the nano catalyst in an electric arc discharge reaction unit; the greenhouse effect gas CO2 is selected as a carbon source, and a thermal chemical series connection plasma is used to help the graphene nucleation of the CO / CO2 mixture and maintain a high growth rate of product seeds, so that large-scale single crystals are obtained; the reaction condition is controllable, and the method can be continuously produced, thereby providing a process basis for solving the current CO2 emission and energy shortage problems.

Description

Technical Field

[0001] This invention belongs to the technical field of carbon nanomaterial preparation, specifically relating to a method for preparing monolayer graphene by CO2 catalytic reduction. Background Technology

[0002] Electrocatalytic CO2 preparation of carbon nanomaterials holds potential for exploring the mechanisms of directional product regulation. It has been reported that under mild aqueous conditions, due to the high thermodynamic stability of CO2, C... 5+ The product has never been synthesized directly using CO2 as the sole carbon source. Therefore, another approach to carbon dioxide conversion is a two-step strategy, where CO2 is first converted to CO, and CO then evolves into other products, such as graphene, in a subsequent chemical reaction. When selecting a suitable and inexpensive carbon source for graphene preparation, CO2, a cost-effective and green raw material for graphene production, can be considered.

[0003] Currently, graphene preparation methods are divided into two types: "top-down" and "bottom-up." Top-down methods mainly include micromechanical exfoliation, liquid-phase exfoliation, and redox methods; bottom-up methods mainly include chemical vapor deposition (CVD), epitaxial growth, and organic synthesis. Top-down methods primarily use graphite as the raw material, employing physical and chemical methods to obtain graphene. Bottom-up methods primarily use carbon-containing materials such as hydrocarbons and single-crystal silicon as raw materials, preparing graphene under high-temperature and ultra-vacuum conditions. Compared to other graphene preparation methods, CVD has advantages such as high product quality, large growth area, and controllable layer number, and its properties are closer to the intrinsic properties of graphene. Further research is needed to develop superior, high-quality, large-area, and practical graphene preparation technologies to achieve better, stronger, and more prominent applications. Carbon dioxide (CO2), in particular, containing both carbon (C) and oxygen (O) atoms, is a more environmentally friendly and safer carbon source for graphene growth. Utilizing thermochemical methods, especially those powered by renewable energy sources such as photovoltaic and wind power, is a very clean and efficient approach, offering advantages such as controllable reaction processes, mild reaction conditions, and recyclable catalysts. Summary of the Invention

[0004] This invention provides a method for preparing monolayer graphene by catalytic reduction of the greenhouse gas CO2. The apparatus for performing this method includes a CO2 tank, a mixed gas tank, a fluidized bed reactor, a two-stage Venturi jet unit, an arc discharge generating unit, a blower, and a gas storage chamber. The fluidized bed reactor includes a shell I with a feed gas inlet at the bottom and a product outlet at the top. One or more heat carriers are disposed within the shell I. The two-stage Venturi jet unit consists of a first-stage Venturi jet and a second-stage Venturi jet connected in series. The product outlet and the mixed gas... The tank is connected to the two inlets of the first-stage Venturi jet. The arc discharge reaction unit includes a shell II. The outlet of the second-stage Venturi jet is connected to one end of the shell II of the arc discharge reaction unit. Multiple discharge electrodes are installed inside the shell II. A product collection glass substrate is inclinedly installed at the outlet end inside the shell II. A cooling device is sleeved on the outside of the outlet end of the shell II and located outside the product collection glass substrate. The gas storage chamber is connected to the outlet of the shell II through a fan. Power supply II is connected to the discharge electrodes, and power supply I is connected to the heating element through a temperature controller. The heating element is located below the heat carrier.

[0005] Before using the device of this invention, the fluidized bed reactor is purged with inert gas until no oxygen is present. Then, the temperature is raised to 1000-1300°C by heating elements and kept constant. CO2 gas is introduced into the fluidized bed reactor from the raw material gas inlet at a flow rate of 800-1000 sccm. Under oxygen-free conditions, at 1000-1300°C, and with the action of a reducing agent, the CO / CO2 gas is reduced to a CO / CO2-containing gas. The CO / CO2-containing gas and a nitrogen-argon mixture containing nano-catalyst are introduced into a two-stage Venturi jet unit from the product outlet and the mixing tank, respectively, and thoroughly mixed. The gas is then mixed with the nano-catalyst, which initially catalyzes the decomposition of the carbon source material. After a DC plasma discharge process, CO decomposes into carbon free radicals, which nucleate and grow on the catalyst surface. Simultaneously, a monolayer structure is obtained by growth in a CO2 atmosphere with a volume concentration of less than 2%. Subsequently, the product is cooled to below 200°C by a cooling device and uniformly deposited on the product collection glass substrate. The gas is collected in the gas storage chamber to obtain monolayer graphene.

[0006] The reducing agent is coke or anthracite particles, which are placed on a heat carrier, which is a stainless steel mesh with pores smaller than the particle size of the reducing agent.

[0007] The CO volume concentration injected into the two-stage Venturi jet unit is above 98%.

[0008] The outlets of the CO2 gas tank and the mixed gas tank are equipped with gas flow meters and valves, and the product outlet of the fluidized bed reactor is equipped with quartz wool to prevent the reducing agent from entering the two-stage Venturi jet unit.

[0009] The furnace temperature of the arc discharge generating unit is 800~1500℃, and the graphene growth temperature is 800~1500℃.

[0010] The graphene nanocatalyst is one or more of NiO, Al2O3, CaCO3, Fe2O3, MgO, SiO2, and ZrO2.

[0011] The graphene product collection device is a 60º tilted glass substrate to obtain the maximum capture area.

[0012] The spacing between the discharge electrodes is 25~35mm.

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

[0014] 1. Using CO2 as a carbon source to prepare graphene can greatly increase its value. This invention couples thermocatalytic CO2 technology with jet plasma technology, which can excite the activation state of carbon monoxide under arc discharge, making it possible to improve the graphene conversion rate;

[0015] 2. The present invention uses high-temperature fluidized bed thermocatalytic reduction technology at the front end and jet plasma technology at the back end. There is a heat transfer process, but less energy is wasted, which has certain economic benefits.

[0016] 3. The nano-scale catalyst particles used have a high proportion of exposed atoms, resulting in more active sites, allowing CO to participate in the reaction more frequently;

[0017] 4. Compared with the traditional graphene growth process that requires a metal substrate, this method is a self-supporting growth of graphene, which provides greater flexibility and no longer needs to consider the additional components that may be introduced by the substrate material.

[0018] 5. Achieve high-value utilization of CO2 products. Through thermocatalytic CO2 coupled with jet plasma technology, the current problem of excessive CO2 emissions can be solved, while ensuring that graphene maintains good quality and a monolayer structure while remaining self-supporting. The method is simple and can be continuously produced. Attached Figure Description

[0019] Figure 1 A schematic diagram of the structure of the apparatus for implementing the method of the present invention;

[0020] Figure 2 The Raman spectrum of graphene in Example 1;

[0021] Figure 3 This is a Raman microscope image of graphene from Example 1;

[0022] In the diagram: 1-CO2 gas tank; 2-mixed gas tank; 3-raw material gas inlet; 4-heating element; 5-heat carrier; 6-power supply I; 7-product outlet; 8-temperature controller; 9-first-stage Venturi jet injector; 10-second-stage Venturi jet injector; 11-discharge electrode; 12-ground wire; 13-product collection glass substrate; 14-cooling device; 15-exhaust fan; 16-gas storage chamber; 17-power supply II. Detailed Implementation

[0023] The present invention will now be described in detail with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described herein; unless otherwise specified, the methods in the embodiments are conventional methods.

[0024] like Figure 1 As shown, the apparatus used in the following embodiments includes a CO2 gas tank 1, a mixing gas tank 2, a fluidized bed reactor, a two-stage Venturi jet unit, an arc discharge generating unit, an exhaust fan 15, and a gas storage chamber 16. The fluidized bed reactor includes a shell I, with a raw material gas inlet 3 at the bottom and a product outlet 7 at the top. Two heat carriers 5 are disposed inside the shell I, and a reducing agent is placed on the heat carriers. The two-stage Venturi jet unit consists of a first-stage Venturi jet 9 and a second-stage Venturi jet 10 connected in series. The product outlet 7 and the mixing gas tank 2 are respectively connected to the two inlets of the first-stage Venturi jet. The arc discharge generating unit includes a shell II, with the outlet of the second-stage Venturi jet connected to the shell II of the arc discharge generating unit. One end of body II is connected, and multiple discharge electrodes 11 (discharge electrodes spaced 30mm apart) are provided inside shell II. A product collection glass substrate 13 is inclinedly provided at the outlet end inside shell II. A cooling device 14 is sleeved on the outside of the outlet end of shell II and located outside the product collection glass substrate. Gas storage chamber 16 is connected to the outlet of shell II through exhaust fan 15. Power supply II 17 is connected to multiple discharge electrodes, and power supply I 6 is connected to heating element 4 through temperature controller 8. The heating element is located below heat carrier 5. Shell II is grounded through ground wire 12. Gas flow meter and valve are provided at the outlet of CO2 gas tank and mixed gas tank. Quartz wool is provided at the product outlet of fluidized bed reactor to prevent reducing agent from entering the two-stage Venturi jet unit. Example 1

[0025] The fluidized bed reactor was purged with nitrogen until no oxygen was present. Coke was placed on the heat carrier 5, and the temperature inside the fluidized bed reactor was raised to 1300℃ using heating element 4 and held constant. CO2 gas was then introduced into the fluidized bed reactor from the feed gas inlet 3 at a flow rate of 800 sccm. Under oxygen-free conditions at 1300℃ and with the help of coke, CO / CO2 was reduced to CO / CO2, at which point the volume concentration of CO was 99.5% and the volume concentration of CO2 was 0.5%. The CO / CO2-containing gas was then passed through the product outlet to a nitrogen-argon mixture containing nano-alumina (the mass-to-volume ratio of alumina to the nitrogen-argon mixture was 30%, and the volume ratio of nitrogen to argon in the nitrogen-argon mixture was...). The mixture (1:1) enters the primary Venturi jet 9 through two inlets and is then thoroughly mixed before entering the secondary Venturi jet 10. It then enters the arc discharge generating unit and undergoes a DC plasma discharge process at a constant temperature of 1100±50℃. CO decomposes into carbon free radicals, which nucleate and grow on the catalyst surface. Simultaneously, the presence of low CO2 content inhibits the growth of the second layer, resulting in a single-layer structure. The product then passes through a cooling device 14, where the temperature drops sharply to below 200℃, and the product is uniformly deposited on a product collection glass substrate. The gas is collected in a gas storage chamber, and the glass substrate with the attached product is removed, yielding high-quality single-layer graphene with a graphene coverage of up to 95% on the glass substrate.

[0026] The Raman spectrum and Raman microscope image of graphene are as follows: Figure 1 , 2 As shown, Figure 1 Raman spectroscopy was performed using a Raman imaging microscope equipped with a ×20 objective lens and a 532 nm excitation laser operating at 2 mW output power. The figures show that the G band and 2D band (located at approximately 1350 cm⁻¹) are... -1 Location, 2690cm -1 (At this point), G / 2D is less than or equal to 0.66 (G / 2D < 0.66). The G / 2D ratio used here refers to the ratio of the peak intensities of these bands. Generally, if the G / 2D intensity ratio is in the range of 0.7, it indicates that it is a single layer. Figure 2 The image shows graphene under a Raman microscope with a resolution of up to 100 μm. As can be seen from the image, the sample is arranged in an orderly honeycomb lattice. Example 2

[0027] The fluidized bed reactor was purged with nitrogen until no oxygen was present. Coke was placed on the heat carrier 5, and the temperature inside the fluidized bed reactor was raised to 1200℃ and held constant. CO2 gas was introduced into the fluidized bed reactor from the feed gas inlet 3 at a flow rate of 1000 sccm. Under oxygen-free conditions, at 1200℃, and with the action of coke, CO / CO2 was reduced to CO / CO2. At this point, the volume concentration of CO was 99% and the volume concentration of CO2 was 1%. The CO / CO2-containing gas was then introduced from the product outlet into a nitrogen-argon mixture containing nano-Al2O3 (the mass-to-volume ratio of nano-Al2O3 to the nitrogen-argon mixture was 35%, and the nitrogen-argon mixture contained both nitrogen and argon gases). The mixture (with a product ratio of 1:1) enters the two inlets of the first-stage Venturi jet 9 from the mixing tank for mixing, and then enters the second-stage Venturi jet 10 for thorough mixing again. After that, it enters the arc discharge generating unit and undergoes a DC plasma discharge process at a constant temperature of 1300±50℃. CO decomposes into carbon free radicals, which nucleate and grow on the catalyst surface. At the same time, the presence of a certain concentration of CO2 inhibits the growth of the second layer, resulting in a single-layer structure. Subsequently, the product is cooled to below 200℃ by a cooling device, and the product is uniformly deposited on the glass substrate. The gas is collected in the gas storage chamber, and the glass substrate with the attached product is removed to obtain high-quality single-layer graphene, in which the graphene coverage on the glass substrate is as high as 92%. Example 3

[0028] The fluidized bed reactor is purged with nitrogen until no oxygen is present. Anthracite particles are placed on the heat carrier 5, and the temperature inside the fluidized bed reactor is heated by the heating element 4 until it reaches 1100°C and is kept constant. CO2 gas is introduced into the fluidized bed reactor from the raw material gas inlet 3 at a flow rate of 900 sccm. Under the conditions of no oxygen, 1100°C, and anthracite, the mixture is reduced to CO / CO2. At this point, the volume concentration of CO is 98% and the volume concentration of CO2 is 2%. CO / CO2 is discharged from the product outlet. A nitrogen-argon mixture containing nano-SiO2 (the mass-to-volume ratio of nano-SiO2 to the nitrogen-argon mixture is 28%, and the volume ratio of nitrogen to argon in the nitrogen-argon mixture is 1:1) is introduced from the mixing tank into the two inlets of the first-stage Venturi jet 9 for mixing. After being thoroughly mixed, it enters the second-stage Venturi jet 10 and then enters the arc discharge generating unit. Under constant temperature of 850±50℃, it undergoes a DC plasma discharge process. CO decomposes into carbon free radicals, which nucleate and grow on the catalyst surface. At the same time, the presence of a certain concentration of CO2 inhibits the growth of the second layer, resulting in a single-layer structure. Subsequently, the product is cooled to below 200℃ by a cooling device, and the product is uniformly deposited on a glass substrate. The gas is collected in the gas storage chamber, and the glass substrate with the attached product is removed to obtain high-quality single-layer graphene, in which the graphene coverage of the glass substrate is as high as 88%.

Claims

1. A method for preparing monolayer graphene by CO2 catalytic reduction, characterized in that, The apparatus for completing this method includes a CO2 gas tank (1), a mixing tank (2), a fluidized bed reactor, a two-stage Venturi jet unit, an arc discharge reaction unit, a blower (15), and a gas storage chamber (16). The fluidized bed reactor includes a shell I, with a raw material gas inlet (3) at the bottom and a product outlet (7) at the top. One or more heat carriers (5) are placed inside the shell I, and a reducing agent is placed on the heat carrier. The two-stage Venturi jet unit consists of a first-stage Venturi jet (9) and a second-stage Venturi jet (10) connected in series. The product outlet (7) and the mixing tank (2) are respectively connected to the two inlets of the first-stage Venturi jet. The arc discharge reaction unit includes a shell II. The outlet of the secondary Venturi jet is connected to one end of the arc discharge reaction unit shell II. Multiple discharge electrodes (11) are provided inside the shell II. A product collection glass substrate (13) is inclinedly provided at the outlet end inside the shell II. A cooling device (14) is sleeved on the outside of the outlet end of the shell II and located outside the product collection glass substrate. The gas storage chamber (16) is connected to the outlet of the shell II through a fan (15). Power supply II (17) is connected to the discharge electrode. Power supply I (6) is connected to the heating element (4) through a temperature controller (8). The heating element is located below the heat carrier (5). The shell II is grounded through a ground wire (12). CO2 gas enters the fluidized bed reactor through the feed gas inlet. Under anaerobic conditions, at 1000-1300℃, and with the aid of a reducing agent, a gas containing CO and CO2 is produced. The CO and CO2-containing gas and a nitrogen-argon mixture containing nanocatalyst enter a two-stage Venturi jet unit from the product outlet and a mixing tank, respectively. After thorough mixing, the mixture enters the arc discharge reaction unit. Under the action of the nanocatalyst, CO decomposes into carbon free radicals, which nucleate and grow on the catalyst surface. Simultaneously, a monolayer structure is obtained in a CO2 atmosphere with a volume concentration of less than 2%. The product is then cooled to below 200℃ by a cooling device and uniformly deposited on a product collection glass substrate, thus producing monolayer graphene.

2. The method for preparing monolayer graphene by CO2 catalytic reduction according to claim 1, characterized in that: The reducing agent is coke or anthracite particles, which are placed on a heat carrier (5). The heat carrier (5) is a stainless steel mesh with a pore size smaller than that of the reducing agent particles.

3. The method for preparing monolayer graphene by CO2 catalytic reduction according to claim 1, characterized in that: The CO2 gas flow rate is 800–1000 sccm.

4. The method for preparing monolayer graphene by CO2 catalytic reduction according to claim 1, characterized in that: Graphene is grown in the arc discharge reaction unit at 800~1500℃.

5. The method for preparing monolayer graphene by CO2 catalytic reduction according to claim 1, characterized in that: The nanocatalyst is one or more of NiO, Al2O3, CaCO3, Fe2O3, MgO, SiO2, and ZrO2; the mass-to-volume ratio of the nanocatalyst to the nitrogen-argon mixture is 25-35% (g:mL).

6. The method for preparing monolayer graphene by CO2 catalytic reduction according to claim 1, characterized in that: The outlets of the CO2 gas tank and the mixed gas tank are equipped with gas flow meters and valves, and the product outlet of the fluidized bed reactor is equipped with quartz wool to prevent the reducing agent from entering the two-stage Venturi jet unit.

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